Mothering begets mothering: the transmission of behavior and its neurobiology across generations

Are 6-month-old foals sensitive to dam's influence?

A recent study has shown that gently handling dams in front of their few days old foals may strongly influence the development of human-foal relationships. In the present study, we test whether 6-month-old foals remain sensitive to their dams' influence. The study was performed on 16 foal-mare dyads, with half of the mares receiving positive contacts from the experimenter in presence of their 6-month-old foals (n = 8) whereas the other mares were not handled (n = 8). All foals were tested 15 and 30-35 days later under various conditions (reaction to a motionless human, approach test, saddle-pad tolerance test). We observe a positive effect of mare' handling on foals' reactions to humans but with a high interindividual variability, suggesting a higher effect of the foals' own behavioral characteristics at this age than at earlier stages.

Early deprivation, but not maternal separation, attenuates rise in corticosterone levels after exposure to a novel environment in both juvenile and adult female rats

Separation from the maternal nest alters the hypothalamic-pituitary-adrenal (HPA) axis stress response in adult male rats, but little research has addressed how separation affects female rats. The following experiments investigated how early maternal separation from postnatal day (PND) 2 to 14 affected stress-induced corticosterone and ACTH after exposure to an open field in juvenile and adult female rats. Female rats were separated for 5 h daily from mother and littermates (early deprivation: ED), separated from mother but not littermates (maternal separation: MS), or animal facility reared (AFR). Male siblings were left with the mother rat during separation. Female rats were exposed to an open field arena either during the juvenile period (PND 30) or during adulthood (PND 80-100). Results show that ED juvenile female rats showed a lower corticosterone stress response than MS and AFR female rats when measured at 5 min post-stress, but no difference at 20 or 60 min post-stress. In adulthood, ED female rats showed comparable elevations of corticosterone as MS and AFR rats at 5 min post-stress but lower elevations at 20 min. In terms of behavior, there were no significant effects of early experience. However, in adulthood, ED and MS rats tended to show a decreased proportion of inner grid crossings of the open field compared to AFR rats, suggesting a tendency for increased anxiety in these two separation groups.

Twice daily long maternal separations in Wistar rats decreases anxiety-like behaviour in females but does not affect males

Prolonged daily separations of rat pups from their mother have been reported to increase anxiety-like behaviour in adult offspring. However, there are an increasing number of studies not showing this. It has been proposed that the effect of long maternal separation (LMS) is partly due to the disruption of maternal care caused by the separations. The aim of the present study was to investigate whether increasing the number of daily separations would produce more robust effects in the adult offspring on anxiety-like behaviour in the defensive withdrawal test, and on spontaneous motor activity. Since previous studies of LMS have revealed sex differences in behaviour, we included both males and females. In our separation paradigm we subjected rat pups to either two daily 3h maternal separations during the first 2 weeks postpartum (LMS), two daily 15 min maternal separations (brief maternal separations, BMS) during the same time period to control for the effects of handling, or to normal husbandry conditions. As adults we found no effects of this LMS paradigm in male rats, although BMS males showed a tendency toward decreased anxiety-like behaviour. In contrast, LMS females showed a decrease in anxiety-like behaviour. We also found significant sex differences that were most prominent in the LMS group, indicating that females are more sensitive to our maternal separation paradigm. The present study suggests that increasing the number of maternal separations does not increase anxiety-like behaviour in neither male nor female Wistar rats.

Maternal factors and monoamine changes in stress-resilient and susceptible mice: cross-fostering effects

Genetic factors influence stressor-provoked monoamine changes associated with anxiety and depression, but such effects might be moderated by early life experiences. To assess the contribution of maternal influences in determining adult brain monoamine responses to a stressor, strains of mice that were either stressor-reactive or -resilient (BALB/cByJ and C57BL/6ByJ, respectively) were assessed as a function of whether they were raising their biological offspring or those of the other strain. As adults, offspring were assessed with respect to stressor-provoked plasma corticosterone elevations and monoamine variations within discrete stressor-sensitive brain regions. BALB/cByJ mice demonstrated poorer maternal behaviors than C57BL/6ByJ dams, irrespective of the pups being raised. In response to a noise stressor, BALB/cByJ mice exhibited higher plasma corticosterone levels and elevated monoamine turnover in several limbic and hypothalamic sites. The stressor-provoked corticosterone increase in BALB/cByJ mice was diminished among males (but not females) raised by a C57BL/6ByJ dam. Moreover, increased prefrontal cortical dopamine utilization was attenuated among BALB/cByJ mice raised by a C57BL/6ByJ dam. These effects were asymmetrical as a C57BL/6ByJ mice raised by a BALB/cByJ dam did not exhibit increased stressor reactivity. It appears that stressors influence multiple neurochemical systems that have been implicated in anxiety and affective disorders. Although monoamine variations were largely determined by genetic factors, maternal influences contributed to stressor-elicited neurochemical changes in some regions, particularly dopamine activation within the prefrontal cortex.

