Eating caused by 6-hydroxydopamine-induced release of noradrenaline in the diencephalon of the rat.

1. Although it is well established that exogenous noradrenaline injected into the diencephalon causes the satiated rat to eat, it is not known whether eating may be induced by release of endogenous diencephalic noradrenaline. In the present experiment 6-hydroxydopamine was injected into the diencephalon of the rat to release catecholamines and produce degeneration of catecholamine-containing neurones.2. Injection into the preoptic area of 0.01-16.0 mug of 6-hydroxydopamine caused satiated rats to eat.3. All doses of 6-hydroxydopamine above 0.01 mug produced long-lasting partial depletion of noradrenaline and dopamine in the region of the brain composed of septum, preoptic area and hypothalamus.4. Repeated injections of 8 mug 6-hydroxydopamine at intervals of several days caused progressively less eating.5. Eating in response to 6-hydroxydopamine was inhibited by pre-treatment with desmethylimipramine, or by pre-treatment with the adrenergic blocking agents phentolamine or MJ-1999.6. Water intake after 6-hydroxydopamine was reduced by pre-treatment with desmethylimipramine or MJ-1999 but was enhanced after pre-treatment with phentolamine.7. It is concluded that release of diencephalic catecholamines by injection of 6-hydroxydopamine causes eating in rats and that the catecholamine responsible for eliciting eating is noradrenaline.