Extracellular amino acid levels in the paraventricular nucleus and the central amygdala in high- and low-anxiety dams rats during maternal aggression: regulation by oxytocin

Considerations for protein and amino acids in standardized reference diet for parthenogenetic marbled crayfish Procambarus virginalis model organism

The concept of a standardized reference diet (SRD) is used in laboratory model organisms to ensure nutritional control between studies and laboratories. Although models using the genetically identical, all female parthenogenetic marbled crayfish (Procambarus virginalis) are growing in popularity, research into nutrition in this species still has many knowledge gaps. To fast track the development of a SRD in terms of protein and amino acids (SRDprotein) for this species, we first analyzed the composition of its body amino acids to determine the ideal protein concept (IPC) of indispensable amino acids in wild-caught P. virginalis (which had an unusually high preponderance of leucine and arginine). Then, we strategically evaluated three common clusters of types of fish feed: (1) ornamental fish feed (SER) fortified with a naturally occurring alga (Spirulina). This type of feed was protein-high in arginine and leucine (SER + SPI) that fulfils the species' IPC for iso-protein (~ 40%), iso-phosphorus (~ 0.8%) and near iso-energetic (~ 475 kcal 100 g-1); (2) freeze-dried live feed consisting of chironomid larvae (CHI) fortified with Spirulina (CHI + SPI) that fulfils the IPC for iso-protein (~ 46%), iso-phosphorus (~ 0.7%) and near iso-energetic (~ 405 kcal 100 g-1); and (3) a commercially standardized 'starter diet' for carnivorous fish larvae (FISH) and post-larval shrimps (SHRIMP) with iso-protein (~ 56%) and iso-phosphorus (~ 1.6%). A total of six diets, embracing a diverse range of proteinaceous feeds, were used in a 100-day ad libitum feeding and growth trial. The FISH group outperformed all the other groups (p < 0.05) and our exploratory multivariate analysis revealed an ideal demand of > 44% protein (tailored to deliver high arginine 3% and leucine 4%, followed by the usual lysine > 3.5% and methionine 1.2%) but also the lowest carbohydrate level (21%). For SRDprotein, our findings show that the FISH diet is ideal and suggest the possibilities of using a CHI + SPI diet for further optimization (more economic use of protein and phosphorus).

Selective breeding of rats for high (HAB) and low (LAB) anxiety-related behaviour: A unique model for comorbid depression and social dysfunctions

Animal models of selective breeding for extremes in emotionality are a strong experimental approach to model psychopathologies. They became indispensable in order to increase our understanding of neurobiological, genetic, epigenetic, hormonal, and environmental mechanisms contributing to anxiety disorders and their association with depressive symptoms or social deficits. In the present review, we extensively discuss Wistar rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviour on the elevated plus-maze. After 30 years of breeding, we can confirm the prominent differences between HAB and LAB rats in trait anxiety, which are accompanied by consistent differences in depressive-like, social and cognitive behaviours. We can further confirm a single nucleotide polymorphism in the vasopressin promotor of HAB rats causative for neuropeptide overexpression, and show that low (or high) anxiety and fear levels are unlikely due to visual dysfunctions. Thus, HAB and LAB rats continue to exist as a reliable tool to study the multiple facets underlying the pathology of high trait anxiety and its comorbidity with depression-like behaviour and social dysfunctions.

Oxytocin: Narrative Expert Review of Current Perspectives on the Relationship with Other Neurotransmitters and the Impact on the Main Psychiatric Disorders

Is a cyclic neuropeptide produced primarily in the hypothalamus and plays an important neuromodulatory role for other neurotransmitter systems, with an impact on behavior, response to danger, stress, and complex social interactions, such as pair bonding and child care. This narrative expert review examines the literature on oxytocin as a brain hormone. We focused on oxytocin structure, distribution, genetics, and the oxytocin receptor system, as well as the relationship of oxytocin with other neurotransmitters and the resulting impacts on the main psychiatric disorders. Oxytocin levels have been correlated over time with mental illness, with numerous studies focusing on oxytocin and the pathophysiology of the main psychiatric disorders, such as autism, schizophrenia, personality disorders, mood, and eating disorders. We highlight the role oxytocin plays in improving symptoms such as anxiety, depression, and social behavior, as the literature suggests. Risk factors and causes for psychiatric disorders range from genetic to environmental and social factors. Oxytocin could impact the latter, being linked with other neurotransmitter systems that are responsible for integrating different situations during the development phases of individuals. Also, these systems have an important role in how the body responds to stressors or bonding with others, helping with the creation of social support groups that could speed up recovery in many situations. Oxytocin has the potential to become a key therapeutic agent for future treatment and prevention strategies concerning the main psychiatric disorders.

