Inhibitory innervation of a lobster muscle.
Inhibitory neuromuscular synapses formed by the common inhibitor (CI) neuron on the distal accessory flexor muscle (DAFM) in the lobster, Homarus americanus, were studied with electrophysiological and electron-microscopic (thin-section and freeze-fracture) techniques. Postsynaptic inhibition as indicated by inhibitory junctional potentials was several-fold stronger on distal compared to proximal muscle fibers. This difference correlated with the results of serial thin-section studies, which showed more inhibitory synapses on distal fibers than on their proximal counterparts. Effects of postsynaptic inhibition on excitatory junctional potentials via current shunting had a morphological correlate in the spatial relationship between inhibitory and excitatory synapses on the distal fibers. Inhibitory synapses were larger than their excitatory counterparts and had fewer glial processes. In freeze-fracture views, inhibitory synapses did not appear as raised plateaus in the P-face as do excitatory synapses, and their active zones were more widely scattered. The intramembrane particles in the inhibitory postsynaptic membrane - representing neurotransmitter receptors - are arranged in parallel rows in the sarcolemmal P-face and have complementary furrows in the sarcolemmal E-face. Altogether, our findings help to describe a population of inhibitory neuromuscular synapses formed by the CI neuron in lobster muscle.
Walrond
J P
JP
Department of Anatomy and Neurobiology, Colorado State University, Fort Collins 80523.
Wiens
T J
TJ
Govind
C K
CK
D000200:Action Potentials; D000818:Animals; D005614:Freeze Fracturing; D009132:Muscles / Q000294:innervation* / Q000648:ultrastructure; D008121:Nephropidae / Q000502:physiology*; D009433:Neural Inhibition; D009469:Neuromuscular Junction / Q000502:physiology* / Q000648:ultrastructure