Studies on the possible role of brain histamine in behaviour.

1. The possible role of brain histamine in behavioural performance was studied in rats using thirst-induced water consumption, continuous (Sidman) avoidance, and reinforcement withdrawal test systems.2. Parenteral administration of a variety of antihistamines to rats decreased thirst-induced water consumption; this effect could be antagonized by administration of histamine directly into the brain by a ventricular cannula.3. When intraventricular doses of histamine were administered to rats at weekly intervals, an adaptation was seen in the effects of the amine on continuous avoidance behaviour. With succeeding doses, the initial period of depression of avoidance responding was shortened and the subsequent rebound stimulation disappeared.4. The results support the hypothesis that histamine in the brain is involved in several behavioural phenomena.