Name: immunostaining of biocytin-filled and processed sections for neurochemical markers
Uploaded: 2016-12-31T13:00:00
Description: Watch this Scientific Journal Video about Immunostaining of Biocytin-filled and Processed Sections for Neurochemical Markers at JoVE.com

The authors would like to acknowledge the support from NIH/NINDS R01 NS069861 and NJCBIR CBIR14IRG024 to VS.

1. Biocytin Filling during Electrophysiology
NOTE: The readers can refer to alternative sources for basic patch-clamp recording techniques and instrumentation19-22, which are not elaborated upon here. The steps detailed here assume that the equipment and procedures for patch-clamp recordings are already established, and the description will be restricted to details related to biocytin-filling and post-hoc immunostaining. All experiments outlined in this manuscript were performed on ra...

<ol>
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V., Zaitsev, A. V., Gonzalez-Burgos, G., Lewis, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophysiological+heterogeneity+of+fast-spiking+interneurons:+chandelier+versus+basket+cells.">Electrophysiological heterogeneity of fast-spiking interneurons: chandelier versus basket cells.</a> PLoS One. 8 (8), e70553 (2013).</li><li>Gupta, A., Elgammal, F. S., Proddutur, A., Shah, S., Santhakumar, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Decrease+in+tonic+inhibition+contributes+to+increase+in+dentate+semilunar+granule+cell+excitability+after+brain+injury.">Decrease in tonic inhibition contributes to increase in dentate semilunar granule cell excitability after brain injury.</a> J Neurosci. 32 (7), 2523-2537 (2012).</li><li>Fish, K. N., Hoftman, G. D., Sheikh, W., Kitchens, M., Lewis, D. 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H., Varga, C., Soltesz, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ivy+and+neurogliaform+interneurons+are+a+major+target+of+mu-opioid+receptor+modulation.">Ivy and neurogliaform interneurons are a major target of mu-opioid receptor modulation.</a> J Neurosci. 31 (42), 14861-14870 (2011).</li><li>Szabadics, J., Soltesz, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+specificity+of+mossy+fiber+innervation+of+GABAergic+cells+in+the+hippocampus.">Functional specificity of mossy fiber innervation of GABAergic cells in the hippocampus.</a> J Neurosci. 29 (13), 4239-4251 (2009).</li><li>Iball, J., Ali, A. 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Critical Steps within the Protocol 
Filling the patched cell with biocytin is the most crucial step to ensure the full recovery of the morphology. For full recovery of the cell, it is essential to select an optimal slice orientation to minimize the severing of processes during slicing. This orientation may differ based on the circuit and cell type under examination. Next, it is essential to allow adequate time for the biocytin to diffuse to the dendrites and axons. Some dyes, ...

