Maternal behavior, pup vocalizations, and pup temperature changes following handling in mice of 2 inbred strains

Urocortin-3 neurons in the perifornical area are critical mediators of chronic stress on female infant-directed behavior

Infant avoidance and aggression are promoted by activation of the Urocortin-3 expressing neurons of the perifornical area of hypothalamus (PeFA^Ucn3) in male and female mice. PeFA^Ucn3 neurons have been implicated in stress, and stress is known to reduce maternal behavior. We asked how chronic restraint stress (CRS) affects infant-directed behavior in virgin and lactating females and what role PeFA^Ucn3 neurons play in this process. Here we show that infant-directed behavior increases activity in the PeFA^Ucn3 neurons in virgin and lactating females. Chemogenetic inhibition of PeFA^Ucn3 neurons facilitates pup retrieval in virgin females. CRS reduces pup retrieval in virgin females and increases activity of PeFA^Ucn3 neurons, while CRS does not affect maternal behavior in lactating females. Inhibition of PeFA^Ucn3 neurons blocks stress-induced deficits in pup-directed behavior in virgin females. Together, these data illustrate the critical role for PeFA^Ucn3 neuronal activity in mediating the impact of chronic stress on female infant-directed behavior.

Ultrasonic vocalizations in laboratory mice: strain, age, and sex differences

Mice produce ultrasonic vocalizations (USVs) in different social contexts across lifespan. There is ethological evidence that pup USVs elicit maternal retrieval and adult USVs facilitate social interaction with a conspecific. Analysis of mouse vocal and social repertoire across strains, sex and contexts remains not well explored. To address these issues, in inbred (C57BL/6, FVB) and outbred (CD-1) mouse strains, we recorded and evaluated USVs as neonates and during adult social encounters (male-female and female-female social interaction). We showed significant strain differences in the quantitative (call rate and duration of USVs) and qualitative vocal analysis (spectrographic characterization) from early stage to adulthood, in line with specific patterns of social behaviors. Inbred C57BL/6 mice produced a lower number of calls with less internal changes and shorter duration; inbred FVB mice displayed more social behaviors and produced more syllables with repeated internal changes; outbred CD-1 mice had an intermediate profile. Our results suggest specific vocal signatures in each mouse strain, thus helping to better define socio-communicative profiles of mouse strains and to guide the choice of an appropriate strain according to the experimental settings.

From Mating to Milk Access: A Review of Reproductive Vocal Communication in Mice

Vocalisations play a central role in rodent communication, especially in reproduction related behaviours. In adult mice (Mus musculus) the emission of ultrasonic vocalisations (USVs) has been observed in courtship and mating behaviour, especially by males. These have been found to have distinctive individual signatures that influence female choice of mating partner. The most recent findings show that vocal communication also has a role in parental cooperation, in that female mice communicate with male partners in ultrasonic frequencies to induce paternal behaviour. Infant vocalisations form the other important part of reproductive vocal communication. Although born deaf, neonatal mice are capable of producing vocalisations since birth. As an altricial species, successful mother-infant communication is essential for survival, and these vocalisations are important modulators of maternal behaviour. Three main types of infant vocalisations have been identified and characterised. Most research has addressed pure USVs, related to stressful situations (e.g., cold, isolation, handling, presence of unfamiliar males or predators), which usually elicit maternal search and retrieval. In addition, broad-band spectrum signals, emitted post-partum during cleaning of foetal membranes, inhibit biting and injury by adults and “wriggling calls,” emitted during suckling, release maternal behaviour (such as licking). Several variables have been identified to modulate vocalisations in mice, including individual characteristics such as strain/genotype, age, sex, and experimental factors such as pharmacological compounds and social context. In recent years, there has been a big increase in the knowledge about the characteristics of vocal communication in rodents due to recent technological advances as well as a growing interest from the neuroscience community. Vocalisation analysis has become an essential tool for phenotyping and evaluating emotional states. In this review, we will (i) provide a comprehensive summary of the current knowledge on mouse reproductive vocal communication and (ii) discuss the most recent findings in order to provide a broad overview on this topic.

Lactobacillus reuteri effects on maternal separation stress in newborn mice

BACKGROUND

Probiotic Lactobacillus reuteri DSM 17938 (LR 17938) is beneficial to infants with colic. To understand its mechanism of action, we assessed ultrasonic vocalizations (USV) and brain pain/stress genes in newborn mice exposed to maternal separation stress.

METHODS

Pups were exposed to unpredictable maternal separation (MSU or SEP) or MSU combined with unpredictable maternal stress (MSU + MSUS or S + S), from postnatal days 5 to 14. USV calls and pain/stress/neuroinflammation-related genes in the brain were analyzed.

