Neuronal analysis of hunting behavior of the pteropod mollusc Clione limacina.

The neurons of the cerebral ganglia controlling the movements of the hunting apparatus of the predatory pelagic pteropod mollusc, Clione limacina, are described in detail. A large group of high-threshold, electrically interconnected neurons, A, was identified, the impulse activity of which leads to the opening of the skin folds and the forward ejection of the hunting tentacles of the clione. Group B neurons which exhibit a constant background activity and which receive powerful inhibitory inputs from the A cells, conversely, induce the contraction and the withdrawal of the hunting tentacles into the head. The third group, are the C neurons, the impulse activity of which leads to the drawing together of the skin folds covering the hunting apparatus. The effect of such mediators as serotonin, dopamine, and gamma aminobutyric acid acid on the identified neurons was investigated. Serotonin depolarizes both A and B neurons, but the activation of the hunting apparatus appears to be an integrated effect: the activated A neurons inhibit the B neurons due to powerful IPSP, interrupting the direct excitatory effect of serotonin. Dopamine in various concentrations exerts the opposite effect: at low concentrations only B cells are activated and the tentacles are withdrawn into the head; at high concentrations the A neurons begin to operate; these neurons inhibit the B cells and activate the hunting apparatus. GABA exerts an integral, well-coordinated effect on the neurons controlling the movements of the hunting apparatus, and effect which is directed toward the activation of hunting behavior: it depolarizes-activates A neurons and hyperpolarizes-inhibits B and C neurons.