La théorie des systèmes développementaux et la construction sociale des maladies mentales1

Dans ce texte, nous proposons un cadre, qui vise à intégrer les contributions des approches constructionnistes et biologiques dans un domaine précis, celui des maladies mentales. Pour ce faire, nous utiliserons quelques propositions récentes faites par des philosophes de la biologie — plus spécifiquement les idées avancées par les tenants de la « théorie des systèmes développementaux » (TSD dans ce qui suit ; Griffiths et Gray, 1994 ; Griffiths et Stoltz, 2000 ; Oyama, 1999) ainsi que la notion d’« enracinement génératif » (generative entrenchment ; Wimsatt, 1986, 1999, 2000).

Gene-environment interplay and psychopathology: multiple varieties but real effects

Gene-environment interplay is a general term that covers several divergent concepts with different meanings and different implications. In this review, we evaluate research evidence on four varieties of gene-environment interplay. First, we consider epigenetic mechanisms by which environmental influences alter the effects of genes. Second, we focus on variations in heritability according to environmental circumstances. Third, we discuss what is known about gene-environment correlations. Finally, we assess concepts and findings on the interaction between specific identified genes and specific measured environmental risks. In order to provide an understanding of what may be involved in gene-environment interplay, we begin our presentation with a brief historical review of prevailing views about the role of genetic and environmental factors in the causation of mental disorders, and we provide a simplified account of some of the key features of how genes 'work'.

Maternal and littermate deprivation disrupts maternal behavior and social-learning of food preference in adulthood: Tactile stimulation, nest odor, and social rearing prevent these effects

Maternal and littermate (social) separation, through artificial rearing (AR), disrupts the development of subsequent maternal behavior and social learning in rats. The addition of maternal-licking-like stimulation during AR, partially reverses some of these effects. However, little is know about the role of social stimuli from littermates and nest odors during the preweaning period, in the development of the adult maternal behavior and social learning. The purpose of this study was to examine the effects of peer- and peer-and-odor rearing on the development of maternal behavior and social learning in rats. Female pups were reared with mothers (mother reared-MR) or without mothers (AR) from postnatal day (PND) 3. AR rats received three different treatments: (1) AR-CONTROL group received minimal tactile stimulation, (2) AR-ODOR females received exposure to maternal nest material inside the AR-isolation-cup environment, (3) AR-SOCIAL group was reared in the cup with maternal nest material and a conspecific of the same-age and same-sex and received additional tactile stimulation. MR females were reared by their mothers in the nest and with conspecifics. In adulthood, rats were tested for maternal behavior towards their own pups and in a social learning task. Results confirm our previous report that AR impairs performance of maternal behavior and the development of a social food preference. Furthermore, social cues from a littermate, in combination with tactile stimulation and the nest odor, reversed the negative effects of complete isolation (AR-CONTROL) on some of the above behaviors. Exposure to the odor alone also had effects on some of these olfactory-mediated behaviors. These studies indicate that social stimulation from littermates during the preweaning period, in combination with odor from the nest and tactile stimulation, contributes to the development of affiliative behaviors.

