Urocortin 1 and 3 impair maternal defense behavior in mice

CRF binding protein activity in the hypothalamic paraventricular nucleus is essential for stress adaptations and normal maternal behaviour in lactating rats

To ensure the unrestricted expression of maternal behaviour peripartum, activity of the corticotropin-releasing factor (CRF) system needs to be minimised. CRF binding protein (CRF-BP) might be crucial for this adaptation, as its primary function is to sequester freely available CRF and urocortin1, thereby dampening CRF receptor (CRF-R) signalling. So far, the role of CRF-BP in the maternal brain has barely been studied, and a potential role in curtailing activation of the stress axis is unknown. We studied gene expression for CRF-BP and both CRF-R within the paraventricular nucleus (PVN) of the hypothalamus. In lactating rats, Crh-bp expression in the parvocellular PVN was significantly higher and Crh-r1 expression in the PVN significantly lower compared to virgin rats. Acute CRF-BP inhibition in the PVN with infusion of CRF(6-33) increased basal plasma corticosterone concentrations under unstressed conditions in dams. Furthermore, while acute intra-PVN infusion of CRF increased corticosterone secretion in virgin rats, it was ineffective in vehicle (VEH)-pre-treated lactating rats, probably due to a buffering effect of CRF-BP. Indeed, pre-treatment with CRF(6-33) reinstated a corticosterone response to CRF in lactating rats, highlighting the critical role of CRF-BP in maintaining attenuated stress reactivity in lactation. To our knowledge, this is the first study linking hypothalamic CRF-BP activity to hypothalamic-pituitary-adrenal axis regulation in lactation. In terms of behaviour, acute CRF-BP inhibition in the PVN under non-stress conditions reduced blanket nursing 60 min and licking/grooming 90 min after infusion compared to VEH-treated rats, while increasing maternal aggression towards an intruder. Lastly, chronic intra-PVN inhibition of CRF-BP strongly reduced maternal aggression, with modest effects on maternal motivation and care. Taken together, intact activity of the CRF-BP in the PVN during the postpartum period is essential for the dampened responsiveness of the stress axis, as well as for the full expression of appropriate maternal behaviour.

Social effects on AVT and CRF systems

Stress and aggression have negative effects on fish welfare and productivity in aquaculture. Thus, research to understand aggression and stress in farmed fish is required. The neuropeptides arginine-vasotocin (AVT) and corticotropin-releasing factor (CRF) are involved in the control of stress and aggression. Therefore, we investigated the effect of agonistic interactions on the gene expression of AVT, CRF and their receptors in juvenile rainbow trout (Oncorhynchus mykiss). The social interactions lead to a clear dominant-subordinate relationship with dominant fish feeding more and being more aggressive. Subordinate fish had an upregulation of the AVT receptor (AVT-R), an upregulation of CRF mRNA levels, and higher plasma cortisol levels. The attenuating effect of AVT on aggression in rainbow trout is proposed to be mediated by AVT-R, and the attenuating effect of the CRF system is proposed to be mediated by CRF.

Sex-Dimorphic Behavioral Alterations and Altered Neurogenesis in U12 Intron Splicing-Defective Zrsr1 Mutant Mice

Mutant mice with respect to the splicing factor Zrsr1 present altered spermatogenesis and infertility. To investigate whether Zrsr1 is involved in the homeostatic control that the hypothalamus exerts over reproductive functions, we first analyzed both differential gene and isoform expression and alternative splicing alterations in Zrsr1 mutant (Zrsr1^mu) hypothalamus; second, we analyzed the spontaneous and social behavior of Zrsr1^mu mice; and third, we analyzed adult cell proliferation and survival in the Zrsr1^mu hypothalamus. The Zrsr1^mu hypothalamus showed altered expression of genes and isoforms related to the glutathione metabolic process, synaptonemal complex assembly, mRNA transport, and altered splicing events involving the enrichment of U12-type intron retention (IR). Furthermore, increased IR in U12-containing genes related with the prolactin, progesterone, and gonadotropin-releasing hormone (GnRH) reproductive signaling pathway was observed. This was associated with a hyperactive phenotype in both males and females, with an anxious phenotype in females, and with increased social interaction in males, instead of the classical aggressive behavior. In addition, Zrsr1^mu females but not males exhibited reduced cell proliferation in both the hypothalamus and the subventricular zone. Overall, these results suggest that Zrsr1 expression and function are relevant to organization of the hypothalamic cell network controlling behavior.

When mothers neglect their offspring: an activated CRF system in the BNST is detrimental for maternal behavior

Becoming a mother is an intense experience that not only changes a woman's life but is also paralleled by multiple central adaptations. These changes evolve before parturition and continue to persist into lactation, thereby ensuring the full commitment of the mother to care for the newborns. Most of our knowledge on these adaptations that drive the peripartum brain come from rodent animal models. On one side, it is known that maternal behavior is initiated and maternal mood is stabilized by an upregulation of the pro-maternal neuropeptide systems' activity of oxytocin and arginine-vasopressin. On the other side, signaling of the rather anti-maternal corticotropin-releasing factor system triggers maternal neglect and increases maternal anxiety. Here, we discuss how the corticotropin-releasing factor system based in the limbic bed nucleus of the stria terminalis negatively affects maternal behavior and maternal mood. Moreover, we apply microdialysis and acute pharmacological interventions to demonstrate how the corticotropin-releasing factor system potentially interacts with the pro-maternal oxytocin system in the posterior bed nucleus of the stria terminalis to trigger certain aspects of maternal behavior.

Mom doesn't care: When increased brain CRF system activity leads to maternal neglect in rodents

Mothers are the primary caregivers in mammals, ensuring their offspring's survival. This strongly depends on the adequate expression of maternal behavior, which is the result of a concerted action of "pro-maternal" versus "anti-maternal" neuromodulators such as the oxytocin and corticotropin-releasing factor (CRF) systems, respectively. When essential peripartum adaptations fail, the CRF system has negative physiological, emotional and behavioral consequences for both mother and offspring often resulting in maternal neglect. Here, we provide an elaborate and unprecedented review on the implications of the CRF system in the maternal brain. Studies in rodents have advanced our understanding of the specific roles of brain regions such as the limbic bed nucleus of the stria terminalis, medial preoptic area and lateral septum even in a CRF receptor subtype-specific manner. Furthermore, we discuss potential interactions of the CRF system with other neurotransmitters like oxytocin and noradrenaline, and present valuable translational aspects of the recent research.