RESULTS

We defined 10 different neonatal call patterns, none of which increased after MSU. Stress reduced overall USV calls. Orally feeding LR 17938 also did not change USV calls after MSU. However, LR 17938 markedly increased vocalizations in mice allowed to stay with their dams. Even though LR 17938 did not change MSU-related calls, LR 17938 modulated brain genes related to stress and pain. Up-regulated genes following LR 17938 treatment were opioid peptides, kappa-opioid receptor 1 genes, and CD200, important in anti-inflammatory signaling. LR 17938 down-regulated CCR2 transcripts, a chemokine receptor, in the stressed neonatal brain.

CONCLUSIONS

USV calls in newborn mice are interpreted as "physiological calls" instead of "cries." Feeding LR 17938 after MSU did not change USV calls but modulated cerebral genes favoring pain and stress reduction and anti-inflammatory signaling.

IMPACT

We defined mouse ultrasonic vocalization (USV) call patterns in this study, which will be important in guiding future studies in other mouse strains. Newborn mice with maternal separation stress have reduced USVs, compared to newborn mice without stress, indicating USV calls may represent "physiological calling" instead of "crying." Oral feeding of probiotic Lactobacillus reuteri DSM 17938 raised the number of calls when newborn mice continued to suckle on their dams, but not when mice were under stress. The probiotic bacteria had a dampening effect on monocyte activation and on epinephrine and glutamate-related stress gene expression in the mouse brain.

Systematic analysis of goal-related movement sequences during maternal behaviour in a female mouse model for Rett syndrome

Rodent dams seek and gather scattered pups back to the nest (pup retrieval), an essential aspect of maternal care. Systematic analysis of the dynamic sequences of goal-related movements that comprise the entire behavioural sequence, which would be ultimately essential for understanding the underlying neurobiology, is not well-characterized. Here, we present such analysis across 3 days in alloparental female mice (Surrogates or Sur) of two genotypes; Mecp2Heterozygotes (Het), a female mouse model for Rett syndrome and their wild type (WT) siblings. We analysed CBA/CaJ and C57BL/6J WT surrogates for within-strain comparisons. Frame-by-frame analysis over different phases was performed manually using DataVyu software. We previously showed that surrogate Het are inefficient at pup retrieval, by end-point analysis such as latency index and errors. Here, the sequence of searching, pup-approach and successful retrieval streamlines over days for WT, while Het exhibits variations in this pattern. Goal-related movements between Het and WT are similar in other phases, suggesting context-driven atypical patterns in Het during the pup retrieval phase. We identified proximal pup approach and pup grooming as atypical tactile interactions between pups and Het. Day-by-day analysis showed dynamic changes in goal-related movements in individual animals across genotypes and strains. Overall, our approach (1) highlights natural variation in individual mice on different days, (2) establishes a "gold-standard" manually curated dataset to help build behavioural repertoires using machine learning approaches, and (3) suggests atypical tactile sensory processing and possible regression in a female mouse model for Rett syndrome.

An acute dose of intranasal oxytocin rapidly increases maternal communication and maintains maternal care in primiparous postpartum California mice

Maternal-offspring communication and care are essential for offspring survival. Oxytocin (OXT) is known for its role in initiation of maternal care, but whether OXT can rapidly influence maternal behavior or ultrasonic vocalizations (USVs; above 50 kHz) has not been examined. To test for rapid effects of OXT, California mouse mothers were administered an acute intranasal (IN) dose of OXT (0.8 IU/kg) or saline followed by a separation test with three phases: habituation with pups in a new testing chamber, separation via a wire mesh, and finally reunion with pups. We measured maternal care, maternal USVs, and pup USVs. In mothers, we primarily observed simple sweep USVs, a short downward sweeping call around 50 kHz, and in pups we only observed pup whines, a long call with multiple harmonics ranging from 20 kHz to 50 kHz. We found that IN OXT rapidly and selectively enhanced the normal increase in maternal simple sweep USVs when mothers had physical access to pups (habituation and reunion), but not when mothers were physically separated from pups. Frequency of mothers' and pups' USVs were correlated upon reunion, but IN OXT did not influence this correlation. Finally, mothers given IN OXT showed more efficient pup retrieval/carrying and greater total maternal care upon reunion. Behavioral changes were specific to maternal behaviors (e.g. retrievals) as mothers given IN OXT did not differ from controls in stress-related behaviors (e.g. freezing). Overall, these findings highlight the rapid effects and context-dependent effect a single treatment with IN OXT has on both maternal USV production and offspring care.

