Name: monitoring the effect of osmotic stress on secretory vesicles and exocytosis
Uploaded: 2018-02-19T13:30:00
Description: Watch this Scientific Journal Video about Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis at JoVE.com

The authors would like to thank the Swedish Research Council (349-2007-8680) for funding and Dalsj&#246;fors K&#246;tt AB (Dalsj&#246;fors, Sweden) for donation of bovine adrenal glands.

1. Cell Culture of Bovine Chromaffin Cells Isolated by Enzymatic Digestion from Adrenal Glands
<ol>
	<li>To isolate chromaffin cells collected from bovine adrenal glands, sterilize cells with 70% ethanol solution. Trim away fat and connective tissue using a scalpel. To remove blood, rinse the adrenal veins using Locke&#39;s solution (NaCl 154 mM, KCl 5.6 mM, NaHCO3 3.6 mM, hydroxyethyl piperazineethanesulfonic acid (HEPES) 5.6 mM at pH 7.4) that has been thermostated to 37 &#176;C.</li>
	<li>To digest the tissue, infla...

<ol>
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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+Mg2++ion-activated+ATPase+and+a+pH+gradient+in+the+storage+of+catecholamines+in+synaptic+vesicles.">Role of Mg2+ ion-activated ATPase and a pH gradient in the storage of catecholamines in synaptic vesicles.</a> Biochemistry. 17 (13), 2517-2523 (1978).</li><li>Terland, O., Flatmark, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ascorbate+as+a+natural+constituent+of+chromaffin+granules+from+the+bovine+adrenal+medulla.">Ascorbate as a natural constituent of chromaffin granules from the bovine adrenal medulla.</a> FEBS letters. 59 (1), 52-56 (1975).</li><li>Camacho, M., Machado, J. D., Montesinos, M. S., Criado, M., Borges, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intragranular+pH+rapidly+modulates+exocytosis+in+adrenal+chromaffin+cells.">Intragranular pH rapidly modulates exocytosis in adrenal chromaffin cells.</a> J Neurochem. 96 (2), 324-334 (2006).</li><li>Jankowski, J. A., Schroeder, T. J., Ciolkowski, E. L., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+characteristics+of+quantal+secretion+of+catecholamines+from+adrenal+medullary+cells.">Temporal characteristics of quantal secretion of catecholamines from adrenal medullary cells.</a> J Biol Chem. 268 (20), 14694-14700 (1993).</li><li>Daniels, A., Williams, R., Wright, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+character+of+the+stored+molecules+in+chromaffin+granules+of+the+adrenal+medulla:+a+nuclear+magnetic+resonance+study.">The character of the stored molecules in chromaffin granules of the adrenal medulla: a nuclear magnetic resonance study.</a> Neurosci. 3 (6), 573-585 (1978).</li><li>Borges, R., Travis, E. R., Hochstetler, S. E., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+external+osmotic+pressure+on+vesicular+secretion+from+bovine+adrenal+medullary+cells.">Effects of external osmotic pressure on vesicular secretion from bovine adrenal medullary cells.</a> J Biol Chem. 272 (13), 8325-8331 (1997).</li><li>Troyer, K. P., Mundorf, M. L., Fries, H. E., Wightman, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Separating+vesicle+fusion+and+exocytosis+in+hypertonic+conditions.">Separating vesicle fusion and exocytosis in hypertonic conditions.</a> Ann NY Acad Sci. 971 (1), 251-253 (2002).</li><li>Brodwick, M. S., Curran, M., Edwards, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+osmotic+stress+on+mast+cell+vesicles+of+the+beige+mouse.">Effects of osmotic stress on mast cell vesicles of the beige mouse.</a> J Membrane Biol. 126 (2), 159-169 (1992).</li><li>Amatore, C., Arbault, S., Bonifas, I., Lemaitre, F., Verchier, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vesicular+exocytosis+under+hypotonic+conditions+shows+two+distinct+populations+of+dense+core+vesicles+in+bovine+chromaffin+cells.">Vesicular exocytosis under hypotonic conditions shows two distinct populations of dense core vesicles in bovine chromaffin cells.</a> Chem Phys Chem. 8 (4), 578-585 (2007).</li><li>Hampton, R. Y., Holz, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+changes+in+osmolality+on+the+stability+and+function+of+cultured+chromaffin+cells+and+the+possible+role+of+osmotic+forces+in+exocytosis.">Effects of changes in osmolality on the stability and function of cultured chromaffin cells and the possible role of osmotic forces in exocytosis.</a> J Cell Biol. 96 (4), 1082-1088 (1983).</li><li>Troyer, K. P., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+separation+of+vesicle+release+from+vesicle+fusion+during+exocytosis.">Temporal separation of vesicle release from vesicle fusion during exocytosis.</a> J Biol Chem. 277 (32), 29101-29107 (2002).</li><li>Pihel, K., Travis, E. R., Borges, R., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exocytotic+release+from+individual+granules+exhibits+similar+properties+at+mast+and+chromaffin+cells.">Exocytotic release from individual granules exhibits similar properties at mast and chromaffin cells.</a> Biophys J. 71 (3), 1633 (1996).</li><li>Jankowski, J. A., Finnegan, J. M., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+ionic+composition+alters+kinetics+of+vesicular+release+of+catecholamines+and+quantal+size+during+exocytosis+at+adrenal+medullary+cells.">Extracellular ionic composition alters kinetics of vesicular release of catecholamines and quantal size during exocytosis at adrenal medullary cells.</a> J Neurochem. 63 (5), 1739-1747 (1994).</li><li>Leszczyszyn, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nicotinic+receptor-mediated+catecholamine+secretion+from+individual+chromaffin+cells.+Chemical+evidence+for+exocytosis.">Nicotinic receptor-mediated catecholamine secretion from individual chromaffin cells. Chemical evidence for exocytosis.</a> J Biol Chem. 265 (25), 14736-14737 (1990).</li><li>Wightman, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporally+resolved+catecholamine+spikes+correspond+to+single+vesicle+release+from+individual+chromaffin+cells.">Temporally resolved catecholamine spikes correspond to single vesicle release from individual chromaffin cells.</a> P Natl Acad Sci. 88 (23), 10754-10758 (1991).</li><li>Fathali, H., Dunevall, J., Majdi, S., Cans, A. -. 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We here present a protocol and the advantages of combining three complementary analytical methods to analyze secretory vesicles and the exocytosis process to gain a better understanding of how a physical force such as osmotic pressure can affect secretory vesicles and the exocytosis process in secretory cells. These methods include carbon fiber microelectrode amperometry, which is an established method for recording exocytosis activity, intracellular electrochemical cytometry, which is used to determine quantal size of v...

