GABA receptor agonists in the medial preoptic area and maternal behavior in lactating rats

Mother-Young Bonding: Neurobiological Aspects and Maternal Biochemical Signaling in Altricial Domesticated Mammals

Mother-young bonding is a type of early learning where the female and their newborn recognize each other through a series of neurobiological mechanisms and neurotransmitters that establish a behavioral preference for filial individuals. This process is essential to promote their welfare by providing maternal care, particularly in altricial species, animals that require extended parental care due to their limited neurodevelopment at birth. Olfactory, auditory, tactile, and visual stimuli trigger the neural integration of multimodal sensory and conditioned affective associations in mammals. This review aims to discuss the neurobiological aspects of bonding processes in altricial mammals, with a focus on the brain structures and neurotransmitters involved and how these influence the signaling during the first days of the life of newborns.

Effects of maternal experience on pup-induced activation of maternal neural circuits in virgin mice

Maternal experience can promote a long-lasting increase in maternal motivation. This maintenance of caregiving behaviors, rather than avoidant or agnostic responses towards young, is advantageous for the survival of subsequent offspring. We have previously reported that maternal motivation is associated with differential immediate early gene expression in central motivation circuits and aversion circuits. Here we ask how these circuits come to differentially respond to infant cues. We used Targeted Recombination in Active Populations (TRAP) to identify cells that respond to pups in maternally hesitant TRAP2;Ai14 virgin female mice. Following an initial 60 min exposure to foster pups, virgin TRAP2;Ai14 mice were injected with 4-hydroxytamoxifen to induce recombination in c-Fos expressing cells and subsequent permanent expression of a red fluorescent reporter. We then examined whether the same cells that encode pup cues are reactivated during maternal memory retrieval two weeks later using c-Fos immunohistochemistry. Whereas initial pup exposure induced c-Fos activation exclusively in the medial preoptic area (MPOA), following repeated experience, c-Fos expression was significantly higher than baseline in multiple regions of maternal and central aversion circuits (e.g., ventral bed nucleus of the stria terminalis, nucleus accumbens, basolateral amygdala, prefrontal cortex, medial amygdala, and ventromedial nucleus of the hypothalamus). Further, cells in many of these sites were significantly reactivated during maternal memory retrieval. These data suggest that cells across both maternal motivation and central aversion circuits are stably responsive to pups and thus may form the cellular representation of maternal memory.

Postpartum State, but Not Maternal Caregiving or Level of Anxiety, Increases Medial Prefrontal Cortex GAD65 and vGAT in Female Rats

Upregulation of the inhibitory neurotransmitter, GABA, is involved in many of the behavioral differences between postpartum and nulliparous female rodents. This is evidenced by studies showing that pharmacological blockade of GABAergic activity impairs maternal caregiving and postpartum affective behaviors. However, the influence of motherhood on the capacity for GABA synthesis or release in the medial prefrontal cortex (mPFC; brain region involved in many social and affective behaviors) is not well-understood. Western blotting was used to compare postpartum and nulliparous rats in protein levels of the 65-kD isoform of glutamic acid decarboxylase (GAD65; synthesizes most GABA released from terminals) and vesicular GABA transporter (vGAT; accumulates GABA into synaptic vesicles for release) in the mPFC. We found that postpartum mothers had higher GAD65 and vGAT compared to virgins, but such differences were not found between maternally sensitized and non-sensitized virgins, indicating that reproduction rather than just the display of maternal caregiving is required. To test whether GAD65 and vGAT levels in the mPFC were more specifically related to anxiety-related behavior within postpartum mothers, we selected 8 low-anxiety and 8 high-anxiety dams based on their time spent in the open arms of an elevated plus maze on postpartum day 7. There were no significant differences between the anxiety groups in either GAD65 or vGAT levels. These data further indicate that frontal cortical GABA is affected by female reproduction and more likely contributes to differences in the display of socioemotional behaviors across, but not within, female reproductive state.

An Integrated Mechanistic Model of Mindfulness-Oriented Recovery Enhancement for Opioid-Exposed Mother-Infant Dyads

A growing body of neurobiological and psychological research sheds light on the mechanisms underlying the development and maintenance of opioid use disorder and its relation to parenting behavior. Perinatal opioid use is associated with risks for women and children, including increased risk of child maltreatment. Drawing from extant data, here we provide an integrated mechanistic model of perinatal opioid use, parenting behavior, infant attachment, and child well-being to inform the development and adaptation of behavioral interventions for opioid-exposed mother-infant dyads. The model posits that recurrent perinatal opioid use may lead to increased stress sensitivity and reward dysregulation for some mothers, resulting in decreased perceived salience of infant cues, disengaged parenting behavior, disrupted infant attachment, and decreased child well-being. We conclude with a discussion of Mindfulness-Oriented Recovery Enhancement as a means of addressing mechanisms undergirding perinatal opioid use, parenting, and attachment, presenting evidence on the efficacy and therapeutic mechanisms of mindfulness. As perinatal opioid use increases in the United States, empirically informed models can be used to guide treatment development research and address this growing concern.

Local administration of bicuculline into the ventrolateral and medial preoptic nuclei modifies sleep and maternal behavior in lactating rats

The preoptic area (POA) is a brain structure classically involved in a wide variety of animal behavior including sleep and maternal care. In the current study, we evaluate the specific effect of disinhibition of two specific regions of the POA, the medial POA nucleus (mPOA) and the ventrolateral POA area (VLPO) on sleep and maternal behavior in lactating rats. For this purpose, mother rats on postpartum day 1 (PPD1) were implanted for polysomnographic recordings and with bilateral cannulae either in the mPOA or in the VLPO. The rats were tested for sleep and maternal behavior on PPD4-8 after the infusion of the GABA-A antagonist, bicuculline (0, 10 or 30 ng/0.2 µl/side). Infusion of bicuculline into the mPOA augmented retrieving and nest building behaviors and reduced both nursing and milk ejections but had almost no effect on sleep. When bicuculine was microinjected into the VLPO, the rats significantly increase the number of retrievings and mouthings and reduced the nursing time without changes in milk ejections, which was associated with an increase in wakefulness and a reduction in light sleep. Our results show that disinhibition of the mPOA, a key area in the control of maternal behavior, increased active maternal behaviors and reduced nursing without affecting wakefulness or sleep time. In contrast, the enhancement of some active maternal behaviors when the drug was infused into the VLPO, a sleep-promoting area, with a concomitant increase in wakefulness suggests that mother rats devote this additional waking time in the active maternal care of the pups. We hypothesize that maternal behavior changes after bicuculine microinjection into the VLPO are caused by a reduction in the sleep drive, rather than a direct effect on maternal behavior.

