Forebrain expression of c-fos due to active maternal behaviour in lactating rats

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.

Lateral septum as a possible regulatory center of maternal behaviors

The lateral septum (LS) is involved in controlling anxiety, aggression, feeding, and other motivated behaviors. Lesion studies have also implicated the LS in various forms of caring behaviors. Recently, novel experimental tools have provided a more detailed insight into the function of the LS, including the specific role of distinct cell types and their neuronal connections in behavioral regulations, in which the LS participates. This article discusses the regulation of different types of maternal behavioral alterations using the distributions of established maternal hormones such as prolactin, estrogens, and the neuropeptide oxytocin. It also considers the distribution of neurons activated in mothers in response to pups and other maternal activities, as well as gene expressional alterations in the maternal LS. Finally, this paper proposes further research directions to keep up with the rapidly developing knowledge on maternal behavioral control in other maternal brain regions.

Top-down, auditory pallial regulation of the social behavior network

Social encounters rely on sensory cues that carry nuanced information to guide social decision-making. While high-level features of social signals are processed in the telencephalic pallium, nuclei controlling social behaviors, called the social behavior network (SBN), reside mainly in the diencephalon. Although it is well known how mammalian olfactory pallium interfaces with the SBN, there is little information for how pallial processing of other sensory modalities can modulate SBN circuits. This is surprising given the importance of complex vocalizations, for example, for social behavior in many vertebrate taxa such as humans and birds. Using gregarious and highly vocal songbirds, female Zebra finches, we asked to what extent auditory pallial circuits provide consequential input to the SBN as it processes social sensory cues. We transiently inactivated auditory pallium of female Zebra finches during song playback and examined song-induced activation in SBN nuclei. Auditory pallial inactivation impaired responses to song specifically within the lateral ventromedial nucleus of the hypothalamus (VMHl), providing the first evidence in vertebrates of a connection between auditory pallium and the SBN. This same treatment elevated feeding behavior, which also correlated with VMHl activation. This suggests that signals from auditory pallium to VMHl can tune the balance between social attention and feeding drive. A descending influence of sensory pallium on hypothalamic circuits could therefore provide a functional connection for the integration of social stimuli with internal state to influence social decision-making.

SIGNIFICANCE

Sensory cues such as vocalizations contain important social information. These social signals can be substantially nuanced, containing information about vocalizer identity, prior experience, valence, and emotional state. Processing these features of vocalizations necessitates processing the fast, complex sound streams in song or speech, which depends on circuits in pallial cortex. But whether and how this information is then transferred to social circuits in limbic and hypothalamic regions remains a mystery. Here, we identify a top-down influence of the songbird auditory pallium on one specific node of the social behavior network within the hypothalamus. Descending functional connections such as these may be critical for the wide range of vertebrate species that rely on intricate sensory communication signals to guide social decision-making.

Oxytocin interactions with central dopamine and serotonin systems regulate different components of motherhood

The role of oxytocin in maternal caregiving and other postpartum behaviours has been studied for more than five decades. How oxytocin interacts with other neurochemical systems to enact these behavioural changes, however, is only slowly being elucidated. The best-studied oxytocin-neurotransmitter interaction is with the mesolimbic dopamine system, and this interaction is essential for maternal motivation and active caregiving behaviours such as retrieval of pups. Considerably less attention has been dedicated to investigating how oxytocin interacts with central serotonin to influence postpartum behaviour. Recently, it has become clear that while oxytocin-dopamine interactions regulate the motivational and pup-approach aspects of maternal caregiving behaviours, oxytocin-serotonin interactions appear to regulate nearly all other aspects including postpartum nursing, aggression, anxiety-like behaviour and stress coping strategy. Collectively, oxytocin's interactions with central dopamine and serotonin systems are thus critical for the entire suite of behavioural adaptations exhibited in the postpartum period, and these sites of interaction are potential pharmacological targets for where oxytocin could help to ameliorate deficits in maternal caregiving and poor postpartum mental health. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

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

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

Habenula orphan G-protein coupled receptors in the pathophysiology of fear and anxiety

The phasic emotion, fear, and the tonic emotion, anxiety, have been conventionally inspected in clinical frameworks to epitomize memory acquisition, storage, and retrieval. However, inappropriate expression of learned fear in a safe environment and its resistance to suppression is a cardinal feature of various fear-related disorders. A significant body of literature suggests the involvement of extra-amygdala circuitry in fear disorders. Consistent with this view, the present review underlies incentives for the association between the habenula and fear memory. G protein-coupled receptors (GPCRs) are important to understand the molecular mechanisms central to fear learning due to their neuromodulatory role. The efficacy of a pharmacological strategy aimed at exploiting habenular-GPCR desensitization machinery can serve as a therapeutic target combating the pathophysiology of fear disorders. Originating from this milieu, the conserved nature of orphan GPCRs in the brain, with some having the highest expression in the habenula can lead to recent endeavors in understanding its functionality in fear circuitry.

