Seawater osmolarity influences bursting pacemaker activity in intact Aplysia californica.

Activity in cell R15 was monitored in a preparation of Aplysia californica in which all sensory inputs and the hemolymph were left intact. R15 exhibited bursting pacemaker activity in situ. Substitution of 93% sea water for normal sea water produced a hyperpolarization of R15 which either silenced the cell or significantly increased the interburst interval in 9 out of 12 of the experiments. Excitatory activity from head ganglia acted to antagonize this inhibitory response. The results provide support for a role of R15 in osmoregulation, and provide a model system in which the interaction of an identified neurosecretory cell, peptide release, and physiological response may be studied.