Chromaffin cells in adrenal glands are neuroendocrine cells that release neurotransmitter molecules into the blood stream. This occurs through a cellular process that involves the docking and fusion of neurotransmitter-filled vesicles, resulting in content release from vesicles to the extracellular space in a process called exocytosis. The neurotransmitters (adrenaline and noradrenaline) in chromaffin cells are actively transported by membrane proteins into large dense core vesicles (LDCVs) and stored at high concentrations (~0.5-1 M)1,2. Accumulation of neurotransmitters inside the LDCVs is accomplished by the affinity of catecholamine molecules to the intravesicular dense core protein matrix comprised of chromogranin proteins (~169 mg/mL)3,4,5,6, and an intravesicular cocktail solution containing key components for catecholamine loading and storage into the vesicle such as ATP (125-300 mM)7, Ca2+ (50-100 &#181;M in the solution and ~40 mM bound to the protein matrix)8, Mg2+ (5 mM)9, ascorbate (10-30 mM)10, and a pH of ~5.511,12. The LDCVs maintain an iso-osmotic condition with the cell cytoplasm (310 mOsm/kg)13, even though the theoretical solute concentration inside the vesicles sum up to more than 750 mM. The composition of the intravesicular components is not only essential for the loading and storage of catecholamines, but also for aggregation of solutes to the dense core protein matrix. This significantly reduces the osmolarity of the vesicles is significantly reduced and can affect the amount catecholamine that is released during exocytosis5,6.
Studies on the effect of extracellular osmotic pressure on the exocytosis process by amperometric recording have reported that high extracellular osmotic pressure inhibits exocytosis activity and reduces the number of neurotransmitters secreted from single vesicle compartments4,14,15,16,17,18,19. The explanations of these observations have speculated on the possible enhancement of macromolecular crowding in the cell cytoplasm inhibiting vesicle fusion events, and an alteration in membrane biophysical properties affecting the number of neurotransmitters released during exocytosis. These thoughts assumed that high extracellular osmotic stress does not affect the vesicle quantal size, which defines the number of neurotransmitter molecules stored in a vesicle compartment at prior stage of triggered exocytosis14,15,17,19,20,21. In amperometric measurements of exocytosis release in single cells, a carbon fiber disc microelectrode is placed in close contact with the cell surface, creating an experimental set up mimicking the synapse configuration, where the amperometric electrode serves as a postsynaptic detector (Figure 1)22,23. By stimulating a cell to exocytosis, one can induce neurotransmitter-filled vesicles to fuse with the cell plasma membrane and release part or the full vesicle content into the extracellular space. These neurotransmitter molecules released at the surface of the electrode can be detected electrochemically if the neurotransmitters are electroactive (e.g., catecholamines) by applying a redox potential of +700 mV vs a Ag/AgCl reference electrode. Consequently, a series of current spikes mark the detection of individual exocytosis events. From the current versus time trace in an amperometric recording, the area under each single amperometric spike represents the charge detected per exocytosis event and can be converted to the mole of neurotransmitters released, using the Faraday equation. Hence, the amperometric recordings provide quantitative information on the amount neurotransmitters expelled from single exocytosis events and report on the frequency of exocytosis events, but do not present quantitative information on the secretory vesicles content before vesicle fusion and neurotransmitter release has been initiated.
Therefore, to get a better understanding of how secretory vesicles in the cell cytoplasm respond to extracellular osmotic stress before the cell is triggered to undergo exocytosis, other complementary analytical methods can be used to enrich this information. For instance, to investigate if osmotic stress alters vesicle volume, transmission electron microscopy (TEM) imaging analysis can be used to measure the vesicle size of cells after chemical fixation. To examine if osmotic stress affects vesicle quantal size, a recently developed amperometric technique called intracellular electrochemical cytometry, can be applied for quantification of vesicle neurotransmitter content at secretory vesicles in their native state when still residing in the cytoplasm of live cells26. In the intracellular electrochemical cytometry technique, a nanotip cylindrical carbon fiber electrode is gently inserted into the cytoplasm of live cells and, by applying a +700 mV potential to this electrode (vs a Ag/AgCl reference electrode), the catecholamine content in vesicles can be quantified by the detection of a redox current spike from single vesicles colliding, adsorbing, and subsequently stochastically rupturing at the electrode surface and thereby releasing their contents against the electrode surface26. Hence, in the amperometric current versus time trace, each single vesicle rupturing event can result in a current transient and, by integrating the area of each current spike, the vesicle quantal size can be calculated using Faraday&#180;s law.
Therefore, by linking the quantitative information gained from vesicle size measurements using TEM imaging together with vesicle quantal size analysis, as recorded by intracellular electrochemical cytometry, vesicle neurotransmitter concentration can also be determined. This allows vesicle characterization when cells are exposed to different osmotic conditions and provides a better view on how vesicles may respond to extracellular osmotic stress at the stage prior to exocytosis. The results from combining these methods have shown that in the presence of extracellular high osmotic pressure, vesicles shrink and adjust their quantal size and comparing the quantitative information on the relative changes from these measurements shows that while shrinking, vesicles adjust their contents and size to maintain a constant neurotransmitter concentration24. Thus, this understanding is valuable in connecting to the observations made on neurotransmitter release in cells exposed to osmotic stress. In these protocols, we describe the use of these three complementary methodologies that allow the characterization of how secretory vesicles in their native environment respond to extracellular osmolality and the effects of this response on the exocytosis process. In addition to our previous observations regarding the effect of high osmotic pressure on exocytosis24, we present additional experiments that describe cell recovery after osmotic shock and the effect of multiple barium stimulations in chromaffin cells.