Altered responsiveness to pups in virgin female mice of the BTBR strain: Insights from pattern of c-Fos expression in brain regions involved in maternal behavior

BTBR is an inbred mouse strain that displays several behavioral alterations resembling the core symptoms of Autism Spectrum Disorder, including deficit in sociability. In the present study, we investigated whether the pup-induced maternal behavior in virgin female mice, a naturally rewarding behavior, is impaired in this strain similarly to social interaction with adult conspecifics. We firstly assessed the maternal responsiveness towards newly born pups expressed by either virgin female mice of the BTBR strain or of the normo-social B6 strain. Next, we examined in both strains the expression of c-Fos as a marker of neuronal activity in selected brain areas involved in the regulation of maternal behavior in rodents including the olfactory bulb, the medial preoptic area and the paraventricular nucleus (PVN). We also examined the effects of pup presentation on oxytocinergic neurons of the PVN, the major brain site of synthesis of oxytocin, which has a pivotal role in facilitation of maternal response and social responsiveness in general. As a final step, we assessed the c-Fos expression pattern comparing the effect of exposure to pups with that induced by exposure to another social stimulus, focusing on other areas implicated in maternal responsiveness as well as in the affective component of social behavior such as pyriform cortex and central and basolateral amygdala. Our data showed that BTBR virgin females are less responsive to presentation of pups in comparison to B6, in parallel with lower activation of brain areas implicated in the maternal and social responsiveness.

A Scientometric Approach to Review the Role of the Medial Preoptic Area (MPOA) in Parental Behavior

Research investigating the neural substrates underpinning parental behaviour has recently gained momentum. Particularly, the hypothalamic medial preoptic area (MPOA) has been identified as a crucial region for parenting. The current study conducted a scientometric analysis of publications from 1 January 1972 to 19 January 2021 using CiteSpace software to determine trends in the scientific literature exploring the relationship between MPOA and parental behaviour. In total, 677 scientific papers were analysed, producing a network of 1509 nodes and 5498 links. Four major clusters were identified: “C-Fos Expression”, “Lactating Rat”, “Medial Preoptic Area Interaction” and “Parental Behavior”. Their content suggests an initial trend in which the properties of the MPOA in response to parental behavior were studied, followed by a growing attention towards the presence of a brain network, including the reward circuits, regulating such behavior. Furthermore, while attention was initially directed uniquely to maternal behavior, it has recently been extended to the understanding of paternal behaviors as well. Finally, although the majority of the studies were conducted on rodents, recent publications broaden the implications of previous documents to human parental behavior, giving insight into the mechanisms underlying postpartum depression. Potential directions in future works were also discussed.

Neural Circuit Mechanisms That Underlie Parental Care

In mammals, parental care is essential for the survival of the young; therefore, it is vitally important to the propagation of the species. These behaviors, differing between the two sexes, are innate, stereotyped, and are also modified by an individual's reproductive experience. These characteristics suggest that neural mechanisms underlying parental behaviors are genetically hardwired, evolutionarily conserved as well as sexually differentiated and malleable to experiential changes. Classical lesion studies on neural control of parental behaviors, mostly done in rats, date back to the 1950s. Recent developments of new methods and tools in neuroscience, which allow precise targeting and activation/inhibition of specific populations of neurons and their projections to different brain structures, have afforded fresh opportunities to dissect and delineate the detailed neural circuit mechanisms that govern distinct components of parental behaviors in the genetically tractably organism, the laboratory mouse (Mus musculus). In this review, we summarize recent discoveries using modern neurobiological tools within the context of traditional lesion studies. In addition, we discuss interesting cross talk between neural circuits that govern parent care with those that regulate other innate behaviors such as feeding and mating.

A Hypothalamic Midbrain Pathway Essential for Driving Maternal Behaviors

Maternal behaviors are essential for the survival of the young. Previous studies implicated the medial preoptic area (MPOA) as an important region for maternal behaviors, but details of the maternal circuit remain incompletely understood. Here we identify estrogen receptor alpha (Esr1)-expressing cells in the MPOA as key mediators of pup approach and retrieval. Reversible inactivation of MPOA^Esr1+ cells impairs those behaviors, whereas optogenetic activation induces immediate pup retrieval. In vivo recordings demonstrate preferential activation of MPOA^Esr1+ cells during maternal behaviors and changes in MPOA cell responses across reproductive states. Furthermore, channelrhodopsin-assisted circuit mapping reveals a strong inhibitory projection from MPOA^Esr1+ cells to ventral tegmental area (VTA) non-dopaminergic cells. Pathway-specific manipulations reveal that this projection is essential for driving pup approach and retrieval and that VTA dopaminergic cells are reliably activated during those behaviors. Altogether, this study provides new insight into the neural circuit that generates maternal behaviors.

Serotonin and motherhood: From molecules to mood

Emerging research points to a valuable role of the monoamine neurotransmitter, serotonin, in the display of maternal behaviors and reproduction-associated plasticity in the maternal brain. Serotonin is also implicated in the pathophysiology of numerous affective disorders and likely plays an important role in the pathophysiology of maternal mental illness. Therefore, the main goals of this review are to detail: (1) how the serotonin system of the female brain changes across pregnancy and postpartum; (2) the role of the central serotonergic system in maternal caregiving and maternal aggression; and (3) how the serotonin system and selective serotonin reuptake inhibitor medications (SSRIs) are involved in the treatment of maternal mental illness. Although there is much work to be done, studying the central serotonin system's multifaceted role in the maternal brain is vital to our understanding of the processes governing matrescence and the maintenance of motherhood.