Oxytocin improves ischemic stroke by reducing expression of excitatory amino acid transporter 3 in rat MCAO model

Various molecular mechanisms are activated in neurons during ischemic stroke. Extracellular glutamate secretion into brain tissue causes neurotoxicity and brain damage. Excitatory amino acid transporter 3 (EAAT3) could remove the extracellular glutamate. Neuroprotective activity of oxytocin (OT) in ischemia of various tissues has been reported. This study investigates the neuroprotective effect of OT in an animal model of middle cerebral artery occlusion (MCAO) and the possible role of EAAT3. Transient MCAO was performed as a model of ischemic stroke in male rats and then OT was administrated intra-nasally. Infarct volume was measured by 2, 3, 5-triphenyl tetrazolium chloride staining. Nissl staining method was performed for the evaluation of neuronal cell morphology. Immunohistochemistry assay was performed to analyze the EAAT3 expression in the ischemic region. OT significantly reduced the infarct volume in the cerebral cortex and striatum after ischemia (P< .05). In addition, OT reduces the number of neurons with pyknotic nuclei that are significantly increased in the ischemic region (P< .01) Immunohistochemistry results showed that although EAAT3 expression increased after ischemia, OT therapy increased EAAT3 expression further (P< .05). Therefore, increased EAAT3 expression could be one of the neuroprotective mechanisms of OT after MCAO.

Early Life Adversity and Adult Social Behavior: Focus on Arginine Vasopressin and Oxytocin as Potential Mediators

Exposure to stress during the early postnatal period (i.e., early life stress, ES) can impact brain physiology and modify individual variability in adult social behavior. Arginine vasopressin (AVP) and oxytocin (OXT) are two centrally released neuropeptides that are involved in shaping essential social behaviors, like aggression, social recognition, and social motivation. AVP and OXT modulate activity in brain regions important for the establishment of social behavior, and may be particularly sensitive to ES. In this review, we discuss whether ES alters the characteristics of the AVP- and OXT- systems in rodents, and whether these changes are associated with later alterations in aggression, social recognition, and social motivation. We have integrated causal studies indicating that (1) ES affects AVP/OXT, and (2) that changing AVP/OXT in affected regions alters social behavior. Although there is encouraging evidence that ES causes AVP- and OXT-system changes, and that these may mediate social behavior, a comprehensive understanding of the exact nature of AVP- and OXT changes and whether they are causal in establishing these behavioral disturbances needs further investigation. As there are indications that ES alters AVP- and OXT characteristics in humans as well, and that these may interact with adult predisposition to psychopathology with social dysfunction, future rodent studies may lay ground for a better understanding of such changes in humans. Ultimately, this may assist in developing therapeutic strategies to target ES effects on social behavior.

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.

Differential activation of arginine-vasopressin receptor subtypes in the amygdaloid modulation of anxiety in the rat by arginine-vasopressin

RATIONALE

The amygdala plays a paramount role in the modulation of anxiety and numerous studies have shown that arginine vasopressin (AVP) elicits anxiogenic effects following either its systemic or septal administration.

OBJECTIVES

The aim of this paper was to study the involvement of vasopressinergic neurotransmission in the amygdaloid modulation of unconditioned anxiety and to ascertain whether or not AVP receptor subtypes may have a differential role in this modulation.

METHODS

Anxiety behavior was evaluated both in Shock-Probe Burying Test and Light-Dark Box following the bilateral microinfusion of AVP alone or AVP together with either AVP 1a or AVP 1b receptor antagonists into the central amygdala (CeA).

