GLYCINE BLOCKS THE PRESSOR-RESPONSE TO L-GLUTAMATE MICROINJECTED INTO THE NUCLEUS-TRACTUS-SOLITARII OF CONSCIOUS RATS

Microinjection of L-glutamate into the nucleus tractus solitarii (NTS) of conscious freely moving Wistar rats (240-260 g) produces presser (+48 +/- 4 mmHg) and bradycardic (-153 +/- 20 bpm) responses. In the present study L-glutamate (2.5 nmol/100 nl) was microinjected before and after microinjection of increasing doses of glycine (10, 25 and 50 nmol/100 nl, N = 6) or saline (vehicle/100 nl, N = 6) into the NTS. Microinjections of increasing doses of glycine into the NTS produced a dose-dependent reduction in the presser but not in the bradycardic responses to L-glutamate. [10 nmol (+29 +/- 5 mmHg and -110 +/- 18 bpm), 25 nmol (+12 +/- 7 mmHg and -88 +/- 21 bpm) and 50 nmol (+4 +/- 2 mmHg and -100 +/- 31 bpm)] The dose-dependent blockade of the presser response to L-glutamate by glycine suggests an inhibitory neuromodulatory role for this amino acid in the sympatho-excitatory activity produced by L-glutamate microinjection into the NTS.