Neuromuscular synapses on the dactyl opener muscle of the lobster Homarus americanus

Abstract

The crustacean dactyl opener neuromuscular system has been studied extensively as a model system that exhibits several forms of synaptic plasticity. We report the ultrastructural features of the synapses on dactyl opener of the lobster (Homarus americanus) as determined by examination of serial thin sections. Several innervation sites supplied by an inhibitory motoneuron have been observed without nearby excitatory innervation, indicating that excitatory and inhibitory inputs to the muscle are not always closely matched. The ultrastructural features of the lobster synapses are generally similar to those described previously for the homologous crayfish muscle, with one major distinction: few dense bars are seen at the presynaptic membranes of these lobster synapses. The majority of the lobster neuromuscular synapses lack dense bars altogether, and the mean number of dense bars per synapse is relatively low. In view of the finding that the physiology of the lobster dactyl opener synapses is similar to that reported for crayfish, these ultrastructural observations suggest that the structural complexity of the synapses may not be a critical factor determining synaptic plasticity.

Temperature dependent modulation of lobster neuromuscular properties by serotonin

“…Here we describe the temperaturedependent physiology of the lobster dactyl opener muscle and its modulation by the circulating neurohormone serotonin (5-HT). The lobster dactyl opener is a popular model system for studies of synaptic plasticity Bykhovskaia et al, 2001;Bykhovskaia et al, 2004;Glusman and Kravitz, 1982;Goy and Kravitz, 1989;Hamilton et al, 2006;Kravitz et al, 1980;Vorob'eva et al, 1999;Worden et al, 1997), as is the homologous crayfish dactyl opener muscle (Beaumont and Zucker, 2000;Delaney et al, 1991;Dixon and Atwood, 1989a;Dixon and Atwood, 1989b;Qian and Delaney, 1997;Vyshedskiy et al, 1998;Vyshedskiy and Lin, 1997;Wang and Zucker, 1998). We demonstrate that (1) thermal change within a biologically relevant range of temperatures profoundly affects the neurophysiological properties of the lobster dactyl opener neuromuscular system, and (2) the modulatory effects of serotonin on neuromuscular function have distinctly different temperature dependencies and extend the thermal range over which motor movements are effective.…”