SYNAPTIC PLASTICITY AND HUMORAL MODULATION OF NEUROMUSCULAR-TRANSMISSION IN THE LOBSTER CLAW OPENER DURING THE MOLT CYCLE

1. Neuromuscular properties of the lobster dactyl opener were studied at different stages of the molt cycle. 2. Excitatory junctional potentials (EJPs) were found to be significantly larger in hard-shelled premolt lobsters than in soft-shelled postmolt animals. 3. Inhibitory junctional potentials (IJPs) were larger in postmolt claw preparations than in premolt ones. 4. Excitatory transmission was also monitored during superfusion with plasma samples obtained from lobsters in vartious stages of the molt cycle (postmolt = AB; intermolt = C; premolt = D2). 5. D2 plasma increased EJP amplitude by an average of 28% relative to baseline levels (in saline), while AB plasma reduced EJP size by an average of 6%. 6. Premolt and postmolt plasma produced opposite effects on quantal content (m); D2 plasma increased m by a mean of 39%, whereas AB plasma caused a mean reduction by 10%, which suggests that humoral factors may act presynaptically to alter transmitter release. 7. These results provide evidence of neuromuscular plasticity in the opener muscle during the molt cycle, and are consistent with changes in claw-opening behavior seen during this cycle.