1)	Preparation
<ol>
<li>To begin, seat the subject in a comfortable chair in front of a computer screen.</li>
<li>Use a tape measure to ensure the distance between the screen and the subject's nasion is 60 cm.</li>
<li>Finally, place a light-blocking mask over the subject's eyes.</li>
</ol>
2) Determining Phosphene Threshold over V1/V2
<ol>
<li>Knowing the subject's phosphene threshold will be important when exploring phosphenic behavior later in this protocol. To determine this threshold, first set the TMS machine to 70% power.</li>
<li>Hold the coil so the top of the figure-8 faces cranial midline.</li>
<li>Begin single-pulse stimulation at a point about 3 cm above the inion.</li>
<li>After each pulse, ask the subject to report any phosphenic experience.</li>
<li>Begin moving the coil in a small search grid around this region (V1/V2).</li>
<li>Determine the location where stimulation elicits consistent and unambiguous phosphene reports from the subject. It has been theorized that TMS will be unable to elicit phosphenes in around 40% of the population, so there is a chance the subject will not report anything. If this is the case, unfortunately, this experiment will not work. The subject should be allowed to leave.</li>
<li>Once the phosphenic "hotspot" has been located, adjust the TMS power output up and down until the subject reports phosphenes for exactly 3 of 6 consecutive pulses. This power level is the subject's V1/V2 threshold. If available, neuronavigation can be used to achieve greater spatial precision when locating and targeting the V1/V2 hotspot.</li>
</ol>
3) Determining Phosphenic Threshold over the V5/MT+ Complex
<ol>
<li>Using the same aforementioned procedure and parameters, we will now determine phosphene threshold over the V5/MT+ complex. To locate this region, begin at a point 3 cm dorsal and 5 cm lateral to the subject's inion.</li>
<li>After each pulse, ask the subject to report any phosphenic experience.</li>
<li>Again, using single pulses, begin a small search grid pattern until unambiguous and consistent phosphenes are elicited.</li>
<li>Finally, adjust the TMS power output up and down until the subject reports phosphenes for exactly 3 of 6 consecutive pulses. This power level is the subject's V5/MT+ complex threshold. Again, if available, neuronavigation can be used to achieve greater spatial precision when locating and targeting the V5/MT+ hotspot.</li>
</ol>
4)	Determining Baseline Phosphene Behavior
<ol>
<li>Once phosphene threshold has been determined for both visual areas, we need to measure baseline phosphenic behavior. To do this, first remove the subject's light-blocking mask.</li>
<li>Next, instruct the subject to stare at a stable fixation cross presented in the center of the computer screen for 60 seconds.</li>
<li>Replace the mask and, over the V1/V2 hot spot, generate a single pulse train for 3-seconds at 120% V1/V2 threshold.</li>
<li>Wait five-seconds and conduct another train.</li>
<li>Again, wait five-seconds and conduct a third train.</li>
<li>After the third single pulse train, ask the subject to describe the location and motive characteristics of any elicited phosphenes. This will be the baseline.</li>
<li>Repeat this same procedure over the V5/MT+ hot spot (remember to reset the TMS power to 120% of the V5/MT+ threshold).</li>
</ol>
5) Condition Number One
<ol>
<li>Once the phophenic baseline has been determined, remove the subject's light-blocking mask once again.</li>
<li>Instruct the subject to stare at a stable fixation cross presented in the center of the computer screen for 60 seconds. This time, rather than a blank screen, we will embed a series of moving dots at several locations around the cross. 
<img src="/files/ftp_upload/2273/2273fig1.jpg" alt="Figure 1" /> 
Figure 1. Adapting stimuli for condition one: simple translational motion. All dots move coherently either to the left or right. 
Make sure all the dots are moving in the same direction. This stimulus should serve to engender visual adaptation: a phenomenon in which changes in neural excitability as induced by prolonged exposure to a stimuli serves to bias the perception of subsequently presented stimuli.</li>
<li>After 60 seconds, replace the mask and, over the V1/V2 hotspot, generate a single pulse train for 3 seconds at 120% V1/V2 threshold.</li>
<li>Wait five-seconds and repeat two more times.</li>
<li>After three trains, ask the subject to report the locations and motive characteristics of any elicited phosphenes. If available, the use of an eye movement tracking system in a dark room can help achieve greater precision and quantitative monitoring of the eye movements made by subjects during phosphene elicitations.</li>
<li>Continue this three-train/report sequence until phosphene behavior returns to baseline activity.</li>
<li>Repeat this procedure for the V5/MT+ complex hotspot.</li>
</ol>
6)	Condition Number Two
<ol>
<li>In this second condition, repeat the same procedure utilized for condition one. This time, however, rather than presenting the subject with a series of dots moving in a singular direction, present the subject with a series of dots each moving in its relative cardinal direction away from a central point - similar to a "star burst" pattern. 
<img src="/files/ftp_upload/2273/2273fig2.jpg" alt="Figure 2" /> 
Figure 2. Adapting stimuli for condition two: radial motion. Dots move in respective cardinal directions either towards or away from a central point.</li>
<li>As before, after 60 seconds, replace the mask, conduct a series of three, 120% threshold trains over V1/V2, ask for a subject report, and continue until baseline returns.</li>
<li>Repeat for V5/MT+.</li>
</ol>
7) Diagram
<ol>
<li>As an option, after each condition (or after all conditions are completed), ask the subject to draw the regions and motive behavior of each series of phopsphenes onto a graph. This is not an integral step but will supply you with another set of interpretable data.</li>
</ol>
8) Representative Results