<table border="0" cellpadding="0" cellspacing="0" style="width:631px;" width="631">
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		<col />
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	</colgroup>
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">NaCl</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">S7653</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">KCl</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">P9333</td>
			<td></td>
		</tr>
		<tr height="27">
			<td height="27" style="height:27px;width:216px;">NaHCO3</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">S5761</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">HEPES</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">H3375</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">MgCl2</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">M-2670</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Glucose</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">G8270</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Collagenase P</td>
			<td style="width:129px;">Roche, Sweden</td>
			<td style="width:119px;">11 213 857 001</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">100-&#181;M Nylon mesh</td>
			<td style="width:129px;">Fisher Sientific</td>
			<td style="width:119px;">08-771-19</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Percoll</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">P1677</td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Collagen IV coated 60 mm plastic dish</td>
			<td style="width:129px;">VWR</td>
			<td style="width:119px;">354416</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Centrifuge</td>
			<td style="width:129px;">Avanti J-20XP</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Borosilicate glass capillary</td>
			<td style="width:129px;">Sutter instrument Co., Novato, CA</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Micropipette puller</td>
			<td style="width:129px;">Narishing Inc., Japan</td>
			<td style="width:119px;">PE-21</td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Epoxy solutions (A and B)</td>
			<td style="width:129px;">Epoxy technology, Billerica, MA</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Beveller</td>
			<td style="width:129px;">Narishing Inc.</td>
			<td style="width:119px;">EG-400</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Inverted Microscope</td>
			<td style="width:129px;">Olympus</td>
			<td style="width:119px;">IX81</td>
			<td></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:216px;">Patch clamp Instrument</td>
			<td style="width:129px;">Molecular Devices, Sunnyvale, CA</td>
			<td style="width:119px;">Axopatch 200B</td>
			<td></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:216px;">Micromanipulator</td>
			<td style="width:129px;">Burleigh Instrument Inc., USA</td>
			<td style="width:119px;">PCS-5000</td>
			<td></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:216px;">Butane Flame</td>
			<td style="width:129px;">Multiflame AB, H&#228;sselholm, Sweden</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Transmission electron microscopy</td>
			<td style="width:129px;">Omega</td>
			<td style="width:119px;">Leo 912 AB</td>
			<td></td>
		</tr>
	</tbody>
</table>

monitoring the effect of osmotic stress on secretory vesicles and exocytosis

Amperometry recording of cells subjected to osmotic shock show that secretory cells respond to this physical stress by reducing the exocytosis activity and the amount of neurotransmitter released from vesicles in single exocytosis events. It has been suggested that the reduction in neurotransmitters expelled is due to alterations in membrane biophysical properties when cells shrink in response to osmotic stress and with assumptions made that secretory vesicles in the cell cytoplasm are not affected by extracellular osmotic stress. Amperometry recording of exocytosis monitors what is released from cells the moment a vesicle fuses with the plasma membrane, but does not provide information on the vesicle content before the vesicle fusion is triggered. Therefore, by combining amperometry recording with other complementary analytical methods that are capable of characterizing the secretory vesicles before exocytosis at cells is triggered offers a broader overview for examining how secretory vesicles and the exocytosis process are affected by osmotic shock. We here describe how complementing amperometry recording with intracellular electrochemical cytometry and transmission electron microscopy (TEM) imaging can be used to characterize alterations in secretory vesicles size and neurotransmitter content at chromaffin cells in relation to exocytosis activity before and after exposure to osmotic stress. By linking the quantitative information gained from experiments using all three analytical methods, conclusions were previously made that secretory vesicles respond to extracellular osmotic stress by shrinking in size and reducing the vesicle quantal size to maintain a constant vesicle neurotransmitter concentration. Hence, this gives some clarification regarding why vesicles, in response to osmotic stress, reduce the amount neurotransmitters released during exocytosis release. The amperometric recordings here indicate this is a reversible process and that vesicle after osmotic shock are refilled with neurotransmitters when placed cells are reverted into an isotonic environment.