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.

The paraventricular nucleus of the thalamus: an integrative node underlying homeostatic behavior

Early anatomical evidence suggested that the paraventricular nucleus of the thalamus (PVT) regulates arousal, as well as emotional and motivated behaviors. We discuss recent studies using modern techniques which now confirm and expand the involvement of the rodent PVT in these functions. Despite the emerging notion that the PVT is implicated in various behavioral processes, a recurrent theme is that activity in this brain region depends on internal state information arriving from the hypothalamus and brainstem, and is influenced by prior experience. We propose that the primary function of the PVT is to detect homeostatic challenges by integrating information about prior experiences, competing needs, and internal state to guide adaptive behavioral responses aimed at restoring homeostasis.

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.

Complete sleep and local field potential analysis regarding estrus cycle, pregnancy, postpartum and post-weaning periods and homeostatic sleep regulation in female rats

Sleep and local field potential (LFP) characteristics were addressed during the reproductive cycle in female rats using long-term (60-70 days) recordings. Changes in homeostatic sleep regulation was tested by sleep deprivation (SDep). The effect of mother-pup separation on sleep was also investigated during the postpartum (PP) period. First half of the pregnancy and early PP period showed increased wakefulness (W) and higher arousal indicated by elevated beta and gamma activity. Slow wave sleep (SWS) recovery was suppressed while REM sleep replacement was complete after SDep in the PP period. Pup separation decreased maternal W during early-, but increased during middle PP while did not affect during late PP. More W, less SWS, higher light phase beta activity but lower gamma activity was seen during the post-weaning estrus cycle compared to the virgin one. Maternal sleep can be governed by the fetuses/pups needs and their presence, which elevate W of mothers. Complete REM sleep- and incomplete SWS replacement after SDep in the PP period may reflect the necessity of maternal REM sleep for the offspring while SWS increase may compete with W essential for maternal care. Maternal experience may cause sleep and LFP changes in the post-weaning estrus cycle.

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.

Adaptations in reward-related behaviors and mesolimbic dopamine function during motherhood and the postpartum period

Initiation and maintenance of maternal behavior is driven by a complex interaction between the physiology of parturition and offspring stimulation, causing functional changes in maternal brain and behavior. Maternal behaviors are among the most robust and rewarding motivated behaviors. Mesolimbic dopamine (DA) system alterations during pregnancy and the postpartum enable enhanced reward-related responses to offspring stimuli. Here, we review behavioral evidence demonstrating postpartum rodents exhibit a bias towards pups and pup-related stimuli in reward-related tasks. Next, we provide an overview of normative adaptations in the mesolimbic DA system induced by parturition and the postpartum, which likely mediate shifts in offspring valence. We also discuss a causal link between dopaminergic dysfunction and disrupted maternal behaviors, which are recapitulated in postpartum depression (PPD) and relevant rodent models. In sum, mesolimbic DA system activation drives infant-seeking behavior and strengthens the mother-infant bond, potentially representing a therapeutic target for reward-related deficits in PPD.

Maternal responsiveness to suckling is modulated by time post-nursing: A behavioural and c-Fos/oxytocin immunocytochemistry study in rabbits

Doe rabbits nurse once/day for approximately 3 minutes, with circadian periodicity, inside the nest box. The amount of suckling received at each bout regulates this behaviour because reducing the litter size to four kits or less disrupts nursing circadian periodicity and increases suckling bout duration. Additionally, the likelihood that does will nurse kits at a given time of day depends on the time elapsed since the last suckling episode and the litter size nursed then. We hypothesised that the time elapsed since the last nursing would impact the number of c-Fos immunoreactive (IR) cells observed after suckling five kits and also that observed before the next nursing ("no kits"). Suckling significantly increased, relative to "no kits", the number of c-Fos-IR cells in the medial preoptic area and lateral septum but not in the bed nucleus of the stria terminalis (BNST), suprachiasmatic nucleus or ventromedial hypothalamus in does nursing at 18 or 24 hours after the previous bout. No effects of suckling were observed in mothers nursing at 6 hours. Does given kits at 3 hours post last suckling refused to nurse but, in the remaining three groups, all does nursed normally. At "no kits", more c-Fos-IR cells were seen (in all regions except the BNST) in does given kits at 24 hours after the last nursing and killed 1 hour later (ie, 4 hours after lights on) than in those killed earlier. The percentage of oxytocinergic (OT) cells co-expressing c-Fos was not modified by nursing in the paraventricular or supraoptic nuclei but, in the latter, the largest number of total OT-IR cells occurred at 18 and 24 hours post-last nursing. In conclusion, the responsiveness of particular forebrain regions involved in regulating circadian rhythms, lactation, and maternal behaviour is modulated by suckling and time of day.

