This protocol is supported by a grant NRF-2015R1A2A1A01003410 from the Ministry of Science, ICT and Future Planning, Republic of Korea.

All experiments involving animals were approved by the institutional Animal Care and Use Committee of Ajou University School of Medicine.
1. Culture Preparation of Dissociated Adult DRG Neuron
<ol>
	<li>Before setting up the culture, pre-coat a 6-well plate with poly-D-lysine and laminin. Incubate a 6-well plate with 0.01% poly-D-lysine at 37&#176;C for 2 h or at 4&#176;C overnight. Then, wash the plate twice with distilled water.</li>
	<li>Incubate the plate with laminin solution at a conce...

<ol>
	<li>Donnelly, D. J., Popovich, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inflammation+and+its+role+in+neuroprotection,+axonal+regeneration+and+functional+recovery+after+spinal+cord+injury.">Inflammation and its role in neuroprotection, axonal regeneration and functional recovery after spinal cord injury.</a> Exp Neurol. 209 (2), 378-388 (2008).</li><li>Festoff, B. W., 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=Minocycline+neuroprotects,+reduces+microgliosis,+and+inhibits+caspase+protease+expression+early+after+spinal+cord+injury.">Minocycline neuroprotects, reduces microgliosis, and inhibits caspase protease expression early after spinal cord injury.</a> J Neurochem. 97 (5), 1314-1326 (2006).</li><li>Bowers, C. A., Kundu, B., Hawryluk, G. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methylprednisolone+for+acute+spinal+cord+injury:+an+increasingly+philosophical+debate.">Methylprednisolone for acute spinal cord injury: an increasingly philosophical debate.</a> Neural Regen Res. 11 (6), 882-885 (2016).</li><li>Gensel, J. C., Kigerl, K. A., Mandrekar-Colucci, S. S., Gaudet, A. D., Popovich, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Achieving+CNS+axon+regeneration+by+manipulating+convergent+neuro-immune+signaling.">Achieving CNS axon regeneration by manipulating convergent neuro-immune signaling.</a> Cell Tissue Res. 349 (1), 201-213 (2012).</li><li>DiSabato, D. J., Quan, N., Godbout, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuroinflammation:+the+devil+is+in+the+details.">Neuroinflammation: the devil is in the details.</a> J Neurochem. 139 Suppl 2, 136-153 (2016).</li><li>Jin, X., Yamashita, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microglia+in+central+nervous+system+repair+after+injury.">Microglia in central nervous system repair after injury.</a> J Biochem. 159 (5), 491-496 (2016).</li><li>Yin, Y., 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=Macrophage-derived+factors+stimulate+optic+nerve+regeneration.">Macrophage-derived factors stimulate optic nerve regeneration.</a> J Neurosci. 23 (6), 2284-2293 (2003).</li><li>Yin, Y., 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=Oncomodulin+is+a+macrophage-derived+signal+for+axon+regeneration+in+retinal+ganglion+cells.">Oncomodulin is a macrophage-derived signal for axon regeneration in retinal ganglion cells.</a> Nat Neurosci. 9 (6), 843-852 (2006).</li><li>Gensel, J. C., 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=Macrophages+promote+axon+regeneration+with+concurrent+neurotoxicity.">Macrophages promote axon regeneration with concurrent neurotoxicity.</a> J Neurosci. 29 (12), 3956-3968 (2009).</li><li>Barrette, B., 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=Requirement+of+myeloid+cells+for+axon+regeneration.">Requirement of myeloid cells for axon regeneration.</a> J Neurosci. 28 (38), 9363-9376 (2008).</li><li>Kwon, M. 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=Contribution+of+macrophages+to+enhanced+regenerative+capacity+of+dorsal+root+ganglia+sensory+neurons+by+conditioning+injury.">Contribution of macrophages to enhanced regenerative capacity of dorsal root ganglia sensory neurons by conditioning injury.</a> J Neurosci. 33 (38), 15095-15108 (2013).</li><li>Niemi, J. P., 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=A+critical+role+for+macrophages+near+axotomized+neuronal+cell+bodies+in+stimulating+nerve+regeneration.">A critical role for macrophages near axotomized neuronal cell bodies in stimulating nerve regeneration.</a> J Neurosci. 33 (41), 16236-16248 (2013).</li><li>Hannila, S. S., Filbin, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+cyclic+AMP+signaling+in+promoting+axonal+regeneration+after+spinal+cord+injury.">The role of cyclic AMP signaling in promoting axonal regeneration after spinal cord injury.</a> Exp Neurol. 209 (2), 321-332 (2008).</li><li>Kwon, M. 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=CCL2+Mediates+Neuron-Macrophage+Interactions+to+Drive+Proregenerative+Macrophage+Activation+Following+Preconditioning+Injury.">CCL2 Mediates Neuron-Macrophage Interactions to Drive Proregenerative Macrophage Activation Following Preconditioning Injury.</a> J Neurosci. 35 (48), 15934-15947 (2015).</li><li>Niemi, J. P., DeFrancesco-Lisowitz, A., Cregg, J. M., Howarth, M., Zigmond, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Overexpression+of+the+monocyte+chemokine+CCL2+in+dorsal+root+ganglion+neurons+causes+a+conditioning-like+increase+in+neurite+outgrowth+and+does+so+via+a+STAT3+dependent+mechanism.">Overexpression of the monocyte chemokine CCL2 in dorsal root ganglion neurons causes a conditioning-like increase in neurite outgrowth and does so via a STAT3 dependent mechanism.</a> Exp Neurol. 275 Pt 1, 25-37 (2016).</li><li>Cafferty, W. B., 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=Conditioning+injury-induced+spinal+axon+regeneration+fails+in+interleukin-6+knock-out+mice.">Conditioning injury-induced spinal axon regeneration fails in interleukin-6 knock-out mice.</a> J Neurosci. 24 (18), 4432-4443 (2004).</li><li>Cai, D., 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=Neuronal+cyclic+AMP+controls+the+developmental+loss+in+ability+of+axons+to+regenerate.">Neuronal cyclic AMP controls the developmental loss in ability of axons to regenerate.</a> J Neurosci. 21 (13), 4731-4739 (2001).</li><li>Neumann, S., Woolf, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regeneration+of+dorsal+column+fibers+into+and+beyond+the+lesion+site+following+adult+spinal+cord+injury.">Regeneration of dorsal column fibers into and beyond the lesion site following adult spinal cord injury.</a> Neuron. 23 (1), 83-91 (1999).</li></ol>

