Maternal aggression: New insights from Egr-1

Enhanced maternal behaviors in a mouse model of congenital blindness

In mammals, mothering is one of the most important prosocial female behavior to promote survival, proper sensorimotor, and emotional development of the offspring. Different intrinsic and extrinsic factors can initiate and maintain these behaviors, such as hormonal, cerebral, and sensory changes. Infant cues also stimulate multisensory systems and orchestrate complex maternal responsiveness. To understand the maternal behavior driven by complex sensory interactions, it is necessary to comprehend the individual sensory systems by taking out other senses. An excellent model for investigating sensory regulation of maternal behavior is a murine model of congenital blindness, the ZRDBA mice, where both an anophthalmic and sighted mice are generated from the same litter. Therefore, this study aims to assess whether visual inputs are essential to driving maternal behaviors in mice. Maternal behaviors were assessed using three behavioral tests, including the pup retrieval test, the home cage maternal behavior test, and the maternal aggression test. Our results show that blind mothers (1) took less time to retrieve their offspring inside the nest, (2) spent more time nursing and licking their offspring in the second- and third-week postpartum, and (3) exhibited faster aggressive behaviors when exposed to an intruder male, compared to the sighted counterparts. This study provides evidence that congenitally blind mothers show more motivation to retrieve the pups, care, and protection towards their pups than sighted ones, likely due to a phenomenon of sensory compensation.

Synthetic Oxytocin and Vasopressin Act Within the Central Amygdala to Exacerbate Aggression in Female Wistar Rats

Exacerbated aggression is a high-impact, but poorly understood core symptom of several psychiatric disorders, which can also affect women. Animal models have successfully been employed to unravel the neurobiology of aggression. However, despite increasing evidence for sex-specificity, little is known about aggression in females. Here, we studied the role of the oxytocin (OXT) and arginine vasopressin (AVP) systems within the central amygdala (CeA) on aggressive behavior displayed by virgin female Wistar rats using immunohistochemistry, receptor autoradiography, and neuropharmacology. Our data show that CeA GABAergic neurons are activated after an aggressive encounter in the female intruder test. Additionally, neuronal activity (pERK) negatively correlated with the display of aggression in low-aggressive group-housed females. Binding of OXT receptors, but not AVP-V1a receptors, was increased in the CeA of high-aggressive isolated and trained (IST) females. Finally, local infusion of either synthetic OXT or AVP enhanced aggression in IST females, whereas blockade of either of these receptors did not affect aggressive behavior. Altogether, our data support a moderate role of the CeA in female aggression. Regarding neuropeptide signaling, our findings suggest that synthetic, but not endogenous OXT and AVP modulate aggressive behavior in female Wistar rats.

Neuroendocrine regulation of female aggression

Classically the neurobiology of aggression has been studied exclusively in males. Thus, females have been considered mildly aggressive except during lactation. Interestingly, recent studies in rodents and humans have revealed that non-lactating females can show exacerbated and pathological aggression similarly to males. This review provides an overview of recent findings on the neuroendocrine mechanisms regulating aggressive behavior in females. In particular, the focus will be on novel rodent models of exaggerated aggression established in non-lactating females. Among the neuromodulatory systems influencing female aggression, special attention has been given to sex-steroids and sex-steroid-sensitive neuronal populations (i.e., the core nuclei of the neural pathway of aggression) as well as to the neuropeptides oxytocin and vasopressin which are major players in the regulation of social behaviors.

Motherhood-induced gene expression in the mouse medial amygdala: Changes induced by pregnancy and lactation but not by pup stimuli

During lactation, adult female mice display aggressive responses toward male intruders, triggered by male-derived chemosensory signals. This aggressive behavior is not shown by pup-sensitized virgin females sharing pup care with dams. The genetic mechanisms underlying the switch from attraction to aggression are unknown. In this work, we investigate the differential gene expression in lactating females expressing maternal aggression compared to pup-sensitized virgin females in the medial amygdala (Me), a key neural structure integrating chemosensory and hormonal information. The results showed 197 genes upregulated in dams, including genes encoding hormones such as prolactin, growth hormone, or follicle-stimulating hormone, neuropeptides such as galanin, oxytocin, and pro-opiomelanocortin, and genes related to catecholaminergic and cholinergic neurotransmission. In contrast, 99 genes were downregulated in dams, among which we find those encoding for inhibins and transcription factors of the Fos and early growth response families. The gene set analysis revealed numerous Gene Ontology functional groups with higher expression in dams than in pup-sensitized virgin females, including those related with the regulation of the Jak/Stat cascade. Of note, a number of olfactory and vomeronasal receptor genes was expressed in the Me, although without differences between dams and virgins. For prolactin and growth hormone, a qPCR experiment comparing dams, pup-sensitized, and pup-naïve virgin females showed that dams expressed higher levels of both hormones than pup-naïve virgins, with pup-sensitized virgins showing intermediate levels. Altogether, the results show important gene expression changes in the Me, which may underlie some of the behavioral responses characterizing maternal behavior.