Neuronal activation in zebra finch parents associated with reintroduction of nestlings

Recent studies of the brain mechanisms of parental behaviors have mainly focused on rodents. Using other vertebrate taxa, such as birds, can contribute to a more comprehensive, evolutionary view. In the present study, we investigated a passerine songbird, the zebra finch (Taeniopygia guttata), with a biparental caring system. Parenting-related neuronal activation was induced by first temporarily removing the nestlings, and then, either reuniting the focal male or female parent with the nestlings (parental group) or not (control group). To identify activated neurons, the immediate early gene product, Fos protein, was labeled. Both parents showed an increased level of parental behavior following reunion with the nestlings, and no sexual dimorphism occurred in the neuronal activation pattern. Offspring-induced parental behavior-related neuronal activation was found in the preoptic, ventromedial (VMH), paraventricular hypothalamic nuclei, and in the bed nucleus of the stria terminalis. In addition, the number of Fos-immunoreactive (Fos-ir) neurons in the nucleus accumbens predicted the frequency of the feeding of the nestlings. No difference was found in Fos expression when the effect of isolation or the presence of the mate was examined. Thus, our study identified a number of nuclei involved in parental care in birds and suggests similar regulatory mechanisms in caring females and males. The activated brain regions show similarities to rodents, while a generally lower number of brain regions were activated in the zebra finch. Furthermore, future studies are necessary to establish the role of the apparently avian-specific neuronal activation in the VMH of zebra finch parents.

The ventromedial hypothalamic circuitry and male alloparental behaviour in a socially monogamous rodent species

As prairie voles (Microtus ochrogaster) display spontaneous biparental care, and the ventromedial hypothalamus (VMH) has been implicated in reproductive behaviour, we conducted experiments to test the hypothesis that the VMH neurochemical circuitry is involved in alloparental behaviours in male prairie voles. We compared alloparental behaviours of adult, sexually naïve male and female voles-both displayed licking/grooming, huddling and retrieving behaviours towards conspecific pups. We also stained for the immediate-early gene encoded early growth protein Egr-1 in the vole brain. The pup-exposed animals showed levels of Egr-1 staining that was higher in the VMH but lower in the amygdala compared to animals exposed to a pup-sized piece of plastic (control). A retrograde tracer, Fluoro-Gold (FG), was injected into the VMH of male voles that were subsequently tested in the pup exposure or control condition. More FG/Egr-1 cells were detected for glutamatergic (GLU) staining in the ventral bed nucleus of the stria terminalis (BNSTv) and medial amygdala (MeA), whereas less FG/Egr-1 cells were stained for gamma-aminobutyric acid (GABA) in the MeA of the pup-exposed group compared to the control group. Further, the ratio of GLU:GABA expression in FG/Egr-1 projection neurons from both the BNSTv and MeA to the VMH was increased following pup exposure. Finally, pharmacological blockade of either dopamine D1 receptor or oxytocin receptor in the VMH impaired the onset of male alloparental behaviour. Together, these data suggest that the VMH may be involved in the onset of alloparental care and play a role in regulating social approach in male prairie voles.

Changes in Cortical Sensitivity to Infant Facial Cues From Pregnancy to Motherhood Predict Mother-Infant Bonding

The transition to motherhood triggers changes in human brain structure that may facilitate mother-infant bonding. Although much research on maternal cortical responses to infant faces has focused on the postpartum period, no previous study has examined whether longitudinal functional changes in the maternal cortex during pregnancy and postpartum are associated with mother-infant bonding. Using electroencephalography, prenatal to postnatal changes in cortical sensitivity (P1, P2, late positive potential, N170 event-related potentials) to infant and adult faces were examined in relation to reported mother-infant bonding in 40 mothers (M_age  = 30.5 years). Prenatal to postnatal increases in P1 and P2 responses to infant faces predicted stronger bonding. Findings suggest that cortical changes in attention allocation rather than in face-specific encoding enhance bonding.

Neural Correlates of Giving Social Support: Differences Between Giving Targeted Versus Untargeted Support

OBJECTIVE

Giving support contributes to the link between social ties and health; however, the neural mechanisms are not known. Giving support in humans may rely on neural regions implicated in parental care in animals. The current studies, therefore, assess the contribution of parental care-related neural regions to giving support in humans and, as a further theoretical test, examine whether the benefits of giving targeted support to single, identifiable individuals in need extend to giving untargeted support to larger societal causes.

