Timing of the photoperiod and the hour of birth in rats

Influence of photoperiod on the time of parturition in the rat. I. — Effect of the length of daily illumination on normal or adrenalectomized animals

“…With a 14 hrs light regime, the births occurred during two main periods : 50 p. 100 before 8 p.m. on (Signoret, 1969) rats (Naaktgeboren and Slijper, 1970) and humans (Kaiser and Halberg,1962). In the rat, a specific effect of light on the time of parturition has been suggested in experiments involving shifts of the light/dark cycle (Lincoln and Porter, 1976) or different lengths of daily illumination (Plaut et al, 1970 ;Mitchell and Yochim, 1970 (Boer et al, 1975 ;Cohen, 1976).…”

“…With a 14 hrs light regime, the births occurred during two main periods : 50 p. 100 before 8 p.m. on (Signoret, 1969) rats (Naaktgeboren and Slijper, 1970) and humans (Kaiser and Halberg,1962). In the rat, a specific effect of light on the time of parturition has been suggested in experiments involving shifts of the light/dark cycle (Lincoln and Porter, 1976) or different lengths of daily illumination (Plaut et al, 1970 ;Mitchell and Yochim, 1970 (Boer et al, 1975 ;Cohen, 1976).Attempts to establish if the pineal gland was involved in this effect of light in the rat have been unsuccessful Lincoln and Doyle, 1978) (Krieger, 1974 ;Ixart et al,1977). Parturition was found to occur invariably during the period when the corticosterone levels were minimal for two different photoperiodic treatments (Lincoln and Porter, 1979).…”

“…Under the control light regime (14L-10D) parturition occurred earlier in the adrenalectomized rats (group CA-) than in the corresponding rats (group C ; P < 0.05). Thus, 17.4 (Plaut et ai., 1970 ;Boer et al, 1975 ;Cohen, 1976 ;Lincoln and Porter, 1976) …”

Influence of photoperiod on the time of parturition in the rat. III. Comparison of different daily light lengths with changes in light timing or light pulse given during darkness

“…As shown in this study and in others (Lincoln and Porter, 1976 ;Bosc, 1981), the apparent difference between the timing of births on the last two days of gestation suggests that the birth mechanism is affected in two different ways on these last two days.…”

Time of birth and daily activity mediated by feeding rhythms in the pregnant rat

“…When caged alone and fed at will they show two main periods of delivery ; the relative number of births during these periods and the respective times they occur on each of the last two days of gestation characterize the photodependent effect (Lincoln and Porter, 1976 ;Bosc, 19811. Between these periods, few or no parturitions occur ; this interval coincides with the dark phase of the photoperiod (Bosc, 1981).…”