There are several critical steps for the generation of this co-culture system. It is important to ensure that the mouse DRG neurons and peritoneal macrophages are prepared fresh and healthy. We have experienced diminished neurite outgrowth activity of the CM when the dissection of all the DRGs took more than 30 min. In addition, the contamination of blood components in peritoneal macrophages also led to a decrease of neurite outgrowth activity in the CM. In order to elicit robust neuron-macrophage interaction by db-cAMP,...

A variety of studies have sought to enhance CNS axon regeneration after the injuries of the spinal cord or brain. Inflammatory reactions, inevitably accompanying the injuries in the nervous system, are traditionally thought to participate in secondary pathological processes leading to the deleterious outcomes1,2. Indeed, methylprednisolone that can suppress inflammatory reactions is the only approved therapy for acute spinal cord injury3. However, more recent studies have provided evidence that macrophages, a representative inflammatory cell type, can participate in the regeneration or repair of injured nervous system4,5,6. For example, infiltrating macrophages following a lens injury produce pro-regenerative molecules to promote the regeneration of the retinal ganglion neurons7,8. In addition, transplanted DRG neurons increased axon growth up the region where macrophages were activated by zymosan9. Moreover, the macrophages at the lesion site can create a growth-permissive milieu for injured peripheral nerves10.
Our work also provided strong evidence that macrophages can contribute to the capacity of axon regeneration in adjacent neurons. We have shown that the activation of macrophages in the dorsal root ganglia (DRG) were essential in the enhanced regenerative capacity of DRG sensory neurons following a preconditioning peripheral nerve injury11. Similar research was independently reported from another laboratory12. We also showed that intraganglionic injection of dibutyryl cyclic AMP (db-cAMP), which is a well-known molecule to enhance the capacity of axon regeneration13, induced the activation of macrophages. The deactivation of macrophages abolished the effects of db-cAMP on neurite outgrowth activity. Subsequent works identified injury-induced expression of CCL2 in neurons as a signal to stimulate macrophages with a pro-regenerative phenotype14,15.
Based on the above experimental results, we have established an in vitro model resembling molecular events that occur in the DRGs following a preconditioning injury model11,14. In this model, db-cAMP is applied to the neuron-macrophage co-cultures eliciting intercellular signaling that leads to the activation of macrophages with a pro-regenerative phenotype. Here, we describe detailed protocols by which we can generate macrophages that secrete molecular factors promoting neurite outgrowth (Figure 1). This experimental model illustrates a concept that macrophages can be stimulated or induced to support axon regeneration following the injuries to nervous system. Our model will also be useful in studying mechanisms in intercellular signaling that leads to the activation of pro-regenerative macrophages.

