EXCITATORY AMINO-ACID RECEPTOR ANTAGONISTS BLOCK THE CARDIOVASCULAR AND ANXIETY RESPONSES ELICITED BY GAMMA-AMINOBUTYRIC-ACID, RECEPTOR BLOCKADE IN THE BASOLATERAL AMYGDALA OF RATS

Blockade of gamma-aminobutyric acid (GABA(A)) receptors in the anterio r basolateral amygdala (BLA) with bicuculline methiodide results in an increase in heart rate, blood pressure and ''anxiety'' in rats. Gluta mate receptors in the BLA are also reported to be involved in elicitin g anxiety responses. The purpose of this study was to investigate the interaction between GABAergic inhibition and glutamatergic excitation in the BLA. Male Wistar rats were implanted with femoral arterial cath eters and bilateral chronic microinjection cannulae into the BLA. Each animal was injected with either artificial cerebrospinal fluid (100 n l), bicuculline methiodide (20 pmo1/100 nl) or bicuculline methiodide + one dose of an antagonist of either the N-methyl-D-aspartate recepto r [AP5 (20 and 100 pmol) and dizocilpine (25 and 125 pmol)] or the non -N-methyl-D-aspartate ionotropic receptor [CNQX (10 and 50 pmol) and G YKI 52466 (50 and 250 pmol)]. Increases in heart rate, blood pressure and ''anxiety'' (as measured in the social interaction test) observed in rats after bicuculline methiodide injections into the BLA were bloc ked in a dose dependent manner with the concurrent injections of eithe r N-methyl-D-aspartate or non-N-methyl-D-aspartate antagonists, sugges ting that activation of both subtypes of glutamate ionotropic receptor s may be necessary for the responses elicited by GABA(A) receptor bloc kade in the anterior basolateral amygdala.