Urocortins and their unfolding role in mammalian social behavior

The corticotropin-releasing factor (CRF) system is well known for its major role in coordinating the endocrine, autonomic and behavioral responses to stress. These functions have been shown to be mediated mainly by the binding of the CRF neuropeptide to its specific receptor CRFR1. Yet, the CRF system comprises several more neuropeptides, including the three urocortins, UCN1, UCN2 and UCN3, of which the latter two bind specifically to a distinct receptor-CRFR2. Unlike the brain-wide abundant expression of CRF and CRFR1, the brain expression of the urocortins and CRFR2 is rather restricted and seems to be focused in limbic areas associated with social behavior. Here, we will review accumulating evidence from recent studies that unfold the role of UCN2 and UCN3 in regulating mammalian social behavior, via activation of CRFR2.

Maternal stress and the MPOA: Activation of CRF receptor 1 impairs maternal behavior and triggers local oxytocin release in lactating rats

Maternal behavior and anxiety are potently modulated by the brain corticotropin-releasing factor (CRF) system postpartum. Downregulation of CRF in limbic brain regions is essential for appropriate maternal behavior and an adaptive anxiety response. Here, we focus our attention on arguably the most important brain region for maternal behavior, the hypothalamic medial preoptic area (MPOA). Within the MPOA, mRNA for CRF receptor subtype 1 (protein: CRFR1, gene: Crhr1) was more abundantly expressed than for subtype 2 (protein: CRFR2, gene: Crhr2), however expression of Crhr1, Crhr2 and CRF-binding protein (protein: CRFBP, gene: Crhbp) mRNA was similar between virgin and lactating rats. Subtype-specific activation of CRFR, predominantly CRFR1, in the MPOA decreased arched back nursing and total nursing under non-stress conditions. Following acute stressor exposure, only CRFR1 inhibition rescued the stress-induced reduction in arched back nursing while CRFR1 activation prolonged the decline in nursing. Furthermore, inhibition of CRFR1 strongly increased maternal aggression in the maternal defense test. CRFR1 activation had anxiogenic actions and reduced locomotion on the elevated plus-maze, however neither CRFR1 nor R2 manipulation affected maternal motivation. In addition, activation of CRFR1, either centrally or locally in the MPOA, increased local oxytocin release. Finally, inhibition of CRFBP (a potent regulator of CRFR activity) in the MPOA did not affect any of the maternal parameters investigated. In conclusion, activity of CRFR in the MPOA, particularly of subtype 1, needs to be dampened during lactation to ensure appropriate maternal behavior. Furthermore, oxytocin release in the MPOA may provide a regulatory mechanism to counteract the negative impact of CRFR activation on maternal behavior.

Low temperatures during ontogeny increase fluctuating asymmetry and reduce maternal aggression in the house mouse, Mus musculus

Maternal aggression is behavior displayed by post-partum lactating female mice toward unfamiliar conspecifics, presumably as a defense against infanticide. A variety of perinatal stressors can impair maternal care in adulthood. Previous studies on associations between developmental perturbations and maternal aggression have produced mixed results. To address this issue, we employed a proxy for developmental instability, fluctuating asymmetry (FA) to further elucidate the relationship between low temperature stress and maternal aggression. FA, small, random deviations from perfect symmetry in bilateral characters is used as a quantitative measure of stress during ontogeny. Dams were either maintained in standard laboratory temperatures (21 ± 2 °C), or cold temperatures (8 ± 2 °C) during gestation. During lactation, their progeny either remained in the temperature condition in which they were gestated or were transferred to the other temperature condition. Four individual measures of FA, a composite of these measures, and three measures of maternal aggression were assessed in the female progeny in adulthood. Exposure to low temperatures during both pre- and early post-natal development increased composite FA and reduced all three measures of maternal aggression compared to controls. Exposure to low temperatures during the pre- or postnatal period alone did not induce either high FA or altered maternal aggression. Certain measures of FA and nest defense were negatively correlated. Our results suggest that low temperatures experienced during gestation and lactation may have important fitness costs. Low maternal aggression towards infanticidal conspecifics is likely to limit the number of offspring surviving into adulthood. Overall, FA appears to be a reliable indicator of chronic developmental stress with implications for fitness.

The neurobiology of parenting: A neural circuit perspective

Social interactions are essential for animals to reproduce, defend their territory, and raise their young. The conserved nature of social behaviors across animal species suggests that the neural pathways underlying the motivation for, and the execution of, specific social responses are also maintained. Modern tools of neuroscience have offered new opportunities for dissecting the molecular and neural mechanisms controlling specific social responses. We will review here recent insights into the neural circuits underlying a particularly fascinating and important form of social interaction, that of parental care. We will discuss how these findings open new avenues to deconstruct infant-directed behavioral control in males and females, and to help understand the neural basis of parenting in a variety of animal species, including humans. Please also see the video abstract here.

CRF-R1 activation in the anterior-dorsal BNST induces maternal neglect in lactating rats via an HPA axis-independent central mechanism

Adequate maternal behavior in rats requires minimal corticotropin-releasing factor receptor (CRF-R) activation in the medial-posterior bed nucleus of the stria terminalis (mpBNST). Based on the architectural heterogeneity of the BNST and its distinct inter-neural connectivity, we tested whether CRF-R manipulation in another functional part, the anterior-dorsal BNST (adBNST), differentially modulates maternal behavior. We demonstrate that in the adBNST, activation of CRF-R1 reduced arched back nursing (ABN) and nursing, whereas activation of CRF-R2 resulted in an initial reduction in nursing but significantly increased the incidence of ABN 5h after the treatment. Following stressor exposure, which is detrimental to maternal care, ABN tended to be protected by CRF-R1 blockade. Maternal motivation, maternal aggression, and anxiety were unaffected by any manipulation. Furthermore, under basal and stress conditions, activation of adBNST CRF-R1 increased plasma ACTH and corticosterone concentrations, whereas stimulation of adBNST CRF-R2 increased basal plasma ACTH and corticosterone concentrations, but blocked the stress-induced increase in plasma corticosterone secretion. Moreover, both the CRF-R1 and -R2 antagonists prevented the stress-induced increase in plasma corticosterone secretion. Importantly, elevated levels of circulating corticosterone induced by intra-adBNST administration of CRF-R1 or -R2 agonist did not impact maternal care. Finally, Crf mRNA expression in the adBNST was increased during lactation; however, Crfr1 mRNA expression was similar between lactating and virgin rats. In conclusion, maternal care is impaired by adBNST CRF-R1 activation, and this appears to be the result of a central action, rather than an effect of elevated circulating levels of CORT. These data provide new insights into potential causes of disturbed maternal behavior postpartum.

