Postnatal stress in mice: Does “stressing” the mother have the same effect as “stressing” the pups?

Abstract

Short- and long-term effects of brief maternal separation, maternal exposure to novel male odor, and standard rearing were compared in NMRI mice. The first condition consisted of 15 min of daily exposure of pups to clean bedding (CB), and the second condition consisted of 15 min of mothers' exposure to the odor of strange males (SM), for 14 days after birth starting from postnatal Day 1. Thus, both conditions entailed the same period of maternal separation. A control mother-offspring group was left undisturbed (nonhandled, N-H). Corticosterone levels of mothers and pups were measured at the end of the last manipulation session. Corticosterone levels were higher in SM mothers, differing from both those of CB and of control dams; CB pups showed the highest corticosterone levels in comparison with the pups belonging to the other groups. Maternal behavior observed as furthest as possible from the daily separation session did not differ among the three groups. The behavioral response to 0.5 mg/kg of apomorphine in 15-day-old pups was enhanced in both CB and SM animals, which suggests an alteration of dopaminergic functioning. Finally, adult CB and SM male mice showed an increase in the percentage of time and entries into the open arms of the plus-maze in comparison to nonhandled males. This study indicates that exposure to ecologically relevant stimuli elicited a stress response in lactating dams. This "social stress" brings about short- and long-term effects in the offspring, even in the absence of any direct manipulation of the pups.

Maternal Exposure to Low Levels of Corticosterone during Lactation Protects the Adult Offspring against Ischemic Brain Damage

“…However, we cannot exclude that the early exposure of pups to maternal corticosterone through the milk in a period of relative adrenocortical quiescence (i.e., in the first 2 weeks of postnatal life) (Sapolsky and Meaney, 1986) might have contributed to the induction of long-lasting changes in the HPA axis. Interestingly, both handled pups and CORT-nursed pups show double levels of corticosterone during lactation (Moles et al, 2004) (also see present data). However, it is noteworthy that direct injections of corticosterone to pups do not result into long-lasting alterations of the HPA axis (Meaney et al, 1987).…”

Maternal care affects the development of maternal behavior in inbred mice

“…In addition, the hormonal states of mothers might be involved (see Bartolomucci et al, 2004;Maccari et al, 1995;Rees, Panesar, Steiner, & Fleming, 2004). In mice, exposure to novel odors from adult males increased the serum corticosterone levels of mothers without changing their maternal behavior and altered the behavioral development of male pups (Moles, Rizzi, & D'Amato, 2004). Fostering itself might increase stress hormones, which, in turn, might affect the development of the maternal behavior of pups through maternal milk.…”

Effects of cage-cleaning frequency on laboratory rat reproduction, cannibalism, and welfare

“…Alternatively, (or in addition) frequent cage-cleaning might have increased cannibalism through more frequent olfactory (e.g. Mennella and Moltz, 1988;Moles et al, 2004) auditory, and/or physical (Lane Petter, 1968Busnel and Molin, 1978) disturbances, or nest disruption and cooling (e.g. Chantry, 1964;Lee and Williams, 1975) at a time when pups were vulnerable.…”

“…Noise certainly reaches a peak during cleaning and is a stressor (Gamble, 1982;Voipio et al, 2006), so cleaning cages as quietly as possible around breeding rats could help prevent cannibalism (Lane Petter, 1968;Busnel and Molin, 1978). Cage-cleaning in an unventilated area of the stock room also increases airborne levels of rodent urinary proteins (Thulin et al, 2002), potentially disseminating unfamiliar conspecific odours between cages-since unfamiliar male odours are known to stress mother rats (Moles et al, 2004), this olfactory disturbance should be avoided where possible. Fig.…”

“…Also, a recording artefact would not fully explain the peak in births midway through the cleaning cycle in the fortnightly treatment. An alternative explanation could be that the noise (Lane Petter, 1968;Busnel and Molin, 1978), circulation of conspecific odours (Moles et al, 2004), or physical disturbance associated with cleaning, even of neighbouring cages, triggered births perhaps through stress or increased activity in the mother. Physical strain, and chronic and acute stress, can shorten gestational duration under some circumstances in humans (Glynn et al, 2001;Hobel and Culhane, 2003) and domestic animals (Silver, 1990), but the effects are little understood, and differ between species.…”