Clycine blocks the pressor response to L-glutamate microinjected into the nucleus tractus solitarii of conscious rats

ABSTRACT

Microinjection of L-glutamate into the nucleous tractus solitarii (NTS) of conscious freely moving Wistar rats (240-260 g) produces pressor (+48 ñ 4mmHg) and bradicardic (-153 ñ 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/100nl, N = 6) into the NTS. Microinjections of increasing doses of glycine into the NTS produced a dose-dependent reduction in the pressor but not in the bradycardic responses to L-glutamate. [10 nmol (+29 ñ 5mmHg and -110 ñ 18 bpm), 15 nmol (+12 ñ 7 mmHg and -88 ñ 21 bpm) and 50 nmol (+4 ñ 2 mmHg and -100 ñ 31 bpm)] The dose-dependent blockade of the pressor 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