Variation in the mu-opioid receptor gene (OPRM1) moderates the influence of maternal sensitivity on child attachment

The endogenous opioid system is thought to play an important role in mother-infant attachment. In infant rhesus macaques, variation in the μ-opioid receptor gene (OPRM1) is related to differences in attachment behavior that emerges following repeated separation from the mother; specifically, infants carrying at least one copy of the minor G allele of the OPRM1 C77G polymorphism show heightened and more persistent separation distress, as well as a pattern of increased contact-seeking behavior directed towards the mother during reunions (at the expense of affiliation with other group members). Research in adult humans has also linked the minor G allele of the analogous OPRM1 A118G polymorphism with greater interpersonal sensitivity. Adopting an interactionist approach, we examined whether OPRM1 A118G genotype and maternal (in)sensitivity are associated with child attachment style, predicting that children carrying the G allele may be more likely to develop an ambivalent attachment pattern in response to less sensitive maternal care. The sample consisted of 191 mothers participating with their children (n = 223) in the Maternal Adversity, Vulnerability and Neurodevelopment (MAVAN) project, a community-based, birth cohort study of Canadian mothers and their children assessed longitudinally across the child's development. Maternal sensitivity was coded from at-home mother-child interactions videotaped when the child was 18 months of age. Child attachment was assessed at 36 months using the Strange Situation paradigm. As predicted, G allele carriers, but not AA homozygotes, showed increasing odds of being classified as ambivalently attached with decreasing levels of maternal sensitivity. Paralleling earlier non-human animal research, this work provides support for the theory that endogenous opioids contribute to the expression of attachment behaviors in humans.

Parenting begets parenting: A neurobiological perspective on early adversity and the transmission of parenting styles across generations

The developing brains of young children are highly sensitive to input from their social environment. Nurturing social experience during this time promotes the acquisition of social and cognitive skills and emotional competencies. However, many young children are confronted with obstacles to healthy development, including poverty, inappropriate care, and violence, and their enhanced sensitivity to the social environment means that they are highly susceptible to these adverse childhood experiences. One source of social adversity in early life can stem from parenting that is harsh, inconsistent, non-sensitive or hostile. Parenting is considered to be the cornerstone of early socio-emotional development and an adverse parenting style is associated with adjustment problems and a higher risk of developing mood and behavioral disorders. Importantly, there is a growing literature showing that an important predictor of parenting behavior is how parents, especially mothers, were parented themselves. In this review, we examine how adversity in early-life affects mothering behavior in later-life and how these effects may be perpetuated inter-generationally. Relying on studies in humans and animal models, we consider evidence for the intergenerational transmission of mothering styles. We then describe the psychological underpinnings of mothering, including responsiveness to young, executive function and affect, as well as the physiological mediators of mothering behavior, including hormones, brain regions and neurotransmitters, and we consider how development in these relevant domains may be affected by adversity experienced in early life. Finally, we explore how genes and early experience interact to predict mothering behavior, including the involvement of epigenetic mechanisms. Understanding how adverse parenting begets adverse parenting in the next generation is critical for designing interventions aimed at preventing this intergenerational cycle of early adversity.

Thinking and doing: the effects of dopamine and oxytocin genes and executive function on mothering behaviours

Animal and human studies suggest that initial expression of maternal behaviour depends on oxytocin and dopamine systems. However, the mechanism by which these systems affect parenting behaviours and the timing of these effects are not well understood. This article explores the role of mothers' executive function in mediating the relation between oxytocin and dopamine gene variants and maternal responsiveness at 48 months post-partum. Participants (n = 157) were mothers recruited in the Maternal Adversity, Vulnerability and Neurodevelopment Study, which assesses longitudinally two cohorts of mothers and children in Canada. We examined single nucleotide polymorphisms (SNPs) related to the dopamine and oxytocin systems (DRD1 rs686, DRD1 rs265976, OXTR rs237885 and OXTR rs2254298), assessed mothers' decision-making at 48 months using the Cambridge Neurological Automated Testing Battery (CANTAB) and evaluated maternal responsiveness from videotaped interactions during the Etch-A-Sketch co-operation task. Mediation analyses showed that OXTR rs2254298 A-carriers had an indirect effect on positive parenting which was mediated by mothers' performance on decision-making task (estimate = 0.115, P < 0.005), while OXTR rs2254298 A-carriers had both direct and indirect effects on physically controlling parenting, also mediated through enhanced performance on decision-making (estimate = -0.059, P < 0.005). Dopamine SNPs were not associated with any measure of executive function or parenting (all P > 0.05). While oxytocin has previously been associated with only the early onset of maternal behaviour, we show that an OXTR polymorphism is involved in maternal behaviour at 48 months post-partum through mothers' executive function. This research highlights the importance of the oxytocin system to maternal parenting beyond infancy.

Parenting begets parenting: A neurobiological perspective on early adversity and the transmission of parenting styles across generations

The developing brains of young children are highly sensitive to input from their social environment. Nurturing social experience during this time promotes the acquisition of social and cognitive skills and emotional competencies. However, many young children are confronted with obstacles to healthy development, including poverty, inappropriate care, and violence, and their enhanced sensitivity to the social environment means that they are highly susceptible to these adverse childhood experiences. One source of social adversity in early life can stem from parenting that is harsh, inconsistent, non-sensitive or hostile. Parenting is considered to be the cornerstone of early socio-emotional development and an adverse parenting style is associated with adjustment problems and a higher risk of developing mood and behavioral disorders. Importantly, there is a growing literature showing that an important predictor of parenting behavior is how parents, especially mothers, were parented themselves. In this review, we examine how adversity in early-life affects mothering behavior in later-life and how these effects may be perpetuated inter-generationally. Relying on studies in humans and animal models, we consider evidence for the intergenerational transmission of mothering styles. We then describe the psychological underpinnings of mothering, including responsiveness to young, executive function and affect, as well as the physiological mediators of mothering behavior, including hormones, brain regions and neurotransmitters, and we consider how development in these relevant domains may be affected by adversity experienced in early life. Finally, we explore how genes and early experience interact to predict mothering behavior, including the involvement of epigenetic mechanisms. Understanding how adverse parenting begets adverse parenting in the next generation is critical for designing interventions aimed at preventing this intergenerational cycle of early adversity.

Maternal childhood adversity and child temperament: an association moderated by child 5-HTTLPR genotype

We examined transgenerational effects of maternal childhood adversity on child temperament and a functional promoter polymorphism, 5-HTTLPR, in the serotonin-transporter gene (SLC6A4) as potential moderators of such maternal influences in 154 mother-child dyads, recruited into a longitudinal birth cohort study. We examined the interactive effects of maternal childhood experience using an integrated measure derived from Childhood Trauma Questionnaire (CTQ) and Parental Bonding Index (PBI). Triallelic genotyping of 5-HTTLPR was performed. A measure of 'negative emotionality/behavioural dysregulation' was derived from the Early Childhood Behaviour Questionnaire at 18 and 36 months. Negative emotionality/behavioural dysregulation was highly stable between 18 and 36 months and predicted psychosocial problems at 60 months. After controlling multiple demographics as well as both previous and concurrent maternal depression there was a significant interaction effect of maternal childhood adversity and offspring 5-HTTLPR genotype on child negative emotionality/behavioural dysregulation (β = 1.03, t(11,115) = 2.71, P < .01). The results suggest a transgenerational effect of maternal developmental history on emotional function in the offspring, describing a pathway that likely contributes to the familial transmission of vulnerability for psychopathology.