EGR1 promotes stemness and predicts a poor outcome of uterine cervical cancer by inducing SOX9 expression

BACKGROUND

Early growth response-1 (EGR1) is a transcription factor involved in the progression of several cancer types. However, the expression and clinical significance of EGR1 in uterine cervical cancer (CC) have not been elucidated.

OBJECTIVE

To investigate the expression, clinical significance and prognostic value of EGR1 in CC.

METHODS

The expression of EGR1 was detected in 13 CCs and paired adjacent tissues with qRT-PCR and in 144 CC tissues with immunohistochemistry (IHC). The IHC scores were used to divide the patients into subsets with low and high EGR1 expression. The correlations between the EGR1 expression and clinicopathological factors were analyzed with the chi-square test, and the prognostic significance of EGR1 expression was evaluated with univariate and multivariate analyses. The functions of EGR1 in the proliferation, invasion and stemness of CC cells were investigated, and the molecular mechanism was assessed by in vitro experiments.

RESULTS

High expression of EGR1 was significantly associated with low survival rates of CC. EGR1 is an independent prognostic biomarker of CC, and its high expression predicted a poor outcome. EGR1 facilitated stemness and thus promoted proliferation and invasion of CC cells. SOX9 played an essential role in the EGR1-induced progression of CC cells.

CONCLUSIONS

EGR1 is an independent prognostic biomarker of CC. High EGR1 expression promoted proliferation, invasion and stemness by increasing SOX9 expression in CC cells. Our results suggested that the EGR1-SOX9 axis may be a potential drug target and that blocking the EGR1-SOX9 axis may be a possible approach to treating CC.

The Role of the Lateral Hypothalamus in Violent Intraspecific Aggression-The Glucocorticoid Deficit Hypothesis

This review argues for a central role of the lateral hypothalamus in those deviant forms of aggression, which result from chronic glucocorticoid deficiency. Currently, this nucleus is considered a key region of the mechanisms that control predatory aggression. However, recent findings demonstrate that it is strongly activated by aggression in subjects with a chronically downregulated hypothalamus-pituitary-adrenocortical (HPA) axis; moreover, this activation is causally involved in the emergence of violent aggression. The review has two parts. In the first part, we review human findings demonstrating that under certain conditions, strong stressors downregulate the HPA-axis on the long run, and that the resulting glucocorticoid deficiency is associated with violent aggression including aggressive delinquency and aggression-related psychopathologies. The second part addresses neural mechanisms in animals. We show that the experimental downregulation of HPA-axis function elicits violent aggression in rodents, and the activation of the brain circuitry that originally subserves predatory aggression accompanies this change. The lateral hypothalamus is not only an integral part of this circuitry, but can elicit deviant and violent forms of aggression. Finally, we formulate a hypothesis on the pathway that connects unfavorable social conditions to violent aggression via the neural circuitry that includes the lateral hypothalamus.

Serotonin-specific lesions of the dorsal raphe disrupt maternal aggression and caregiving in postpartum rats

The behavioral modifications associated with early motherhood, which include high aggression, caring for the young, and low anxiety, are all affected by acute pharmacological manipulation of serotonin signaling. However, the effects on all these behaviors of permanently disrupting serotonin signaling from one of its primary sources, the dorsal raphe nucleus (DR), have not been examined in detail. To address this, serotonin-specific lesions centered on the dorsomedial DR (DRdm; DR subregion strongly implicated in emotional behaviors) were induced at mid-pregnancy (day 15) or early postpartum (day 2) in rats using a saporin-conjugated neurotoxin targeting the serotonin transporter (Anti-SERT-SAP). Prepartum or postpartum Anti-SERT-SAP reduced DRdm serotonin immunoreactivity by ∼40-65%, and postpartum Anti-SERT-SAP also reduced it in the ventromedial and lateral wings of the DR, as well as in the median raphe. Serotonin-immunoreactive fibers were significantly reduced in the anterior hypothalamus, but not medial preoptic area, of lesioned dams. Pre- or postpartum lesions both greatly reduced maternal aggression, but while prepartum lesions did not affect later undisturbed maternal caregiving, the larger postpartum lesions prevented the postpartum decline in kyphotic nursing and reduced pup licking. Serotonin lesions did not affect pup retrieval, but the prepartum lesions temporarily increased maternal hovering over and licking the pups observed immediately after the disruptive retrieval tests. Dams' anxiety-like behaviors and litter weight gains were unaffected by the lesions. These findings suggest that DRdm serotonin projecting to the AH is particularly critical for maternal aggression, but that more widespread disruption of midbrain raphe serotonin is necessary to greatly impair maternal caregiving. Postpartum anxiety may rely more on other neurochemical systems or different midbrain serotonergic cell populations.

