GABA RECEPTORS IN THE REGION OF THE DORSOMEDIAL HYPOTHALAMUS OF RATS REGULATE ANXIETY IN THE ELEVATED PLUS-MAZE TEST .1. BEHAVIORAL MEASURES

Gamma-aminobutyric acid (GABA) receptor blockade in the region of the dorsomedial hypothalamus (DMH) elicits a constellation of responses in cluding increases in heart rate, blood pressure, respiration, aversive behavioral responses and experimental anxiety as measured by the 'con flict' test. The aim of the present study was to assess the effects of enhancing and blocking GABA receptors in the DMH of rats placed on th e elevated plus-maze test of anxiety. Male Sprague-Dawley rats were im planted with chronic microinjection cannulae in the DMH bilaterally at sites where injection of 50 pmol of the GABA(A) antagonist bicucullin e methiodide (BMI) elicited an increase in heart rate of at least 50 b eats/min under anesthesia. After recovery, the responses of these rats were tested on the elevated plus-maze following injections of saline, the GABA(A) agonist muscimol and the GABA(A) antagonists BMI and picr otoxin. Injection of muscimol caused a dose dependent 'anxiolytic-like ' effect while both BMI and picrotoxin caused increases in the experim ental anxiety on the elevated plus-maze. Microinjection of muscimol in to other non-cardiostimulatory regions of the hypothalamus did not sig nificantly affect the responding of rats on the plus-maze. These resul ts support the hypothesis that GABA(A) receptors in a discrete cardios timulatory region of the DMH regulate experimental anxiety in rats.