Neurons dissociated from rat myenteric plexus retain differentiated properties when grown in cell culture. III. Synaptic interactions and modulatory effects of neurotransmitter candidates.

We have used intracellular recordings to study synaptic interactions between myenteric neurons grown in dissociated cell culture. Intracellular stimulation of individual myenteric neurons caused several types of synaptic effects in nearby neurons: fast excitatory synaptic potentials mediated by nicotinic acetylcholine receptors; slow, non-cholinergic synaptic potentials; dual transmission having both fast cholinergic and slow non-cholinergic components and inhibition of spontaneously occurring fast nicotinic synaptic potentials. Fast nicotinic synaptic potentials were elicited by about 40% of neurons tested and often occurred spontaneously. The fast synaptic potentials were similar to those that have been studied in other autonomic neurons with respect to their estimated reversal potential and their sensitivity to cholinergic antagonists. The amplitudes of the fast synaptic potentials declined if evoked at frequencies greater than 0.5 Hz. Potentiation of the fast synaptic potentials was observed following high-frequency stimulation of presynaptic neurons. Several transmitter candidates modulated fast cholinergic transmission. Substance P and vasoactive intestinal peptide promoted nicotinic transmission by causing increased amplitudes of evoked and spontaneous fast synaptic potentials and an increased frequency of spontaneous synaptic potentials. gamma-Aminobutyrate and [Met]enkephalin both caused decreased amplitudes and frequency of nicotinic synaptic potentials. Serotonin depressed synaptic potentials in some neurons while enhancing them or having no effect in others. Slow, non-cholinergic, synaptic potentials were elicited by about 10% of neurons tested. These synaptic effects lasted 15-300s, caused depolarizations of 3-15 mv and were accompanied by increased neuronal input resistance. The transmitter(s) causing these slow synaptic potentials has not yet been identified.(ABSTRACT TRUNCATED AT 250 WORDS)