Maternal behaviour in lactating rats stimulates c-fos in glutamate decarboxylase-synthesizing neurons of the medial preoptic area, ventral bed nucleus of the stria terminalis, and ventrocaudal periaqueductal gray

Medial preoptic circuits governing instinctive social behaviors

The medial preoptic area (MPOA) has long been implicated in maternal and male sexual behavior. Modern neuroscience methods have begun to reveal the cellular networks responsible, while also implicating the MPOA in other social behaviors, affiliative social touch, and aggression. The social interactions rely on input from conspecifics whose most important modalities in rodents are olfaction and somatosensation. These inputs bypass the cerebral cortex to reach the MPOA to influence the social function. Hormonal inputs also directly act on MPOA neurons. In turn, the MPOA controls social responses via various projections for reward and motor output. The MPOA thus emerges as one of the major brain centers for instinctive social behavior. While key elements of MPOA circuits have been identified, a synthesis of these new data is now provided for further studies to reveal the mechanisms by which the area controls social interactions.

Parental brain through time: The origin and development of the neural circuit of mammalian parenting

This review consolidates current knowledge on mammalian parental care, focusing on its neural mechanisms, evolutionary origins, and derivatives. Neurobiological studies have identified specific neurons in the medial preoptic area as crucial for parental care. Unexpectedly, these neurons are characterized by the expression of molecules signaling satiety, such as calcitonin receptor and BRS3, and overlap with neurons involved in the reproductive behaviors of males but not females. A synthesis of comparative ecology and paleontology suggests an evolutionary scenario for mammalian parental care, possibly stemming from male-biased guarding of offspring in basal vertebrates. The terrestrial transition of tetrapods led to prolonged egg retention in females and the emergence of amniotes, skewing care toward females. The nocturnal adaptation of Mesozoic mammalian ancestors reinforced maternal care for lactation and thermal regulation via endothermy, potentially introducing metabolic gate control in parenting neurons. The established maternal care may have served as the precursor for paternal and cooperative care in mammals and also fostered the development of group living, which may have further contributed to the emergence of empathy and altruism. These evolution-informed working hypotheses require empirical validation, yet they offer promising avenues to investigate the neural underpinnings of mammalian social behaviors.

Sexually dimorphic oxytocin receptor-expressing (OXTR) neurons in the anteroventral periventricular nucleus (AVPV) in the postpartum female mouse are involved in maternal behavior

Maternal care is crucial for the survival and development of offspring. Oxytocin modulates maternal behavior by binding to oxytocin receptors (OXTRs) in various parts of the brain. Previously, we showed that OXTRs are expressed in the anteroventral periventricular nucleus (AVPV) of female, but not male mice. Because the AVPV is involved in the regulation of maternal behavior and oxytocin enhances its induction, this finding leads to the hypothesis that the female specific population of OXTR neurons in the AVPV regulates maternal behavior. To address this hypothesis, OXTR-Venus reporter mice were used to assess if expression levels of OXTR in the AVPV are changed during the postpartum period. The total number of OXTR-Venus neurons was significantly greater in postpartum dams compared to virgin females. To assess efferent projections of the AVPV-OXTR neurons, a Cre-dependent fluorescent protein (tdTomato) expressing a viral vector was injected into one side of the AVPV of female OXTR-Cre mice. Fibers expressing tdTomato were found in hypothalamic areas containing oxytocin neurons (the supraoptic and paraventricular nuclei) and the midbrain areas (the ventral tegmental area and periaqueductal gray) that are involved in the regulation of maternal motivation. To assess if activity of the AVPV-OXTR neurons is involved in the regulation of maternal behaviors, a chemogenetic approach was employed. Specific inhibition of activity of AVPV-OXTR neurons completely abolished pup retrieval and nest building behaviors. Collectively, these findings demonstrate that AVPV-OXTR neurons in postpartum female mice constitute an important node in the neural circuitry that regulates maternal behavior.

Enhanced pup retrieval behaviour in a mouse model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy to affect women of reproductive-age world-wide. Hyperandrogenism is both a hallmark feature of PCOS, and is hypothesised to be an underlying mechanism driving the development of the condition in utero. With circulating hormones known to profoundly influence maternal responses in females, we aimed to determine whether maternal behaviour is altered in a well-described prenatally androgenised (PNA) mouse model of PCOS. Mouse dams were administered with dihydrotestosterone or vehicle on days 16, 17 and 18 of pregnancy. Maternal responses were assessed in both the dihydrotestosterone-injected dams following parturition and in their adult female PNA offspring. Exposure of dams to excess androgens during late pregnancy had no detrimental effects on pregnancy outcomes, including gestation length, pup survival and gestational weight gain, or on subsequent maternal behaviour following parturition. By contrast, PNA virgin females, modelling PCOS, exhibited enhanced maternal behaviour when tested in an anxiogenic novel cage environment, with females rapidly retrieving pups and nesting with them. In comparison, most control virgin females failed to complete this retrieval task in the anxiogenic environment. Assessment of progesterone receptor and oestrogen receptor α immunoreactivity in the brains of virgin PNA and control females revealed increased numbers of oestrogen receptor α positive cells in the brains of PNA females in regions well known to be important for maternal behaviour. This suggests that increased oestrogenic signalling in the neural circuit that underlies maternal behaviour may be a possible mechanism by which maternal behaviour is enhanced in PNA female mice.

