1. Responses to the iontophoretic application of 5‐hydroxytryptamine (5‐HT), dopamine and noradrenaline were examined in neurones of the submucous plexus of guinea‐pig small intestine. 2. Every neurone was excited by 5‐HT. 3. In a proportion of cells, dopamine or noradrenaline caused an increase in membrane potential. This response was only observed in cells which received in inhibitory innervation. The responses closely resembled inhibitory synaptic potentials evoked by transmural stimulation. 4. Both inhibitory synaptic potentials and inhibitory responses to dopamine and noradrenaline were blocked by methysergide. 5. It seems possible that these two catecholamines may interact with similar receptors to those activated by inhibitory transmitter.
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