The brain is known for diversity in the structural and functional characteristics of its individual neuronal elements. Understanding the roles of distinct neuronal types in brain function and pathology requires characterization and unambiguous identification of neurons. Structurally, the morphological features defined by somato-dendritic location determine the potential inputs that a given neuron receives, while the pattern of axonal arborization identifies potential postsynaptic targets. The structural diversity of neurons has been appreciated since the days of Ram&#243;n y Cajal&#39;s seminal histological studies1. The advent of single-cell recording techniques revealed that structurally distinct neurons also show differences in firing patterns and synaptic characteristics. The diversity in structure and physiology is particularly evident in GABAergic inhibitory neurons2,3. In addition, it has become increasingly apparent that structurally similar neurons can express different neurochemical markers and show corresponding functional differences4. Similarly, neurons with the same neurochemical markers can have distinct structures and functions5-10. Thus, in practice, the analysis of the functional characteristics of neurons and their role in the network entails defining both the morphological and neurochemical identities. Even with the advent of reporter mouse lines targeting specific neurochemical markers, it is often necessary to determine morphology and subtype identity based on immunohistology11.
The standard method used to characterize cells recorded in acute brain slices is to fill them with biocytin or neurobiotin during the recording, fix the sections in paraformaldehyde (PFA) following the recordings, and use immunohistochemistry to reveal the morphology and neurochemistry. Since the thickness of sections for slice physiology are typically 300 &#181;m or more, and because most antibodies fail to penetrate all the way through that depth, the slices need to be re-sectioned to 60 &#181;m or less to allow for simultaneous immunostaining for biocytin and neurochemical markers12-14. Unfortunately, resectioning is laborious; risks loss of tissue during sectioning; and can lead to differential tissue shrinkage, complicating morphological reconstructions. Additionally, prior knowledge of morphology could help narrow down the candidate markers that are likely to be expressed by the cells. We have modified the standard biocytin immunohistology protocols to allow serial processing of sections first for the recovery of morphology and then for the identification of potential neurochemical markers.
Immunohistochemistry is the study of antigen distribution in tissues or cells and can be visualized using an enzyme, fluorescent labels, radioactive elements, or gold colloid particles15. The procedure involves using primary antibodies to specifically tag and amplify one or more specific antigens, followed by the use of fluorescent secondary antibodies targeting the primary antibody for visualization. Due to the need to distinguish the fluorescence spectra of each secondary antibody without overlap, only a limited number of antigens can be examined simultaneously. Thus, prior knowledge of morphology could be useful in selecting the candidate neurochemical markers for cell classification. Conceptually, the rationale behind serial processing of already-stained sections is based on the premise that immunolabeling for one protein or peptide should not interfere with antigenicity and subsequent immunolabeling for a structurally independent peptide16. This lack of interference is due to the binding of the antibodies to a specific protein epitope on an antigen and therefore allows for the simultaneous staining of multiple antigens in the same tissue. The number of antigens revealed by immunostaining is limited by the need for non-overlapping spectra of the fluorescent secondary antibodies and by the need to target individual antigens with antibodies raised in different species so as to eliminate cross-reactivity17,18. While this is the reasoning behind serial rather than simultaneous labeling with two distinct antibodies that may interact, to our knowledge, immunostaining for a second antigen has not been reported after the completion of immunolabeling for one or more antigens on mounted sections. Here, we describe a method for serial immunostaining of previously stained and mounted sections. While we detail this process for a serial immunolabeling procedure for the recovery of morphology followed by staining for protein/peptide markers in thick sections, the same procedures can be used in standard, thin histological sections as well. In addition, we describe a practical approach to fill recorded neurons with biocytin and the process to dislodge the electrode from the cell upon completion of recordings to optimize the filling of the axonal and dendritic arbors of neurons, as presented in our recent work6,8.
The most crucial advantage of the procedure described here is that the morphology of the recorded cell can be fully recovered and imaged before attempting to resection or immunostain the slices. Although issues with the penetration of certain antibodies may render it necessary to resection slices for secondary immunostaining, the procedures detailed here would eliminate the need to reconstruct complex neurons from multiple sections and would avoid issues due to tissue loss and differential shrinkage, which can compromise reconstruction following resectioning. An added advantage is that the process will reduce cost, time, effort, and expensive antibodies by limiting immunostaining and re-sectioning to slices in which biocytin-filled neurons are recovered. The most practical aspect is the additional immunostaining that can be performed on sections stained months before using the aforementioned technique. In particular, the recovery of morphology would considerably reduce the potential that physiological data from the cells is discarded due to an inability to obtain a basic morphological characterization of the cell type.

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			<td height="20" style="height:20px;width:335px;">NaCl&#160;</td>
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			<td height="20" style="height:20px;">KCL&#160;</td>
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			<td height="24" style="height:24px;">Na2HPO4&#160;</td>
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			<td>S7907</td>
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			<td height="24" style="height:24px;">KH2PO4&#160;</td>
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			<td height="20" style="height:20px;">Triton X-100</td>
			<td>Sigma</td>
			<td>T8787</td>
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			<td height="20" style="height:20px;">Guinea pig anti CB1&#160;</td>
			<td>Sigma</td>
			<td>Af530-1</td>
			<td>Immunostaining</td>
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		<tr height="20">
			<td height="20" style="height:20px;">Mouse anti CCK</td>
			<td>CURE, UCLA</td>
			<td>courtesy of G. Ohning</td>
			<td>Immunostaining</td>
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			<td height="20" style="height:20px;">Rabbit anti Parvalbumin</td>
			<td>Swant</td>
			<td>PV27</td>
			<td>Immunostaining</td>
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			<td height="20" style="height:20px;">Streptavidin, Alexa Fluor conjugate</td>
			<td>Molecular Probes</td>
			<td>S11227</td>
			<td>Immunostaining</td>
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			<td height="20" style="height:20px;">Normal goat serum</td>
			<td>Sigma</td>
			<td>G9023</td>
			<td>Immunostaining</td>
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			<td>Immunostaining</td>
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			<td height="20" style="height:20px;">Labnet orbit low speed shaker</td>
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			<td>Immunostaining</td>
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			<td height="20" style="height:20px;">Forceps</td>
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			<td>Immunostaining</td>
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			<td height="20" style="height:20px;">Slide folders</td>
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			<td>71520</td>
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			<td height="20" style="height:20px;">Vibratome VT 1200 S</td>
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			<td>14048142066</td>
			<td>Electrophysiology</td>
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			<td height="20" style="height:20px;">Multiclamp 700B amplifier</td>
			<td>Molecular devices</td>
			<td>Multiclamp 700B</td>
			<td>Electrophysiology</td>
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			<td height="20" style="height:20px;">pCLAMP 10 Software</td>
			<td>Molecular devices</td>
			<td>pCLAMP 10&#160;</td>
			<td>Electrophysiology</td>
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		<tr height="20">
			<td height="20" style="height:20px;">Digitizer</td>
			<td>Molecular Devices</td>
			<td>Digidata 1440 digitizer</td>
			<td>Electrophysiology</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Filter tips</td>
			<td>Nalgene</td>
			<td>171-0020</td>
			<td>Electrophysiology</td>
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			<td height="20" style="height:20px;">Sonicator</td>
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			<td>15-335-100</td>
			<td>Electrophysiology</td>
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			<td height="20" style="height:20px;">Microloaders</td>
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			<td height="20" style="height:20px;">Biocytin</td>
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immunostaining of biocytin-filled and processed sections for neurochemical markers