Genetic variation in oxytocin rs2740210 and early adversity associated with postpartum depression and breastfeeding duration

Mothers vary in duration of breastfeeding. These individual differences are related to a variety of demographic and individual maternal factors including maternal hormones, mood and early experiences. However, little is known about the role of genetic factors. We studied single-nucleotide polymorphisms (SNPs) in the OXT peptide gene (rs2740210; rs4813627) and the OXT receptor gene (OXTR rs237885) in two samples of mothers from the Maternal adversity, Vulnerability and Neurodevelopment study (MAVAN), a multicenter (Hamilton and Montreal, Canada) study following mothers and their children from pregnancy until 7 years of age. Data from the Hamilton site was the primary sample (n = 201) and data from Montreal was the replication sample (n = 151). Breastfeeding duration, maternal mood (measured by the CES-D scale) and early life adversity (measured by the CTQ scale) were established during 12 months postpartum. In our primary sample, polymorphisms in OXT rs2740210, but not the other SNPs, interacted with early life adversity to predict variation in breastfeeding duration (overall F8,125  = 2.361, P = 0.021; interaction effect b = -8.12, t = -2.3, P = 0.023) and depression (overall F8,118  = 5.751, P ≤ 0.001; interaction effect b = 6.06, t = 3.13, P = 0.002). A moderated mediation model showed that higher levels of depression mediated the inverse relation of high levels of early life adversity to breastfeeding duration, but only in women possessing the CC genotype [effect a' = -3.3401, 95% confidence interval (CI) = -7.9466 to -0.0015] of the OXT SNP and not in women with the AA/AC genotype (a' = -1.2942, ns). The latter findings (moderated mediation model) were replicated in our Montreal sample (a' = -0.277, 95% CI = -0.7987 to -0.0348 for CC; a' = -0.1820, ns for AA/AC).

Dopamine receptors D1 and D2 are related to observed maternal behavior

The dopamine pathway and especially the dopamine receptors 1 and 2 (DRD1 and DRD2) are implicated in the regulation of mothering in rats. Evidence for this in humans is lacking. Here, we show that genetic variation in both DRD1 and DRD2 genes in a sample of 187 Caucasian mothers predicts variation in distinct maternal behaviors during a 30-min mother-infant interaction at 6 months postpartum. Two DRD1 single-nucleotide polymorphisms (SNPs rs265981 and rs686) significantly associated with maternal orienting away from the infant (P = 0.002 and P = 0.003, respectively), as did DRD1 haplotypes (P = 0.03). Two DRD2 SNPs (rs1799732 and rs6277) significantly associated with maternal infant-directed vocalizing (P = 0.001 and P = 0.04, respectively), as did DRD2 haplotypes (P = 0.01). We present evidence for heterosis in DRD1 where heterozygote mothers orient away from their infants significantly less than either homozygote group. Our findings provide important evidence that genetic variation in receptors critical for mothering in non-human species also affect human maternal behaviors. The findings also highlight the importance of exploring multiple dimensions of the complex human mothering phenotype.

Serotonin transporter allelic variation in mothers predicts maternal sensitivity, behavior and attitudes toward 6-month-old infants

Maternal behavior in the new mother is a multidimensional set of responses to infant cues that are influenced by the mother's early life experiences. In this study, we wanted to test if mothers' early life experiences and mothers' genotype have interactive effects on maternal behaviors and attitudes, something which has not been previously explored. In a sample of 204 mothers, we assessed maternal genotype at the serotonin transporter-linked polymorphic region (5-HTTLPR) and an adjacent upstream polymorphism (rs25531), together giving rise to three alleles: short (S), L(G) and L(A). Controlling for maternal age and parity, we showed that this genotype can predict differences in maternal sensitivity at 6 months postpartum: mothers with an S (or the functionally similar L(G)) allele were more sensitive than mothers who lacked the allele during a 30-min recorded mother-infant interaction (F (4,140) = 3.43; P = 0.01). Furthermore, we found highly significant gene-environment interactions in association with maternal behavior, such that mothers with no S or L(G) alleles oriented away more frequently from their babies if they also reported more negative early care quality (F (5,138) = 3.28; P = 0.008). Finally, we found significant gene-environment associations with maternal attitudes; mothers with the S allele and with greater early care quality scored higher on ratings of their perceived attachment to their baby (F (5,125) = 3.27; P = 0.008). The regression results show significant interactions between the reported quality of care mothers received from their own parents and genotype on both their frequency of orienting away from the infant during the interaction (F(5, 138) = 3.28; P = 0.008, Fig. 1a) and their perceived attachment feelings to the infant (F(5, 125) = 3.27; P = 0.008, Fig. 1b); however the direction of the effects for these two outcome measures were different from one another. With increasing care quality, mothers with the L(A)L(A) genotype (no S or L(G) allele) oriented away less frequently, while S or L(G) allele carriers showed no significant change. In contrast, with increasing early care quality. L(A)L(A) (no S or L(G) allele) mothers scored lower on perceived attachment to their infants, whereas S or L(G) allele carrying mothers scored higher. [corrected].

Oxytocin receptors in the nucleus accumbens shell are involved in the consolidation of maternal memory in postpartum rats

Female rats with maternal experience display a shorter onset of maternal responsiveness compared to those with no prior experience. This phenomenon called 'maternal memory' is critically dependent on the nucleus accumbens (NA) shell. We hypothesized that activation of OT receptors in the NA shell facilitates maternal memory. In Experiment 1, postpartum female rats given 1 hour of maternal experience were infused following the experience with either a high or low dose of an OT antagonist into the NA shell and tested for maternal behavior after a 10-day pup isolation period. Females receiving a high dose of the antagonist showed a significantly longer latency to exhibit full maternal behavior after the pup isolation period compared to females that received vehicle or a high dose of antagonist in a control region. In Experiment 2, postpartum female rats were infused with either a high or low dose of OT into the NA shell after a 15-minute maternal experience and tested for maternal behavior after a 10-day pup isolation period. There were no significant differences between the females infused with OT and females treated with a vehicle infused into the NA shell or with OT infused into the control region. One possible reason for a lack of facilitation is a floor effect, since females in the control groups displayed a rapid maternal response after the pup isolation period. These findings suggest that OT receptors, likely in combination with other neurotransmitters, in the NA shell play a role in the consolidation of maternal memory.

Complete maternal deprivation affects social, but not spatial, learning in adult rats

The effects of maternal deprivation on learning of social and spatial tasks were investigated in female adult rats. Pups were reared artificially and received "lickinglike" tactile stimulation (AR animals) or were reared with their mothers (MR animals). In adulthood, subjects were tested on paradigms of spatial learning and on paradigms involving learning of social cues. Results showed that maternal deprivation did not affect performance on spatial learning, but it did impair performance on the three social learning tasks. The AR animals made no distinction between a new and a previously presented juvenile conspecific. AR animals also responded less rapidly than MR animals at test for maternal behavior 2 weeks after a postpartum experience with pups. Finally, AR animals did not develop a preference for a food previously eaten by a familiar conspecific whereas MR animals did. This study indicates that animals reared without mother and siblings show no deficits in spatial tasks while showing consistent deficits in learning involving social interactions.