Effects of opioids on the parental brain in health and disease

The epidemic of opioid use disorder (OUD) directly affects millions of women of child-bearing age. Unfortunately, parenting behaviors - among the most important processes for human survival - are vulnerable to the effects of OUD. The standard of care for pregnant women with OUD is opioid maintenance therapy (OMT), of which the primary objective is to mitigate addiction-related stress. The aim of this review is to synthesize current information specific to pregnancy and parenting that may be affected by OUD. We first summarize a model of the parental brain supported by animal research and human neuroimaging. We then review animal models of exogenous opioid effects on parental brain and behavior. We also present preliminary data for a unifying hypothesis that may link different effects of exogenous opioids on parenting across species and in the context of OMT. Finally, we discuss future directions that may inform research and clinical decision making for peripartum women with OUD.

Resilience priming: Translational models for understanding resiliency and adaptation to early life adversity

Despite the increasing attention to early life adversity and its long-term consequences on health, behavior, and the etiology of neurodevelopmental disorders, our understanding of the adaptations and interventions that promote resiliency and rescue against such insults are underexplored. Specifically, investigations of the perinatal period often focus on negative events/outcomes. In contrast, positive experiences (i.e. enrichment/parental care//healthy nutrition) favorably influence development of the nervous and endocrine systems. Moreover, some stressors result in adaptations and demonstrations of later-life resiliency. This review explores the underlying mechanisms of neuroplasticity that follow some of these early life experiences and translates them into ideas for interventions in pediatric settings. The emerging role of the gut microbiome in mediating stress susceptibility is also discussed. Since many negative outcomes of early experiences are known, it is time to identify mechanisms and mediators that promote resiliency against them. These range from enrichment, quality parental care, dietary interventions and those that target the gut microbiota.

Born to Cry: A Genetic Dissection of Infant Vocalization

Infant vocalizations are one of the most fundamental and innate forms of behavior throughout avian and mammalian orders. They have a critical role in motivating parental care and contribute significantly to fitness and reproductive success. Dysregulation of these vocalizations has been reported to predict risk of central nervous system pathologies such as hypoxia, meningitis, or autism spectrum disorder. Here, we have used the expanded BXD family of mice, and a diallel cross between DBA/2J and C57BL/6J parental strains, to begin the process of genetically dissecting the numerous facets of infant vocalizations. We calculate heritability, estimate the role of parent-of-origin effects, and identify novel quantitative trait loci (QTLs) that control ultrasonic vocalizations (USVs) on postnatal days 7, 8, and 9; a stage that closely matches human infants at birth. Heritability estimates for the number and frequency of calls are low, suggesting that these traits are under high selective pressure. In contrast, duration and amplitude of calls have higher heritabilities, indicating lower selection, or their importance for kin recognition. We find suggestive evidence that amplitude of infant calls is dependent on the maternal genotype, independent of shared genetic variants. Finally, we identify two loci on Chrs 2 and 14 influencing call frequency, and a third locus on Chr 8 influencing the amplitude of vocalizations. All three loci contain strong candidate genes that merit further analysis. Understanding the genetic control of infant vocalizations is not just important for understanding the evolution of parent–offspring interactions, but also in understanding the earliest innate behaviors, the development of parent–offspring relations, and the early identification of behavioral abnormalities.

Sociability and synapse subtype-specific defects in mice lacking SRPX2, a language-associated gene

The FoxP2 transcription factor and its target genes have been implicated in developmental brain diseases with a prominent language component, such as developmental verbal dyspraxia and specific language impairment. How FoxP2 affects neural circuitry development remains poorly understood. The sushi domain protein SRPX2 is a target of FoxP2, and mutations in SRPX2 are associated with language defects in humans. We have previously shown that SRPX2 is a synaptogenic protein that increases excitatory synapse density. Here we provide the first characterization of mice lacking the SRPX2 gene, and show that these mice exhibit defects in both neural circuitry and communication and social behaviors. Specifically, we show that mice lacking SRPX2 show a specific reduction in excitatory VGlut2 synapses in the cerebral cortex, while VGlut1 and inhibitory synapses were largely unaffected. SRPX2 KO mice also exhibit an abnormal ultrasonic vocalization ontogenetic profile in neonatal pups, and reduced preference for social novelty. These data demonstrate a functional role for SRPX2 during brain development, and further implicate FoxP2 and its targets in regulating the development of vocalization and social circuits.

