Adrenocortical response to stress in fasted and unfasted artificially reared 12‐day‐old rat pups

Abstract

Recent studies have compared artificially reared (AR) rats with dam-reared rats on behavioral outcomes but, despite the fact that they are deprived of their mothers during the stress hyporesponsive period (SHRP), little is known about the effects of AR on the development of the stress response. In this study, the corticosterone (CORT) response to a stressor (saline injection ip) on postnatal Day 12 was assessed in rat pups that had been either dam-reared (DR) or artificially reared since Day 5. In the preceding 24 hr, half the pups in the DR group were maternally deprived (DEP). To control for the food deprivation consequent to maternal deprivation in these groups, half the pups in the AR groups also underwent 24-hr food deprivation (DEP). In the nondeprived condition AR pups did not differ from DR pups on untreated CORT levels or on levels at 1-hr poststress (i.e., all rats demonstrated low levels of CORT characteristic of the SHRP). In contrast, both maternally deprived DR pups and food-deprived AR pups exhibited increased untreated CORT levels as well as a significant increase at 30-min poststress, but CORT elevations were lower in the AR groups than in the DR groups. Thus, long-term maternal deprivation through artificial rearing in rats does not affect the reduced CORT levels and reduced CORT responsiveness associated with the SHRP; however, if animals are food deprived, then all show increased basal CORT levels and a greater CORT response to stress, although this response is lower in AR groups than in DR groups. These results suggest that rat pups artificially reared with adequate nutrition will still exhibit the SHRP.

Artificial rearing alters the response of rats to natural and drug-mediated rewards

“…They also tended to avoid the center of the open field, suggesting increased emotionality and fearfulness in a novel setting (Gonzalez et al, 2001;Kaneko et al, 1996). Conversely, infant (Ward, Xing, Carnide, Slivchak, & Wainwright, 2004) and adult (Kelly, Mahoney, Randich, & West, 1991) AR rats did not differ in stressinduced corticosterone levels compared to MR rats, although some differences in stress responsiveness were evident under conditions of food deprivation (Ward et al, 2004) or exposure to ethanol (Kelly et al, 1991).…”

“…There is little known to date about the stress responsiveness of AR rats. The only reports thus far indicate that infant (Ward et al, 2004) and adult (Kelly et al, 1991) AR rats did not differ in stress-induced corticosterone levels from MR controls, unless they were also food deprived for 24 hr, where they showed a lower corticosterone response to an injection stressor compared to similarly deprived MR rats (Ward et al, 2004). These findings are in contrast to reports of increased endocrine stress reactivity shown in adult maternally separated rats (Hsu et al, 2003;Liu et al, 2000;Meaney et al, 2002;Plotsky & Meaney, 1993), suggesting that the AR procedure may not lead to the same HPA axis activation seen in maternal separation.…”

Effects of early deprivation and maternal separation on pup‐directed behavior and HPA axis measures in the juvenile female rat

“…Conversely, maternal separation as well as artificial rearing decrease maternal licking and crouching behavior in adulthood; however, only artificial rearing has a robust disruptive effect on juvenile maternal behavior (Gonzalez & Fleming, 2002;Gonzalez, Lovic, Ward, Wainwright, & Fleming, 2001;Lovic et al, 2001;Rees and Fleming, 2001). Whether these effects of artificial rearing on maternal behavior are due to changes in the HPA axis remain unclear, although research has shown that artificial rearing does not affect baseline or stress-induced levels of corticosterone (Burton, Chatterjee, Chatterjee-Chakraborty, Lovic, Grella, Steiner, & Fleming, 2007;Ward, Xing, Carnide, Slivchak, & Developmental Psychobiology Wainwright, 2004). This, along with the present data, suggests that the effects of early preweaning experiences on both juvenile and adult maternal behavior may not be linked to changes in the HPA axis.…”

Effect of Complete Maternal and Littermate Deprivation on Morphine-Induced Fos-Immunoreactivity in the Adult Male Rat Brain

“…By allowing direct control of many of the variables associated with the maternal environment, it provides another model to study the role of early life experience in behavioral development. Previous work in our laboratory suggested differences in HPA axis function between preweaning male AR and maternally reared (MR) rats (17). In addition, male AR rats displayed a greater response to both natural and drug-mediated rewards than male MR rats (18).…”