Judith A. Ramaley

The development of daily changes in serum corticosterone in pre-weanling rats

Abstract The development of daily changes in serum corticosterone (B) values was followed in maturing Sprague-Dawley derived rats raised from birth on a 14 hour light:10 hour dark cycle or received from the breeder on the day of weaning, and placed in a 14:10 cycle, In shipped rats., initial values of B were high at 8 AM on day 22 but had dropped by day 26. Evening values of B(8 PM) were similar in 22 and 26 day old rats. A significant difference between the noon and 8 pm values of B was obtained at 18 days of age in females and 19 days of age in males. Samples taken every 4 hours on days 19 and 20, before weaning, revealed a daily pattern similar to that of adults except that high values were obtained at 8 AM on day 19 and on day 20 at the time of a trough period in older rats. The evening peak was also longer in duration, failing to fall at midnight as in 26 day old rats. It is concluded that the pattern of the adrenal rhythm matures over a three or four day period in the preweanling rat.

Prepubertal cyclicity in feeding behavior and body weight regulation in the female rat.

Abstract Periodic alterations in feeding behavior were observed in the weanling female rat between 21 and 50 days of age. Systematic changes were detected by spectral analysis in total eating time, number of meals, meal duration and body weight gain, and were found to be related to the occurrence of vaginal opening (VO) and the subsequent vaginal cycle. Although periodic alterations in food intake per 100 g body weight and meal size occurred prior to puberty, no consistent changes in these parameters were noted on the day of VO or at the first proestrus period. While ovariectomy at 21 days of age did not affect the steady increase in either food intake or body weight before puberty, it did abolish the periodic changes noted in relative food intake and body weight gain during this period. These data suggest the importance of ovarian hormones in generating prepubertal 4-day cyclicity in feeding behavior.

Effects of early handling upon puberty: Correlations with adrenal stress responsiveness☆

Handling of rat pups for 5 min once a week prior to weaning to permit weighing of the litter significantly delays vaginal opening and ovulation and is associated with a reduction in the response to an ether stress administered at 60 days of age. Handling combined with replacement of the bedding material results in a further delay in puberty and a further reduction in the stress response. It is therefore necessary to follow uniform handling procedures in any study of a developmental process.

Effects of Ovariectomy on Dexamethasone Suppression of the Adrenal Axis in Adult Rats

Three weeks after ovariectomy, adult female rats had lower basal levels of serum corticosterone (B), which did not display a daily rhythm, and reduced responses to ether stress, measured by blood levels of B 15 min after ether exposure. Ovariectomized (OVX) females were more sensitive to dexamethasone (DEX) suppression of the ether induced stress response, reaching basal levels at a dose of 50 mug DEX/100 g b.w. At this dose, B levels were reduced by only 30% over saline-control values in intact rats. DEX-treated intact rats displayed a short-term suppression, reaching a maximum 2 h after the injection followed by a rebound 7 h post-injection and a second suppression period evident by 11 h post-injection. OVX rats showed a steadily increasing suppression that began 1 h after injection and persisted to the last sample time at 11 h post-injection. The disappearance of DEX from peripheral blood was followed by means of radioimmunoassay and no difference was found between intact and OVX rats either in the basal state or 15 min after ether stress. It can be concluded that ovarian steroids condition the sensitivity of the adrenal axis to DEX suppression and that the differences in DEX sensitivity we have previously noted between prepubertal and adult rats can be accounted for by a change in gonadal status rather than by a critical developmental event in the adrenal axis itself.

The Pubertal Process in the Rat

The purpose of this experiment was to trace the development of animals treated with exogenous corticosterone in order to determine whether maturation progressed more slowly but in a continuous fashion

Adrenal Function in Rats Given PMS Before Puberty: Response to Ether Stress

This study reports the effects of precociously inducedpuberty upon basal serum corticosterone levels and the response to ether stress (ES) in maturing female rats. Precocious puberty was produced by 2

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

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.

Effects of Dexamethasone Before and After Puberty on the Daily Corticosterone Rhythm

Female Sprague-Dawley-derived rats were injected at 25 days of age (prepubertal) or 60 days of age (adult) with 1 mug dexamethasone/100 g b.w. either before the beginning of the daily rise in serum corticosterone (at 10.00 or 12.00 h in adults and 10.00 h in prepubertal rats) or after the daily rise had begun (at 14.00 h in adults, and 12.00 or 14.00 h in perpubertal rats). Blood samples were collected by decapitation at 16.00, 20.00 and 24.00 h on that day and 04.00, 08.00 and 16.00 h the following day. In adults, dexamethasone (DEX) given at 10.00 shifted the corticosterone (B) peak to 04.00. In prepubertal rats, DEX given before the B rise did not shift the subsequent peak and the patterns of B did not diverge from controls. DEX given at 12.00 or 14.00 shifted the peak to 24.00 h. At 08.00 the next day, B was depressed in adults but normal in prepubertal rats. At 16.00 h, both age groups showed depressed B in comparison to controls. Prepubertal rats appear to respond differently to dexamethasone than do adults.

Effects of Corticosterone Treatment on Puberty in Female Rats

Summary To study the role of excess corticosterone on regulating puberty onset without the added component of a stressful route of administration, corticosterone was made available ad libitum in the drinking water beginning at weaning age (22 days of age). The lowest dose (16 μg of corticoster-one/ml of 4% ethanol in tap water) did not delay puberty but did suppress the normal peak of corticosterone at 1600 hr. The next dose (24 μg) also suppressed the evening corticosterone peak. In these rats, vaginal opening was normal but ovulation was delayed in comparison to controls given 4% ethanol in tap water or tap water alone. Growth rates in the rats given 16 or 24 μg were normal. The two high concentrations (160 and 240 μg of corticosterone/ml 4% ethanol of in tap water) delayed both vaginal opening and ovulation, produced high levels of corticosterone in the blood at 0800 and 2300 hr and a depression of corticoster-one at 1600 hr, and were associated with significant growth retardation. It is concluded that a normal adrenal rhythm is not required for puberty onset and that the ability of exogenous corticosterone to delay puberty onset can be mediated through routes other than growth retardation alone. This work was supported by NSF Grant No. 74-21733. Mary Alyce Vornholt and Tim Grinbergs provided expert technical help.

Pituitary Gonadotrophin-Releasing Hormone Responsiveness in the Prepubertal Period:Effect of Delayed Puberty Onset

Daily administration of 4% ethanol in the drinking water resulted in a significant delay in puberty onset. First ovulation occurred in controls at 35.4 ± 0.9 days and in ethanol-treated animals at 41.