Suppression of drinking and induction of sedation by a dopamine agonist is blocked by small doses of spiperone.

ET 495 (piribedil) produced significant hypodipsia in thirsty rats at 5 and 20 mg . kg-1, the effect being greater at the lower dose. At 5 mg . kg-1 ET 495 also induced a significant sedating effect, a characteristic of small doses of dopamine agonists. Both the hypodipsic and sedating effects of ET 495 were completely reversed by pretreatment with spiperone. The slight hypodipsia produced at 20 mg . kg-1 was accompanied by signs of low intensity behavioural stereotypy. The stereotypy, unlike the other behavioural effects of ET 495 treatment, was not antagonized by spiperone pretreatment.