Name: the neuromuscular junction: measuring synapse size, fragmentation and changes in synaptic protein density using confocal fluorescence microscopy
Uploaded: 2014-12-26T14:00:00
Description: Watch this Scientific Journal Video about The Neuromuscular Junction: Measuring Synapse Size, Fragmentation and Changes in Synaptic Protein Density Using Confocal Fluorescence Microscopy at JoVE.com

This work was supported by the National Health and Medical Research Council [570930]. Imaging was carried out at the Bosch Institute Advanced Microscopy Facility. Former members of the lab, whose work is cited, are thanked for their contributions to developing these methods.

NOTE: Design, conduct and reporting of animal experiments should take account of current guidelines 24. Such work must be approved in advance by the local animal welfare authority (in our case the Animal Ethics Committee of the University of Sydney).
1. Euthanasia of the Animal and Muscle Dissection
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	<li>Transfer the mouse from the holding room to a separate room where it is euthanized with an intraperitoneal injection of pentobarbitone solution (30 mg/kg) using the mouse handling method detailed...

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The protocols described here have enabled us to reliably measure and quantify changes in the properties of the NMJ across a range of conditions, including normal aging and disease states. The methods described for en face NMJ images will allow researchers to compare the area of pre- and postsynaptic specializations and the area of synaptic overlap/alignment. To compare the relative intensity of pre- and postsynaptic proteins the second protocol, which uses transverse optical sections, is preferred. The third protocol spe...

The neuromuscular junction (NMJ) is the critical relay synapse that mediates communication between the nervous system and skeletal muscle. It is required for all voluntary movement. Fluorescence microscopy has long been used to study the effects of transgenes on the mouse NMJ 1-3 or to compare the effects of age, diet, exercise and disease upon rodent NMJs 4-11. Such studies have taught us much about the physiology and pathophysiology of the NMJ, but the diverse parameters reported (e.g., AChR area, endplate area, perimeter length, fragmentation indices) often make it difficult to compare the findings of these studies. There is an increasing expectation for pre-clinical researchers to be able to demonstrate reproducibility, particularly in studies with rodent models of disease 12. The protocols described here were refined through a series of studies that investigated developmental, physiological and pathophysiological changes to the NMJ. Such studies require measurement of the area of synaptic specializations at the mouse motor endplate and the relative density of packing of synaptic proteins within postsynaptic specializations13-15.
The utility of these methods is illustrated by recent studies in a mouse model of anti-MuSK myasthenia gravis. Daily injections of IgG from anti-MuSK-positive myasthenia gravis patients into adult mice caused them to become weak within 2 weeks 16. Confocal maximum-projection images of muscle sections that were double-labeled for synaptophysin (in nerve-terminals) and postsynaptic AChRs revealed a progressive decline in the area of AChR staining as the primary change. Importantly the rate of decline was sufficient to explain comparable declines in the amplitude of synaptic potentials, failure of synaptic transmission and muscle weakness 17,18. Qualitatively similar findings were reported by other research groups 10,19. The same NMJ measurement methods have since been used to assess the impact of three drugs for treating anti-MuSK myasthenia gravis in this mouse model 20,21.
Sedentary aging can lead to loss of neuromuscular connections. The protocols described here have revealed an age-associated decline in the area of nerve terminal synaptophysin at motor endplates as mice progress into old age. The same methods revealed that voluntary exercise could largely prevent the reduction in presynaptic nerve terminal area 22, consistent with previous work by other groups 4. Loss of neuromuscular connections also occurs in the SOD1G93A mouse model of amyotrophic lateral sclerosis 9,23.
The studies mentioned above demonstrate that a variety of health conditions may lead to reductions in the area of either pre- or post-synaptic specializations at the NMJ. This may result in impaired synaptic function or may herald complete loss of the neuromuscular connection. Three protocols are described that allow quantitation of the area and density of synaptic specializations. The purpose of the first protocol is to provide a practical and reproducible measure of the areas of pre- and post-synaptic specializations and their alignment at mammalian NMJs, using fluorescence microscopy. Two-dimensional maximum projection confocal images and image analysis with NIH ImageJ is used to detect changes in the area of synaptophysin staining (synaptic vesicles), postsynaptic AChRs and synaptic overlap area. Confocal imaging parameters (gain and offset level) are optimized for each NMJ so as to maximize the visual information used to discern the area of synaptic specialization. Neuromuscular failure can also result from changes in the density of postsynaptic AChR and/or other synaptic proteins. The second protocol can be applied to detect changes in the relative density of postsynaptic proteins such as MuSK, rapsyn, dystroglycan, phosphorylated Src kinase and phosphorylated AChR 18,21.
In myasthenia gravis, a reduced density of AChR within the postsynaptic membrane is the immediate cause of synaptic failure and muscle weakness. The third protocol describes a Fluorescence Resonance Energy Transfer (FRET) method to assess changes in the proximity of adjacent AChRs within postsynaptic membranes 14,15. This method detects energy transfer between neighboring AChRs labeled with fluorescent-&#945;-bungarotoxin (BGT). FRET occurs only when the fluorescent donor and acceptor probes are less than 10 nm apart. This can reveal (submicroscopic) changes in the tightness of AChR packing that may directly relate to the amplitude of synaptic potentials.
These three protocols, refined over the past decade, provide complementary measures of NMJ integrity in a consistent and reproducible way. Use of standardized protocols and parameters should facilitate comparison of the effects of genes and environmental interventions upon the mammalian NMJ.

