Name: immunohistochemical and calcium imaging methods in wholemount rat retina
Uploaded: 2014-10-13T13:00:00
Description: Watch this Scientific Journal Video about Immunohistochemical and Calcium Imaging Methods in Wholemount Rat Retina at JoVE.com

We thank Dr. S. Stella and Helen Vuong for contributions to the calcium imaging protocol. We thank Dr. K. Sheets for filming the interview scenes. We thank Dr. Arlene Hirano for her comments on the manuscript. This research and development project was conducted by the authors at the David Geffen School of Medicine at UCLA and is made possible by a contract agreement that was awarded and administered by the U.S. Army Medical Research &#38; Materiel Command (USAMRMC) and the Telemedicine &#38; Advanced Technology Research Center (TATRC), at Fort Detrick, MD under Contract Number: W81XWH-10-2-0077. Support for these studies also came from NIH EY04067 and a VA Merit Review (NB). NCB is a VA Career Research Scientist.

All experiments were carried out in accordance with the guidelines for the welfare of experimental animals issued by the U.S. Public Health Service Policy on Human Care and Use of Laboratory Animals and the University of California-Los Angeles (UCLA) Animal Research Committee. Male and female adult Sprague-Dawley rats (Charles River Lab, Wilmington, MA) between the age of 3-5 weeks were used.
1. Animal and Tissue Preparation for Wholemount Retina and Immunohistochemistry Protocol
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In this article, we have described two different techniques: 1) Immunohistochemistry to show Fluo-4 localization to the ganglion cells in retinal wholemounts, and 2) Calcium imaging to analyze calcium dynamics in retinal ganglion cells and their axons.
Immunohistochemistry using wholemounts has been used to reveal the localization of proteins in the rodent retina20-23. However, there are a few limitations. The quality of the staining relies heavily on the ability of the antibody to ...

Retinal ganglion cells (RGCs) express L-, N-, P/Q- and T-type VGCC as determined through pharmacological blockade of these components of the whole cell Ca channel current1,2. VGCC are transmembrane multimeric proteins that are involved in transmitter release, gene transcription, cell regulation and synaptic plasticity3,4,5. Functional VGCCs are made up of at least three distinct classes of subunits: large, transmembrane &#945;&#173;1 pore forming subunits that establish the channel&#8217;s biophysical and pharmacological properties, primarily extracellular auxiliary &#945;&#173;2&#948; subunits and intracellular &#946; subunits. The latter two form heteromeric complexes with different &#945;&#173;1 subunits and alter the gating kinetics and trafficking of the channels to the plasma membrane6.
Over recent decades, many techniques have been employed to study protein expression, such as immunohistochemistry, enzyme-linked immunosorbent assay, western analysis and flow cytometry. These techniques require the use of specific antibodies for the detection of a given protein of interest and provide powerful tools for the localization and distribution of specific proteins in different tissues. Techniques used to detect and quantify mRNA expression levels of a particular protein such as northern blot analysis, RT-PCR, real-time quantitative RT-PCR, in situ hybridization, cDNA microarrays and ribonuclease protection assay provide an alternative approach when antibodies are not readily available or if expression levels of a particular protein are low7. However, one limitation to the use of such molecular techniques is the required identification of the gene sequence.
To localize proteins in the retina, immunohistochemistry can be performed on wholemount retinas. Due to the accessibility of the RGCs, the wholemount preparation provides an excellent platform to study the localization of specific proteins to the RGC somata and their axons.
In addition to their localization, some functional properties of the VGCCs in RGCs can be demonstrated through the use of calcium imaging techniques. We describe a calcium imaging protocol to selectively label RGCs with a calcium indicator dye to measure intracellular calcium dynamics. The contribution of different VGCCs to the calcium signal in different cellular compartments can be isolated with the use of subtype-specific Ca channel blockers.
Perhaps one of the most beneficial aspects of the calcium imaging technique described here is the ability to simultaneously and independently record from multiple RGCs and their axons. Although many physiological techniques, such as whole cell patch clamp recording, provide high temporal resolution recordings of membrane currents, the somatic or axonal source of these currents recorded cannot be discriminated and recordings can only be made from a single neuron at a time. Multielectrode arrays (MEAs) are capable of simultaneously recording spikes from many cells, but can neither detect nor discriminate the activation of, for example, different subtypes of calcium channels.&#160; MEAs preferentially record from cells that are located in close proximity to a given electrode8 and record from cells that generate large spikes9. Optical imaging methods provide an alternative strategy to enable the simultaneous and independent recordings of whole populations of cells that can be integrated with the information obtained from single cell microelectrode and patch clamp recording and MEA recording.&#160; Although the calcium imaging techniques described here were employed to study the calcium dynamics of RGCs, patch clamp and MEAs can also be used in parallel to further elucidate the ionic currents and spiking properties of RGCs.
Since displaced amacrine cells make up approximately 60% of the neuronal population in the ganglion cell layer in the mouse retina10, our goal was to use a loading technique that selectively labels RGCs with a synthetic calcium indicator dye in a wholemount preparation. Although synthetic calcium indicator dyes provide an excellent platform for the study of intracellular calcium dynamics, its widespread use has been hindered by the inability to effectively load specific populations of neurons within a given network.&#160; Many techniques such as bulk loading11 and electroporation8,12 have been performed to load entire populations of cells, however, such techniques do not discriminate between specific cell types. Genetically encoded calcium indicators provide the ability to selectively label specific populations of cells, however, such methods require the generation of transgenic animals13. Our technique describes a method to selectively label RGCs in the wholemount preparation via optic nerve stump injection of a calcium indicator dye.
Taken together, the structural and physiological techniques outlined in this article provide a platform to study the localization and contribution of the VGCCs to the calcium signal in RGCs and their axons.&#160;

