The developmental psychobiology of behavioural plasticity in mice: the role of social experiences in the family unit

Small perturbations of young animals' sensory experience or hormonal milieu have been shown to alter ontogenetic pathways and to potentially produce h uge effects on CNS functioning and behaviour later in life. From a social p oint of view, variables such as the expression of affiliative bonding and o f playful interactions among littermates, the quantity/quality of maternal care, or episodes of maternal or sibling deprivation during critical phases in development, seem to interfere as epigenetic factors with the rigidly o rdered temporal sequences of events that occur during the ontogenesis of CN S. This leads to the onset of adaptive neurodevelopmental changes, which ar e observable within a continuum that encompasses both "normal" individual v ariability and potential behavioural disorganisation, which in turn will pr obably be related to profound alteration in the establishment of adult soci al competence. The present review summarises the more recent work in mice d ealing with short-term, as well as long-term modifications, in naturally oc curring species-typical social and non-social responses as a function of th e early manipulation of social characteristics of the family unit (such as litter gender composition and time of weaning). These analyses were carried out on infant animals, i.e. during the ontogenetic state of the establishm ent of social bonding, as well as on pre-pubertal and adult mice and on lac tating adult females. Critical issues, such as the respective roles of sibl ing-sibling and dam-offspring interactions in the shaping of "sibling effec ts", are also addressed. Overall, these studies indicate that, within their natural range of variation, early patterns of social stimulation are power ful determinants of subsequent behaviour of developing altricial rodents, a nd confirm that early social life events warrant attention because they can strongly affect neurobehavioural development. Evidence of a relationship b etween social events occurring during early rearing (i.e. when dramatic tra nsitions in neuroendocrine and neurochemical CNS systems occur) and individ ual behavioural variability in the infant and adult response to the effects of psychostimulants abused by humans is presented. A better understanding of the mechanisms that mediate such remarkable plasticity might have great psychobiological as well as clinical importance, especially when considerin g the issue of vulnerability of abuse. (C) 1998 Elsevier Science Ltd. All r ights reserved.