RESULTS

AVP microinfusion elicited at low (1 ng/side) but not at high doses (10 ng/side) anxiogenic-like responses in the Shock-Probe Burying Test but not in the Light-Dark Box. SSR149415, an AVP 1b antagonist unlike Manning compound, an AVP 1a antagonist, fully prevented AVP effects in the Shock-Probe Burying Test when it was administered simultaneously with AVP. In addition, oxytocin receptor blockade also failed to affect AVP effects. No effects of any AVP antagonist by itself were observed in both anxiety paradigms.

CONCLUSIONS

Our results indicate that AVP 1b receptor contribute to the amygdaloid modulation of anxiety at least in the context of the Shock-Probe Burying Test since no effects were noticed in the Light-Dark Box. It remains to the future to ascertain whether AVP receptor subtypes have indeed differential actions either in the modulation of global or specific features of unconditioned anxiety.

The neurocircuitry involved in oxytocin modulation of methamphetamine addiction

The role of oxytocin in attenuating the abuse of licit and illicit drugs, including the psychostimulant methamphetamine, has been examined with increased ferocity in recent years. This is largely driven by the potential application of oxytocin as a pharmacotherapy. However, the neural mechanisms by which oxytocin modulates methamphetamine abuse are not well understood. Recent research identified an important role for the accumbens core and subthalamic nucleus in this process, which likely involves an interaction with dopamine, glutamate, GABA, and vasopressin. In addition to providing an overview of methamphetamine, the endogenous oxytocin system, and the effects of exogenous oxytocin on drug abuse, we propose a neural circuit through which exogenous oxytocin modulates methamphetamine abuse, focusing on its interaction with neurochemicals within the accumbens core and subthalamic nucleus. A growing understanding of exogenous oxytocin effects at a neurochemical and neurobiological level will assist in its evaluation as a pharmacotherapy for drug addiction.

Construction of a robust and sensitive arginine biosensor through ancestral protein reconstruction

Biosensors for signaling molecules allow the study of physiological processes by bringing together the fields of protein engineering, fluorescence imaging, and cell biology. Construction of genetically encoded biosensors generally relies on the availability of a binding "core" that is both specific and stable, which can then be combined with fluorescent molecules to create a sensor. However, binding proteins with the desired properties are often not available in nature and substantial improvement to sensors can be required, particularly with regard to their durability. Ancestral protein reconstruction is a powerful protein-engineering tool able to generate highly stable and functional proteins. In this work, we sought to establish the utility of ancestral protein reconstruction to biosensor development, beginning with the construction of an l-arginine biosensor. l-arginine, as the immediate precursor to nitric oxide, is an important molecule in many physiological contexts including brain function. Using a combination of ancestral reconstruction and circular permutation, we constructed a Förster resonance energy transfer (FRET) biosensor for l-arginine (cpFLIPR). cpFLIPR displays high sensitivity and specificity, with a Kd of ∼14 µM and a maximal dynamic range of 35%. Importantly, cpFLIPR was highly robust, enabling accurate l-arginine measurement at physiological temperatures. We established that cpFLIPR is compatible with two-photon excitation fluorescence microscopy and report l-arginine concentrations in brain tissue.

Stress as a one-armed bandit: Differential effects of stress paradigms on the morphology, neurochemistry and behavior in the rodent amygdala

Neuroplasticity may be defined as the ability of the central nervous system (CNS) to respond to changes in the internal and external environment and it is well established that some stimuli have the ability to facilitate or impair neuroplasticity depending on the pre-existing milieu. A classic example of a stimulus that can both facilitate and impair neuroplasticity is stress. Indeed, the ability of CNS to respond to acute stress is often dependent upon the prior stress history of the individual. While responses to acute stress are often viewed as adaptive in nature, stress reactivity in subjects with prior chronic stress experiences are often linked to neuropsychiatric disorders, including major depressive disorder, post-traumatic stress disorder (PTSD) and anxiety. In rodent studies, chronic stress exposure produces structural and functional alterations in the hippocampus and medial prefrontal cortex that are consistent across different types of stress paradigms. Conversely, the amygdala appears to exhibit differential structural and functional responses to stress that are dependent on a variety of factors, including the type of stressor performed and the duration of the stress paradigm. This is most evident in output measures including morphological analysis of amygdala neurons, measurement of glutamatergic tone in amygdalar subdivisions and the analysis of amygdala-centric behaviors. Accordingly, this review will provide an overview of the effects of stress on the structural and functional plasticity of the rodent amygdala, especially in relation to the differential effects of repeated or chronic stress paradigms on dendritic architecture, neurochemistry of the glutamatergic system and behavior.