Prevention of alcohol-heightened aggression by CRF-R1 antagonists in mice: critical role for DRN-PFC serotonin pathway

Alcohol can escalate aggressive behavior in a significant subgroup of rodents, humans, and nonhuman primates. The present study investigated whether blockade of corticotropin-releasing factor receptor type 1 (CRF-R1) could prevent the emergence of alcohol-heightened aggression in mice. The serotonin (5-HT) pathway from the dorsal raphe nucleus (DRN) to the medial prefrontal cortex (mPFC) by CRF-R1 was investigated as a possible target for the prevention of alcohol-heightened aggressive behavior. Male CFW mice that reliably exhibited aggressive behaviors after consuming 1 g/kg of alcohol received systemic or intra-DRN administration of CRF-R1 antagonists, CP-154,526 or MTIP, before a confrontation with a male conspecific. Blockade of DRN CRF-R1 receptors with both antagonists significantly reduced only alcohol-heightened aggression, whereas systemic administration reduced both alcohol-heightened and species-typical aggression. Next, a 5-HT1A agonist, 8-OH-DPAT, was coadministered with CP-154,526 into the DRN to temporarily disrupt 5-HT activity. This manipulation abolished the antiaggressive effects of intra-DRN CP-154,526. In the mPFC, in vivo microdialysis revealed that extracellular 5-HT levels were increased in mice that consumed alcohol and were then injected with CP-154,526, both systemically or intra-DRN. Neither alcohol nor CP-154,526 alone affected 5-HT release in the mPFC. The present results suggest the DRN as a critical site for CRF-R1 to modulate alcohol-heightened aggression via action on the serotonergic DRN-PFC pathway.

Hypoactivation of CRF receptors, predominantly type 2, in the medial-posterior BNST is vital for adequate maternal behavior in lactating rats

Maternal behavior ensures the proper development of the offspring. In lactating mammals, maternal behavior is impaired by stress, the physiological consequence of central corticotropin-releasing factor receptor (CRF-R) activation. However, which CRF-R subtype in which specific brain area(s) mediates this effect is unknown. Here we confirmed that an intracerebroventricularly injected nonselective CRF-R antagonist enhances, whereas an agonist impairs, maternal care. The agonist also prolonged the stress-induced decrease in nursing, reduced maternal aggression and increased anxiety-related behavior. Focusing on the bed nucleus of the stria terminalis (BNST), CRF-R1 and CRF-R2 mRNA expression did not differ in virgin versus lactating rats. However, CRF-R2 mRNA was more abundant in the posterior than in the medial BNST. Pharmacological manipulations within the medial-posterior BNST showed that both CRF-R1 and CRF-R2 agonists reduced arched back nursing (ABN) rapidly and after a delay, respectively. After stress, both antagonists prevented the stress-induced decrease in nursing, with the CRF-R2 antagonist actually increasing ABN. During the maternal defense test, maternal aggression was abolished by the CRF-R2, but not the CRF-R1, agonist. Anxiety-related behavior was increased by the CRF-R1 agonist and reduced by both antagonists. Both antagonists were also effective in virgin females but not in males, revealing a sexual dimorphism in the regulation of anxiety within the medial-posterior BNST. In conclusion, the detrimental effects of increased CRF-R activation on maternal behavior are mediated via CRF-R2 and, to a lesser extent, via CRF-R1 in the medial-posterior BNST in lactating rats. Moreover, both CRF-R1 and CRF-R2 regulate anxiety in females independently of their reproductive status.

Central corticotropin releasing factor and social stress

Social interactions are a main source of stress in vertebrates. Social stressors, as well as other stressors, activate the hypothalamic–pituitary–adrenal (HPA) axis resulting in glucocorticoid release. One of the main components of the HPA axis is corticotropin releasing factor (CRF). The neuropeptide CRF is part of a peptide family including CRF, urocortin 1–3, urotensin 1–3, and sauvagine. The actions of the CRF family are mediated by at least two different receptors with different anatomical distribution and affinities for the peptides. The CRF peptides affect several behavioral and physiological responses to stress including aggression, feeding, and locomotor activity. This review will summarize recent research in vertebrates concerning how social stress interacts with components of the CRF system. Consideration will be taken to the different models used for social stress ranging from social isolation, dyadic interactions, to group dominance hierarchies. Further, the temporal effect of social stressor from acute, intermittent, to chronic will be considered. Finally, strains selected for specific behavior or physiology linked to social stress will also be discussed.

The CRF system and social behavior: a review

The corticotropin-releasing factor (CRF) system plays a key role in a diversity of behaviors accompanying stress, anxiety and depression. There is also substantial research on relationships between social behaviors and the CRF system in a variety of taxa including fish, birds, rodents, and primates. Some of these relationships are due to the broad role of CRF and urocortins in stress and anxiety, but these peptides also modulate social behavior specifically. For example, the social interaction (SI) test is often used to measure anxiety-like behavior. Many components of the CRF system including CRF, urocortin1, and the R1 receptor have been implicated in SI, via general effects on anxiety as well as specific effects depending on the brain region. The CRF system is also highly responsive to chronic social stressors such as social defeat and isolation. Animals exposed to these stressors display a number of anxiety- and stress-related behaviors, accompanied by changes in specific components the CRF system. Although the primary focus of CRF research on social behavior has been on the deleterious effects of social stress, there are also insights on a role for CRF and urocortins in prosocial and affiliative behaviors. The CRF system has been implicated in parental care, maternal defense, sexual behavior, and pair bonding. Species differences in the ligands and CRF receptors have been observed in vole and bird species differing in social behavior. Exogenous administration of CRF facilitates partner preference formation in monogamous male prairie voles, and these effects are dependent on both the CRF R1 and R2 receptors. These findings are particularly interesting as studies have also implicated the CRF and urocortins in social memory. With the rapid progress of social neuroscience and in understanding the complex structure of the CRF system, the next challenge is in parsing the exact contribution of individual components of this system to specific social behaviors.

