Expression of Fos-like immunoreactivity in the preoptic area of maternally behaving virgin and postpartum rats

Activation of lateral preoptic neurons is associated with nest-building in male mice

Nest-building behavior is a widely observed innate behavior. A nest provides animals with a secure environment for parenting, sleep, feeding, reproduction, and temperature maintenance. Since animal infants spend their time in a nest, nest-building behavior has been generally studied as parental behaviors, and the medial preoptic area (MPOA) neurons are known to be involved in parental nest-building. However, nest-building of singly housed male mice has been less examined. Here we show that male mice spent longer time in nest-building at the early to middle dark phase and at the end of the dark phase. These two periods are followed by sleep-rich periods. When a nest was removed and fresh nest material was introduced, both male and female mice built nests at Zeitgeber time (ZT) 6, but not at ZT12. Using Fos-immunostaining combined with double in situ hybridization of Vgat and Vglut2, we found that Vgat- and Vglut2-positive cells of the lateral preoptic area (LPOA) were the only hypothalamic neuron population that exhibited a greater number of activated cells in response to fresh nest material at ZT6, compared to being naturally awake at ZT12. Fos-positive LPOA neurons were negative for estrogen receptor 1 (Esr1). Both Vgat-positive and Vglut2-positive neurons in both the LPOA and MPOA were activated at pup retrieval by male mice. Our findings suggest the possibility that GABAergic and glutamatergic neurons in the LPOA are associated with nest-building behavior in male mice.

Oxytocin Receptor-Expressing Neurons in the Medial Preoptic Area Are Essential for Lactation, whereas Those in the Lateral Septum Are Not Critical for Maternal Behavior

INTRODUCTION

In nurturing systems, the oxytocin (Oxt)-oxytocin receptor (Oxtr) system is important for parturition, and essential for lactation and parental behavior. Among the nerve nuclei that express Oxtr, the lateral septal nucleus (LS) and medial preoptic area (MPOA) are representative regions that control maternal behavior.

METHODS

We investigated the role of Oxtr- and Oxtr-expressing neurons, located in the LS and MPOA, in regulating maternal behavior by regulating Oxtr expression in a region-specific manner using recombinant mice and adeno-associated viruses. We quantified the prolactin (Prl) concentrations in the pituitary gland and plasma when Oxtr expression in the MPOA was reduced.

RESULTS

The endogenous Oxtr gene in the neurons of the LS did not seem to play an essential role in maternal behavior. Conversely, decreased Oxtr expression in the MPOA increased the frequency of pups being left outside the nest and reduced their survival rate. Deletion of Oxtr in MPOA neurons prevented elevation of Prl levels in plasma and pituitary at postpartum day 2.

DISCUSSION/CONCLUSION

Oxtr-expressing neurons in the MPOA are involved in the postpartum production of Prl. We confirmed the essential functions of Oxtr-expressing neurons and the Oxtr gene itself in the MPOA for the sustainability of maternal behavior, which involved Oxtr-dependent induction of Prl.

Rho kinase inhibitors ameliorate cognitive impairment in a male mouse model of methamphetamine-induced schizophrenia

Schizophrenia (SCZ) is a severe psychiatric disorder characterized by positive symptoms, negative symptoms, and cognitive deficits. Current antipsychotic treatment in SCZ improves positive symptoms but has major side effects and little impact on negative symptoms and cognitive impairment. The pathoetiology of SCZ remains unclear, but is known to involve small GTPase signaling. Rho kinase, an effector of small GTPase Rho, is highly expressed in the brain and plays a major role in neurite elongation and neuronal architecture. This study used a touchscreen-based visual discrimination (VD) task to investigate the effects of Rho kinase inhibitors on cognitive impairment in a methamphetamine (METH)-treated male mouse model of SCZ. Systemic injection of the Rho kinase inhibitor fasudil dose-dependently ameliorated METH-induced VD impairment. Fasudil also significantly suppressed the increase in the number of c-Fos-positive cells in the infralimbic medial prefrontal cortex (infralimbic mPFC) and dorsomedial striatum (DMS) following METH treatment. Bilateral microinjections of Y-27632, another Rho kinase inhibitor, into the infralimbic mPFC or DMS significantly ameliorated METH-induced VD impairment. Two proteins downstream of Rho kinase, myosin phosphatase-targeting subunit 1 (MYPT1; Thr696) and myosin light chain kinase 2 (MLC2; Thr18/Ser19), exhibited increased phosphorylation in the infralimbic mPFC and DMS, respectively, after METH treatment, and fasudil inhibited these increases. Oral administration of haloperidol and fasudil ameliorated METH-induced VD impairment, while clozapine had little effect. Oral administration of haloperidol and clozapine suppressed METH-induced hyperactivity, but fasudil had no effect. These results suggest that METH activates Rho kinase in the infralimbic mPFC and DMS, which leads to cognitive impairment in male mice. Rho kinase inhibitors ameliorate METH-induced cognitive impairment, perhaps via the cortico-striatal circuit.