<table>
	<tbody>
		<tr>
			<td>Cell culture insert transparent PET membrane 0.4&#956;m pore size</td>
			<td>Corning,Falcon</td>
			<td>353090</td>
			<td>Transparent PET membrane with 0.4-&#956;m pore size, for 6-well plate</td>
		</tr>
		<tr>
			<td>70-&#956;m nylon cell strainer</td>
			<td>Corning, Falcon</td>
			<td>352350</td>
			<td></td>
		</tr>
		<tr>
			<td>8-well culture slide</td>
			<td>Biocoat</td>
			<td>354632</td>
			<td>with a uniform application of Poly-D-Lysine</td>
		</tr>
		<tr>
			<td>Red blood cell lysis buffer</td>
			<td>Qiagen</td>
			<td>158904</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase from Clostridium histolyticum</td>
			<td>Sigma-Aldrich</td>
			<td>C9407-100MG</td>
			<td></td>
		</tr>
		<tr>
			<td>Neurobasal medium</td>
			<td>Thermo Fisher Scientific, Gibco</td>
			<td>21103-049</td>
			<td>Containing 1% glutamax and 1% penicilin-streptomycin</td>
		</tr>
		<tr>
			<td>B-27 supplement, serum free</td>
			<td>Thermo Fisher Scientific, Gibco</td>
			<td>17504-044</td>
			<td>extracellular solution</td>
		</tr>
		<tr>
			<td>Glutamax</td>
			<td>Thermo Fisher Scientific, Gibco</td>
			<td>35050-061</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-streptomycin</td>
			<td>Thermo Fisher Scientific, Gibco</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly-D-lysine Hydrobromide</td>
			<td>Sigma-Aldrich</td>
			<td>P6407-5MG</td>
			<td></td>
		</tr>
		<tr>
			<td>Laminin</td>
			<td>Thermo Fisher Scientific, Invitrogen</td>
			<td>23017-015</td>
			<td></td>
		</tr>
		<tr>
			<td>Adenosine 3&#39;, 5&#39;-cyclic monophosphate, N6,O2&#39;-dibutyryl-, sodium salt</td>
			<td>Merck Millipore Corporation, Calbiochem</td>
			<td>28745</td>
			<td></td>
		</tr>
		<tr>
			<td>10% Normal Goat Serum</td>
			<td>Thermo Fisher Scientific</td>
			<td>16210072</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton-X-100</td>
			<td>Daejung Chemical and Metal Co</td>
			<td>8566-4405</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti &#946; III tubulin (Tuj-1)</td>
			<td>Promega Corporation</td>
			<td>G7121</td>
			<td>Mouse monoclonal antibody</td>
		</tr>
		<tr>
			<td>Goat anti-Mouse IgG (H+L) secondary antibody</td>
			<td>Thermo Fisher Scientific, Invitrogen</td>
			<td>A11005</td>
			<td></td>
		</tr>
		<tr>
			<td>Hemacytometer</td>
			<td>Marienfeld-Superior</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell culture CO2 incubator</td>
			<td>Panasonic</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Dissecting stereomicroscope</td>
			<td>Carl Zeiss</td>
			<td>Stemi DV4</td>
			<td></td>
		</tr>
		<tr>
			<td>Twist shaker</td>
			<td>FINEPCR</td>
			<td>Tw3t</td>
			<td></td>
		</tr>
		<tr>
			<td>Tabletop centrifuge</td>
			<td>Sorvall</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal microscope</td>
			<td>Olympus America Inc</td>
			<td>IX71</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS (Fetal Bovine Serum)</td>
			<td>VWR International, Hyclone</td>
			<td>SH30919.03</td>
			<td></td>
		</tr>
		<tr>
			<td>Friedman Pearson Rongeurs</td>
			<td>FST (Fine Science Tools)</td>
			<td>16021-14</td>
			<td>Stainless steel, 14cm, curved, single joint action</td>
		</tr>
		<tr>
			<td>Fine Scissors - Tungsten Carbide &#38; ToughCut</td>
			<td>FST (Fine Science Tools)</td>
			<td>14558-11</td>
			<td>sharp, serrated</td>
		</tr>
		<tr>
			<td>Dumont #7 Forceps</td>
			<td>FST (Fine Science Tools)</td>
			<td>11272-30</td>
			<td>Dumoxel, 0.07 x 0.04mm, curved</td>
		</tr>
		<tr>
			<td>Vannas Spring Scissors</td>
			<td>FST (Fine Science Tools)</td>
			<td>15000-00</td>
			<td>straight, 3mm cutting-edge, sharp</td>
		</tr>
		<tr>
			<td>Qualitron DW-41 Micro-Centrifuge</td>
			<td>Artisan Technology Group</td>
			<td>DW-41</td>
			<td>Input Voltage: 115VAC</td>
		</tr>
	</tbody>
</table>

neuron-macrophage co-cultures to activate macrophages secreting molecular factors with neurite outgrowth activity

There is strong evidence that macrophages can participate in the regeneration or repair of injured nervous system. Here, we describe a protocol in which macrophages are induced to produce conditioned medium (CM) that promotes neurite outgrowth. Adult dorsal root ganglion (DRG) neurons are acutely dissociated and plated. After the neurons are stably attached, peritoneal macrophages are co-cultured on a cell culture insert overlaid on the same well. Dibutyryl cyclic AMP (db-cAMP) is applied to the co-cultures for 24 h, after which the cell culture insert containing the macrophages is moved to another well to collect CM for 72 h. The CM from the co-cultures treated with db-cAMP, when applied to a separate adult DRG neuron culture, exhibits robust neurite outgrowth activity. The CM obtained from the db-cAMP-treated cultures consisting of single cell type alone, either DRG neuron or peritoneal macrophage, did not exhibit neurite outgrowth activity. This indicates that the interaction between neurons and macrophages is indispensable for the activation of macrophages secreting molecular factors with neurite outgrowth activity into CM. Thus, our co-culture paradigm will also be useful to study intercellular signaling in the neuron-macrophage interaction to stimulate the macrophages to be endowed with a pro-regenerative phenotype.

We describe a protocol that can generate macrophages capable of secreting molecular factors with neurite outgrowth activity. The macrophage CM obtained from the co-cultures treated with db-cAMP resulted in robust neurite outgrowth when applied to a separate DRG neuron culture (Figure 2A). In comparison, CM obtained from the PBS-treated co-cultures did not induce neurite outgrowth in our 15-h culture duration (Figure 2B). When db-...

Watch this Scientific Journal Video about Neuron-Macrophage Co-cultures to Activate Macrophages Secreting Molecular Factors with Neurite Outgrowth Activity at JoVE.com

Neuron-Macrophage Co-cultures to Activate Macrophages Secreting Molecular Factors with Neurite Outgrowth Activity

The current protocol presents experimental procedures to stimulate cultured macrophages to be endowed with capacity to release molecular factors that promote neurite outgrowth. Treatment of cAMP to the neuron-macrophage co-cultures induces the macrophages to produce conditioned medium that possesses strong neurite outgrowth activity.

