Restriction of environmental space attenuates locomotor activity and hippocampal acetylcholine release in male rats.

We examined the effects of the restriction of environmental space on hippocampal acetylcholine release and spontaneous locomotor activity. Four days after the housing in a large or small cage, sampling for microdialysis study was begun. The locomotor activity counts exhibited significant daily changes in all rats in either the large or small cage. But, the mean locomotor activity counts in rats in the small cage was significantly less than that in the large cage. In contrast, the amount of acetylcholine collected per 20-min sample exhibited significant diurnal changes in all six rats in the large cage and in 5 of 6 rats in the small cage. The mean acetylcholine release in the rat in the small cage was significantly lower than that in the rat in the large cage during the dark phase, but not during the light phase. In addition, during the dark phase, hippocampal acetylcholine release was closely associated with spontaneous activity in all six rats in the large cage but not in 3 of 6 rats in the small cage. The present study suggests that the restriction of environmental space somehow interfere with the spontaneous locomotor activity and hippocampal acetylcholine release during the dark phase.