Evidence that inhibitory motor neurons of the guinea-pig small intestine exhibit fast excitatory synaptic potentials mediated via P2X receptors

Intracellular recordings were used to study the contribution of nicotinic and P-2X receptors to synaptic transmission to morphologically identified myenteric neurons of guinea-pig ileum. Hexamethonium (100 mu M) abolished fast excitatory synaptic potentials (EPSPs) in all orally projecting neurons, but fast EPSPs in anally projecting neurons were resistant to this antagonist. The non-cholinergic fast EPSPs were virtually abolished by suramin (100 mu M). This suggests that P-2X receptors are important in descending motility reflexes. However, suramin and hexamethonium together did not affect descending inhibitory reflexes when applied to the site of transmission between interneurons in this pathway. These data suggest that P-2X receptors are not involved in transmission between descending interneurons, but may be important for transmission to inhibitory motor neurons. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.