Glutamate modulates neurotransmission in the submucosal plexus of guinea-pig small intestine

EFFECTS of:glutamate on synaptic transmission in the submucosal plexus of g uinea-pig small intestine were studied with intracellular electrophysiologi cal recording methods. Glutamate suppressed stimulus-evoked slow excitatory :postsynaptic potentials (EPSPs) and increased the amplitude of slow inhibi tory postsynaptic potentials (IPSPs) in submucosal neurons. The actions of glutamate:were mimicked by the group I metabotropic glutamate receptor (mGl uRs) agonist DHPG, but not by the group II agonist S-4C3HPG, the group III agonist L-AP4, or selective agonists for ionotropic glutamate: receptors (i GluRs). Glutamate actions were suppressed by the selective group I mGluRs a ntagonist S-4CPG, but not by group II and III mGluRs antagonist CPPG or iGl uRs antagonists. Glutamate suppressed substance P- and 5-HT-evoked slow EPS P-like responses and potentiated norepinephrine-induced slow IPSP-like resp onses. The results suggest that group I mGIuRs mediate glutamate-induced su ppression of EPSPs and potentiation of slow IPSPs in S-type uniaxonal submu cosal neurons. (C) 1999 Lippincott Williams & Wilkins.