Dynamics of defense and alimentary reactions in the development of sensitization in edible snails.

Changes in defense and alimentary behavior as well as in the reactions of command and motor neurons of these types of behavior during the development of sensitization were investigated in edible snails. Following a one-time exposure of the head of the mollusc to a 50% solution of quinine, brief (50-70 min) and prolonged (hours or days) facilitation of the defense reactions of the animals and of the responses of the command neurons of defense behavior in response to tactile and chemical sensory stimuli was discovered. The alimentary behavior of the snails and the reactions of the modulatory neurons of alimentary behavior in response to the presentation of carrot juice was suppressed in sensitized snails. Differences were observed in the dynamics of defense responses to tactile and chemical sensory stimulations in one and the same sensitized animals. Brief facilitation of the responses during sensitization correlated primarily with the depolarization of the membrane potential of the neurons of defense behavior and with an increase in excitability of the plasma membrane. Prolonged facilitation of the responses was determined primarily by change in the efficiency of synaptic transmission. The described model of the development of sensitization may be the basis for the study of the molecular and cellular mechanisms underlying learning.