There is strong evidence that macrophages can participate in the regeneration or repair of injured nervous system. Here, we describe a protocol in which ...

The overall goal of this procedure is to generate macrophages that can secrete molecular factors promoting neurite growth. This method can help answer key questions on how neurons and macrophages interact with each other to activate the pro-regenerative macrophagicphenotype to promote excellent regeneration. The main advantage of this technique is that we use Cyclic AMP, an adenosine serum molecule, which is much more physiologic enzymesone used in previous studies to stimulate macrophages with the pro-regenerative phenotype.We first had the idea for this method when we found that macrophage activation is essential in the enhancement of axion growth capacity and those can produce excellent neurons following precaution in permanent lobe injury. Before setting up the culture, precode a six well plate with poly-D Lycine and laminin. Next, incubate the six well plate with 0.01 poly-D Lycine at 37 degrees Celsius for two hours or at four degrees Celsius overnight.After that, wash the plate twice with distilled water. Then incubate the plate with laminin solution at a concentration of three micrograms per milliliter for two hours at room temperature. Following this, wash the plate twice with distilled water and dry the plate at room temperature for at least one hour.Now, incise the skin overlying the vertebral column of a euthanized mouse with a surgical blade and dissect the pair of vertebral muscles bilaterally to expose the vertebral bones. Remove the vertebral bones meticulously using a narrow-tipped surgical rongeur until the DRG are fully exposed. Under a dissecting microscope, remove the DRG bilaterally from S1 all the way up to the C1 level using iridectomy scissors and fine tipped forceps.Transfer the DRG to a 1.5 milliliter eppendorf tube using a blue pipette tip with a cut off end. Then remove DMEM after a quick spin for several seconds using a minicentrifuge. Add one milliliter of DMEM containing 125 units per milliliter type 11 collagenous and incubate the tube for 90 minutes with a gentle rotation using a twister shaker at 37 degrees Celsius.Afterward, discard collagenase containing DMEM and add one milliliter of fresh DMEM. Transfer the DRG to a 15 milliliter conical tube using a blue pipette tip with a cut off end. Then pipette up and down gently at least 15 times to make a homogenous cell suspension.Centrifuge the tube at 239 G for three minutes and carefully discard the supernatant with floating debris. Add one milliliter of neurobasil medium supplemented with B27 and re-suspend the cell pellet by gently pipetting up and down five to ten times. Next pass the cell suspension through a 70 micrometer cell strainer overlayed on top of a 50 milliliter conical tube.Then plate all the collected DRG neurons onto two wells of the six well plate. To prepare primary peritoneal macrophages from an adult mouse, incise the abdominal skin delicately to expose the peritoneum and avoid cutting the peritoneum to prevent a leakage of lavage fluid. Next puncture the peritoneum using a syringe with a 22 gauge needle and inject 10 milliliters of ice cold PBS into the peritoneal cavity.Gently massage the peritoneum for one to two minutes. Then pull out the needle and squeeze out the PBS through the needle puncture site and collect the lavage fluid in a 50 milliliter conical tube. Afterward centrifuge the lavage fluid at 239 g for 10 minutes at four degrees Celsius to pellet the cellular components.Subsequently re-suspend the pellet with three milliliters of the red blood cell lysis buffer for three minutes at room temperature. Then centrifuge the cell suspension again at 239 g for 10 minutes at four degrees Celsius. Re-suspend the pelletted cells in one milliliter of neurobasil B27 medium.Plate half of all collected macrophages on a cell culture insert with the effective area of 4.2 centimeters squared, which is placed on top of the well of dissociated DRG. Four hours after the neuron macrophage have been co-cultured add two microliters of 100 micromolar DB cyclic amp solution to the neuron macrophage co-cultures. After 24 hours, fill an empty well with one milliliter of macrophage culture medium in the same six well plate.Transfer the cell culture insert in the neuron macrophage co-culture to the empty well with macrophage culture medium. After 72 hours, centrifuge the macrophage conditioned medium at 239 times g for five minutes to remove the cellular components. Pass the supernatant through a 0.2 micrometer filter to remove any remaining cellular debris.In this procedure, precoat an eight well chamber slide with poly-D lycine and laminin. Then obtain the dissociated adult DRG neurons and neurobasil medium, supplemented with B27 using the same methods as described previously. Plate five times 10 to the four cells per well onto a precoated eight well chamber slide.Next place the chamber slide in a 37 degree Celsius incubator for two hours allowing the cells to attach to the bottom. Then replace the culture medium with the thawed, conditioned medium that is preheated at 37 degrees Celsius. 15 hours after the initial plating, remove the medium and wash the cells with PBS once, then add 200 microliters of ice cold, 4%paraformaldehyde solution to the wells and incubate the cells with the paraformaldehyde solution for 20 minutes at four degrees Celsius.Subsequently, incubate the fixed cells with primary antibody solution diluted with 10%normal goat serum for four hours at room temperature or overnight at four degrees Celsius. Afterward, take images using a fluorescence microscope to visualize neurite outgrowth. The macrophage conditioned medium obtained from the co-cultures treated with DB cyclic AMP resulted in robust neurite outgrowth when applied to a separate DRG neuron culture.In comparison, conditioned medium obtained from the PBS treated co-cultures did not induce neurite outgrowth. When DB cyclic AMP is treated to the culture with macrophage alone, conditioned medium was not effective in supporting neurite outgrowth. This suggests that neuron macrophage interaction is indispensable to stimulate macrophages to be endowed with a pro-regenerative capacity.We also tested the conditioned medium obtained from DB cyclic AMP treated neuron only culture and found no neurite outgrowth. It is important to remember that neurons and microplates should be prepared fresh and healthy. We experienced diminished neurite outgrowth activity of the constant medium when dissection lasted too long or peritoneum macrophages were contaminated with blood components.In this protocol, the dissociated DRG neurons were fiscally separated from the macrophages on the cell culture insert. Therefore our co-culture system will allow the identification of cellular factors responsible for intercellular signaling that mediate the activation of fully regenerative macrophages.

