Altered responsiveness of medullary depressor neurones to L-glutamate and D-serine in SHR rats

We have investigated the effects of microinjection of L-glutamate, D-serine and glycine into the caudal ventrolateral medulla (CVLM) of spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats. In SHR the depressor responses to L-glutamate were significantly enhanced compared to WKY rats, while those to the NMDA-glycine site agonists, D-serine and glycine (in the presence of strychnine) were significantly diminished. Depressor responses to NMDA and D-serine could be blocked with 5-fluro-indole-2-carboxylic acid (FICA, an NMDA-glycine site antagonist). In support of our previous findings, the larger responses of NMDA-glutamate site agonists and smaller responses of NMDA-glycine site agonists in SHR, may suggest that SHR have reduced levels of the endogenous glutamate antagonist, kynurenic acid.