Sexual phenotype drives variation in endocrine responses to social challenge in a quasi-clonal animal

In many species, males tend to behave more aggressively than females and female aggression often occurs during particular life stages such as maternal defence of offspring. Though many studies have revealed differences in aggression between the sexes, few studies have compared the sexes in terms of their neuroendocrine responses to contest experience. We investigated sex differences in the endocrine response to social challenge using mangrove rivulus fish, Kryptolebias marmoratus. In this species, sex is determined environmentally, allowing us to produce males and hermaphrodites with identical genotypes. We hypothesized that males would show elevated androgen levels (testosterone and 11-ketotestosterone) following social challenge but that hermaphrodite responses might be constrained by having to maintain both testicular and ovarian tissue. To test this hypothesis, we staged fights between males and between hermaphrodites, and then compared contest behaviour and hormone responses between the sexes. Hermaphrodites had significantly higher oestradiol but lower 11-ketotestosterone than males before contests. Males took longer to initiate contests but tended to fight more aggressively and sustain longer fights than hermaphrodites. Males showed a dramatic post-fight increase in 11-ketotestosterone but hermaphrodites did not. Thus, despite being genetically identical, males and hermaphrodites exhibit dramatically different fighting strategies and endocrine responses to contests.

Oxytocin Receptors in the Anteromedial Bed Nucleus of the Stria Terminalis Promote Stress-Induced Social Avoidance in Female California Mice

BACKGROUND

The neuropeptide oxytocin (OT) is a key regulator of social and emotional behaviors. The effects of OT are context dependent, and it has been proposed that OT increases the salience of both positive and negative social cues. Here we tested whether the bed nucleus of the stria terminalis (BNST) mediates anxiogenic effects of OT.

METHODS

First, we studied the effects of systemic administration of an OT receptor (OTR) antagonist L-368,899 on social behavior in male and female California mice exposed to social defeat. We examined the effect of L-368,899 on G protein activation and used early growth response factor 1 immunohistochemistry to identify potential sites of OTR action. Finally, we examined the effects of L-368,899 infused in the BNST on behavior.

RESULTS

A single dose of systemic L-368,899 increased social approach in stressed female mice and decreased social approach in male mice naïve to defeat. L-368,899 prevented OT activation of G proteins and did not activate G proteins in the absence of OT. Intranasal OT, which reduces social approach in female mice but not male mice, increased early growth response factor 1 immunoreactivity in the nucleus accumbens core and anteromedial BNST in female mice but not in male mice. Stressed female mice that received an infusion of L-368,899 into the anteromedial BNST but not the nucleus accumbens core increased social approach and decreased social vigilance responses.

CONCLUSIONS

Our results suggest that OTR activation in anteromedial BNST induces a vigilance response in which individuals avoid, yet attend to, unfamiliar social contexts. Our results suggest that OTR antagonists may have unappreciated therapeutic potential for stress-induced psychiatric disorders.

The role of central and medial amygdala in normal and abnormal aggression: A review of classical approaches

The involvement of the amygdala in aggression is supported by overwhelming evidence. Frequently, however, the amygdala is studied as a whole, despite its complex internal organization. To reveal the role of various subdivisions, here we review the involvement of the central and medial amygdala in male rivalry aggression, maternal aggression, predatory aggression, and models of abnormal aggression where violent behavior is associated with increased or decreased arousal. We conclude that: (1) rivalry aggression is controlled by the medial amygdala; (2) predatory aggression is controlled by the central amygdala; (3) hypoarousal-associated violent aggression recruits both nuclei, (4) a specific upregulation of the medial amygdala was observed in hyperarousal-driven aggression. These patterns of amygdala activation were used to build four alternative models of the aggression circuitry, each being specific to particular forms of aggression. The separate study of the roles of amygdala subdivisions may not only improve our understanding of aggressive behavior, but also the differential control of aggression and violent behaviors of various types, including those associated with various psychopathologies.

Genotypic differences in intruder-evoked immediate early gene activation in male, but not female, vasopressin 1b receptor knockout mice

Background

The neuropeptide arginine vasopressin (Avp) modulates social behaviors via its two centrally expressed receptors, the Avp 1a receptor and the Avp 1b receptor (Avpr1b). Recent work suggests that, at least in mice, Avp signaling through Avpr1b within the CA2 region of the hippocampus is critical for normal aggressive behaviors and social recognition memory. However, this brain area is just one part of a larger neural circuit that is likely to be impacted in Avpr1b knockout (−/−) mice. To identify other brain areas that are affected by altered Avpr1b signaling, genotypic differences in immediate early gene activation, i.e. c-FOS and early growth response factor 1 (EGR-1), were quantified using immunocytochemistry following a single exposure to an intruder.

Results

In females, no genotypic differences in intruder-evoked c-FOS or EGR-1 immunoreactivity were observed in any of the brain areas measured. In males, while there were no intruder-evoked genotypic differences in c-FOS immunoreactivity, genotypic differences were observed in EGR-1 immunoreactivity within the ventral bed nucleus of the stria terminalis and the anterior hypothalamus; with Avpr1b −/− males having less EGR-1 immunoreactivity in these regions than controls.