Maternally separated rats show deficits in maternal care in adulthood

Although there is considerable research on the phenomenology, neuroendocrinology, neuroanatomy, and sensory control of maternal behavior, little is known about the influences of early postnatal and postweaning experiences on the development of maternal behavior. The purpose of this study was to assess how early life separation from the mother rat affects development of the offspring's juvenile and adult maternal behavior. From postnatal Days 1 to 17, 3 female rats within each litter were separated (SEP) from the mother and the rest of the litter for 5 hr daily while 3 of their sisters were not maternally separated (NSEP). On postnatal Day 21, all subjects were weaned and randomly assigned to one of three juvenile conditions. One female from both SEP and NSEP groups was either isolated (I), given a social conspecific (S), or given 1- to 4-day-old pups (P) for 5 consecutive days. Maternal behavior of SEP and NSEP animals was assessed and recorded on each of the 5 days. Once all animals reached adulthood, they were mated, gave birth, and were assessed for their maternal behavior. We found that the effects of maternal separation on juvenile maternal-like behaviors were minimal. On the other hand, maternal separation reduced adult maternal licking and crouching over pups. In addition, there was a significant interaction between postnatal and juvenile experience on maternal crouching in maternal animals. These results are discussed in terms of the variety of possible behavioral, endocrine, and neurochemical mechanisms that mediate the effects of early life experiences on adult maternal behavior.

Decreases in calmodulin binding proteins and calmodulin dependent protein phosphorylation in the medial preoptic area at the onset of maternal behavior in the rat

The onset of maternal behavior is characterized by the action of certain hormones, neuropeptides and neurotransmitters and a concomitant increase in the expression of c-Fos in the medial preoptic area (MPOA) but the signaling events that lie between have not been characterized. Because several of these hormones, neuropeptides and neurotransmitters function by activating Ca(2+)/calmodulin (CaM) mediated signaling pathways, many of which can lead to c-Fos expression, the goal of the current work was to identify calmodulin binding proteins (CaMBPs) or specific CaM-dependent phosphoproteins that might be involved. Probing of SDS-PAGE gels of extracts from the hippocampus, parietal cortex, basolateral amygdala and MPOA with recombinant (35)S-VU1-calmodulin (CaM) revealed 30 Ca(2+)-dependent and 4-6 Ca(2+)-independent CaMBPs. Statistically significant maternal behavior-related decreases in four Ca(2+)-dependent CaMBPs ( approximately 31 kDa, 50% decrease; approximately 33 kDa, 32%; approximately 50 kDa, 35%; approximately 60 kDa, 33%) were observed specifically in the MPOA. Numerous proteins were phosphorylated in a Ca(2+) CaM-dependent manner with two (MWs approximately 61 Da, approximately 58 kDa) showing a lack of phosphophorylation only in the MPOA. The selective decrease in CaMBPs coupled with the absence of CaM-dependent phosphoproteins implies that changes in Ca(2+)/CaM-mediated signaling may mediate some of the MPOA-specific processes during the onset of maternal behavior in the rat.

Loss of calcineurin from the medial preoptic area of primiparous rats

Western blot analyses reveal that calcineurin A (CNA), which is present in the hippocampus, basolateral amygdala, parietal cortex, and MPOA of virgin males and females, is undetectable only in the MPOA of primiparous females regardless of whether they had postpartum pup contact or not. In contrast, CNB was expressed at unchanging levels in the PC and MPOA. Similarly, G(alphao) and PKA(RI) were expressed at high levels in all of the brain regions of virgin males, virgin females, and primiparous females, supporting the concept that this loss of CNA is a specific event. Understanding how and why the expression of CNA, the sole neuronal Ca2+/CaM-dependent protein phosphatase, is down-regulated specifically in the MPOA of primiparous females may yield some insight into the signal transduction events that mediate the onset of mammalian maternal behavior.

Intergenerational effects of complete maternal deprivation and replacement stimulation on maternal behavior and emotionality in female rats

The present study investigated the effects of early rearing experiences on the development of maternal behavior in Sprague-Dawley female rats. Pups from individual litters were assigned to four different groups on Day 3 of life. From days 4 to 20 of life, these were reared artificially, without mother and receiving minimal "licking-like" tactile stimulation (AR-MIN), or maximal stimulation (AR-MAX) or were reared with their mothers (MR-CONTROL and MR-SHAM). At 70-100 days all AR and MR animals were mated and then observed with their own offspring, culled to eight pups. After maternal testing open-field tests were conducted. The female offspring in these litters (all raised by their MR and AR mothers) were reared to adulthood and then observed interacting with their offspring. Results show that in adulthood AR mothers engaged in significantly fewer pup-retrievals and less pup-licking (genital and body), and crouching, but significantly more non-maternal tail-chasing, digging, and hanging/climbing. As well, they were more active in the open field. Comparisons between the two AR groups and the MR groups, showed that most of the differences were between the AR-MIN and MR groups, with the AR-MAX animals showing levels of behavior between the two, and differing from neither. Analyses of covariance indicated that early experience and adult emotional behavior both influence adult maternal behavior, but their effects are independent of one another. A cross-generational effect of artificial rearing was also found. Daughters of AR and MR mothers that were observed after the birth of their own litters in adulthood showed a pattern of behavior that mimicked the pattern shown by their mothers. These results are discussed in terms of the variety of possible behavioral, endocrine, and neurochemical mechanisms that mediate the effects of early experiences on adult maternal behavior.

The effects of medial preoptic area and amygdala lesions on maternal behavior in the juvenile rat

The present study was designed to determine whether the medial preoptic area (MPOA) and the amygdala (AMYG) are involved in the expression of "maternal" behavior in juvenile rats as they are in the adult. Juveniles show many behaviors that are similar to the maternal behaviors shown by the postpartum female rat. Whether these behaviors are social in function, as opposed to parental, and hence mediated by different mechanisms from those regulating adult maternal behavior is not known. To test the roles of the MPOA and AMYG in mediating these behaviors, 21-day-old female juvenile rats received MPOA, AMYG, or SHAM (MPOA/AMYG) lesions and were tested at 22 days of age for maternal and other responses to pups. Major findings demonstrate that MPOA lesions disrupt components of maternal behavior, including retrieving and nest building, while AMYG lesions facilitate these behaviors. These findings indicate striking similarities between the juvenile and rat brain for parental responding.

Mother rats bar-press for pups: effects of lesions of the mpoa and limbic sites on maternal behavior and operant responding for pup-reinforcement

This series of studies explored the operant response rates for pup-reinforcement of female Sprague Dawley rats that were either postpartum or cycling and sustained lesions of the medial preoptic area (mpoa), the lateral amygdala, the nucleus accumbens, or sham lesions. The last experiment tested the effects on operant responding of preventing direct access to pups in mpoa and sham-lesioned postpartum mothers. All animals were trained prior to mating on an FR-1 bar-press schedule to criterion (50 presses in 30 min) for a food (Froot Loops) reward in an operant chamber. At the end of pregnancy animals that were to be tested postpartum were provided in their home cages with six newborn foster pups; mother-litter interactions were observed on the last 3 days of pregnancy and throughout the postpartum period. On each of these same days after a period of separation from pups, females were tested in the operant box for delivery of rat pups. With each bar-press response, a rat pup rather than a Fruit Loop was delivered down a gentle shoot into the hopper. Non-postpartum, but maternal, multiparous animals who were showing estrous cycles were tested using the same procedures. The first and second studies showed that animals (both postpartum and as cycling multiparous animals) with mpoa lesions exhibited a significant reduction in bar-press rate for pup reinforcement in the operant box. In postpartum animals, amygdala lesions also produced a bar-press deficit, whereas nucleus accumbens lesions did not. All lesioned groups showed deficits in maternal responding in the home cage and deficits in retrieval in the operant box. These results indicate that systems associated with the mpoa mediate both the stereotypical maternal behaviors and pup-reinforcement. In contrast, the expression of home cage maternal behavior is dependent on the integrity of both the amygdala and nucleus accumbens, whereas operant responding need not be. These results indicate a dissociation of mechanisms mediating expression of the species-typical maternal behavior and pup-reinforcement.

