Vol. 283, Issue 2, 969-976, November 1997

Excitatory Amino Acid Receptor Antagonists Block the Cardiovascular and Anxiety Responses Elicited by -Aminobutyric Acid_A Receptor Blockade in the Basolateral Amygdala of Rats¹

T. J. Sajdyk and A. Shekhar

Department of Psychiatry, Pharmacology and Toxicology, and Program in Medical Neurobiology, Indiana University School of Medicine, Indianapolis, Indiana

Blockade of -aminobutyric acid (GABA_A) receptors in the anterior basolateral amygdala (BLA) with bicuculline methiodide results in an increase in heart rate, blood pressure and "anxiety" in rats. Glutamate receptors in the BLA are also reported to be involved in eliciting 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 catheters and bilateral chronic microinjection cannulae into the BLA. Each animal was injected with either artificial cerebrospinal fluid (100 nl), bicuculline methiodide (20 pmol/100 nl) or bicuculline methiodide + one dose of an antagonist of either the N-methyl-D-aspartate receptor [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 GYKI 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 blocked in a dose dependent manner with the concurrent injections of either N-methyl-D-aspartate or non-N-methyl-D-aspartate antagonists, suggesting that activation of both subtypes of glutamate ionotropic receptors may be necessary for the responses elicited by GABA_A receptor blockade in the anterior basolateral amygdala.