Influence of Immune System Activation in Early Ontogenesis on Aggressiveness and Sexual Motivation in Adult Wistar Rats

Stresses in early ontogenesis can influence anxiety-depressive, defensive and social behavior, as well as the immune and hormonal reactivity of adult animals. The model of early pro-inflammatory stress assumes activation of the immune system by the introduction of bacterial lipopolysaccharide (LPS) in early ontogenesis. Whether neonatal LPS stress impacts aggressive behavior or sexual motivation is still unknown. Pathological aggressiveness and disorders in sexual behavior are characteristic of many neuropsychiatric diseases, therefore, the study of the prerequisites for their occurrence is highly relevant. On the 3rd and 5th day after birth, the rats were injected with either LPS at a dose of 50 µg/kg (LPS group) or saline solution (SAL group, control). The aggressive behavior of adult rats in the resident-intruder test after a week of social isolation was analyzed, as well as the sexual preference of males or females in a three-chamber test. The behavior of rats was compared with baseline levels of corticosterone and interleukin 1-beta in blood serum. The males of the LPS group compared with the control had more attacks on the intruder in the resident-intruder test, and the number of attacks did not decrease by the end of the experiment. The males of the LPS group had an increased interaction time with the female at the diestrus stage in the social preference test of males and females. There were no changes in aggressive behavior in females after the administration of LPS in early ontogenesis. The baseline level of interleukin-1-beta was higher in males, and corticosterone was higher in females, there were no differences between the LPS and SAL groups in biochemical parameters. The results obtained indicate an increase in aggressiveness provoked by social isolation, as well as sexual motivation in adult males after early pro-inflammatory stress, i.e., a change in the motivational and emotional component in social behavior.