neuron-macrophage-co-cultures-to-activate-macrophages-secreting

Research

JoVE Journal

Neuroscience

Assaying Locomotor Activity to Study Circadian Rhythms and Sleep Parameters in Drosophila

Most life forms exhibit daily rhythms in cellular, physiological and behavioral phenomena that are driven by endogenous circadian (&equiv;24 hr) pacemakers or clocks. Malfunctions in the human circadian system are associated with numerous diseases or disorders. Much progress towards our understanding of the mechanisms underlying circadian rhythms has emerged from genetic screens whereby an easily measured behavioral rhythm is used as a read-out of clock function. Studies using Drosophila have made seminal contributions to our understanding of the cellular and biochemical bases underlying circadian rhythms. The standard circadian behavioral read-out measured in Drosophila is locomotor activity. In general, the monitoring system involves specially designed devices that can measure the locomotor movement of Drosophila. These devices are housed in environmentally controlled incubators located in a darkroom and are based on using the interruption of a beam of infrared light to record the locomotor activity of individual flies contained inside small tubes. When measured over many days, Drosophila exhibit daily cycles of activity and inactivity, a behavioral rhythm that is governed by the animal's endogenous circadian system. The overall procedure has been simplified with the advent of commercially available locomotor activity monitoring devices and the development of software programs for data analysis. We use the system from Trikinetics Inc., which is the procedure described here and is currently the most popular system used worldwide. More recently, the same monitoring devices have been used to study sleep behavior in Drosophila. Because the daily wake-sleep cycles of many flies can be measured simultaneously and only 1 to 2 weeks worth of continuous locomotor activity data is usually sufficient, this system is ideal for large-scale screens to identify Drosophila manifesting altered circadian or sleep properties.

Assaying Locomotor Activity to Study Circadian Rhythms and Sleep Parameters in Drosophila

We describe procedures for recording daily locomotor activity rhythms of Drosophila and subsequent data analysis. Locomotor activity rhythms are a reliable behavioral output of animal circadian clocks and are used as the standard readout of clock function when studying circadian mutants or examining how the environment regulates the circadian system.

Most life forms exhibit daily rhythms in cellular, physiological and behavioral phenomena that are driven by endogenous circadian (&equiv;24 hr) ...

Derivation of Enriched Oligodendrocyte Cultures and Oligodendrocyte/Neuron Myelinating Co-cultures from Post-natal Murine Tissues

Identifying the molecular mechanisms underlying OL development is not only critical to furthering our knowledge of OL biology, but also has implications for understanding the pathogenesis of demyelinating diseases such as Multiple Sclerosis (MS). Cellular development is commonly studied with primary cell culture models. Primary cell culture facilitates the evaluation of a given cell type by providing a controlled environment, free of the extraneous variables that are present in vivo. While OL cultures derived from rats have provided a vast amount of insight into OL biology, similar efforts at establishing OL cultures from mice has been met with major obstacles. Developing methods to culture murine primary OLs is imperative in order to take advantage of the available transgenic mouse lines. 
Multiple methods for extraction of OPCs from rodent tissue have been described, ranging from neurosphere derivation, differential adhesion purification and immunopurification 1-3. While many methods offer success, most require extensive culture times and/or costly equipment/reagents. To circumvent this, purifying OPCs from murine tissue with an adaptation of the method originally described by McCarthy &amp; 
de Vellis 2 is preferred. This method involves physically separating OPCs from a mixed glial culture derived from neonatal rodent cortices. The result is a purified OPC population that can be differentiated into an OL-enriched culture. This approach is appealing due to its relatively short culture time and the unnecessary requirement for growth factors or immunopanning antibodies. 
While exploring the mechanisms of OL development in a purified culture is informative, it does not provide the most physiologically relevant environment for assessing myelin sheath formation. Co-culturing OLs with neurons would lend insight into the molecular underpinnings regulating OL-mediated myelination of axons. For many OL/neuron co-culture studies, dorsal root ganglion neurons (DRGNs) have proven to be the neuron type of choice. They are ideal for co-culture with OLs due to their ease of extraction, minimal amount of contaminating cells, and formation of dense neurite beds. While studies using rat/mouse myelinating xenocultures have been published 4-6, a method for the derivation of such OL/DRGN myelinating co-cultures from post-natal murine tissue has not been described. Here we present detailed methods on how to effectively produce such cultures, along with examples of expected results. These methods are useful for addressing questions relevant to OL development/myelinating function, and are useful tools in the field of neuroscience.

This article describes methods to derive enriched populations of murine oligodendrocyte precursor cells (OPCs) in primary culture, which differentiate to produce mature oligodendrocytes (OLs). In addition, this report describes techniques to produce murine myelinating co-cultures by seeding mouse OPCs onto a neurite bed of mouse dorsal root ganglion neurons (DRGNs).

