GABA receptors in the region of the dorsomedial hypothalamus of rats regulate anxiety in the elevated plus-maze test. I. Behavioral measures.

Gamma-aminobutyric acid (GABA) receptor blockade in the region of the dorsomedial hypothalamus (DMH) elicits a constellation of responses including increases in heart rate, blood pressure, respiration, aversive behavioral responses and experimental anxiety as measured by the 'conflict' 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 the elevated plus-maze test of anxiety. Male Sprague-Dawley rats were implanted with chronic microinjection cannulae in the DMH bilaterally at sites where injection of 50 pmol of the GABAA antagonist bicuculline methiodide (BMI) elicited an increase in heart rate of at least 50 beats/min under anesthesia. After recovery, the responses of these rats were tested on the elevated plus-maze following injections of saline, the GABAA agonist muscimol and the GABAA antagonists BMI and picrotoxin. Injection of muscimol caused a dose dependent 'anxiolytic-like' effect while both BMI and picrotoxin caused increases in the experimental anxiety on the elevated plus-maze. Microinjection of muscimol into other non-cardiostimulatory regions of the hypothalamus did not significantly affect the responding of rats on the plus-maze. These results support the hypothesis that GABAA receptors in a discrete cardiostimulatory region of the DMH regulate experimental anxiety in rats.