Plasticity of paternity: Effects of fatherhood on synaptic, intrinsic and morphological characteristics of neurons in the medial preoptic area of male California mice

Parental care by fathers enhances offspring survival and development in numerous species. In the biparental California mouse, Peromyscus californicus, behavioral plasticity is seen during the transition into fatherhood: adult virgin males often exhibit aggressive or indifferent responses to pups, whereas fathers engage in extensive paternal care. In this species and other biparental mammals, the onset of paternal behavior is associated with increased neural responsiveness to pups in specific brain regions, including the medial preoptic area of the hypothalamus (MPOA), a region strongly implicated in both maternal and paternal behavior. To assess possible changes in neural circuit properties underlying this increased excitability, we evaluated synaptic, intrinsic, and morphological properties of MPOA neurons in adult male California mice that were either virgins or first-time fathers. We used standard whole-cell recordings in a novel in vitro slice preparation. Excitatory and inhibitory post-synaptic currents from MPOA neurons were recorded in response to local electrical stimulation, and input/output curves were constructed for each. Responses to trains of stimuli were also examined. We quantified intrinsic excitability by measuring voltage changes in response to square-pulse injections of both depolarizing and hyperpolarizing current. Biocytin was injected into neurons during recording, and their morphology was analyzed. Most parameters did not differ significantly between virgins and fathers. However, we document a decrease in synaptic inhibition in fathers. These findings suggest that the onset of paternal behavior in California mouse fathers may be associated with limited electrophysiological plasticity within the MPOA.

Thalamic integration of social stimuli regulating parental behavior and the oxytocin system

Critically important components of the maternal neural circuit in the preoptic area robustly activated by suckling were recently identified. In turn, suckling also contributes to hormonal adaptations to motherhood, which includes oxytocin release and consequent milk ejection. Other reproductive or social stimuli can also trigger the release of oxytocin centrally, influencing parental or social behaviors. However, the neuronal pathways that transfer suckling and other somatosensory stimuli to the preoptic area and oxytocin neurons have been poorly characterized. Recently, a relay center of suckling was determined and characterized in the posterior intralaminar complex of the thalamus (PIL). Its neurons containing tuberoinfundibular peptide 39 project to both the preoptic area and oxytocin neurons in the hypothalamus. The present review argues that the PIL is a major relay nucleus conveying somatosensory information supporting maternal behavior and oxytocin release in mothers, and may be involved more generally in social cue evoked oxytocin release, too.

Pup exposure facilitates retrieving behavior via the oxytocin neural system in female mice

Parental behavior in mammals is innate, but it is also facilitated by social experience, specifically social interactions between the parent and infant. Social interactions with infants also induce the alloparental behavior of virgin animals. Oxytocin (OT) plays an important role in mediating alloparental behavior. Although parental behavior is modulated by the medial preoptic area (MPOA) and adjacent regions, it is unclear how OT acts in these regions as a control mechanism of alloparental behavior promoted by adult-pup interaction. The aim of this study was to investigate the role of OT for facilitating effects of adult-pup interactions on alloparental behavior via neural activity of preoptic area (POA), including MPOA and adjacent area. For this purpose, we conducted behavioral tests and examined the neural activity of the OT system in POA. Virgin female mice that were repeatedly exposed to pups showed shorter retrieving latencies and higher number of c-Fos expressing neurons in POA, particular in lateral preoptic area (LPO) compared to control animals that were exposed to pups only one time. In addition, repeated pup exposure increased the proportion of OT neurons and OTR neurons expressing c-Fos in POA. The concentration of OT also significantly increased in the POA. Finally, infusion of an OT antagonist into the POA area blocked the facilitating effects of repeated pup exposure on retrieving behavior. These results demonstrated that the facilitating effects of repeated pup exposure on alloparental behavior occurred via an organizational role of the OT system.

GABA Receptors in the Medial Preoptic Area Modulate the Onset of Oestradiol-Induced Maternal Behaviour in Hysterectomised-Ovariectomised, Pregnant Rats

We studied the participation of GABA neurotransmission in the medial preoptic area (mPOA) with respect to the onset of the pup retrieval response and nest building. Pregnant female rats were implanted with bilateral cannulae in the mPOA on day 12 of pregnancy and, on day 16, the females were hysterectomised and ovariectomised and given 200 μg/kg of oestradiol benzoate. Two days later, the females received one of the following intracerebral drug treatments: GABA_B agonist baclofen (200 ng); GABA_B antagonist phaclofen (1 μg); GABA_A antagonist bicuculline (60 ng); or physiological saline. Five minutes after intracerebral infusion, three foster pups were introduced into the females' home cage. The subjects were observed for pup grouping (retrieval) during 15 min, after which the pups were left with the female. During the next 12 h, an observation was made every 1 h to determine whether the pups had been grouped (retrieved) or not. The GABA_B agonist baclofen reduced the proportion of females retrieving pups from 4 to 8 h following pup introduction. By contrast, both the GABA_A antagonist bicuculline and the GABA_B antagonist phaclofen enhanced the proportion of females retrieving pups during the first 3 h of observation. The latency to pup retrieval in subjects treated with the GABA_B agonist baclofen was significantly longer than that in subjects given any of the antagonists. All females built a nest but baclofen reduced nest quality. These data show that activation of GABA_B receptors in the mPOA has an inhibitory effect on basic maternal behaviours, whereas blockade of either the GABA_A or GABA_B receptor facilitates pup retrieval. It is possible that reduced GABAergic tone in the mPOA is a key element in the initiation of maternal behaviours in postparturient rats.

Estradiol in the Preoptic Area Regulates the Dopaminergic Response to Cocaine in the Nucleus Accumbens

The sex-steroid hormone estradiol (E2) enhances the psychoactive effects of cocaine, as evidenced by clinical and preclinical studies. The medial preoptic area (mPOA), a region in the hypothalamus, is a primary neural locus for neuroendocrine integration, containing one of the richest concentrations of estrogen receptors in the CNS and also has a key role in the regulation of naturally rewarding behaviors. However, whether estradiol enhances the neurochemical response to cocaine by acting in the mPOA is still unclear. Using neurotoxic lesions and microdialysis, we examined whether the mPOA modulates cocaine-induced neurochemical activity in the nucleus accumbens. Tract tracing and immunohistochemical staining were used to determine whether projections from the mPOA to the ventral tegmental area (VTA) are sensitive to estrogen signaling. Finally, estradiol microinjections followed by microdialysis were used to determine whether estrogenic signaling in the mPOA modulates cocaine-induced changes of dopamine in the nucleus accumbens. Results showed that lesions of the mPOA or microinjections of estradiol directly into the mPOA increased cocaine-induced release of dopamine in the nucleus accumbens. Immunohistochemical analyses revealed that the mPOA modulates cocaine responsiveness via projections to both dopaminergic and GABAergic neurons in the VTA, and that these projections are sensitive to estrogenic stimulation. Taken together, these findings point to a novel estradiol-dependent pathway that modulates cocaine-induced neurochemical activity in the mesolimbic system.

