Caractéristiques comportementales et psychopharmacologiques de rats élevés en haute densité de population.

Behavioral and pharmacological tests were performed on rats (males Wistar A.F.) maintained either during 6 weeks at 20 or 5 in a cage (40×40×17 cm) or during 6 weeks at 20 and during 8 days at 5 in cage. When compared to 5/cage-reared rats, overcrowded rats (20/cage) exhibit a lessened locomotor activity in the open field, staircase test, and Y maze; rearings, intrasession habituation, and spontaneous alternation were not altered. It seems difficult to relate this lessened locomotor activity to an enhanced emotionality level. Although overcrowded rats showed heavier adrenals, their susceptibility to restraint-induced gastric ulcers, their 'neophobic' responses to new food, and their sensitivity to the stimulating effect of oxazepam in the Y maze were not modified. Sensitivity to amphetamine-induced stereotyped behavior and to pentobarbital-induced hypnosis was found to be increased in overcrowded rats. Apomorphine-induced stereotypy and barbital sleeping time were not modified. All these data (except the fact that barbital onset of hypnosis was delayed in overcrowded rats) may suggest an altered hepatic metabolism in rats reared at 20 in a cage. In overcrowded rats an enhanced amphetamine-induced stereotyped behavior was associated with a lessened locomotor activity. Moreover, after 8 days at 5 in a cage, this increased sensitivity to amphetamine (and to pentobarbital) completely disappeared, whereas locomotor activity was not fully restored. This suggests that amphetamine sensitivity is not related to the predrug activity level of the animals. [ABSTRACT FROM AUTHOR]