Long-term consequences of neonatal rearing on central corticotropin-releasing factor systems in adult male rat offspring

In a series of studies on the long-term consequences of neonatal rearing, we compared hypothalamic and extrahypothalamic central corticotropin-releasing factor (CRF) systems in male rats reared under conditions of animal facility rearing, nonhandling (HMS0), handling with brief maternal separation for 15 min (HMS15), or handling with moderate maternal separation for 180 min (HMS180) daily from postnatal days 2-14. CRF-like immunoreactivity (CRFir) was elevated in lumbar cerebrospinal fluid of adult HMS180 and HMS0 rats relative to the other groups. In the paraventricular nucleus, central nucleus of the amygdala, bed nucleus of the stria terminalis, and locus coeruleus, CRFir and CRF mRNA levels were significantly elevated in HMS0 and HMS180 rats. Neonatal maternal separation was associated with regionally specific alterations in CRF receptor type 1 (CRF1) mRNA density in HMS180 rats. No rearing-associated differences in CRF2alpha binding were apparent in either the lateral septum or the ventromedial hypothalamus. These findings indicate that early rearing conditions can permanently alter the developmental set-point of central CRF systems, and potentially influence the expression of behavioral and endocrine responses to stress throughout life, thereby providing a possible neurobiological substrate for the relationship between early life events and increased vulnerability for hypothalamic-pituitary-adrenal axis and coping skill alterations and the frequency of mood disorders in patients with a history of such experiences.

Early experience in humans is associated with changes in neuropeptides critical for regulating social behavior

The formation of social attachments is a critical component of human relationships. Infants begin to bond to their caregivers from the moment of birth, and these social bonds continue to provide regulatory emotional functions throughout adulthood. It is difficult to examine the interactions between social experience and the biological origins of these complex behaviors because children undergo both brain development and accumulate social experience at the same time. We had a rare opportunity to examine children who were reared in extremely aberrant social environments where they were deprived of the kind of care-giving typical for our species. The present experiment in nature provides insight into the role of early experience on the brain systems underlying the development of emotional behavior. These data indicate that the vasopressin and oxytocin neuropeptide systems, which are critical in the establishment of social bonds and the regulation of emotional behaviors, are affected by early social experience. The results of this experiment suggest a potential mechanism whose atypical function may explain the pervasive social and emotional difficulties observed in many children who have experienced aberrant care-giving. The present findings are consistent with the view that there is a critical role for early experience in the development of the brain systems underlying basic aspects of human social behavior.

Nongenomic inheritance of emotional reactivity in Japanese quail

Avian scientific literature includes few reports on the influence of characteristics of mothers on the behavior of their offspring. By comparing young domestic Japanese quail raised by adoptive mothers with high levels of general emotional reactivity (E+ mothers) to young raised by adoptive mothers with low levels of general emotional reactivity (E- mothers), we evaluated the influence of characteristics of mothers on the behavioral development of their offspring. Our results revealed that general emotional reactivity was higher in young raised by E+ mothers than in young raised by E- mothers. These differences were significant in the presence of mothers as well as after separation from them, suggesting direct as well as long-term maternal influence. Young raised by E+ mothers also presented delayed increases in weight.

Experiential and hormonal correlates of maternal behavior in teen and adult mothers

This study explores the role of cortisol and early life experiences in the regulation of maternal behavior and mood in teen and adult mothers. Primiparous mothers (n=119) (teen mothers < 19 years, n=42), young mothers (19-25 years, n= 4), and mature mothers, (>25 years, n=43) were assessed for their maternal behavior, mood, and hormonal profile at approximately 6 weeks postpartum. Outcome measures were analyzed as a function of age and early life experience. Results showed an interaction between age and type of maternal behavior, where teen mothers engaged in more instrumental (e.g. changing diapers, adjusting clothes) less affectionate (e.g., stroking, kissing, patting) behavior, and mature mothers engaged in more affectionate and less instrumental behavior. When groups were reassessed based on early life experience (consistency of care during the first 12 years of life: consistent care; having at least one consistent caregiver, inconsistent care; having multiple and changing caregivers), an interaction was also found between consistency of care and type of behavior shown, where mothers who received inconsistent care engaged in more instrumental and less affectionate behavior. Compared to mature mothers, teen mothers who were breast feeding also had higher salivary cortisol levels, and high cortisol in teen mothers related to decreased fatigue and increased energy. These results suggest that early life experiences are linked to mothering behavior and are consistent with the emerging human and animal literature on intergenerational effects of mothering style.