Central V1b receptor antagonism in lactating rats: impairment of maternal care but not of maternal aggression

Maternal behaviour in rodents is mediated by the central oxytocin and vasopressin systems, amongst others. The role of vasopressin, acting via the V1a receptor (V1aR), on maternal care and maternal aggression has recently been described. However, a potential involvement of the V1b receptor (V1bR) in maternal behaviour has only been demonstrated in knockout mice. The present study aimed to examine the effects of central pharmacological manipulation of the V1bR on maternal behaviour in lactating Wistar rats. On pregnancy day 18, female rats were implanted with a guide cannula targeting the lateral ventricle. After parturition, dams received an acute central infusion of a specific V1bR agonist (d[Leu4,Lys8]VP) or V1bR antagonist (SSR149415) once daily, followed by observations of maternal care [lactation day (LD) 1], maternal motivation in the pup retrieval test (LD 2), anxiety-related behaviour on the elevated plus-maze (LD 3) and maternal aggression in the maternal defence test followed by maternal care monitoring (LD 4). Our data demonstrate that, under nonstress conditions, the V1bR antagonist decreased the occurrence of both nursing and mother-pup interaction, whereas the V1bR agonist did not affect either parameter. Under stress conditions (i.e. after the maternal defence test), mother-pup interaction was decreased by infusion of the V1bR antagonist. During the maternal defence test, neither treatment affected aggressive or non-aggressive behaviour. Finally, neither treatment altered maternal motivation or anxiety. In conclusion, central V1bR antagonism modulates aspects of maternal care but not of maternal aggression or maternal motivation in lactating rats. These findings further extend our knowledge on the vasopressin system as a vital mediator of maternal behaviour.

Maternal aggression in rodents: brain oxytocin and vasopressin mediate pup defence

The most significant social behaviour of the lactating mother is maternal behaviour, which comprises maternal care and maternal aggression (MA). The latter is a protective behaviour of the mother serving to defend the offspring against a potentially dangerous intruder. The extent to which the mother shows aggressive behaviour depends on extrinsic and intrinsic factors, as we have learned from studies in laboratory rodents. Among the extrinsic factors are the pups' presence and age, as well as the intruders' sex and age. With respect to intrinsic factors, the mothers' innate anxiety and the prosocial brain neuropeptides oxytocin (OXT) and arginine vasopressin (AVP) play important roles. While OXT is well known as a maternal neuropeptide, AVP has only recently been described in this context. The increased activities of these neuropeptides in lactation are the result of remarkable brain adaptations peripartum and are a prerequisite for the mother to become maternal. Consequently, OXT and AVP are significantly involved in mediating the fine-tuned regulation of MA depending on the brain regions. Importantly, both neuropeptides are also modulators of anxiety, which determines the extent of MA. This review provides a detailed overview of the role of OXT and AVP in MA and the link to anxiety.

Perinatal thiamine deficiency-induced spontaneous abortion and pup-killing responses in rat dams

OBJECTIVES

The current study attempts to determine whether thiamine (B1 vitamin) deficiency and chronic alcohol-related thiamine-deficient (TD) status, disturb maternal behavior towards pups.

METHODS

During gestation and lactation, Wistar rat dams were exposed to the following treatments: (i) prenatal TD dams; (ii) perinatal TD dams; (iii) postnatal TD dams; (iv) 12% alcohol/water drinking mothers; (v) ad libitum control dams. Pair-feeding treatments controlled malnutrition related to thiamine deficiency; (vi) prenatal pair-fed (PF) dams; (vii) perinatal PF dams; (viii) postnatal PF dams and included also the control of alcohol consummation: (ix) PF saccharose dams. Dams were observed for gestation outcome and for apparent disorders of the maternal behavior related to the pups at parturition.