METHODS

For study 1 (n = 45, M (SD) age = 21.98 (3.29), 69% females), participants completed a giving support task, followed by an emotional faces task in the functional magnetic resonance imaging scanner. For study 2 (n = 382, M (SD) age = 43.03 (7.28), 52% females), participants self-reported on their giving support behavior and completed an emotional faces task in the functional magnetic resonance imaging scanner.

RESULTS

In study 1, giving targeted (versus untargeted) support resulted in greater feelings of social connection and support effectiveness. Furthermore, greater septal area activity, a region centrally involved in parental care in animals, to giving targeted support was associated with less right amygdala activity to an emotional faces task (r = -.297, 95% confidence interval = -.547 to -.043). Study 2 replicated and extended this association to show that self-reports of giving targeted support were associated with less amygdala activity to a different emotional faces task, even when adjusting for other social factors (r = -.105, 95% confidence interval = -.200 to -.011). Giving untargeted support was not related to amygdala activity in either study.

CONCLUSIONS

Results highlight the unique benefits of giving targeted support and elucidate neural pathways by which giving support may lead to health.

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.

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.

Functional circuit architecture underlying parental behaviour

Parenting is essential for the survival and wellbeing of mammalian offspring but we lack a circuit-level understanding of how distinct components of this behaviour are orchestrated. Here we investigate how Galanin-expressing neurons in the medial preoptic area (MPOA^Gal) coordinate motor, motivational, hormonal and social aspects of parenting. These neurons integrate inputs from a large number of brain areas, whose activation depends on the animal’s sex and reproductive state. Subsets of MPOA^Gal neurons form discrete pools defined by their projection sites. While the MPOA^Gal population is active during all episodes of parental behaviour, individual pools are tuned to characteristic aspects of parenting. Optogenetic manipulation of MPOA^Gal projections mirrors this specificity, affecting discrete parenting components. This functional organization, reminiscent of the control of motor sequences by pools of spinal cord neurons, provides a new model for how discrete elements of a social behaviour are generated at the circuit level.

Effects of pre- and neonatal undernutrition on the kyphotic response and c-Fos activity in the caudal periaqueductal gray of primiparous lactating Wistar rats

In rodents, the most representative component of maternal behavior that meets the purpose of newborn nutrition is the kyphotic posture. During this posture, the mother maintains a unique environment for the protection, thermal regulation and breast-feeding of the progeny. The aim of this study was to investigate possible deficiencies in the kyphotic posture of adult lactating dams with pre- and neonatal undernutrition evoked by their own pups suckling in a home-cage situation. Wistar dams that had been previously exposed to perinatal undernutrition were mated at 90days of age, and pregnancy was confirmed by vaginal smears. Before testing if the perinatal underfed dam affected behavior, pups were removed (4h), and both the maternal response and the kyphotic posture were video-recorded (1h) and analyzed at 4 and 12days of lactation. Pre- and post-test litter weight gain was obtained. To immunostain the caudal periaqueductal gray, the litter was separated from their dams 24h before suckling stimulation. The results showed that underfed dams significantly reduced the duration of high kyphosis by choosing unconventional postures (prone and partial kyphosis). The body weight of the F1 offspring was significantly reduced, and the underfed F0 dams showed reduced c-Fos immunostaining at the caudal periaqueductal gray. The findings showed that early underfed dams have deficiencies in the mechanisms underlying the kyphosis, possibly because the pups' cues to evoke this posture were suboptimal and/or because the dam expressed deficient nursing. The results suggest that the abnormal kyphotic posture may affect the mother-litter bonds and have long-term effects on neonatal brain functions.

P2 purinergic receptor antagonists disrupt maternal behavior in lactating rats

The involvement of purinergic signaling in several brain functions has been recognized, but the modulation on maternal behavior by the purinergic system is not established, even though there are functional interactions between the purinergic and oxytocinergic systems. Therefore, the aim of our study was to investigate whether central administration of P2 receptor antagonists affected the maternal behavior of lactating rats and c-Fos immunoreactivity in the forebrain. On day 7 of lactation, female rats were treated with vehicle (5μL; i.c.v.), suramin (9.4-75.0μg/5μL; i.c.v.) or PPADS (9.4-75.0μg/5μL; i.c.v.) 30min before the experiment began. The maternal behavior was evaluated during the 30min following suramin or PPADS administration. In addition, c-Fos-positive nuclei were counted in the medial preoptic area (MPOA) and in the bed nucleus of the stria terminalis (BNST), and neurons that were double-labeled for c-Fos/OT were counted in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus of lactating rats. The results show that P2 receptor antagonists decreased maternal care and decreased neuronal activation in the MPOA and BNST and activation of oxytocinergic neurons in hypothalamic nuclei. Our results indicate that the purinergic system modulates maternal behavior and neuronal activation induced by suckling during lactation.

