GABAA receptors in the amygdala: role in feeding in fasted and satiated rats.

The purpose of this study was to clarify further the site of action in the amygdala as well as functional characteristics of feeding in response to two GABA receptor agonists. Guide cannulae for microinjection were implanted stereotaxically in the rat just above the central nucleus of the amygdala (CNA). Microinjections of 0.05, 0.25, 0.5 or 1.0 nmol muscimol, a GABAA-selective receptor agonist, produced a dose- and time-dependent decrease of food intake in both the satiated and fasted rat. The bilateral injection of muscimol into the amygdala was more effective than a unilateral injection during the first 2 h, although the overall effects were similar. Microinjection of 0.1 nmol bicuculline methiodide, a GABAA receptor antagonist, into the CNA significantly blocked this inhibitory effect of 0.05 and 0.5 nmol muscimol again in both the satiated and fasted rat. Doses of 0.05, 0.5, 5.0 and 10.0 nmol of the selective GABAB agonist, baclofen, injected into homologous sites in the CNA did not alter food intake. These findings support the viewpoint that the amygdala and its central nucleus comprise a pivotal region involved in the mechanisms underlying the control of feeding behavior. Further, it is envisaged that hypophagic or anorexic responses are induced through the activation of GABAA receptors by the presynaptic release of GABA from neurons which form a component of the anatomical system for hunger and satiety.