Identifying the molecular mechanisms underlying OL development is not only critical to furthering our knowledge of OL biology, but also has implications ...

Dissection and Culture of Chick Statoacoustic Ganglion and Spinal Cord Explants in Collagen Gels for Neurite Outgrowth Assays

The sensory organs of the chicken inner ear are innervated by the peripheral processes of statoacoustic ganglion (SAG) neurons. Sensory organ innervation depends on a combination of axon guidance cues1 and survival factors2 located along the trajectory of growing axons and/or within their sensory organ targets. For example, functional interference with a classic axon guidance signaling pathway, semaphorin-neuropilin, generated misrouting of otic axons3. Also, several growth factors expressed in the sensory targets of the inner ear, including Neurotrophin-3 (NT-3) and Brain Derived Neurotrophic Factor (BDNF), have been manipulated in transgenic animals, again leading to misrouting of SAG axons4. These same molecules promote both survival and neurite outgrowth of chick SAG neurons in vitro5,6.
Here, we describe and demonstrate the in vitro method we are currently using to test the responsiveness of chick SAG neurites to soluble proteins, including known morphogens such as the Wnts, as well as growth factors that are important for promoting SAG neurite outgrowth and neuron survival. Using this model system, we hope to draw conclusions about the effects that secreted ligands can exert on SAG neuron survival and neurite outgrowth. 
SAG explants are dissected on embryonic day 4 (E4) and cultured in three-dimensional collagen gels under serum-free conditions for 24 hours. First, neurite responsiveness is tested by culturing explants with protein-supplemented medium. Then, to ask whether point sources of secreted ligands can have directional effects on neurite outgrowth, explants are co-cultured with protein-coated beads and assayed for the ability of the bead to locally promote or inhibit outgrowth. We also include a demonstration of the dissection (modified protocol7) and culture of E6 spinal cord explants. We routinely use spinal cord explants to confirm bioactivity of the proteins and protein-soaked beads, and to verify species cross-reactivity with chick tissue, under the same culture conditions as SAG explants. These in vitro assays are convenient for quickly screening for molecules that exert trophic (survival) or tropic (directional) effects on SAG neurons, especially before performing studies in vivo. Moreover, this method permits the testing of individual molecules under serum-free conditions, with high neuron survival8.

We demonstrate how to dissect and culture chick E4 statoacoustic ganglion and E6 spinal cord explants. Explants are cultured under serum-free conditions in 3D collagen gels for 24 hours. Neurite responsiveness is tested with growth factor-supplemented medium and with protein-coated beads.

The sensory organs of the chicken inner ear are innervated by the peripheral processes of statoacoustic ganglion (SAG) neurons. Sensory organ innervation ...

Three Dimensional Vestibular Ocular Reflex Testing Using a Six Degrees of Freedom Motion Platform

The vestibular organ is a sensor that measures angular and linear accelerations with six degrees of freedom (6DF). Complete or partial defects in the vestibular organ results in mild to severe equilibrium problems, such as vertigo, dizziness, oscillopsia, gait unsteadiness nausea and/or vomiting. A good and frequently used measure to quantify gaze stabilization is the gain, which is defined as the magnitude of compensatory eye movements with respect to imposed head movements. To test vestibular function more fully one has to realize that 3D VOR ideally generates compensatory ocular rotations not only with a magnitude (gain) equal and opposite to the head rotation but also about an axis that is co-linear with the head rotation axis (alignment). Abnormal vestibular function thus results in changes in gain and changes in alignment of the 3D VOR response.
Here we describe a method to measure 3D VOR using whole body rotation on a 6DF motion platform. Although the method also allows testing translation VOR responses 1, we limit ourselves to a discussion of the method to measure 3D angular VOR. In addition, we restrict ourselves here to description of data collected in healthy subjects in response to angular sinusoidal and impulse stimulation.
Subjects are sitting upright and receive whole-body small amplitude sinusoidal and constant acceleration impulses. Sinusoidal stimuli (f = 1 Hz, A = 4&deg;) were delivered about the vertical axis and about axes in the horizontal plane varying between roll and pitch at increments of 22.5&deg; in azimuth. Impulses were delivered in yaw, roll and pitch and in the vertical canal planes. Eye movements were measured using the scleral search coil technique 2. Search coil signals were sampled at a frequency of 1 kHz.
The input-output ratio (gain) and misalignment (co-linearity) of the 3D VOR were calculated from the eye coil signals 3.
Gain and co-linearity of 3D VOR depended on the orientation of the stimulus axis. Systematic deviations were found in particular during horizontal axis stimulation. In the light the eye rotation axis was properly aligned with the stimulus axis at orientations 0&deg; and 90&deg; azimuth, but gradually deviated more and more towards 45&deg; azimuth.
The systematic deviations in misalignment for intermediate axes can be explained by a low gain for torsion (X-axis or roll-axis rotation) and a high gain for vertical eye movements (Y-axis or pitch-axis rotation (see Figure 2). Because intermediate axis stimulation leads a compensatory response based on vector summation of the individual eye rotation components, the net response axis will deviate because the gain for X- and Y-axis are different.
In darkness the gain of all eye rotation components had lower values. The result was that the misalignment in darkness and for impulses had different peaks and troughs than in the light: its minimum value was reached for pitch axis stimulation and its maximum for roll axis stimulation.
Case Presentation
Nine subjects participated in the experiment. All subjects gave their informed consent. The experimental procedure was approved by the Medical Ethics Committee of Erasmus University Medical Center and adhered to the Declaration of Helsinki for research involving human subjects.
Six subjects served as controls. Three subjects had a unilateral vestibular impairment due to a vestibular schwannoma. The age of control subjects (six males and three females) ranged from 22 to 55 years. None of the controls had visual or vestibular complaints due to neurological, cardio vascular and ophthalmic disorders.
The age of the patients with schwannoma varied between 44 and 64 years (two males and one female). All schwannoma subjects were under medical surveillance and/or had received treatment by a multidisciplinary team consisting of an othorhinolaryngologist and a neurosurgeon of the Erasmus University Medical Center. Tested patients all had a right side vestibular schwannoma and underwent a wait and watch policy (Table 1; subjects N1-N3) after being diagnosed with vestibular schwannoma. Their tumors had been stabile for over 8-10 years on magnetic resonance imaging.