We here describe the protocol for how combining TEM imaging together with two electrochemical methodologies, carbon fiber amperometry and intracellular electrochemical cytometry, can provide information that gains a broader view alluding to the effect of extracellular osmotic pressure on secretory vesicles and the exocytosis process. By comparing representative amperometric recordings of exocytosis release at single chromaffin cells using the experimental set up (shown in Figure 1), a signif...

Watch this Scientific Journal Video about Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis at JoVE.com

Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis

Osmotic stress affects exocytosis and the amount of neurotransmitter released during this process. We demonstrate how combining electrochemical methods together with transmission electron microscopy can be used to study the effect of extracellular osmotic pressure on exocytosis activity, vesicle quantal size, and the amount of neurotransmitter released during exocytosis.

Amperometry recording of cells subjected to osmotic shock show that secretory cells respond to this physical stress by reducing the exocytosis activity ...

The overall goal of this combined analytical methodology is to provide information on how secretory vesicles in cells respond to a physical force, such as extracellular osmotic pressure, and how adjustments of these organelles further affect the exocytosis process. This method can help answer key questions in the neuroscience field such as, how do secretory vesicles directly respond to changes in the extracellular environment or to drug treatment? The main advantage of this approach is to monitor direct effects on vesicular content at live cells and knowing to distinguish alteration in their reh-chemical-ed release before and after exocytosis is treated.To obtain a flat disk electrode surface, place the electrode in the holder of a microgrinder and bevel each carbon fiber electrode at an angle of 45 degrees. Afterward, mark the capillary for future reference of how to locate the disk electrode surface at a 45 degree angle when placing the electrode near cells for exocytosis measurement. To perform amperometric recording at single cells, mount the freshly beveled and tested carbon fiber disk microelectrode in the electrode holder of the head stage that is used with a potentiostat.Before use, place each carbon fiber microelectrode in a test solution to monitor the study state current using cyclic voltammetry. For a cyclic voltammetry scan, apply a triangle potential waveform from negative 0.2 volts to positive 0.8 volts against a silver-silver chloride reference electrode at 100 milivolts per second to ensure good reaction kinetics. For amperometry recording of exocytosis, place the Petri dish with cultured chromaffin cells in isotonic buffer on an inverted microscope in a Faraday cage.Use a microscope heating stage to maintain a temperature of 37 degrees Celsius during the cell experiments. Next, use a low-noise patch clamp instrument to apply a constant potential of positive 700 millivolts at the working electrode. For recording exocytosis of chromaffin cells, digitalize the signal at 10 kilohertz and apply an internal low-pass Bessel filter at two kilohertz to filter the recorded signal.Note that the oval disk electrode needs to be placed flat on top of the cells and parallel to the surface of the Petri dish. Also, electrodes are beveled the same day as experiments to ensure a clean electrode surface. To stimulate the cell exocytosis, position a glass micropipette filled with five millimolar barium chloride solution at a distance of at least 20 micrometers away from the cell.Then, apply a five seconds injection pulse of five millimolar barium chloride solution on the cell's surface to stimulate the cell exocytosis. Place the stem pipette in the solution and stimulate the cell exocytosis by applying a barium injection pulse while recording the amperometric current transients for approximately three minutes. To compare the exocytotic responses in isotonic conditions to hypertonic conditions, incubate the cells for 10 minutes in hypertonic buffer solution.Thereafter, apply a barium injection pulse to stimulate exocytosis, and perform three minutes of amperometric recording. For the reversible response of cells, incubate the cells again for 10 minutes in an isotonic buffer solution. Stimulate the cells by applying a barium injection pulse and perform three minutes of recording of the exocytotic response.To fabricate the electrodes for vesicular quantal size measurements, prepare a carbon fiber electrode with a diameter of five micrometers. Under a microscope, use a scalpel to cut the carbon fiber that is extending out of the glass tip so that only 30 to 100 micrometers is left. Use a butane flame to prepare a flame-etched tip of the carbon fiber electrode.To achieve an evenly-etched, cylindrical-shaped electrode tip, hold the cylindrical-shaped carbon fiber electrode while rotating it. And place the carbon fiber extending from the glass into the blue edge of the butane flame until the tip of the carbon develops a red color. After flame etching, place the electrode under a microscope to evaluate the electrode tip.The etched electrode tip size should be about 50 to 100 nanometers in diameter. Next, insert the cylindrical nanotip microelectrode into the epoxy solution for three minutes followed by a 15 seconds dipping of the electrode tip into the acetone solution. This allow the epoxy to seal the potential gap space between the carbon fiber and the insulating gas capillary wall.While the acetone clears the epoxy off the etched carbon fiber electrode surface. To cure the epoxy, bake the electrodes in an oven overnight at 100 degrees Celsius. Before use, test the steady state current of each carbon fiber microelectrode using cyclic voltammetry.For experiments, use only electrodes that display a plateau current around 1.5 to 2.5 nanoamperes. For intracellular amperometry measurements, place the cells under the microscope and use the same experimental settings of the potentiostat. Prevent significant physical damage to the cell.Insert the nanotip cylindrical microelectrode into the cell by adding a gentle mechanical force. Just enough to push the electrode through the cell plasma membrane and into the cell cytoplasm using a micromanipulator. After insertion, and with the cell membrane sealed around the cylindrical electrode, start the amperometric recording in-situ at the live cell.At the oxidation potential applied to the electrode, vesicles adsorbed to the electrode surface and stochastically rupture. Hence, there is no need for any kind of stimulus to initiate this process. To determine the osmotic effect on vesicular quantal size, collect the intracellular cytometry measurements from a group of cells that have been incubated in isotonic and in hypertonic buffer using the experimental condition.The effect of extracellular osmolality on exocytosis activity is presented as the frequency of exocytosis events when chromaffin cells are stimulated with barium solution in isotonic, then hypertonic, and finally in isotonic conditions. This data shows an inhibition in exocytosis activity at cells experiencing osmotic stress and a partial recovery can be achieved after cells returned to an isotonic environment. The control experiment shows the frequency of exocytosis events after three consecutive barium stimulations at chromaffin cells in isotonic conditions.This shows that multiple barium stimulation within the time frame used in these experiments are causing a reduction in exocytosis activity by consecutive cell stimulation. After watching this video, you should have a good understanding of how to perform these complimentary analytical methods that allow you to compare how secretory vesicles and the exocytosis process are affected by alterations in the extracellular environment.