Electrophysiological characterization of medial preoptic neurons in lactating rats and its modulation by hypocretin-1

The medial preoptic area (mPOA) undergoes through neuroanatomical changes across the postpartum period, during which its neurons play a critical role in the regulation of maternal behavior. In addition, this area is also crucial for sleep-wake regulation. We have previously shown that hypocretins (HCRT) within the mPOA facilitate active maternal behaviors in postpartum rats, while the blockade of endogenous HCRT in this area promotes nursing and sleep. To explore the mechanisms behind these HCRT actions, we aimed to evaluate the effects of juxta-cellular HCRT-1 administration on mPOA neurons in urethane-anesthetized postpartum and virgin female rats. We recorded mPOA single units and the electroencephalogram (EEG) and applied HCRT-1 juxta-cellular by pressure pulses. Our main results show that the electrophysiological characteristics of the mPOA neurons and their relationship with the EEG of postpartum rats did not differ from virgin rats. Additionally, neurons that respond to HCRT-1 had a slower firing rate than those that did not. In addition, administration of HCRT increased the activity in one group of neurons while decreasing it in another, both in postpartum and virgin rats. The mechanisms by which HCRT modulate functions controlled by the mPOA involve different cell populations.

Effects of music exposure during pregnancy on maternal behavior in mother rats

Several studies have demonstrated the possibility of positive effects of exposure to music during pregnancy on mental function in humans and animals. Although there remains a core belief in the positive effects of music during pregnancy, the underlying neurobehavioral mechanisms of these effects remain unknown. In this study, we aimed to clarify the relationship between maternal nurturing behavior and the oxytocinergic system to elucidate the effect of music on mental health during pregnancy in an experimental investigation using animal models. Pregnant rats were exposed to Mozart sonatas, and their nurturing behavior after delivery was assessed using behavioral analyses. The neural activities of the oxytocinergic system, which are associated with nurturing behavior, were investigated using FosB immunohistochemistry. Music during pregnancy significantly increased the licking behavior of mothers towards pups, which is representative of positive nurturing behavior. In contrast, this alteration in maternal behavior was shown to have no marked effect on the structure or activity of the oxytocinergic system. This study provided possible evidence that exposure to music during pregnancy had a positive effect on postnatal maternal behavior. The results also suggest that the oxytocinergic system, considered a strong candidate for the neural system that regulates maternal behavior, may not be associated with this behavioral change. Understanding the relationship between other neural systems, physiological responses, and nurturing behaviors will provide a more comprehensive explanation of the mechanisms by which music exposure during pregnancy has a positive effect on mental health.

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Pregnant rats were exposed to Mozart sonatas and their nurturing behavior was investigated.

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Exposure to music during pregnancy has a positive effect on postnatal maternal behavior.

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Maternal behavior had no marked effect on the structure or activity of the oxytocinergic neurons.

Role of Hypocretin in the Medial Preoptic Area in the Regulation of Sleep, Maternal Behavior and Body Temperature of Lactating Rats

Hypocretins (HCRT), also known as orexins, includes two neuroexcitatory peptides, HCRT-1 and HCRT-2 (orexin A y B, respectively), synthesized by neurons located in the postero-lateral hypothalamus, whose projections and receptors are widely distributed throughout the brain, including the medial preoptic area (mPOA). HCRT have been associated with a wide range of physiological functions including sleep-wake cycle, maternal behavior and body temperature, all regulated by the mPOA. Previously, we showed that HCRT in the mPOA facilitates certain active maternal behaviors, while the blockade of HCRT-R1 increases the time spent in nursing. As mother rats mainly sleep while they nurse, we hypothesize that HCRT in the mPOA of lactating rats reduce sleep and nursing, while intra-mPOA administration of a dual orexin receptor antagonist (DORA) would cause the opposite effect. Therefore, the aim of this study was to determine the role of HCRT within the mPOA, in the regulation and integration of the sleep-wake cycle, maternal behavior and body temperature of lactating rats. For that purpose, we assessed the sleep-wake states, maternal behavior and body temperature of lactating rats following microinjections of HCRT-1 (100 and 200 µM) and DORA (5 mM) into the mPOA. As expected, our data show that HCRT-1 in mPOA promote wakefulness and a slightly increase in body temperature, whereas DORA increases both NREM and REM sleep together with an increment of nursing and milk ejection. Taken together, our results strongly suggest that the endogenous reduction of HCRT within the mPOA contribute to the promotion of sleep, milk ejection and nursing behavior in lactating rats.