Maternal defense is modulated by beta adrenergic receptors in lateral septum in mice

Maternal defense (offspring protection) is a critical and highly conserved component of maternal care in mammalian systems that involves dramatic shifts in a female's behavioral response to social cues. Numerous changes occur in neuronal signaling and connectivity in the postpartum female, including decreases in norepinephrine (NE) signaling in subregions of the CNS. In this study using a strain of mice selected for maternal defense, we examined whether possible changes in NE signaling in the lateral septum (LS) could facilitate expression of maternal aggression. In separate studies that utilized a repeated measures design, mice were tested for maternal defense following intra-LS injections of either the β-adrenergic receptor agonist isoproterenol (10 μg or 30 μg) or vehicle (Experiment 1), the β-adrenergic receptor antagonist propranolol (2 μg) or vehicle (Experiment 2), or the β1-receptor antagonist, atenolol (Experiment 3). Mice were also evaluated for light-dark performance and pup retrieval. Thirty micrograms of the agonist isoproterenol significantly decreased number of attacks and time aggressive relative to vehicle without affecting pup retrieval or light-dark box performance. In contrast, the antagonist propranolol significantly increased maternal aggression (lowered latency to attack and increased total attack time) without altering light-dark box test. The β1-specific antagonist, atenolol, significantly decreased latency to attack (1 μg vs. vehicle) without altering other measures. Although the findings were identified in a unique strain of mice, the results of these studies support the hypothesis that changes in NE signaling in LS during the postpartum period contribute to the expression of offspring protection.

Changes in CNS response to neurotensin accompany the postpartum period in mice

Neurotensin (NT) is a highly conserved neuropeptide in mammals. Recent studies suggest that altered NT neurotransmission in postpartum females could promote the emergence of some maternal behaviors, including offspring protection. Here we evaluated how virgin and postpartum brains from mice selected for high maternal defense differ in response to NT. Virgin and postpartum mice were injected with either vehicle or 0.1 μg NT icv and brains were evaluated for c-Fos immunoreactivity, an indirect marker of neuronal activity. Using ANOVA analysis, common significant responses to NT were found in both female groups in four brain regions, including supraoptic nucleus, ventromedial nucleus, bed nucleus of stria terminalis dorsal, and a subregion of lateral septum (LS). For postpartum mice, only one additional region showed a significant response to NT relative to vehicle, whereas for virgin mice seven unique brain regions showed a significant c-Fos response: nucleus accumbens shell, paraventricular nucleus, central amygdala, and substantia nigra. Using a principal components analysis of c-Fos, we identified regions within each group with highly correlated activity. As expected, virgin and postpartum mice (vehicle conditions) showed different activity hubs and in the postpartum group the hubs matched regions linked to maternal care. The response to injected NT was different in the maternal and virgin groups with maternal mice showing a stronger coordinated activity in periaqueductal gray whereas virgin mice showed a stronger septal and amygdala linking of activity. Together, these results indicate neuronal responses of virgin and postpartum mice to NT and highlight pathways by which NT can alter maternal responses.

Leptin signaling modulates the activity of urocortin 1 neurons in the mouse nonpreganglionic Edinger-Westphal nucleus

A recent study systematically characterized the distribution of the long form of the leptin receptor (LepRb) in the mouse brain and showed substantial LepRb mRNA expression in the nonpreganglionic Edinger-Westphal nucleus (npEW) in the rostroventral part of the midbrain. This nucleus hosts the majority of urocortin 1 (Ucn1) neurons in the rodent brain, and because Ucn1 is a potent satiety hormone and electrical lesioning of the npEW strongly decreases food intake, we have hypothesized a role of npEW-Ucn1 neurons in leptin-controlled food intake. Here, we show by immunohistochemistry that npEW-Ucn1 neurons in the mouse contain LepRb and respond to leptin administration with induction of the Janus kinase 2-signal transducer and activator of transcription 3 pathway, both in vivo and in vitro. Furthermore, systemic leptin administration increases the Ucn1 content of the npEW significantly, whereas in mice that lack LepRb (db/db mice), the npEW contains considerably reduced amount of Ucn1. Finally, we reveal by patch clamping of midbrain Ucn1 neurons that leptin administration reduces the electrical firing activity of the Ucn1 neurons. In conclusion, we provide ample evidence for leptin actions that go beyond leptin's well-known targets in the hypothalamus and propose that leptin can directly influence the activity of the midbrain Ucn1 neurons.

Brain serotonin receptors and transporters: initiation vs. termination of escalated aggression

RATIONALE

Recent findings have shown a complexly regulated 5-HT system as it is linked to different kinds of aggression.

OBJECTIVE

We focus on (1) phasic and tonic changes of 5-HT and (2) state and trait of aggression, and emphasize the different receptor subtypes, their role in specific brain regions, feed-back regulation and modulation by other amines, acids and peptides.

RESULTS

New pharmacological tools differentiate the first three 5-HT receptor families and their modulation by GABA, glutamate and CRF. Activation of 5-HT(1A), 5-HT(1B) and 5-HT(2A/2C) receptors in mesocorticolimbic areas, reduce species-typical and other aggressive behaviors. In contrast, agonists at 5-HT(1A) and 5-HT(1B) receptors in the medial prefrontal cortex or septal area can increase aggressive behavior under specific conditions. Activation of serotonin transporters reduce mainly pathological aggression. Genetic analyses of aggressive individuals have identified several molecules that affect the 5-HT system directly (e.g., Tph2, 5-HT(1B), 5-HT transporter, Pet1, MAOA) or indirectly (e.g., Neuropeptide Y, αCaMKII, NOS, BDNF). Dysfunction in genes for MAOA escalates pathological aggression in rodents and humans, particularly in interaction with specific experiences.

