Differential expression of c-fos and tyrosine hydroxylase mRNA in the adrenal gland of the infant rat: evidence for an adrenal hyporesponsive period.
Rats exhibit a stress hyporesponsive period from postnatal day (PND) 4-14 in which the neonate displays a minimal corticosterone response to stress. We used the maternal deprivation model to test whether this adrenocortical hyporesponsiveness to stress results from a decrease in adrenal sensitivity to ACTH. Neonates (PND 6, 9, and 12) were injected ip with dexamethasone to block endogenous ACTH release, and 4 h later injected with graded doses of ACTH and killed. In another experiment, neonates were injected with isotonic saline and adrenal glands were collected at 30, 60, and 120 min post injection to examine c-fos and tyrosine hydroxylase mRNA levels using in situ hybridization. Maternally deprived pups demonstrated elevated corticosterone levels at the two highest ACTH doses and showed a greater magnitude in glucocorticoid secretion compared with the nondeprived pups. Maternally deprived pups given a saline injection exhibited elevated basal and stress-induced levels of corticosterone, in contrast to the nondeprived pups that showed a minimal response. Strikingly, maternally deprived pups exhibited elevated levels of adrenocortical c-fos mRNA, whereas the nondeprived pups did not. In contrast, the pattern of c-fos gene expression in the adrenal medulla in both groups did not display any correlation with glucocorticoid secretion. Tyrosine hydroxylase gene expression in the adrenal medulla was observed in both nondeprived and maternally deprived pups, with the latter exhibiting an earlier response of greater magnitude. These results demonstrate that the suppression of steroidogenesis occurs directly in the adrenal cortex and provide further evidence for an adrenal hyporesponsive period in the rat.
Okimoto
Darren K
DK
Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA.
Blaus
Alison
A
Schmidt
Mathias V
MV
Schmidt
Mathias
M
Gordon
M Kathleen
MK
Dent
Gersham W
GW
Levine
Seymour
S
D000311:Adrenal Glands / Q000254:growth & development* / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D003345:Corticosterone / Q000097:blood; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D016762:Genes, fos / Q000235:genetics*; D005938:Glucocorticoids / Q000494:pharmacology; D007091:Image Processing, Computer-Assisted; D017403:In Situ Hybridization; D008297:Male; D008426:Maternal Deprivation; D015347:RNA Probes; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000235:genetics; D051381:Rats; D020318:Rats, Long-Evans; D017207:Rats, Sprague-Dawley; D014446:Tyrosine 3-Monooxygenase / Q000096:biosynthesis* / Q000235:genetics
D005938:Glucocorticoids; D015347:RNA Probes; D012333:RNA, Messenger; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D014446:Tyrosine 3-Monooxygenase; D003345:Corticosterone