Social condition affects hormone secretion and exploratory behavior in rats

Abstract

Studies of behavior, endocrinology and physiology have described experiments in which animals housed in groups or in isolation were normally tested individually. The isolation of the animal from its group for testing is perhaps the most common situation used today in experimental procedures, i.e., there is no consideration of the acute stress which occurs when the animal is submitted to a situation different from that it is normally accustomed to, i.e., group living. In the present study, we used 90 male 120-day-old rats (Rattus norvegicus) divided into 5 groups of 18 animals, which were housed 3 per cage, in a total of 6 cages. The animals were tested individually or with their groups for exploratory behavior. Hormones were determined by radioimmunoassay using specific kits. The results showed statistically significant differences between testing conditions in terms of behavior and of adrenocorticotrophic hormone (ACTH: from 116.8 ± 15.27 to 88.77 ± 18.74 when in group and to 159.6 ± 11.53 pg/ml when isolated), corticosterone (from 561.01 ± 77.04 to 1036.47 ± 79.81 when in group and to 784.71 ± 55.88 ng/ml when isolated), luteinizing hormone (from 0.84 ± 0.09 to 0.58 ± 0.05 when in group and to 0.52 ± 0.06 ng/ml when isolated) and prolactin (from 5.18 ± 0.33 to 9.37 ± 0.96 when in group and to 10.18 ± 1.23 ng/ml when isolated) secretion, but not in terms of follicle-stimulating hormone or testosterone secretion. The most important feature observed was that in each cage there was one animal with higher ACTH levels than the other two; furthermore, the exploratory behavior of this animal was different, indicating the occurrence of almost constant higher vigilance in this animal (latency to leave the den in group: 99.17 ± 34.95 and isolated: 675.3 ± 145.3 s). The data indicate that in each group there is an animal in a peculiar situation and its behavior can be detected by ACTH determination in addition to behavioral performance.

Social isolation-induced changes in the hypothalamic–pituitary–adrenal axis in the rat

“…Abnormalities in the behavioral response of isolated rats to distinct challenges have been associated with functional changes in the endocrine response, although differences in social isolation procedures or test environments among studies have led to apparently discrepant results. For example, the basal level of corticosterone in plasma was found to be either unchanged (Morinan and Leonard 1980;Viveros et al 1988;Haller and Halàsz 1999), increased (Rivier and Vale 1987;Greco et al 1990;Genaro et al 2004;Sandstrom and Hart 2005) or decreased (Miachon et al 1993;Sanchez et al 1998;Chida et al 2005) in socially isolated animals.…”

The comparison of immobility time in experimental rat swimming models

“…Blood samples were centrifuged at 2000 g at 4°C and plasma was separated and frozen at −20°C until it was time to measure the hormones. Plasma corticosterone was determined by radioimmunoassay (RIA) (Niswender et al, 1968(Niswender et al, , 1969Genaro et al, 2004). Plasma CT was measured using ethanol extraction (Vecsei, 1979).…”

Proposal of non-invasive experimental model to induce scoliosis in rats

“…To minimize the possible influence of space in the containment box in relation to the animals' growth, four rats were placed in each box 20 . The reduction in body weight may be due to the functional limitation exerted by the vest, considering that no alterations were observed in response to the central nervous system, especially in the hypothalamus with behavior reflexes 21 .…”