Inactivation of the melanin concentrating hormone system impairs maternal behavior

In order to prepare the mother for the demands of pregnancy and lactation, the maternal brain is subjected to a number of adaptations. Maternal behaviors are regulated by complex neuronal interactions. Here, we show that the melanin concentrating hormone (MCH) system is an important regulator of maternal behaviors. First, we report that melanin concentrating hormone receptor 1 knockout (MCHR1 KO) mice display a disruption of maternal behavior. Early postpartum MCHR1 KO females exhibit poor nesting, deficits in pup retrieval and maternal aggression. In addition, ablation of MCH receptors results in decreased milk production and prolactin mRNA levels. Then we show that these results are in line with those obtained in wild type mice (WT) treated with the specific MCHR1 antagonist GW803430. Furthermore, following pups retrieval, MCHR1 KO mice display a lower level of Fos expression than WT mice in the ventral tegmental area, and nucleus accumbens. With the progression of the lactation period, however, the MCHR1 KO mice improve maternal care towards their pups. This is manifested by an increase in the pups׳ survival rate and the decrease in pups׳ retrieval time beyond the second day after parturition. In conclusion, we show that the MCH system plays a significant role in the initiation of maternal behavior. In this context, MCH may play a role in integrating information from multiple sources, and connecting brain reward, homeostatic and regulatory systems.

Seizure-like activity in a juvenile Angelman syndrome mouse model is attenuated by reducing Arc expression

Angelman syndrome (AS) is a neurodevelopmental disorder arising from loss-of-function mutations in the maternally inherited copy of the UBE3A gene, and is characterized by an absence of speech, excessive laughter, cognitive delay, motor deficits, and seizures. Despite the fact that the symptoms of AS occur in early childhood, behavioral characterization of AS mouse models has focused primarily on adult phenotypes. In this report we describe juvenile behaviors in AS mice that are strain-independent and clinically relevant. We find that young AS mice, compared with their wild-type littermates, produce an increased number of ultrasonic vocalizations. In addition, young AS mice have defects in motor coordination, as well as abnormal brain activity that results in an enhanced seizure-like response to an audiogenic challenge. The enhanced seizure-like activity, but not the increased ultrasonic vocalizations or motor deficits, is rescued in juvenile AS mice by genetically reducing the expression level of the activity-regulated cytoskeleton-associated protein, Arc. These findings suggest that therapeutic interventions that reduce the level of Arc expression have the potential to reverse the seizures associated with AS. In addition, the identification of aberrant behaviors in young AS mice may provide clues regarding the neural circuit defects that occur in AS and ultimately allow new approaches for treating this disorder.

Foster dams rear fighters: strain-specific effects of within-strain fostering on aggressive behavior in male mice

It is well known that genes and environment interact to produce behavioral phenotypes. One environmental factor with long-term effects on gene transcription and behavior is maternal care. A classic paradigm for examining maternal care and genetic interactions is to foster pups of one genetic strain to dams of a different strain ("between-strain fostering"). In addition, fostering to a dam of the same strain ("within-strain fostering") is used to reduce indirect effects, via behavioral changes in the dams, of gestation treatments on offspring. Using within-and between-strain fostering we examined the contributions of genetics/prenatal environment, maternal care, and the effects of fostering per se, on adult aggressive behavior in two inbred mouse strains, C57BL/6J (B6) and DBA/2J (DBA). We hypothesized that males reared by dams of the more aggressive DBA strain would attack intruders faster than those reared by B6 dams. Surprisingly, we found that both methods of fostering enhanced aggressive behavior, but only in B6 mice. Since all the B6 offspring are genetically identical, we asked if maternal behavior of B6 dams was affected by the relatedness of their pups. In fact, B6 dams caring for foster B6 pups displayed significantly reduced maternal behaviors. Finally, we measured vasopressin and corticotrophin releasing hormone mRNA in the amygdalae of adult B6 males reared by foster or biological dams. Both genes correlated with aggressive behavior in within-strain fostered B6 mice, but not in mice reared by their biological dams. In sum, we have demonstrated in inbred laboratory mice, that dams behave differently when rearing their own newborn pups versus pups from another dam of the same strain. These differences in maternal care affect aggression in the male offspring and transcription of Avp and Crh in the brain. It is likely that rearing by foster dams has additional effects and implications for other species.

Modulation of nociception by social factors in rodents: contribution of the opioid system

RATIONALE

The opioid system is involved in the regulation of several behavioral and physiological responses, controlling pain, reward, and addictive behaviors. Opioid administration, depending on drugs and doses, usually affects sociability reducing interactions between conspecifics, whereas some affiliative behaviors such as sexual activity, social grooming, and play behavior increase the endogenous opioid activity.

OBJECTIVES

The possible interaction between endogenous opioids released during socio/sexual behavior and their analgesic effect on pain response is reviewed in the rodent literature.