Mother rats bar-press for pups: effects of lesions of the mpoa and limbic sites on maternal behavior and operant responding for pup-reinforcement

This series of studies explored the operant response rates for pup-reinforcement of female Sprague Dawley rats that were either postpartum or cycling and sustained lesions of the medial preoptic area (mpoa), the lateral amygdala, the nucleus accumbens, or sham lesions. The last experiment tested the effects on operant responding of preventing direct access to pups in mpoa and sham-lesioned postpartum mothers. All animals were trained prior to mating on an FR-1 bar-press schedule to criterion (50 presses in 30 min) for a food (Froot Loops) reward in an operant chamber. At the end of pregnancy animals that were to be tested postpartum were provided in their home cages with six newborn foster pups; mother-litter interactions were observed on the last 3 days of pregnancy and throughout the postpartum period. On each of these same days after a period of separation from pups, females were tested in the operant box for delivery of rat pups. With each bar-press response, a rat pup rather than a Fruit Loop was delivered down a gentle shoot into the hopper. Non-postpartum, but maternal, multiparous animals who were showing estrous cycles were tested using the same procedures. The first and second studies showed that animals (both postpartum and as cycling multiparous animals) with mpoa lesions exhibited a significant reduction in bar-press rate for pup reinforcement in the operant box. In postpartum animals, amygdala lesions also produced a bar-press deficit, whereas nucleus accumbens lesions did not. All lesioned groups showed deficits in maternal responding in the home cage and deficits in retrieval in the operant box. These results indicate that systems associated with the mpoa mediate both the stereotypical maternal behaviors and pup-reinforcement. In contrast, the expression of home cage maternal behavior is dependent on the integrity of both the amygdala and nucleus accumbens, whereas operant responding need not be. These results indicate a dissociation of mechanisms mediating expression of the species-typical maternal behavior and pup-reinforcement.

Plasticity in the maternal circuit: effects of experience and partum condition on brain astrocyte number in female rats

Female rats that have received a maternal experience undergo enhanced c-fos expression in a number of brain sites when reexposed to pups. The present 2 studies examined changes in the expression of another brain protein, glial fibrillary acidic protein (GFAP), which is a major unit of the astrocytic cytoskeleton. In both experiments, primiparous and multiparous female rats were given varying amounts of postpartum contact with pups and overdosed after varying intervals, with no pups. Brains were prepared for GFAP immunohistochemical analysis. In both studies, Day 5 postpartum multiparous subjects given additional postpartum contact with pups, when compared with pup-exposed primiparous subjects, were found to have significantly higher numbers of GFAP positive cells in the medial preoptic area of the hypothalamus, an area critical for the expression of maternal behavior, but not in control sites. In Experiment 2, an opposite effect of parity was found in the medial amygdala and habenula.

Neuroanatomical basis of maternal memory in postpartum rats: selective role for the nucleus accumbens

The experience of interacting with pups causes long-term changes in mothers' brains that mediate long-term changes in maternal behavior. As little as 1 hr of pup experience postpartum results in enhanced maternal responses to pups 10 days later. This experiment investigated the effects of lesions in multiple neural sites that have been implicated either in the actual expression of maternal behavior or in learning and memory within other behavioral contexts on the initiation and the long-term experience-based retention of maternal behavior. Electrolytic lesions were performed either before or after a 1-hr or 24-hr maternal experience. Rats sustaining lesions of the nucleus accumbens (NACC), whether administered before parturition and experience or immediately after a brief experience, failed to show a maternal experience effect. NACC lesions sustained 24 hr after a maternal experience did not disrupt long-term retention of the maternal behavior.

Neurobiology of mother-infant interactions: experience and central nervous system plasticity across development and generations

The optimal coordination between the new mammalian mother and her young involves a sequence of behaviors on the part of each that ensures that the young will be adequately cared for and show healthy physical, emotional, and social development. This coordination is accomplished by each member of the relationship having the appropriate sensitivities and responses to cues that characterize the other. Among many mammalian species, new mothers are attracted to their infants' odors and some recognize them based on their odors; they also respond to their infants' vocalizations, thermal properties, and touch qualities. Together these cues ensure that the mother will nurse and protect the offspring and provide them with the appropriate physical and stimulus environment in which to develop. The young, in turn, orient to the mother and show a suckling pattern that reflects a sensitivity to the mothers odor, touch, and temperature characteristics. This article explores the sensory, endocrine, and neural mechanisms that underlie this early mother-young relationship, from the perspective of, first, the mother and, then, the young, noting the parallels between them. It emphasizes the importance of learning and plasticity in the formation and maintenance of the mother-young relationship and mediation of these experience effects by the brain and its neurochemistry. Finally, it discusses ways in which the infants' early experiences with their mothers (or the absence of these experiences) may come to influence how they respond to their own infants when they grow up, providing a psychobiological mechanism for the inter-generational transmission of parenting styles and responsiveness.

Mother rats bar-press for pups: effects of lesions of the mpoa and limbic sites on maternal behavior and operant responding for pup-reinforcement

This series of studies explored the operant response rates for pup-reinforcement of female Sprague Dawley rats that were either postpartum or cycling and sustained lesions of the medial preoptic area (mpoa), the lateral amygdala, the nucleus accumbens, or sham lesions. The last experiment tested the effects on operant responding of preventing direct access to pups in mpoa and sham-lesioned postpartum mothers. All animals were trained prior to mating on an FR-1 bar-press schedule to criterion (50 presses in 30 min) for a food (Froot Loops) reward in an operant chamber. At the end of pregnancy animals that were to be tested postpartum were provided in their home cages with six newborn foster pups; mother-litter interactions were observed on the last 3 days of pregnancy and throughout the postpartum period. On each of these same days after a period of separation from pups, females were tested in the operant box for delivery of rat pups. With each bar-press response, a rat pup rather than a Fruit Loop was delivered down a gentle shoot into the hopper. Non-postpartum, but maternal, multiparous animals who were showing estrous cycles were tested using the same procedures. The first and second studies showed that animals (both postpartum and as cycling multiparous animals) with mpoa lesions exhibited a significant reduction in bar-press rate for pup reinforcement in the operant box. In postpartum animals, amygdala lesions also produced a bar-press deficit, whereas nucleus accumbens lesions did not. All lesioned groups showed deficits in maternal responding in the home cage and deficits in retrieval in the operant box. These results indicate that systems associated with the mpoa mediate both the stereotypical maternal behaviors and pup-reinforcement. In contrast, the expression of home cage maternal behavior is dependent on the integrity of both the amygdala and nucleus accumbens, whereas operant responding need not be. These results indicate a dissociation of mechanisms mediating expression of the species-typical maternal behavior and pup-reinforcement.