A circuit from the locus coeruleus to the anterior cingulate cortex modulates offspring interactions in mice

Social sensitivity to other individuals in distress is crucial for survival. The anterior cingulate cortex (ACC) is a structure involved in making behavioral choices and is influenced by observed pain or distress. Nevertheless, our understanding of the neural circuitry underlying this sensitivity is incomplete. Here, we reveal unexpected sex-dependent activation of ACC when parental mice respond to distressed pups by returning them to the nest ("pup retrieval"). We observe sex differences in the interactions between excitatory and inhibitory ACC neurons during parental care, and inactivation of ACC excitatory neurons increased pup neglect. Locus coeruleus (LC) releases noradrenaline in ACC during pup retrieval, and inactivation of the LC-ACC pathway disrupts parental care. We conclude that ACC maintains sex-dependent sensitivity to pup distress under LC modulation. We propose that ACC's involvement in parenting presents an opportunity to identify neural circuits that support sensitivity to the emotional distress of others.

Prepulse inhibition of the acoustic startle reflex impairment by 5-HT2A receptor activation in the inferior colliculusis prevented by GABAA receptor blockade in the pedunculopontine tegmental nucleus

The relationship between serotonin dysfunction and schizophrenia commenced with the discovery of the effects of lysergic acid diethylamide (LSD) that has high affinity for 5-HT_2A receptors. Activation of these receptors produces perceptual and behavioural changes such as illusions, visual hallucinations and locomotor hyperactivity. Using prepulse inhibition (PPI) of the acoustic startle, which is impaired in schizophrenia,we aimed to investigate:i) the existence of a direct and potentially inhibitory neural pathway between the inferior colliculus (IC) and the pedunculopontine tegmental nucleus (PPTg) involved in the mediation of PPI responses by a neural tract tracing procedure;ii) if the microinjection of the 5-HT_2A receptors agonist DOI in IC would activate neurons in this structure and in the PPTg by a c-Fos protein immunohistochemistry study;iii) whether the deficits in PPI responses, observed after the administration of DOI in the IC, could be prevented by the concomitant microinjection of the GABA_A receptor antagonist bicuculline in the PPTg.Male Wistar rats were used in this study. An IC-PPTg reciprocated neuronal pathway was identified by neurotracing. The number of c-Fos labelled cells was lower in the DOI group in IC and PPTg, suggesting that this decrease could be due to the high levels of GABA in both structures. The concomitant microinjections of bicuculline in PPTg and DOI in IC prevented the PPI deficit observed after the IC microinjection of DOI. Ourfindings suggest that IC 5-HT_2A receptors may be at least partially involved in the regulation of inhibitory pathways mediating PPI response in IC and PPTg structures.

Neural activation associated with maternal and aversive interactions with pups in the Mongolian gerbil (Meriones unguiculatus)

According to approach-avoidance model, virgin female laboratory rats display maternal behaviour when the tendency to approach and interact with the pup is stronger than avoiding it. A positive neural mechanism that includes the medial preoptic area (mPOA)/bed nucleus of the stria terminalis (BNST) and a negative mechanism that involves the anterior hypothalamic nucleus (AHN)/ventromedial nucleus (VMN)/ periaqueductal grey (PAG) underlie to these behaviours. Unlike virgin rats, which avoid the pups, virgin females Mongolian gerbils (Meriones unguiculatus) can be immediately either maternal or aggressive with the pups. Furthermore, the Mongolian gerbil is monogamous and biparental species. Despite these difference, we hypothesised that maternal and aggressive interaction with the pups could activate mPOA/BNST and AHN/VMH/PAG, respectively, and that maternal response could be associated with high concentrations of estradiol (E₂). Twenty virgin maternal females and 20 aggressive toward the pups were selected. Ten maternal females interacted with the pups (MAT-pups) and 10 with candy (MAT-candy). Of the 20 aggressive females, 10 interacted with the pups (AGG-pups) and 10 with candy (AGG-candy). Immediately after the test, blood samples were taken to quantify E₂. The brains were dissected for c-Fos immunohistochemistry. MAT-pups females had significantly higher activation in mPOA/BNST than MAT-candy females, while AGG-pups showed significant activation in AHN/VMH/PAG compared with AGG-candy females. The maternal response was associated with high concentrations of E₂. These results suggested a positive and a negative mechanism in the regulation of maternal behaviour in the Mongolian gerbil, and that the immediate maternal response could be due to high E₂ concentrations.

