Nitric oxide induces aspects of egg-laying behavior in Aplysia.

Aplysia egg laying is a complex behavior requiring synchronized activity in many organs. Aspects of the behavior are synchronized via the direct effects of peptide bag cell neurohormones and via stimuli arising during the behavior. Stimuli synchronizing egg laying were examined by treating A. fasciata with a nitric oxide (NO) donor. NO elicited normal appetitive and consummatory behaviors leading to the deposition of cordons containing egg capsules without eggs. The sites at which NO acts were investigated. The latency to egg deposition in response to a NO donor was shorter than that in response to other stimuli, consistent with NO acting at downstream sites from those affected by the other stimuli. The NO donor does not act on neurons in the head ganglia presynaptic to the bag cells or on the bag cells. Ligating the small hermaphroditic duct connecting the gonad to the accessory genital mass blocked egg laying in response to bag cell homogenates, but not in response to exogenous NO, indicating that NO does not act on the gonad. NO is released by transport of eggs along the small hermaphroditic duct, and NO directly acts on the accessory genital mass which packages eggs. NO also acts at a second site, independent of the effect on the accessory genital mass. A NO donor activates appetitive behaviors that normally precede egg laying even in A. californica that are unable to lay eggs.