The long lasting effects of electrical simulation of the medial preoptic area and medial amygdala on maternal behavior in female rats

A program of repeated electrical (kindling-like) stimulation of the medial preoptic area (MPOA) or the medial amygdala (MedAmyg) on maternal and other behaviors were investigated. Stimulation was applied daily for 14 days (or until a stage 3 motor seizure was observed) using 2 s trains of biphasic square wave pulses at 60 Hz, 1 ms duration and 300-500 microA. Confirmation of afterdischarge using these parametres was established. In the first experiment, maternally experienced (but not post-partum) MedAmyg stimulated animals became maternal more slowly than did MedAmyg not stimulated animals or than MPOA stimulated animals. In the second experiment, virgin animals were used. MPOA stimulation enhanced the female's preference for pup associated environments in the conditioned place preference (CPP) paradigm. MedAmyg stimulation had no effect on CPP performance, but produced a decreased preference for pup odors in a modified hole board test and increased 'anxiety' in the open field. These results confirm that the MPOA and the MedAmyg are involved in facilitating and attenuating maternal responsiveness and related (precursor?) behaviors, respectively. It appears that chronic (kindling-like) stimulation of these neural substrates enhances their functions.

Cortisol, hedonics, and maternal responsiveness in human mothers

New mothers are more attracted to the body odor of newborn infants than are nonmothers. In this study we investigated the relation of postpartum hormones and of prior experience with infants to this enhanced maternal attraction to infant odors. New mothers were asked to complete a hedonics task, using a pleasantness scale to provide an attraction score to different odorants presented on a cotton substrate in a 1-pt Baskin-Robbins container. Mothers were "blind" to the contents of the container. Participants also completed an extensive set of 100-item likert scales concerning their attitudes toward infants, care taking, own maternal adequacy, and other interpersonal relations. Mothers were videotaped interacting with their infants and provided salivary samples prior to the interaction. Salivary samples were assayed by radioimmunoassay (RIA) for salivary concentrations of cortisol, progesterone, and testosterone. Results show that first-time mothers with higher cortisol concentrations were more attracted to their own infant's body odor. Mothers with higher cortisol levels were also better able to recognize their own infants' odors. While cortisol was not related to attitudinal measures of maternal responsiveness, mothers with more prior experience interacting with infants exhibited both more attraction to infant odors and more positive maternal attitudes. Together, prior maternal experience and postpartum cortisol explain a significant proportion of the variance in mothers' attraction to newborn infant odors. These relations are discussed in terms of the variety of "meanings" cortisol could have during the postpartum period.

Hormonal and experiential correlates of maternal responsiveness during pregnancy and the puerperium in human mothers

Two studies were undertaken (1) to determine whether human mothers undergo a change in maternal responsiveness during pregnancy before the birth of the baby, as shown for other mammalian species, and (2) to establish whether a relation exists between changes in maternal feelings and attitudes and changes in hormones. In both studies prospective first-time mothers completed an extensive set of questionnaires, covering a broad range of issues, including a set of 76- to 100-item likert scales concerning attitudes toward infants, childbirth, pregnancy, caretaking, and other interpersonal relationships. In the first cross-sectional study, mothers completed the questionnaires at one of seven time points, ranging from prior to pregnancy to 3 months postpartum. In the longitudinal study, questionnaires were completed repeatedly throughout this same time period. In addition, blood was taken at these same time points and assayed by RIA for plasma concentrations of the steroids, estradiol, progesterone, testosterone, and cortisol. The primary findings are (1) feelings of nurturance grow during pregnancy and from pregnancy to postpartum; in the cross-sectional study, for most of the factors relating to infants or mothering, pregnancy and postpartum responses were more positive than prepregnancy responses; in the longitudinal study, many of these factors also showed elevations across pregnancy itself, as well as further elevations with the birth of the infant. (2) Pregnancy hormones were not related to the growth of attachment to the infant across pregnancy. (3) However, the pattern of change in the ratio of estradiol to progesterone from early to late pregnancy was related to postpartum attachment feelings. (4) Finally, hormonal correlates of attachment feelings may reflect effects both on feelings of nurturance directly and, indirectly, on mothers' feelings of well-being.

Plasticity in the maternal circuit: effects of maternal experience on Fos-Lir in hypothalamic, limbic, and cortical structures in the postpartum rat

To determine what brain sites are activated during the acquisition and retention of a maternal experience in postpartum rats, 3 studies examined the number of cells showing Fos-like immunoreactivity (Fos-lir) in brains following reexposure to pups and pup-associated cues in maternally experienced and inexperienced rats. Day 1 postpartum rats were given a 2- or 4-hr interactive experience with pups and then reexposed to pups in a perforated box, or to a neutral stimulus (perforated box only) 4 or 10 days later. At the end of the test phase, brains were prepared for immunohistochemical detection of Fos-lir. The brain sites showing the most consistent difference between experienced and inexperienced rats were the medical preoptic area, the basolateral amygdala, the parietal cortex, and the prefrontal cortex.

Chemical and behavioral stimulation from females accelerates recrudescence in male Syrian hamsters exposed to short days

Interaction with female hamsters maintained under long photoperiods (LP) accelerates behavioral recrudescence in short photoperiod (SP) males. In this experiment, the authors investigated the effects of various types of female sociosexual cues on different measures of reproductive recrudescence in the male. Five groups of SP males were exposed to different female cues for 3 weeks (Weeks 12 to 15). At Week 16, males were allowed to interact with estrus females; behavioral, physiological, and fecundity measures were monitored. The results show that all measures responded in a pseudo-dose-dependent manner to the different female cues presented. SP males not exposed to any female cues and those exposed to distal visual, auditory, and volatile pheromonal cues from estrus females did not copulate, deposit sperm, or impregnate estrus females presented to them at Week 16. SP males allowed direct access to the bedding of estrus females showed marked improvements on these same reproductive measures by Week 16. However, SP males that interacted with LP females between Weeks 12 and 15 showed the greatest level of reproductive function at Week 16. These results show that the type of female sociosexual stimulation is important in accelerating reproductive recrudescence; whereas interaction with LP females may be important in accelerating behavioral recrudescence, both interaction with and exposure to the bedding of LP females may be important in accelerating physiological and reproductive success measures.

Plasticity in the maternal circuit: effects of maternal experience on Fos-Lir in hypothalamic, limbic, and cortical structures in the postpartum rat

To determine what brain sites are activated during the acquisition and retention of a maternal experience in postpartum rats, 3 studies examined the number of cells showing Fos-like immunoreactivity (Fos-lir) in brains following reexposure to pups and pup-associated cues in maternally experienced and inexperienced rats. Day 1 postpartum rats were given a 2- or 4-hr interactive experience with pups and then reexposed to pups in a perforated box, or to a neutral stimulus (perforated box only) 4 or 10 days later. At the end of the test phase, brains were prepared for immunohistochemical detection of Fos-lir. The brain sites showing the most consistent difference between experienced and inexperienced rats were the medical preoptic area, the basolateral amygdala, the parietal cortex, and the prefrontal cortex.