Visual adaptation to the uni-directional motive stimuli should elicit an identical phosphenic movement over V1/V2. 
<img src="/files/ftp_upload/2273/2273fig3.jpg" alt="Figure 3" /> 
Figure 3. Examples of phosphenes induced from V1/V2 in the right and left hemisphere during condition one (based on the drawings of subjects). 
The V5/MT+ complex phosphenes should also be affected, such that the phosphene now will appear as a sum of the motion direction in the adapting stimulus and the baseline phosphene.
However, visual adaptation to the starburst pattern should elicit an identical starburst phosphenic movement from the V5/MT+ complex, but should not change the V1/V2 baseline. 
<img src="/files/ftp_upload/2273/2273fig4.jpg" alt="Figure 4" /> 
Figure 4. Examples of phosphenes induced from the V5/MT+ complex in the right and left hemisphere during condition two (based on the drawings of subjects).

<ol>
	<li>Pascual-Leone, A., Davey, M., Wassermann, E. M., Rothwell, J., Puri, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Handbook of Transcranial Magnetic Stimulation. , (2002).</li><li>Walsh, V., Pascual-Leone, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Transcranial Magnetic Stimulation: A Neurochronometrics of Mind. , (2005).</li><li>Silvanto, J., Muggleton, N. G., Cowey, A., Walsh, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+adaptation+reveals+state-dependent+effects+of+transcranial+magnetic+stimulation.">Neural adaptation reveals state-dependent effects of transcranial magnetic stimulation.</a> European Journal of Neuroscience. 25, 1874-1881 (2007).</li><li>Silvanto, J., Pascual-Leone, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=State-Dependency+of+Transcranial+Magnetic+Stimulation.">State-Dependency of Transcranial Magnetic Stimulation.</a> Brain Topography. 21, 1-10 (2008).</li><li>Silvanto, J., Cattaneo, Z., Battelli, L., Pascual-Leone, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Baseline+cortical+excitablility+determines+whether+TMS+disrupts+or+facilitates+behavior.">Baseline cortical excitablility determines whether TMS disrupts or facilitates behavior.</a> Journal of Neurophysiology. 99, 2725-2730 (2008).</li><li>Silvanto, J., Muggleton, N. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Testing+the+validity+of+the+TMS+state-dependency+approach:+targeting+functionally+distinct+motion-selective+neural+populations.">Testing the validity of the TMS state-dependency approach: targeting functionally distinct motion-selective neural populations.</a> Neuroimage. 40, 1841-1848 (2008).</li><li>Tootell, R. B., Rappas, J. B., Kwong, K. K., Malach, R., Born, R. T., Brady, T. J., Rosen, B. R., Belliveau, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+analysis+of+human+MT+and+related+visual+cortical+areas+using+magnetic+resonance+imaging.">Functional analysis of human MT and related visual cortical areas using magnetic resonance imaging.</a> Journal of Neuroscience. 15, 3215-3230 (1995).</li><li>Singh, K. D., Smith, A. T., Greenlee, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatiotemporal+frequency+and+direction+sensitivities+of+human+visual+areas+measured+using+fMRI.">Spatiotemporal frequency and direction sensitivities of human visual areas measured using fMRI.</a> Neuroimage. 12, 550-564 (2000).</li><li>Rutchmann, R. M., Schrauf, M., Greenlee, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brain+activation+during+dichoptic+presentation+of+optic+flow+stimuli.">Brain activation during dichoptic presentation of optic flow stimuli.</a> Exp Brain Res. 134, 533-537 (2000).</li><li>Morrone, M. C., Tosetti, M., Montanaro, D., Fiorentini, A., Cioni, G., Burr, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+cortical+area+that+responds+specifically+to+optic+flow+revealed+by+fMRI.">A cortical area that responds specifically to optic flow revealed by fMRI.</a> Nat. Neuroscience. 3, 1322-1328 (2000).</li></ol>

