The effect of two different light intensities on spontaneous period and phase angle difference of caecotrophy rhythm in the rabbit

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Abstract
The circadian cecotrophy rhythm of the rabbit was monitored in LD [light:dark] 12:12 and continuous light of 2 different intensities. The length of the free-running rhythm and the phase angle of the entrained rhythm were influenced by aftereffects for a considerable time span of up to 75 days. The free-running period in LL of 1200 lx was significantly longer (24.94 .+-. 0.71 h (SD)) than in 10 lx (24.23 .+-. 0.39 h (SD)). In 10 lx the cecotrophy rhythm ran free monophasically, even in those rabbits practicing cecotrophy twice in LD 12:12. This confirms initial observations made in 300 lx. In LL of 1200 lx, splitting occurred in 4 out of 8 animals. The entrainment following reinsertion of the LD 12:12 after LL depended on the strength of the zeitgeber and the phase of the rhythm at the end of LL. A correlation existed between the phase angle difference and the length of the spontaneous period: the shorter the spontaneous period, the less negative was the p.a.d. [phase angle difference]. The cecotrophy rhythm of the rabbit probably accords in several chronobiological characteristics to the activity rhythm of nocturnal rodents.

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