Behavioral and hormonal effects of partner familiarity in periadolescent rat pairs upon novelty exposure

Citation
Ml. Terranova et al., Behavioral and hormonal effects of partner familiarity in periadolescent rat pairs upon novelty exposure, PSYCHONEURO, 24(6), 1999, pp. 639-656
Citations number
50
Categorie Soggetti
Neurosciences & Behavoir
Journal title
PSYCHONEUROENDOCRINOLOGY
ISSN journal
03064530 → ACNP
Volume
24
Issue
6
Year of publication
1999
Pages
639 - 656
Database
ISI
SICI code
0306-4530(199908)24:6<639:BAHEOP>2.0.ZU;2-I
Abstract
In periadolescent rats, social interactions are typically characterized by elevated levels of playful and affiliative behavior. Aim of the present stu dy was to assess the behavioral and hormonal effects of partner familiarity upon the separation and reunion in a novel environment of established pair s of periadolescent subjects. At weaning (post-natal day, PND 21), Sprague- Dawley rats were pair housed with a non-sibling subject of the same age and sex. On PND 35, the members of each pair were separated for a 24-h period, and randomly assigned to different experimental groups: (1) sacrificed bef ore separation; (2) sacrificed immediately after the isolation period; (3-4 ) placed individually in a novel cage for 30 min either in low-light or in high-light conditions; (5-6) reunited for 30 min in a novel cage either wit h their previous cagemate (familiar, FAM); or (7-8) with an unfamiliar rat (UNF) of the same age and sex, in either light conditions. During reunion, the occurrence of social and non-social behaviors was scored. Blood samples were collected at the end of the session from all groups and assayed for c orticosterone (CORT). The separation of the two members of an established p air did not affect baseline CORT levels. Upon reunion, the presence of a co nspecific exerted a significant buffering effect on the novelty-induced inc rease in CORT levels. Such an effect of the social companion appeared more marked in males than in females, and in FAM compared to UNF pairs. Interest ingly, FAM rats also expressed a significantly higher amount of social inve stigation and play-soliciting behavior compared to UNF animals. Behavioral results, together with previous data, suggest that periadolescent rats hous ed in established pairs develop a sort of amicable relationship. The overal l CORT output measured at the end of the session is also in line with this interpretation. As a whole, these findings indicate that periadolescence is a time period during rat development, during which social variables play a very important role in modulating both behavioral and physiological respon ses to novelty in a fashion that does not completely overlap with data on a dult subjects. (C) 1999 Elsevier Science Ltd. All rights reserved.