Cellular mechanisms underlying the effect of a single exposure to neonatal handling on neurotrophin-3 in the brain of 1-day-old rats

Effects of maternal separation on behavior and brain damage in adult rats exposed to neonatal hypoxia-ischemia

Animal studies suggest that maternal separation, a widely used paradigm to study the effects of early life adversity, exerts a profound and life-long impact on both brain and behavior. The aim of the current study was to investigate whether adverse early life experiences interact with neonatal hypoxia-ischemia, affecting the outcome of this neurological insult at both functional and structural levels during adulthood. Rat pups were separated from their mothers during postnatal days 1-6, for either a short (15 min) or prolonged (180 min) period, while another group was left undisturbed. On postnatal day 7, a subgroup from each of the three postnatal manipulations was exposed to a hypoxic-ischemic episode. Behavioral examination took place approximately at three months of age and included tests of learning and memory (Morris water maze, novel object and novel place recognition), as well as motor coordination (rota-rod). We found that both prolonged maternal separation and neonatal hypoxia-ischemia impaired the animals' spatial learning and reference memory. Deficits in spatial but not visual recognition memory were detected only in hypoxic-ischemic rats. Interestingly, prolonged maternal separation prior to neonatal hypoxia-ischemia augmented the reference memory impairments. Histological analysis of infarct size, hippocampal area and thickness of corpus callosum did not reveal any exacerbation of damage in hypoxic-ischemic rats that were maternally separated for a prolonged period. These are the first data suggesting that an adverse postnatal environmental manipulation of just 6 days causes long-term effects on spatial learning and memory and may render the organism more vulnerable to a subsequent insult.

Pre-reproductive maternal enrichment influences offspring developmental trajectories: motor behavior and neurotrophin expression

Environmental enrichment is usually applied immediately after weaning or in adulthood, with strong effects on CNS anatomy and behavior. To examine the hypothesis that a pre-reproductive environmental enrichment of females could affect the motor development of their offspring, female rats were reared in an enriched environment from weaning to sexual maturity, while other female rats used as controls were reared under standard conditions. Following mating with standard-reared males, all females were housed individually. To evaluate the eventual transgenerational influence of positive pre-reproductive maternal experiences, postural and motor development of male pups was analyzed from birth to weaning. Moreover, expression of Brain Derived Neurotrophic Factor and Nerve Growth Factor in different brain regions was evaluated at birth and weaning. Pre-reproductive environmental enrichment of females affected the offspring motor development, as indicated by the earlier acquisition of complex motor abilities displayed by the pups of enriched females. The earlier acquisition of motor abilities was associated with enhanced neurotrophin levels in striatum and cerebellum. In conclusion, maternal positive experiences were transgenerationally transmitted, and influenced offspring phenotype at both behavioral and biochemical levels.

Neonatal handling alters the structure of maternal behavior and affects mother-pup bonding

During early life, a mother and her pups establish a very close relationship, and the olfactory learning of the nest odor is very important for the bond formation. The olfactory bulb (OB) is a structure that plays a fundamental role in the olfactory learning (OL) mechanism that also involves maternal behavior (licking and contact). We hypothesized that handling the pups would alter the structure of the maternal behavior, affect OL, and alter mother-pup relationships. Moreover, changes in the cyclic AMP-response element binding protein phosphorylation (CREB) and neurotrophic factors could be a part of the mechanism of these changes. This study aimed to analyze the effects of neonatal handling, 1 min per day from postpartum day 1 to 10 (PPD 1 to PPD 10), on the maternal behavior and pups' preference for the nest odor in a Y maze (PPD 11). We also tested CREB's phosphorylation and BDNF signaling in the OB of the pups (PPD 7) by Western blot analysis. The results showed that handling alters mother-pups interaction by decreasing mother-pups contact and changing the temporal pattern of all components of the maternal behavior especially the daily licking and nest-building. We found sex-dependent changes in the nest odor preference, CREB and BDNF levels in pups OB. Male pups were more affected by alterations in the licking pattern, and female pups were more affected by changes in the mother-pup contact (the time spent outside the nest and nursing).

Social influences on neurobiology and behavior: epigenetic effects during development

The quality of the social environment can have profound influences on the development and activity of neural systems with implications for numerous behavioral and physiological responses, including the expression of emotionality. Though social experiences occurring early in development may be particularly influential on the developing brain, there is continued plasticity within these neural circuits amongst juveniles and into early adulthood. In this review, we explore the evidence derived from studies in rodents which illustrates the social modulation during development of neural systems, with a particular emphasis on those systems in which a long-term effect is observed. One possible explanation for the persistence of dynamic changes in these systems in response to the environment is the involvement of epigenetic mechanisms, and here we discuss recent studies which support the role of these mechanisms in mediating the link between social experiences, gene expression, neurobiological changes, and behavioral variation. This literature raises critical questions about the interaction between neural systems, the concordance between neural and behavioral changes, sexual dimorphism in effects, the importance of considering individual differences in response to the social environment, and the potential of an epigenetic perspective in advancing our understanding of the pathways leading to variations in mental health.