No conflicts of interest declared.

This experiment gets at the heart of state dependency. Neurons in V1/V2 are thought to correspond with simple, directional movement.7,8 Therefore, adaptation to the uni-directional motive stimuli increased the excitability of neurons registering this movement - as such, they should be the first to react to the TMS pulse. The V5/MT+ complex also contains neurons tuned to simple translational motion, therefore the phosphenes induced from this region should also be affected by the adapting stimulus. However, th...

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<td>Light Blocking Eye Mask</td>
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<td>Tape Measure</td>
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<td>Blank Graph Paper</td>
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<td>Stimuli Developed &amp; Presented on Computer using Adobe Photoshop</td>
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<td>Any Single Pulse Capable TMS Device</td>
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state-dependency effects on tms:  a look at motive phosphene behavior

Transcranial magnetic stimulation (TMS) is a non-invasive neurostimulatory and neuromodulatory technique that can transiently or lastingly modulate cortical excitability (either increasing or decreasing it) via the application of localized magnetic field pulses.1,2 Within the field of TMS, the term state dependency refers to the initial, baseline condition of the particular neural region targeted for stimulation. As can be inferred, the effects of TMS can (and do) vary according to this primary susceptibility and responsiveness of the targeted cortical area.3,4,5

In this experiment, we will examine this concept of state dependency through the elicitation and subjective experience of motive phosphenes. Phosphenes are visually perceived flashes of small lights triggered by electromagnetic pulses to the visual cortex. These small lights can assume varied characteristics depending upon which type of visual cortex is being stimulated. In this particular study, we will be targeting motive phosphenes as elicited through the stimulation of V1/V2 and the V5/MT+ complex visual regions.6

Watch this Scientific Journal Video about State-Dependency Effects on TMS:  A Look at Motive Phosphene Behavior at JoVE.com

State-Dependency Effects on TMS:  A Look at Motive Phosphene Behavior

In this article, we examine the effects of visually relevant state dependency on TMS induced motive phosphenic presentations.

Transcranial magnetic stimulation (TMS) is a non-invasive neurostimulatory and neuromodulatory technique that can transiently or lastingly modulate ...

state-dependency-effects-on-tms-a-look-at-motive-phosphene-behavior

Universidad de Cartagena UDEC

Research

JoVE Journal

Neuroscience

10.5K Views.  Beth Israel Deaconess Medical Center. In this article, we examine the effects of visually relevant state dependency on TMS induced motive phosphenic presentations. 

Video: State-Dependency Effects on TMS:  A Look at Motive Phosphene Behavior

The NeuroStar TMS Device: Conducting the FDA Approved Protocol for Treatment of Depression

The Neuronetics NeuroStar Transcranial Magnetic Stimulation (TMS) System is a class II medical device that produces brief duration, pulsed magnetic fields. These rapidly alternating fields induce electrical currents within localized, targeted regions of the cortex which are associated with various physiological and functional brain changes.1,2,3
In 2007, O'Reardon et al., utilizing the NeuroStar device, published the results of an industry-sponsored, multisite, randomized, sham-stimulation controlled clinical trial in which 301 patients with major depression, who had previously failed to respond to at least one adequate antidepressant treatment trial, underwent either active or sham TMS over the left dorsolateral prefrontal cortex (DLPFC). The patients, who were medication-free at the time of the study, received TMS five times per week over 4-6 weeks.4
The results demonstrated that a sub-population of patients (those who were relatively less resistant to medication, having failed not more than two good pharmacologic trials) showed a statistically significant improvement on the Montgomery-Asberg Depression Scale (MADRS), the Hamilton Depression Rating Scale (HAMD), and various other outcome measures. In October 2008, supported by these and other similar results5,6,7, Neuronetics obtained the first and only Food and Drug Administration (FDA) approval for the clinical treatment of a specific form of medication-refractory depression using a TMS Therapy device (FDA approval K061053).
In this paper, we will explore the specified FDA approved NeuroStar depression treatment protocol (to be administered only under prescription and by a licensed medical profession in either an in- or outpatient setting).