monitoring-effect-osmotic-stress-on-secretory-vesicles

Research

JoVE Journal

Neuroscience

Brain Imaging Investigation of the Memory-Enhancing Effect of Emotion

Emotional events tend to be better remembered than non-emotional events1,2. One goal of cognitive and affective neuroscientists is 
to understand the neural mechanisms underlying this enhancing effect of emotion on memory. A method that has proven particularly influential in the 
investigation of the memory-enhancing effect of emotion is the so-called subsequent memory paradigm (SMP). This method was originally used to investigate the 
neural correlates of non-emotional memories3, and more recently we and others also applied it successfully to studies of emotional memory (reviewed in4, 5-7). 
Here, we describe a protocol that allows investigation of the neural correlates of the memory-enhancing effect of emotion using the SMP in conjunction with 
event-related functional magnetic resonance imaging (fMRI). An important feature of the SMP is that it allows separation of brain activity specifically 
associated with memory from more general activity associated with perception. Moreover, in the context of investigating the impact of emotional stimuli, 
SMP allows identification of brain regions whose activity is susceptible to emotional modulation of both general/perceptual and memory-specific processing. 
This protocol can be used in healthy subjects8-15, as well as in clinical patients where there are alterations in the neural correlates of emotion perception 
and biases in remembering emotional events, such as those suffering from depression and post-traumatic stress disorder (PTSD)16, 17.

We present a protocol that uses functional magnetic resonance imaging to investigate the neural correlates of the memory-enhancing effect of emotion. This protocol allows identification of brain activity specifically linked to memory-related processing, contrary to more general perceptual processing, and can be used with healthy and clinical populations.

Emotional events tend to be better remembered than non-emotional events1,2. One goal of cognitive and affective neuroscientists is 
to understand the ...

Brain Imaging Investigation of the Impairing Effect of Emotion on Cognition

Emotions can impact cognition by exerting both enhancing (e.g., better memory for emotional events) and impairing (e.g., increased emotional distractibility) effects (reviewed in 1). Complementing our recent protocol 2 describing a method that allows investigation of the neural correlates of the memory-enhancing effect of emotion (see also 1, 3-5), here we present a protocol that allows investigation of the neural correlates of the detrimental impact of emotion on cognition. The main feature of this method is that it allows identification of reciprocal modulations between activity in a ventral neural system, involved in 'hot' emotion processing (HotEmo system), and a dorsal system, involved in higher-level 'cold' cognitive/executive processing (ColdEx system), which are linked to cognitive performance and to individual variations in behavior (reviewed in 1). Since its initial introduction 6, this design has proven particularly versatile and influential in the elucidation of various aspects concerning the neural correlates of the detrimental impact of emotional distraction on cognition, with a focus on working memory (WM), and of coping with such distraction 7,11, in both healthy 8-11 and clinical participants 12-14.

We present a protocol that allows investigation of the neural mechanisms mediating the detrimental impact of emotion on cognition, using functional magnetic resonance imaging. This protocol can be used with both healthy and clinical participants.

Emotions can impact cognition by exerting both enhancing (e.g., better memory for emotional events) and impairing (e.g., increased emotional ...