CONCLUSIONS

Feedback to autoreceptors of the 5-HT(1) family and modulation via heteroreceptors are important in the expression of aggressive behavior. Tonic increase of the 5-HT(2) family expression may cause escalated aggression, whereas the phasic increase of 5-HT(2) receptors inhibits aggressive behaviors. Polymorphisms in the genes of 5-HT transporters or rate-limiting synthetic and metabolic enzymes of 5-HT modulate aggression, often requiring interaction with the rearing environment.

Behavioral and pharmacogenetics of aggressive behavior

Serotonin (5-HT) has long been considered as a key transmitter in the neurocircuitry controlling aggression. Impaired regulation of each subtype of 5-HT receptor, 5-HT transporter, synthetic and metabolic enzymes has been linked particularly to impulsive aggression. The current summary focuses mostly on recent findings from pharmacological and genetic studies. The pharmacological treatments and genetic manipulations or polymorphisms of aspecific target (e.g., 5-HT1A receptor) can often result in inconsistent results on aggression, due to "phasic" effects of pharmacological agents versus "trait"-like effects of genetic manipulations. Also, the local administration of a drug using the intracranial microinjection technique has shown that activation of specific subtypes of 5-HT receptors (5-HT1A and 5-HT1B) in mesocorticolimbic areas can reduce species-typical and other aggressive behaviors, but the same receptors in the medial prefrontal cortex or septal area promote escalated forms of aggression. Thus, there are receptor populations in specific brain regions that preferentially modulate specific types of aggression. Genetic studies have shown important gene-environment interactions; it is likely that the polymorphisms in the genes of 5-HT transporters or rate-limiting synthetic and metabolic enzymes of 5-HT (e.g., MAOA) determine the vulnerability to adverse environmental factors that escalate aggression. We also discuss the interaction between the 5-HT system and other systems. Modulation of 5-HT neurons in the dorsalraphe nucleus by GABA, glutamate and CRF profoundly regulate aggressive behaviors. Also, interactions of the 5-HT system with other neuropeptides(arginine vasopressin, oxytocin, neuropeptide Y, opioid) have emerged as important neurobiological determinants of aggression. Studies of aggression in genetically modified mice identified several molecules that affect the 5-HT system directly (e.g., Tph2, 5-HT1B, 5-HT transporter, Pet1, MAOA) or indirectly[e.g., BDNF, neuronal nitric oxide (nNOS), aCaMKII, Neuropeptide Y].The future agenda delineates specific receptor subpopulations for GABA, glutamate and neuropeptides as they modulate the canonical aminergic neurotransmitters in brainstem, limbic and cortical regions with the ultimate outcome of attenuating or escalating aggressive behavior.

Urocortin 3 modulates social discrimination abilities via corticotropin-releasing hormone receptor type 2

Urocortin 3 (UCN3) is strongly expressed in specific nuclei of the rodent brain, at sites distinct from those expressing urocortin 1 and urocortin 2, the other endogenous ligands of corticotropin-releasing hormone receptor type 2 (CRH-R2). To determine the physiological role of UCN3, we generated UCN3-deficient mice, in which the UCN3 open reading frame was replaced by a tau-lacZ reporter gene. By means of this reporter gene, the nucleus parabrachialis and the premammillary nucleus were identified as previously unknown sites of UCN3 expression. Additionally, the introduced reporter gene enabled the visualization of axonal projections of UCN3-expressing neurons from the superior paraolivary nucleus to the inferior colliculus and from the posterodorsal part of the medial amygdala to the principal nucleus of the bed nucleus of the stria terminalis, respectively. The examination of tau-lacZ reporter gene activity throughout the brain underscored a predominant expression of UCN3 in nuclei functionally connected to the accessory olfactory system. Male and female mice were comprehensively phenotyped but none of the applied tests provided indications for a role of UCN3 in the context of hypothalamic-pituitary-adrenocortical axis regulation, anxiety- or depression-related behavior. However, inspired by the prevalent expression throughout the accessory olfactory system, we identified alterations in social discrimination abilities of male and female UCN3 knock-out mice that were also present in male CRH-R2 knock-out mice. In conclusion, our results suggest a novel role for UCN3 and CRH-R2 related to the processing of social cues and to the establishment of social memories.

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.

CRF-1 antagonist and CRF-2 agonist decrease binge-like ethanol drinking in C57BL/6J mice independent of the HPA axis

Recent evidence suggests that corticotropin-releasing factor (CRF) receptor (CRFR) signaling is involved in modulating binge-like ethanol consumption in C57BL/6J mice. In this report, a series of experiments were performed to further characterize the role of CRFR signaling in binge-like ethanol consumption. The role of central CRFR signaling was assessed with intracerebroventricular (i.c.v.) infusion of the nonselective CRFR antagonist, alpha-helical CRF(9-41) (0, 1, 5, 10 microg/1 microl). The contribution of central CRF type 2 receptor (CRF(2)R) signaling was assessed with i.c.v. infusion of the selective CRF(2)R agonist, urocortin (Ucn) 3 (0, 0.05, 0.1, or 0.5 microg/1 microl). The role of the hypothalamic-pituitary-adrenal (HPA) axis was assessed by pretreating mice with intraperitoneal (i.p.) injection of (1) the corticosterone synthesis inhibitor, metyrapone (0, 50, 100, 150 mg/kg) or (2) the glucocorticoid receptor antagonist, mifepristone (0, 25, 50 mg/kg), and (3) by using radioimmunoassay to determine whether binge-like ethanol intake influenced plasma corticosterone levels. Finally, we determined whether the ability of the CRF(1)R antagonist, CP-154,526 (CP; 0, 10, 15 mg/kg, i.p.), to blunt binge-like drinking required normal HPA axis signaling by comparing the effectiveness of CP in adrenalectomized (ADX) and normal mice. Results showed that i.c.v. infusion of a 1 microg dose of alpha-helical CRF(9-41) significantly attenuated binge-like ethanol consumption relative to vehicle treatment, and i.c.v. infusion of Ucn 3 dose-dependently blunted binge-like drinking. On the other hand, metyrapone nonselectively reduced both ethanol and sucrose consumption, mifepristone did not alter ethanol drinking, and binge-like drinking did not correlate with plasma corticosterone levels. Finally, i.p. injection of CP significantly attenuated binge-like ethanol intake in both ADX and normal mice. Together, these results suggest that binge-like ethanol intake in C57BL/6J mice is modulated by CRF(1)R and CRF(2)R signaling, such that blockade of CRF(1)R or activation of CRF(2)R effectively reduces excessive ethanol intake. Furthermore, normal HPA axis signaling is not necessary to achieve binge-like drinking behavior.