Neuroanatomical and neurochemical basis of parenting: Dynamic coordination of motivational, affective and cognitive processes

This article is part of a Special Issue "Parental Care". Becoming a parent is arguably the most profound transforming experience in life. It is also inherently very emotionally and physically demanding, such that the reciprocal interaction with the young changes the brain and behavior of the parents. In this review, we examine the neurobiological mechanisms of parenting primarily discussing recent research findings in rodents and primates, especially humans. We argue that it is essential to consider parenting within a conceptual framework that recognizes the dynamics of the reciprocal mother-young relationship, including both the complexity and neuroplasticity of its underlying mechanisms. Converging research suggests that the concerted activity of a distributed network of subcortical and cortical brain structures regulates different key aspects of parenting, including the sensory analysis of infant stimuli as well as motivational, affective and cognitive processes. The interplay among these processes depends on the action of various neurotransmitters and hormones that modulate the timely and coordinated execution of caregiving responses of the maternal circuitry exquisitely attuned to the young's affect, needs and developmental stage. We conclude with a summary and a set of questions that may guide future research.

Common and divergent psychobiological mechanisms underlying maternal behaviors in non-human and human mammals

Maternal interactions with young occupy most of the reproductive period for female mammals and are absolutely essential for offspring survival and development. The hormonal, sensory, reward-related, emotional, cognitive and neurobiological regulators of maternal caregiving behaviors have been well studied in numerous subprimate mammalian species, and some of the importance of this body of work is thought to be its relevance for understanding similar controls in humans. We here review many of the important biopsychological influences on maternal behaviors in the two best studied non-human animals, laboratory rats and sheep, and directly examine how the conceptual framework established by some of the major discoveries in these animal "models" do or do not hold for our understanding of human mothering. We also explore some of the limits for extrapolating from non-human animals to humans. We conclude that there are many similarities between non-human and human mothers in the biological and psychological factors influencing their early maternal behavior and that many of the differences are due to species-characteristic features related to the role of hormones, the relative importance of each sensory system, flexibility in what behaviors are exhibited, the presence or absence of language, and the complexity of cortical function influencing caregiving behaviors.

Emotion and mood adaptations in the peripartum female:complementary contributions of GABA and oxytocin

Peripartum hormones and sensory cues from young modify the maternal brain in ways that can render females either at risk for, or resilient to, elevated anxiety and depression. The neurochemical systems underlying these aspects of maternal emotional and mood states include the inhibitory neurotransmitter GABA and the neuropeptide oxytocin (OXT). Data from laboratory rodents indicate that increased activity at the GABA(A) receptor contributes to the postpartum suppression of anxiety-related behaviour that is mediated by physical contact with offspring, whereas dysregulation in GABAergic signalling results in deficits in maternal care, as well as anxiety- and depression-like behaviours during the postpartum period. Similarly, activation of the brain OXT system accompanied by increased OXT release within numerous brain sites in response to reproductive stimuli also reduces postpartum anxiety- and depression-like behaviours. Studies of peripartum women are consistent with these findings in rodents. Given the similar consequences of elevated central GABA and OXT activity on maternal anxiety and depression, balanced and partly reciprocal interactions between these two systems may be essential for their effects on maternal emotional and mood states, in addition to other aspects of postpartum behaviour and physiology.

Preoptic inputs and mechanisms that regulate maternal responsiveness

The preoptic area is a well-established centre for the control of maternal behaviour. An intact medial preoptic area (mPOA) is required for maternal responsiveness because lesion of the area abolishes maternal behaviours. Although hormonal changes in the peripartum period contribute to the initiation of maternal responsiveness, inputs from pups are required for its maintenance. Neurones are activated in different parts of the mPOA in response to pup exposure. In the present review, we summarise the potential inputs to the mPOA of rodent dams from the litter that can activate mPOA neurones. The roles of potential indirect effects through increased prolactin levels, as well as neuronal inputs to the preoptic area, are described. Recent results on the pathway mediating the effects of suckling to the mPOA suggest that neurones containing the neuropeptide tuberoinfundibular peptide of 39 residues in the posterior thalamus are candidates for conveying the suckling information to the mPOA. Although the molecular mechanism through which these inputs alter mPOA neurones to support the maintenance of maternal responding is not yet known, altered gene expression is a likely candidate. Here, we summarise gene expression changes in the mPOA that have been linked to maternal behaviour and explore the idea that chromatin remodelling during mother-infant interactions mediates the long-term alterations in gene expression that sustain maternal responding.

c-Fos expression in the paternal mouse brain induced by communicative interaction with maternal mates

BACKGROUND

Appropriate parental care by fathers greatly facilitates health in human family life. Much less is known from animal studies regarding the factors and neural circuitry that affect paternal behavior compared with those affecting maternal behavior. We recently reported that ICR mouse sires displayed maternal-like retrieval behavior when they were separated from pups and caged with their mates (co-housing) because the sires receive communicative interactions via ultrasonic and pheromone signals from the dams. We investigated the brain structures involved in regulating this activity by quantifying c-Fos-immunoreactive cells as neuronal activation markers in the neural pathway of male parental behavior.

RESULTS

c-Fos expression in the medial preoptic area (mPOA) was significantly higher in sires that exhibited retrieval behavior (retrievers) than those with no such behavior (non-retrievers). Identical increased expression was found in the mPOA region in the retrievers stimulated by ultrasonic vocalizations or pheromones from their mates. Such increases in expression were not observed in the ventral tegmental area (VTA), nucleus accumbens (NAcc) or ventral palladium (VP). On the following day that we identified the families of the retrievers or non-retrievers, c-Fos expression in neuronal subsets in the mPOA, VTA, NAcc and VP was much higher in the retriever sires when they isolated together with their mates in new cages. This difference was not observed in the singly isolated retriever sires in new cages. The non-retriever sires did not display expression changes in the four brain regions that were assessed.