<table border="0" cellpadding="0" cellspacing="0" width="676">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Straight scissors</td>
			<td style="width:112px;">WPI</td>
			<td style="width:119px;">14124-G</td>
			<td style="width:229px;">dissecting tools</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Straight Forceps</td>
			<td style="width:112px;">WPI</td>
			<td style="width:119px;">501985</td>
			<td>dissecting tools</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">curved iris scissors</td>
			<td style="width:112px;">WPI</td>
			<td>504487</td>
			<td>dissecting tools</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Cellulose filter paper</td>
			<td style="width:112px;">Millipore</td>
			<td style="width:119px;">HABP04700</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hibernate A</td>
			<td>Invitrogen</td>
			<td><a href="http://products.invitrogen.com/ivgn/en/US/adirect/invitrogen?cmd=catProductDetail&amp;productID=A1247501">A12475-01</a></td>
			<td>Media</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Vectashield</td>
			<td>Vector</td>
			<td>H-1000&#160;</td>
			<td><a href="https://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=1&amp;cad=rja&amp;sqi=2&amp;ved=0CC0QFjAA&amp;url=http%3A%2F%2Fwww.vectorlabs.com%2Fcatalog.aspx%3FcatID%3D279&amp;ei=VAHbUb_fBceeiQLK2IHIDw&amp;usg=AFQjCNHijFTTB8p19FMPQ5hg_qTawXU9mA&amp;sig2=FJCfB9fzKR_TmjxoGvhLcg&amp;bvm=bv.48705608,d.cGE">Mounting Media for Fluorescence</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fluo-4 pentapotassium</td>
			<td>Invitrogen</td>
			<td>F-14200</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Isoflurane</td>
			<td>Abbott Laboratories</td>
			<td>05260-05</td>
			<td>anesthesia</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microscope slide</td>
			<td style="width:112px;">Fisher Scientific</td>
			<td style="width:119px;">22-178-277</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Zeiss LSM 5 Pascal microscope</td>
			<td style="width:112px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Axioplan 40x (NA 0.8) objective lens</td>
			<td style="width:112px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Alexa Fluor 488 Goat Anti-Rabbit IgG (H+L) Antibody</td>
			<td style="width:112px;">Molecular Probes</td>
			<td style="width:119px;">A-11034</td>
			<td>Secondary antibody</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">RBPMS</td>
			<td style="width:112px;">ProSci, Poway, CA</td>
			<td style="width:119px;"></td>
			<td>A rabbit polyclonal antibody&#160;was generated against the N-terminus of the RBPMS&#160;polypeptide (RBPMS4-24), GGKAEKENTPSEANLQEEEVR, by a commercial vendor (ProSci, Poway, CA).</td>
		</tr>
	</tbody>
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immunohistochemical and calcium imaging methods in wholemount rat retina

