Effects of hypothalamic peptide hormones on the electrical activity of Aplysia neurons

The effect of luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) on the electrical activity of neurons in the abdominal ganglion of Aplysia californica was studied. Where tested, TRH had no effect. The neurosecretory white-cell neurons were the most responsive of the neurons tested with LHRH. Bath applications of 1 micro M LHRH increased firing rates in 4 of 5 white cells for extended periods of time. The increased rates persisted in an LHRH-deficient bath. A similar result was obtained with bath applications of the LHRH agonist analog D-Ala6, des-Gly10-LHRH-ethylamide. The iontophoresis of LHRH onto white-cell somata either produced no change in electrical activity or initiated an increase in firing rate and bursting patterns which outlasted the application period. Two types of white cells are suggested by the white-cell responsiveness to LHRH. The white cells responsive to the decapeptide are candidate model neurons for studying the membrane actions of LHRH.