CONCLUSION

The mPOA neurons appeared to be activated by direct communicative interactions with mate dams, including ultrasonic vocalizations and pheromones. The mPOA-VTA-NAcc-VP neural circuit appears to be involved in paternal retrieval behavior.

Melanin-concentrating hormone in the medial preoptic area reduces active components of maternal behavior in rats

Melanin-concentrating hormone (MCH) is an inhibitory neuropeptide mainly synthesized in neurons of the lateral hypothalamus and incerto-hypothalamic area of mammals that has been implicated in behavioral functions related to motivation. During lactation, this neuropeptide is also expressed in the medial preoptic area (mPOA), a key region of the maternal behavior circuitry. Notably, whereas MCH expression in the mPOA progressively increases during lactation, maternal behavior naturally declines, suggesting that elevated MCHergic activity in the mPOA inhibit maternal behavior in the late postpartum period. To explore this idea, we assessed the maternal behavior of early postpartum females following bilateral microinfusions of either MCH (50 and 100 ng/0.2 μl/side) or the same volume of vehicle into the mPOA. As expected, females receiving 100 ng MCH into the mPOA exhibited significant deficits in the active components of maternal behavior, including retrieving and nest building. In contrast, nursing, as well as other behaviors, including locomotor activity, exploration, and anxiety-like behavior, were not affected by intra-mPOA MCH infusion. The present results, together with previous findings showing elevated expression of this neuropeptide toward the end of the postpartum period, suggest that modulation of mPOA function by MCH may contribute to the weaning of maternal responsiveness characteristic of the late postpartum period.

Impaired GABAB receptor signaling dramatically up-regulates Kiss1 expression selectively in nonhypothalamic brain regions of adult but not prepubertal mice

Kisspeptin, encoded by Kiss1, stimulates reproduction and is synthesized in the hypothalamic anteroventral periventricular and arcuate nuclei. Kiss1 is also expressed at lower levels in the medial amygdala (MeA) and bed nucleus of the stria terminalis (BNST), but the regulation and function of Kiss1 there is poorly understood. γ-Aminobutyric acid (GABA) also regulates reproduction, and female GABAB1 receptor knockout (KO) mice have compromised fertility. However, the interaction between GABAB receptors and Kiss1 neurons is unknown. Here, using double-label in situ hybridization, we first demonstrated that a majority of hypothalamic Kiss1 neurons coexpress GABAB1 subunit, a finding also confirmed for most MeA Kiss1 neurons. Yet, despite known reproductive impairments in GABAB1KO mice, Kiss1 expression in the anteroventral periventricular and arcuate nuclei, assessed by both in situ hybridization and real-time PCR, was identical between adult wild-type and GABAB1KO mice. Surprisingly, however, Kiss1 levels in the BNST and MeA, as well as the lateral septum (a region normally lacking Kiss1 expression), were dramatically increased in both GABAB1KO males and females. The increased Kiss1 levels in extrahypothalamic regions were not caused by elevated sex steroids (which can increase Kiss1 expression), because circulating estradiol and testosterone were equivalent between genotypes. Interestingly, increased Kiss1 expression was not detected in the MeA or BNST in prepubertal KO mice of either sex, indicating that the enhancements in extrahypothalamic Kiss1 levels initiate during/after puberty. These findings suggest that GABAB signaling may normally directly or indirectly inhibit Kiss1 expression, particularly in the BNST and MeA, and highlight the importance of studying kisspeptin populations outside the hypothalamus.

Genes showing altered expression in the medial preoptic area in the highly social maternal phenotype are related to autism and other disorders with social deficits

Background

The mother-child relationship is the most fundamental social bond in mammals, and previous studies indicate that the medial preoptic area (MPOA) contributes to this increase in sociability. It is possible that the same genes that lead to elevated sociability in one condition (the maternal state) might also be dysregulated in some disorders with social deficits (e.g. autism). In this study, we examined whether there was enrichment (greater than chance overlap) for social deficit disorder related genes in MPOA microarray results between virgin and postpartum female mice. We utilized microarrays to assess large scale gene expression changes in the MPOA of virgin and postpartum mice. The Modular Single Set Enrichment Test (MSET) was used to determine if mental health disorder related genes were enriched in significant microarray results. Additional resources, such as ToppCluster, NIH DAVID, and weighted co-expression network analysis (WGCNA) were used to analyze enrichment for specific gene clusters or indirect relationships between significant genes of interest. Finally, a subset of microarray results was validated using quantitative PCR.

Results

Significant postpartum MPOA microarray results were enriched for multiple disorders that include social deficits, including autism, bipolar disorder, depression, and schizophrenia. Together, 98 autism-related genes were identified from the significant microarray results. Further, ToppCluser and NIH DAVID identified a large number of postpartum genes related to ion channel activity and CNS development, and also suggested a role for microRNAs in regulating maternal gene expression. WGCNA identified a module of genes associated with the postpartum phenotype, and identified indirect links between transcription factors and other genes of interest.

Conclusion

The transition to the maternal state involves great CNS plasticity and increased sociability. We identified multiple novel genes that overlap between the postpartum MPOA (high sociability) and mental health disorders with low sociability. Thus, the activity or interactions of the same genes may be altering social behaviors in different directions in different conditions. Maternity also involves elevated risks for disorders, including depression, psychosis, and BPD, so identification of maternal genes common to these disorders may provide insights into the elevated vulnerability of the maternal brain.

