Kynurenic acid microinjected into the nucleus tractus solitarius of rat blocks the arterial baroreflex but not responses to glutamate

The selective excitatory amino acid antagonist kynurenic acid was bilaterally microinjected into the nucleus tractus solitarius of rats to determine its effects on the arterial baroreflex and on the cardiovascular responses to glutamate and nonglutamate agonists injected at the same site. Kynurenic acid blocked the responses to N-methyl-D-aspartate and kainate as well as the baroreflex, but did not block the response to glutamate, quisqualate, or acetylcholine. The data may suggest that glutamate is not a neurotransmitter in the baroreflex arc or that only certain glutamate receptors are integral to the baroreflex in the nucleus tractus solitarius.