Early behavioural enrichment in the form of handling renders mouse pups unresponsive to anxiolytic drugs and increases NGF levels in the hippocampus

Early life experiences, such as early handling, can influence neural development of rodents leading to changes in physiological and behavioural reactivity to stress. These effects are likely to be mediated by changes in maternal behaviour. This study analyzed the effects of different manipulations of the rearing environment on maternal behaviour and the behavioural and physiological response to mild challenges in CD-1 mouse pups early during development. Litters underwent either 15 min of neonatal handling (H) or were exposed briefly to an unfamiliar male intruder from postnatal (PND) days 2 to 14 (MI). Both groups were compared with litters which were not manipulated (NH). Compared to NH subjects, licking behaviour in the MI group was increased only on the first day of introduction of the male intruder, while the H group showed an increase in maternal behaviour on PND 10. On PND 8, pups ultrasonic vocalizations were recorded upon treatment with an anxiolytic drug (chlordiazepoxide 0, 2, or 7.5mg/kg). Results indicate that, although there were no differences among the groups when mice were injected with vehicle, handled subjects did not reduce their calling rate following drug administration, in contrast to the NH and MI groups. Following maternal separation and novelty exposure on PND 9, levels of hippocampal NGF increased significantly only in the H group. These data suggest that active pup manipulations in the form of handling favour behavioural and neural plasticity resulting in the maintenance of a high level of arousal and in increased neurotrophin levels in response to an acute manipulation. Changes in hippocampal levels of NGF might be involved in the appraisal of subtle changes in the early social environment.

Acute perinatal asphyxia at birth has long-term effects on behavioural arousal and maternal behaviour in lactating rats

This study analysed the long-term consequences of an asphyctic event at birth on maternal behaviour and emotionality in rats. Pregnant Wistar rats were delivered by Caesarean section and the pups, still in the uterus horns, were placed into a water bath at 37 degrees C for periods of 0 (Caesarean delivery, CD) or 20 min (asphyxia, CD+20). Control subjects were born by vaginal delivery (VD). Subsequently, pups were given to surrogate mothers, weaned at 21 days, and mated at adulthood. After giving birth, differences in maternal competence and behavioural arousal were assessed observing: (i) maternal behaviour after reunion with the pups following a 3h separation, on postpartum day (PPD) 4; (ii) behaviour in an elevated plus-maze test, on postpartum day 7; and (iii) performance in a fear conditioning test, in which subjects learned to associate a conditional stimulus with an aversive unconditioned stimulus (postpartum days 7-8). Results indicate that subjects in the CD+20 group showed a deficit in maternal care, taking a longer time to retrieve the whole litter and often failing to retrieve all pups. Both CD and CD+20 groups showed higher behavioural activity in the plus-maze. In addition, when tested in the fear conditioning paradigm, the CD+20 group showed a lower latency to perform freezing behaviour in the auditory cue trial. The changes in behavioural arousal described suggest that the dopaminergic system may be a potential neurochemical target for an early hypoxic insult and indicate maternal behaviour as a useful endpoint to study the effects of early birth insult on brain function.

Long-term effects of acute perinatal asphyxia on rat maternal behavior

In this study we used a rat model of graded perinatal asphyxia to study the long-term consequences of this manipulation on rat maternal behavior at adulthood. Rats were delivered by cesarean (C) section and the pups, still in the uterus horns, were placed into a water bath at 37 degrees C for periods of 0 (controls) or 20 min (asphyxia). Subsequently, female pups were given to surrogate mothers, weaned at 21 days postnatally and then left undisturbed until adulthood, when they were mated. Once they gave birth, on postnatal days (Pnds) 1, 3, 5, 7, 9, 11 and 13 they were observed in the home cage five times per day to assess their maternal behavior in an undisturbed condition. In addition, maternal behavior was observed for 30 min in a novel cage on Pnds 4 and 8. Perinatal asphyxia affected maternal behavior in the home cage, hypoxic females being more often found outside the nest area and performing more often behaviors such as self-grooming. Principal component analysis confirmed a more 'active' behavioral profile for hypoxic females. Hypoxic mothers were characterized by a longer latency to perform on-nest behavior and by a reduced frequency of pup retrieval and licking in the novel cage. No significant differences in corticosterone secretion in response to an acute stressor were found in dams belonging to the different treatments or in the body weights of the offspring. These results are suggestive of an arousal deficit due to perinatal hypoxia and point to the dopaminergic system as a potential neurochemical target for an early hypoxic insult.