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.

Oxytocin Facilitates Allomaternal Behavior under Stress in Laboratory Mice

Oxytocin (Oxt) controls reproductive physiology and various kinds of social behaviors, but the exact contribution of Oxt to different components of parental care still needs to be determined. Here, we illustrate the neuroanatomical relations of the parental nurturing-induced neuronal activation with magnocellular Oxt neurons and fibers in the medial preoptic area (MPOA), the brain region critical for parental and alloparental behaviors. We used genetically-targeted mouse lines for Oxt, Oxt receptor (Oxtr), vasopressin receptor 1a (Avpr1a), vasopressin receptor 1b (Avpr1b), and thyrotropin-releasing hormone (Trh) to systematically examine the role of Oxt-related signaling in pup-directed behaviors. The Oxtr-Avpr1a-Avpr1b triple knock-out (TKO), and Oxt-Trh-Avpr1a-Avpr1b quadruple KO (QKO) mice were grossly healthy and fertile, except for their complete deficiency in milk ejection and modest deficiency in parturition secondary to maternal loss of the Oxt or Oxtr gene. In our minimal stress conditions, pup-directed behaviors in TKO and QKO mothers and fathers, virgin females and males were essentially indistinguishable from those of their littermates with other genotypes. However, Oxtr KO virgin females did show decreased pup retrieval in the pup-exposure assay performed right after restraint stress. This stress vulnerability in the Oxtr KO was abolished by the additional Avpr1b KO. The general stress sensitivity, as measured by plasma cortisol elevation after restraint stress or by the behavioral performance in the open field (OF) and elevated plus maze (EPM), were not altered in the Oxtr KO but were reduced in the Avpr1b KO females, indicating that the balance of neurohypophysial hormones affects the outcome of pup-directed behaviors.

Cellular Composition of the Preoptic Area Regulating Sleep, Parental, and Sexual Behavior

The preoptic area (POA) has long been recognized as a sleep center, first proposed by von Economo. The POA, especially the medial POA (MPOA), is also involved in the regulation of various innate functions such as sexual and parental behaviors. Consistent with its many roles, the MPOA is composed of subregions that are identified by different gene and protein expressions. This review addresses the current understanding of the molecular and cellular architecture of POA neurons in relation to sleep and reproductive behavior. Optogenetic and pharmacogenetic studies have revealed a diverse group of neurons within the POA that exhibit different neural activity patterns depending on vigilance states and whose activity can enhance or suppress wake, non-rapid eye movement (NREM) sleep, or rapid eye movement (REM) sleep. These sleep-regulating neurons are not restricted to the ventrolateral POA (VLPO) region but are widespread in the lateral MPOA and LPOA as well. Neurons expressing galanin also express gonadal steroid receptors and regulate motivational aspects of reproductive behaviors. Moxd1, a novel marker of sexually dimorphic nuclei (SDN), visualizes the SDN of the POA (SDN-POA). The role of the POA in sleep and other innate behaviors has been addressed separately; more integrated observation will be necessary to obtain physiologically relevant insight that penetrates the different dimensions of animal behavior.

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.