In this article, we examine the methodology and considerations relevant to the FDA approved depression treatment protocol using the Neuronetics NeuroStar TMS device.

The Neuronetics NeuroStar Transcranial Magnetic Stimulation (TMS) System is a class II medical device that produces brief duration, pulsed magnetic ...

Cryopreservation of Cortical Tissue Blocks for the Generation of Highly Enriched Neuronal Cultures

In this study, we outline a standardized protocol for the successful cryopreservation and thawing of cortical brain tissue blocks to generate highly enriched neuronal cultures. For this protocol the freezing medium used is 10% dimethyl sulfoxide (DMSO) diluted in Hank's Buffered Salt Solution (HBSS). Blocks of cortical tissue are transferred to cryovials containing the freezing medium and slowly frozen at -1&deg;C/min in a rate-controlled freezing container. Post-thaw processing and dissociation of frozen tissue blocks consistently produced neuronal-enriched cultures which exhibited rapid neuritic growth during the first 5 days in culture and significant expansion of the neuronal network within 10 days. Immunocytochemical staining with the astrocytic marker glial fibrillary acidic protein (GFAP) and the neuronal marker beta-tubulin class III, revealed high numbers of neurons and astrocytes in the cultures. Generation of neural precursor cell cultures after tissue block dissociation resulted in rapidly expanding neurospheres, which produced large numbers of neurons and astrocytes under differentiating conditions. This simple cryopreservation protocol allows for the rapid, efficient, and inexpensive preservation of cortical brain tissue blocks, which grants increased flexibility for later generation of neuronal, astrocyte, and neuronal precursor cell cultures.

Here, we describe a method for efficient cryopreservation and thawing of cortical brain tissue blocks to generate highly enriched neuronal cultures. This simple protocol provides flexibility for later generation of neuronal, astrocyte, and neuronal precursor cell cultures.

In this study, we outline a standardized protocol for the successful cryopreservation and thawing of cortical brain tissue blocks to generate highly ...

Studying the Integration of Adult-born Neurons

Neurogenesis occurs in adult mammalian brains in the sub-ventricular zone (SVZ) of the lateral ventricle and in the sub-granular zone (SGZ) of the hippocampal dentate gyrus throughout life. Previous reports have shown that adult hippocampal neurogenesis is associated with diverse brain disorders, including epilepsy, schizophrenia, depression and anxiety (1). Deciphering the process of normal and aberrant adult-born neuron integration may shed light on the etiology of these diseases and inform the development of new therapies.
SGZ adult neurogenesis mirrors embryonic and post-natal neuronal development, including stages of fate specification, migration, synaptic integration, and maturation. However, full integration occurs over a prolonged, 6-week period. Initial synaptic input to adult-born SGZ dentate granule cells (DGCs) is GABAergic, followed by glutamatergic input at 14 days (2). The specific factors which regulate circuit formation of adult-born neurons in the dentate gyrus are currently unknown.
Our laboratory uses a replication-deficient retroviral vector based on the Moloney murine leukemia virus to deliver fluorescent proteins and hypothesized regulatory genes to these proliferating cells. This viral technique provides high specificity and resolution for analysis of cell birth date, lineage, morphology, and synaptogenesis.
A typical experiment often employs two or three viruses containing unique label, transgene, and promoter elements for single-cell analysis of a desired developmental process in vivo. The following protocol describes a method for analyzing functional newborn neuron integration using a single green (GFP) or red (dTomato) fluorescent protein retrovirus and patch-clamp electrophysiology.

A way to study the integration of newborn dentate granule cells in adult animals is described. This technique uses an engineered retrovirus to label newborn neurons, followed by electrophysiological recordings to determine in vivo functional integration.

