The effects of long-term isolation on physiology and behavior in male guinea pigs

Abstract

Studied were isolation induced effects in guinea pigs. Males (CM) living in two colonies (12 males, 12 females, each) were compared to males (IM) born in the colonies and kept isolated from their 2nd month of age. The findings were: (1) At 19 months of age CM showed higher testosterone and cortisol titers, higher adrenal tyrosine hydroxylase activities and higher seminal vesicles weights than IM. Body, spleen, and adrenal weights did not differ. Thus gonadal, adrenomedullary, and adrenocortical activities appear higher in CM. Adrenal functioning indicates that isolation per se is no more stressful than group living. (2) At their 13th month of age CM and IM did not differ in their behaviors during a 1 hr open-field exposure. This is not considered to result from similar ‘emotional temperaments’ but rather from an inappropriate procedure to study ‘emotionality’ in adult guinea pigs. (3) At their 14th month of age CM and IM were placed into the home cage of a male experienced fighter for 15 min. The agonistic encounters between the resident and CM occurred more frequently and were more escalated than between the resident and IM. IM may be a weaker stimulus for attack possibly due to a decreased production of androgen dependent pheromones as indicated by the decreased seminal vesicles weights. (4) Eight IM placed into the colonies at their 16th month of age lost 16.3 to 20.9% of their initial body weights. Three IM died within 8 days although they were not attacked by CM. The 5 surviving males gained low ranking social positions, showed a high degree of arousal and probably were not able to reproduce. The isolation induced effects in guinea pigs are compared to those found in other rodents and are discussed in relation to the species different social organizations.