Siberian chipmunks (Eutamias sibiricus) were kept individually in small cages attached to a running wheel. Under continuous illumination of two different light intensities (0.4-0.9 lux and 400-1200 lux) the influence of Rolipram, a putative new antidepressant, on the period length tau was tested. Under both conditions Rolipram caused a lengthening of tau, a decrease of activity time alpha and an increase of rest time delta, resulting in a decrease of the alpha/delta ratio. These effects of Rolipram could be due to a slowing down of the circadian oscillatory system or an influence on the sensitivity towards light.

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