On the Benefits of Giving Social Support

People who are socially integrated and have strong social ties live happier, longer lives. The link between social connection and well-being is commonly explained in terms of the benefits of receiving care and support from others. However, the benefits of giving care and support to others for the support provider are often overlooked. We review emerging findings that suggest when, why, and how giving support to others provides benefits to the self. We identify possible mechanisms by which these benefits arise and outline boundary conditions that influence such benefits. To gain a richer understanding of the association between social ties and well-being, an important future research direction is to not only consider the support receiver but also emphasize the support provider.

Structural and Functional Plasticity in the Maternal Brain Circuitry

Parenting recruits a distributed network of brain structures (and neuromodulators) that coordinates caregiving responses attuned to the young's affect, needs, and developmental stage. Many of these structures and connections undergo significant structural and functional plasticity, mediated by the interplay between maternal hormones and social experience while the reciprocal relationship between the mother and her infant forms and develops. These alterations account for the remarkable behavioral plasticity of mothers. This review will examine the molecular and neurobiological modulation and plasticity through which parenting develops and adjusts in new mothers, primarily discussing recent findings in nonhuman animals. A better understanding of how parenting impacts the brain at the molecular, cellular, systems/network, and behavioral levels is likely to significantly contribute to novel strategies for treating postpartum neuropsychiatric disorders in new mothers, and critical for both the mother's physiological and mental health and the development and well-being of her young.

Absence epileptic activity in Wistar Albino Glaxo Rijswijk rat mothers

Absence epileptic activity was analyzed during pregnancy, the postpartum period and after weaning to establish alterations of seizures throughout the reproductive cycle. Wistar Albino Glaxo Rijswijk (WAG/Rij) rats were used in the study as a model of absence epilepsy and because their seizures do not interfere with rearing offspring. The number of spike-wave discharges (SWDs) was gradually elevated from the 19th pregnancy day to delivery. Meanwhile, the characteristics of individual SWDs did not change suggesting that SWD generation remained the same. In the postpartum and postweaning periods, the number of SWDs was not increased in the absence of pups. However, returning the pups to mothers resulted in a markedly elevated number of SWDs for 1h. If pups were taken away after 30min, the number of SWDs dropped immediately suggesting that the presence of pups increased the SWD number. The time mothers spent with the litter and in kyphosis suckling posture were in correlation with their SWD number further suggesting the importance of interaction with pups in SWD induction. Suckling elevates prolactin levels but surprisingly, its intracerebroventricular injection markedly reduced SWD number in suckled WAG/Rij mothers suggesting that the SWD-inducing effect of suckling is not mediated by prolactin. Rather, the elevated prolactin level may provide some protection against pro-epileptic effects of suckling. In conclusion, we first identified periods within the reproductive cycle with increased absence epileptic activity, implying that more attention should be devoted to epileptic activity changes in mothers.

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.

Previous and recent maternal experiences modulate pups' incentive value relative to a male without affecting maternal behavior in postpartum estrous rats

This study extends the behavioral analysis of the postpartum estrus (PPE) which represents a unique period in the female rat's lifetime when maternal and sexual motivations co-exist. The aim of this study was to explore how previous and recent maternal experiences influence the maternal responses to pups when confronted with a male in a preference test or when they are presented independently in the home cage. To achieve this objective, we firstly compared the maternal behavior in the home cage and the preference for pups or a male in a Y-maze of primiparous and multiparous females approximately twelve hours after delivery. No differences were observed in the active and passive components of the maternal behavior of primiparous and multiparous rats; however second-time mothers made more efforts to gain access to the pups and tended to spend more time with them in the Y-maze than maternally inexperienced dams. In a second experiment, we assessed the influence of recent maternal experience with pups on PPE females' behavior by comparing pups vs. male preference and maternal behavior of females that had experienced continuous or limited (approximately two hours) interaction with their litters after parturition was completed. PPE rats subjected to reduced interaction with their pups preferred the male, while females continuously exposed to pups chose them over the male. This change in females' preference was not accompanied by significant alterations of maternal performance in the home cage, although anogenital licking tended to decrease in females with limited mother-litter interaction. Together, the results of these experiments indicate that previous and recent maternal experiences influence the motivational responses of PPE females, and that these effects are more evident when both motivations compete.

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.

Suckling-induced Fos activation and melanin-concentrating hormone immunoreactivity during late lactation

AIMS

Melanin-concentrating hormone (MCH) is implicated in the control of food intake, body weight regulation and energy homeostasis. Lactation is an important physiological model to study the hypothalamic integration of peripheral sensory signals, such as suckling stimuli and those related to energy balance. MCH can be detected in the medial preoptic area (MPOA), especially around the 19th day of lactation, when this hormone is described as displaying a peak synthesis followed by a decrease after weaning. The physiological significance of this phenomenon is unclear. Therefore, we aimed to investigate hypothalamic changes associated to sensory stimulation by the litter, in special its influence over MCH synthesis.

