ENHANCED SENSITIVITY OF MEDULLARY DEPRESSOR NEURONS TO N-METHYL-D-ASPARTATE-GLYCINE SITE ANTAGONISTS IN THE SPONTANEOUSLY HYPERTENSIVE RAT

1. The effects of the specific N-methyl-D-aspartate (NMDA)-glycine sit e antagonist 5-fluoro indole-2-carboxylic acid (FICA) and NMDA, microi njected into the vasodepressor caudal ventrolateral medulla, were comp ared in spontaneously hypertensive rats (SHR) and in Wistar-Kyoto (WKY ) rats, 2. 5-Fluoro indole-2-carboxylic acid elicited a significant pr esser response (+20.0+4.9 mmHg) in SHR, but no change was found in the basal blood pressure of WKY rats, 3. The depressor response due to NM DA microinjection was significantly larger in SHR (-48.0+/-4 mmHg) tha n in WKY rats (-23.0+/-1.9 mmHg), 4. Pre-injection of FICA attenuated the depressor effects of NMDA significantly, this blockade being signi ficantly more pronounced in SHR (37.0+/-2.7 mmHg) than in WKY rats (12 .0+/-1.2 mmHg), 5. The enhanced responses to PICA may reflect the lowe r levels of the endogenous NMDA-glycine antagonist kynurenic acid in S HR compared with WKY rats.