Sex-specific parenting and depression evoked by preoptic inhibitory neurons

The role of preoptic GABAergic inhibitory neurons was addressed in parenting, anxiety and depression. Pup exposure and forced swimming resulted in similar c-Fos activation pattern in neurons expressing vesicular GABA transporter in the preoptic area with generally stronger labeling and different distributional pattern in females than in males. Chemogenetic stimulation of preoptic GABAergic cells resulted in elevated maternal motivation and caring behavior in females and mothers but aggression toward pups in males. Behavioral effects were the opposite following inhibition of preoptic GABAergic neurons suggesting their physiological relevance. In addition, increased anxiety-like and depression-like behaviors were found following chemogenetic stimulation of the same neurons in females, whereas previous pup exposure increased only anxiety-like behavior suggesting that not the pups, but overstimulation of the cells can lead to depression-like behavior. A sexually dimorphic projection pattern of preoptic GABAergic neurons was also identified, which could mediate sex-dependent parenting and associated emotional behaviors.

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Preoptic GABAergic neurons promote maternal behaviors in females mice

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Activation of preoptic GABAergic neurons induces pup-directed aggression in males

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Projection pattern of preoptic GABAergic neurons is sexually dimorphic

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Depression-like behaviors are provoked by stimulation of preoptic GABAergic neurons

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.

Changes in maternal motivation across reproductive states in mice: A role for prolactin receptor activation on GABA neurons

The survival of newborn offspring in mammals is dependent on sustained maternal care. Mammalian mothers are highly motivated to interact with and care for offspring, however, it is unclear how hormonal signals act on neural circuitry to promote maternal motivation during the transition to motherhood. In this study we aimed to establish methods that enable us to evaluate change in maternal motivation across the reproductive life cycle in female mice. Using two behavioural testing paradigms; a novel T-maze retrieval test and a barrier climbing test, we found that pup retrieval behaviour was low in virgin and pregnant mice compared to lactating females, indicating that maternal motivation arises around the time of parturition. Furthermore, in reproductively experienced females, maternal motivation declined over time after weaning of pups. As we have previously shown that lactogenic action mediated through the prolactin receptor (Prlr) in the medial preoptic area (MPOA) is essential for the expression of maternal behaviour, we aimed to investigate the role of lactogenic hormones in promoting pup-related motivational behaviours. With GABAergic neurons expressing Prlr in multiple brain regions important for maternal behaviour, we conditionally deleted Prlr from GABA neurons. Compared to control females, lactating GABA neuron-specific Prlr knockout mice showed slower and incomplete pup retrieval behaviour in the T-maze test. Testing of anxiety behaviour on an elevated plus maze indicated that these mice did not have increased anxiety levels, suggesting that lactogenic action on GABA neurons is necessary for the full expression of motivational aspects of maternal behaviour during lactation.

Opioid use during pregnancy can impair maternal behavior and the Maternal Brain Network: A literature review

Opioid Use Disorder (OUD) is a global epidemic also affecting women of reproductive age. A standard form of pharmacological treatment for OUD is Opioid Maintenance Therapy (OMT) and buprenorphine has emerged as the preferred treatment for pregnant women with OUD relative to methadone. However, the consequences of BUP exposure on the developing Maternal Brain Network and mother-infant dyad are not well understood. The maternal-infant bond is dependent on the Maternal Brain Network, which is responsible for the dynamic transition from a "nulliparous brain" to a "maternal brain". The Maternal Brain Network consists of regions implicated in maternal care (e.g., medial preoptic area, nucleus accumbens, ventral pallidum, ventral tegmentum area) and maternal defense (e.g., periaqueductal gray). The endogenous opioid system modulates many of the neurochemical changes in these areas during the transition to motherhood. Thus, it is not surprising that exogenous opioid exposure during pregnancy can be disruptive to the Maternal Brain Network. Though less drastic than misused opioids, OMTs may not be without risk of disrupting the neural and molecular structures of the Maternal Brain Network. This review describes the Maternal Brain Network as a framework for understanding how pharmacological differences in exogenous opioid exposure can disrupt the onset and maintenance of the maternal brain and summarizes opioid and OMT (in particular buprenorphine) use in the context of pregnancy and maternal behavior. This review also highlights future directions for evaluating exogenous opioid effects on the Maternal Brain Network in the hopes of raising awareness for the impact of the opioid crisis not only on exposed infants, but also on mothers and subsequent mother-infant bonds.

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.

Fos expression in the medial preoptic area and nucleus accumbens of female Japanese quail (Coturnix japonica) after maternal induction and interaction with chicks

The neural system underlying maternal caregiving has often been studied using laboratory rodents and a few other mammalian species. This research shows that the medial preoptic area (mPOA) integrates sensory cues from the young that, along with hormonal and other environmental signals, control maternal acceptance of neonates. The mPOA then activates the mesolimbic system to drive maternal motivation and caregiving activities. How components of this neural system respond to maternal experience and exposure to young in non-mammals has rarely been examined. To gain more insight into this question, virgin female Japanese quail (Coturnix japonica) were induced to be maternal through four days of continuous exposure to chicks (Maternal), or were not exposed to chicks (Non-Maternal). Chicks were removed overnight from the Maternal group and half the females from each group were then exposed to chicks for 90 minutes (Exposed), or not exposed to chicks (Non-Exposed), before euthanasia. The number of Fos-immunoreactive (Fos-ir) cells was examined as a marker of neuronal activation. As expected, repeated exposure to chicks induced caregiving behavior in the Maternal females, which persisted after the overnight separation, suggesting the formation of a maternal memory. In contrast, Non-Maternal females were aggressive and rejected the chicks when exposed to them. Exposed females, whether or not they were given prior experience with chicks (i.e., regardless if they accepted or rejected chicks during the exposure before euthanasia), had more Fos-ir cells in the mPOA compared to Non-Exposed females. In the nucleus accumbens (NAC), the number of Fos-ir cells was high in all Maternal females whether or not they were Exposed to chicks again before euthanasia. In the lateral bed nucleus of the stria terminalis, a site involved in general stress responding, groups did not differ in the number of Fos-ir cells. These data indicate a conserved role for the mPOA and NAC in maternal caregiving across vertebrates, with the mPOA acutely responding to the salience rather than valence of offspring cues, and the NAC showing longer-term changes in activity after a positive maternal experience even without a recent exposure to young.