Conclusions

These data are the first to identify specific brain areas that may be a part of a neural circuit that includes Avpr1b-expressing cells in the CA2 region of the hippocampus. It is thought that this circuit, when working properly, plays a role in how an animal evaluates its social context.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-016-0310-7) contains supplementary material, which is available to authorized users.

Recent advances in understanding the role of the hypothalamic circuit during aggression

The hypothalamus was first implicated in the classic “fight or flight” response nearly a century ago, and since then, many important strides have been made in understanding both the circuitry and the neural dynamics underlying the generation of these behaviors. In this review, we will focus on the role of the hypothalamus in aggression, paying particular attention to recent advances in the field that have allowed for functional identification of relevant hypothalamic subnuclei. Recent progress in this field has been aided by the development of new techniques for functional manipulation including optogenetics and pharmacogenetics, as well as advances in technology used for chronic in vivo recordings during complex social behaviors. We will examine the role of the hypothalamus through the complimentary lenses of (1) loss of function studies, including pharmacology and pharmacogenetics; (2) gain of function studies, including specific comparisons between results from classic electrical stimulation studies and more recent work using optogenetics; and (3) neural activity, including both immediate early gene and awake-behaving recordings. Lastly, we will outline current approaches to identifying the precise role of the hypothalamus in promoting aggressive motivation and aggressive action.

Ventral premammillary nucleus as a critical sensory relay to the maternal aggression network

Maternal aggression is under the control of a wide variety of factors that prime the females for aggression or trigger the aggressive event. Maternal attacks are triggered by the perception of sensory cues from the intruder, and here we have identified a site in the hypothalamus of lactating rats that is highly responsive to the male intruder--the ventral premammillary nucleus (PMv). The PMv is heavily targeted by the medial amygdalar nucleus, and we used lesion and immediate-early gene studies to test our working hypothesis that the PMv signals the presence of a male intruder and transfers this information to the network organizing maternal aggression. PMv-lesioned dams exhibit significantly reduced maternal aggression, without affecting maternal care. The Fos analysis revealed that PMv influences the activation of hypothalamic and septal sites shown to be mobilized during maternal aggression, including the medial preoptic nucleus (likely to represent an important locus to integrate priming stimuli critical for maternal aggression), the caudal two-thirds of the hypothalamic attack area (comprising the ventrolateral part of the ventromedial hypothalamic nucleus and the adjacent tuberal region of the lateral hypothalamic area, critical for the expression of maternal aggression), and the ventral part of the anterior bed nuclei of the stria terminalis (presently discussed as being involved in controlling neuroendocrine and autonomic responses accompanying maternal aggression). These findings reveal an important role for the PMv in detecting the male intruder and how this nucleus modulates the network controlling maternal aggression.

Excessive aggression as model of violence: a critical evaluation of current preclinical methods

RATIONALE

Preclinical experimental models of pathological aggressive behavior are a sorely understudied and difficult research area.

OBJECTIVES

How valid, reliable, productive, and informative are the most frequently used animal models of excessive aggressive behavior?

METHODS

The rationale, key methodological features, supporting data, and arguments as well as their disadvantages and limitations of the most frequently used animal models for excessive aggressive behavior are summarized and their validity and reliability are evaluated.

RESULTS

Excessive aggressive behavior is validly and reliably seen in (1) a proportion of feral-derived rats and selectively bred mice; (2) rats with compromised adrenal function resulting in a hypoglucocorticoid state; (3) a significant minority of mice, rats, and monkeys after consumption of a moderate dose of alcohol; and (4) resident animals of various species after social instigation. Limitations of these procedures include restrictive animal research regulations, the requirement of expertise in surgical, pharmacological, and behavioral techniques, and the behaviorally impoverished mouse strains that are used in molecular genetics research. Promising recent initiatives for novel experimental models include aggressive behaviors that are evoked by optogenetic stimulation and induced by the manipulation of early social experiences such as isolation rearing or social stress.

CONCLUSIONS

One of the most significant challenges for animal models of excessive, potentially abnormal aggressive behavior is the characterization of distinctive neurobiological mechanisms that differ from those governing species-typical aggressive behavior. Identifying novel targets for effective intervention requires increased understanding of the distinctive molecular, cellular, and circuit mechanisms for each type of abnormal aggressive behavior.

The neurobiology of abnormal manifestations of aggression--a review of hypothalamic mechanisms in cats, rodents, and humans