The effects of olfactory and somatosensory desensitization on Fos-like immunoreactivity in the brains of pup-exposed postpartum rats

Fos-like immunoreactivity (fos-lir) was examined in sites within the "maternal circuit" in postpartum female rats that received various sensory desensitizations and were exposed to pups for 1 or 2 hr. Neither olfactory bulbectomy nor thelectomy (nipple removal) significantly reduced the fos-lir in the anterior medial preoptic area (MPOA), although reductions following bulbectomy in medial amygdala did occur. Peripherally induced hyposmia by ZnSo4 reduced fos-lir in the olfactory structures (olfactory bulbs, piriform cortex, and olfactory tubercle), in medial and cortical nuclei of the amygdala, but not in anterior MPOA. Application of the topical anesthetic Emla to the ventrum only reduced fos-lir in the somatosensory cortex. Combined olfactory and ventral desensitizations produced marginal reductions in posterior MPOA. It is suggested that the MPOA is primarily involved as part of the effector system in the expression of the behavior. In contrast, the amygdala is involved in processing sensory cues received from pups during dam-litter interactions.

Activation of Fos-like immunoreactivity in the medial preoptic area and limbic structures by maternal and social interactions in rats

The researchers examined the number of cells showing Fos-like immunoreactivity (Fos-lir) in the brains of hormonally primed parturient rat dams immediately following their first behavioral interactions with pups. Groups were exposed to newborn pups (pup), adult conspecifics (social), or a new food (food), or they were left alone in cages (control/isolate) for a 1-hr period. Rats were then killed, and their brains were prepared for immunohistochemical detection of Fos-lir. Rats in the pup group had higher numbers of cells showing. Fos-lir within the medial preoptic area (MPOA) nuclei than did the social, control/isolate, and, marginally, food groups and higher levels of Fos-lir in a number of amygdaloid nuclei (medial and cortical) and in cingulate and somatosensory cortices than did control/isolate or food groups. Fos-lir in amygdala did not differ between pup and social groups. There were also group differences in Fos-labeling in the olfactory bulbs, with the pup group showing the highest densities. These results show elevated expression of Fos-lir in brain structures that were activated during the expression of maternal behavior, including the olfactory structures, amygdala, and MPOA.

Neuropsychology of maternal behavior in the rat: c-fos expression during mother-litter interactions

This series of studies used the pattern of nuclear Fos-like immunoreactivity (Fos-lir) to map the functional pathways in the brain that mediate the onset and retention of maternal behavior. In the first two experiments, parturient rat dams were exposed to either pups or to other stimuli on Day 1 postpartum. Dams interacting with pups were either intact or sustained ventral somatosensory, olfactory, or combined desensitizations. Results showed that 1) all intact pup-interacting dams showed elevated levels of Fos-lir in the medial preoptic area (MPOA) and the medial and cortical amygdala as compared to control groups, and 2) olfactory and ventral somatosensory desensitization, either alone or in combination, did not decrease Fos-lir in the MPOA. However, olfactory desensitizations did decrease Fos-lir in the medial amygdala and the combined desensitizations significantly reduced Fos-lir in both the basolateral and central amygdala. In the third study, dams were either exposed to pups or to other stimuli and were subsequently reexposed to pups or to pup cues. Regardless of prior maternal experience, females who were able to interact with pups upon reexposure showed increased Fos-lir in the MPOA, the basolateral and central nuclei of the amygdala, and the nucleus accumbens when compared to females which did not interact with pups. Taken together, these studies suggest that the neuroanatomy of maternal behavior is a complex one, involving multiple systems that interconnect with the MPOA and that mediate the many behavioral processes activated when an animal responds maternally.

Noradrenergic involvement in the consolidation of maternal experience in postpartum rats

If postpartum rats are separated from pups following cesarean delivery, their maternal responsiveness declines such that in tests on day 10 they show maternal onset latencies that do not differ from those shown by virgin rats. If, however, dams are permitted a 1-h experience with pups within 36 h of cesarean delivery, rats exhibit a high level of responsiveness to foster pups on day 10 after c-section. The present research investigates the effect of the noradrenergic system in the long-term consolidation of a brief maternal experience in new mother rats. Groups of dams were cesarean delivered and were either given pups for a brief period 36 h after section (experienced) or received no experience (inexperienced). Immediately following the experience phase, dams were injected with different concentrations of the beta-adrenergic antagonist, propranolol (0, 0.5, 1.0, 5.0 mg/kg), or the adrenergic agonist, isoproterenol (0, 0.25 or 0.5 mg/kg). Ten days after cesarean delivery rats were given maternal induction tests. Rats receiving 60 min of experience and injected with propranolol exhibited significantly longer maternal onset latencies than did saline-injected rats, although their latencies were not as long as shown by the maternally inexperienced groups. In contrast, rats receiving 15 min of experience and injected with isoproterenol exhibited significantly shorter onset latencies than did saline-injected rats, whether or not they exhibited maternal behavior during the initial 15 min exposure period. These results suggest that the noradrenergic system is involved in the consolidation of a maternal experience.

Postpartum factors related to mother's attraction to newborn infant odors

Hedonic responses to a variety of infant (general body, urine, and feces) and noninfant (lotion, cheese, and spice) odorants were compared in four groups of subjects: new mothers, mothers a 1-month postpartum, and female and male nonparents. Using standard scaling procedures, subjects rated each of the odorants twice on a scale from extremely unpleasant (-20.5) to extremely pleasant (+20.5). In addition, all subjects completed a set of attitude questionnaires, and mothers also answered a childbirth questionnaire and were observed while feeding their infants.

The effects of a social support group on depression, maternal attitudes and behavior in new mothers

The present study examined the effects of a postpartum Social Support Group intervention on mood state, attitudes and behavior of new mothers. Intervention conditions consisted of an eight session Social Support intervention (n = 44), a no intervention condition (n = 83) and a Group-by-Mail intervention (n = 15). Attitudinal and behavioral assessments were made before and after the interventions at 6 and 20 weeks postpartum, respectively. The primary results indicate that regardless of intervention condition mothers undergo an improvement in mood from 2 weeks to 5 months postpartum. Although the Social Support intervention did not alleviate maternal depression and, in fact, may be detrimental to depressed mothers' self-confidence, it did increase mothers' proximal attention to their infants.

Effects of transections to the vomeronasal nerves or to the main olfactory bulbs on the initiation and long-term retention of maternal behavior in primiparous rats

While the onset of maternal behavior at parturition is mediated by hormones, the maintenance of maternal behavior during the first few postpartum weeks depends on experiences acquired while the dam interacts with pups (Rosenblatt, 1990). In fact, if female rats are permitted as little as 2 h or maternal experience within 36 h after Cesarean delivery, they exhibit heightened maternal behavior during maternal induction tests 10 days later; in contrast, dams separated from young at the time of Cesarean delivery and not permitted a maternal experience fail to respond maternally in tests 10 days later (Orpen & Fleming, 1987). In this study we investigated the role of chemosensory input through the vomeronasal and main olfactory systems in this maternal experience effect. Six groups of primiparous females were tested for maternal behavior to foster pups presented 9-10 days after Cesarean delivery: three groups were permitted to interact with pups for a 2-h period 36 h after Cesarean delivery; and three groups were separated from pups until testing and were given no maternal experience. Within each experience condition, one group sustained bilateral section of the vomeronasal nerves, one sustained bilateral coronal cuts through the midsection of the main olfactory bulbs, and one group sustained small medial olfactory bulb cuts. The results showed that animals sustaining vomeronasal or olfactory transections, regardless of experience condition, exhibited significantly reduced latencies to maternal behavior in maternal induction tests. However, these chemosensory disruptions did not prevent an additional facilitation of maternal behavior produced by a prior maternal experience.