RESULTS

From the nine experimental groups studied, only pre- and perinatal TD dams exhibited spontaneous abortion (33.36 and 41.66%, respectively) followed by pups-killing responses where, respectively, 4 dams/7 (57.14%) and 5 dams/7 (71.43%) showed disruption of maternal behavior and appearance of cannibalism towards pups which all were killed within 48 hours after parturition. Spontaneous abortion and pup-killing responses were not observed in the dams of any other experimental group, suggesting that perinatal disturbances of hormonal factors underlay these maternal disorders.

DISCUSSION

Previous studies reported that thiamine deficiency-induced degeneration of dopamine neurons may be related to mouse-killing aggression in rats. The present study suggests that perinatal thiamine deficiency-induced alteration of dopaminergic neurons in maternal brain could be a trigger factor of pup-killing responses. Central dopamine and oxytocin have been strongly associated with both the onset and maintenance of maternal behavior and the regulation of maternal aggressiveness as well. Our studies suggest that estrogen control oxytocin levels in brain structures of pregnancy-terminated rats via dopamine transmission. Thiamine may modulate cAMP/Ca2+ -dependent estradiol-triggered responses which in turn control dopamine synthesis. Consequently, thiamine deficiency induced perinatally triggers pup-killing responses in pregnancy-terminated rats by the following toxic effects: (i) disturbances of estrogen production and/or release affecting dopamine synthesis; (ii) alterations of dopamine inhibition on central oxytocinergic system-related maternal aggressiveness. Likewise, our results indicate also that perinatal thiamine deficiency alone induces spontaneous abortion, reduces litter size, and lowers birth weight, which together suggest changing in the fetoplacental estrogen receptor alpha/progesterone receptor A ratio during gestation, via autocrine/paracrine regulation disturbances. Those hypotheses should be confirmed by further investigations.

Oxytocin regulates changes of extracellular glutamate and GABA levels induced by methamphetamine in the mouse brain

Oxytocin (OT), a neurohypophyseal neuropeptide, affects adaptive processes of the central nervous system. In the present study, we investigated the effects of OT on extracellular levels of glutamate (Glu) and γ-aminobutyric acid (GABA) induced by methamphetamine (MAP) in the medial prefrontal cortex (mPFC) and dorsal hippocampus (DHC) of freely moving mice, using in vivo microdialysis coupled to high-performance liquid chromatography and fluorescence detection. The results showed that OT had no effect on basal Glu levels, but attenuated MAP-induced Glu increase in the mPFC and decrease in the DHC. OT increased the basal levels of extracellular GABA in mPFC and DHC of mice, and inhibited the MAP-induced GABA decrease in DHC. Western blot results indicated that OT significantly inhibited the increased glutamatergic receptor (NR1 subunit) levels in the PFC after acute MAP administration, whereas OT further enhanced the elevated levels of glutamatergic transporter (GLT1) induced by MAP in the hippocampus of mice. Atosiban, a selective inhibitor of OT receptor, antagonized the effects of OT. The results provided the first neurochemical evidence that OT, which exerted its action via its receptor, decreased Glu release induced by MAP, and attenuated the changes in glutamatergic neurotransmission partially via regulation of NR1 and GLT1 expression. OT-induced extracellular GABA increase also suggests that OT acts potentially as an inhibitory neuromodulator in mPFC and DHC of mice.

Childhood aggression, callous-unemotional traits and oxytocin genes

Given the known behavior effects of oxytocin,and in particular its putative effect on trust, affiliation and anxiety, we hypothesized that oxytocin may be involved in the development and expression of callous-unemotional traits in children with aggressive antisocial behavior. We recruited 162 children between the ages of 6 and 16. The majority of subjects were Caucasian (84.0%) compared to African-Canadian (4.9%) and others (11.1%). The oxytocin and oxytocin receptor gene polymorphisms were genotyped and analyzed for possible association with child aggression in a case–control study design as well as with callous-unemotional traits in a within cases analysis. We did not have significant findings with our tested OXTR markers in the case–control analysis. We found the OXTR_rs237885 AA genotype carriers to score higher than AC or CC genotype carriers on the callous-unemotional traits. This result remained significant following correction for multiple testing. No other markers were found to be significant. However, the haplotype consisting of the OXTR_rs237885 A allele and OXTR_rs2268493 A allele was associated with significantly higher callous-unemotionals cores than other haplotypes. This is the first known study to show a significant association between callous unemotional traits in children and adolescents with extreme, persistent pervasive aggression and a polymorphism on the oxytocin receptor. Given the small sample size and the possibility of false positive effects, the need to replicate and verify these findings is required.