Thalamic neuropeptide mediating the effects of nursing on lactation and maternal motivation

Nursing has important physiological and psychological consequences on mothers during the postpartum period. Tuberoinfundibular peptide of 39 residues (TIP39) may contribute to its effects on prolactin release and maternal motivation. Since TIP39-containing fibers and the receptor for TIP39, the parathyroid hormone 2 receptor (PTH2 receptor) are abundant in the arcuate nucleus and the medial preoptic area, we antagonized TIP39 action locally to reveal its actions. Mediobasal hypothalamic injection of a virus encoding an antagonist of the PTH2 receptor markedly decreased basal serum prolactin levels and the suckling-induced prolactin release. In contrast, injecting this virus into the preoptic area had no effect on prolactin levels, but did dampen maternal motivation, judged by reduced time in a pup-associated cage during a place preference test. In support of an effect of TIP39 on maternal motivation, we observed that TIP39 containing fibers and terminals had the same distribution within the preoptic area as neurons expressing Fos in response to suckling. Furthermore, TIP39 terminals closely apposed the plasma membrane of 82% of Fos-ir neurons. Retrograde tracer injected into the arcuate nucleus and the medial preoptic area labeled TIP39 neurons in the posterior intralaminar complex of the thalamus (PIL), indicating that these cells but not other groups of TIP39 neurons project to these hypothalamic regions. We also found that TIP39 mRNA levels in the PIL markedly increased around parturition and remained elevated throughout the lactation period, demonstrating the availability of the peptide in postpartum mothers. Furthermore, suckling, but not pup exposure without physical contact, increased Fos expression by PIL TIP39 neurons. These results indicate that suckling activates TIP39 neurons in the PIL that affect prolactin release and maternal motivation via projections to the arcuate nucleus and the preoptic area, respectively.

Maternal Separation during Breastfeeding Induces Gender-Dependent Changes in Anxiety and the GABA-A Receptor Alpha-Subunit in Adult Wistar Rats

Different models of rodent maternal separation (MS) have been used to investigate long-term neurobiological and behavioral changes, associated with early stress. However, few studies have involved the analysis of sex-related differences in central anxiety modulation. This study investigated whether MS during breastfeeding affected adult males and females in terms of anxiety and brain GABA-A receptor-alpha-subunit immunoreactivity. The brain areas analyzed were the amygdale (AM), hippocampus (HP), medial prefrontal cortex (mPFC), medial preoptic area (POA) and paraventricular nucleus (PVN). Rats were housed under a reversed light/dark cycle (lights off at 7∶00 h) with access to water and food ad libitum. Animals underwent MS twice daily during the dark cycle from postnatal day 1 to postnatal day 21. Behavior was tested when rats were 65-70 days old using the elevated plus maze and after brains were treated for immunohistochemistry. We found that separated females spent more time in the open arms and showed more head dipping behavior compared with controls. The separated males spent more time in the center of the maze and engaged in more stretching behavior than the controls. Immunohistochemistry showed that separated females had less immunostained cells in the HP, mPFC, PVN and POA, while separated males had fewer immunolabeled cells in the PFC, PVN and AM. These results could indicate that MS has gender-specific effects on anxiety behaviors and that these effects are likely related to developmental alterations involving GABA-A neurotransmission.

Effects of noradrenergic alpha-2 receptor antagonism or noradrenergic lesions in the ventral bed nucleus of the stria terminalis and medial preoptic area on maternal care in female rats

RATIONALE

Maternal behavior in laboratory rats requires a network of brain structures including the ventral bed nucleus of the stria terminalis (BSTv) and medial preoptic area (mPOA). Neurotransmitter systems in the BSTv and mPOA influencing maternal behaviors are not well understood, although norepinephrine is an excellent candidate because the BSTv contains the densest noradrenergic fiber plexus in the forebrain and norepinephrine in the mPOA is known to influence other female reproductive functions.

OBJECTIVES

We hypothesized that downregulated noradrenergic activity in the BSTv and mPOA is necessary for mothering.

METHODS

Postpartum mother-litter interactions were observed after BSTv infusion of yohimbine (an α2 autoreceptor antagonist that increases norepinephrine release), and after BSTv or mPOA infusion of the more selective α2 autoreceptor antagonist idazoxan. Lastly, noradrenergic input to the BSTv/mPOA was selectively lesioned in nulliparous rats with anti-DBH-saporin to determine if this would facilitate mothering.

RESULTS

BSTv yohimbine almost abolished retrieval of pups but did not significantly affect dams' ability to initiate contact, lick, or nurse them. BSTv idazoxan disrupted retrieval somewhat less than yohimbine, but significantly reduced nursing. mPOA idazoxan impaired retrieval more severely than that found after BSTv infusion. Anti-DBH-saporin almost eliminated noradrenergic terminals in the BSTv and reduced them by over 60% in the mPOA, but did not promote maternal responding. It also did not affect females' anxiety-related behavior.

CONCLUSIONS

Downregulated noradrenergic activity in the BSTv and mPOA is necessary for postpartum maternal behavior in rats, but eliminating this system alone is insufficient to promote maternal behaviors in nulliparous females.

Experience-facilitated improvements in pup retrieval; evidence for an epigenetic effect

The quality and quantity of maternal care received during infancy are highly predictive of successful infant development. It has been well established, primarily in rats, that the combination of hormonal and infant stimuli at birth modifies neural circuits that regulate maternal responsiveness. During subsequent interactions, infant stimuli are more likely to elicit rapid maternal responsiveness. Some species, such as humans, can display maternal care in the absence of the endocrine events of pregnancy and birth. Similarly, virgin C57BL/6J female mice, display maternal care toward infants, and experience with infants elicits long-lasting increases in maternal care. We hypothesized that these experience-induced changes in behavior may be mediated by chromatin modifications, which in turn change expression of genes that promote maternal care. One site of action is the medial preoptic area (MPOA). To test our hypothesis we treated virgin female mice with sodium butyrate, a histone deacetylase inhibitor. This treatment potentiated maternal responsiveness as well as the expression of several genes: estrogen receptor β (Esr2), oxytocin (Oxt), and cyclicAMP response element binding protein (CREB) binding protein (Crebbp; a histone acetyltransferase) in the MPOA. These data suggest that experience induces high levels of maternal care via epigenetic modifications.

Functional mapping of the neural circuitry of rat maternal motivation: effects of site-specific transient neural inactivation

The present review focuses on recent studies from our laboratory examining the neural circuitry subserving rat maternal motivation across postpartum. We employed a site-specific neural inactivation method by infusion of bupivacaine to map the maternal motivation circuitry using two complementary behavioural approaches: unconditioned maternal responsiveness and choice of pup- over cocaine-conditioned incentives in a concurrent pup/cocaine choice conditioned place preference task. Our findings revealed that, during the early postpartum period, distinct brain structures, including the medial preoptic area, ventral tegmental area and medial prefrontal cortex infralimbic and anterior cingulate subregions, contribute a pup-specific bias to the motivational circuitry. As the postpartum period progresses and the pups grow older, it is further revealed that maternal responsiveness becomes progressively less dependent on the medial preoptic area and medial prefrontal cortex infralimbic activity, and more distributed in the maternal circuitry, such that additional network components, including the medial prefrontal cortex prelimbic subregion, are recruited with maternal experience, and contribute to the expression of late postpartum maternal behaviour. Collectively, our findings provide strong evidence that the remarkable ability of postpartum females to successfully care for their developing infants is subserved by a distributed neural network that carries out efficient and dynamic processing of complex, constantly changing incoming environmental and pup-related stimuli, ultimately allowing the progression of appropriate expression and waning of maternal responsiveness across the postpartum period.

