Sprague-Dawley albino rats were reared in one of three social environments: isolation, low density, or high density. Baseline activity, measured by photobeam crossings in a 15-min session, was assessed for 16 consecutive days. The response to 1 and 10 mg/kg of scopolamine and .05 and .1 mg/kg of physostigmine was then assessed. It was found that isolated animals were more active than socially reared animals, and that this isolation-induced increased activity was not eliminated with repeated handling and behavioral testing. The activity of the animals in a low-density of group was not significantly greater than that of animals raised in a high-density group. Scopolamine and physostigmine were both found to decrease activity, but there was not a differential effect of the drugs on animals raised in the three social environments. It was concluded that tactile stimulation does not alter the effects of isolation-rearing and that a baseline activity level can be established for the investigation of the physiological bases of the behavioral effects of isolation-rearing.
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