In this paper we describe the tools, reagents, and the practical steps that are needed for: 1) successful preparation of wholemount retinas for immunohistochemistry and, 2) calcium imaging for the study of voltage gated calcium channel (VGCC) mediated calcium signaling in retinal ganglion cells. The calcium imaging method we describe circumvents issues concerning non-specific loading of displaced amacrine cells in the ganglion cell layer.

Immunolabeling with specific antibodies provides a platform to study the localization of particular proteins of interest in the retina and the calcium imaging technique permits the study of the contribution of the VGCCs to the calcium dynamics in the retinal ganglion cells and their axons.
By using an antibody against the ganglion cell protein RBPMS (RNA binding protein with multiple splicing) that selectively labels RGCs19, we were able to show that the Fluo-4 labeling is limited t...

Watch this Scientific Journal Video about Immunohistochemical and Calcium Imaging Methods in Wholemount Rat Retina at JoVE.com

Immunohistochemical and Calcium Imaging Methods in Wholemount Rat Retina

Immunohistochemistry protocols are used to study the localization of a specific protein in the retina. Calcium imaging techniques are employed to study calcium dynamics in retinal ganglion cells and their axons.

In this paper we describe the tools, reagents, and the practical steps that are needed for: 1) successful preparation of wholemount retinas for ...

immunohistochemical-calcium-imaging-methods-wholemount-rat

Research

JoVE Journal

Neuroscience

Functional Calcium Imaging in Developing Cortical Networks

A hallmark pattern of activity in developing nervous systems is spontaneous, synchronized network activity. Synchronized activity has been observed in intact spinal cord, brainstem, retina, cortex and dissociated neuronal culture preparations. During periods of spontaneous activity, neurons depolarize to fire single or bursts of action potentials, activating many ion channels. Depolarization activates voltage-gated calcium channels on dendrites and spines that mediate calcium influx. Highly synchronized electrical activity has been measured from local neuronal networks using field electrodes. This technique enables high temporal sampling rates but lower spatial resolution due to integrated read-out of multiple neurons at one electrode. Single cell resolution of neuronal activity is possible using patch-clamp electrophysiology on single neurons to measure firing activity. However, the ability to measure from a network is limited to the number of neurons patched simultaneously, and typically is only one or two neurons. The use of calcium-dependent fluorescent indicator dyes has enabled the measurement of synchronized activity across a network of cells. This technique gives both high spatial resolution and sufficient temporal sampling to record spontaneous activity of the developing network.
A key feature of newly-forming cortical and hippocampal networks during pre- and early postnatal development is spontaneous, synchronized neuronal activity (Katz &amp; Shatz, 1996; Khaziphov &amp; Luhmann, 2006). This correlated network activity is believed to be essential for the generation of functional circuits in the developing nervous system (Spitzer, 2006). In both primate and rodent brain, early electrical and calcium network waves are observed pre- and postnatally in vivo and in vitro (Adelsberger et al., 2005; Garaschuk et al., 2000; Lamblin et al., 1999). These early activity patterns, which are known to control several developmental processes including neuronal differentiation, synaptogenesis and plasticity (Rakic &amp; Komuro, 1995; Spitzer et al., 2004) are of critical importance for the correct development and maturation of the cortical circuitry.
In this JoVE video, we demonstrate the methods used to image spontaneous activity in developing cortical networks. Calcium-sensitive indicators, such as Fura 2-AM ester diffuse across the cell membrane where intracellular esterase activity cleaves the AM esters to leave the cell-impermeant form of indicator dye. The impermeant form of indicator has carboxylic acid groups which are able to then detect and bind calcium ions intracellularly.. The fluorescence of the calcium-sensitive dye is transiently altered upon binding to calcium. Single or multi-photon imaging techniques are used to measure the change in photons being emitted from the dye, and thus indicate an alteration in intracellular calcium. Furthermore, these calcium-dependent indicators can be combined with other fluorescent markers to investigate cell types within the active network.

