Entrainment of the Adrenal Rhythm to Photoperiod Prior to Puberty: Effects of Early Experience on the Adrenal Rhythm and Puberty

Abstract

The purpose of this study was to determine whether exposure to a cycle of light and dark before the onset of the adrenal rhythm would be necessary in order for rats to develop a normal rhythm of peripheral corticosterone when placed in a test photoperiod at weaning age. Rats were reared in constant light (LL) until weaning age, at which time they were placed in a cycle of 14 h light, 10 h dark (14:10). Females born and reared in 14:10 had peak corticosterone values at 14.00 h on days 22 and 26, and at 18.00 h on days 32 and 36. Males did not display a clear-cut rhythm at 22 or 26 days but had peak corticosterone at 18.00 h on days 32 and 36. Males and females reared in LL until weaning had no rhythm as a group in 14:10 at 24 days of age, but had a corticosterone peak at 18.00 h on days 28 and 40. Females born and reared in LL and exposed to 14:10 for 1 day developed an adrenal rhythm regardless of the age at exposure, but only 25 day old animals showed a normal pattern for their age group. Puberty was advanced in rats exposed to a single day of 14:10 at 25 days of age, but was delayed in younger rats (22 days old), and was unaffected by light exposure in older rats (28 days of age). It can be concluded that early exposure to light-dark cycles is not required for the normal development of an adrenal rhythm in the weanling rat, and that the setting of the corticosterone rhythm to the photoperiod can occur quite rapidly. Rats at 25-26 days of age are able to respond differently to a light cycle challenge than younger rats. A photoperiodic stimulus at that time can advance the onset of puberty.

Hormonal changes in the immature rat after administration of pregnant mare serum gonadotrophin: influence of body weight

“…Interestingly, the ACTH levels in the under-60 g rats tended to be higher (although only significantly so at 16.00 h) than in the over-60 g rats, but in spite of similar (if not higher) levels of ACTH in the under-60 g PMSG-treated group, corticosterone levels in the under-60 g rats were low and similar to those seen in the untreated animals. There was no obvious evening peak of corticosterone as would be expected from the ACTH rhythm, nor was there a midday peak in the untreated rats as noted from day 26 by Ramaley (1976). Pregnant mare serum gonadotrophin stimulates a rise in plasma corticosterone over the midday hours, 2 days after injection (Ramaley & Olson, 1974;Ramaley & Bartosik, 1975a), and this was noted in our over-60 g rats with particularly high concentrations occurring at 13.00 and 15.00h.…”

“…around days 25-26 of life, the following increases in hormone levels have been reported: a rise in LH, which also showed afternoon surges from about 5 days before puberty (Meijs-Roelofs, Kramer & Sander, 1983), a rise in prolactin, showing morning and evening surges (Döhler & Wuttke, 1976;Kimura & Kawakami, 1981), a rise in GH, with a pulsatile pattern of release (Ojeda & Jameson, 1977//;Isaksson, Nutting, Kostyo & Reagan, 1978;Eden, 1979) and a rise in unbound oestradiol (Puig-Duran, Greenstein & MacKinnon, 1979). In addition, progesterone (Morera, Audi, Betrand & Saez, 1978) and corticosterone (Ramaley, 1976) levels rise at this time with the adult circadian pattern of release (Ramaley, 1972(Ramaley, , 1978Ramaley & Bartosik, 19756); TSH levels remain low over this prepubertal period (Cons el al. 1975).…”

“…Several reports in the literature have shown that inducing a depletion of either corticosterone, prolactin or GH delays the onset of puberty, indicating that they all exert a positive modulatory effect on this phenomenon (Ramaley, 1976(Ramaley, , 1978Gelato et al 1978;Ramaley & Phares, 1980;Advis, Richards & Ojeda, 1981;Advis, Smith-White & Ojeda, 1981 ). In this report we have shown that endogenous levels of these three hormones were all low in the animals that could not be induced to first ovulation by PMSG, and we have also shown in another set of experiments that injection of any one of these hormones allowed PMSG to exert its ovulatory effect (C. A. Wilson, unpublished results).…”

Testicular expression of the Lin28/let-7 system: Hormonal regulation and changes during postnatal maturation and after manipulations of puberty

“…In Experiment 3 , photoperiodic manipulation was used as another model of perturbed puberty. Based on previous evidence showing that either changes in melatonin levels or photoperiod/day length modify the timing of puberty 42 43 44 , male rats were submitted to constant darkness (CD) during lactation, between PND-10 to -15. Groups of rats reared in standard photoperiod conditions (14-h light/10-h dark) served as controls.…”