Name: use of synaptic zinc histochemistry to reveal different regions and laminae in the developing and adult brain
Uploaded: 2017-10-29T13:00:00
Description: Watch this Scientific Journal Video about Use of Synaptic Zinc Histochemistry to Reveal Different Regions and Laminae in the Developing and Adult Brain at JoVE.com

This work was supported by grants from the National Center for Research Resources (2G12RR03060-26A1); The National Institute on Minority Health and Health Disparities (8G12MD007603-27) from the National Institutes of Health; Professional Staff Congress-City University of New York (PSC-CUNY); and Faculty Research Grant (FRG II) American University of Sharjah. We thank Vidyasagar Sriramoju for introducing us to these methods.

The following protocol follows the animal care guidelines established by the Institutional Animal Care and Use Committee (IACUC) at The City College of New York, which conform to all appropriate state and federal guidelines. Anesthesia is appropriate for ferrets, and should be modified according to species studied.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56547/56547fig1.jpg" /> 
Figure 1: Flowchart outlining the major steps invol...

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The current study employs a histochemical technique based on a modified version of the Danscher (1982) method10, whereby synaptic zinc localization may be detected and visualized in the brain. This method essentially works by injecting the animal with the zinc chelator sodium selenite (Na2SeO3) (15 mg/kg). Following injection, the selenite travels to the brain and binds to free zinc that is localized to presynaptic vesicles of zinc containing neurons. Zinc ions bound to molec...

Histological stains have traditionally been used to aid in the identification of cortical areas in various species by revealing differences in architectonic features. The combined use of histochemical techniques such as for Nissl substance, cytochrome oxidase (CO) reactivity, or myelin can prove fruitful as they reveal similar areal boundaries in the adult brain. However, these histochemical stains do not always adequately reveal clear boundaries between cortical areas and layers in the immature brain.
In the central nervous system, zinc has several critical functions that include stabilizing DNA structure, acting as an enzyme cofactor, participating in numerous regulatory functions, and acting as a neuromodulator through its presence in synaptic vesicles1. Synaptic zinc is unique as it can be visualized using histological methods, whereas protein-bound zinc cannot be visualized2. This feature has been exploited to reveal the synaptic zinc pattern in different cortical regions, and synaptic zinc histochemistry has been used in a number of studies. A subset of glutamatergic neurons in the cerebral cortex contain zinc in the presynaptic vesicles within their axon terminals3,4. Histochemical studies have revealed a heterogeneous distribution of synaptic zinc in the cerebral cortex5,6,7. There appears to be a different areal and laminar distribution of histochemically reactive zinc in different cortical regions (e.g., visual versus somatosensory cortex), or layers (e.g., zinc levels in the supragranular and infragranular layers of primary visual cortex are substantially higher than in thalamocortical input layer IV with relatively low synaptic zinc levels)5,8,9. The heterogeneity in synaptic zinc staining observed in the cortex is especially advantageous as it facilitates areal and laminar identification.
Here we present a detailed description of a synaptic zinc histochemical procedure, which is a modified version of Danscher&#39;s 1982 method10. This method utilizes selenite injected intraperitoneally (IP) into animals as a chelating agent. The selenite travels to the brain to react with pools of free zinc found in vesicles of a subset of glutamatergic synapses in the brain. This reaction yields a precipitate that can be enhanced subsequently by silver development2,10,11.
This procedure reveals laminar and areal patterns of synaptic zinc staining; densitometric analysis may be used to assess these patterns both qualitatively and quantitatively in the adult and immature brain to study effects of other interventions, such as sensory, environmental, pharmacological, or genetic manipulations. Moreover, one may also want to assess potential developmental changes in the distribution of synaptic zinc in other cortical or subcortical structures in other model systems. The quantitative information that densitometric analysis provides in this method can be advantageous for following brain development over time. This protocol provides a companion to other immuno- and histochemical markers to reveal laminar and areal boundaries.