Mothering during early development influences subsequent emotional and social behaviour in Japanese quail

The aim of the present study was to investigate the influence of mothers on the emotional reactivity and social behaviour in young precocial Japanese quail. We used a classical method of maternal deprivation. Ethological tests and observations analysed and compared the behaviour of young artificially raised quail to that of young raised by adoptive maternal quail. After separation from mothers, brooded young were more fearful (frightened easily) in the presence of humans (human-observer tests) and more neophobic in novel environments (open-field and hole-in-the-wall tests) than young raised artificially. As chicks rarely expressed fear during the brooding period, no differences related to mothering could be observed at that time. In separation tests, brooded chicks jumped significantly more frequently than non-brooded chicks and later, observations of groups revealed that brooded chicks remained closer to one another than non-brooded chicks. Social motivation of brooded chicks appeared to be higher. These results indicate that, during their first days of life, mothers influence the emotional and social behaviour of their young.

Early life genetic, epigenetic and environmental factors shaping emotionality in rodents

Childhood trauma is known to increase risk for emotional disorders and addiction. However, little is currently understood about the neurodevelopmental basis of these effects, or how genetic and epigenetic factors interact with the environment to shape the systems subserving emotionality. In this review, we discuss the use of rodent models of early life emotional experience to study these issues in the laboratory and present some of our pertinent findings. In rats, postnatal maternal separation can produce lasting increases in emotional behavior and stressor-reactivity, together with alterations in various brain neurotransmitter systems implicated in emotionality, including corticotropin-releasing factor, serotonin, norepinephrine, and glutamate. Genetic differences between inbred mouse strains have been exploited to further study how maternal behavior affects emotional development using techniques such as cross-fostering and generation of inter-strain hybrids. Together with our own recent data, the findings of these studies demonstrate the pervasive influence of maternal and social environments during sensitive developmental periods and reveal how genetic factors determine how these early life experiences can shape brain and behavior throughout life.

The effects of adrenalectomy and corticosterone replacement on maternal behavior in the postpartum rat

It is well known that the hypothalamic-pituitary-adrenal (HPA) axis is activated during stress. Recent work suggests it is also implicated in the regulation of "normal" behaviors. The present studies investigated the effects of adrenalectomy and of varying glucocorticoid concentrations on adult maternal behavior in primiparous rats. In two studies, rats in late pregnancy were adrenalectomized or given sham surgeries and were tested for maternal behavior. In the first study, primiparous rats were given 0, 25, 100, 300, or 500 microg/ml of corticosterone in their drinking water. In the second study, primiparous rats were given either control or corticosterone time-release pellets. Blood samples were taken to ensure that rats demonstrated levels of corticosterone in blood that were relative to doses received. In studies one and two, primiparous adrenalectomized rats showed slightly, but significantly, lower levels of some maternal behaviors, including licking and time in nest, than primiparous sham rats. Primiparous rats given higher doses of corticosterone replacement showed higher levels of these maternal behaviors than primiparous rats given lower doses of corticosterone. In conclusion, adrenalectomy decreases, but does not abolish, maternal behavior. Corticosterone replacement reverses these effects. Corticosterone is not necessary for the initiation or maintenance of maternal behavior but plays a role in the modulation of ongoing maternal behavior.

Moderate level alcohol during pregnancy, prenatal stress, or both and limbic-hypothalamic-pituitary-adrenocortical axis response to stress in rhesus monkeys

This study examined the relationship between moderate-level prenatal alcohol exposure, prenatal stress, and postnatal response to a challenging event in 6-month-old rhesus monkeys. Forty-one rhesus monkey (Macaca mulatta) infants were exposed prenatally to moderate level alcohol, maternal stress, or both. Offspring plasma cortisol and adrenocorticotrophic hormone (ACTH) were determined from blood samples before maternal separation and after separation. Behavioral observations were made repeatedly across separation. Moderate-level prenatal alcohol exposure was associated with significantly higher plasma ACTH response to maternal separation. Offspring exposed to prenatal alcohol, prenatal stress, and prenatal alcohol and stress showed reduced behavioral adaptation to stress compared with controls. Baseline, 2-hr, and 26-hr plasma ACTH levels were intercorrelated and predicted behavior during separation.

