Influence of oxytocin on integration of postsynaptic potentials in molluscan neurons.

1. Intracellular recordings were made from identified and non-identified neurons in perioesophageal ganglionic ring with buccal ganglia of the mollusc, Helix pomatia. The influence of oxytocin (OXT) on neuronal integration: space and temporal summations of postsynaptic potentials (PSPs) in various neurons was investigated. The obtained data indicated that these PSPs were cholinergic PSPs. 2. Ten minute exposure to 10(-8) M OXT had no effects on the resting membranes, but triggered secondary mechanisms, which lead to enhancement of the excitatory PSP (EPSR) amplitudes and the decrease of the decay time constant (tau EPSR) obtained from the falling phase of the EPSP. 3. The enhancement of the EPSP amplitude and the decrease of tau EPSP after OXT application evoked the appearance of action potential under space summation of two spontaneous EPSPs and made easier the appearance of action potential under temporal summation of EPSPs produced by paired afferent stimuli, when the corresponding interstimuli interval was smaller than tau EPSP in the presence of OXT. 4. Ten minute exposure to 10(-8) M OXT made the integrated amplitude of the excitatory acetylcholine response and the inhibitory dopamine response in the neuron E5 more positive only when the interval between applications of these mediators was smaller than the time constant of desensitization of acetylcholine receptors in the presence of OXT. 5. The pharmacological studies showed that drugs, which elevate intracellular cyclic AMP levels, mimicked the influence of OXT on integration of PSPs in the investigated neurons.