RESULTS

Direct evidence for socially mediated opioid changes resulting in increase in nociceptive threshold derives from studies exploring the effects of defeat experiences, social isolation, maternal, sexual behavior, and social reunion among kin or familiar animals in laboratory rodents. Indirect evidence for endogenous activation of the opioid system, possibly affecting pain sensitivity, derives from studies investigating the relevance of natural social reward using the conditioned place preference protocols or analyzing ultrasonic vocalizations associated to positive affective contexts. Finally, genetic and epigenetic factors that affect the opioid system during development are reported to be involved in modulating the response to social stimuli as well as nociception.

CONCLUSIONS

All studies highlight the relevance of affiliative contact behavior between conspecifics that is responsible for the activation of the endogenous mu-opioid system, inducing nociceptive threshold increase.

Translating mouse vocalizations: prosody and frequency modulation

Mental illness can include impaired abilities to express emotions or respond to the emotions of others. Speech provides a mechanism for expressing emotions, by both what words are spoken and by the melody or intonation of speech (prosody). Through the perception of variations in prosody, an individual can detect changes in another's emotional state. Prosodic features of mouse ultrasonic vocalizations (USVs), indicated by changes in frequency and amplitude, also convey information. Dams retrieve pups that emit separation calls, females approach males emitting solicitous calls, and mice can become fearful of a cue associated with the vocalizations of a distressed conspecific. Because acoustic features of mouse USVs respond to drugs and genetic manipulations that influence reward circuits, USV analysis can be employed to examine how genes influence social motivation, affect regulation, and communication. The purpose of this review is to discuss how genetic and developmental factors influence aspects of the mouse vocal repertoire and how mice respond to the vocalizations of their conspecifics. To generate falsifiable hypotheses about the emotional content of particular calls, this review addresses USV analysis within the framework of affective neuroscience (e.g. measures of motivated behavior such as conditioned place preference tests, brain activity and systemic physiology). Suggested future studies include employment of an expanded array of physiological and statistical approaches to identify the salient acoustic features of mouse vocalizations. We are particularly interested in rearing environments that incorporate sufficient spatial and temporal complexity to familiarize developing mice with a broader array of affective states.

Unusual repertoire of vocalizations in the BTBR T+tf/J mouse model of autism

BTBR T+ tf/J (BTBR) is an inbred mouse strain that displays social abnormalities and repetitive behaviors analogous to the first and third diagnostic symptoms of autism. Here we investigate ultrasonic vocalizations in BTBR, to address the second diagnostic symptom of autism, communication deficits. As compared to the commonly used C57BL/6J (B6) strain, BTBR pups called more loudly and more frequently when separated from their mothers and siblings. Detailed analysis of ten categories of calls revealed an unusual pattern in BTBR as compared to B6. BTBR emitted high levels of harmonics, two-syllable, and composite calls, but minimal numbers of chevron-shaped syllables, upward, downward, and short calls. Because body weights were higher in BTBR than B6 pups, one possible explanation was that larger thoracic size was responsible for the louder calls and different distribution of syllable categories. To test this possibility, we recorded separation calls from FVB/NJ, a strain with body weights similar to BTBR, and 129X1/SvJ, a strain with body weights similar to B6. BTBR remained the outlier on number of calls, displaying low numbers of complex, upward, chevron, short, and frequency steps calls, along with high harmonics and composites. Further, developmental milestones and growth rates were accelerated in BTBR, indicating an unusual neurodevelopmental trajectory. Overall, our findings demonstrate strain-specific patterns of ultrasonic calls that may represent different lexicons, or innate variations in complex vocal repertoires, in genetically distinct strains of mice. Particularly intriguing is the unusual pattern of vocalizations and the more frequent, loud harmonics evident in the BTBR mouse model of autism that may resemble the atypical vocalizations seen in some autistic infants.

Ultrasonic vocalizations: a tool for behavioural phenotyping of mouse models of neurodevelopmental disorders

In neonatal mice ultrasonic vocalizations have been studied both as an early communicative behaviour of the pup-mother dyad and as a sign of an aversive affective state. Adult mice of both sexes produce complex ultrasonic vocalization patterns in different experimental/social contexts. Vocalizations are becoming an increasingly valuable assay for behavioural phenotyping throughout the mouse life-span and alterations of the ultrasound patterns have been reported in several mouse models of neurodevelopmental disorders. Here we also show that the modulation of vocalizations by maternal cues (maternal potentiation paradigm) - originally identified and investigated in rats - can be measured in C57BL/6 mouse pups with appropriate modifications of the rat protocol and can likely be applied to mouse behavioural phenotyping. In addition we suggest that a detailed qualitative evaluation of neonatal calls together with analysis of adult mouse vocalization patterns in both sexes in social settings, may lead to a greater understanding of the communication value of vocalizations in mice. Importantly, both neonatal and adult USV altered patterns can be determined during the behavioural phenotyping of mouse models of human neurodevelopmental and neuropsychiatric disorders, starting from those in which deficits in communication are a primary symptom.