Aggression research was for long dominated by the assumption that aggression-related psychopathologies result from the excessive activation of aggression-promoting brain mechanisms. This assumption was recently challenged by findings with models of aggression that mimic etiological factors of aggression-related psychopathologies. Subjects submitted to such procedures show abnormal attack features (mismatch between provocation and response, disregard of species-specific rules, and insensitivity toward the social signals of opponents). We review here 12 such laboratory models and the available human findings on the neural background of abnormal aggression. We focus on the hypothalamus, a region tightly involved in the execution of attacks. Data show that the hypothalamic mechanisms controlling attacks (general activation levels, local serotonin, vasopressin, substance P, glutamate, GABA, and dopamine neurotransmission) undergo etiological factor-dependent changes. Findings suggest that the emotional component of attacks differentiates two basic types of hypothalamic mechanisms. Aggression associated with increased arousal (emotional/reactive aggression) is paralleled by increased mediobasal hypothalamic activation, increased hypothalamic vasopressinergic, but diminished hypothalamic serotonergic neurotransmission. In aggression models associated with low arousal (unemotional/proactive aggression), the lateral but not the mediobasal hypothalamus is over-activated. In addition, the anti-aggressive effect of serotonergic neurotransmission is lost and paradoxical changes were noticed in vasopressinergic neurotransmission. We conclude that there is no single 'neurobiological road' to abnormal aggression: the neural background shows qualitative, etiological factor-dependent differences. Findings obtained with different models should be viewed as alternative mechanisms rather than conflicting data. The relevance of these findings for understanding and treating of aggression-related psychopathologies is discussed. This article is part of a Special Issue entitled 'Extrasynaptic ionotropic receptors'.

Differential efferent projections of the anterior, posteroventral, and posterodorsal subdivisions of the medial amygdala in mice

The medial amygdaloid nucleus (Me) is a key structure in the control of sociosexual behavior in mice. It receives direct projections from the main and accessory olfactory bulbs (AOB), as well as an important hormonal input. To better understand its behavioral role, in this work we investigate the structures receiving information from the Me, by analysing the efferent projections from its anterior (MeA), posterodorsal (MePD) and posteroventral (MePV) subdivisions, using anterograde neuronal tracing with biotinylated and tetrametylrhodamine-conjugated dextranamines. The Me is strongly interconnected with the rest of the chemosensory amygdala, but shows only moderate projections to the central nucleus and light projections to the associative nuclei of the basolateral amygdaloid complex. In addition, the MeA originates a strong feedback projection to the deep mitral cell layer of the AOB, whereas the MePV projects to its granule cell layer. The Me (especially the MeA) has also moderate projections to different olfactory structures, including the piriform cortex (Pir). The densest outputs of the Me target the bed nucleus of the stria terminalis (BST) and the hypothalamus. The MeA and MePV project to key structures of the circuit involved in the defensive response against predators (medial posterointermediate BST, anterior hypothalamic area, dorsomedial aspect of the ventromedial hypothalamic nucleus), although less dense projections also innervate reproductive-related nuclei. In contrast, the MePD projects mainly to structures that control reproductive behaviors [medial posteromedial BST, medial preoptic nucleus, and ventrolateral aspect of the ventromedial hypothalamic nucleus], although less dense projections to defensive-related nuclei also exist. These results confirm and extend previous results in other rodents and suggest that the medial amygdala is anatomically and functionally compartmentalized.

Both oxytocin and vasopressin are mediators of maternal care and aggression in rodents: from central release to sites of action

In the mammalian peripartum period, the activity of both the brain oxytocin and vasopressin system is elevated as part of the physiological adaptations occurring in the mother. This is reflected by increased expression and intracerebral release of oxytocin and vasopressin, as well as increased neuropeptide receptor expression and binding. In this review we discuss the functional role of the brain oxytocin and vasopressin system in the context of maternal behavior, specifically maternal care and maternal aggression in rodents. In order to enable the identification of significant and peptide-specific contributions to the display of maternal behavior, various complementary animal models of maternal care and/or maternal aggression were studied, including rats selectively bred for differences in anxiety-related behavior (HAB and LAB dams), monitoring of local neuropeptide release during ongoing maternal behavior, and local pharmacological or genetic manipulations of the neuropeptide systems. The medial preoptic area was identified as a major site for oxytocin- and vasopressin-mediated maternal care. Furthermore, both oxytocin and vasopressin release and receptor activation in the central amygdala and the bed nucleus of the stria terminalis play an important role for maternal aggression. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Neurotensin induced Egr-1 activity is altered in the postpartum period in mice

Neurotensin (NT) is a 13 amino acid neuropeptide that is identical in mice and humans and is released from and acts upon a number of social brain regions. Recent work indicates NT neurotransmission may be altered in postpartum females and support the onset of some maternal behaviors. In a recent study, we highlighted how virgin and postpartum brains from mice selected for high offspring protection differ in response to injected NT (0.1 μg) relative to vehicle when examining c-Fos profiles across the CNS. In this companion study we use a second marker for brain activity, Egr-1, and evaluate multiple brain regions. Common significant increased Egr-1 responses to NT (relative to vehicle) were found in both female groups only in ventromedial hypothalamus. In lateral periaqueductal gray, virgin mice showed a significant Egr-1 increase with NT (relative to vehicle), but maternal mice did not. When comparing NT injections, virgin (relative to maternal) mice had significantly higher activity in five regions, including anterior hypothalamus, lateral hypothalamus, somatosensory cortex, paraventricular nucleus, and zona incerta; no regions were higher in maternal mice. A Principal Components Analysis was also used for data mining and in virgin mice, greater changes in activity hubs were found with NT (relative to vehicle) than for maternal mice. Overall, a lower sensitivity to NT in terms of Egr-1 reactivity in the maternal state was highlighted and this is consistent with previous c-Fos results. These findings provide additional insight into the mechanisms by which NT functions in the CNS.