Sex differences and developmental effects of manipulations of oxytocin on alloparenting and anxiety in prairie voles

In adult animals, peptide hormones, including oxytocin and arginine vasopressin, have been implicated in both parental behavior and the modulation of anxiety. The purpose of this study was to examine the consequences of developmental manipulations of oxytocin for the later expression of alloparental behavior as well as behavioral responses to a novel environment, the elevated plus maze (EPM). Prairie voles (Microtus ochrogaster), a cooperatively breeding species, were selected for this study. On neonatal Day 1, pups received an ip injection of oxytocin or oxytocin antagonist, or were controls, receiving either saline or handling only. At 21 and approximately 60 days of age, each animal was tested for parental care toward novel stimulus pups. At approximately 67 days, an EPM test was administered. Control females at 60 days of age were more likely to attack pups and spent less time in the open arm of the EPM, both of which might reflect higher levels of anxiety in females than males. In males, neonatal treatment with oxytocin antagonist was associated with reductions in parental care, especially during the initial exposure to pups on Day 21. Female behavior was not significantly changed as a function of neonatal treatments. Findings to date implicate vasopressin in the behavioral changes in males, that in later life followed a single exposure to an oxytocin antagonist, and suggest caution in the clinical use of agents such as Atosiban, which may have the potential to influence infant development.

Both oxytocin and vasopressin may influence alloparental behavior in male prairie voles

Neuropeptides, especially oxytocin (OT) and arginine vasopressin (AVP), have been implicated in several features of monogamy including alloparenting. The purpose of the present study was to examine the role of OT and AVP in alloparental behavior in reproductively naïve male prairie voles. Males received intracerebroventricular (ICV) injections of artificial cerebrospinal fluid (aCSF), OT, an OT receptor antagonist (OTA), AVP, an AVP receptor antagonist (AVPA), or combinations of OTA and AVPA and were subsequently tested for parental behavior. Approximately 45 min after treatment, animals were tested for behavioral responses to stimulus pups. In a 10-min test, spontaneous alloparental behavior was high in control animals. OT and AVP did not significantly increase the number of males that showed parental behavior, although more subtle behavioral changes were observed. Combined treatment with AVPA and OTA (10 ng each) significantly reduced male parental behavior and increased attacks; following a lower dose (1 ng OTA/1 ng AVPA), males were less likely to display kyphosis and tended to be slower to approach pups than controls. Since treatment with only one antagonist did not interfere with the expression of alloparenting, these results suggest that access to either OT or AVP receptors may be sufficient for the expression of alloparenting.

Developing a sense of safety: the neurobiology of neonatal attachment

Clinical data suggests a strong negative impact of traumatic attachments on adult mental illness, presumably through organizing brain development. To further explore this clinical issue, a mammalian model of imprinting was developed to characterize the neural basis of attachment in both healthy and traumatic attachments. The altricial neonatal rat must learn the mother's odor for nipple attachment, huddling, and orienting to the mother, all of which are required for pup survival. While it appears maladaptive to depend upon learning for attachment, the unique learning system of neonatal pups greatly enhances odor-preference learning and attachment while pups are confined to the nest. This heightened learning is expressed behaviorally as an enhanced ability to acquire learned odor preferences and a decreased ability to acquire learned odor aversions. Specifically, both odor-milk and odor-shock (0.5 mA) conditioning result in odor-preference acquisition. It appears as though there are at least three brain structures underlying the neonatal rat's sensitive period for heightened odor learning: (1) odor learning is encoded in the olfactory bulb; (2) the hyperfunctioning noradrenergic locus coeruleus (LC) appears to support preference conditioning through release of NE; and (3) the hypofunctioning amygdala appears to underlie pups' difficulty in learning odor aversions. Overall, this suggests that the CNS of altricial infants is specialized for optimizing attachments to their caregiver.

Developing a sense of safety: the neurobiology of neonatal attachment

Clinical data suggests a strong negative impact of traumatic attachments on adult mental illness, presumably through organizing brain development. To further explore this clinical issue, a mammalian model of imprinting was developed to characterize the neural basis of attachment in both healthy and traumatic attachments. The altricial neonatal rat must learn the mother's odor for nipple attachment, huddling, and orienting to the mother, all of which are required for pup survival. While it appears maladaptive to depend upon learning for attachment, the unique learning system of neonatal pups greatly enhances odor-preference learning and attachment while pups are confined to the nest. This heightened learning is expressed behaviorally as an enhanced ability to acquire learned odor preferences and a decreased ability to acquire learned odor aversions. Specifically, both odor-milk and odor-shock (0.5 mA) conditioning result in odor-preference acquisition. It appears as though there are at least three brain structures underlying the neonatal rat's sensitive period for heightened odor learning: (1) odor learning is encoded in the olfactory bulb; (2) the hyperfunctioning noradrenergic locus coeruleus (LC) appears to support preference conditioning through release of NE; and (3) the hypofunctioning amygdala appears to underlie pups' difficulty in learning odor aversions. Overall, this suggests that the CNS of altricial infants is specialized for optimizing attachments to their caregiver.

