The range of entrainment of the locomotor activity rhythm of the cockroach Leucophaea maderae is increased at both the upper and the lower limit by Li administration. This is not due to an increase of the Zeitgeber effect of light on the internal oscillators of the cockroach, as we tested by decreasing the in tensity of the light of a 14:10 LD cycle. The threshold at which free run or relative coordination occurred was found to be 4· 10 -11 W/cm 2 (528 nm) and varied interindividually for 4 orders of magnitude. This threshold does not correlate with period length in DD. Adding Li leads only in 1 out of 15 cases to resynchronization, and this was due to a strong period lengthening in this particular animal rather than to an increased sensitivity of the oscillator to the Zeitgeber. Comparing populations, the mean threshold of synchronization under Li was the same as under water. If in the same individual the threshold was determined first under water, then under Li, synchronization was ameliorated. Age or after effects could be responsible for these results. Li seems to interact with coupling of oscillators.

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.

To cite this article: Petra Reinhard (1985) Effect of lithium chloride on the lower range of entrainment in ABSTRACT The lower range of entrainment of Syrian hamster's locomotor activity rhythm is reduced by lithium chloride administration. The lithium effect can be explained as the result of a decrease in light sensitivity and a period lenghtening.

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