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Two structural adaptations for regulating transmitter release at lobster neuromuscular synapses
J P Walrond1, C K Govind, S E Huestis
1Department of Anatomy and Neurobiology, Colorado State University, Fort Collins 80523.
Summary
Lobster walking leg muscles show regional differences in how motor neurons release neurotransmitters. This occurs through distinct structural changes in excitatory and inhibitory synapses, impacting muscle activation.
Area of Science:
- Neuroscience
- Muscle Physiology
- Comparative Anatomy
Background:
- The lobster walking leg's distal accessory flexor muscle (DAFM) exhibits regional variations in motor neuron transmitter release.
- Both excitatory and inhibitory motor neurons innervate five muscle fiber bundles within the DAFM.
Purpose of the Study:
- To investigate the structural basis for differential transmitter release in the DAFM.
- To understand how synapse structure influences neurotransmission in different muscle regions.
Main Methods:
- Analysis of thin sections and freeze-fracture electron microscopy of DAFM muscle fiber bundles.
- Immunohistochemical staining for GABA to visualize inhibitory synapses.
Main Results:
- Excitatory synapses on the distal bundle have larger active zones with more intramembrane particles (putative Ca2+ channels) than proximal bundles.
- Inhibitory motor neurons form more varicosities on the distal bundle compared to the proximal bundle.
- These structural differences correlate with differential transmitter release and postsynaptic potentials.
Conclusions:
- Regional differentiation in DAFM transmitter release is mediated by distinct mechanisms in excitatory and inhibitory neurons.
- Excitatory transmission is modulated by active zone structure, while inhibitory transmission is regulated by synapse number.