Dietary glutamate: interactions with the enteric nervous system.

Area of Science:

• Neuroscience
• Gastroenterology
• Neurophysiology

Background:

• Dietary protein digestion increases small intestine glutamate.
• Glutamate is an excitatory neurotransmitter in the central nervous system (CNS).
• A prevailing belief suggests glutamate functions similarly in the enteric nervous system (ENS).

Purpose of the Study:

• To investigate if glutamatergic signaling in the ENS mimics its excitatory role in the CNS.
• To re-evaluate the dogma of glutamatergic neurophysiology in the ENS.

Main Methods:

• Pharmacological analysis of glutamate receptor agonists and antagonists.
• Immunohistochemical localization of glutamate transporters and receptors in ENS neurons.
• Recording of electrical and synaptic activity in ENS neurons, mucosal secretion, and muscle contraction.

Main Results:

• ENS neurons express glutamate and the EAAC-1 glutamate transporter.
• L-glutamate and glutamatergic agonists did not excite ENS neurons.
• Glutamatergic agonists did not stimulate mucosal secretion or alter intestinal muscle contractions.

Conclusions:

• The hypothesis that glutamatergic neurotransmission in the ENS recapitulates CNS function was not supported.
• Excitatory glutamatergic neurotransmission in the CNS does not directly translate to the ENS.