Brain orchestration of pregnancy and maternal behavior in mice: A longitudinal morphometric study

Reproduction induces changes within the brain to prepare for gestation and motherhood. However, the dynamic of these central changes and their relationships with the development of maternal behavior remain poorly understood. Here, we describe a longitudinal morphometric neuroimaging study in female mice between pre-gestation and weaning, using new magnetic resonance imaging (MRI) resources comprising a high-resolution brain template, its associated tissue priors (60-µm isotropic resolution) and a corresponding mouse brain atlas (1320 regions of interest). Using these tools, we observed transient hypertrophies not only within key regions controlling gestation and maternal behavior (medial preoptic area, bed nucleus of the stria terminalis), but also in the amygdala, caudate nucleus and hippocampus. Additionally, unlike females exhibiting lower levels of maternal care, highly maternal females developed transient hypertrophies in somatosensory, entorhinal and retrosplenial cortices among other regions. Therefore, coordinated and transient brain modifications associated with maternal performance occurred during gestation and lactation.

The glutamatergic system in the preoptic area is involved in the retention of maternal behavior in maternally experienced female rats

Maternally experienced female rats show high maternal behavior performance for a long time after acquisition of maternal experience, although the mechanisms responsible for the retention of maternal behavior are not well understood. The medial preoptic area (MPOA) plays an important role in the onset and maintenance of maternal behavior in female rats. We aimed to determine whether maternal experience affects the glutamatergic system in the MPOA for the retention of maternal behavior in female rats. First, to determine the effects of maternal experience in the postpartum period on dendritic spines, which are the postsynaptic component of excitatory glutamatergic neurotransmission, we examined the number of dendritic spines on MPOA neurons of primiparous mothers that had experienced mothering until weaning (sufficiently experienced mothers) and of primiparous mothers that were separated from their pups on the day of parturition (insufficiently experienced mothers). The number of mushroom spines, but not other types of spine, was significantly greater in the sufficiently experienced mothers compared with that in the insufficiently experienced mothers. Next, to determine the effects of maternal experience in the postpartum period on the expression of ionotropic glutamate receptors, we measured the mRNA levels of AMPA receptor subunits (GluA1-A4) and NMDA receptor subunits (GluN1, GluN2A-2D) in the MPOA of primiparous female rats that were kept with pups until brain sampling. As a result, we found that the mRNA levels of GluA3 and GluN2B were significantly higher in primiparous females on the day of weaning compared with those in primiparous females on the day of parturition. Additionally, we examined the effects of CNQX, an AMPA receptor antagonist, and MK-801, an NMDA receptor antagonist, injected into the MPOA on maternal behavior in maternally experienced primiparous female rats. Maternal behavioral activity was significantly reduced when CNQX or MK-801 was injected into the MPOA. These findings indicate that long-term maternal experience in the postpartum period up-regulates glutamatergic neurotransmission by increasing the number of mushroom spines and glutamate receptor expression, which may be involved in the retention of maternal behavior in maternally experienced female rats.

Reorganization of perineuronal nets in the medial Preoptic Area during the reproductive cycle in female rats

Perineuronal nets (PNNs) are aggregations of extracellular matrix associated with specific neuronal populations in the central nervous system, suggested to play key roles in neural development, synaptogenesis and experience-dependent synaptic plasticity. Pregnancy and lactation are characterized by a dramatic increase in neuroplasticity. However, dynamic changes in the extracellular matrix associated with maternal circuits have been mostly overlooked. We analyzed the structure of PNNs in an essential nucleus of the maternal circuit, the medial preoptic area (mPOA), during the reproductive cycle of rats, using the Wisteria floribunda (WFA) label. PNNs associated to neurons in the mPOA start to assemble halfway through gestation and become highly organized prior to parturition, fading through the postpartum period. This high expression of PNNs during pregnancy appears to be mediated by the influence of estrogen, progesterone and prolactin, since a hormonal simulated-gestation treatment induced the expression of PNNs in ovariectomized females. We found that PNNs associated neurons in the mPOA express estrogen receptor α and progesterone receptors, supporting a putative role of reproductive hormones in the signaling mechanisms that trigger the assembly of PNNs in the mPOA. This is the first report of PNNs presence and remodeling in mPOA during adulthood induced by physiological variables.