The influences of standard laboratory cages on rodents and the validity of research data

Standard cages for laboratory animals are often small, minimalist and barren. Such cages can compromise animal welfare, indicating that there are welfare-based reasons for improving their designs. However, a second issue, that is, whether animals from standard laboratory housing and husbandry conditions provide valid research data, also indicates that cage designs and husbandry methods need to be improved. This paper reviews various influences of standard laboratory cage design and husbandry. These include their effects on the repeatability of studies, models of neuro-degenerative disease, sensory development, physiology, and behaviour, the effects of standard social housing and standard handling, and the effects of maternal experience on the responses of offspring. These studies show that the development and responses of animals from standard laboratory housing and husbandry conditions are often unrepresentative and idiosyncratic, indicating that data are likely to have reduced external validity. An underlying question is whether animals from standard, barren laboratory cages are ‘abnormal’ and therefore might not provide valid baseline data. In terms of animal welfare, these studies indicate that standard laboratory housing may sometimes be associated both with reduced welfare and with reduced benefits gained from research. It is suggested that in a similar manner to the use of production measures when assessing cages for production animals, laboratory cages could be assessed in terms of their suitability to provide valid research data.

Long-term effects of prenatal morphine exposure on maternal behaviors differ from the effects of direct chronic morphine treatment

Previous studies have demonstrated that chronic morphine treatment of pregnant rats alters maternal behavior. Other studies have shown long-term effects of prenatal exposure to morphine, including changes in reproductive behavior in adult females. The present study investigated the effects of prenatal morphine exposure on a variety of maternal behaviors such as nursing, maternal activities, nonmaternal activities, and pup retrieval. Prenatal morphine exposure increased active and decreased passive nursing. There were no differences in maternal activities such as presence in the nest, contact with pups, grooming of pups, and/or manipulation of nest shavings. In the retrieval test, prenatally morphine-exposed mothers were faster in carrying the first pup, retrieving the first pup back to the nest, and returning all pups to the nest than prenatally saline-exposed mothers. Maternal and nonmaternal activities also were affected by the light: dark cycle. All saline- and morphine-exposed mothers nursed more, were more often in the nest, and more often in contact with greater than half of their litter during the light than the dark sessions. On the other hand, nonmaternal activities increased during the dark sessions: Mothers cared for themselves (groomed, ate) more and displayed more rearing and sniffing. Mothers spent more time resting with their eyes closed during the light sessions regardless of prenatal drug exposure. The present study demonstrated that the effect of morphine on maternal behavior is different in adult exposed and prenatally exposed mothers. While direct morphine treatment impaired maternal behaviors, prenatal morphine exposure has the opposite effect.

Pregnant female guinea pigs adapt easily to a new social environment irrespective of their rearing conditions

For male guinea pigs, the social rearing conditions are crucial for the course of social interactions and endocrine stress responses in later life. While colony-reared males adjust easily to new social situations, high levels of aggression and extreme endocrine responses are found in males that were raised in pairs [Psychoneuroendocrinology 23 (1998) 891]. This study investigated whether the same finding also applies to females. Therefore, 8 females reared in mixed-sexed colonies of 8-10 males and 12-13 females (designated as CF) and 8 females reared in mixed-sexed pairs (designated as PF) were transferred to an unknown colony for 3 days. Control females remained in their respective housing conditions. Serum cortisol concentrations (CORT) were determined before, during and after the transfer. The behavior of the CF and PF was recorded on the first, second and third day of transfer. All females adjusted easily to the new social situation, but frequencies of some behavioral patterns were significantly different between CF and PF. In the new social situation, PF displayed social orientation as well as defensive aggressive and avoidance behavior more frequently than CF. On the day of transfer, resident males displayed courtship behavior more frequently towards PF than CF. CORT did not differ between PF and CF either before, during or after the transfer. Furthermore, the transfer to the new social situation did not result in significantly increased CORT 4 h later either in CF or PF. We conclude that-in contrast to male guinea pigs-females are able to adapt to unfamiliar conspecifics independently of their social rearing conditions.