Vibrodissociation of Neurons from Rodent Brain Slices to Study Synaptic Transmission and Image Presynaptic Terminals

Mechanical dissociation of neurons from the central nervous system has the advantage that presynaptic boutons remain attached to the isolated neuron of interest. This allows for examination of synaptic transmission under conditions where the extracellular and postsynaptic intracellular environments can be well controlled. A vibration-based technique without the use of proteases, known as vibrodissociation, is the most popular technique for mechanical isolation. A micropipette, with the tip fire-polished to the shape of a small ball, is placed into a brain slice made from a P1-P21 rodent. The micropipette is vibrated parallel to the slice surface and lowered through the slice thickness resulting in the liberation of isolated neurons. The isolated neurons are ready for study within a few minutes of vibrodissociation. This technique has advantages over the use of primary neuronal cultures, brain slices and enzymatically isolated neurons including: rapid production of viable, relatively mature neurons suitable for electrophysiological and imaging studies; superior control of the extracellular environment free from the influence of neighboring cells; suitability for well-controlled pharmacological experiments using rapid drug application and total cell superfusion; and improved space-clamp in whole-cell recordings relative to neurons in slice or cell culture preparations. This preparation can be used to examine synaptic physiology, pharmacology, modulation and plasticity. Real-time imaging of both pre- and postsynaptic elements in the living cells and boutons is also possible using vibrodissociated neurons. Characterization of the molecular constituents of pre- and postsynaptic elements can also be achieved with immunological and imaging-based approaches.

This report demonstrates a technique for mechanical isolation of individual viable neurons retaining attached presynaptic boutons. Vibrodissociated neurons have the advantages of rapid production, excellent pharmacological control and improved space-clamp without influence from neighboring cells. This method can be used for imaging of synaptic elements and patch-clamp recording.

Mechanical dissociation of neurons from the central nervous system has the advantage that presynaptic boutons remain attached to the isolated neuron of ...

Modeling Neural Immune Signaling of Episodic and Chronic Migraine Using Spreading Depression In Vitro

Migraine and its transformation to chronic migraine are healthcare burdens in need of improved treatment options. We seek to define how neural immune signaling modulates the susceptibility to migraine, modeled in vitro using spreading depression (SD), as a means to develop novel therapeutic targets for episodic and chronic migraine. SD is the likely cause of migraine aura and migraine pain. It is a paroxysmal loss of neuronal function triggered by initially increased neuronal activity, which slowly propagates within susceptible brain regions. Normal brain function is exquisitely sensitive to, and relies on, coincident low-level immune signaling. Thus, neural immune signaling likely affects electrical activity of SD, and therefore migraine. Pain perception studies of SD in whole animals are fraught with difficulties, but whole animals are well suited to examine systems biology aspects of migraine since SD activates trigeminal nociceptive pathways. However, whole animal studies alone cannot be used to decipher the cellular and neural circuit mechanisms of SD. Instead, in vitro preparations where environmental conditions can be controlled are necessary. Here, it is important to recognize limitations of acute slices and distinct advantages of hippocampal slice cultures. Acute brain slices cannot reveal subtle changes in immune signaling since preparing the slices alone triggers: pro-inflammatory changes that last days, epileptiform behavior due to high levels of oxygen tension needed to vitalize the slices, and irreversible cell injury at anoxic slice centers. 
In contrast, we examine immune signaling in mature hippocampal slice cultures since the cultures closely parallel their in vivo counterpart with mature trisynaptic function; show quiescent astrocytes, microglia, and cytokine levels; and SD is easily induced in an unanesthetized preparation. Furthermore, the slices are long-lived and SD can be induced on consecutive days without injury, making this preparation the sole means to-date capable of modeling the neuroimmune consequences of chronic SD, and thus perhaps chronic migraine. We use electrophysiological techniques and non-invasive imaging to measure neuronal cell and circuit functions coincident with SD. Neural immune gene expression variables are measured with qPCR screening, qPCR arrays, and, importantly, use of cDNA preamplification for detection of ultra-low level targets such as interferon-gamma using whole, regional, or specific cell enhanced (via laser dissection microscopy) sampling. Cytokine cascade signaling is further assessed with multiplexed phosphoprotein related targets with gene expression and phosphoprotein changes confirmed via cell-specific immunostaining. Pharmacological and siRNA strategies are used to mimic and modulate SD immune signaling.

Modeling Neural Immune Signaling of Episodic and Chronic Migraine Using Spreading Depression In Vitro

Migraine and its transformation to chronic migraine are immense healthcare burdens in need of improved treatment options. We seek to define how neural immune signaling modulates the susceptibility to migraine, modeled in vitro using spreading depression in hippocampal slice cultures, as a means to develop novel therapeutic targets.

Migraine and its transformation to chronic migraine are healthcare burdens in need of improved treatment options.  We seek to define how neural immune ...

In Vivo Two-photon Imaging Of Experience-dependent Molecular Changes In Cortical Neurons

The brain's ability to change in response to experience is essential for healthy brain function, and abnormalities in this process contribute to a variety of brain disorders1,2. To better understand the mechanisms by which brain circuits react to an animal's experience requires the ability to monitor the experience-dependent molecular changes in a given set of neurons, over a prolonged period of time, in the live animal. While experience and associated neural activity is known to trigger gene expression changes in neurons1,2, most of the methods to detect such changes do not allow repeated observation of the same neurons over multiple days or do not have sufficient resolution to observe individual neurons3,4. Here, we describe a method that combines in vivo two-photon microscopy with a genetically encoded fluorescent reporter to track experience-dependent gene expression changes in individual cortical neurons over the course of day-to-day experience. 
One of the well-established experience-dependent genes is Activity-regulated cytoskeletal associated protein (Arc)5,6. The transcription of Arc is rapidly and highly induced by intensified neuronal activity3, and its protein product regulates the endocytosis of glutamate receptors and long-term synaptic plasticity7. The expression of Arc has been widely used as a molecular marker to map neuronal circuits involved in specific behaviors3. In most of those studies, Arc expression was detected by in situ hybridization or immunohistochemistry in fixed brain sections. Although those methods revealed that the expression of Arc was localized to a subset of excitatory neurons after behavioral experience, how the cellular patterns of Arc expression might change with multiple episodes of repeated or distinctive experiences over days was not investigated. 
In vivo two-photon microscopy offers a powerful way to examine experience-dependent cellular changes in the living brain8,9. To enable the examination of Arc expression in live neurons by two-photon microscopy, we previously generated a knock-in mouse line in which a GFP reporter is placed under the control of the endogenous Arc promoter10. This protocol describes the surgical preparations and imaging procedures for tracking experience-dependent Arc-GFP expression patterns in neuronal ensembles in the live animal. In this method, chronic cranial windows were first implanted in Arc-GFP mice over the cortical regions of interest. Those animals were then repeatedly imaged by two-photon microscopy after desired behavioral paradigms over the course of several days. This method may be generally applicable to animals carrying other fluorescent reporters of experience-dependent molecular changes4.

