[Role of the humoral factor and postsynaptic sensitization in heterosynaptic facilitation]

It is shown that heterosynaptic facilitation of the synaptic transmission in the giant neurons of the cerebral ganglion in Planorbis corneus develops due to the diffuse neurohumoral effects on the pre- and postsynaptic structures but not as a result of the local synaptic influences on the presynaptic mechanisms. Using the new biological object it has been confirmed that serotonin from the perfuse solution was a source of the facilitatory action on the n-cholinergic synaptic transmission. It was established that conditioning stimulations facilitated not only the n-cholinergic synaptic transmission but also the ionophoretic acetylcholine potentials. Amplitudes of EPSPs and acetylcholinic potentials increased 4-6 times, while the postsynaptic membrane impedance increased only by 20%. Based on such data it is summarized that sensitization of n-cholinergic receptors of the postsynaptic membrane contributed much to the heterosynaptic facilitation. The possible role of n-cholinergic receptors of the postsynapcit membrane in the processes of the heterosynaptic facilitation and of the conditional training is discussed.