Neurogenesis occurs in adult mammalian brains in the sub-ventricular zone (SVZ) of the lateral ventricle and in the sub-granular zone (SGZ) of the ...

Investigations on Alterations of Hippocampal Circuit Function Following Mild Traumatic Brain Injury

Traumatic Brain Injury (TBI) afflicts more than 1.7 million people in the United States each year and even mild TBI can lead to persistent neurological impairments 1. Two pervasive and disabling symptoms experienced by TBI survivors, memory deficits and a reduction in seizure threshold, are thought to be mediated by TBI-induced hippocampal dysfunction 2,3. In order to demonstrate how altered hippocampal circuit function adversely affects behavior after TBI in mice, we employ lateral fluid percussion injury, a commonly used animal model of TBI that recreates many features of human TBI including neuronal cell loss, gliosis, and ionic perturbation 4-6.
	Here we demonstrate a combinatorial method for investigating TBI-induced hippocampal dysfunction. Our approach incorporates multiple ex vivo physiological techniques together with animal behavior and biochemical analysis, in order to analyze post-TBI changes in the hippocampus. We begin with the experimental injury paradigm along with behavioral analysis to assess cognitive disability following TBI. Next, we feature three distinct ex vivo recording techniques: extracellular field potential recording, visualized whole-cell patch-clamping, and voltage sensitive dye recording. Finally, we demonstrate a method for regionally dissecting subregions of the hippocampus that can be useful for detailed analysis of neurochemical and metabolic alterations post-TBI.
	These methods have been used to examine the alterations in hippocampal circuitry following TBI and to probe the opposing changes in network circuit function that occur in the dentate gyrus and CA1 subregions of the hippocampus (see Figure 1). The ability to analyze the post-TBI changes in each subregion is essential to understanding the underlying mechanisms contributing to TBI-induced behavioral and cognitive deficits. 
	The multi-faceted system outlined here allows investigators to push past characterization of phenomenology induced by a disease state (in this case TBI) and determine the mechanisms responsible for the observed pathology associated with TBI.

A multi-faceted approach to investigating functional changes to hippocampal circuitry is explained. Electrophysiological techniques are described along with the injury protocol, behavioral testing and regional dissection method. The combination of these techniques can be applied in similar fashion for other brain regions and scientific questions.

Traumatic Brain Injury (TBI) afflicts more than 1.7 million people in the United States each year and even mild TBI can lead to persistent neurological ...

A Procedure for Implanting a Spinal Chamber for Longitudinal In Vivo Imaging of the Mouse Spinal Cord

Studies in the mammalian neocortex have enabled unprecedented resolution of cortical structure, activity, and response to neurodegenerative insults by repeated, time-lapse in vivo imaging in live rodents. These studies were made possible by straightforward surgical procedures, which enabled optical access for a prolonged period of time without repeat surgical procedures. In contrast, analogous studies of the spinal cord have been previously limited to only a few imaging sessions, each of which required an invasive surgery. As previously described, we have developed a spinal chamber that enables continuous optical access for upwards of 8 weeks, preserves mechanical stability of the spinal column, is easily stabilized externally during imaging, and requires only a single surgery. Here, the design of the spinal chamber with its associated surgical implements is reviewed and the surgical procedure is demonstrated in detail. Briefly, this video will demonstrate the preparation of the surgical area and mouse for surgery, exposure of the spinal vertebra and appropriate tissue debridement, the delivery of the implant and vertebral clamping, the completion of the chamber, the removal of the delivery system, sealing of the skin, and finally, post-operative care. The procedure for chronic in vivo imaging using nonlinear microscopy will also be demonstrated. Finally, outcomes, limitations, typical variability, and a guide for troubleshooting are discussed.

A Procedure for Implanting a Spinal Chamber for Longitudinal In Vivo Imaging of the Mouse Spinal Cord

In this video, we describe a procedure for implanting a chronic optical imaging chamber over the dorsal spinal cord of a live mouse. The chamber, surgical procedure, and chronic imaging are reviewed and demonstrated.

Studies in the mammalian neocortex have enabled unprecedented resolution of cortical structure, activity, and response to neurodegenerative insults by ...