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

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

Neurotensin inversely modulates maternal aggression

Neurotensin (NT) is a versatile neuropeptide involved in analgesia, hypothermia, and schizophrenia. Although NT is released from and acts upon brain regions involved in social behaviors, it has not been linked to a social behavior. We previously selected mice for high maternal aggression (maternal defense), an important social behavior that protects offspring, and found significantly lower NT expression in the CNS of highly protective females. Our current study directly tested NT's role in maternal defense. Intracerebroventricular (i.c.v.) injections of NT significantly impaired defense in terms of time aggressive and number of attacks at all doses tested (0.05, 0.1, 1.0, and 3.0 microg). Other maternal behaviors, including pup retrieval, were unaltered following NT injections (0.05 microg) relative to vehicle, suggesting specificity of NT action on defense. Further, i.c.v. injections of the NT receptor 1 (NT1) antagonist, SR 48692 (30 microg), significantly elevated maternal aggression in terms of time aggressive and attack number. To understand where NT may regulate aggression, we examined Fos following injection of either 0.1 microg NT or vehicle. Thirteen of 26 brain regions examined exhibited significant Fos increases with NT, including regions expressing NT1 and previously implicated in maternal aggression, such as lateral septum, bed nucleus of stria terminalis, paraventricular nucleus, and central amygdala. Together, our results indicate that NT inversely regulates maternal aggression and provide the first direct evidence that lowering of NT signaling can be a mechanism for maternal aggression. To our knowledge, this is the first study to directly link NT to a social behavior.

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.

Deletion of corticotropin-releasing factor binding protein selectively impairs maternal, but not intermale aggression

Corticotropin-releasing factor (CRF) binding protein (CRF-BP) is a secreted protein that acts to bind and limit the activity of the neuropeptides, CRF and urocortin (Ucn) 1. We previously selected for high maternal defense (protection of offspring) in mice and found CRF-BP to be elevated in the CNS of selected mice. We also previously determined that both CRF and Ucn 1 are potent inhibitors of offspring protection when administered centrally. Thus, elevated CRF-BP could promote defense by limiting endogenous actions of CRF or Ucn 1. To test this hypothesis, we crossed the deletion for CRF-BP into the mice selected for high maternal defense and evaluated offspring protection and other maternal behaviors. CRF-BP knockout (KO) mice exhibited significant deficits in maternal aggression relative to wild-type (WT) mice in three different measures. Other maternal features were almost identical between groups, including dam and pup weight, litter size, nursing time, and pup retrieval. Both groups performed similarly in a forced swim stress test and aggression in both groups was reduced following the swim test. Virgin KO female mice exhibited higher levels of anxiety-like behavior in terms of decreased time in the light portion of the light/dark box test. For males, no differences in light/dark box or swim test were found. However, increased anxiety-like behavior in male KO mice was identified in terms of contact and approach to a novel object both with and without previous exposure to the swim test. No differences in isolation induced resident intruder male aggression were found between groups. Together, these results indicate that loss of CRF-BP selectively impairs maternal, but not intermale aggression and that loss of the gene induces anxiety-like behavior in males and females, but there are sex differences in terms of how that anxiety is revealed.

Altered dopamine signaling in naturally occurring maternal neglect

BACKGROUND

Child neglect is the most common form of child maltreatment, yet the biological basis of maternal neglect is poorly understood and a rodent model is lacking.

METHODOLOGY/PRINCIPAL FINDINGS

The current study characterizes a population of mice (MaD1) which naturally exhibit maternal neglect (little or no care of offspring) at an average rate of 17% per generation. We identified a set of risk factors that can predict future neglect of offspring, including decreased self-grooming and elevated activity. At the time of neglect, neglectful mothers swam significantly more in a forced swim test relative to nurturing mothers. Cross-fostered offspring raised by neglectful mothers in turn exhibit increased expression of risk factors for maternal neglect and decreased maternal care as adults, suggestive of possible epigenetic contributions to neglect. Unexpectedly, offspring from neglectful mothers elicited maternal neglect from cross-fostered nurturing mothers, suggesting that factors regulating neglect are not solely within the mother. To identify a neurological pathway underlying maternal neglect, we examined brain activity in neglectful and nurturing mice. c-Fos expression was significantly elevated in neglectful relative to nurturing mothers in the CNS, particularly within dopamine associated areas, such as the zona incerta (ZI), ventral tegmental area (VTA), and nucleus accumbens. Phosphorylated tyrosine hydroxylase (a marker for dopamine production) was significantly elevated in ZI and higher in VTA (although not significantly) in neglectful mice. Tyrosine hydroxylase levels were unaltered, suggesting a dysregulation of dopamine activity rather than cell number. Phosphorylation of DARPP-32, a marker for dopamine D1-like receptor activation, was elevated within nucleus accumbens and caudate-putamen in neglectful versus nurturing dams.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that atypical dopamine activity within the maternal brain, especially within regions involved in reward, is involved in naturally occurring neglect and that MaD1 mice are a useful model for understanding the basis of naturally occurring neglect.

Urocortin and the brain

Urocortin is a member of the corticotropin-releasing hormone (CRH) family of peptides. In the brain, its potent suppression of food intake is mediated by CRH receptors (CRHR). Urocortin also participates in the regulation of anxiety, learning, memory, and body temperature, and it shows neuroprotection. This review will summarize the location of urocortin-producing neurons and their projections, the pharmacological evidence of its actions in the CNS, and information acquired from knockout mice. Urocortin interacts with leptin, neuropeptide Y, orexin, and corticotropin in the brain. Also produced by the GI tract, heart, and immune cells, urocortin has blood concentrations ranging from 13 to 152 pg/ml. Blood-borne urocortin stimulates the cerebral endothelial cells composing the blood-brain barrier and crosses the blood-brain barrier by a unique transport system. Overall, urocortin acts on a broad neuronal substrate as a neuromodulator important for basic survival.

