TIME COURSE OF FAILURE AND RESUMPTION OF EXCITATORY AND INHIBITORY TRANSMISSION IN THE

1. Functional changes in neuromuscular transmission following denervation of the coxal depressor muscle of the cockroach Periplaneta americana have been studied by intracellular recording. 2. Miniature postsynaptic potentials, both excitatory (MEPSPs) and inhibitory (MIPSPs), disappeared by about 24 h following nerve section or crush when animals were maintained at 26°C. Generally this was accompanied by the disappearance of excitatory and inhibitory junctional potentials. 3. When animals were kept at 15°C, the onset of failure was delayed markedly, and excitatory transmission ceased a few days before inhibitory transmission, as found previously. 4. Excitatory transmission resumed before inhibitory transmission: in animals maintained at 26°C after nerve crush, MEPSPs reappeared at 11 days and MIPSPs at 28 days. The resumption of transmission was accompanied by the reappearance of junctional potentials. 5. It appears likely that the differences between excitatory and inhibitory transmission, in the timing of failure and of resumption of potentials, are related to the sizes of the axons innervating the coxal muscle of the insect leg