Age-diminished motor neuronal function of central neuron L7 in Aplysia

The efficacy of central neuron L₇ to elicit gill pinnule contractions was tested in mature and old Aplysia. The difference in age between groups was no less than 70 days and as much as 150 days. Spike trains in L₇ were necessary to elicit pinnule contractions in both age groups. Spike rates of 8 spikes per second and higher elicited pinnule contractions that were significantly smaller in old than in mature animals. Synaptic acitivity in the pinnule muscles innervated by L₇ was recorded extracellularly during contractions, and it was significantly less facilitated by spike trains in old as compared to that in mature Aplysia. This suggests that the reduction of facilitated synaptic transmission between L₇ and pinnule muscles results in diminished motor neuron function.