Pharmacological manipulation of DNA methylation normalizes maternal behavior, DNA methylation, and gene expression in dams with a history of maltreatment

The quality of parental care received during development profoundly influences an individual's phenotype, including that of maternal behavior. We previously found that female rats with a history of maltreatment during infancy mistreat their own offspring. One proposed mechanism through which early-life experiences influence behavior is via epigenetic modifications. Indeed, our lab has identified a number of brain epigenetic alterations in female rats with a history of maltreatment. Here we sought to investigate the role of DNA methylation in aberrant maternal behavior. We administered zebularine, a drug known to alter DNA methylation, to dams exposed during infancy to the scarcity-adversity model of low nesting resources, and then characterized the quality of their care towards their offspring. First, we replicate that dams with a history of maltreatment mistreat their own offspring. Second, we show that maltreated-dams treated with zebularine exhibit lower levels of adverse care toward their offspring. Third, we show that administration of zebularine in control dams (history of nurturing care) enhances levels of adverse care. Lastly, we show altered methylation and gene expression in maltreated dams normalized by zebularine. These findings lend support to the hypothesis that epigenetic alterations resulting from maltreatment causally relate to behavioral outcomes.

Sexually dimorphic oxytocin receptor-expressing neurons in the preoptic area of the mouse brain

Oxytocin is involved in the regulation of social behaviors including parental behaviors in a variety of species. Oxytocin triggers social behaviors by binding to oxytocin receptors (OXTRs) in various parts of the brain. OXTRs are present in the preoptic area (POA) where hormone-sensitive sexually dimorphic nuclei exist. The present study was conducted to examine whether sex differences exist in the distribution of neurons expressing OXTRs in the POA. Using OXTR-Venus (an enhanced variant of yellow fluorescent protein) mice, the distribution of OXTR-Venus cells in the POA was compared between sexes. The total number of OXTR-Venus cells in the medial POA (MPOA) was significantly greater in females than in males. No detectable OXTR-Venus cells were observed in the anteroventral periventricular nucleus (AVPV) within the MPOA in most of the brain sections from males. We further examined the total number of OXTR-Venus cells in the AVPV and the rest of the MPOA between the sexes. The total number of OXTR-Venus cells in the AVPV in females (615 ± 43) was significantly greater than that in males (14 ± 2), whereas the total number of OXTR-Venus cells in the rest of the MPOA did not differ significantly between the sexes. Thus, the sexually dimorphic expression of OXTR-Venus specifically occurred in the AVPV, but not in the rest of the MPOA. We also examined whether the expression of OXTR in the AVPV is driven by the female gonadal hormone, estrogen. Immunocytochemistry and single-cell RT-PCR revealed the presence of the estrogen receptor α in OXTR-Venus cells in the female AVPV. Moreover, ovariectomy resulted in the absence of OXTR-Venus expression in the AVPV, whereas estrogen replacement therapy restored OXTR-Venus expression. These results demonstrate that the expression of OXTR in the AVPV is primarily female specific and estrogen dependent. The presence of the sexually dimorphic expression of OXTR in the AVPV suggests the involvement of OXTR neurons in the AVPV in the regulation of female-specific behavior and/or physiology.

Experience-dependent mechanisms in the regulation of parental care

Maternal behavior is a defining characteristic of mammals, which is regulated by a core, conserved neural circuit. However, mothering behavior is not always a default response to infant conspecifics. For example, initial fearful, fragmented or aggressive responses toward infants in laboratory rats and mice can give way to highly motivated and organized caregiving behaviors following appropriate hormone exposure or repeated experience with infants. Therefore hormonal and/or experiential factors must be involved in determining the extent to which infants access central approach and avoidance neural systems. In this review we describe evidence supporting the idea that infant conspecifics are capable of activating distinct neural pathways to elicit avoidant, aggressive and parental responses from adult rodents. Additionally, we discuss the hypothesis that alterations in transcriptional regulation within the medial preoptic area of the hypothalamus may be a key mechanism of neural plasticity involved in programming the differential sensitivity of these neural pathways.

Small cells with big implications: Microglia and sex differences in brain development, plasticity and behavioral health

Brain sex differences are programmed largely by sex hormone secretions and direct sex chromosome effects in early life, and are subsequently modulated by early life experiences. The brain's resident immune cells, called microglia, actively contribute to brain development. Recent research has shown that microglia are sexually dimorphic, especially during early life, and may participate in sex-specific organization of the brain and behavior. Likewise, sex differences in immune cells and their signaling in the adult brain have been found, although in most cases their function remains unclear. Additionally, immune cells and their signaling have been implicated in many disorders in which brain development or plasticity is altered, including autism, schizophrenia, pain disorders, major depression, and postpartum depression. This review summarizes what is currently known about sex differences in neuroimmune function in development and during other major phases of brain plasticity, as well as the current state of knowledge regarding sex-specific neuroimmune function in psychiatric disorders.

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.

