Contribution of a humoral factor to postsynaptic sensitization in heterosynaptic facilitation

Abstract

It was shown that heterosynaptic facilitation develops in the cerebral ganglia giant neurons of the freshwater gastropod molluskPlanorbis corn eus due to diffuse neurohumoral influences on pre- and postsynaptic structures and not local synaptic action on presynaptic mechanisms. It was also found that n-cholinergic synaptic mechanisms come under this facilitatory influence. Serotonin is the source of facilitation in neurons of bothPlanorbis corneus cerebral ganglion and those of the aplysia abdominal ganglion. Seeing that: a) conditioning stimuli facilitate the effects produced by iontophoretic acetylcholine application, as well as n-cholinergic synaptic transmission and b) the amplitude of EPSP and acetylcholine potential increase 4–6 times during facilitation when the input impedance of the post-synaptic membrane is increased by just 20%, it was deduced that the postsynaptic membrane of the giant neuron makes a significant contribution to heterosynaptic facilitation of the sensitization of n-cholinergic receptors. The part played by n-cholinergic receptors of the postsynaptic membrane in heterosynaptic facilitation and conditioned reflex habituation is discussed.