<table border="0" cellpadding="0" cellspacing="0" width="865">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">Name of Material/ Equipment</td>
			<td style="width:91px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:341px;">Comments/Description</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Scanning confocal microscope</td>
			<td style="width:91px;">Leica</td>
			<td style="width:119px;">DM IRE2 with&#160; TCS SP2 system</td>
			<td>Most scanning confocal microscopes should be suitable.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;"></td>
			<td style="width:91px;">Zeiss</td>
			<td>LSM 510 Meta&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;"></td>
			<td style="width:91px;">Leica</td>
			<td>SPE-II</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Alexa555-a-bungarotoxin (red-BGT)</td>
			<td style="width:91px;">Life technologies</td>
			<td style="width:119px;">B35451</td>
			<td>Used for labelling AChRs</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:315px;">Alexa647-&#945;-bungarotoxin (far-red-BGT)</td>
			<td style="width:91px;">Life technologies</td>
			<td>B35450</td>
			<td>Far red fluorescence: barely visible through the eyepiece&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">rabbit anti-synaptophysin</td>
			<td style="width:91px;">Life technologies</td>
			<td>18-0130</td>
			<td>Different batches of primary antibody differ in effective working dilution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">FITC-anti-rapsyn mab1234</td>
			<td>Milipore</td>
			<td style="width:119px;">FCMAB134F</td>
			<td>Monoclonal antibody conjugated to FITC</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">FITC-donkey anti-rabbit IgG</td>
			<td style="width:91px;">Jackson</td>
			<td>711-095-152</td>
			<td>Polyclonal secondary antibodies can vary in quality according to source and batch</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Optimal Cutting Temperature compound (O.T.C.)</td>
			<td style="width:91px;">ProSciTech</td>
			<td>IA018</td>
			<td>Cryostat embedding matrix for freezing&#160; muscles</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">DABCO</td>
			<td>Sigma</td>
			<td align="right">10981</td>
			<td>Mounting medium that slows photobleaching of fluorophors</td>
		</tr>
	</tbody>
</table>

the neuromuscular junction: measuring synapse size, fragmentation and changes in synaptic protein density using confocal fluorescence microscopy

The neuromuscular junction (NMJ) is the large, cholinergic relay synapse through which mammalian motor neurons control voluntary muscle contraction. Structural changes at the NMJ can result in neurotransmission failure, resulting in weakness, atrophy and even death of the muscle fiber. Many studies have investigated how genetic modifications or disease can alter the structure of the mouse NMJ. Unfortunately, it can be difficult to directly compare findings from these studies because they often employed different parameters and analytical methods. Three protocols are described here. The first uses maximum intensity projection confocal images to measure the area of acetylcholine receptor (AChR)-rich postsynaptic membrane domains at the endplate and the area of synaptic vesicle staining in the overlying presynaptic nerve terminal. The second protocol compares the relative intensities of immunostaining for synaptic proteins in the postsynaptic membrane. The third protocol uses Fluorescence Resonance Energy Transfer (FRET) to detect changes in the packing of postsynaptic AChRs at the endplate. The protocols have been developed and refined over a series of studies. Factors that influence the quality and consistency of results are discussed and normative data are provided for NMJs in healthy young adult mice.

Measurement of Synaptic Area at the NMJ
Any estimate of area relies upon the drawing of a boundary to define the extent of synaptic specializations. In healthy young adult muscles NMJ images should display well-defined boundaries for both AChR and synaptophysin staining (Figure 2A and B). Fluorescence intensity for both AChR and synaptophysin rises sharply at the boundary between the peri-synaptic and synaptic portion of the motor endplate (<s...

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The Neuromuscular Junction: Measuring Synapse Size, Fragmentation and Changes in Synaptic Protein Density Using Confocal Fluorescence Microscopy

The neuromuscular junction (NMJ) is altered in a variety of conditions that can sometimes culminate in synaptic failure. This report describes fluorescence microscope-based methods to quantify such structural changes.

The neuromuscular junction (NMJ) is the large, cholinergic relay synapse through which mammalian motor neurons control voluntary muscle contraction. ...

Research

JoVE Journal

Neuroscience

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