In Vivo Two-photon Imaging Of Experience-dependent Molecular Changes In Cortical Neurons

Experience-dependent molecular changes in neurons are essential for the brain's ability to adapt in response to behavioral challenges. An in vivo two-photon imaging method is described here that allows the tracking of such molecular changes in individual cortical neurons through genetically encoded reporters.

The brain's ability to change in response to experience is essential for healthy brain function, and abnormalities in this process contribute to a variety ...

Stereotaxic Infusion of Oligomeric Amyloid-beta into the Mouse Hippocampus

Alzheimer&#8217;s disease is a neurodegenerative disease affecting the aging population. A key neuropathological feature of the disease is the over-production of amyloid-beta and the deposition of amyloid-beta plaques in brain regions of the afflicted individuals. Throughout the years scientists have generated numerous Alzheimer&#8217;s disease mouse models that attempt to replicate the amyloid-beta pathology. Unfortunately, the mouse models only selectively mimic the disease features. Neuronal death, a prominent effect in the brains of Alzheimer&#8217;s disease patients, is noticeably lacking in these mice. Hence, we and others have employed a method of directly infusing soluble oligomeric species of amyloid-beta - forms of amyloid-beta that have been proven to be most toxic to neurons - stereotaxically into the brain. In this report we utilize male C57BL/6J mice to document this surgical technique of increasing amyloid-beta levels in a select brain region. The infusion target is the dentate gyrus of the hippocampus because this brain structure, along with the basal forebrain that is connected by the cholinergic circuit, represents one of the areas of degeneration in the disease. The results of elevating amyloid-beta in the dentate gyrus via stereotaxic infusion reveal increases in neuron loss in the dentate gyrus within 1 week, while there is a concomitant increase in cell death and cholinergic neuron loss in the vertical limb of the diagonal band of Broca of the basal forebrain. These effects are observed up to 2 weeks. Our data suggests that the current amyloid-beta infusion model provides an alternative mouse model to address region specific neuron death in a short-term basis. The advantage of this model is that amyloid-beta can be elevated in a spatial and temporal manner.

Here, we present a protocol for direct stereotaxic brain infusion of amyloid-beta. This methodology provides an alternative in vivo mouse model to address the short-term effects of amyloid-beta on brain neurons.

Alzheimer&#8217;s disease is a neurodegenerative disease affecting the aging population. A key neuropathological feature of the disease is the ...

Characterization of Immune Cell-derived Extracellular Vesicles and Studying Functional Impact on Cell Environment

The neuroinflammatory state of the central nervous system (CNS) plays a key role in physiological and pathological conditions. Microglia, the resident immune cells in the brain, and sometimes the infiltrating bone marrow-derived macrophages (BMDMs), regulate the inflammatory profile of their microenvironment in the CNS. It is now accepted that the extracellular vesicle (EV) populations from immune cells act as immune mediators. Thus, their collection and isolation are important to identify their contents but also evaluate their biological effects on recipient cells. The present data highlight chronological requirements for EV isolation from microglia cells or blood macrophages including the ultracentrifugation and size-exclusion chromatography (SEC) steps. A non-targeted proteomic analysis permitted the validation of protein signatures as EV markers and characterized the biologically active EV contents. Microglia-derived EVs were also functionally used on primary culture of neurons to assess their importance as immune mediators in the neurite outgrowth. The results showed that microglia-derived EVs contribute to facilitate the neurite outgrowth in vitro. In parallel, blood macrophage-derived EVs were functionally used as immune mediators in spheroid cultures of C6 glioma cells, the results showing that these EVs control the glioma cell invasion in vitro. This report highlights the possibility to evaluate the EV-mediated immune cell functions but also understand the molecular bases of such a communication. This deciphering could promote the use of natural vesicles and/or the in vitro preparation of therapeutic vesicles in order to mimic immune properties in the microenvironment of CNS pathologies.

The present report highlights chronological requirements for extracellular vesicle (EV) isolation from microglia or blood macrophages. Microglia-derived EVs were evaluated as regulators of the neurite outgrowth while blood macrophage-derived EVs were studied in the control of C6 glioma cell invasion in in vitro assays. The goal is to better understand these EV functions as immune mediators in specific microenvironments.

The neuroinflammatory state of the central nervous system (CNS) plays a key role in physiological and pathological conditions. Microglia, the resident ...

