Intrahypothalamic noradrenaline injection in the rat enhances operant licking but not lever pressing for milk reward.

Injection of noradrenaline into the hypothalamus of the rat produces poor performance of lever pressing for liquid food reinforcement at moderate ratio values, even though such injection facilitates intake of liquid food available without an operant requirement. The present work shows that a tube-licking operant response was more facilitated and less suppressed by noradrenaline than a lever-pressing response. Noradrenaline produced rear-limb ataxia which might have affected lever pressing more than licking, but results of manipulating the height of the tube suggested that this was unlikely. It is concluded that the operant performance deficit is more evident with lever pressing than with a response naturally involved in ingestion.