Molluscan ovulation hormone containing neurons and age-related reproductive decline

Behavioural and neurophysiological experiments were conducted to examine the state of the neurosecretory caudodorsal cells (CDCs) during female reproductive decline in the freshwater snail Lymnaea stagnalis. Old animals that had ceased egg laying do not respond to an oviposition-inducing stimulus. Female reproductive organs in such animals are still intact, though less sensitive to CDC-hormone. The CDC contents of old nonlaying snails are still effective in producing ovulation in young animals. The electrophysiological properties of the CDCs of old nonlaying snails only differ from those of egg-laying snails in one respect; the duration of the afterdischarge is longer. This difference is not directly related to age but to egg-laying activity of the snails since the afterdischarge in old layers did not differ significantly from that in young layers. It is concluded that the CDCs of old nonlaying animals are in principle still intact. Female reproductive decline and subsequent cessation of female reproduction in Lymnaea may result from impairment of input to the CDCs.