Live Imaging of Nicotine Induced Calcium Signaling and Neurotransmitter Release Along Ventral Hippocampal Axons

Sustained enhancement of axonal signaling and increased neurotransmitter release by the activation of pre-synaptic nicotinic acetylcholine receptors (nAChRs) is an important mechanism for neuromodulation by acetylcholine (ACh). The difficulty with access to probing the signaling mechanisms within intact axons and at nerve terminals both in vitro and in vivo has limited progress in the study of the pre-synaptic components of synaptic plasticity. Here we introduce a gene-chimeric preparation of ventral hippocampal (vHipp)&#8211;accumbens (nAcc) circuit in vitro that allows direct live imaging to analyze both the pre- and post-synaptic components of transmission while selectively varying the genetic profile of the pre- vs post-synaptic neurons. We demonstrate that projections from vHipp microslices, as pre-synaptic axonal input, form multiple, reliable glutamatergic synapses with post-synaptic targets, the dispersed neurons from nAcc. The pre-synaptic localization of various subtypes of nAChRs are detected and the pre-synaptic nicotinic signaling mediated synaptic transmission are monitored by concurrent electrophysiological recording and live cell imaging. This preparation also provides an informative approach to study the pre- and post-synaptic mechanisms of glutamatergic synaptic plasticity in vitro.

We developed a gene-chimeric preparation of ventral hippocampal &#8211; accumbens circuit in vitro that allows direct live imaging to analyze presynaptic mechanisms of nicotinic acetylcholine receptors (nAChRs) mediated synaptic transmission. This preparation also provides an informative approach to study the pre- and post-synaptic mechanisms of synaptic plasticity.

Sustained enhancement of axonal signaling and increased neurotransmitter release by the activation of pre-synaptic nicotinic acetylcholine receptors ...

High-Resolution Quantitative Immunogold Analysis of Membrane Receptors at Retinal Ribbon Synapses

Retinal ganglion cells (RGCs) receive excitatory glutamatergic input from bipolar cells. Synaptic excitation of RGCs is mediated postsynaptically by NMDA receptors (NMDARs) and AMPA receptors (AMPARs). Physiological data have indicated that glutamate receptors at RGCs are expressed not only in postsynaptic but also in perisynaptic or extrasynaptic membrane compartments. However, precise anatomical locations for glutamate receptors at RGC synapses have not been determined. Although a high-resolution quantitative analysis of glutamate receptors at central synapses is widely employed, this approach has had only limited success in the retina. We developed a postembedding immunogold method for analysis of membrane receptors, making it possible to estimate the number, density and variability of these receptors at retinal ribbon synapses. Here we describe the tools, reagents, and the practical steps that are needed for: 1) successful preparation of retinal fixation, 2) freeze-substitution, 3) postembedding immunogold electron microscope (EM) immunocytochemistry and, 4) quantitative visualization of glutamate receptors at ribbon synapses.

The postembedding immunogold method is one of the most effective ways to provide high-resolution analyses of the subcellular localization of specific molecules. Here we describe a protocol to quantitatively analyze glutamate receptors at retinal ribbon synapses.

Retinal ganglion cells (RGCs) receive excitatory glutamatergic input from bipolar cells. Synaptic excitation of RGCs is mediated postsynaptically by NMDA ...

Using Linear Agarose Channels to Study Drosophila Larval Crawling Behavior

Drosophila larval crawling is emerging as a powerful model to study neural control of sensorimotor behavior. However, larval crawling behavior on flat open surfaces is complex,&#160;including: pausing, turning, and meandering. This complexity in the repertoire of movement hinders detailed analysis of the events occurring during a single crawl stride cycle. To overcome this obstacle, linear agarose channels were made that constrain larval behavior to straight, sustained, rhythmic crawling. In principle, because agarose channels and the Drosophila larval body are both optically clear, the movement of larval structures labeled by genetically-encoded fluorescent probes can be monitored in intact, freely-moving larvae. In the past, larvae were placed in linear channels and crawling at the level of whole organism, segment, and muscle were analyzed1. In the future, larvae crawling in channels can be used for calcium imaging to monitor neuronal activity. Moreover, these methods can be used with larvae of any genotype and with any researcher-designed channel. Thus the protocol presented below is widely applicable for studies using the Drosophila larva as a model to understand motor control.