MAIN METHODS

Female Wistar rats (n=56) were euthanized everyday from lactation days 15-21, with or without suckling stimulus (WS and NS groups, respectively). MCH and Fos immunoreactivity were evaluated in the MPOA and lateral and incerto-hypothalamic areas (LHA and IHy).

KEY FINDINGS

Suckling stimulus induced Fos synthesis in all regions studied. An increase on the number of suckling-induced Fos-ir neurons could be detected in the LHA after the 18th day. Conversely, the amount of MCH decreased in the MPOA from days 15-21, independent of suckling stimulation. No colocalization between MCH and Fos could be detected in any region analyzed.

SIGNIFICANCE

Suckling stimulus is capable of stimulating hypothalamic regions not linked to maternal behavior, possibly to mediate energy balance aspects of lactation. Although dams are hyperphagic before weaning, this behavioral change does not appear to be mediated by MCH.

Species differences in behavior and cell proliferation/survival in the adult brains of female meadow and prairie voles

Microtine rodents display diverse patterns of social organization and behaviors, and thus provide a useful model for studying the effects of the social environment on physiology and behavior. The current study compared the species differences and the effects of oxytocin (OT) on anxiety-like, social affiliation, and social recognition behaviors in female meadow voles (Microtus pennsylvanicus) and prairie voles (Microtus ochrogaster). Furthermore, cell proliferation and survival in the brains of adult female meadow and prairie voles were compared. We found that female meadow voles displayed a higher level of anxiety-like behavior but lower levels of social affiliation and social recognition compared to female prairie voles. In addition, meadow voles showed lower levels of cell proliferation (measured by Ki67 staining) and cell survival (measured by BrdU staining) in the ventromedial hypothalamus (VMH) and amygdala (AMY), but not the dentate gyrus of the hippocampus (DG), than prairie voles. Interestingly, the numbers of new cells in the VMH and AMY, but not DG, also correlated with anxiety-like, social affiliation, and social recognition behaviors in a brain region-specific manner. Finally, central OT treatment (200 ng/kg, icv) did not lead to changes in behavior or cell proliferation/survival in the brain. Together, these data indicate a potential role of cell proliferation/survival in selected brain areas on different behaviors between vole species with distinct life strategies.

Brain Reward Pathway Dysfunction in Maternal Depression and Addiction: A Present and Future Transgenerational Risk

Two research areas that could benefit from a greater focus on the role of the reward pathway are maternal depression and maternal addiction. Both depression and addiction in mothers are mediated by deficiencies in the reward pathway and represent substantial risks to the health of offspring and future generations. This targeted review discusses maternal reward deficits in depressed and addicted mothers, neural, genetic, and epigenetic mechanisms, and the transgenerational transmission of these deficits from mother to offspring. Postpartum depression and drug use disorders may entail alterations in the reward pathway, particularly in striatal and prefrontal areas, which may affect maternal attachment to offspring and heighten the risk of transgenerational effects on the oxytocin and dopamine systems. Alterations may involve neural circuitry changes, genetic factors that impact monoaminergic neurotransmission, as well as growth factors such as BDNF and stress-associated signaling in the brain. Improved maternal reward-based preventative measures and treatments may be specifically effective for mothers and their offspring suffering from depression and/or addiction.

Autism: Oxytocin, serotonin, and social reward

Over 70 years since the first description of the disease, disrupted social behavior remains a core clinical feature of autistic spectrum disorder. The complex etiology of the disorder portends the need for a better understanding of the brain mechanisms that enable social behaviors, particularly those that are relevant to autism which is characterized by a failure to develop peer relationships, difficulty with emotional reciprocity and imitative play, and disrupted language and communication skills. Toward this end, the current review will examine recent progress that has been made toward understanding the neural mechanisms underlying consociate social attachments.

Central corticosterone disrupts behavioral and neuroendocrine responses during lactation

Administration of a high dose of chronic peripheral corticosterone during the postpartum period has been shown to lead to reduced maternal care, but the interference of acute corticosterone, mimicking a situation of acute stress, on maternal behavior has not been well established. Therefore, the aim of our study was to investigate the influence of acute central corticosterone on behavioral and neuroendocrine responses during lactation. On day 7 of lactation, female rats were treated with vehicle (5 μL; i.c.v.) or corticosterone (10 ng/5 μL; i.c.v.) 30 min before the start of the experiment. To evaluate maternal behavior, the pups were returned to the side of their home cages opposite the previous nest, and the resulting behavior of the lactating rats was filmed for the next 30 min. Plasma levels of oxytocin and the amount of milk consumed by the pups were evaluated 15 min after the onset of suckling. In addition, the double-labeled c-Fos/oxytocin neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) and c-Fos immunoreactivity in medial preoptic area (MPOA) neurons were quantified for each lactating rat. Corticosterone decreased maternal care, plasma oxytocin levels, milk consumption by the pups, the activation of oxytocinergic neurons in hypothalamic nuclei, and c-Fos immunoreactivity in MPOA neurons. Our results indicate that changes in the behavioral responses of lactating rats treated with corticosterone may be related to disruption of the neuroendocrine control of oxytocin secretion.

