Catecholaminergic mechanisms of feeding-related lateral hypothalamic activity in the monkey

The functional role of the catecholaminergic mechanism in the lateral hypothalamus (LHA), in feeding behavior of the monkey was investigated by single neuron activity recording and electrophoretic application of dopamine (DA), noradrenaline (NA) and their antagonists. The feeding paradigm had 4 phases: cue light (CL) signaled start of bar press; bar press (BP, 20-30 times); short cue tone (CT) triggered by last bar press signaled presentation of food; and ingestion-reward (RW). Of 312 neurons tested, 189 (61%) responded in one or more phases of the feeding task. Two types of response were observed: CL- or CT-related transient, and BP- or RW-related long-lasting responses. These feeding-related responses depended on the nature of the food and on the hunger-satiety level. DA excited or inhibited different neurons, while NA mainly inhibited firing. DA-sensitive neurons responded more often in the feeding task than insensitive neurons due mainly to differences in responsiveness to CL on (chi 2 test, P less than 0.01), at motor initiation, and during BP (P less than 0.05). Spiperone blocked the former two responses. NA-sensitive neurons responded more often in the feeding task due to responsiveness during BP and RW (P less than 0.01). Sotalol blocked some BP-related responses, and phenoxybenzamine and sotalol blocked the CT-related responses. The data suggest that dopaminergic and noradrenergic inputs in the LHA are crucial in task initiation and reward processing, respectively. Integration of these catecholaminergic and other inputs in the LHA might be important in accomplishing motivated feeding.