Endocrine Factors in Isolation-Induced Aggressiveness in Rodents

Abstract

Aggressive behavior develops in mice and rats housed individually for 3 weeks and 3-6 months, respectively. In isolated mice and rats, the weight of adrenals was increased while that of spleen decreased. In rats the liver was also significantly increased. Body weights in isolated rodents are higher than the corresponding weights of grouped animals. In isolated mice, norepinephrine content of adrenals is elevated. Hypophysectomized and orchidectomized mice fail to develop aggressiveness when isolated. Such animals will acquire fighting behavior after administration of testosterone. Adrenalectomized isolated mice develop aggressiveness to full extent but somewhat slower than unoperated controls. It is concluded that an intact pituitarygonadal axis is prerequisite for acquisition of fighting behavior, whereas the adrenal glands ‘ have only a modulating influence and are not essential. (Endocrinology78: 679, 1966)