GABA stimulation and blockade in the hypothalamus and midbrain: effects on feeding and locomotor activity.

Microinjections of the gamma-aminobutyric acid (GABA) antagonist, bicuculline methiodide (BM) (100 ng), into the anterolateral hypothalamus (LH) increased ingestion of sweet milk. A subsequent injection of BM 48 hrs. later produced a type of kindling effect consisting of feeding related automatisms, such as gnawing and biting. The behavioral effects of injections of 100 ng of GABA into the LH were variable. GABA injections into the ventromedial hypothalamus (VMH) reliably increased food intake. GABA injections into the origin of the nigrostriatal dopamine (DA) neurons in the substantia nigra (SN) suppressed it. Similar injections into the origin of the mesolimbic DA cells in the ventral tegmental area (VTA) had no effect on feeding behavior. Following BM injections into the SN, a moderate increase in tilt box activity was observed. A second injection of the GABA blocker 6 days later exaggerated this effect. Short latency extreme hyperactivation was accompanied by unidirectional barrel rolling which persisted until blocked by local injections of GABA.