Abstract
Under moist conditions, terrestrial pulmonates tend to increase their general behavioral activity. Hydration of these animals resulted in decreased hemolymph osmolarity and increased activity. In the dehydrated condition, this phenomenon is shown to be reversible. Using the giant African snail, Achatina fulica, we examined the induction of behavior electrophysiologically. From their morphological appearance and the characteristics of intracellular recordings, some giant neurons were identified on the surface of each ganglion. Using autoactive neurons, the effects of osmotic stress on electrical activity were examined by changing the bathing medium. As a result, higher electrical activity was obtained by hypertonic saline and lower activity was induced by hypotonic saline in isolated ganglia. On the contrary, in intact snails possessing the cerebral ganglion which contains the osmoreceptor, these effects became reversible. In a neuron of the parietal ganglion, electrical activity was induced by hypotonic saline and suppressed by hypertonic saline. These results correspond well with our theory on the induction of behavior in terrestrial pulmonates by hemolymph osmotic pressure.