Spontaneous activity of developing neuronal networks can be measured using AM-ester forms of calcium-sensitive indicator dyes. Changes in intracellular calcium, indicating neuronal activation, are detected as transient changes in indicator fluorescence with one- or two-photon imaging. This protocol can be adapted for a range of developmentally-dependent neuronal networks in vitro.

A hallmark pattern of activity in developing nervous systems is spontaneous, synchronized network activity. Synchronized activity has been observed in ...

Wholemount Immunohistochemistry for Revealing Complex Brain Topography

The repeated and well-understood cellular architecture of the cerebellum make it an ideal model system for exploring brain topography. Underlying its relatively uniform cytoarchitecture is a complex array of parasagittal domains of gene and protein expression. The molecular compartmentalization of the cerebellum is mirrored by the anatomical and functional organization of afferent fibers. To fully appreciate the complexity of cerebellar organization we previously refined a wholemount staining approach for high throughput analysis of patterning defects in the mouse cerebellum. This protocol describes in detail the reagents, tools, and practical steps that are useful to successfully reveal protein expression patterns in the adult mouse cerebellum by using wholemount immunostaining. The steps highlighted here demonstrate the utility of this method using the expression of zebrinII/aldolaseC as an example of how the fine topography of the brain can be revealed in its native three-dimensional conformation. Also described are adaptations to the protocol that allow for the visualization of protein expression in afferent projections and large cerebella for comparative studies of molecular topography. To illustrate these applications, data from afferent staining of the rat cerebellum are included.

Neural circuits are topographically organized into functional compartments with specific molecular profiles. Here, we provide the practical and technical steps for revealing global brain topography using a versatile wholemount immunohistochemical staining approach. We demonstrate the utility of the method using the well-understood cytoarchitecture and circuitry of cerebellum.

The repeated and well-understood cellular architecture of the cerebellum make it an ideal model system for exploring brain topography. Underlying its ...

In vivo Neuronal Calcium Imaging in C. elegans

The nematode worm C. elegans is an ideal model organism for relatively simple, low cost neuronal imaging in vivo. Its small transparent body and simple, well-characterized nervous system allows identification and fluorescence imaging of any neuron within the intact animal. Simple immobilization techniques with minimal impact on the animal's physiology allow extended time-lapse imaging. The development of genetically-encoded calcium sensitive fluorophores such as cameleon 1 and GCaMP 2 allow in vivo imaging of neuronal calcium relating both cell physiology and neuronal activity. Numerous transgenic strains expressing these fluorophores in specific neurons are readily available or can be constructed using well-established techniques. Here, we describe detailed procedures for measuring calcium dynamics within a single neuron in vivo using both GCaMP and cameleon. We discuss advantages and disadvantages of both as well as various methods of sample preparation (animal immobilization) and image analysis. Finally, we present results from two experiments: 1) Using GCaMP to measure the sensory response of a specific neuron to an external electrical field and 2) Using cameleon to measure the physiological calcium response of a neuron to traumatic laser damage. Calcium imaging techniques such as these are used extensively in C. elegans and have been extended to measurements in freely moving animals, multiple neurons simultaneously and comparison across genetic backgrounds. C. elegans presents a robust and flexible system for in vivo neuronal imaging with advantages over other model systems in technical simplicity and cost.