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.

Evidence for a role of oxytocin receptors in the long-term establishment of dominance hierarchies

Exposure to stress can affect the establishment of dominance hierarchies. In our model, a social hierarchy established by two male rats during a first encounter is not maintained 1 week later. If one of the two rats is stressed, the stressed rat becomes subordinate and the hierarchy that is formed is maintained. In this study, we investigated the changes in the expression of oxytocin (Otr) and vasopressin (V1aR) receptor genes in the medial amygdala (MeA) and the lateral septum (LS) in the hours following hierarchy establishment under both stressed and basal conditions. We found that the potentiation of a social hierarchy induced by stress is accompanied by social status- and region-specific changes in the expression of Otr mRNA in the MeA 3 h after the social encounter. At this time point, no evidence was found for the regulation of V1aR mRNA in any of the brain regions examined. Results from pharmacological experiments involving the microinfusion of a specific OTR antagonist immediately after the acquisition of a subordinate status under basal, non-stress conditions suggested a role for this receptor in the MeA on the long-term establishment of the subordinate status. Altogether, these findings highlight a role for the oxytocinergic system in the mechanisms through which stress facilitates the long-term establishment of a social hierarchy.

Effects of chronic and intermittent cocaine treatment on dominance, aggression, and oxytocin levels in post-lactational rats

RATIONALE

Little is known about mechanisms underlying female rodent aggression during the late postpartum period with no pups present. Studies of aggression, dominance, and oxytocin (OT) response in cocaine-treated females are sparse.

OBJECTIVES

This study was designed to examine dominance (drinking success) and aggression in a limited-access drinking model of water competition. Acute OT level measures were made on postpartum day (PPD) 36 in several brain regions of interest. Chronic and intermittent cocaine- and saline-treated and untreated rats 10 days post-weaning were tested (without pups) over PPDs 31-35 following cessation of cocaine treatment 10-30 days before testing.

METHODS

Subjects were water-deprived overnight, and triads consisting of an untreated control (UN), a chronic continuous saline-treated (CS), and chronic continuous cocaine-treated (CC; 30 mg/kg/day throughout gestation) or a UN, an intermittent saline-treated (IS), and an intermittent cocaine-treated (IC; 30 mg/kg two consecutive days every 4 days throughout gestation until PPD 20) female were tested for aggression and drinking behavior during 5 min sessions on five consecutive days. The amygdala, medial preoptic area (MPOA), and ventral tegmental area were assayed for OT levels.

RESULTS

CC and IC females were more aggressive than controls, but only IC females drank more often than controls. OT levels were lower in the MPOA of IC and CC females than in controls.

CONCLUSIONS

Findings demonstrate that long after cessation of treatment, CC- and IC-treated non-lactating females (no pups present) had higher rates of aggression, altered drinking behavior, and acutely lower MPOA OT levels.

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.

Estrogen receptor beta regulates the expression of tryptophan-hydroxylase 2 mRNA within serotonergic neurons of the rat dorsal raphe nuclei

