Studies on bursting pacemaker potential activity in molluscan neurons. III. Effects of hormones.

Vertebrate peptides and hormones have been appled to a number of identified neurosecretory and ono-neurosecretory cells in two molluscan preparations. Active peptide hormones included vasopressin and analogues. Active steriod hormones included aldosterone and hydrocortisone. Peptide effects were present at 10-9 M concentration of peptide, were confined to two neurosecrotory cells and consisted of long lasting changes in the membrane properties of these cells (characterized either by the initiation or potentiation of bursting pacemaker potential activity in these cells). The regulatory changes in membrane properties induced by the peptides were unlike the transient conductance changes produced by conventional neurotransmitters. Steroid effects were observed at 10-6M concentration of steroid and consisted of an increase in membrane potential and conductance which was dependent on the species of divalent cations present. The net effect of peptide activation would be to increase the release of neurosecretory material form the cell terminals, while the net effect of the steroids would be to decrease the release of this material. The results obtained with these invertebrate preparations may serve to describe new forms of cellular communication in the nervous system whereby peptides and steroids modulate electrical activity.