Maternal programming of sexual behavior and hypothalamic-pituitary-gonadal function in the female rat

Variations in parental care predict the age of puberty, sexual activity in adolescence and the age at first pregnancy in humans. These findings parallel descriptions of maternal effects on phenotypic variation in reproductive function in other species. Despite the prevalence of such reports, little is known about potential biological mechanisms and this especially true for effects on female reproductive development. We examined the hypothesis that parental care might alter hypothalamic-pituitary-ovarian function and thus reproductive function in the female offspring of rat mothers that vary pup licking/grooming (LG) over the first week postpartum. As adults, the female offspring of Low LG mothers showed 1) increased sexual receptivity; 2) increased plasma levels of luteinizing hormone (LH) and progesterone at proestrus; 3) an increased positive-feedback effect of estradiol on both plasma LH levels and gonadotropin releasing-hormone (GnRH) expression in the medial preoptic region; and 4) increased estrogen receptor α (ERα) expression in the anterioventral paraventricular nucleus, a system that regulates GnRH. The results of a cross-fostering study provide evidence for a direct effect of postnatal maternal care as well as a possible prenatal influence. Indeed, we found evidence for increased fetal testosterone levels at embryonic day 20 in the female fetuses of High compared to Low LG mothers. Finally, the female offspring of Low LG mothers showed accelerated puberty compared to those of High LG mothers. These data suggest maternal effects in the rat on the development of neuroendocrine systems that regulate female sexual behaviour. Together with studies revealing a maternal effect on the maternal behavior of the female offspring, these findings suggest that maternal care can program alternative reproductive phenotypes in the rat through regionally-specific effects on ERα expression.

Natural variations in postpartum maternal care in inbred and outbred mice

The role of maternal care in mediating variation in offspring phenotype has been examined in the rat and demonstrates that mother-infant interactions are critical for inducing long-term changes in behavior. Though phenotypic differences between mice strains are often attributed to genetic factors, the influence of early maternal environment has not been extensively explored. To understand maternal influence on phenotype in mice, we must first explore the nature of differences in behavior. In the present study, we examine aspects of maternal care differentiating mice strains and explore the relationship between postpartum behavior and measures obtained by a standard test of maternal responsivity (Retrieval Test). We compared inbred 129Sv (n=25), C57BL/6J (n=23), and outbred Swiss (n=23) lactating female mice. Swiss females had shorter latencies to retrieve and crouch over pups (P<.01), whereas 129Sv females had shorter latencies to nestbuild (P<.05). Conversely, observations of homecage behavior indicate that 129Sv females nestbuild less frequently. 129Sv females also engaged in very low levels of pup licking/grooming (P<.001) and long periods of nursing/contact (P<.05) with pups compared to C57BL/6J and Swiss females. Temporal analysis suggests that the magnitude of these differences varies both within and between days. No significant correlations were found between any aspect of maternal responsivity and postpartum behavior. These results illustrate that through detailed analysis of maternal behavior in mice, variations between strains can be observed. These variations represent strain specific strategies for promoting growth and survival of offspring during infancy that may also mediate "epigenetic" differences in phenotype in adulthood.

Affiliative behavior, ultrasonic communication and social reward are influenced by genetic variation in adolescent mice

Social approach is crucial for establishing relationships among individuals. In rodents, social approach has been studied primarily within the context of behavioral phenomena related to sexual reproduction, such as mating, territory defense and parental care. However, many forms of social interaction occur before the onset of reproductive maturity, which suggests that some processes underlying social approach among juvenile animals are probably distinct from those in adults. We conducted a longitudinal study of social investigation (SI) in mice from two inbred strains to assess the extent to which genetic factors influence the motivation for young mice to approach one another. Early-adolescent C57BL/6J (B6) mice, tested 4–6 days after weaning, investigated former cage mates to a greater degree than BALB/cJ (BALB) mice, irrespective of the sex composition within an interacting pair. This strain difference was not due to variation in maternal care, the phenotypic characteristics of stimulus mice or sensitivity to the length of isolation prior to testing, nor was it attributable to a general difference in appetitive motivation. Ultrasonic vocalization (USV) production was positively correlated with the SI responses of mice from both strains. Interestingly, several USV characteristics segregated with the genetic background of young mice, including a higher average frequency and shorter duration for the USVs emitted by B6 mice. An assessment of conditioned place preference responses indicated that there was a strain-dependent difference in the rewarding nature of social contact. As adolescent mice aged, SI responses gradually became less sensitive to genetic background and more responsive to the particular sex of individuals within an interacting pair. We have thus identified a specific, genetic influence on the motivation of early-adolescent mice to approach one another. Consistent with classical theories of motivation, which propose a functional relationship between behavioral approach and reward, our findings indicate that reward is a proximal mechanism through which genetic factors affect social motivation during early adolescence.

