Glutamate-induced calcium transients in rat neurons of the dorsal motor nucleus of the vagus

The dorsal motor nucleus of the vagus (DMNV) integrates peripheral and central signals and sends efferent output to the gastrointestinal system. Glutamate, the major excitatory neurotransmitter of the central nervous system, causes increases in intracellular calcium in DMNV neurons. The mechanisms by which glutamate activates calcium signaling in the DMNV were examined. DMNV neurons were isolated from neonatal rat brainstem using microdissection and enzymatic digestion. Exposure to glutamate caused intracellular Ca2+ increments in greater than 80% of cells. Removal of extracellular Ca2+ abolished intracellular Ca2+ transients. Kynurenic acid, a nonspecific glutamate receptor antagonist, abolished intracellular Ca2+ transients. Exposure to glutamate while blocking AMPA receptors with GYKI 52466 abolished the Ca2+ response. Exposure to (S) AMPA, an AMPA receptor agonist, caused intracellular Ca2+ increments in 97% of cells. Activation and antagonism of NMDA and kainate receptors produced no changes compared to control experiments. NiCl, a nonspecific Ca2+ channel blocker, abolished intracellular Ca2+ transients. Blocking T-type Ca2+ channels with mibefradil abolished the Ca2+ response in 76% of cells. Blockade of L-type and N-type Ca2+ channels did not affect the Ca2+ response. Glutamate mediates intracellular Ca2+ currents in DMNV neurons via the AMPA receptor and T-type Ca2+ channels, allowing influx of extracellular Ca2+.