The effects of excitatory amino acids on isolated gut segments of the rat

Glutamate and aspartate are excitatory neurotransmitters in both central an d peripheral nervous systems, acting on ionotropic and metabotropic recepto rs. In our study we have examined the effects of glutamate, aspartate, N-me thyl-D-aspartate (NMDA), kainic acid and (+/-)- 1-aminocyclopentane-cis-1,3 -dicarboxylic acid (ACPD) on tone and spontaneous activity of isolated rat gastric fundus, jejunum, ileum, ascending colon and rectum. Both glutamate and aspartate produced concentration-dependent tonic contractions of rat fu ndus and rectum; the other gut segments used in the study were not responsi ve. While only NMDA and kainic acid produced concentration-dependent tonic contractions of isolated rat gastric fundus, all three type-selective agoni sts of glutamate receptors (NMDA, kainic acid and ACPD) produced tonic cont ractions of isolated rat rectum. The results of our study suggest that glut amate and aspartate in rat gastric fundus activate excitatory intrinsic neu rons through only ionotropic receptors (NMDA and non-NMDA receptors), while the same action in rat rectum is mediated through both ionotropic and meta botropic receptors. (C) 1999 The Italian Pharmacological Society.