Oestrogen-independent, experience-induced maternal behaviour in female mice

Nulliparous female mice that have not experienced mating, pregnancy or parturition show near immediate spontaneous maternal behaviour when presented with foster pups. The fact that virgin mice display spontaneous maternal behaviour indicates that the hormonal events of pregnancy and parturition are not necessary to produce a rapid onset of maternal behaviour in mice. However, it is not known how similar maternal behaviour is between virgin and lactating mice. In the present study, we show that naturally postpartum females are faster to retrieve pups and spend more time crouching over pups than spontaneously maternal virgin females, and that these differences diminish with increased maternal experience. Moreover, 4 days of experience with pups induced pup retrieval on a novel T-maze. Furthermore, the effects of experience on subsequent maternal responsiveness are not dependent on gonadal hormones because ovariectomised females with 4 days of pup experience show pup retrieval on a novel T-maze similar to that of postpartum mice. Four days of maternal experience also induced T-maze pup retrieval in ovariectomised aromatase knockout female mice that was not significantly different from the maternal responsiveness of ovariectomised wild-type littermates. These data suggest that maternal experience can induce maternal behaviour in females that have never been exposed to oestradiol at any time in development or adulthood. Finally, ovariectomised pup-experienced females continue to retrieve pups on a novel T-maze 1 month after the initial experience, suggesting that, even in the absence of oestradiol, maternal experience produces long-lasting modifications in maternal responsiveness.

Mother-pup interactions during a short olfactory deprivation period in young rats

The effects of short-term bilateral naris occlusion (inducing olfactory deprivation) on mother-pup interactions, suckling behavior and hormonal status during post-natal development in Wistar rats were studied. Bilateral naris occlusion was performed on 8-day-old rat pups and its effects were evaluated at Day 9 and at Day 15. The narins opened spontaneously between Day 12 and 14. Olfactory-deprived pups exhibited a greater level of corticosterone at both ages versus untreated or sham animals. Olfactory deprivation via naris occlusion, in young rats, alters mother-pup interactions with a decrease in the duration of mother-pup retrieving and an increase in pup licking. Olfactory-deprived pups showed also a lower mean duration of nursing and a decrease in nipple attachment, which appeared related to difficulties in finding the nipple. Olfactory-deprived pups had difficulty recognizing their nest. These behavioral alterations were accompanied by a diminution in milk ingested and growth retardation associated with a reduced level of thyroxin at both 9 and 15 days of age.

GABA(A) receptor signaling in the lateral septum regulates maternal aggression in mice

Maternal aggression (maternal defense) is a fierce aggression produced by lactating females toward intruders that plays an important role in protection of vulnerable offspring. Enhancement of GABA(A) receptor signaling by benzodiazepines increases maternal aggression, and we recently found indirect evidence that lateral septum (LS) could be a key site where benzodiazepines elevate aggression. In this study, we directly tested the hypothesis that activation of GABA(A) receptors in LS would promote maternal aggression while inhibition of this receptor would decrease aggression. Site-directed injections to LS were made using the GABA(A) receptor antagonist, bicuculline (3-30 ng), or the GABA(A) receptor agonists, chlordiazepoxide, a benzodiazepine (2.5-5 microg), and muscimol (0.05-5 ng). Maternal aggression and other behavioral measures were then evaluated in lactating mice. Neither GABA(A) receptor agonist elevated aggression, which could reflect a ceiling effect. However, 7 ng of the GABA(A) receptor antagonist, bicuculline, in LS significantly decreased maternal aggression without altering other maternal behaviors or light-dark box performance, suggesting some GABA(A) receptor signaling in LS is required for full maternal aggression expression. Together, these results confirm a role for GABA(A) receptor signaling in LS in the regulation of maternal aggression.

The changing role of the medial preoptic area in the regulation of maternal behavior across the postpartum period: facilitation followed by inhibition

Maternal behavior in rats undergoes considerable plasticity in parallel to the developmental stage of the pups, resulting in distinct patterns of maternal behavior and care at different postpartum time points. The medial preoptic area (mPOA) of the hypothalamus is one critical neural substrate underlying the onset and early expression of maternal behavior in rats but little is known about its specific functional role in the evolving expression of maternal behavior across the postpartum period. The present study uses a reversible local neural inactivation method to examine the role of the mPOA in the regulation of maternal behavior throughout the postpartum period, particularly extending into the late postpartum, a little examined period. This approach avoids the compensatory plasticity in CNS that occurs after permanent lesions, and allows the repeated testing of same individuals. Early (PPD7-8) and late (PPD13-14) postpartum maternal behavior was evaluated in female rats following infusions of bupivacaine or vehicle into the mPOA or into control areas. As expected, mPOA inactivation severely but transiently disrupted early postpartum maternal behavior whereas infusion of vehicle or inactivation of adjacent control sites did not. Later in the postpartum period, however, transient mPOA inactivation facilitated the expression of maternal behaviors, highly contrasting the behavioral expression levels characteristic of late postpartum. Results strongly demonstrate that the mPOA is differentially engaged throughout postpartum in orchestrating appropriate maternal responses with the developmental stage of the pups.

