Pre- and postweaning excretion of puberty-influencing chemosignals in house mice

Activity Dependent Modulation of Granule Cell Survival in the Accessory Olfactory Bulb at Puberty

The vomeronasal system (VNS) is specialized in the detection of salient chemical cues triggering social and neuroendocrine responses. Such responses are not always stereotyped, instead, they vary depending on age, sex, and reproductive state, yet the mechanisms underlying this variability are unclear. Here, by analyzing neuronal survival in the first processing nucleus of the VNS, namely the accessory olfactory bulb (AOB), through multiple bromodeoxyuridine birthdating protocols, we show that exposure of female mice to male soiled bedding material affects the integration of newborn granule interneurons mainly after puberty. This effect is induced by urine compounds produced by mature males, as bedding soiled by younger males was ineffective. The granule cell increase induced by mature male odor exposure is not prevented by pre-pubertal ovariectomy, indicating a lesser role of circulating estrogens in this plasticity. Interestingly, the intake of adult male urine-derived cues by the female vomeronasal organ increases during puberty, suggesting a direct correlation between sensory activity and AOB neuronal plasticity. Thus, as odor exposure increases the responses of newly born cells to the experienced stimuli, the addition of new GABAergic inhibitory cells to the AOB might contribute to the shaping of vomeronasal processing of male cues after puberty. Consistently, only after puberty, female mice are capable to discriminate individual male odors through the VNS.

Bobwhite quail (Colinus virginianus) hatchlings track the direction of human gaze

Gaze following allows individuals to detect the locus of attention of both conspecifics and other species. However, little is known about how this ability develops. We explored the emergence of bobwhite quail hatchlings' ability to track human gaze by assessing their avoidance behavior in an open arena under five testing conditions: (1) a Direct Gaze condition, in which an experimenter looking down was positioned above one of two approach areas; (2) a Gaze Follow condition in which an experimenter, positioned equidistant between two approach areas, directed his/her gaze towards one of the areas; (3) a Masked Gaze Follow condition, in which the experimenter wore a mask during the Gaze Follow test; (4) a Deprived Face Experience condition, in which hatchlings were deprived of experience with human faces prior to the Gaze Follow test; and (5) a Control condition in which no experimenter was present during testing. Results revealed that hatchlings from the Direct Gaze condition preferred the non-gazed approach area at all ages tested. Hatchlings from the Gaze Follow condition preferred the non-gazed approach area at 48 and 72 h, but not at 24 h of age. In contrast, hatchlings from the Masked Gaze Follow, Deprived Face and Control conditions did not prefer either approach area at any age tested. These results indicate that experience with human faces plays a key role in the rapid emergence of gaze following behavior in bobwhite quail hatchlings.

Family composition and menarcheal age: Anti-inbreeding strategies

Family composition (e.g., the absence of a father) is associated with pubertal timing in women, although the socioendocrinology of the human primate is poorly understood. To better understand social influences on sexual maturation, retrospective data were collected on menarcheal age and family composition from a sample of approximately 1,938 participants from a college population. Absence of a biological father, the presence of half- and step-brothers, and living in an urban environment were associated with earlier menarche. The presence of sisters in the household while growing up, especially older sisters, was associated with delayed menarche. Menarcheal age was not affected by number of brothers in the household, nor was there an effect of birth order. Body weight and race were also associated with menarche. The present findings advance the literature as they are suggestive of putative human pheromones that modulate sexual maturation to promote gene survival and prevent inbreeding, as occurs in rodents and nonhuman primates.

Attractivity and social preferences in mice (Mus musculus domesticus): the role of prepubertal sexual segregation and of precocious weaning

Mice (Mus musculus domesticus) were raised (Postnatal Day 15 to 25) in single- or mixed-sex litters and precociously (Day 15) or regularly (Day 25) weaned. When they were faced as adults with a basic social choice--between two stimulus mice raised in litters of different sex composition but both of the same sex as the chooser--mice raised in mixed-sex litters were preferred. In the sociosexual choice-between a male and a female, both from the single- or the mixed-sex group--the opposite-sex preference was expressed. Both these preferences were abolished by the sexual segregation of the choosers. This variable hardly affected potential mate choice--between two stimulus mice both of the opposite sex of the chooser but raised in litters of different sex composition. Data indicate that socially mediated behavioral plasticity has a major role in the early shaping of adult individual differences both in attractive stimulus properties and in sociosexual preferences.