Behavioral and pharmacological investigation of anxiety and maternal responsiveness of postpartum female rats in a pup elevated plus maze

The present study investigated the validity of a novel pup-based repeated elevated plus maze task to detect reduced anxiety and increased maternal responsiveness in postpartum female rats and explored the roles of dopamine D2, serotonin transporter and GABA/benzodiazepine receptors in the mediation of these processes. Sprague-Dawley postpartum or nulliparous female rats were tested 4 times every other day on postpartum days 4, 6 and 8 in an elevated plus maze with 4 pups or 4 pup-size erasers placed on each end of the two open arms. When tested with erasers, untreated postpartum mother rats entered the open arms proportionally more than nulliparous rats. They also tended to spend more time in the open arms, indicating reduced anxiety. When tested with pups, postpartum rats retrieved pups into the closed arms, entered the open arms and closed arms more and had a higher moving speed than nulliparous rats, indicating increased maternal responsiveness. Both haloperidol (0.1 or 0.2 mg/kg, sc) and fluoxetine (5 or 10 mg/kg, ip) dose- and time-dependently decreased the percentage of time spent in the open arms and speed, but did not affect the percentage of open arm entries. Diazepam (1.0 or 2.0 mg/kg, ip) did not affect pup retrieval, open arm time/entry in lactating rats. Thus, the percentage of open arm entries appears to be the most sensitive measure of anxiety in postpartum female rats, while speed could be used to index maternal responsiveness to pups, which are likely mediated by the dopamine D2 and serotonin transporter systems.

The exposure to Trichilia catigua (catuaba) crude extract impairs fertility of adult female rats but does not cause reproductive damage to male offspring

ETHNOPHARMACOLOGICAL RELEVANCE

Trichilia catigua is broadly used in folk medicine due to its mental and physical tonic activities and stimulant effects. In animal models, its antidepressant-like effects have been associated with the dopaminergic (DA) system modulation, which has an important role on maternal behavior and male offspring reproductive development.

AIM OF THE STUDY

Since little is known about the adverse effects of the exposure to T. catigua crude extract (CAT) in rats, specially regarding maternal homeostasis and offspring development, the aim of the present study was to evaluate whether CAT exposure may influence maternal toxicity parameters and behavior or disrupt male offspring physical and reproductive development.

MATERIAL AND METHODS

Dams were treated daily (by gavage) with 400mg/kg of CAT or vehicle (control=CTR) throughout pregnancy and lactation. Fertility and maternal behavior tests were conducted in dams. Male offspring reproductive and behavioral parameters were analyzed.

RESULTS

Dams exposed to CAT showed increased pre- and post-implantation losses rates when compared to CTR group. No significant changes regarding maternal behavior or male offspring parameters were observed.

CONCLUSION

In conclusion, maternal exposure to CAT interfered with implantation during the initial phases of pregnancy but did not induce changes on maternal behavior or male offspring reproductive and behavioral parameters.

Stress, sex, and addiction: potential roles of corticotropin-releasing factor, oxytocin, and arginine-vasopressin

Stress sensitivity and sex are predictive factors for the development of neuropsychiatric disorders. Life stresses are not only risk factors for the development of addiction but also are triggers for relapse to drug use. Therefore, it is imperative to elucidate the molecular mechanisms underlying the interactions between stress and drug abuse, as an understanding of this may help in the development of novel and more effective therapeutic approaches to block the clinical manifestations of drug addiction. The development and clinical course of addiction-related disorders do appear to involve neuroadaptations within neurocircuitries that modulate stress responses and are influenced by several neuropeptides. These include corticotropin-releasing factor, the prototypic member of this class, as well as oxytocin and arginine-vasopressin that play important roles in affiliative behaviors. Interestingly, these peptides function to balance emotional behavior, with sexual dimorphism in the oxytocin/arginine-vasopressin systems, a fact that might play an important role in the differential responses of women and men to stressful stimuli and the specific sex-based prevalence of certain addictive disorders. Thus, this review aims to summarize (i) the contribution of sex differences to the function of dopamine systems, and (ii) the behavioral, neurochemical, and anatomical changes in brain stress systems.