Implantation of Osmotic Pumps and Induction of Stress to Establish a Symptomatic, Pharmacological Mouse Model for DYT/PARK-ATP1A3 Dystonia

Genetically modified mouse models face limitations, especially when studying movement disorders, where most of the available transgenic rodent models do not present a motor phenotype resembling the clinical aspects of the human disease. Pharmacological mouse models allow for a more direct study of the pathomechanisms and their effect on the behavioral phenotype. Osmotic pumps connected to brain cannulas open up the possibility of creating pharmacological mouse models via local and chronic drug delivery. For the hereditary movement disorder of rapid-onset dystonia-parkinsonism, the loss-of-function mutation in the &#945;3-subunit of the Na+/K+-ATPase can be simulated by a highly specific blockade via the glycoside ouabain. In order to locally block the &#945;3-subunit in the basal ganglia and the cerebellum, which are the two brain structures believed to be heavily involved in the pathogenesis of rapid-onset dystonia-parkinsonism, a bilateral cannula is stereotaxically implanted into the striatum and an additional single cannula is introduced into the cerebellum. The cannulas are connected via vinyl tubing to two osmotic pumps, which are subcutaneously implanted on the back of the animals and allow for the chronic and precise delivery of ouabain. The pharmacological mouse model for rapid-onset dystonia-parkinsonism carries the additional advantage of recapitulating the clinical and pathological features of asymptomatic and symptomatic mutation carriers. Just like mutation carriers of rapid-onset dystonia parkinsonism, the ouabain-perfused mice develop dystonia-like movements only after additional exposure to stress. We demonstrate a mild stress paradigm and introduce two modified scoring systems for the assessment of a motor phenotype.

We provide a protocol to generate a pharmacological DYT/PARK-ATP1A3 dystonia mouse model via implantation of cannulas into basal ganglia and cerebellum connected to osmotic pumps. We describe the induction of dystonia-like movements via application of a motor challenge and the characterization of the phenotype via behavioral scoring systems.

Genetically modified mouse models face limitations, especially when studying movement disorders, where most of the available transgenic rodent models do ...

Osmotic Pump-based Drug-delivery for In Vivo Remyelination Research on the Central Nervous System

Demyelination has been identified in not only multiple sclerosis (MS), but also other central nervous system diseases such as Alzheimer's disease and autism. As evidence suggests that remyelination can effectively ameliorate the disease symptoms, there is an increasing focus on drug development to promote the myelin regeneration process. Thus, a region-selectable and result-reliable drug delivery technique is required to test the efficiency and specificity of these drugs in vivo. This protocol introduces the osmotic pump implant as a new drug delivery approach in the lysolecithin-induced demyelination mouse model. The osmotic pump is a small implantable device that can bypass the blood-brain barrier (BBB) and deliver drugs steadily and directly to specific areas of the mouse brain. It can also effectively improve the bioavailability of drugs such as peptides and proteins with a short half-life. Therefore, this method is of great value to the field of central nervous system myelin regeneration research.

Osmotic Pump-based Drug-delivery for In Vivo Remyelination Research on the Central Nervous System

Demyelination takes place in multiple central nervous system diseases. A reliable in vivo drug delivery technique is necessary for remyelinating drug testing. This protocol describes an osmotic pump-based method that allows long-term drug delivery directly into the brain parenchyma and improves the drug bioavailability, with broad application in remyelination research.

Demyelination has been identified in not only multiple sclerosis (MS), but also other central nervous system diseases such as Alzheimer's disease and ...

Examining the Effect of Pesticides on Caenorhabditis elegans Neurons

Caenorhabditis elegans is a powerful model organism used in many research laboratories to understand the consequences of exposure to chemical pollutants, pesticides, and a wide variety of toxic substances. These nematodes are easy to work with and can be used to generate novel research findings, even in the undergraduate biology laboratory. A multi-week laboratory series of authentic, student-driven research projects trains students in a toolkit of techniques and approaches in behavioral measurements, cell biology, and microscopy that they then apply to their projects. One technique in that toolkit is quantifying the percentage of neurons exhibiting neurodegenerative damage following exposure to a chemical toxicant like a pesticide. Young adult C. elegans nematodes can be exposed to different concentrations of commercially available pesticides or other types of toxicants for 2-24 h. Then, undergraduate students can visualize different neuron subtypes using fluorescent-expressing strains of C. elegans. These techniques do not require sophisticated image processing software and are effective at even low magnifications, making the need for expensive confocal microscopy unnecessary. This paper demonstrates how to treat the nematodes with pesticides and how to image and score the neurons. It also provides a straightforward protocol for the microscopy and analysis of neuron morphology. The materials used for this technique are inexpensive and readily available in most undergraduate biology departments. This technique can be combined with behavioral measures like locomotion, basal slowing, or egg-laying to conduct a potentially publishable series of experiments and give undergraduate students an authentic research experience at a very low cost.

Examining the Effect of Pesticides on Caenorhabditis elegans Neurons

Young adult Caenorhabditis elegans nematodes are exposed to different concentrations of commercial pesticides or other toxicants for 2-24 h. Then, different neurons can be visualized using fluorescent-expressing strains. This paper demonstrates how to expose nematodes to pesticides and assess neuron damage.

Caenorhabditis elegans is a powerful model organism used in many research laboratories to understand the consequences of exposure to chemical pollutants, ...