In vivo Neuronal Calcium Imaging in C. elegans

With its small transparent body, well-documented neuroanatomy and a host of amenable genetic techniques and reagents, C. elegans makes an ideal model organism for in vivo neuronal imaging using relatively simple, low-cost techniques. Here we describe single neuron imaging within intact adult animals using genetically encoded fluorescent calcium indicators.

The nematode worm C. elegans is an ideal model organism  for relatively simple, low cost neuronal imaging in vivo. Its small transparent body and simple, ...

Immunohistochemical Analysis in the Rat Central Nervous System and Peripheral Lymph Node Tissue Sections

Immunohistochemistry (IHC) provides highly specific, reliable and attractive protein visualization. Correct performance and interpretation of an IHC-based multicolor labeling is challenging, especially when utilized for assessing interrelations between target proteins in the tissue with a high fat content such as the central nervous system (CNS).
Our protocol represents a refinement of the standard immunolabeling technique particularly adjusted for detection of both structural and soluble proteins in the rat CNS and peripheral lymph nodes (LN) affected by neuroinflammation. Nonetheless, with or without further modifications, our protocol could likely be used for detection of other related protein targets, even in other organs and species than here presented.

We here present an optimized, detailed protocol for double immunostaining in formalin-fixed, paraffin-embedded rat central nervous system (CNS) and peripheral lymph node (LN) tissue sections.

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

Transpupillary Two-Photon In Vivo Imaging of the Mouse Retina

The retina transforms light signals from the environment into electrical signals that are propagated to the brain. Diseases of the retina are prevalent and cause visual impairment and blindness. Understanding how such diseases progress is critical to formulating new treatments. In vivo&#160;microscopy in animal models of disease is a powerful tool for understanding neurodegeneration and has led to important progress towards treatments of conditions ranging from Alzheimer&#39;s disease to stroke. Given that the retina is the only central nervous system structure inherently accessible by optical approaches, it naturally lends itself towards in vivo imaging. However, the native optics of the lens and cornea present some challenges for effective imaging access.
This protocol outlines methods for in vivo two-photon imaging of cellular cohorts and structures in the mouse retina at cellular resolution, applicable for both acute- and chronic-duration imaging experiments. It presents examples of retinal ganglion cell (RGC), amacrine cell, microglial, and vascular imaging using a suite of labeling techniques including adeno-associated virus (AAV) vectors, transgenic mice, and inorganic dyes. Importantly, these techniques extend to all cell types of the retina, and suggested methods for accessing other cellular populations of interest are described. Also detailed are example strategies for manual image postprocessing for display and quantification. These techniques are directly applicable to studies of retinal function in health and disease.

In vivo imaging is a powerful tool for the study of biology in health and disease. This protocol describes transpupillary imaging of the mouse retina with a standard two-photon microscope. It also demonstrates different in vivoimaging methods to fluorescently label multiple cellular cohorts of the retina.

The retina transforms light signals from the environment into electrical signals that are propagated to the brain. Diseases of the retina are prevalent ...