Altered maternal profiles in corticotropin-releasing factor receptor 1 deficient mice

Background

During lactation, the CNS is less responsive to the anxiogenic neuropeptide, corticotropin-releasing factor (CRF). Further, central injections of CRF inhibit maternal aggression and some maternal behaviors, suggesting decreased CRF neurotransmission during lactation supports maternal behaviors. In this study, we examined the maternal profile of mice missing the CRF receptor 1 (CRFR1). Offspring of knockout (CRFR1-/-) mice were heterozygote to offset possible deleterious effects of low maternal glucocorticoids on pup survival and all mice contained a mixed 50:50 inbred/outbred background to improve overall maternal profiles and fecundity.

Results

Relative to littermate wild-type (WT) controls, CRFR1-/- mice exhibited significant deficits in total time nursing, including high arched-back, on each test day. Consistent with decreased nursing, pups of CRFR1-deficient dams weighed significantly less than WT offspring. Licking and grooming of pups was significantly higher in WT mice on postpartum Day 2 and when both test days were averaged, but not on Day 3. Time off nest was higher for CRFR1-/- mice on Day 2, but not on Day 3 or when test days were averaged. Licking and grooming of pups did not differ on Day 2 when this measure was examined as a proportion of time on nest. CRFR1-/- mice showed significantly higher nest building on Day 3 and when tests were averaged. Mean pup number was almost identical between groups and no pup mortality occurred. Maternal aggression was consistently lower in CRFR1-/- mice and in some measures these differences approached, but did not reach significance. Because of high variance, general aggression results are viewed as preliminary. In terms of sites of attacks on intruders, CRFR1-/- mice exhibited significantly fewer attacks to the belly of the intruder on Day 5 and when tests were averaged. Performance on the elevated plus maze was similar between genotypes. Egr-1 expression differences in medial preoptic nucleus and c-Fos expression differences in bed nucleus of stria terminalis between genotype suggest possible sites where loss of gene alters behavioral output.

Conclusion

Taken together, the results suggest that the presence of an intact CRFR1 receptor supports some aspects of nurturing behavior.

Artificial selection for increased maternal defense behavior in mice

Maternal aggression is directed towards intruders by lactating females and is critical for defense of offspring. Within-family selection for increased maternal defense in outbred house mice (Mus domesticus; Hsd:ICR strain) was applied to one selected (S) line, using total duration of attacks in a 3-min test as the selection criterion. One control (C) line was maintained and both lines were propagated by 13 families in each generation. Prior to selection, heritability of maternal aggression was estimated to be 0.61 based on mother-offspring regression. Duration of attacks responded to selection with a mean realized heritability of 0.40 (corrected for within-family selection) after eight generations. At generation 5, the S and C line also differed significantly for litter size at birth and at mid-lactation (both lower in S), average individual pup mass at midlactation (higher in S), and pup retrieval latency (longer in S), but not for other maternal measures that we studied (e.g., dam mass). Additionally, number of entries to middle and closed plus maze compartments was significantly higher in S mice in Generation 5. This is the first study to select for high maternal defense and these mice will be made available as a tool for understanding the genetic and neural basis of maternal aggression.

GABA enhancement of maternal defense in mice: possible neural correlates

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

Maternal aggression: New insights from Egr-1

Lactating mice display fierce aggression towards novel, male mice. This study compares neuronal activity in the brains of aggression-tested (T) and -untested (U) mice using early growth response factor 1 (Egr-1; also known as Krox 24, NGFI-A, Zif268, Tis8, and ZENK) as a measure of neuronal activity. Animals were sampled 90 min after either a sham or real 7-min test with a male intruder, after which their brains were examined for immunoreactivity to Egr-1 (Egr-IR). Significant increases in Egr-IR in T mice were identified in 11 of 40 brain regions, including paraventricular nucleus of the hypothalamus; anterior and lateral hypothalamus (both posterior portion); ventromedial hypothalamus; lateral periaqueductal gray; and medial, central, and basolateral amygdala. Posterodorsal (MePD) and posteroventral medial amygdala were examined for the first time in association with maternal aggression. MePD, a region associated with both sexual and aggressive behaviors in rats, hamsters, and mice, showed increased Egr-IR in association with testing. Taken together, the results from this study provide new insights into the neural circuits regulating maternal behaviors.

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.

The urocortin 1 neurocircuit: Ethanol-sensitivity and potential involvement in alcohol consumption

One of the hallmarks of alcoholism is continued excessive consumption of alcohol-containing beverages despite the negative consequences of such behavior. The neurocircuitry regulating alcohol consumption is not well understood. Recent studies have shown that the neuropeptide urocortin 1 (Ucn1), a member of the corticotropin-releasing factor (CRF) family of peptides, could be an important player in the regulation of alcohol consumption. This evidence is accumulated along three directions of research: (1) Ucn 1-containing neurons are extremely sensitive to alcohol; (2) the Ucn1 neurocircuit may contribute to the genetic predisposition to high alcohol intake in mice and rats; (3) manipulation of the Ucn1 system alters alcohol consumption and sensitivity. This paper reviews the current knowledge of the Ucn1 neurocircuit and the evidence for its involvement in alcohol-related behaviors, and proposes a mechanism for its involvement in the regulation of alcohol consumption.

Altered gene expression in mice selected for high maternal aggression

We previously applied selective breeding on outbred mice to increase maternal aggression (maternal defense). In this study, we compared gene expression within a continuous region of the central nervous system (CNS) involved in maternal aggression (hypothalamus and preoptic regions) between lactating selected (S) and nonselected control (C) mice (n= 6 per group). Using microarrays representing over 40,000 genes or expressed sequence tags, two statistical algorithms were used to identify significant differences in gene expression: robust multiarray and the probe logarithmic intensity error method. Approximately 200 genes were identified as significant using an intersection from both techniques. A subset of genes was examined for confirmation by real-time polymerase chain reaction (PCR). Significant decreases were found in S mice for neurotensin and neuropeptide Y receptor Y2 (both confirmed by PCR). Significant increases were found in S mice for neuronal nitric oxide synthase (confirmed by PCR), the K+ channel subunit, Kcna1 (confirmed by PCR), corticotrophin releasing factor binding protein (just above significance using PCR; P= 0.051) and GABA A receptor subunit 1A (not confirmed by PCR, but similar direction). S mice also exhibited significantly higher levels of the neurotransmitter receptor, adenosine A1 receptor and the transcription factors, c-Fos, and Egr-1. Interestingly, for 24 genes related to metabolism, all were significantly elevated in S mice, suggesting altered metabolism in these mice. Together, this study provides a list of candidate genes (some previously implicated in maternal aggression and some novel) that may play an important role in the production of this behavior.