A Neural Model of Empathic States in Attachment-Based Psychotherapy

We build on a neuroanatomical model of how empathic states can motivate caregiving behavior, via empathy circuit-driven activation of regions in the hypothalamus and amygdala, which in turn stimulate a mesolimbic-ventral pallidum pathway, by integrating findings related to the perception of pain in self and others. On this basis, we propose a network to capture states of personal distress and (weak and strong forms of) empathic concern, which are particularly relevant for psychotherapists conducting attachment-based interventions. This model is then extended for the case of self-attachment therapy, in which conceptualized components of the self serve as both the source of and target for empathic resonance. In particular, we consider how states of empathic concern involving an other that is perceived as being closely related to the self might enhance the motivation for self-directed bonding (which in turn is proposed to lead the individual toward more compassionate states) in terms of medial prefrontal cortex-mediated activation of these caregiving pathways. We simulate our model computationally and discuss the interplay between the bonding and empathy protocols of the therapy.

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.

Oxytocin modulation of neural circuits for social behavior

Oxytocin is a hypothalamic neuropeptide that has gained attention for the effects on social behavior. Recent findings shed new light on the mechanisms of oxytocin in synaptic plasticity and adaptively modifying neural circuits for social interactions such as conspecific recognition, pair bonding, and maternal care. Here, we review several of these newer studies on oxytocin in the context of previous findings, with an emphasis on social behavior and circuit plasticity in various brain regions shown to be enriched for oxytocin receptors. We provide a framework that highlights current circuit-level mechanisms underlying the widespread action of oxytocin. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 169-189, 2017.

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.

Toward a systems-oriented approach to the role of the extended amygdala in adaptive responding

Research into the structure and function of the basal forebrain macrostructure called the extended amygdala (EA) has recently seen considerable growth. This paper reviews that work, with the objectives of identifying underlying themes and developing a common goal towards which investigators of EA function might work. The paper begins with a brief review of the structure and the ontological and phylogenetic origins of the EA. It continues with a review of research into the role of the EA in both aversive and appetitive states, noting that these two seemingly disparate avenues of research converge on the concept of reinforcement - either negative or positive - of adaptive responding. These reviews lead to a proposal as to where the EA may fit in the organization of the basal forebrain, and an invitation to investigators to place their findings in a unifying conceptual framework of the EA as a collection of neural ensembles that mediate adaptive responding.

Current Models and Future Directions for Understanding the Neural Circuitries of Maternal Behaviors in Rodents

Maternal behaviors in rodents include a number of subcomponents, such as nursing, nest building, licking and grooming of pups, pup retrieval, and maternal aggression. Because each behavior involves a unique motor pattern, a unique ensemble neural circuitry must underlie each behavior. To what extent there is overlap in terms of brain regions and specific neurons for each circuit is being actively investigated. This review will first examine overlapping and separate components of pup retrieval and maternal aggression circuitries while examining a central role for medial preoptic area (MPA) in both behaviors. With an emphasis on experimental approaches, the review will then highlight recent findings and propose future directions for understanding maternal behavior regulation. Finally, examples for why studying the neural basis of maternal behaviors can bring insights to other areas of neuroscience, such as feeding, addiction, and anxiety and aggression regulation will be provided.

Maternally responsive neurons in the bed nucleus of the stria terminalis and medial preoptic area: Putative circuits for regulating anxiety and reward

Postpartum neuropsychiatric disorders are a major source of morbidity and mortality and affect at least 10% of childbearing women. Affective dysregulation within this context has been identified in association with changes in reproductive steroids. Steroids promote maternal actions and modulate affect, but can also destabilize mood in some but not all women. Potential brain regions that mediate these effects include the medial preoptic area (mPOA) and ventral bed nucleus of the stria terminalis (vBNST). Herein, we review the regulation of neural activity in the mPOA/vBNST by environmental and hormonal concomitants in puerperal females. Such activity may influence maternal anxiety and motivation and have significant implications for postpartum affective disorders. Future directions for research are also explored, including physiological circuit-level approaches to gain insight into the functional connectivity of hormone-responsive maternal circuits that modulate affect.

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.

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.

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.

Early undernourishment interferes with the maternal aggressive response triggered by an intruder entering the homing cage

The maternal aggressive response (MAR) against intruders is temporarily expressed during lactation in association with the rearing and protection of offspring to promote their survival and growth in the nest. This normal component of maternal behaviour requires both the hormonal changes occurring at the end of pregnancy and the presence of pups for its establishment. Because early food restriction in the rat results in long-term maternal deficiencies, we analysed in Wistar rats the effects of perinatal undernutrition on the MAR to an intruder at days 1, 4, and 8 postpartum. The data showed that undernourished dams exhibited significant reductions of sniffing frequency on days 4 and 8 and significant increases of biting on day 4 and of lateral attacks on postpartum days 4 and 8. The finding of an altered MAR during the lactating period may be relevant for the survival and long-term behavioural development of the progeny.