In vivo Calcium Imaging in Mouse Inferior Olive

Inferior olive (IO), a nucleus in the ventral medulla, is the only source of climbing fibers that form one of the two input pathways entering the cerebellum. IO has long been proposed to be crucial for motor control and its activity is currently considered to be at the center of many hypotheses of both motor and cognitive functions of the cerebellum. While its physiology and function have been relatively well studied on single-cell level in vitro, presently there are no reports on the organization of the IO network activity in living animals. This is largely due to the extremely challenging anatomical location of the IO, making it difficult to subject to conventional fluorescent imaging methods, where an optic path must be created through the entire brain located dorsally to the region of interest.
Here we describe an alternative method for obtaining state-of-the-art -level calcium imaging data from the IO network. The method takes advantage of the extreme ventral location of the IO and involves a surgical procedure for inserting a gradient-refractive index (GRIN) lens through the neck viscera to come into contact with the ventral surface of the calcium sensor GCaMP6s-expressing IO in anesthetized mice. A representative calcium imaging recording is shown to demonstrate the feasibility to record IO neuron activity after the surgery. While this is a non-survival surgery and the recordings must be conducted under anesthesia, it avoids damage to life-critical brainstem nuclei and allows conducting large variety of experiments investigating spatiotemporal activity patterns and input integration in the IO. This procedure with modifications could be used for recordings in other, adjacent regions of the ventral brainstem.

In vivo Calcium Imaging in Mouse Inferior Olive

We present a protocol to expose the brainstem of adult mouse from the ventral side. By using a gradient-refractive index lens with a miniature microscope, calcium imaging can be used to examine the activity of inferior olive neural somata in vivo.

Inferior olive (IO), a nucleus in the ventral medulla, is the only source of climbing fibers that form one of the two input pathways entering the ...

Brain Pericyte Calcium and Hemodynamic Imaging in Transgenic Mice In Vivo

Recent advances in protein biology and mouse genetics have made it possible to measure intracellular calcium fluctuations of brain cells in vivo and to correlate this with local hemodynamics. This protocol uses transgenic mice that have been prepared with a chronic cranial window and express the genetically encoded calcium indicator, RCaMP1.07, under the &#945;-smooth muscle actin promoter to specifically label mural cells, such as vascular smooth muscle cells and ensheathing pericytes. Steps are outlined on how to prepare a tail vein catheter for intravenous injection of fluorescent dyes to trace blood flow, as well as how to measure brain pericyte calcium and local blood vessel hemodynamics (diameter, red blood cell velocity, etc.) by two photon microscopy in vivo through the cranial window in ketamine/xylazine anesthetized mice. Finally, details are provided for the analysis of calcium fluctuations and blood flow movies via the image processing algorithms developed by Barrett et al. 2018, with an emphasis on how these processes can be adapted to other cellular imaging data.

Brain Pericyte Calcium and Hemodynamic Imaging in Transgenic Mice In Vivo

This protocol presents steps to acquire and analyze fluorescent calcium images from brain ensheathing pericytes and blood flow data from nearby blood vessels in anesthetized mice. These techniques are useful for studies of mural cell physiology and can be adapted to investigate calcium transients in any cell type.

Recent advances in protein biology and mouse genetics have made it possible to measure intracellular calcium fluctuations of brain cells in vivo and to ...

Subcellular Imaging of Neuronal Calcium Handling In Vivo

Calcium (Ca2+) imaging has been largely used to examine neuronal activity, but it is becoming increasingly clear that subcellular Ca2+ handling is a crucial component of intracellular signaling. The visualization of subcellular Ca2+ dynamics in vivo,&#160;where neurons can be studied in their native, intact circuitry, has proven technically challenging in complex nervous systems. The transparency and relatively simple nervous system of the nematode Caenorhabditis elegans enable the cell-specific expression and in vivo visualization of fluorescent tags and indicators. Among these are fluorescent indicators that have been modified for use in the cytoplasm as well as various subcellular compartments, such as the mitochondria. This protocol enables non-ratiometric Ca2+ imaging in vivo with a subcellular resolution that permits the analysis of Ca2+ dynamics down to the level of individual dendritic spines and mitochondria. Here, two available genetically encoded indicators with different Ca2+ affinities are used to demonstrate the use of this protocol for measuring relative Ca2+ levels within the cytoplasm or mitochondrial matrix in a single pair of excitatory interneurons (AVA). Together with the genetic manipulations and longitudinal observations possible in C. elegans, this imaging protocol may be useful for answering questions regarding how Ca2+ handling regulates neuronal function and plasticity.