A method is described to measure three-dimensional vestibulo ocular reflexes (3D VOR) in humans using a six degrees of freedom (6DF) motion simulator. The gain and misalignment of the 3D angular VOR provide a direct measure of the quality of vestibular function. Representative data on healthy subjects are provided

The vestibular organ is a sensor that measures angular and linear accelerations with six degrees of freedom (6DF). Complete or partial defects in the ...

Simultaneous Pre- and Post-synaptic Electrophysiological Recording from Xenopus Nerve-muscle Co-cultures

Much information about the coupling of presynaptic ionic currents with the release of neurotransmitter has been obtained from invertebrate preparations, most notably the squid giant synapse1. However, except for the preparation described here, few vertebrate preparations exist in which it is possible to make simultaneous measurements of neurotransmitter release and presynaptic ionic currents. Embryonic Xenopus motoneurons and muscle cells can be grown together in simple culture medium at room temperature; they will form functional synapses within twelve to twenty-four hours, and can be used to study nerve and muscle cell development and synaptic interactions for several days (until overgrowth occurs). Some advantages of these co-cultures over other vertebrate preparations include the simplicity of preparation, the ability to maintain the cultures and work at room temperature, and the ready accessibility of the synapses formed2-4. The preparation has been used widely to study the biophysical properties of presynaptic ion channels and the regulation of transmitter release5-8. In addition, the preparation has lent itself to other uses including the study of neurite outgrowth and synaptogenesis9-12, molecular mechanisms of neurotransmitter release13-15, the role of diffusible messengers in neuromodulation16,17, and in vitro synaptic plasticity18-19.

Simultaneous Pre- and Post-synaptic Electrophysiological Recording from Xenopus Nerve-muscle Co-cultures

This video demonstrates the procedures used to grow primary cultures of embryonic Xenopus nerve and muscle cells and the usefulness of this preparation for making simultaneous pre- and post-synaptic patch clamp recordings.

Much information about the coupling of  presynaptic ionic currents with the release of neurotransmitter has been obtained  from invertebrate preparations, ...

Preparation of Neuronal Co-cultures with Single Cell Precision

Microfluidic embodiments of the Campenot chamber have attracted great interest from the neuroscience community. These interconnected co-culture platforms can be used to investigate a variety of questions, spanning developmental and functional neurobiology to infection and disease propagation. However, conventional systems require significant cellular inputs (many thousands per compartment), inadequate for studying low abundance cells, such as primary dopaminergic substantia nigra, spiral ganglia, and Drosophilia melanogaster neurons, and impractical for high throughput experimentation. The dense cultures are also highly locally entangled, with few outgrowths (&#60;10%) interconnecting the two cultures. In this paper straightforward microfluidic and patterning protocols are described which address these challenges: (i) a microfluidic single neuron arraying method, and (ii) a water masking method for plasma patterning biomaterial coatings to register neurons and promote outgrowth between compartments. Minimalistic neuronal co-cultures were prepared with high-level (&#62;85%) intercompartment connectivity and can be used for high throughput neurobiology experiments with single cell precision.

Protocols for single neuron microfluidic arraying and water masking for the in-chip plasma patterning of biomaterial coatings are described. Highly interconnected co-cultures can be prepared using minimal cell inputs.

Microfluidic embodiments of the Campenot chamber have attracted great interest from the neuroscience community. These interconnected co-culture platforms ...

Intravital Imaging of Axonal Interactions with Microglia and Macrophages in a Mouse Dorsal Column Crush Injury

Traumatic spinal cord injury causes an inflammatory reaction involving blood-derived macrophages and central nervous system (CNS)-resident microglia. Intra-vital two-photon microscopy enables the study of macrophages and microglia in the spinal cord lesion in the living animal. This can be performed in adult animals with a traumatic injury to the dorsal column. Here, we describe methods for distinguishing macrophages from microglia in the CNS using an irradiation bone marrow chimera to obtain animals in which only macrophages or microglia are labeled with a genetically encoded green fluorescent protein. We also describe a injury model that crushes the dorsal column of the spinal cord, thereby producing a simple, easily accessible, rectangular lesion that is easily visualized in an animal through a laminectomy. Furthermore, we will outline procedures to sequentially image the animals at the anatomical site of injury for the study of cellular interactions during the first few days to weeks after injury.

Two-photon intravital imaging can be used to investigate interactions among different cell types in the spinal cord in their native tissue environment in a bone marrow chimeric animal with a dorsal column traumatic spinal cord crush injury.