Prefrontal cortex is associated with the rapid onset of parental behavior in inexperienced adult mice (C57BL/6)

There is significant variability in the immediate behavioral response displayed by inexperienced adult mice when exposed to pups for the first time. The aim of this study was to determine which brain regions were engaged (higher c-Fos-immunoreactivity, c-Fos-ir) when virgin females, that were exposed to pups for 15 or 60 min, displayed full parental behavior (FPB), partial parental behavior (PPB), or non-parental behavior (NPB), or virgin males displayed PPB or infanticidal behavior (IB). The number of c-Fos-ir neurons in the prelimbic cortex (PL) was higher in parental females than in the NPB group (after a 15-min exposure), and the group not exposed to pups (NE). C-Fos expression in the nucleus accumbens (NA) was increased in most groups of females exposed to pups compared to NE. Higher c-Fos-ir was also found in the shell subregion of the NA in infanticidal males, compared to males NE. The cortical (CoA) and medial (MA) amygdala also showed higher c-Fos-ir in parental females compared to NE animals. However, PPB and IB male groups also exhibited higher c-Fos-ir in the CoA and MA compared to the NE group. The expression of c-Fos in the different subregions of medial preoptic area and the ventromedial nucleus of the hypothalamus was not specifically associated with either parental or infanticidal behavior. No brain activation in males was specifically associated with infanticidal behavior. Our results suggest that 15 min of exposure to pups is enough to detect brain regions associated with parental behavior (PL) or pups processing (NA, MA, CoA) in mice. The PL might participate in the immediate onset of parental behavior in virgin females, coordinating and planning its rapid execution.

Raising overlapping litters: Differential activation of rat maternal neural circuitry after interacting with newborn or juvenile pups

The maternal behaviour of a rat dynamically changes during the postpartum period, adjusting to the characteristics and physiological needs of the pups. This adaptation has been attributed to functional modifications in the maternal circuitry. Maternal behaviour can also flexibly adapt according to different litter compositions. Thus, mothers with two overlapping litters can concurrently take care of neonate and juvenile pups, mostly directing their attention to the newborns. We hypothesised that the maternal circuitry of these mothers would show a differential activation pattern after interacting with pups depending on the developmental stage of their offspring. Thus, we evaluated the activation of several areas of the maternal circuitry in mothers of overlapping litters, using c-Fos immunoreactivity as a marker of neuronal activation, after interacting with newborns or juveniles. The results showed that mothers with overlapping litters display different behavioural responses towards their newborn and their juvenile pups. Interestingly, these behavioural displays co-occurred with specific patterns of activation of the maternal neural circuitry. Thus, a similar expression of c-Fos was observed in some key brain areas of mothers that interacted with newborns or juveniles, such as the medial preoptic area and the nucleus accumbens, whereas a differential activation was quantified in the ventral region of the bed nucleus of the stria terminalis, the infralimbic and prelimbic subregions of the medial prefrontal cortex and the basolateral and medial nuclei of the amygdala. We posit that the specific profile of activation of the neural circuitry controlling maternal behaviour in mothers with overlapping litters enables dams to respond adequately to the newborn and the juvenile pups.

Maternal care activates the ventral tegmental area but not dopaminergic cells in the rat

The ventral tegmental area (VTA), together with the preoptic area, is part of a neural circuit necessary for the expression of maternal behaviour (MB); destruction of either area disrupts MB in postpartum rats. Central to the proposal of VTA activation are dopaminergic cells, for which the cell bodies lie in the VTA and project to forebrain structures. This mesolimbic system is a motivational circuit involved in rewarding behaviours such as sex and MB. Despite their recognised importance, surprisingly, unlike the preoptic area, there are no anatomical descriptions of the pattern of VTA activation or of the dopaminergic cell activation, specifically in relation to MB in the rat. In the present study, we explore the possible activation (as indicated by Fos protein via immunohistochemistry) of the anterior and medial portions of the VTA and in the dopaminergic cells in these regions, as well as in the medial preoptic area, in lactating rats, at postpartum day 7 (after a 12-hour mother/pups separation), and in dioestrous females. After 12 hours, mothers were perfused at that moment or after a 90 minutes of interaction, or not, with their pups. We found a strong significant Fos induction in both the preoptic area and in the anterior portion of VTA in dams that interacted with their pups. The number of dopaminergic cells that coexpressed Fos did not differ across groups. Additionally, we determined Fos and GABA colocalisation in the anterior part of the VTA and found dense GABAergic processes, possibly varicosities, in the area of increased Fos expression. The results of the present study support a proposed GABAergic pathway from medial preoptic area to VTA cells, critical for the expression of MB. Future experiments are warranted to explore the neurochemical identity of the Fos and no-Fos expressing cells that are recipients of GABAergic processes in the VTA, aiming to better understand the neural circuitry of the VTA in relation to MB.

