[Heterosynaptic facilitation in giant neurons of the cerebral ganglion of the horned Planorbis].

Heterosynaptic facilitation evoked in the giant neuron of the Planorbis corneus cerebral ganglion by stimulation of the remote visceral nerve was more effective than facilitation achieved by paired stimulation of cerebral nerves. Its effectiveness depended not on the efficacy of the heterosynaptic input to the giant neuron, but on the strength of the connections between the chosen heterosynaptic input with neurons surrounding the giant cell. This finding as well as prolonged latency and slow rise-time of facilitation may indicate that the latter is of neurosecreory origin. The existence of a mechanism of drastic increase in the efficacy of synaptic connections may play an important role in animal habituation and during conditioning in particular, though such plasticsynaptic changes do not reflect the specificity of the conditioned reflex.