Subcellular Imaging of Neuronal Calcium Handling In Vivo

The current methods describe a non-ratiometric approach for high-resolution, sub-compartmental calcium imaging in vivo in Caenorhabditis elegans using readily available genetically encoded calcium indicators.

Calcium (Ca2+) imaging has been largely used to examine neuronal activity, but it is becoming increasingly clear that subcellular Ca2+ handling is a ...

Two-Photon and Wide-Field Calcium Imaging in the Superior Colliculus

Calcium Imaging in Mouse Superior Colliculus

The superior colliculus (SC), an evolutionarily conserved midbrain structure in all vertebrates, is the most sophisticated visual center before the emergence of the cerebral cortex. It receives direct inputs from ~30 types of retinal ganglion cells (RGCs), with each encoding a specific visual feature. It remains elusive whether the SC simply inherits retinal features or if additional and potentially de novo processing occurs in the SC. To reveal the neural coding of visual information in the SC, we provide here a detailed protocol to optically record visual responses with two complementary methods in awake mice. One method uses two-photon microscopy to image calcium activity at single-cell resolution without ablating the overlaying cortex, while the other uses wide-field microscopy to image the whole SC of a mutant mouse whose cortex is largely undeveloped. This protocol details these two methods, including animal preparation, viral injection, headplate implantation, plug implantation, data acquisition, and data analysis. The representative results show that the two-photon calcium imaging reveals visually evoked neuronal responses at single-cell resolution, and the wide-field calcium imaging reveals&#160;neural activity across the entire SC. By combining these two methods, one can reveal the neural coding in the SC at different scales, and such combination can also be applied to other brain regions.

Author Spotlight: Unveiling Neural Coding and Mechanisms of Visual Processing in the Superior Colliculus 

This protocol details the procedure for imaging calcium responses in the superior colliculus (SC) of awake mice, including imaging single-neuron activity with two-photon microscopy while leaving the cortex intact in wild-type mice, and imaging the entire SC with wide-field microscopy in partial-cortex mutant mice.

The superior colliculus (SC), an evolutionarily conserved midbrain structure in all vertebrates, is the most sophisticated visual center before the ...

Evaluating Calcium Activity in Retinal Ganglion Cells Layer

Calcium Imaging In Electrically Stimulated Flat-Mounted Retinas

Retinal dystrophies are a leading cause of blindness worldwide. Extensive efforts are underway to develop advanced retinal prostheses that can bypass the impaired light-sensing photoreceptor cells in the degenerated retina, aiming to partially restore vision by inducing visual percepts. One common avenue of investigation involves the design and production of implantable devices with a flexible physical structure, housing a high number of electrodes. This enables the efficient and precise generation of visual percepts. However, with each technological advancement, there arises a need for a reliable and manageable ex vivo method to verify the functionality of the device before progressing to in vivo experiments, where factors beyond the device's performance come into play. This article presents a comprehensive protocol for studying calcium activity in the retinal ganglion cell layer (GCL) following electrical stimulation. Specifically, the following steps are outlined: (1) fluorescently labeling the rat retina using genetically encoded calcium indicators, (2) capturing the fluorescence signal using an inverted fluorescence microscope while applying distinct patterns of electrical stimulation, and (3) extracting and analyzing the calcium traces from individual cells within the GCL. By following this procedure, researchers can efficiently test new stimulation protocols prior to conducting in vivo experiments.

Author Spotlight: An Innovative Approach to Neural Electrical Stimulation Using Calcium Imaging 

Retinal prostheses have the ability to generate visual perceptions. To advance the development of new prostheses, ex vivo methods are needed to test devices before implantation. This article provides a comprehensive protocol for studying calcium activity in the retinal ganglion cell layer when subjected to electrical stimulation.

Retinal dystrophies are a leading cause of blindness worldwide. Extensive efforts are underway to develop advanced retinal prostheses that can bypass the ...