Somatosensory control of the onset and retention of maternal responsiveness in primiparous Sprague-Dawley rats

The role of perioral and ventral-trunk somatosensory stimulation from pups mediating the initial expression of maternal behavior and its long-term retention 8 days later, was investigated. Six groups of female rats were permitted to physically interact with four 1-5-day-old foster pups for 1 h, 36 h after Cesarean delivery on gestation day 21. Prior to this maternal experience, dams were subjected to: reduced cutaneous rostral snout sensitivity (anaptia) by injection of lidocaine into the mystacial pads; reduced ventral-trunk sensations by occlusion of the entire ventrum with a full spandex jacket; both manipulations; or control manipulations. Additional groups of females not receiving a maternal experience (inexperienced) also received the somatosensory deprivation or control manipulations. During retention testing, rats in the singly manipulated experienced groups exhibited reduced latencies to become maternal in comparison to their inexperienced counterparts (approximately 3 days vs. 8 days). However, rats previously rendered both anaptic and ventrally-occluded responded like inexperienced rats in showing a long latency to become maternal (8 days). Thus, reduction of either perioral or ventral somatosensory contact from pups did not block the maternal experience effect, but reduction of both of these inputs did.

Sexual experience effects are blocked both by the protein-synthesis inhibitor, cycloheximide, and by the noncompetitive NMDA antagonist, MK-801

Three studies were done to determine the effects of a brief 2-h sexual experience on the maintenance of sexual behavior in male rats; the effects on the experience-based maintenance of sexual behavior of gonadal hormones (study 1), a protein-synthesis inhibitor (study 2), and an N-methyl-D-aspartate receptor blocker (study 3) were determined. Naive male rats were provided with a 2-h sexual experience with sexually receptive hormonally "primed" females or they received no experience. In the first study animals under each of these conditions then underwent castration or sham surgery. In the second study animals under each of the experience conditions received either cycloheximide (CYX) or saline (SAL; 1.5 or 3.0 mg/kg CYX or SAL sc, 10 min after the experience). In study 3 experienced and inexperienced animals received either 0.07 or 0.10 mg/kg MK-801 ip (15 min before the experience). In all studies animals were tested for sexual behavior 3, 6, and 9 days after surgery or injection. These studies showed that the most consistent effect of a 2-h sexual experience was to facilitate the initiation of mounting, especially on the first test; they show, further, that most experience effects were reduced or eliminated if animals were castrated between experience and test, if they received a drug (CYX) at the time of the experience that blocks the synthesis of proteins, or if they received an NMDA receptor antagonist prior to the experience.

The effects of short day exposure on seasonal and circadian reproductive rhythms of female golden hamsters

Four groups of female golden hamsters were exposed to short photoperiods (SP, LD 10:14) for 4, 14, 20, or 27 weeks and tested for physiological markers (uterine weight and estrous cycles) and behavioral (lordosis, approach and aggressive behaviors) measures while in contact with a stud male. After behavioral testing, females were ovariectomized and, during the next 2 weeks, were tested twice more (with a stud male) after replacement with 0.33 microgram (low dose) and 1.0 microgram (high dose) EB plus progesterone (500 micrograms). Results show that, after 14 weeks of SP conditions, uterine weights and percentage of females showing normal estrous cycles are at a minimum. This is mirrored by minimal levels of lordosis and maximal levels of aggressive and approach behavior at week 14. Physiological measures did not fully recover (to preregression levels) until week 27; however, behavioral measures show an earlier recovery by week 20. SP exposure also affects the circadian patterning of behaviors: Females that show lordosis at week 14 did so later in the day than did females tested at other weeks. Females in the regressed state also fail to show a significant decrease in approach behaviors (and a significant increase in receptive behaviors) over the course of the circadian day, a pattern seen in nonregressed females. Following hormone replacement with the low EB (+P) dose, females do not become receptive; however, at the higher dose, all but the week 14 group show increased receptivity.(ABSTRACT TRUNCATED AT 250 WORDS)

MK801, an NMDA antagonist, blocks acquisition of a spatial task but does not block maternal experience effects

Two studies were conducted to determine the effect on learning and memory of MK801, an N-methyl-D-aspartate (NMDA) antagonist that acts through noncompetitive blockade of the ion channel associated with the NMDA receptor. In the first study we found a dose-dependent impairment in the acquisition of a modified radial-arm maze task, resulting from injections (IP) of MK801 10 minutes prior to training. The retention of that learning, as measured by the amount of training required for reacquisition on the following day, was unaffected by the drug. In contrast, in the second study, MK801 did not block the experience-based facilitation of maternal responding seen 8 days after one hour of exposure to pups: experienced dams showed facilitated onset of maternal behavior, relative to inexperienced dams, regardless of the drug they received. However, injections of MK-801, either just before or just after the maternal experience, did lead to some deficits in maternal responding on the first day of testing. We have previously shown that these maternal experience effects are blocked by injections (ICV, SC) of cycloheximide, a protein synthesis inhibitor. These results suggest that the NMDA system does not mediate all, if any, of cycloheximide's effects on maternal experience and, furthermore, that the NMDA system may mediate some but not all forms of learning.

The effects of short day exposure on seasonal and circadian reproductive rhythms in male golden hamsters

Male golden hamsters were exposed to long (LD 14:10) or short (LD 10:14) photoperiods (Groups LP and SP, respectively) and tested 4 times over a 30-week period. At each test time, animals were tested twice, once in their subjective night and once in their subjective day. During each test animals were observed for approach and copulatory behaviors in response to hormonally primed receptive females. To determine gonadal condition, changes in testes size and sperm production over weeks in SP or LP condition were also measured. Results show that SP conditions induce gonadal regression (at 9 weeks) and recrudescence (at 17 weeks); gonadal function was fully restored by 21 weeks in SP. This pattern is mirrored by a decline in copulatory behaviors during regression, followed by a resumption of sexual behaviors during gonadal recrudescence. In contrast, approach measures showed an inverse pattern; males showed the highest level of approach behaviors at week 13, during gonadal quiescence. Short day conditions also induce changes in the circadian patterning of copulatory behaviors: whereas LP animals always showed more mounts, intromissions and ejaculations in the dark than in the light, between 1 to 13 weeks in short day conditions. SP animals show equal levels of copulatory behavior in the dark and in the light. At the time of gonadal recrudescence, SP animals start to show circadian patterns of sexual behaviors comparable to LP animals. These differences were not found for approach behaviors. The relationship between the different behavioral systems and physiological measures, and the effects on these of short day exposure are discussed.

