Effects of acute or chronic administration of low doses of a dopamine agonist on drinking and locomotor activity in the rat.

Low doses of piribedil (0.25-5.0 mg/kg) administered acutely produced reliable decrements in locomotor activity in thirsty and non-thirsty animals, the greatest effect occurring at the highest dose. A sequence of ten daily injections of piribedil produced indications of the development of tolerance, at the two highest doses (2.5 and 5.0 mg/kg) in thirsty animals. The smallest doses used, given either acutely or chronically, produced a weak enhancement of drinking behaviour within the first 15 min of a drinking test, as shown by a reduction in latency to drink and an increase in the amount of water consumption. Tolerance did develop with respect to drinking behaviour; animals treated chronically with piribedil displayed higher levels of drinking at several dose levels when compared with acutely treated subjects. The tolerance displayed at the two highest doses could have a close affinity with that shown with regard to locomotor activity.