Neuromuscular transmission in an insect visceral muscle

Abstract

The electrical properties of the muscles of locust oviduct have been examined using intracellular recordings. The muscle cells are both dye and electrically coupled. They possess a wide array of spontaneous electrical activity ranging from slow oscillations of membrane potential to action potentials. In addition to possessing spontaneous electrical activity, certain regions of the oviduct are under motor control. The amplitude of evoked excitatory junction potentials (EJPs) increased step wise revealing innervation from a maximum of three motor units. These EJPs underwent summation and facilitation, and reached a critical threshold at which point the membrane revealed an active response. Bath applied glutamate, aspartate, proctolin, and octopamine were tested for their ability to alter resting potential and EJPs. L-glutamate (1.6 X 10(-5) M and above) produced a dose-dependent depolarization of membrane potential accompanied by a reduction in amplitude of EJPs. Although L-aspartate resulted in similar effects, the concentrations required were higher than those for glutamate. Proctolin (6.3 X 10(-11) M-6.0 X 10(-9) M) resulted in a dose-dependent depolarization but had little or no effect on amplitude of EJPs. Application of D, L-octopamine (3.2 X 10(-5) M-1.7 X 10(-4) M) induced a small hyperpolarization and a reduction in amplitude of EJP. It is suggested that contractions of locust oviduct appear to be regulated by a combination of a classical neurotransmitter such as glutamate, along with the neuromodulators octopamine and proctolin.

A neurohormonal role for serotonin in the control of locust oviducts

“…2). We have previously demonstrated that the innervation to locust oviducts is confined to the common oviduct and lower lateral oviduct terminating at the insertion of the ovarioles (see Lange et al, 1984a;Orchard and Lange, 1986). The upper lateral oviducts, into which the ovarioles insert are not innervated.…”

“…The third preparation included the lower lateral and common oviducts that have previously been shown to be the innervated region (see Fig. 3; Lange et al, 1984a;Orchard and Lange, 1986). All three preparations were maintained under saline and pharmacological agents were applied by removing a known volume of saline and replacing with an equivalent volume of saline containing the test substance.…”

Structure and action of buccalin: a modulatory neuropeptide localized to an identified small cardioactive peptide-containing cholinergic motor neuron of Aplysia californica.

“…Our data, together with growing evidence for cotransmission at other invertebrate (e.g., refs. [18][19][20][21][22][23] as well as vertebrate (e.g., refs. 24-26) muscles, reinforce the idea that synapses can transmit complex chemical signals that may fine tune the response of the postsynaptic cell.…”

Two Functional but Noncomplementing Drosophila Tyrosine Decarboxylase Genes

“…Selective diffusion of octopamine into the CNS or ovaries could not only explain the achieved rescue but could also explain the enhanced ability of octopamine versus tyramine feeding to suppress the dTdc2 RO54 sterility phenotype (Table I). In other insects, octopamine relaxes ovarian muscles to allow the release of mature eggs into the oviducts (32,33). In the locust Locusta migratoria, this occurs via activation of octopamine-2B receptors, which leads to a rise in cAMP (34).…”