Effects of cycloheximide on the retention of olfactory learning and maternal experience effects in postpartum rats

We have previously shown that cycloheximide, a protein synthesis inhibitor, blocks retention of experimentally based material responding in postpartum rats. In the following study, we investigated further the effect of this drug on maternal experience effects and, in particular, on the retention of olfactory learning. Dams were injected SC with cycloheximide or saline following a one-hour maternal experience with pups scented with one of two artificial odorants. When tested eight days later, saline but not cycloheximide animals demonstrated a preference for the odor which they had experience on pups. Animals were then tested for maternal responsiveness with pups that were scented with an odor that was either the same or different from the one used in the maternal experience. All animals receiving cycloheximide, regardless of the pup odor at testing, exhibited long latencies to become maternal, replicating our earlier finding that the retention of learning in maternal behavior is susceptible to disruption by protein synthesis inhibitors. A similar disruption of the experience effect was found when the pup odor at testing was different from the exposure odor. This suggests that olfactory learning may normally play a role in the mediation of postpartum experience effects.

Experience-hormone interactions and maternal behavior in rats

Three studies were conducted to determine the effects of reproductive condition and hormonal background on the acquisition and retention of a prior maternal experience. In the first study five experience conditions were compared. All animals gave birth and received either no postpartum contact with pups or 1/2 hr, 1 hr, 2 hr or 24 hr of pup contact and were tested for maternal behavior 10 days later. Animals receiving pregnancy and parturitional experience, but minimal social experience with young, exhibited significantly longer maternal onset latencies than did groups receiving 2 or 24 hr of prior experience; also, comparisons of 10- and 30-day retention intervals indicated that animals tested 10 days after a 24-hr experience exhibited shorter latencies than those tested 30 days later. Thus, the duration of the postpartum experience and the interval since prior experience both affect the level of maternal responsiveness shown. In the second study six groups of females were tested. Four groups were permitted one day of interaction with pups either after parturition (primiparous animals) or following pup induction procedures (nulliparous animals) and were tested for their maternal responsiveness to foster pups 25-35 days later, either on day 19 of a subsequent pregnancy or following resumption of estrous cycling. For most measures of maternal behavior there were significant main experience and test effects; experienced and pregnant animals exhibited shorter latencies to retrieve, lick and crouch over pups than did inexperienced and cycling animals, respectively. Significant interactions were also found for genital licking latency as well as for retrieval and crouch frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Transition to motherhood and the self: Measurement, stability, and change

Different ways of conceptualizing and measuring change in attitudes during transition to motherhood are examined. A series of analyses was performed on data from a cross-sectional sample (N = 667) and a smaller longitudinal sample (n = 48) to demonstrate sound psychometric properties for 2 new scales and to show construct comparability across different phases of childbearing. For Childbearing Attitudes Questionnaire, results demonstrated equality of covariance for 16 scales and comparability of structure and meaning of 4 higher order factors--identification with motherhood, social orientation, self-confidence, and negative aspects of giving birth. For Mothering Self-Definition Questionnaire, results demonstrated equality of covariance of 5 scales and comparability of structure and meaning of a single higher order factor, interpreted as reflecting positive feelings about one's mothering characteristics. Analyses of correlations and mean differences identified areas of change and stability.

Cycloheximide blocks the retention of maternal experience in postpartum rats

Two studies were done to determine the effects of cycloheximide (CYX), a protein synthesis inhibitor, on maternal experience effects in rats. In the first study eight groups received a 2-h maternal experience 36 h after cesarean (c)-section and two groups received no post c-section experience. Among the experienced groups, two received icv injections of CYX or saline (SAL) 30 min before the maternal experience, two received CYX or SAL 10 min after the experience, and two received the injections 24 h after the experience. One inexperienced group received CYX and the other received SAL 36 h after c-section. Tests for maternal behavior occurred 10 days after c-section. CYX was not able to block or disrupt the "acquisition" or expression of ongoing maternal behavior during the 2-h experience phase. However, CYX was able to block the long-term "retention" of a 2-h maternal experience if the drug was present during or immediately after the experience, prior to "consolidation." The second study investigated the effects of CYX administered immediately after the maternal experience on the expression and retention of maternal behavior 4 and 6 days after c-section, to determine whether the hormonally mediated short-onset latencies of the 4-day group would be blocked by CYX. Eight groups of animals were tested for maternal behavior. Four were tested 4 days after c-section and four were tested 6 days after c-section. Within each of these groups two were experienced and two inexperienced; within each experience condition one group received CYX and one received SAL. Day 4 groups exhibited shorter onset latencies than Day 6 groups. There was also a CYX-SAL difference in maternal onset latencies among experienced Day 6 groups but not among Day 4 groups. These data indicate that the blocking effects of CYX can be seen only when hormonal priming of maternal behavior is no longer in evidence.

Sex differences in small-magnitude heart-rate responses to sexual and infant-related stimuli: a psychophysiological approach

Small-magnitude (2-3 beats per minute) heart-rate responses can show sex differences if assessed with a psychophysiological approach in which temporally fine-grained methods are used to determine topographical differences. Such differences emerged when 15 males and 37 females were shown videosegments depicting emotional scenes. Specifically, males accelerated to erotic segments (couples making love), while females accelerated to segments showing babies crying. In addition, the peak development of baby-cry-elicited accelerations occurred about 1 second before that of erotic segment-elicited accelerations. The results are consistent with a preparatory-response interpretation, but more research is needed both to investigate the generality of these sex differences in heart-rate responses, and to determine the role of experiential and psychosocial factors.

Effects of maternal hormones on 'timidity' and attraction to pup-related odors in female rats

The present study was designed to determine whether changes in 'emotionality' and responses to odorants that occur in the postpartum rat are due to the same configuration of hormones that facilitate the expression of maternal behavior. Ovariectomized females were implanted with silastic capsules containing progesterone and estradiol or cholesterol for a 19-21 day period and were tested 1 or 7 days later for emergence behavior, ambulation in the open-field and responses to nesting-material containing different odorants. All females were given two tests in which clean nest-material was presented and two with lactating nest material. In comparison to cholesterol animals hormonally primed animals emerged more rapidly into the open-field, crossed more squares while in the field and spent more time around the odor stimulus. Moreover, hormonally primed animals crossed more squares in the region around the odor source when lactating nest odor was present than when it was not and, under the lactating nest odor condition, crossed more squares in the stimulus region than did any other group. This study suggests that the Bridges' regimen of progesterone and estradiol reduces general 'timidity,' reflected in open-field performance, and increases attraction to pup-related odors. These hormone-induced behavioral changes may well contribute to the heightened maternal responsiveness also produced by these hormones.

Changes in the marital relationship during the transition to first time motherhood: effects of violated expectations concerning division of household labor

This research combined cross-sectional and longitudinal analyses to evaluate the hypothesis that violated expectations with respect to sharing child care and housekeeping responsibilities contribute to women's dissatisfactions with their marital relationships after the birth of their first child. The cross-sectional sample consisted of 670 women who completed questionnaires at one of six phases in relation to birth. The longitudinal sample consisted of 48 women who filled out questionnaires late in pregnancy and at three periods postpartum. The results showed, consistent with previous findings, that women reported less positive feelings about their husbands during the postpartum period than during pregnancy, and that women reported doing much more of the housework and child care than they had expected. Moreover, regression analyses indicated, as predicted, that violated expectations concerning division of labor were related to negative feelings postpartum concerning some aspects of the marital relationship. Additional findings suggested that the negative implications of the birth of a baby for the marital relationship may not be as great as has been emphasized in previous literature, and that expectancy violations affect some parts of the relationship but not necessarily the core affective feeling.