A molting hormone, 20-hydroxyecydsone appears to reduce synaptic efficacy in crayfish fast extensor muscle fibers by binding to the presynaptic glutamate autoreceptors

Abstract

20-Hydroxyecydsone (20-HE) is a hormone that reduces the likelihood of intense muscle contractions during the delicate stage of molting in crustaceans. The following investigation aimed to discover whether or not 20-HE reduces the amplitude of excitatory postsynaptic potentials (EPSPs) in the neuromuscular junction of crayfish fast extensor muscle fibers in the same way that excess glutamate lowers EPSP amplitude; that is, the hormone binds to presynaptic glutamate autoreceptors, signaling the presynaptic terminal to release less neurotransmitter. In our first experiment, we exposed a crayfish tail to standard crayfish saline and then to 10mM 20-HE and found that the hormone lowered the EPSP amplitude. In our second experiment, we exposed a crayfish tail first to standard crayfish saline, then to 1mM L-glutamic acid solution and finally, to 10mM 20-HE plus 1mM L-glutamic acid solution, and found that the addition of 20-HE did not lower the EPSP amplitude more than did the glutamate by itself. Our results suggested that 20-HE works at the presynaptic glutamate autoreceptors to lower EPSP efficacy.