Neural control of the posterior cardiac plate and pyloric regions of the mantis shrimp Squilla oratoria: neurogenic and myogenic activities of muscles

Summary

• 1. Muscles of the posterior cardiac plate (pcp) and pyloric regions in the stomach of Squilla are innervated by motoneurons located in the stomatogastric ganglion (STG). The pattern of innervation of various muscles in these regions was determined using electrophysiological methods.

• 2. The dilator muscles are singly or doubly innervated by the pyloric dilator neurons (PDs). The constrictor muscles are singly or doubly innervated by the pcp neuron (PCP) or the pyloric neurons (PYs). These muscles are sequentially activated by pcp-pyloric motor outputs produced by the PCP, PY, and PD. All muscles can generate an all-or-nothing spike.

• 3. The constrictor muscles generate spikes followed by depolarizing afterpotentials which lead to a sustained depolarization with repetitive spikes. The PYs can entrain rhythmic spike discharges of these muscles.

• 4. The spike of muscles remains unchanged by bath application of tetrodotoxin (10^-7 M) to suppress neuronal impulse activities, but it is blocked by Mn²⁺ (10 mM).

• 5. The constrictor muscle isolated from the STG displays an endogenous property of spontaneous membrane oscillation that produces a train of spikes. Brief depolarizing or hyperpolarizing stimuli can trigger or terminate an oscillatory potential, respectively, and reset the subsequent rhythm.

• 6. The possible functions of myogenicity under the control of discharges of motoneurons in the pyloric constrictor neuromuscular system are discussed.