Effects of repeated maternal separation on anxiety- and depression-related phenotypes in different mouse strains

Genetic factors and early life adversity both play a major role in the etiology of mood and anxiety disorders. Previous studies have shown that postnatal maternal separation (MS) can produce lasting abnormalities in emotion-related behavior and neuroendocrine responses to stress in rodents. The present study sought to examine the effects of repeated MS in eight different inbred strains of mice (129S1/SvImJ, 129P3/J, A/J, BALB/cJ, BALB/cByJ C57BL/6J, DBA/2J, FVB/NJ). Pups were separated from their dam and littermates for 180 min/day ('MS') or 15 min/day ('handling'), or left undisturbed ('facility-reared') from postnatal days P0-P13, and tested as adults for anxiety- and depression-related behaviors. Results demonstrated no clear and consistent effects of MS or handling on behavioral phenotypes in any of the strains tested. In all strains, MS produced an increase in maternal care on reunion with pups, which may have modified MS effects. Data demonstrate that the MS procedure employed does not provide a robust model of early life stress effects on the anxiety- and depression-related behaviors in the mouse strains tested.

How social experiences influence the brain

Social experiences throughout life influence gene expression and behavior, however, early in development these influences have a particularly profound effect. In mammals, mother-infant interactions are the primary source of social stimulation and result in long-term changes in offspring phenotype. This has previously been demonstrated in rodents and primates, however, recent studies in rats have advanced our understanding of how these influences are achieved at a mechanistic level, through epigenetic modification, and provide a model for studying the transmission of social behavior across generations. These studies emphasize the importance of a life-history approach to the study of brain development; incorporating information about genetic background, prenatal and postnatal maternal care received, and post-weaning social interactions of an individual, in addition to the social environment experienced by previous generations.

A review of the methods of studies on infant ultrasound production and maternal retrieval in small rodents

Ultrasonic vocalizations or calls produced by young rodents have been associated with aspects of maternal behavior, in particular retrieving. We reviewed the methods of study used by investigators on each topic, focusing on intrinsic or subject variables and extrinsic or experimental variables. Intrinsic variables included the species studied, genotypes employed, number and sex composition of the litters, and the ages of mothers and pups. Extrinsic variables for studies on ultrasonic calling included: eliciting stimuli, test surroundings, and the length of observation. Extrinsic variables in studies of maternal retrieval included the testing procedure and the length of observation. The methods used in studies within each topic vary greatly. In an effort to facilitate progress in the areas, especially with respect to isolating individual genes with a contribution to ultrasonic call production or studying the effects of pharmaceutical agents on either behavior, we propose some standardization of nomenclature and/or procedure in four areas: (1) the stimuli or situations used to elicit ultrasonic calls, (2) the length of observation in ultrasonic call studies, (3) the number of pups per litter and the sex composition of litters in both ultrasonic call and maternal retrieval studies and finally, (4) the apparatus or testing situation used in studies of pup retrieval.

Maternal-care behavior and life-history traits in house mice (Mus domesticus) artificially selected for high voluntary wheel-running activity

To test the hypothesis that selective breeding for high voluntary wheel running negatively affects maternal performance in house mice, we observed maternal behavior and compared litter size and mass, in replicate lines of selected (N=4) and control (N=4) mice from generations 20 and 21 of an artificial selection experiment. At generation 21, selected-line females ran 2.8-times more revolutions per day than females from random-bred control lines, when tested at approximately 6 weeks of age as part of the normal selection protocol. After giving birth, dams from selected and control lines exhibited similar frequencies of maternal behaviors and also spent similar amounts of time in general locomotor activity at litter ages of both 9 and 16 days. Dams from selected lines also performed equally well as controls in repeated pup-retrieval trials. At first parturition, selected-line dams averaged 2.4 g smaller in body mass as compared with dams from the control lines; however, neither litter size nor litter mass at birth (generation 20) or at weaning (generation 21) differed significantly between selected and control lines. We conclude that, at least under the husbandry conditions employed, maternal behavior and reproductive output at first parturition are genetically independent of wheel-running behavior.