Dysfunctions of the brain 5-HT system are often associated with affective disorders, such as depression. The raphe nuclei target the limbic system and most forebrain areas and constitute the main source of 5-HT in the brain. All 5-HT neurons express tryptophan hydroxylase-2 (TPH2), the brain specific, rate-limiting enzyme for 5-HT synthesis. Estrogen receptor (ER) beta agonists have been shown to attenuate anxiety- and despair-like behaviors in rodent models. Therefore, we tested the hypothesis that ER beta may contribute to the regulation of gene expression in 5-HT neurons of the dorsal raphe nuclei (DRN) by examining the effects of systemic and local application of the selective ER beta agonist diarylpropionitrile (DPN) on tph2 mRNA expression. Ovariectomized (OVX) female rats were injected s.c. with DPN or vehicle once daily for 8 days. In situ hybridization revealed that systemic DPN-treatment elevated basal tph2 mRNA expression in the caudal and mid-dorsal DRN. Behavioral testing of all animals in the open field (OF) and on the elevated plus maze (EPM) on days 6 and 7 of treatment confirmed the anxiolytic nature of ER beta activation. Another cohort of female OVX rats was stereotaxically implanted bilaterally with hormone-containing wax pellets flanking the DRN. Pellets contained 17-beta-estradiol (E), DPN, or no hormone. Both DPN and E significantly enhanced tph2 mRNA expression in the mid-dorsal DRN. DPN also increased tph2 mRNA in the caudal DRN. DPN- and E-treated rats displayed a more active stress-coping behavior in the forced-swim test (FST). No behavioral differences were found in the OF or on the EPM. These data indicate that ER beta acts at the level of the rat DRN to modulate tph2 mRNA expression and thereby influence 5-HT synthesis in DRN subregions. Our results also suggest that local activation of ER beta neurons in the DRN may be sufficient to decrease despair-like behavior, but not anxiolytic behaviors.

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.

Effects of oxytocin on methamphetamine-induced conditioned place preference and the possible role of glutamatergic neurotransmission in the medial prefrontal cortex of mice in reinstatement

Accumulating evidence has shown the neuroactive properties of oxytocin (OT), a neurohypophyseal neuropeptide, and its ability to reduce the abuse potential of drugs. The present study investigated the effects of OT on the conditioned place preference (CPP) induced by methamphetamine (MAP, 2.0 mg/kg, i.p.) in mice and the possible role of glutamatergic neurotransmission in the reinstatement of CPP. The results showed that OT (0.1, 0.5, 2.5 microg, i.c.v.) significantly inhibited the acquisition and facilitated the extinction of MAP-induced CPP and abolished the reinstatement of CPP induced by restraint stress. This effect of OT could be attenuated by atosiban (Ato, 2.0 microg, i.c.v.), a selective OT-receptor antagonist. OT failed to block the expression and the reinstatement of CPP induced by MAP challenge. Extracellular glutamate (Glu) levels in the medial prefrontal cortex (mPFC) were determined using microdialysis coupled to a high-performance liquid chromatography (HPLC) with a fluorescence detection system. The results indicated that OT markedly inhibited extracellular Glu levels induced by restraint stress in CPP mice, but not those induced by MAP priming. Ato also attenuated the effects of OT on the changes in Glu levels. Therefore, these findings suggest that OT inhibits drug reward-related behaviors induced by MAP via the OT receptor, and OT blocks the reinstatement of CPP, at least partially, by interfering with the glutamatergic system in the mPFC.

Predation threat exerts specific effects on rat maternal behaviour and anxiety-related behaviour of male and female offspring

Differences in the rate of maternal behaviours received by rodent offspring are associated with differential programming of molecular and behavioural components of anxiety and stress-related functions. To determine the degree to which maternal behaviours are sensitive to environmental conditions, Long-Evans rat dams were exposed to the odour of a predator (cat) at two different time points during the first week postpartum. Exposure on the day of birth (DOB), but not the third day following birth, increased levels of maternal care in predator-exposed dams relative to dams exposed to a control condition across the first 5 days post-partum. As adults, female offspring of dams exposed on DOB exhibited a less-anxious phenotype in a novel open-field, spending more time in the center and less time displaying thigmotaxis. In contrast, under the same conditions, male offspring showed the opposite behavioural response, consistent with an increasingly anxious phenotype. Results from a subsequent stressor test (response to a predator odour) were consistent with the notion that the rearing effects were specific to anxiety-related behaviours in offspring. Accordingly, we showed that rearing conditions did not affect GR mRNA or NGFI-A expression in the hippocampus of offspring or cross-fostered offspring. The dissociation between stress and anxiety, as well as the sex-specific alterations in behaviour, may reflect the specificity inherent to neural programming in the face of naturalistic early life conditions.