Development of stress‐induced responses in preweanling rats

Abstract

This study examined in postnatal Days 7, 14, and 21 male rats the effects of social isolation and social isolation with administration of brief foot shocks on the development of stress-induced behavioral and pituitary-adrenal hormone responses. Day 21 rats appeared similar to adult rats in their repsonses to the two test conditions. That is, exposure to either isolation or to shock increased both pituitary-adrenal hormone secretion and tail-flick latencies but only administration of shock potentiated freezing and ultrasonic vocalizations. Younger rats differed from Day 21 rats in their responses to the two test conditions. In both tests, Day 7 rats produced the highest number of ultrasounds, which may be due to a significant decrease in body temperature. In contrast, in Day 14 pups, exposure to shock significantly reduced isolation-induced ultrasonic vocalizations. Additional age-dependent differences were found in the analgesic responses of Days 7 and 14 rats. Day 7 rats exposed to stress became consistently hyperalgesic whereas Day 14 rats showed only a short-lasting analgesic response. Although in Days 7 and 14 rats exposure to the two stress conditions produced significant elevations in pituitary-adrenal hormone concentrations, plasma levels were lower than those measured in Day 21 rats. To summarize, preweanling rats exhibit varied age-dependent responses when exposed to different stress environments.

Behavioral and hormonal responses to stress in the newborn mouse: Effects of maternal deprivation and chlordiazepoxide

“…Physiologically, one of the reliable indices of a response to environmental perturbations is the release of adrenocorticotropin (ACTH) from the pituitary resulting in elevations of plasma corticosterone (CORT). The data available indicate that in the rat pup at postnatal Day 14, HPA activity and UVZ are inversely correlated (Takahashi, Turner, & Kalin, 1991). However, because no significant CORT or ACTH elevation could be detected in these studies at earlier ages, no conclusion can be drawn about a possible relationship between UVZ and HPA axis activity during early development.…”

Neurobiology of infant attachment

“…Older pups, past the sensitive period, have an amygdala that participates in learning and easily form odor aversions (Sullivan et al, 2000a). odor), learned odor aversions (also called conditioned fear), passive avoidance and inhibitory conditioning. These behaviors normally emerge at PN10-11 (the end of the sensitive period) but can be delayed or advanced ontogenetically simply by removing the source of CORT or by prematurely elevating CORT levels (Bialik, Pappas, & Roberts, 1984;Blozovski & Cudennec, 1980;Collier et al, 1979;review-Myslivecek, 1997;Takahashi, 1994;Takahashi & Rubin, 1993;Takahashi, Turner, & Kalin, 1991). Previous work has shown potent CORT effects on the neonatal LC, amygdala, hippocampus, frontal cortex and HPA axis that last until adulthood using the maternal deprivation paradigm (Dent, Smith, & Levine, 2001;Eghbal-Ahmadi, Avishai-Eliner, Hatalski, & Baram, 1999;Francis, Caldji, Champagne, Plotsky, & Meaney, 1999;Swiergiel, Takahashi, & Kalin, 1993).…”

Dual Circuitry for Odor-Shock Conditioning during Infancy: Corticosterone Switches between Fear and Attraction via Amygdala

“…First, the sensitive period is related to the "stress hyporesponsive period" when the pups' low CORT level is not raised by most stressful stimuli (i.e., restraint, shock) (Rosenfeld et al, 1992;Grino et al, 1994;Levine, 2001). Second, both unlearned fear, such as the pups' freezing (immobilization) response to unfamiliar male odor, and the activation of the amygdala by predator odor emerge as the sensitive period ends (Takahashi et al, 1991;Takahashi, 1992;Weidenmayer and Barr, 2001;Moriceau et al, 2004). Predator odor-induced freezing and coincident amygdala activation can be evoked precociously by injecting CORT in sensitive-period pups (Takahashi et al, 1991;Takahashi, 1992;Weidenmayer and Barr, 2001;Moriceau et al, 2004).…”

“…Second, both unlearned fear, such as the pups' freezing (immobilization) response to unfamiliar male odor, and the activation of the amygdala by predator odor emerge as the sensitive period ends (Takahashi et al, 1991;Takahashi, 1992;Weidenmayer and Barr, 2001;Moriceau et al, 2004). Predator odor-induced freezing and coincident amygdala activation can be evoked precociously by injecting CORT in sensitive-period pups (Takahashi et al, 1991;Takahashi, 1992;Weidenmayer and Barr, 2001;Moriceau et al, 2004). Third, adrenalectomizing pups can prolong the infants' unique sensitive-period learning, such as attenuated fear and inhibitory conditioning (Collier et al, 1979;Blozovski and Cudennec, 1980;Bialik et al, 1984;Myslivecek, 1997;Moriceau and Sullivan, 2004b), as well as extend the learning-induced changes of the olfactory bulb characteristic of the sensitive period (Moriceau and Sullivan, 2004b).…”