Traumatic spinal cord injury causes an inflammatory reaction involving blood-derived macrophages and central nervous system (CNS)-resident microglia. ...

A Human-machine-interface Integrating Low-cost Sensors with a Neuromuscular Electrical Stimulation System for Post-stroke Balance Rehabilitation

A stroke is caused when an artery carrying blood from heart to an area in the brain bursts or a clot obstructs the blood flow to brain thereby preventing delivery of oxygen and nutrients. About half of the stroke survivors are left with some degree of disability. Innovative methodologies for restorative neurorehabilitation are urgently required to reduce long-term disability. The ability of the nervous system to reorganize its structure, function and connections as a response to intrinsic or extrinsic stimuli is called neuroplasticity. Neuroplasticity is involved in post-stroke functional disturbances, but also in rehabilitation. Beneficial neuroplastic changes may be facilitated with non-invasive electrotherapy, such as neuromuscular electrical stimulation (NMES) and sensory electrical stimulation (SES). NMES involves coordinated electrical stimulation of motor nerves and muscles to activate them with continuous short pulses of electrical current while SES involves stimulation of sensory nerves with electrical current resulting in sensations that vary from barely perceivable to highly unpleasant. Here, active cortical participation in rehabilitation procedures may be facilitated by driving the non-invasive electrotherapy with biosignals (electromyogram (EMG), electroencephalogram (EEG), electrooculogram (EOG)) that represent simultaneous active perception and volitional effort. To achieve this in a resource-poor setting, e.g., in low- and middle-income countries, we present a low-cost human-machine-interface (HMI) by leveraging recent advances in off-the-shelf video game sensor technology. In this paper, we discuss the open-source software interface that integrates low-cost off-the-shelf sensors for visual-auditory biofeedback with non-invasive electrotherapy to assist postural control during balance rehabilitation. We demonstrate the proof-of-concept on healthy volunteers.

A novel low-cost human-machine interface for interactive post-stroke balance rehabilitation system is presented in this article. The system integrates off-the-shelf low-cost sensors towards volitionally driven electrotherapy paradigm. The proof-of-concept software interface is demonstrated on healthy volunteers.

A stroke is caused when an artery carrying blood from heart to an area in the brain bursts or a clot obstructs the blood flow to brain thereby preventing ...

Investigating Functional Regeneration in Organotypic Spinal Cord Co-cultures Grown on Multi-electrode Arrays

Adult higher vertebrates have a limited potential to recover from spinal cord injury. Recently, evidence emerged that propriospinal connections are a promising target for intervention to improve functional regeneration. So far, no in vitro model exists that grants the possibility to examine functional recovery of propriospinal fibers. Therefore, a representative model that is based on two organotypic spinal cord sections of embryonic rat, cultured next to each other on multi-electrode arrays (MEAs) was developed. These slices grow and, within a few days in vitro, fuse along the sides facing each other. The design of the used MEAs permits the performance of lesions with a scalpel blade through this fusion site without inflicting damage on the MEAs. The slices show spontaneous activity, usually organized in network activity bursts, and spatial and temporal activity parameters such as the location of burst origins, speed and direction of their propagation and latencies between bursts can be characterized. Using these features, it is also possible to assess functional connection of the slices by calculating the amount of synchronized bursts between the two sides. Furthermore, the slices can be morphologically analyzed by performing immunohistochemical stainings after the recordings. 
Several advantages of the used techniques are combined in this model: the slices largely preserve the original tissue architecture with intact local synaptic circuitry, the tissue is easily and repeatedly accessible and neuronal activity can be detected simultaneously and non-invasively in a large number of spots at high temporal resolution. These features allow the investigation of functional regeneration of intraspinal connections in isolation in vitro in a sophisticated and efficient way.

Here we present a protocol that is based on spinal cord slices cultured on multi-electrode arrays to study functional regeneration of propriospinal connections in vitro.

Adult higher vertebrates have a limited potential to recover from spinal cord injury. Recently, evidence emerged that propriospinal connections are a ...

In Vivo Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes

In vivo microdialysis is a powerful technique to collect ISF from awake, freely-behaving animals based on a dialysis principle. While microdialysis is an established method that measures relatively small molecules including amino acids or neurotransmitters, it has been recently used to also assess dynamics of larger molecules in ISF using probes with high molecular weight cut off membranes. Upon using such probes, microdialysis has to be run in a push-pull mode to avoid pressure accumulated inside of the probes. This article provides step-by-step protocols including stereotaxic surgery and how to set up microdialysis lines to collect proteins from ISF. During microdialysis, drugs can be administered either systemically or by direct infusion into ISF. Reverse microdialysis is a technique to directly infuse compounds into ISF. Inclusion of drugs in the microdialysis perfusion buffer allows them to diffuse into ISF through the probes while simultaneously collecting ISF. By measuring tau protein as an example, the author shows how its levels are altered upon stimulating neuronal activity by reverse microdialysis of picrotoxin. Advantages and limitations of microdialysis are described along with the extended application by combining other in vivo methods.

In Vivo Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes

In vivo microdialysis has enabled collection of molecules present in brain interstitial fluid (ISF) from awake, freely-behaving animals. In order to analyze relatively large molecules in ISF, the current article specifically focuses on the microdialysis protocol using probes with high molecular weight cut off membranes.

In vivo microdialysis is a powerful technique to collect ISF from awake, freely-behaving animals based on a dialysis principle. While microdialysis is an ...