The entrainment of the circadian caecotrophy rhythm with different light‐dark time ratios

Abstract

The circadian caecotrophy rhythm of 15 rabbits of a group 1 and 12 rabbits of a group 2 was continuously monitored in LD 12:12, 14:10, 16:8, 18:6, 20:4, and 22:2. The photoperiod was extended in opposite directions either by advancing the onset (group 1) or by delaying the end (group 2) of the photoperiod. The response of the animals to photoperiod extension differed significantly both between the groups and within either group during the different steps of photoperiod extension. Generally the caecotrophy rhythm was advanced in group one and delayed in group two. The shift rate at the respective new LD schedule was determined by the phasically changing sensitivity of the rabbit to light stimulation. The results showed that the rabbit is entrained predominantly non-parametrically, while the LD timeratio is of importance mainly for the precision of phase control.

Presence and properties of a circadian rhythm in the rabbit's electrocorticogram

“…So, they are not due to an alternating presence and absence of illumination, which induce appreciable differences in the level of retinal maintained "dark" discharge (Arden and Söderberg, 1959) and in this way influence the activity of nearly all parts of the nervous system and, thus, all bodily functions. Using this as a criterion, it can be stated that the presence of genuine circadian rhythms in the rabbit has been established for locomotor activity (Van Hof-van Duin, 1971), food intake (Hörnicke, 1978), caecotrophy (Hörnicke and Batsch, 1977;Jilge, 1983), retinal photic sensitivity (Brandenburg et al, 1981(Brandenburg et al, , 1983Bobbert and van Wiechen, 1983) and flash-evoked cortical responses (Bobbert et al, 1978a, b, c). On the other hand, the occurrence of supposedly "circadian" changes in the EEG has been described for man (Frank, 1961;Heninger et al, 1969) and for monkeys (Kripke et al, 1969) and rabbits (Narebski et al, 1969;Sainio, 1974;Sainio and Putkonen, 1975) while being exposed to the normal or artificial 24 h L:D alternations.…”

“…It was previously established that in rabbits which have been exposed to suitable artificial (Bobbert et al, 1978a, b;Bobbert and Brandenburg, 1982) or natural (Bobbert et al, 1978c) light-dark alternations there is afterwards a circadian rhythm in the visually evoked cortical responses and in the photic sensitivity of the retina to flashes (Bobbert et al, 1981;1983) and to prolonged illumination (Bobbert and van Wiechen, 1983). These rhythms have a block-shaped time course in which the sharp phase-transitions occur at moments that are "programmed" by the light on-and light off-transients of the preceding 24 hrs LD schedule (Bobbert et al, 1978b, c).…”

Diversity and Development of Circadian Rhythms in the European Rabbit

“…Wherever these daily patterns have been studied under controlled, constant conditions they could be shown to represent true, endogenous circadian rhythms (7,42,48,52,53,58,(69)(70)(71)(72)(73)(74). Without an external zeitgeber the behavioral and physiological rhythms start to free-run, with a period of stable length and minimal day-to-day variability exhibited within 30-70 days of implementing constant conditions (3,50,74) (Fig.…”

Postanaesthetic effects of ketamine–midazolam and ketamine–medetomidine on gastrointestinal transit time in rabbits anaesthetised with isoflurane

“…In rabbits fed ad libitum, food ingested in the morning persists for three to four hours longer in the gastrointestinal tract than food ingested in the afternoon 24 . In contrast, the retention time is greater for food consumed in the afternoon in rabbits fed only during the diurnal period 25 . For this reason, all the rabbits in this study were fed at the same time.…”