HYPOTHALAMIC SITES MEDIATING CARDIOVASCULAR EFFECTS OF MICROINJECTED BICUCULLINE AND EAAS IN RATS

Microinjection of the gamma-aminobutyric acid(A), receptor antagonist bicuculline methiodide (BMI) into either the dorsomedial hypothalamic nucleus (DMH) or the nearby paraventricular hypothalamic nucleus (PVN) has been reported to evoke marked tachycardia and modest presser effe cts. We compared the effects of microinjecting BMI and excitatory amin o acids (EAAs) into 1) the DMH, 2) the PVN, and 3) an intermediate are a between the two nuclei. In conscious rats, microinjection of (in pmo l) 10 BMI, 0.5 kainic acid, or 5 N-methyl-D-aspartate into the DMH mar kedly increased heart rate and slightly elevated arterial pressure, wh ereas injections into other regions provoked changes that progressivel y declined in magnitude with increasing distance from the nucleus. A s imilar pattern was evident in urethan-anesthetized rats, where the sho rtest latency to onset of BMI-induced increases in heart rate was seen after injection into the DMH. These findings demonstrate that the car diovascular changes seen after microinjection of BMI or EAAs into the medial hypothalamus result from an action in the DMH and not from spre ad to the PVN.