A single injection of 17beta-estradiol at the time of pup presentation promotes the onset of maternal behavior in pregnancy-terminated rats

Female rats that are hysterectomized and ovariectomized on day 15 of pregnancy (15HO) and presented with pups 48 h later show maternal behavior after 2 or 3 days of pup exposure. In contrast, if 15HO females are administered (sc) 20 microg/kg of estradiol benzoate (EB) on day 15 of pregnancy after HO, they show near immediate maternal behavior when pups are presented 48 h later. EB has typically been administered on day 15 because of the underlying assumption that EB exerts genomic effects which require a long duration before being expressed in changes in neuronal phenotype. In light of the more recent evidence that estradiol can generate rapid changes in cellular function, we examined whether injection of a water-soluble form of 17beta-estradiol (E(2)) can facilitate maternal behavior in pregnancy-terminated females when it is administered at the time of pup presentation rather than at the time of HO. Female rats treated with 100 microg/kg of E(2) showed a robust facilitation of maternal behavior, requiring a median of 1 day of pup exposure before showing maternal behavior, compared with 3 days in vehicle-treated rats.

Medial preoptic area interactions with dopamine neural systems in the control of the onset and maintenance of maternal behavior in rats

The medial preoptic area (MPOA) and dopamine (DA) neural systems interact to regulate maternal behavior in rats. Two DA systems are involved: the mesolimbic DA system and the incerto-hypothalamic DA system. The hormonally primed MPOA regulates the appetitive aspects of maternal behavior by activating mesolimbic DA input to the shell region of the nucleus accumbens (NAs). DA action on MPOA via the incerto-hypothalamic system may interact with steroid and peptide hormone effects so that MPOA output to the mesolimbic DA system is facilitated. Neural oxytocin facilitates the onset of maternal behavior by actions at critical nodes in this circuitry. DA-D1 receptor agonist action on either the MPOA or NAs can substitute for the effects of estradiol in stimulating the onset of maternal behavior, suggesting an overlap in underlying cellular mechanisms between estradiol and DA. Maternal memory involves the neural plasticity effects of mesolimbic DA activity. Finally, early life stressors may affect the development of MPOA-DA interactions and maternal behavior.

Ethanol exposure during late gestation and nursing in the rat: effects upon maternal care, ethanol metabolism and infantile milk intake

Ethanol experiences, during late gestation as well as during nursing, modify the behavioral dynamics of the dam/pup dyad, and leads to heightened ethanol intake in the offspring. This study focuses on: a) behavioral and metabolic changes in intoxicated dams with previous exposure to ethanol during pregnancy and b) infantile consumption of milk when the dam is either under the effects of ethanol or sober. Pregnant rats received water, 1.0 or 2.0 g/kg ethanol, and were administered with water or ethanol during the postpartum period. Intoxication during nursing disrupted the capability of the dam to retrieve the pups and to adopt a crouching posture. These disruptions were attenuated when dams had exposure to ethanol during pregnancy. Ethanol experiences during gestation did not affect pharmacokinetic processes during nursing, whereas progressive postpartum ethanol experience resulted in metabolic tolerance. Pups suckling from intoxicated dams, with previous ethanol experiences, ingested more milk than did infants suckling from ethanol-intoxicated dams without such experience. Ethanol gestational experience results in subsequent resistance to the drug's disruptions in maternal care. Consequently, better maternal care by an intoxicated dam with ethanol experience during gestation facilitates access of pups to milk which could be contaminated with ethanol.

Circulating prolactin, MPOA prolactin receptor expression and maternal aggression in lactating rats

Maternal aggression is most intense in lactating rats from the 3rd to the 12th day postpartum. The purpose of this study was to determine if plasma prolactin (PRL) and prolactin receptor (PRL-R(L)) mRNA expression in the medial preoptic area (MPOA) of lactating rats are altered in association with maternal aggression. Lactating Sprague Dawley rats were divided into five groups and exposed for 10 min to an intruder male or to an object on postpartum day 8. Trunk blood and the brain of the dams were collected 30 or 240 min after exposure and from a non-exposed group. Lower levels of prolactin were found 30 min after the aggression test. No change was detected in the number of cells expressing PRL-R(L) mRNA by in situ hybridization histochemistry (ISHH) as a function of testing. However, the correlation between plasma PRL and PRL-R(L) mRNA expression in the mothers changed from positive in control females to negative in intruder exposed animals. These data support the concept that a maternal aggressive experience, while acutely altering PRL secretion, fails to affect PRL-R(L) mRNA expression.

Curt Richter and the female rat

Richter fully appreciated the fundamental biological importance of sex differences, in particular the challenges of female reproductive function to the two classes of behavior that most engaged him, endogenous rhythms and "self-regulatory" behaviors. Indeed, his contributions in these areas justify honoring him as one of the founders of behavioral neuroendocrinology. During the 1920s Richter, together with Wang, Kinder and other students, performed elegant phenomenological and mechanistic studies of sex differences in rats' spontaneous locomotor activity, nest building, and food intake. All of these behaviors display rhythms entrained to the ovarian cycle in female rats, and Richter's analyses of them formed the bases of many current areas of behavioral neuroscience. Slightly later, Richter made fundamentally important discoveries related to nutrient self-selection in pregnant and lactating rats, including changes in micronutrient and macronutrient selection. These data played a major role in the development of his concept of behavioral regulation of homeostasis. Unfortunately, some of these discoveries are rarely recalled. This is both historically regrettable and potentially an impediment to contemporary research progress.

GABA enhancement of maternal defense in mice: possible neural correlates

Previous studies have shown that low doses of GABA(A) receptor agonists facilitate maternal defense of offspring (maternal aggression), without significantly affecting other maternal behaviors. In addition, it has been demonstrated that endogenous changes in GABAergic neurotransmission occur in association with lactation. This study investigated the effects of GABA(A) receptor agonist, chlordiazepoxide (CDP), a benzodiazepine (BDZ), on maternal behaviors including aggression, and identified brain regions with altered activity in association with treatment. Another aim of the study was to determine whether CDP injections could prevent decreases in maternal aggression that occur with pup separation. Intraperitoneal injections of 1 mg/kg of CDP significantly increased maternal defense without affecting other maternal behaviors, although a trend towards elevated nursing was noted. CDP significantly reduced c-Fos in lateral septum (LS) and caudal periaqueductal gray (cPAG) in behaviorally-experienced mice relative to vehicle-injected controls. In behaviorally-naïve subjects, CDP also decreased c-Fos in LS, but in cPAG this decrease was just above significance (p=0.051). CDP was not sufficient to "rescue" maternal aggression when pup stimulus was removed. Overall, these studies provide further insights into the role for GABA in maternal behaviors, including aggression, and how and where BDZs may act to modulate behavior.