Hypocretin-1 dose-dependently modulates maternal behaviour in mice

Increases in neuronal activity of hypocretin (HCRT), a peptide involved in arousal, and in HCRT-1 receptor mRNA expression have recently been identified in association with lactation. HCRT is released within brain regions regulating maternal behaviour and it is possible that increased HCRT neurotransmission during lactation supports maternal care. The present study examined for the first time the behavioural effects of HCRT on lactating mice. At intermediate doses, intracerebroventricular (i.c.v.) injections of HCRT-1 (0.06 and 0.1 microg) elevated levels of licking and grooming of pups (but not self-grooming) and number of nursing bouts without affecting other behaviours. At the highest dose, HCRT-1 (0.3 microg, i.c.v) delayed latency to nurse, decreased nursing, increased time off nest, and decreased maternal aggression. Intraperitoneal injections of the HCRT-1 receptor antagonist, SB-334867, exhibited a general trend towards increasing time spent low-arched back nursing (P = 0.053) and decreasing licking and grooming of pups while high-arched back nursing (P = 0.052). This suggests that the endogenous release of HCRT, working independently or dependently with other neuromodulators, may be necessary for full maternal behaviour expression. Possible sites of HCRT action in enhancing and impairing maternal care were identified via examinations of c-Fos immunoreactivity in association with i.c.v. HCRT injections. Together, these finding support the idea of HCRT modulating maternal behaviour, with intermediate levels (0.06 and 0.1 microg) supporting (even augmenting) some behaviours, but with levels that are too high (0.3 microg HCRT, i.c.v.), maternal behaviour and aggression are suppressed.

Distribution of corticotropin-releasing factor and urocortin 1 in the vole brain

Brain receptor patterns for the corticotropin-releasing factor (CRF) receptors, CRF1 and CRF2, are dramatically different between monogamous and promiscuous vole species, and CRF physiologically regulates pair bonding behavior in the monogamous prairie vole. However, it is uncertain whether species differences also exist in the neuroanatomical distribution of the endogenous ligands for the CRF1 and CRF2 receptors, such as CRF and urocortin-1 (Ucn1). We compared the expression of CRF and Ucn1 in four vole species, monogamous prairie and pine voles, and promiscuous meadow and montane voles, using in situ hybridization of CRF and Ucn1 mRNA. Our results reveal that CRF mRNA expression patterns in all four vole species appear highly conserved throughout the brain, including the olfactory bulb, nucleus accumbens, bed nucleus of the stria terminalis, medial preoptic area, central amygdala, hippocampus, posterior thalamus, and cerebellum. Similarly, Ucn1 mRNA primarily localized to the Edinger-Westphal nucleus in all four vole species. Immunocytochemistry in prairie and meadow voles confirmed localization of CRF and Ucn1 protein to these previously identified brain regions. These data demonstrate a striking dichotomy between the extraordinary species diversity of brain receptor patterns when compared to the highly conserved brain distributions of their respective ligands. Our findings generate novel hypotheses regarding the evolutionary mechanisms underlying the neural circuitry of species-typical social behaviors.

Distribution of urocortin 3 neurons innervating the ventral premammillary nucleus in the rat brain

Urocortin 3 (Ucn 3) is a recently described peptide of the corticotropin-releasing factor family. Neurons expressing Ucn 3 mRNA and peptide are distributed in specific brain areas, including the median preoptic nucleus, the perifornical area (PFx), and the medial nucleus of the amygdala (MEA). Fibers immunoreactive to Ucn 3 are confined to certain brain nuclei, being particularly dense in the ventral premammillary nucleus (PMV). In studies involving electrolytic lesions and analysis of Fos distribution according to behavioral paradigms, the PMV has been potentially implicated in conspecific aggression and sexual behavior. However, the role that Ucn 3 plays in this pathway has not been explored. Therefore, we investigated the origins of the urocortinergic innervation of the PMV of Wistar rat in an attempt to map the brain circuitry and identify likely related functions. We injected the retrograde tracer cholera toxin b subunit into the PMV and found that 88% of the Ucn 3-immunoreactive fibers in the PMV originate in the dorsal MEA, and that few originate in the PFx. As a control, we injected the anterograde tracer biotin dextran amine into both regions. We observed that the PMV is densely innervated by the MEA, and scarcely innervated by the PFx. The MEA is a secondary relay of the vomeronasal system and projects amply to hypothalamic nuclei related to hormonal and behavioral adjustments, including the PMV. Although physiological studies should also be performed, we hypothesize that Ucn 3 participates in such pathways, conveying sensory information to the PMV, which in turn modulates behavioral and neuroendocrine responses.

Resolving Apparent Contradictions Concerning the Relationships Among Fear or Anxiety and Aggression During Lactation: Theoretical Comment on D'Anna, Stevenson, and Gammie (2005)

Pregnancy and lactation involve dramatic changes in behavior and physiology necessary for the successful production and sustenance of offspring. This requires numerous processes to emerge and be coordinated in a finely tuned manner. Reduced corticotropin releasing factor (CRF) receptor activity and hypothalamic-pituitary-adrenal function are thought to be involved in numerous functions during lactation, such as reducing fear and anxiety, which in turn, is proposed to disinhibit aggressive behaviors. K. L. D'Anna, S. A. Stevenson, and S. C. Gammie (2005) reported that central infusion of urocortin 1 and 3, anxiogenic peptides that bind to CRF receptors, reduce maternal aggression in lactating mice and alter neural c-fos expression. However, the relationship between stress hormones and where they act, emotional state, and aggression during lactation is complicated, and our understanding of how these factors influence each other might benefit from a comprehensive reevaluation of these literatures. ((c) 2005 APA, all rights reserved).