Maternal treatment with fluoxetine promotes testicular alteration in male rat pups

Fluoxetine (FLX) is a selective serotonin reuptake inhibitor (SSRI) antidepressant commonly prescribed during pregnancy and lactation. Pre- and post-partum depression, as well as SSRI treatment during these periods, may change maternal care, interfering with offspring development. Moreover, it is known that SSRIs may alter testes structure and function in offspring. The present study investigated the effects of maternal FLX exposure on maternal behaviour and testes function in offspring. Female Wistar rats were treated with 7.5mgkg-1 FLX or tap water (control group) by gavage from the Day 1 of pregnancy until 21 days after birth (postnatal Day (PND) 21). Maternal behaviour was evaluated and morphofunctional analyses of offspring testes were conducted on PND 21 and 50. There were no significant differences between the FLX-treated and control groups regarding maternal behaviour. Nor did maternal treatment with FLX have any effect on bodyweight gain, anogenital distance, day of preputial separation, testis weight and the gonadosomatic index in male offspring. However, there was a decreased number of Sertoli cells at both PND 21 and 50 in FLX-exposed male offspring. The findings of the present study demonstrate that maternal exposure to FLX can impair testicular function in weanling and pubertal animals.

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.

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.

PROGRESS ON THE PATERNAL BRAIN: THEORY, ANIMAL MODELS, HUMAN BRAIN RESEARCH, AND MENTAL HEALTH IMPLICATIONS

With a secure foundation in basic research across mammalian species in which fathers participate in the raising of young, novel brain-imaging approaches are outlining a set of consistent brain circuits that regulate paternal thoughts and behaviors in humans. The newest experimental paradigms include increasingly realistic baby-stimuli to provoke paternal cognitions and behaviors with coordinated hormone measures to outline brain networks that regulate motivation, reflexive caring, emotion regulation, and social brain networks with differences and similarities to those found in mothers. In this article, on the father brain, we review all brain-imaging studies on PubMed to date on the human father brain and introduce the topic with a selection of theoretical models and foundational neurohormonal research on animal models in support of the human work. We discuss potentially translatable models for the identification and treatment of paternal mood and father-child relational problems, which could improve infant mental health and developmental trajectories with potentially broad public health importance.

Cocaine sensitization increases kyphosis and modulates neural activity in adult nulliparous rats

Although data from both animals and humans suggests that adult cocaine use can have long term effects on behavior, it is unknown if prior cocaine use affects future maternal behavior in nulliparous females. In the current study, cocaine or saline was administered to adult female rats for 10 days, the animals were withdrawn from cocaine for 7 days, and the females were then exposed to donor pups to induce the expression of maternal behavior. Nulliparous females sensitized to cocaine were more likely to retrieve pups, spent more time caring for the pups, and were more likely to express full maternal behavior on day 8 of pup exposure. The fMRI data revealed significant effects of pup exposure in the hippocampal CA1 region, and effects of cocaine in the anterior thalamus and periaqueductal gray. Prior adult cocaine use may have lasting effects on offspring care, and this effect is not dependent on pup mediated effects or the endocrine changes of gestation and lactation. The present findings provide support for the hypothesis that maternal motivation to exhibit maternal behavior is enhanced by prior cocaine sensitization, possibly due to cross sensitization between cocaine and the natural reward of maternal behavior.

Chemosensory cues affect amygdaloid neurogenesis and alter behaviors in the socially monogamous prairie vole

The current study examined the effects of pheromonal exposure on adult neurogenesis and revealed the role of the olfactory pathways on adult neurogenesis and behavior in the socially monogamous prairie vole (Microtus ochrogaster). Subjects were injected with a cell proliferation marker [5-bromo-2'-deoxyuridine (BrdU)] and then exposed to their own soiled bedding or bedding soiled by a same- or opposite-sex conspecific. Exposure to opposite-sex bedding increased BrdU labeling in the amygdala (AMY), but not the dentate gyrus (DG), of female, but not male, voles, indicating a sex-, stimulus-, and brain region-specific effect. The removal of the main olfactory bulbs or lesioning of the vomeronasal organ (VNOX) in females reduced BrdU labeling in the AMY and DG, and inhibited the male bedding-induced BrdU labeling in the AMY, revealing the importance of an intact olfactory pathway for amygdaloid neurogenesis. VNOX increased anxiety-like behavior and altered social preference, but it did not affect social recognition memory in female voles. VNOX also reduced the percentage of BrdU-labeled cells that co-expressed the neuronal marker TuJ1 in the AMY, but not the DG. Together, our data indicate the importance of the olfactory pathway in mediating brain plasticity in the limbic system as well as its role in behavior.