Effects of a Neonatal Immune Challenge on Reproductive Development and Associated Behaviors in Siberian Hamsters (Phodopus sungorus)

Abstract

Environmental stressors have the potential to disrupt early development in ways that could adversely impact fitness. Studies have demonstrated that animals exposed to postnatal lipopolysaccharide (LPS) show signs of delayed puberty, such as delayed vaginal opening and first estrus. This study investigated the effects of a neonatal immune challenge on subsequent adult reproductive physiology and behavior, and explored possible mediating mechanisms. Hamsters received LPS or saline injections on postnatal day (pnd) 3 and 5, as there is heightened sensitivity of the GnRH pulse generator at these time points. Female reproductive maturity was determined by monitoring for vaginal patency, beginning on pnd 25 and every five days thereafter until maturity. Male reproductive maturity was determined by using the left testis length and width to estimate testis weight beginning on pnd 25 and each subsequent week until reproductive maturity. At pnd 75 animals were placed in staged mating pairs with reproductively mature individuals of the opposite sex. Rejection, grooming and sniffing behaviors were scored for all females, and the lordosis quotient was calculated for receptive females. Mounting, intromission and ejaculation were scored in males. Preliminary data showed a decrease in food intake and body mass, as well as delay in reproductive maturity for animals treated with LPS. Female receptivity and other reproductive behaviors were varied by the LPS challenge. The results of this study contribute to a greater understanding of the behavioral responses to early immune challenges and possible ways in which animals may adjust to this common stressor.