Curvilinear relationships between mu-opioid receptor labeling and undirected song in male European starlings (Sturnus vulgaris)

Female-directed communication in male songbirds has been reasonably well studied; yet, relatively little is known about communication in other social contexts. Songbirds also produce song that is not clearly directed towards another individual (undirected song) when alone or in flocks. Although the precise functions of undirected song may differ across species, this type of song is considered important for flock maintenance, song learning or practice. Past studies show that undirected song is tightly coupled to analgesia and positive affective state, which are both mediated by opioid activity. Furthermore, labeling for the opioid met-enkephalin in the medial preoptic nucleus (POM) correlates positively with undirected song production. We propose that undirected song is facilitated and maintained by opioid receptor activity in the POM and other brain regions involved in affective state, analgesia, and social behavior. To provide insight into this hypothesis, we used immunohistochemistry to examine relationships between undirected song and mu-opioid receptors in male starlings. Polynomial regression analyses revealed significant inverted-U shaped relationships between measures of undirected song and mu-opioid receptor labeling in the POM, medial bed nucleus of the stria terminalis (BSTm), and periaqueductal gray (PAG). These results suggest that low rates of undirected song may stimulate and/or be maintained by mu-opioid receptor activity; however, it may be that sustained levels of mu-opioid receptor activity associated with high rates of undirected song cause mu-opioid receptor down-regulation. The results indicate that mu-opioid receptor activity in POM, BSTm, and PAG may underlie previous links identified between undirected song, analgesia, and affective state.

Maternal neglect with reduced depressive-like behavior and blunted c-fos activation in Brattleboro mothers, the role of central vasopressin

Early mother-infant relationships exert important long-term effects in offspring and are disturbed by factors such as postpartum depression. We aimed to clarify if lack of vasopressin influences maternal behavior paralleled by the development of a depressive-like phenotype. We compared vasopressin-deficient Brattleboro mothers with heterozygous and homozygous normal ones. The following parameters were measured: maternal behavior (undisturbed and separation-induced); anxiety by the elevated plus maze; sucrose and saccharin preference and forced swim behavior. Underlying brain areas were examined by c-fos immunocytochemistry among rest and after swim-stress. In another group of rats, vasopressin 2 receptor agonist was used peripherally to exclude secondary changes due to diabetes insipidus. Results showed that vasopressin-deficient rats spend less time licking-grooming their pups through a centrally driven mechanism. There was no difference between genotypes during the pup retrieval test. Vasopressin-deficient mothers tended to explore more the open arms of the plus maze, showed more preference for sucrose and saccharin and struggled more in the forced swim test, suggesting that they act as less depressive. Under basal conditions, vasopressin-deficient mothers had more c-fos expression in the medial preoptic area, shell of nucleus accumbens, paraventricular nucleus of the hypothalamus and amygdala, but not in other structures. In these areas the swim-stress-induced activation was smaller. In conclusion, vasopressin-deficiency resulted in maternal neglect due to a central effect and was protective against depressive-like behavior probably as a consequence of reduced activation of some stress-related brain structures. The conflicting behavioral data underscores the need for more sex specific studies.

Neuroanatomical substrates of the disruptive effect of olanzapine on rat maternal behavior as revealed by c-Fos immunoreactivity

Olanzapine is one of the most widely prescribed atypical antipsychotic drugs in the treatment of schizophrenia. Besides its well-known side effect on weight gain, it may also impair human parental behavior. In this study, we took a preclinical approach to examine the behavioral effects of olanzapine on rat maternal behavior and investigated the associated neural basis using the c-Fos immunohistochemistry. On postpartum days 6-8, Sprague-Dawley mother rats were given a single injection of sterile water or olanzapine (1.0, 3.0 or 5.0mg/kg, sc). Maternal behavior was tested 2h later, after which rats were sacrificed and brain tissues were collected. Ten brain regions that were either implicated in the action of antipsychotic drugs and/or in the regulation of maternal behavior were examined for c-Fos immunoreactivity. Acute olanzapine treatment dose-dependently disrupted various components of maternal behavior (e.g., pup retrieval, pup licking, nest building, crouching) and increased c-Fos immunoreactivity in the medial prefrontal cortex (mPFC), nucleus accumbens shell and core (NAs and NAc), dorsolateral striatum (DLSt), ventral lateral septum (LSv), central amygdala (CeA) and ventral tegmental area (VTA), important brain areas generally implicated in the incentive motivation and reward processing. In contrast, olanzapine treatment did not alter c-Fos in the medial preoptic nucleus (MPN), ventral bed nucleus of the stria terminalis (vBST) and medial amygdala (MeA), the core brain areas directly involved in the mediation of rat maternal behavior. These findings suggest that olanzapine disrupts rat maternal behavior primarily by suppressing incentive motivation and reward processing via its action on the mesocorticolimbic dopamine systems, other limbic and striatal areas, but not by disrupting the core processes involved in the mediation of maternal behavior in particular.

An fMRI study of caring vs self-focus during induced compassion and pride

This study examined neural activation during the experience of compassion, an emotion that orients people toward vulnerable others and prompts caregiving, and pride, a self-focused emotion that signals individual strength and heightened status. Functional magnetic resonance images (fMRI) were acquired as participants viewed 55 s continuous sequences of slides to induce either compassion or pride, presented in alternation with sequences of neutral slides. Emotion self-report data were collected after each slide condition within the fMRI scanner. Compassion induction was associated with activation in the midbrain periaqueductal gray (PAG), a region that is activated during pain and the perception of others' pain, and that has been implicated in parental nurturance behaviors. Pride induction engaged the posterior medial cortex, a region that has been associated with self-referent processing. Self-reports of compassion experience were correlated with increased activation in a region near the PAG, and in the right inferior frontal gyrus (IFG). Self-reports of pride experience, in contrast, were correlated with reduced activation in the IFG and the anterior insula. These results provide preliminary evidence towards understanding the neural correlates of important interpersonal dimensions of compassion and pride. Caring (compassion) and self-focus (pride) may represent core appraisals that differentiate the response profiles of many emotions.

