Evidence for a glutamatergic neural pathway in the myenteric plexus

Am J Physiol. 1991 Oct;261(4 Pt 1):G693-700. doi: 10.1152/ajpgi.1991.261.4.G693.

Abstract

The objective of this study was to determine whether L-glutamate (L-Glu) may serve as a neurotransmitter candidate in the guinea pig myenteric plexus. We observed that [3H]Glu and gamma-[3H]aminobutyric acid were synthesized from [3H]glutamine and released from neurons of the myenteric plexus during K+ and 1,1-dimethyl-4-phenylpiperazinium-evoked depolarization in a concentration-dependent manner. Muscle tension studies performed on ileal longitudinal muscle-myenteric plexus (LM-MP) preparations revealed that L-Glu [mean effective dose (ED50) 2.5 x 10(-5) M] produced concentration-dependent contractions, which were unaffected by hexamethonium but abolished by tetrodotoxin, atropine, and magnesium, suggesting that L-Glu acts via N-methyl-D-aspartate (NMDA)-type receptors that stimulate a cholinergic neural pathway unaffected by ganglionic blockade. In addition, L-Glu (ED50 4 x 10(-5) M) and NMDA (ED50 2 x 10(-4) M) stimulated concentration-dependent release of [3H]acetylcholine (ACh) from LM-MP sections, which was inhibited by tetrodotoxin, magnesium, and the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid (AP-5). L-Glu-mediated release of [3H]ACh was enhanced by theophylline (10-6 M) and 3-isobutyl-1-methylxanthine (1 mM) and was significantly reduced by the adenylate cyclase inhibitor, 2',5'-dideoxyadenosine (10(-4) M) and somatostatin-14 (10(-6) M), which inhibits adenosine 3',5'-cyclic monophosphate (cAMP)-dependent cholinergic transmission in the myenteric plexus. These studies suggest that L-Glu may serve as an excitatory neurotransmitter in the myenteric plexus via its action on NMDA-type receptors, which are coupled to cAMP-dependent release of ACh.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylcholine / metabolism
  • Animals
  • Cyclic AMP / physiology
  • Electrophysiology
  • Glutamates / physiology*
  • Glutamic Acid
  • Guinea Pigs
  • Ileum / innervation
  • In Vitro Techniques
  • Male
  • Muscle Contraction
  • Myenteric Plexus / metabolism
  • Myenteric Plexus / physiology*
  • Neural Pathways / physiology
  • Parasympathetic Nervous System / physiology
  • Synaptic Transmission
  • gamma-Aminobutyric Acid / metabolism

Substances

  • Glutamates
  • Glutamic Acid
  • gamma-Aminobutyric Acid
  • Cyclic AMP
  • Acetylcholine