Neuropeptide activation of an identifiable buccal ganglion motoneuron in Aplysia

Application of the neuropeptide egg-laying hormone (ELH) of Aplysia to buccal ganglia activates a cell which has an axon in buccal nerve B4(17). The ELH-activated axon innervates buccal mass muscle 15(12). Criteria to identify and to record intracellularly from the ELH-activated neuron prior to ELH application were developed, and properties of the intracellularly recorded response were observed. Of two major inputs into 15 activated by stimulation of nerve B4, the ELH-activated cell always corresponded to the one showing the lesser degree of facilitation at 1 Hz. ELH-containing extracts caused a slow smooth depolarization of this cell, leading to action potentials, which were not driven by discrete EPSPs. The response was not due to disinhibition, as IPSPs did not ordinarily occur prior to ELH application, although IPSPs sometimes occurred at high rates as ELH-containing extracts were washed off. ELH-containing Sephadex G-50 fractions activated the cell in both normal and high magnesium-low calcium media. On the basis of the location of its cell body and the amount and rate of decay of facilitation of its input into 15, the author suggests that the ELH-activated cell is the same as the previously identified 15 motoneuron, B16.