INHIBITION BY ETHANOL OF THE CARDIOVASCULAR EFFECTS OF GLUTAMATE IN THE NUCLEUS OF THE SOLITARY TRACT

This study investigates whether ethanol affects the cardiovascular cha nges evoked by the excitatory amino acid glutamate in the nucleus of t he solitary tract (NTS). Male Sprague-Dawley rats were anesthetized wi th urethane and instrumented for microinjection of drugs into the NTS. In 28 animals, an initial dose-response curve for glutamate (37, 74, and 148 pmol/60 nL) was obtained. In eight animals (control group), th e dose-response curve was unchanged when it was tested after microinje ction of 60 nL of saline into the NTS. In contrast, the prior intra-NT S administration of ethanol (25 or 50 mM) consistently inhibited the h ypotensive and bradycardic effects of glutamate. The specificity of th is inhibitory response was corroborated by the inability of intra-NTS administrations of ethanol (50 mM) to affect the hypotensive and brady cardic responses to nicotine (922 pmol, 1.84 nmol, and 3.98 nmol). The se results indicate that the cardiovascular effects of glutamate can b e antagonized by ethanol in the NTS. This inhibitory effect, in turn, may provide a basis for the hypertensinogenic action of ethanol in hum ans.