Effects of temperature on reproductive neuroendocrine function in Aplysia californica

Egg laying in the gastropod mollusk Aplysia californica is a temperature-dependent behavior, facilitated by warm temperature and attenuated by cold. The purpose of this work was to determine which components of the reproductive axis controlling egg laying are affected by temperature. There were three neural/reproductive tissues investigated: (1) the head ganglia that transmit neural signals to the neuroendocrine bag cells, (2) the bag cells that synthesize and secrete egg-laying hormone (ELH), and (3) the ovotestis that extrudes eggs into the hermaphroditic duct in response to ELH. There was no significant effect of temperature on the ability of ELH to stimulate egg laying, suggesting that temperature does not alter responsiveness of the ovotestis to hormonal stimulation. There was evidence that the bag cells play a secondary role in mediating the effects of temperature on egg-laying behavior, that is, using both bioassays and radioimmunoassay for detection or measurement of ELH, hormone secretion was shown to be inhibited by cooler temperatures in some preparations. However, the inconsistency of this response suggested that the primary effect of temperature is upstream from the bag cells. Results from an experiment in which the head ganglia were chemically stimulated to activate bag cell electrical activity suggested that the primary site of temperature regulation lies within the head ganglia.