Terranova M L, Cirulli F, Laviola G
Department of Psychology, Università degli Studi di Roma La Sapienza, Italy.
Psychoneuroendocrinology. 1999 Aug;24(6):639-56. doi: 10.1016/s0306-4530(99)00019-0.
In periadolescent rats, social interactions are typically characterized by elevated levels of playful and affiliative behavior. Aim of the present study was to assess the behavioral and hormonal effects of partner familiarity upon the separation and reunion in a novel environment of established pairs 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 before 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 with 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 corticosterone (CORT). The separation of the two members of an established pair did not affect baseline CORT levels. Upon reunion, the presence of a conspecific exerted a significant buffering effect on the novelty-induced increase 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. Interestingly, FAM rats also expressed a significantly higher amount of social investigation and play-soliciting behavior compared to UNF animals. Behavioral results, together with previous data, suggest that periadolescent rats housed in established pairs develop a sort of amicable relationship. The overall 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 responses to novelty in a fashion that does not completely overlap with data on adult subjects.
在青春期前后的大鼠中，社交互动通常表现为嬉戏和亲和行为水平升高。本研究的目的是评估伴侣熟悉程度对处于青春期前后的既定配对实验对象在新环境中分离和重聚时的行为及激素影响。在断奶时（出生后第21天，即PND 21），将斯普拉格-道利大鼠与同年龄、同性别的非同胞对象成对饲养。在PND 35时，将每对大鼠的成员分开24小时，然后随机分配到不同的实验组：（1）在分离前处死；（2）在隔离期结束后立即处死；（3 - 4）分别置于低光照或高光照条件下的新笼子中30分钟；（5 - 6）在新笼子中与之前的同笼伙伴（熟悉，FAM）重聚30分钟；或（7 - 8）与同年龄、同性别的陌生大鼠（UNF）在任一种光照条件下重聚30分钟。在重聚期间，对社交和非社交行为的发生情况进行评分。在实验结束时从所有组采集血样，并检测皮质酮（CORT）。既定配对的两只大鼠分离并不影响基线CORT水平。重聚时，同种个体的存在对新环境诱导的CORT水平升高具有显著的缓冲作用。这种社交伙伴的作用在雄性大鼠中比在雌性大鼠中更明显，并且在熟悉组（FAM）比陌生组（UNF）配对中更显著。有趣的是，与陌生组动物相比，熟悉组大鼠还表现出显著更多的社交探究和玩耍邀请行为。行为结果与先前的数据表明，成对饲养的青春期前后大鼠形成了一种友好关系。在实验结束时测得的总体CORT输出也符合这一解释。总体而言，这些发现表明青春期前后是大鼠发育过程中的一个时期，在此期间社交变量在调节对新环境的行为和生理反应方面起着非常重要的作用，其方式与成年实验对象的数据并不完全重叠。
