GABA and hypothalamic feeding systems. I. Topographic analysis of the effects of microinjections of muscimol

Intrahypothalamic injections of the gamma-aminobutyric acid (GABA) agonist, muscimol (50 ng/μl), in volumes from 0.1 to 0.5 μl were made and the effects on feeding observed. The results of a topographical analysis of the hypothalamus indicated that both the paraventricular (PVH) and ventromedial (VMH) hypothalamic nuclei may be separate, though not necessarily independent, foci of a medial, GABA-sensitive satiety system. Microinjections of muscimol into these areas resulted in a dose-dependent increase in food intake. The effects of muscimol were blocked by local pretreatments with the GABA antagonist, bicuculline methiodide and behaviorally specific (water intake, in the absence of food was not affected). Opposite effects (suppression of feeding) were observed after muscimol injections into the region lateral to the fornix, suggesting that the excitatory lateral hypothalamic feeding system also may have GABAergic components.