Prolactin-induced and neuronal activation in the brain of mother mice

Nursing has important consequences on mothers. To separate the prolactin-mediated and the neuronally-mediated actions of nursing, neurons directly affected by prolactin were visualized using pSTAT5 immunohistochemistry in relation to Fos-expressing neurons in suckled mother mice. In response to pup exposure following 22-h pup deprivation, we found a markedly elevated number of pSTAT5-containing neurons in several brain regions, including the lateral septum, medial amygdaloid nucleus, subparafascicular area, caudal periaqueductal gray, dorsal raphe, lateral parabrachial nucleus, nucleus of the solitary tract, and the periventricular, medial preoptic, paraventricular, arcuate and ventromedial nuclei of the hypothalamus. Pup exposure also induced Fos expression in all of these brain regions except the arcuate and ventromedial hypothalamic nuclei. Bromocriptine treatment known to reduce prolactin levels eliminated pSTAT5 from most brain regions while it did not affect Fos activation following suckling. The degree of colocalization for pSTAT5 and Fos ranged from 8 to 80% in the different brain regions suggesting that most neurons responding to pup exposure in mother mice are driven either by prolactin or direct neuronal input from the pups, while the number of neurons affected by both types of inputs depends on the examined brain area. In addition, both pSTAT5 and Fos were also double-labeled with estrogen receptor alpha (ERα) in mother mice, which revealed a very high degree of colocalization between pSTAT5 and ERα with much less potential interaction between Fos- and ERα-containing neurons suggesting that estrogen-sensitive neurons are more likely to be affected by prolactin than by direct neuronal activation.

Oxytocin and Parental Behaviors

The oxytocin/vasopressin ancestor molecule has been regulating reproductive and social behaviors for more than 500 million years. In all mammals, oxytocin is the hormone indispensable for milk-ejection during nursing (maternal milk provision to offspring), a process that is crucial for successful mammalian parental care. In laboratory mice, a remarkable transcriptional activation occurs during parental behavior within the anterior commissural nucleus (AC), the largest magnocellular oxytocin cell population within the medial preoptic area (although the transcriptional activation was limited to non-oxytocinergic neurons in the AC). Furthermore, there are numerous recent reports on oxytocin's involvement in positive social behaviors in animals and humans. Given all those, the essential involvement of oxytocin in maternal/parental behaviors may seem obvious, but basic researchers are still struggling to pin down the exact role oxytocin plays in the regulation of parental behaviors. A major aim of this review is to more clearly define this role. The best conclusion at this moment is that OT can facilitate the onset of parental behavior, or parental behavior under stressful conditions.In this chapter, we will first review the basics of rodent parental behavior. Next, the neuroanatomy of oxytocin systems with respect to parental behavior in laboratory mice will be introduced. Then, the research history on the functional relationship between oxytocin and parental behavior, along with advancements in various techniques, will be reviewed. Finally, some technical considerations in conducting behavioral experiments on parental behavior in rodents will be addressed, with the aim of shedding light on certain pitfalls that should be avoided, so that the progress of research in this field will be facilitated. In this age of populism, researchers should strive to do even more scholarly works with further attention to methodological details.

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.

Antipsychotic drugs on maternal behavior in rats

Rat maternal behavior is a complex social behavior. Many clinically used antipsychotic drugs, including the typical drug haloperidol and the atypical drugs clozapine, risperidone, olanzapine, quetiapine, aripiprazole, and amisulpride, disrupt active maternal responses (e.g. pup retrieval, pup licking, and nest building) to various extents. In this review, I present a summary of recent studies on the behavioral effects and neurobiological mechanisms of antipsychotic action on maternal behavior in rats. I argue that antipsychotic drugs at clinically relevant doses disrupt active maternal responses primarily by suppressing maternal motivation. Atypical drug-induced sedation also contributes to their disruptive effects, especially that on pup nursing. Among many potential receptor mechanisms, dopamine D2 receptors and serotonin 5-HT2A/2C receptors are shown to be critically involved in the mediation of the maternal disruptive effects of antipsychotic drugs, with D2 receptors contributing more to typical antipsychotic-induced disruptions, whereas 5-HT2A/2C receptors contributing more to atypical drug-induced disruptions. The nucleus accumbens shell-related reward circuitry is an essential neural network in the mediation of the behavioral effects of antipsychotic drugs on maternal behavior. This research not only helps understand the extent and mechanisms of impact of antipsychotic medications on human maternal care, but is also important for enhancing our understanding of the neurochemical basis of maternal behavior. It is also valuable for understanding the complete spectrum of therapeutic effects and side-effects of antipsychotic treatment. This knowledge may facilitate the development of effective intervening strategies to help patients coping with such undesirable effects.