Using Linear Agarose Channels to Study Drosophila Larval Crawling Behavior

The Drosophila larva is a powerful model system to study neural control of behavior. This publication describes the use of linear agarose channels to elicit sustained bouts of linear crawling and methods to quantify the dynamics of larval structures during repetitive crawling behavior.

Drosophila larval crawling is emerging as a powerful model to study neural control of sensorimotor behavior. However, larval crawling behavior on flat ...

Combining Optogenetics with Artificial microRNAs to Characterize the Effects of Gene Knockdown on Presynaptic Function within Intact Neuronal Circuits

The purpose of this protocol is to characterize the effect of gene knockdown on presynaptic function within intact neuronal circuits. We describe a workflow on how to combine artificial microRNA (miR)-mediated RNA interference with optogenetics to achieve selective stimulation of manipulated presynaptic boutons in acute brain slices. The experimental approach involves the use of a single viral construct and a single neuron-specific promoter to drive the expression of both an optogenetic probe and artificial miR(s) against presynaptic gene(s). When stereotactically injected in the brain region of interest, the expressed construct makes it possible to stimulate with light exclusively the neurons with reduced expression of the gene(s) under investigation. This strategy does not require the development and maintenance of genetically modified mouse lines and can in principle be applied to other organisms and to any neuronal gene of choice. We have recently applied it to investigate how the knockdown of alternative splice isoforms of presynaptic P/Q-type voltage-gated calcium channels (VGCCs) regulates short-term synaptic plasticity at CA3 to CA1 excitatory synapses in acute hippocampal slices. A similar approach could also be used to manipulate and probe the neuronal circuitry in vivo.

This protocol provides a workflow on how to combine artificial microRNA-mediated RNA interference with optogenetics to stimulate specifically presynaptic boutons with reduced expression of selective gene(s) within intact neuronal circuits.

The purpose of this protocol is to characterize the effect of gene knockdown on presynaptic function within intact neuronal circuits. We describe a ...

FM Dye Cycling at the Synapse: Comparing High Potassium Depolarization, Electrical and Channelrhodopsin Stimulation

FM dyes are used to study the synaptic vesicle (SV) cycle. These amphipathic probes have a hydrophilic head and hydrophobic tail, making them water-soluble with the ability to reversibly enter and exit membrane lipid bilayers. These styryl dyes are relatively non-fluorescent in aqueous medium, but insertion into the outer leaflet of the plasma membrane causes a &#62;40X increase in fluorescence. In neuronal synapses, FM dyes are internalized during SV endocytosis, trafficked both within and between SV pools, and released with SV exocytosis, providing a powerful tool to visualize presynaptic stages of neurotransmission. A primary genetic model of glutamatergic synapse development and function is the Drosophila neuromuscular junction (NMJ), where FM dye imaging has been used extensively to quantify SV dynamics in a wide range of mutant conditions. The NMJ synaptic terminal is easily accessible, with a beautiful array of large synaptic boutons ideal for imaging applications. Here, we compare and contrast the three ways to stimulate the Drosophila NMJ to drive activity-dependent FM1-43 dye uptake/release: 1) bath application of high [K+] to depolarize neuromuscular tissues, 2) suction electrode motor nerve stimulation to depolarize the presynaptic nerve terminal, and 3) targeted transgenic expression of channelrhodopsin variants for light-stimulated, spatial control of depolarization. Each of these methods has benefits and disadvantages for the study of genetic mutation effects on the SV cycle at the Drosophila NMJ. We will discuss these advantages and disadvantages to assist the selection of the stimulation approach, together with the methodologies specific to each strategy. In addition to fluorescent imaging, FM dyes can be photoconverted to electron-dense signals visualized using transmission electron microscopy (TEM) to study SV cycle mechanisms at an ultrastructural level. We provide the comparisons of confocal and electron microscopy imaging from the different methods of Drosophila NMJ stimulation, to help guide the selection of future experimental paradigms.

Synaptic vesicle (SV) cycling is the core mechanism of intercellular communication at neuronal synapses. FM dye uptake and release are the primary means of quantitatively assaying SV endo- and exocytosis. Here, we compare all the stimulation methods to drive FM1-43 cycling at the Drosophila neuromuscular junction (NMJ) model synapse.

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FM Dye Cycling at the Synapse: Comparing High Potassium Depolarization, Electrical and Channelrhodopsin Stimulation