Changes in the intensity of maternal aggression and central oxytocin and vasopressin V1a receptors across the peripartum period in the rat

Maternal aggressive behaviour, which protects the offspring from harm, is one component of maternal behaviour. Not only maternal aggression, but also maternal care and social behaviour in general, is regulated by the brain oxytocin (OXT) and vasopressin (AVP) systems. In the present study, we quantified the intensity of maternal aggression using the maternal defence test at key time points throughout pregnancy, parturition and lactation. Furthermore, we quantified changes in central OXT and arginine AVP V1a receptor (V1a-R) binding in brain regions known to be important in regulating maternal aggression, aiming to investigate whether central changes coincide with the intensity of this behaviour. The intensity of aggression was found to dramatically change over the peripartum period, with its first appearance on the day before parturition. Aggression intensity fell immediately after parturition, although it increased during days 4-7 of lactation, before almost disappearing at weaning. OXT receptor (OTR) and V1a-R binding also showed changes through the peripartum period. OTR binding was highest at parturition within the bed nucleus of the stria terminalis and medial preoptic area and on days 4-7 of lactation in the lateral septum (LS) compared to any other time point during the peripartum period. OTR binding positively correlated with the peak of maternal aggression, suggesting that OXT may act in the LS to facilitate the expression of aggressive behaviour. At parturition, V1a-R binding was at its highest levels in the paraventricular nucleus and central amygdala (CeA) and, in the LS, V1a-R binding positively correlated with aggressive behaviour. V1a-R mRNA expression was also increased within the CeA at parturition. Taken together, the observed fluctuations in OTR and V1a-R binding in the neural circuitry important for regulating maternal behaviour may ensure that maternal aggression is expressed at the correct time during the peripartum period.

Independent and additive contributions of postvictory testosterone and social experience to the development of the winner effect

The processes through which salient social experiences influence future behavior are not well understood. Winning fights, for example, can increase the odds of future victory, yet little is known about the internal mechanisms that underlie such winner effects. Here, we use the territorial California mouse (Peromyscus californicus) to investigate how the effects of postvictory testosterone (T) release and winning experience individually mediate positive changes in future winning ability and antagonistic behavior. Male mice were castrated and implanted with T capsules to maintain basal levels of this hormone. We found that males form a robust winner effect if they win three separate territorial disputes and experience a single T surge roughly 45 min after each encounter. Meanwhile, males exhibit only an intermediate winner effect if they either 1) acquire three previous wins but do not experience a change in postvictory T or 2) acquire no previous wins but experience three separate T pulses. The results indicate that the effect of postvictory T must be coupled with that of winning experience to trigger the maximum positive shift in winning ability, which highlights the importance of social context in the development of the winner effect. At the same time, however, postvictory T and winning experience are each capable of increasing future winning ability independently, and this finding suggests that these two factors drive plasticity in antagonistic behavior via distinct mechanistic channels. More broadly, our data offer insight into the possible ways in which various species might be able to adjust their behavioral repertoire in response to social interactions through mechanisms that are unlinked from the effects of gonadal steroid action.

Dopamine and mesotocin neurotransmission during the transition from incubation to brooding in the turkey

We investigated the neuroendocrine changes involved in the transition from incubating eggs to brooding of the young in turkeys. Numbers of mesotocin (MT; the avian analog of mammalian oxytocin) immunoreactive (ir) neurons were higher in the nucleus paraventricularis magnocellularis (PVN) and nucleus supraopticus, pars ventralis (SOv) of late stage incubating hens compared to the layers. When incubating and laying hens were presented with poults, all incubating hens displayed brooding behavior. c-fos mRNA expression was found in several brain areas in brooding hens. The majority of c-fos mRNA expression by MT-ir neurons was observed in the PVN and SOv while the majority of c-fos mRNA expression in dopaminergic (DAergic) neurons was observed in the ventral part of the nucleus preopticus medialis (POM). Following intracerebroventricular injection of DA or oxytocin (OT) receptor antagonists, hens incubating eggs were introduced to poults. Over 80% of those injected with vehicle or the D1 DA receptor antagonist brooded poults, while over 80% of those receiving the D2 DA receptor antagonist or the OT receptor antagonist failed to brood the poults. The D2 DA/OT antagonist groups also displayed less c-fos mRNA in the dorsal part of POM and the medial part of the bed nucleus of the stria terminalis (BSTM) areas than did the D1 DA/vehicle groups. These data indicate that numerous brain areas are activated when incubating hens initially transition to poult brooding behavior. They also indicate that DAergic, through its D2 receptor, and MTergic systems may play a role in regulating brooding behaviors in birds.