Electrophysiological recordings of cells using the patch clamp technique have allowed for the identification of different neuronal types based on firing patterns. The inclusion of biocytin/neurobiotin in the recording electrode permits post-hoc recovery of morphological details, which are necessary to determine the dendritic arborization and the regions targeted by the axons of the recorded neurons. However, given the presence of morphologically similar neurons with distinct neurochemical identities and functions, immunohistochemical staining for cell-type-specific proteins is essential to definitively identify neurons. To maintain network connectivity, brain sections for physiological recordings are prepared at a thickness of 300 &#181;m or greater. However, this thickness often hinders immunohistological postprocessing due to issues with antibody penetration, necessitating the resectioning of the tissue. Resectioning of slices is a challenging art, often resulting in the loss of tissue and morphology of the cells from which electrophysiological data was obtained, rendering the data unusable. Since recovery of morphology would limit data loss and guide in the selection of neuronal markers, we have adopted a strategy of recovering cell morphology first, followed by secondary immunostaining. We introduce a practical approach to biocytin filling during physiological recordings and subsequent serial immunostaining for the recovery of morphology, followed by the restaining of sections to determine the neurochemical identity. We report that sections that were filled with biocytin, fixed with paraformaldehyde (PFA), stained, and coverslipped can be removed and restained with a second primary antibody days later. This restaining involves the removal of the coverslip, the washing of sections in a buffer solution, and the incubation of primary and secondary antibodies to reveal the neurochemical identity. The method is advantageous for eliminating data loss due to an inability to recover morphology and for narrowing down the neurochemical markers to be tested based on morphology.

Upon successful completion, the sections retain the biocytin fill and the immunolabeling performed in step 2 and can be imaged using confocal or epifluorescence microscopy. In addition, the processed sections will also show immunostaining for the antigen labeled during the subsequent processing in step 3. In the section illustrated in Figure&#160;2, the morphology of a biocytin-filled neuron in a thick section (300 &#181;m) was revealed using streptavidin visualized in re...

Watch this Scientific Journal Video about Immunostaining of Biocytin-filled and Processed Sections for Neurochemical Markers at JoVE.com

Immunostaining of Biocytin-filled and Processed Sections for Neurochemical Markers

This protocol presents a method for the morphological recovery of neurons patched during electrophysiological recordings using biocytin filling and subsequent immunohistochemical postprocessing. We show that thick biocytin-filled sections that were stained and coverslipped can be restained with a second primary antibody days&#160;or months later.

Electrophysiological recordings of cells using the patch clamp technique have allowed for the identification of different neuronal types based on firing ...

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Immunohistochemistry (IHC) provides highly specific, reliable and attractive protein visualization. Correct performance and interpretation of an IHC-based ...

Assessing Primary Neurogenesis in Xenopus Embryos Using Immunostaining

Assessing Primary Neurogenesis in Xenopus Embryos Using Immunostaining

Primary neurogenesis is a dynamic and complex process during embryonic development that sets up the initial layout of the central nervous system. During ...

Quadruple Immunostaining of the Olfactory Bulb for Visualization of Olfactory Sensory Axon Molecular Identity Codes

The mouse olfactory system is often used to study mechanisms of neural circuit formation&#12288;because of its simple anatomical structure. An Olfactory ...

Toluidine Blue Staining of Resin-Embedded Sections for Evaluation of Peripheral Nerve Morphology

Peripheral nerves extend throughout the body, innervating target tissues with motor or sensory axons. Due to widespread distribution, peripheral nerves ...

Diagnosis of Hirschsprung's Disease by Immunostaining Rectal Suction Biopsies for Calretinin, S100 Protein and Protein Gene Product 9.5

Hirschsprung&#39;s disease (HD) is a congenital intestinal disease that is clinically manifested as an inability to pass meconium in infants or as ...

Identifying Cell Surface Markers of Primary Neural Stem and Progenitor Cells by Metabolic Labeling of Sialoglycan

Neural stem and progenitor cells (NSPCs) are the cellular basis for the complex structures and functions of the brain. They are located in specialized ...