Intracellular study of effects of histamine on electrical behaviour of myenteric neurones in guinea-pig small intestine.

The actions of histamine on myenteric neurones were investigated with intracellular recording methods in guinea-pig small intestine. The actions of histamine at the ganglion cell soma were: membrane depolarization, increased input resistance, suppression of post-spike hyperpolarizing potentials, augmented excitability and repetitive spike discharge. Excitability was enhanced also at spike initiation sites remote from the cell body. Both H1, and H2, receptors were involved in the response to histamine. Dimaprit mimicked the responses to histamine in 80% and 2-methylhistamine in 50% of the trials. Cimetidine was an antagonist for histamine in 82% and for dimaprit in all of the trials. Pyrilamine blocked the actions of histamine in 59% of the cells and always blocked the action of 2-methylhistamine. Histamine mimicked slow synaptic excitation in the neurones, but was ruled out as a neurotransmitter for the slow excitatory post-synaptic potential (e.p.s.p.). Histamine either did not affect the responses to 5-hydroxytryptamine, substance P and acetylcholine or it potentiated the responses to these putative neurotransmitters for slow synaptic excitation. The results support the possibility that histamine released from mast cells by circulating peptidergic messengers, by neurotransmitters or during anaphylaxis could influence enteric nervous function.