Dissecting the hypothalamic pathways that underlie innate behaviors

Many complex behaviors that do not require learning are displayed and are termed innate. Although traditionally the subject matter of ethology, innate behaviors offer a unique entry point for neuroscientists to dissect the physiological mechanisms governing complex behaviors. Since the last century, converging evidence has implicated the hypothalamus as the central brain area that controls innate behaviors. Recent studies using cutting-edge tools have revealed that genetically-defined populations of neurons residing in distinct hypothalamic nuclei and their associated neural pathways regulate the initiation and maintenance of diverse behaviors including feeding, sleep, aggression, and parental care. Here, we review the newly-defined hypothalamic pathways that regulate each innate behavior. In addition, emerging general principles of the neural control of complex behaviors are discussed.

Distinct preoptic-BST nuclei dissociate paternal and infanticidal behavior in mice

Paternal behavior is not innate but arises through social experience. After mating and becoming fathers, male mice change their behavior toward pups from infanticide to paternal care. However, the precise brain areas and circuit mechanisms connecting these social behaviors are largely unknown. Here we demonstrated that the c-Fos expression pattern in the four nuclei of the preoptic-bed nuclei of stria terminalis (BST) region could robustly discriminate five kinds of previous social behavior of male mice (parenting, infanticide, mating, inter-male aggression, solitary control). Specifically, neuronal activation in the central part of the medial preoptic area (cMPOA) and rhomboid nucleus of the BST (BSTrh) retroactively detected paternal and infanticidal motivation with more than 95% accuracy. Moreover, cMPOA lesions switched behavior in fathers from paternal to infanticidal, while BSTrh lesions inhibited infanticide in virgin males. The projections from cMPOA to BSTrh were largely GABAergic. Optogenetic or pharmacogenetic activation of cMPOA attenuated infanticide in virgin males. Taken together, this study identifies the preoptic-BST nuclei underlying social motivations in male mice and reveals unexpected complexity in the circuit connecting these nuclei.

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.

Effects of diethylstilbestrol exposure during gestation on both maternal and offspring behavior

Endocrine disruption during gestation impairs the physical and behavioral development of offspring. However, it is unclear whether endocrine disruption also impairs maternal behavior and in turn further contributes to the developmental and behavioral dysfunction of offspring. We orally administered the synthetic non-steroidal estrogen diethylstilbestrol (DES) to pregnant female C57BL/6J mice from gestation day 11-17 and then investigated the maternal behavior of mothers. In addition, we examined the direct effects of in utero DES exposure and the indirect effects of aberrant maternal behavior on offspring using the cross-fostering method. In mothers, endocrine disruption during gestation decreased maternal behavior. In addition, endocrine disruption of foster mother influenced anxiety-related behavior and passive avoidance learning of pups regardless of their exposure in utero. The influence of DES exposure in utero, irrespective of exposure to the foster mother, was also shown in female offspring. These results demonstrate the risks of endocrine disruptors on both mother as well as offspring and suggest that developmental deficits may stem from both in utero toxicity and aberrant maternal care.

Suckling induces a daily rhythm in the preoptic area and lateral septum but not in the bed nucleus of the stria terminalis in lactating rabbit does

Maternal behavior in the rabbit is restricted to a brief nursing period every day. Previously, we demonstrated that this event induces daily rhythms of Period1 (PER1) protein, the product of the clock gene Per1, in oxytocinergic and dopaminergic populations in the hypothalamus of lactating rabbit does. This is significant for the periodic production and ejection of milk, but the activation of other areas of the brain has not been explored. Here, we hypothesised that daily suckling would induce a rhythm in the preoptic area, lateral septum, and bed nucleus of the stria terminalis, which are important areas for the expression of maternal behavior in mammals, including the rabbit. To this end, we analysed PER1 expression in those areas through a complete 24-h cycle at lactation day 7. Does were scheduled to nurse during either the day at 10:00 h [zeitgeber time (ZT)03] or the night at 02:00 h (ZT19). Non-pregnant, non-lactating females were used as controls. In contrast to control females, lactating does showed a clear, significant rhythm of PER1 that shifted in parallel with the timing of nursing in the preoptic area and lateral septum. We determined that the maximal expression of PER1 at 8 h after scheduled nursing decreased significantly at 24 and 48 h after the absence of suckling. This effect was more pronounced in the lateral septum than in the preoptic area. We conclude that daily suckling is a powerful stimulus inducing rhythmic activity in brain structures in the rabbit that appear to form part of a maternal entrainable circuit.

