Role of bag cells in egg deposition ofAplysia brasiliana

Summary

The spontaneous discharge of the neurosecretory bag cells causes ovulation in the marine gastropod,Aplysia brasiliana, but the overt head movements that subsequently deposit the eggs on the substrate are initiated before the bag cells fire (see accompanying paper). Injection of homogenized abdominal ganglia (HAG) containing bag cells into intact animals triggers (1) release of eggs from the ovotestis, (2) similar head movements associated with egg deposition and (3) a sustained period of inhibited feeding. We now report that the full expression of the overt behavioral effects of HAG injections are influenced by egg movement through the reproductive tract. When egg movement is blocked at the small hermaphroditic duct (SHD) near the ovotestis, HAG injected animals show significantly decreased head oscillations compared to mock operated controls. Furthermore, SDH ligated animals do not stop responding to food after HAG injections, unlike mock operated animals that show complete inhibition of feeding. Thus movement of eggs through the reproductive tract beyond the SHD is required for normal head movements and feeding inhibition. Artificial “egg” movement through a cannula in the reproductive tract indicates that neither HAG injection nor movement of artificial “eggs” alone triggers head movements effectively. However, the combination of HAG and artificial “eggs” triggers behaviors quantitatively more similar to those with normal egg movement. Finally, denervation of the reproductive tract does not prevent the normal occurrence of head movements following HAG injection when eggs are allowed to move normally. These results suggest the hypothesis that the release of bag cell hormones and the subsequent movement of eggs normally maintain the previously initiated head movements so that egg laying behaviors stop when all of the eggs are deposited.