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.

Neuromolecular basis of parental behavior in laboratory mice and rats: with special emphasis on technical issues of using mouse genetics

To support the well-being of the parent-infant relationship, the neuromolecular mechanisms of parental behaviors should be clarified. From neuroanatomical analyses in laboratory rats, the medial preoptic area (MPOA) has been shown to be of critical importance in parental retrieving behavior. More recently, various gene-targeted mouse strains have been found to be defective in different aspects of parental behaviors, contributing to the identification of molecules and signaling pathways required for the behavior. Therefore, the neuromolecular basis of "mother love" is now a fully approachable research field in modern molecular neuroscience. In this review, we will provide a summary of the required brain areas and gene for parental behavior in laboratory mice (Mus musculus) and rats (Rattus norvegicus). Basic protocols and technical considerations on studying the mechanism of parental behavior using genetically-engineered mouse strains will also be presented.

GABAA receptor signaling in caudal periaqueductal gray regulates maternal aggression and maternal care in mice

Maternal aggression (maternal defense) is exhibited by lactating females towards intruders and contributes to the protection of offspring. Enhancement of Gamma-Aminobutyric acid (GABA)(A) receptor signaling by benzodiazepines elevates maternal aggression, and we previously found indirect evidence (via c-Fos immunohistochemistry) that caudal periaqueductal gray (cPAG) and lateral septum (LS) could be sites where benzodiazepines increase aggression. We recently found that GABA(A) receptor signaling in LS modulates maternal aggression, and in this study, we tested the hypothesis that GABA(A) receptor signaling in cPAG also regulates this behavior. Site-directed injections to cPAG were made in lactating mice using the GABA(A) receptor antagonist, bicuculline (3-9 ng) or the GABA(A) receptor positive modulator, chlordiazepoxide (CDP), a benzodiazepine (2.5-20 microg). Maternal aggression, other maternal behaviors, and anxiety-like measures (using the light-dark box) were then examined. GABA(A) receptor positive modulator did not increase aggression, which could have resulted from a ceiling effect. However, 8 ng and 9 ng of bicuculline in cPAG significantly decreased maternal aggression without altering other maternal behaviors or light-dark box performance, suggesting some GABA(A) receptor signaling in cPAG is required for full maternal aggression expression. Additionally, 7 ng of bicuculline significantly increased licking/grooming of pups, and decreased the number of transitions between the light and dark compartments of the light-dark box without affecting aggression. Given these results indicating that antagonizing GABA(A) receptor in cPAG dose-dependently promotes offspring grooming behavior while impairing aggression, it is possible that the cPAG represents a key site for decision making (aggression versus other behaviors) in the lactating female.

c-Fos identification of neuroanatomical sites associated with haloperidol and clozapine disruption of maternal behavior in the rat

Rat maternal behavior is a complex social behavior. Most antipsychotic drugs disrupt active maternal responses (e.g., pup retrieval, pup licking and nest building). Our previous work shows that typical antipsychotic haloperidol disrupts maternal behavior by blocking dopamine D(2) receptors, whereas atypical clozapine works by blocking 5-HT(2A/2C) receptors. The present study used c-Fos immunohistochemistry technique, together with pharmacological tools and behavioral observations, and delineated the neuroanatomical bases of the disruptive effects of haloperidol and clozapine. Postpartum female rats were treated with haloperidol (0.2 mg/kg sc) or clozapine (10.0 mg/kg sc), with or without pretreatment of quinpirole (a selective dopamine D(2)/D(3) agonist, 1.0 mg/kg sc) or 2,5-dimethoxy-4-iodo-amphetamine (DOI, a selective 5-HT(2A/2C) agonist, 2.5 mg/kg sc). They were then sacrificed 2 h later after a maternal behavior test was conducted. Brain regions that have been previously implicated in the regulation of rat maternal behavior and/or in the antipsychotic action were examined. Behaviorally, both haloperidol and clozapine disrupted pup retrieval, pup licking and nest building. Pretreatment of quinpirole, but not DOI, reversed the haloperidol-induced disruptions. In contrast, pretreatment of DOI, but not quinpirole, reversed the clozapine-induced deficits. Neuroanatomically, the nucleus accumbens (both the shell and core), dorsolateral striatum and lateral septum showed increased c-Fos expression to the treatment of haloperidol. In contrast, the nucleus accumbens shell showed increased expression of c-Fos to the treatment of clozapine. More importantly, pretreatment of quinpirole and DOI produced opposite response profiles in the brain regions where haloperidol and clozapine had an effect. Based on these findings, we concluded that haloperidol disrupts active maternal behavior primarily by blocking dopamine D(2) receptors in a neural circuitry involving the nucleus accumbens, dorsolateral striatum and lateral septum. In contrast, clozapine appears to disrupt maternal behavior mainly by blocking serotonin 5-HT(2A/2C) receptors in the nucleus accumbens shell.

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.