Trpc2-deficient lactating mice exhibit altered brain and behavioral responses to bedding stimuli

The trpc2 gene encodes an ion channel involved in pheromonal detection and is found in the vomeronasal organ. In tprc2(-/-) knockout (KO) mice, maternal aggression (offspring protection) is impaired and brain Fos expression in females in response to a male are reduced. Here we examine in lactating wild-type (WT) and KO mice behavioral and brain responses to different olfactory/pheromonal cues. Consistent with previous studies, KO dams exhibited decreased maternal aggression and nest building, but we also identified deficits in nighttime nursing and increases in pup weight. When exposed to the bedding tests, WT dams typically ignored clean bedding, but buried male-soiled bedding from unfamiliar males. In contrast, KO dams buried both clean and soiled bedding. Differences in brain Fos expression were found between WT and KO mice in response to either no bedding, clean bedding, or soiled bedding. In the accessory olfactory bulb, a site of pheromonal signal processing, KO mice showed suppressed Fos activation in the anterior mitral layer relative to WT mice in response to clean and soiled bedding. However, in the medial and basolateral amygdala, KO mice showed a robust Fos response to bedding, suggesting that regions of the amygdala canonically associated with pheromonal sensing can be active in the brains of KO mice, despite compromised signaling from the vomeronasal organ. Together, these results provide further insights into the complex ways by which pheromonal signaling regulates the brain and behavior of the maternal female.

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

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

Vasopressin released within the central amygdala promotes maternal aggression

Vasopressin regulates important aspects of social behaviour. Although vasopressin is more prominent in the expression of male social behaviours, we recently demonstrated its role in the fine-tuned maintenance of maternal care in lactating rats. Here, we investigate the involvement of brain vasopressin in the regulation of maternal aggression in lactating Wistar rats selectively bred for either high (HAB) or low (LAB) anxiety-related behaviour. The genetically determined elevation in vasopressin mRNA expression was confirmed within the hypothalamic paraventricular nucleus of virgin and lactating HAB rats and was additionally found in limbic brain areas. Lactating HAB dams are more maternally aggressive as part of their generally higher level of maternal care compared with LAB rats. Using intracerebral microdialysis, we describe increased vasopressin release within the central amygdala, but not the paraventricular nucleus, during maternal aggression only in HAB dams. Moreover, the release of vasopressin within the central amygdala was positively correlated with the display of offensive behaviour. Blockade of local vasopressin actions by bilateral administration of a selective vasopressin V1a receptor antagonist into the central amygdala reduced maternal aggression in HAB dams, whereas synthetic vasopressin increased the low level of aggression in LAB rats. Vasopressin receptor binding within the central amygdala or the paraventricular nucleus was similar in HAB and LAB females. In conclusion, vasopressin is an important neuropeptide regulating maternal aggressive behaviour, thus further extending its involvement in female social behaviour. Differences in intracerebral vasopressin release within the central amygdala rather than local vasopressin receptor binding contribute to the level of maternal aggression.

Trpc2 gene impacts on maternal aggression, accessory olfactory bulb anatomy and brain activity

The Trpc2 gene codes for an ion channel found in the vomeronasal organ (VNO). Studies using the Trpc2(-/-) (KO) mouse have exploited the gene's role in signal transduction to explore the VNO's role in pheromonally mediated behaviors. To date, no study has evaluated the impact of the Trpc2 gene on activity within the brain. In this study, we examine the gene's effect on brain regions governing maternal aggression. We intruder-tested lactating dams and then quantified Fos immunoreactivity (Fos-IR) in the vomeronasal amygdala, hypothalamus, olfactory regions and accessory olfactory bulb (AOB). Our data confirm previous reports that loss of the Trpc2 gene severely diminishes maternal aggression. We also show that deletion of the gene results in differential hypotrophy of the glomerular layer (GlA) of the AOB, with the anterior portion the GlA resembling that of wild-type mice, and the posterior portion reduced or absent. This anatomy is suggestive of residual functioning in the apical VNO of these animals. Our Fos study describes an impact of the deletion on a network of 21 brain regions involved in emotion, aggression and olfaction, suggesting that signals from the VNO mediate activity throughout the brain. Home-cage observations of KO dams show specific deficits in nest-building, suggesting a role for pup pheromones in inducing and maintaining pup-directed maternal behaviors as well as maternal aggression.

Oxytocin: the great facilitator of life

Oxytocin (Oxt) is a nonapeptide hormone best known for its role in lactation and parturition. Since 1906 when its uterine-contracting properties were described until 50 years later when its sequence was elucidated, research has focused on its peripheral roles in reproduction. Only over the past several decades have researchers focused on what functions Oxt might have in the brain, the subject of this review. Immunohistochemical studies revealed that magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei are the neurons of origin for the Oxt released from the posterior pituitary. Smaller cells in various parts of the brain, as well as release from magnocellular dendrites, provide the Oxt responsible for modulating various behaviors at its only identified receptor. Although Oxt is implicated in a variety of "non-social" behaviors, such as learning, anxiety, feeding and pain perception, it is Oxt's roles in various social behaviors that have come to the fore recently. Oxt is important for social memory and attachment, sexual and maternal behavior, and aggression. Recent work implicates Oxt in human bonding and trust as well. Human disorders characterized by aberrant social interactions, such as autism and schizophrenia, may also involve Oxt expression. Many, if not most, of Oxt's functions, from social interactions (affiliation, aggression) and sexual behavior to eventual parturition, lactation and maternal behavior, may be viewed as specifically facilitating species propagation.

