title: The newborn rat's stress system readily habituates to repeated and prolonged maternal separation, while continuing to respond to stressors in context dependent fashion.
abstract: Adrenal corticosterone secretion of newborn mice rapidly desensitizes to repeated maternal absence. The present study investigated the effects of novelty exposure, maternal care and genotype on this phenomenon. Maternal separation (MS) took place on postnatal days (pnd) 3-5. In Wistar rats, the degree of novelty in the MS-environment was varied by exposing pups to: (i) "home separation": pups remained in the home cage; (ii) "novel separation": pups were placed individually in a novel cage. Maternal care was recorded on pnd 1 to 4. To investigate the effect of genotype, we also examined Long Evans in the "home separation" condition. Basal and stress-induced ACTH and corticosterone levels were measured. Adrenal tyrosine hydroxylase (TH) and melanocortin receptor-2 (MCR-2) proteins served as markers for adrenal function. We show, in both rat strains, that the rise in plasma corticosterone induced by a single 8h-MS on pnd 5 was abolished, when this separation procedure had also been performed on pnd 3 and 4. Habituation to maternal absence occurred irrespective of housing conditions. However, pups in the "home separation" condition received less maternal care upon reunion than those placed in the "novel separation". These "home separation" pups appeared more responsive to a subsequent acute novelty-stressor, and their adrenal TH and MCR-2 were higher. Long Evans rats appeared more stress responsive than the Wistars, in the home separation condition. In conclusion, separation environment, maternal care and genotype do not affect adrenal desensitization to repeated 8 h-MS itself, but may modulate the adrenal stress-responsiveness of separated pups.
authors.affiliation: Division of Medical Pharmacology, Leiden/Amsterdam Center for Drug Research, Leiden University Medical Center, Leiden University, Gorlaeus Laboratories, The Netherlands. n.daskalakis@lacdr.leidenuniv.nl
authors.forename: Nikolaos P
authors.initials: NP
authors.lastname: Daskalakis
authors.forename: Sanne E F
authors.initials: SE
authors.lastname: Claessens
authors.forename: Jasper J L
authors.initials: JJ
authors.lastname: Laboyrie
authors.forename: Leo
authors.initials: L
authors.lastname: Enthoven
authors.forename: Melly S
authors.initials: MS
authors.lastname: Oitzl
authors.forename: Danielle L
authors.initials: DL
authors.lastname: Champagne
authors.forename: E Ronald
authors.initials: ER
authors.lastname: de Kloet
mesh_terms: D000311:Adrenal Glands / Q000378:metabolism; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000818:Animals; D000831:Animals, Newborn; D003345:Corticosterone / Q000097:blood*; D004777:Environment; D006799:Housing, Animal; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism* / Q000503:physiopathology; D008426:Maternal Deprivation; D010913:Pituitary-Adrenal System / Q000378:metabolism / Q000503:physiopathology; D051381:Rats; D020318:Rats, Long-Evans; D017208:Rats, Wistar; D044103:Receptor, Melanocortin, Type 2 / Q000378:metabolism; D013045:Species Specificity; D013315:Stress, Psychological / Q000097:blood / Q000378:metabolism* / Q000503:physiopathology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D044103:Receptor, Melanocortin, Type 2; D000324:Adrenocorticotropic Hormone; D014446:Tyrosine 3-Monooxygenase; D003345:Corticosterone