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

Abstract

These studies investigated behavioral and hormonal responses to stress in developing mice. Experiment 1 examined the effects of 24-hr maternal deprivation on corticosterone (CORT) secretion and ultrasonic vocalization (UVZ) rate in 4-, 8-, and 12-day-old mice. At these ages, exposure to a novel environment resulted in minimal changes in CORT secretion. Maternal deprivation increased pups' CORT secretion in an age-dependent fashion but did not affect their UVZ rate. The aim of experiment 2 was to test the effects of chlordiazepoxide (CDP), an anxiolytic compound, on CORT secretion and UVZ in both normally reared and in maternally deprived 8-day-old mice. CDP administration elevated CORT secretion in a dose-dependent fashion, producing larger CORT increases in deprived (DEP) animals. CDP affected UVZ only in nondeprived (NDEP) animals: UVZ rate was decreased by high CDP doses. Overall, these findings demonstrate that the infant mouse shows a period of stress hyporesponsiveness similar to the rat and that maternal presence contributes to inhibit adrenocortical activity. CDP administration, but not novelty exposure, increased CORT secretion in 8-day-old normally reared mice suggesting that during the stress hyporesponsive period, the HPA axis is capable of responding only to specific stimuli. Changes in HPA axis activity and UVZ rate resulting from maternal deprivation and/or CDP challenge do not seem to be directly related.

Neonatal behaviors associated with ultrasonic vocalizations in mice (mus musculus): A slow‐motion analysis

“…In particular, six main behavioral patterns were observed: locomotion, head rising, wall climbing, probing, paddling, and lying still. Present data are congruent with previous studies on mice (Fox, 1965; for the same strain and age, see Cirulli, Adriani, & Laviola, 1997;Cirulli et al, 1994). USVs were emitted in conjunction with all behavioral categories analyzed, but they were more frequently emitted with those involving movement.…”

“…Results from previous investigations suggest that in response to isolation, there is loose integration of different behavioral patterns, contrasting with our findings (Cirulli et al, 1994;Hofer, 1987;Hofer et al, 1998;Hofer et al, 2001). However, this apparent discrepancy may be due to the different analyses performed: While other studies scored a selection of behaviors, including USV emission, in a given time period, we analyzed simultaneously the different behavioral patterns accompanying and immediately preceding and following the USV.…”

“…According with previous studies focused on neonatal rodent behavior (Cirulli et al, 1994;Spear et al, 1986), the following behavioral patterns were scored: locomotion (general translocation of the body of at least 1 cm in the glass container), lying still (no visible movement of the animal), head rising (a single rising of the head up and forward), wall climbing (alternating forelimb placing movements on the wall of the container), probing (pushing the snout against floor or walls of the apparatus), paddling (regularly alternating forelimb placing movements on the floor of the container, which do not cause any locomotor movement of the body), and roll and curl (roll, vigorous side-toside rolling movements while on the back; curl, a convex arching of back while on side or back, bringing head in a closer apposition to hump/hindlimb region).…”

“…Some studies have scored a selection of behaviors in addition to USV emission, but have not taken into account the simultaneous analysis of these behavioral manifestations. These studies reported that the overall patterns of infant behavioral activity are unrelated to USV emission profile (Cirulli, Santucci, Laviola, Alleva, & Levine, 1994;Hofer & Shair, 1987;Kraebel et al, 2002), suggesting that there is only a very loose integration of behaviors that constitute the pup response to isolation (Hofer & Shair, 1987). Furthermore, a recent and elegant work by Hofer, Shair, Masmela, and Brunelli (2001) showed how continued selection for divergent levels of the 10-day-old rat USV response to isolation did not affect other behavioral responses to isolation, with the exception of urination/defecation: Rats emitting USVs at a higher rate had a more pronounced anxiety-like response.…”

“…Behavior was scored in detail upon a slow-motion replay of videorecorded tapes at a speed decreased 25 times. At the age tested, a peak in the USV emission rate occurs (Branchi et al, 1998;Elwood & Keeling, 1982) and the pup behavioral repertoire is complex, though different from the adult one (Cirulli et al, 1994;Fox, 1965;Spear, Penson, & Linville, 1986;Williams & Scott, 1953). In particular, we performed (a) a temporal class analysis to describe behavioral patterns both temporally related to USV as well as unrelated to USV and (b) a USV feature analysis to characterize percentage of USV emissions as well as latency and duration of USVs in dependence to the behavioral pattern performed.…”