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 huge effects on CNS functioning and behaviour later in life. From a social point of view, variables such as the expression of affiliative bonding and of 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 ordered temporal sequences of events that occur during the ontogenesis of CNS. This leads to the onset of adaptive neurodevelopmental changes, which are observable within a continuum that encompasses both "normal" individual variability and potential behavioural disorganisation, which in turn will probably be related to profound alteration in the establishment of adult social competence. The present review summarises the more recent work in mice dealing with short-term, as well as long-term modifications, in naturally occurring species-typical social and non-social responses as a function of the 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 stage of the establishment of social bonding, as well as on pre-pubertal and adult mice and on lactating adult females. Critical issues, such as the respective roles of sibling-sibling and dam-offspring interactions in the shaping of "sibling effects", are also addressed. Overall, these studies indicate that, within their natural range of variation, early patterns of social stimulation are powerful determinants of subsequent behaviour of developing altricial rodents, and confirm that early social life events warrant attention because they can strongly affect neurobehavioural development. Evidence of a relationship between social events occurring during early rearing (i.e. when dramatic transitions in neuroendocrine and neurochemical CNS systems occur) and individual 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 considering the issue of vulnerability to drug abuse.

Spatial integration in infant sable antelope, Hippotragus niger

I studied the relationship between the timing of birth relative to other births in the social group, and the rate of spatial integration into the herd in six cohorts of semi-free-ranging infant sable antelope at the National Zoological Park's Conservation and Research Center near Front Royal, Virginia. All calves spent the initial few days of life resting in seclusion ('hiding'), and interacted with mothers and other conspecifics only during activity bouts. With time, calves became increasingly likely to rest apart from the herd with other calves in crèches, and by 6 weeks of age, calves remained with the herd throughout all resting and activity bouts. The rate of spatial integration for individual calves depended upon the calf's birth date and the availability of peers of similar age (birth clustering). Only the first few calves born in each cohort were observed in crèches, and crèche groups synchronized their entry into the herd. First-born calves remained in crèches longer and began resting with the herd later in life than calves born later in the cohort. Last-born calves typically did not form crèches, but instead rested with the herd from an early age. Other infants may serve as social cover during the time that infants form crèches and when they first begin to accompany the herd. The observed individual differences in the rate of spatial integration may represent individual adjustments in response to the varying degrees of protection offered by the spatial environment. Copyright 1998 The Association for the Study of Animal Behaviour.

On mouse pups and their lactating dams: behavioral consequences of early exposure to oxazepam and interacting factors

Behavioral analysis in animal models appears to be a valuable and sensitive tool for detecting subtle alterations in CNS function, which can be produced by early exposure to small perturbations of sensory experience, hormonal milieu, or exposure to psychotropic agents devoid of major teratogenic potential. Concerning anxiolytics, the more recent work in mice, which is here summarized, was carried out by putting the emphasis on changes in naturally occurring species-typical social responses as a function of early exposure to benzodiazepines. For adult females, on the behavior expressed during the early postpartum period, whereas for infant subjects, on the ontogenetic stage of the establishment of social bonding. Critical issues such as the choice of fostering procedure and rearing conditions are also addressed. Evidences of relationships between changes in social milieu taking place during early rearing-i.e., when dramatic transitions in the neurochemical target system occur- and the adult behavioral response to challenges with BDZ agents are presented. These data strengthen the notion that the modes of reaction of adult animals to the joint influence of physiological and environmental (stimulus) variables are under the influence of events in early ontogenesis. Therefore, a better understanding of the mechanisms-as unveiled by an appropriate use of drug tools-that mediate such a plasticity might have considerable psychobiological and clinical-therapeutical relevance.

Pheromonally accelerated puberty is enhanced by previous experience of the same stimulus

The influence of rearing conditions on pheromone-induced puberty acceleration was tested on Swiss mice. Litters were reared in one of three conditions: with either both parents, or with two females, or finally with two females in the presence of urinary pheromonal cues from adult males, which are known to induce puberty acceleration. Nine days after weaning the females were exposed to either prepubertal or adult male urine. In the groups reared with either both parents or with two females and the pheromonal cues from stranger males, females treated with adult male urine presented heavier uteri and more cornified vaginal smears than females reared in the same conditions but subsequently treated with prepubertal males urine. In the group reared simply with two females, the differences in both uterus weight and vaginal smears did not reach statistical significance. The data support the notion that early experience of pheromonal cues may influence the response to pheromones in a later period, even if the preweaning exposure to males had no direct influence on early signs of puberty onset.