Hypothalamic-Pituitary-Adrenal Axis Activity of Newborn Mice Rapidly Desensitizes to Repeated Maternal Absence but Becomes Highly Responsive to Novelty

• Published in: Endocrinology (Philadelphia) Vol. 149; no. 12; pp. 6366 - 6377
• Main Authors: Enthoven, L, Oitzl, M. S, Koning, N, van der Mark, M, de Kloet, E. R
• Format: Journal Article
• Language: English
• Published: Chevy Chase, MD Endocrine Society 01-12-2008; Oxford University Press
• Subjects: Adrenocorticotropic hormone; Adrenocorticotropic Hormone - blood; Animals; Animals, Newborn; Biological and medical sciences; Body Weight - physiology; c-Fos protein; Corticosterone; Corticosterone - blood; Corticotropin-Releasing Hormone - genetics; Desensitization; Exploratory Behavior - physiology; Female; Fundamental and applied biological sciences. Psychology; Ghrelin; Ghrelin - genetics; Glucocorticoid receptors; Glucocorticoids; Glucose metabolism; Hypothalamic-pituitary-adrenal axis; Hypothalamo-Hypophyseal System - metabolism; Hypothalamo-Hypophyseal System - physiology; Hypothalamus; In Situ Hybridization; Juveniles; Maternal Deprivation; Mice; Mineralocorticoid receptors; mRNA; Novelty; Pituitary; Pituitary-Adrenal System - metabolism; Pituitary-Adrenal System - physiology; Proto-Oncogene Proteins c-fos - genetics; Receptors; Receptors, Glucocorticoid - genetics; Receptors, Mineralocorticoid - genetics; Separation; Stress, Psychological - physiopathology; Vertebrates: endocrinology; Human; Endocrine gland; Adrenal glands; Rodentia; Central nervous system; Hypothalamus; Encephalon; Vertebrata; Mammalia; Newborn; Mouse; Animal; Pituitary gland
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2008-0238

In CD1 mice we investigated the hypothalamic-pituitary-adrenal (HPA) axis response to maternal separation for 8 h daily from postnatal d 3 to 5. At d 3 a slow separation-induced corticosterone response developed that peaked after 8 h, and the pups became responsive to stressors. On the second and third day, the response to 8 h separation rapidly attenuated, whereas the response to novelty did not, a pattern reflected by the hypothalamic c-fos mRNA response. If maternal separation and exposure to novelty were combined, then after the third such daily exposure, the sensitivity to the stressor was further enhanced. Meanwhile, basal corticosterone and ACTH levels were persistently suppressed 16 h after pups were reunited with their mothers. To explain the HPA axis desensitization after repeated separation, we found that circulating ghrelin levels increased and glucose levels decreased after all periods of maternal separation, ruling out a role of altered metabolism. Glucocorticoid feedback was not involved either because a glucocorticoid receptor antagonist amplified the corticosterone response after the first but became ineffective after the third separation. In contrast, a mineralocorticoid receptor antagonist decreased and increased corticosterone levels after the first and third period of separation, respectively. In conclusion, the newborn’s HPA axis readily desensitizes to repeated daily maternal separation, but continues to respond to novelty in a manner influenced by a central mineralocorticoid receptor- rather than glucocorticoid receptor-mediated mechanism.