Maternal profiling of corticotropin-releasing factor receptor 2 deficient mice in association with restraint stress

Mice deficient in corticotropin-releasing factor receptor 2 (CRF2) (C57BL/6J:129Sv background) exhibit impaired maternal defense (protection of offspring) and are more reactive to stressors than wild-type mice. To further understand CRF2's role in maternal behavior, we crossed the knockout mice with a line bred for high maternal defense that also has elevated maternal care relative to inbred lines. Maternal care was normal in knockout mice (relative to wild-type). Maternal defense was impaired as previously observed. Exposure to a mild stressor (15 min restraint) did not trigger deficits in maternal defense in either genotype as determined by a two-way repeated measures ANOVA analysis. However, when examining difference scores between unrestrained and restrained conditions, knockout mice exhibited significant decreases in maternal defense with stress, suggesting knockouts are more susceptible to a mild stressor's effects. To gain possible insights into brain activity differences between WT and KO mice, we examined c-Fos expression in association with stress. Unrestrained KO mice exhibited significantly lower c-Fos levels relative to unrestrained WT mice in 9 regions, including lateral septum and periaqueductal gray. For WT mice, restraint stress triggered c-Fos activity increases in 3 regions while for KO mice, restraint stress triggered c-Fos increases in 16 regions. Taken together, our results suggest both altered behavioral and c-Fos responses to stress in lactating CRF2 KO mice.

Neuroanatomical specificity of conditioned responses to cocaine versus food in mice

Neural circuits implicated in drug conditioning, craving and relapse overlap extensively with those involved in natural reward and reinforcement. To determine whether specificity could be detected in conditioned brain responses to drugs versus food, male outbred HSD:ICR mice were conditioned to a common environment using either 20 mg/kg cocaine (ip) or a familiar food (under food restriction). The mice were then re-exposed to the same environment without the reinforcer and patterns of brain activation were compared using immunohistochemical detection of Fos. Conditioned place preference tests were conducted first to establish relative potency of each reward and facilitate analysis of correlations between Fos and motivation. Place preference was stronger for cocaine than food. Food- but not cocaine-paired cues increased Fos in the paraventricular hypothalamic nucleus whereas the opposite occurred for prefrontal, cingulate and piriform cortices. Individual differences in cocaine place preference were negatively correlated with Fos in the prefrontal cortex. One difference between drugs and natural reinforcers may be lack of feedback from the periphery for drugs which may circumvent control from the hypothalamus in the development of reinforcement circuits.

Integrative focus on dynamic motor patterns and age hierarchy in the expression of aggression

In this study, we analyzed the dynamic motor patterns of attack or defense and age hierarchy to investigate aggression in African mole-rats Cryptomys foxi and the house mouse Mus musculus. The objective is to verify if the social order of dominance is associated with age hierarchy within the social group. Using the resident-intruder experimental model, we created a series of dyadic encounters that comprised of a standard adult mouse or rat paired with groups of aggressive and hierarchically age-ranked small animals in a territorial aggression test. Our results indicate that though the adult animals displayed the highest level of aggression, indicating their dominant status, there was no age-related hierarchical formation in the expression of aggression. In the non-territorial aggression test in which rats or mice were grouped together, animals displayed low levels of aggression compared to the territorial test and no hierarchical age-related order. These results indicate that the magnitude of aggression expressed by animals in the social group, based on their motor patterns of attack and defense, seem to depend on individual competitive strategies in reaction to various environmental challenges and not necessarily on age hierarchy.

Effects of daily and acute restraint stress during lactation on maternal aggression and behavior in mice

A decreased reactivity to stressors during lactation might heighten the expression of maternal care (including defense of offspring) by minimizing the extent to which stress can impact maternal care. Although stressors applied during pregnancy have variable effects on maternal aggression (or defense of offspring), to date no study has examined the effects of stress applied during the postpartum period on maternal aggression. In this study, we examined the effects of both daily and acute restraint stress (30 min) applied postpartum on maternal aggression and other maternal behaviors. Daily restraint (ending 2 h before testing) did not alter any measure of maternal behavior, including nursing, licking and grooming of pups and pup retrieval, or any measure of maternal aggression. In contrast, acute stress significantly impaired total time aggressive and number of attacks, but pup retrieval was normal. c-Fos levels were significantly elevated in a number of brain regions in association with acute stress, including lateral septum (LS), caudal periaqueductal gray and medial amygdala (MeA), suggesting possible sites where stress reactivity could alter aggression. Together, the results indicate that acute restraint stress impairs maternal aggression and provide a starting point for future studies examining how stress reactivity pathways may intersect with maternal aggression pathways.