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.

Histone deacetylase inhibition induces long-lasting changes in maternal behavior and gene expression in female mice

In many species, including mice, maternal responsiveness is experience-dependent and permanent, lasting for long periods (months to years). We have shown that after brief exposures to pups, virgin female mice continue to respond maternally toward pups for at least one month. Administration of a histone deacetylase inhibitor (HDACi) reduces the amount of maternal experience required to affect maternal behavior and gene expression. In this set of studies, we examined the epigenetic mechanisms that underlie these motivated behaviors. We assessed whether the effects of HDACi persisted 1 month after the initial experience (in the absence of continued pup experience or HDACi treatment) and whether the maintenance of maternal memory was associated with stable changes in gene expression. Using chromatin immunoprecipitation, we examined whether Esr2 and Oxt gene expression might be mediated by recruitment of the histone acetyltransferase cAMP response element binding protein (CBP) to their promoter regions after maternal memory consolidation. We report that HDACi treatment induced long-lasting changes in maternal responsiveness. Maternal learning was associated with increased recruitment of CBP to the Esr2 and Oxt gene promoters during the consolidation of maternal memory as well as a persistent increase in estrogen receptor-β (Esr2) mRNA and decreased expression of the de novo DNA methyltransferase Dnmt3a within the medial preoptic area. The consolidation of the maternal experience may involve the CBP recruitment and stable changes in gene expression, which maintain increased maternal responsiveness for long periods of time.

Neonatal Exposure to Sevoflurane in Mice Causes Deficits in Maternal Behavior Later in Adulthood

Background:

In animal models, exposure to general anesthetics induces widespread increases in neuronal apoptosis in the developing brain. Subsequently, abnormalities in brain functioning are found in adulthood, long after the anesthetic exposure. These abnormalities include not only reduced learning abilities but also impaired social behaviors, suggesting pervasive deficits in brain functioning. But the underlying features of these deficits are still largely unknown.

Methods:

Six-day-old C57BL/6 female mice were exposed to 3% sevoflurane for 6 h with or without hydrogen (1.3%) as part of the carrier gas mixture. At 7–9 weeks of age, they were mated with healthy males. The first day after parturition, the maternal behaviors of dams were evaluated. The survival rate of newborn pups was recorded for 6 days after birth.

Results:

Female mice that received neonatal exposure to sevoflurane could mate normally and deliver healthy pups similar to controls. But these dams often left the pups scattered in the cage and nurtured them very little, so that about half of the pups died within a couple of days. Yet, these dams did not show any deficits in olfactory or exploratory behaviors. Notably, pups born to sevoflurane-treated dams were successfully fostered when nursed by control dams. Mice coadministered of hydrogen gas with sevoflurane did not exhibit the deficits of maternal behaviors.

Conclusion:

In an animal model, sevoflurane exposure in the developing brain caused serious impairment of maternal behaviors when fostering their pups, suggesting pervasive impairment of brain functions including innate behavior essential to species survival.

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.

siRNA silencing of estrogen receptor-α expression specifically in medial preoptic area neurons abolishes maternal care in female mice

The medial preoptic area has been shown to be intricately involved in many behaviors, including locomotion, sexual behavior, maternal care, and aggression. The gene encoding estrogen receptor-α (ERα) protein is expressed in preoptic area neurons, and a very dense immunoreactive field of ERα is found in the preoptic region. ERα knockout animals show deficits in maternal care and sexual behavior and fail to exhibit increases in these behaviors in response to systemic estradiol treatment. In the present study, we used viral-vector mediated RNA interference to silence ERα expression specifically in the preoptic area of female mice and measured a variety of behaviors, including social and sexual aggression, maternal care, and arousal activity. Suppression of ERα in the preoptic area almost completely abolished maternal care, significantly increasing the latency to pup retrieval and significantly reducing the time the moms spent nursing and licking the pups. Strikingly, maternal aggression toward a male intruder was not different between control and preoptic ERα-silenced mice, demonstrating the remarkably specific role of ERα in these neurons. Reduction of ERα expression in preoptic neurons significantly decreased sexual behavior in female mice and increased aggression toward both sexual partners and male intruders in a seminatural environment. Estrogen-dependent increases in arousal, measured by home cage activity, were not mediated by ERα expression in the preoptic neurons we targeted, as ERα-suppressed mice had increases similar to control mice. Thus, we have established that a specific gene in a specific group of neurons is required for a crucially important natural behavior.

