Duration of the persistence of movement activity in rats induced by single injections of haloperidol

Abstract

Previous studies have demonstrated that catalepsy induced by single injections of haloperidol at a dose of 2.5 mg/kg can be reproduced over the period of two weeks (testing was performed on days 2, 7, and 14) without repeated injections of haloperidol, merely by placing the animals in the test chamber [1]. Development of a conditioned passive escape reflex increases the intensity of catalepsy. Reproduction of the passive escape reflex is associated with reproduction of catalepsy in a modified form [2]. However, catalepsy has been shown not to be reproducible in all animals.The aim of the present work was to compare the behavior of rats in an open field test using intact animals and animals which did not reproduce catalepsy.Experiments were conducted using 250 male Wistar rats (150-200 g). Experimental animals received intraperitoneal doses of haloperidol (2.5 mg/kg). Animals were tested for catalepsy using a special experimental chamber, as described previously [1, 2]. Two series of experiments were performed, using 170 and 80 animals in the first and second series respectively.In the first series of experiments, some animals were tested for reproduction of catalepsy on the second day after haloperidol injections. Of all animals tested, only those not reproducing catalepsy were selected (15 animals, group 1). The remaining animals were not tested for catalepsy (18 animals, group 2). Immediately after testing for the reproduction of catalepsy, the selected nontested and intact animals (in total, 50) were studied in an open field test. This experimental scheme was followed in subsequent experiments of this series.On day 7, some of the animals were tested for the reproduction of catalepsy without having been tested previously on day 2. Immediately after these animals were tested for catalepsy, nontested and intact animals (in total, 60) were studied in the open field test.On day 14, catalepsy testing was performed only on those animals which had not been tested on days 2 or 7. Immediately after this, tested, nontested, and intact animals (in total, 60) were studied in the open field test.In the second series of experiments, carried out using 20 rats, a defensive conditioned passive reflex requiring escape from the dark sector was developed using a single combination, by standard methods. Immediately after development of the conditioned passive reflex, animals received i.p. haloperidol (2.5 mg/kg). A method described previously, [1, 2] was then used to determine the level of the resulting catalepsy.These animals were subsequently tested for reproduction of the conditioned reflex and for reproduction of catalepsy on day 2, without a repeat dose of haloperidol.Controls consisted of a group of 20 untrained animals, which were given haloperidol at the same dose. These animals were tested in parallel with the trained animals on day 2, again without administration of haloperidol.The conditioned passive escape reflex was developed in a further 20 animals, without administration of haloperidot. Retention of the conditioned r...