Antidepressants during pregnancy and lactation: defining exposure and treatment issues

The majority of psychiatric illness onsets early in an individual's life, typically before or during the reproductive years. The increased incidence of major depression, dysthymia, and panic disorder in women compared with men underscores the likelihood that the clinician will encounter the clinical dilemma of medication use during pregnancy and lactation. The emergence of specialized clinics at several academic centers specifically to investigate and address issues in Perinatal psychiatry illustrates this conundrum best. The extant literature derived from human studies suggests that maternal mental illness and stress may have an adverse impact on obstetrical outcome. These clinical investigations are complemented by a burgeoning series of laboratory studies in rodents and nonhuman primates, showing the profound deleterious impact of maternal stress during the perinatal and neonatal periods on the development of the offspring. Data obtained from pharmaceutical registries, cohort studies, toxicology centers, and case series have consistently failed to show an adverse effect associated with in utero antidepressant exposure. Despite these advances and treatment guidelines proposed by the various academic leaders, investigations describing the extent of fetal/neonatal exposure, clinical methods for minimizing such exposure, and clinical treatment guidelines that include the physiological impact of pregnancy are sparse. The available literature shows distinct pharmacokinetic profiles of the selective serotonin reuptake inhibitors in placental passage and breast milk. Preliminary animal studies have shown higher than expected central nervous system concentrations associated with exposure during pregnancy and mathematical modelling for calculating infant exposure when nursing. The clinical import of these data will require further investigations of central nervous system bioavailability in the fetus and neonate.

Effects of prenatal alcohol exposure on rat pups' ability to elicit retrieval behavior from dams

Research on fetal alcohol syndrome (FAS) has historically held that postnatal deficits result directly from prenatal alcohol exposure. Such exposure may alter infant behavior, and this in turn may affect maternal responsiveness and consequently increase the infant's risk for postnatal deficits. This study examined the effect of prenatal alcohol exposure on postnatal blood ethanol concentrations, pup development, and the ability of pups to elicit retrieval behaviors from the dam. Dams given access to a 15% ethanol solution throughout gestation and lactation showed blood ethanol concentrations of 0.1%, whereas their pups had concentrations below the sensitivity of the test. Prenatal alcohol exposure was shown to have pharmacological effects on the pup's righting reflex and nutritional effects on its rate of weight gain. Control pups were better able to elicit retrieval behavior from control and alcoholic dams than were fetally alcoholic pups. These results indicate that the condition of the pup can influence maternal responsiveness which, in turn, can influence pup development.

Chronic exposure to a novel odor increases pups' vocalizations, maternal care, and alters dopaminergic functioning in developing mice

This study was designed to assess the stress effect of manipulation of the olfactory environment in developing mice. In a first experiment it was found that mouse pups could be stressed (as measured by an increase in ultrasonic calls) by removing the litter from the dam for 15 min/day for the first 14 days of life and exposing them to a novel odor (clean bedding). This stress procedure also produced a long-term modification in maternal behavior. The stress response (ultrasounds) and the modification of maternal behavior were prevented by providing the litter with home cage bedding during maternal separation. In a second experiment it was demonstrated that early stress influenced apomorphine-induced wall climbing behavior in 15-day-old mice, suggesting stress-induced alterations in the dopaminergic system. Pups exposed to clean bedding during infancy exhibited more wall climbing behavior than pups never separated from the mother. Moreover, preventing the early stress response during mother-offspring separation, by providing pups with home cage bedding, eliminated the increase in apomorphine-induced wall climbing. Taken together these results suggest that olfactory cues are decisive in characterizing stressful situations inducing both immediate and long-lasting effects in mouse pups.

Early development in mice: I. Genotype and post-natal maternal effects

The co-actions of genetic effects and the post-natal maternal rearing environment on the development of weight, 9 reflex responses, and survival have been tested by the cross-fostering method in two inbred mice strains--CBA/H and NZB. Pups of the two strains were not treated differentially by the mothers and experimental handling did not systematically affect pup development. Comparisons of unfostered, infostered, and cross-fostered pups show (1) in 16 cases out of 34, reflex development was affected by the pup strain, and in 10 cases out of 34 by the foster mother strain; (2) survival is only affected by the pup strain; (3) weight development is affected by strain of both the pup and the mother as well as their interactions. The adopted pups' scores were situated outside the range of the two non-adopted groups for certain reflexes as well as for weight. Two non-exclusive hypotheses are proposed: the mother strain can affect pup development (1) either through differences in stimulation provided by the mothers (2) or through differences in milk composition.