<table>
	<tbody>
		<tr>
			<td>Euthasol (Euthanasia solution)</td>
			<td>Henry Schein</td>
			<td>710101</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium selenite</td>
			<td>Sigma-Aldrich</td>
			<td>214485</td>
			<td></td>
		</tr>
		<tr>
			<td>Ketamine (Ketaved)</td>
			<td>Henry Schein</td>
			<td>48858</td>
			<td>100 mg/ml injectables</td>
		</tr>
		<tr>
			<td>Xylazine (Anased)</td>
			<td>Henry Schein</td>
			<td>33198</td>
			<td>100 mg/ml injectables</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>F8775</td>
			<td>Dilute to 4%</td>
		</tr>
		<tr>
			<td>Gum arabic</td>
			<td>Sigma-Aldrich</td>
			<td>G9752-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>Citric acid</td>
			<td>Sigma-Aldrich</td>
			<td>C1909</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium citrate</td>
			<td>Sigma-Aldrich</td>
			<td>W302600</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydroquinone</td>
			<td>Sigma-Aldrich</td>
			<td>H9003</td>
			<td></td>
		</tr>
		<tr>
			<td>Silver lactate</td>
			<td>Sigma-Aldrich</td>
			<td>85210</td>
			<td></td>
		</tr>
		<tr>
			<td>Fish gelatine</td>
			<td>Sigma-Aldrich</td>
			<td>G7765</td>
			<td></td>
		</tr>
		<tr>
			<td>Cytochrome c</td>
			<td>Sigma-Aldrich</td>
			<td>C2506</td>
			<td>(Type III, from equine heart)</td>
		</tr>
		<tr>
			<td>Catalse</td>
			<td>Sigma-Aldrich</td>
			<td>C10</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Domino</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Xylene</td>
			<td>Fisher Scientific</td>
			<td>X5P-1GAL</td>
			<td></td>
		</tr>
		<tr>
			<td>Permount</td>
			<td>Fisher Scientific</td>
			<td>SP15-500</td>
			<td></td>
		</tr>
		<tr>
			<td>100% Ethanol</td>
			<td>Fisher Scientific</td>
			<td>A406-20</td>
			<td>Used for dehydration prior to slide mounting</td>
		</tr>
		<tr>
			<td>Coverslips</td>
			<td>Brain Research Laboratories</td>
			<td>#3660-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Frosted unsubbed slides</td>
			<td>Brain Research Laboratories</td>
			<td>#3875-FR</td>
			<td></td>
		</tr>
		<tr>
			<td>Microtome</td>
			<td>American Optical Company</td>
			<td>860</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope</td>
			<td>Olympus</td>
			<td>BX-60</td>
			<td></td>
		</tr>
		<tr>
			<td>Adope Photoshop</td>
			<td>Adobe Systems, San Jose, CA</td>
			<td></td>
			<td>To assemble images</td>
		</tr>
		<tr>
			<td>ImageJ</td>
			<td>Free software can be downloaded at http://rsb.info.nih.gov/ij/</td>
			<td></td>
			<td>For densometric measurements</td>
		</tr>
		<tr>
			<td>Plastic tray</td>
			<td>Any standard plastic tray may be used</td>
			<td></td>
			<td>to immerse slides in developer solution</td>
		</tr>
		<tr>
			<td>Hot plate</td>
			<td>Any standard hotplate may be used</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

use of synaptic zinc histochemistry to reveal different regions and laminae in the developing and adult brain

Characterization of anatomical and functional brain organization and development requires accurate identification of distinct neural circuits and regions in the immature and adult brain. Here we describe a zinc histochemical staining procedure that reveals differences in staining patterns among different layers and brain regions. Others have utilized this procedure not only to reveal the distribution of zinc-containing neurons and circuits in the brain, but also to successfully delineate areal and laminar boundaries in the developing and adult brain in several species. Here we illustrate this staining procedure with images from developing and adult ferret brains. We reveal a zinc-staining pattern that serves as an anatomical marker of areas and layers, and can be reliably used to distinguish visual cortical areas in the developing and adult visual cortex. The main goal of this protocol is to present a histochemical method that allows the accurate identification of layers and regions in the developing and adult brain where other methods fail to do so. Secondarily, in conjunction with densitometric image analysis, this method allows one to assess the distribution of synaptic zinc to reveal potential changes throughout development. This protocol describes in detail the reagents, tools, and steps necessary to successively stain frozen brain sections. Although this protocol is described using ferret brain tissue, it can easily be adapted for use in rodents, cats, or monkeys as well as in other brain regions.

The major steps involved in this protocol to stain brain sections for synaptic zinc are presented in a flowchart in Figure 1. The protocol can be divided into three phases: 1) Perfusion and tissue collection, 2) Tissue preparation and staining, and 3) Zinc histochemistry. Briefly, during the first phase of the protocol, the animal is anesthetized and injected IP with the appropriate dose of sodium selenite. After a sufficient time period (ideally 60 - 90 min)...

Watch this Scientific Journal Video about Use of Synaptic Zinc Histochemistry to Reveal Different Regions and Laminae in the Developing and Adult Brain at JoVE.com

Use of Synaptic Zinc Histochemistry to Reveal Different Regions and Laminae in the Developing and Adult Brain

We describe a histochemical procedure that reveals characteristic laminar and areal zinc staining patterns in different brain regions. The zinc-staining pattern may be used in conjunction with other anatomical markers to reliably distinguish layers and regions in the developing and adult brain.

Characterization of anatomical and functional brain organization and development requires accurate identification of distinct neural circuits and regions ...

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