[The neurons that determine the passive defense reaction in the pteropod mollusk Clione limacina].

Pd13 neurons have been identified in pedal ganglia. They are always excited with a short latency following tactile stimulation of the head. Then the passive-defensive reaction is arisen. Activation of neuron Pd13 induces inhibition of the whole locomotor generator. A number of neurons (P1 2, 3, 4 and 5) excited only after strong tactile stimulation have been identified in pleural ganglia. Activation of a certain pleural neuron induces inhibition of the whole locomotor generator. Inhibitory pleural neurons have synaptic contact with Pd13 neurons. Each spike in the pleural neuron is followed by one EPSP in Pd13 neuron. These relations are able to potentiation, soon changed by habituation. So, after strong tactile stimulation of the head, excitation of pleural neurons increases the activity of Pd13 neuron. Cerucal and ergotamine block the inhibition effect from Pd13 and pleural neurons on motoneurons, which testifies to the dopaminergic nature.