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.

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.

Limbic brain activation for maternal acoustic perception and responding is different in mothers and virgin female mice

Mothers are primed to become maternal through hormonal changes during pregnancy and delivery of young, virgin females need experience with young for performing maternally. The activation of brain areas controlling maternal behavior can be studied by stimulus-induced expression of the immediate-early gene Fos and immunocytochemical labeling of the FOS protein in activated cells. With this technique we identified areas of the mouse limbic system stimulated by acoustically adequate or inadequate models of pup ultrasounds that, if perceived as adequate, direct the search for lost pups (phonotaxis). Behavioral observations and neural activation data suggest that adequate (50 kHz long tones) and inadequate ultrasound models (50 kHz short or 20 kHz long tones) are differently processed in limbic areas of mothers and virgin females with 1 or 5 days of pup-caring experience depending on the news value and the recognition of the stimuli: High numbers of FOS-positive cells in the medial preoptic area, lateral septum, and bed nucleus of the stria terminalis (mothers and virgins) relate to the salience (news value) of the perceived sounds; contextual stress may be reflected by high activation in parts of the amygdala and the ventromedial hypothalamus (virgins); high activation in the piriform cortex suggests associative learning of adequate sounds and in the entorhinal cortex remembering associations of adequate sounds with pups (virgins). Thus brain areas were differently activated in animals with maternal emotions, however different responses to pup cues depending on how they got primed to behave maternally and on how they evaluated the stimulation context.

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.

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.

Patterns of fos-like immunoreactivity in the brains of parent ring doves (Streptopelia risoria) given tactile and nontactile exposure to their young

Neuronal activation was examined by fos immunohistochemistry in ring doves (Streptopelia risoria) reunited with their young after overnight separation. In an initial study, squab-exposed parents showed more fos immunoreactivity (ir) in the preoptic area (POA) and lateral hypothalamus (LH) than squab-deprived parents. In a 2nd study, parents allowed free access to young and those separated from young by a wire mesh partition showed more fos-ir in the POA, LH, and lateral septum than box-exposed controls. Contact with young also increased fos-ir in the medial preoptic nucleus and bed nucleus of the stria terminalis, but noncontact exposure did not. Conversely, nontactile squab exposure stimulated more fos-ir in the POA than did free access to young, which suggests POA involvement in appetitive aspects of parenting.

Effects of maternal behavior induction and pup exposure on neurogenesis in adult, virgin female rats

The states of pregnancy and lactation bring about a range of physiological and behavioral changes in the adult mammal that prepare the mother to care for her young. Cell proliferation increases in the subventricular zone (SVZ) of the female rodent brain during both pregnancy and lactation when compared to that in cycling, diestrous females. In the present study, the effects of maternal behavior induction and pup exposure on neurogenesis in nulliparous rats were examined in order to determine whether maternal behavior itself, independent of pregnancy and lactation, might affect neurogenesis. Adult, nulliparous, Sprague-Dawley, female rats were exposed daily to foster young in order to induce maternal behavior. Following the induction of maternal behavior each maternal subject plus females that were exposed to pups for a comparable number of test days, but did not display maternal behavior, and subjects that had received no pup exposure were injected with bromodeoxyuridine (BrdU, 90 mg/kg, i.v.). Brain sections were double-labeled for BrdU and the neural marker, NeuN, to examine the proliferating cell population. Increases in the number of double-labeled cells were found in the maternal virgin brain when compared with the number of double-labeled cells present in non-maternal, pup-exposed nulliparous rats and in females not exposed to young. No changes were evident in the dentate gyrus of the hippocampus as a function of maternal behavior. These data indicate that in nulliparous female rats maternal behavior itself is associated with the stimulation of neurogenesis in the SVZ.