Decrease of kappa-opioid receptor mRNA level in ventral tegmental area of male mice after repeated experience of aggression

The motivation to flock correlates with vocal-social behaviors and dopamine-related gene expression in male European starlings

It is proposed that songbird flocks are partly reinforced by positive social interactions, however not all flock mate interactions are positive. The combination of both positive and negative social interactions with flock mates may play a role in the motivation for birds to flock. The nucleus accumbens (NAc), medial preoptic area (POM), and ventral tegmental area (VTA) are implicated in vocal-social behaviors in flocks, including singing. Dopamine (DA) within these regions modifies motivated, reward-directed behaviors. Here, we begin to test the hypothesis that individual social interactions and DA within these regions are involved in the motivation to flock. Vocal-social behaviors were recorded in eighteen male European starlings in mixed-sex flocks in fall, when starlings are highly social and form large flocks. Males were then singly removed from their flock and the motivation to flock was quantified as the amount of time spent attempting to join a flock following separation. We used quantitative real-time polymerase chain reaction to measure expression of DA-related genes in the NAc, POM, and VTA. Birds producing high levels of vocal behaviors were more highly motivated to flock and had higher tyrosine hydroxylase (the rate-limiting enzyme in DA synthesis) expression in the NAc and VTA. Birds that received high levels of agonistic behaviors were less motivated to flock and had higher DA receptor subtype 1 expression in the POM. Overall, our findings suggest that interplay between social experience and DA activity in NAc, POM, and VTA plays a key role in social motivation in flocking songbirds.

Prenatal exposure to valproic acid reduces social responses and alters mRNA levels of opioid receptor and pre-pro-peptide in discrete brain regions of adolescent and adult male rats

Altered social behaviours are a hallmark of several psychiatric and developmental disorders. Clinical and preclinical data have demonstrated that prenatal exposure to valproic acid (VPA), an anti-epileptic and mood stabiliser, is associated with impaired social responses, and thus provides a useful model for the evaluation of neurobiological mechanisms underlying altered social behaviours. The opioid system is widely recognised to regulate and modulate social behaviours, however few studies have examined if the endogenous opioid system is altered in animal models of social impairment. The present study examined social behavioural responses of adolescent and adult male rats prenatally exposed to VPA, and the expression of mRNA encoding opioid receptors and pre-pro-peptides in discrete brain regions. Adolescent and adult rats prenatally exposed to VPA spent less time engaging in social behaviours in the direct social interaction test and exhibited reduced sociability and social novelty preference in the 3-chamber sociability test, compared to saline-treated counterparts. The VPA-exposed adolescent rats exhibited significantly reduced kappa opioid receptor (oprk1) and pre-pro-dynorphin (pdyn) mRNA expression in the cerebral cortex, and reduced oprk1 and nociceptin/orphanin FQ (oprl1) mRNA expression in the hypothalamus. Adult rats prenatally exposed to VPA exhibited decreased mRNA expression of oprk1 and pdyn in hypothalamus, reduced pro-opiomelanocortin(pomc) in the striatum and an increase in delta opioid receptor (oprd1) mRNA in the amygdaloid cortex, when compared to saline-treated counterparts. Mu opioid receptor (oprm1) mRNA expression did not differ between saline and VPA-exposed rats in any region examined. The data demonstrate that impaired social behaviours in adolescent and adult rats prenatally exposed to VPA is accompanied by altered mRNA expression of opioid receptors and pre-pro-peptides in a region specific manner. In particular, both adolescent and adult VPA-exposed rats exhibit reduced oprk1-pdyn mRNA expression in several brain regions, which are associated with deficits in social behavioural responding in the model.

Prodynorphin and kappa opioid receptor mRNA expression in the brain relates to social status and behavior in male European starlings

Numerous animal species display behavioral changes in response to changes in social status or territory possession. For example, in male European starlings only males that acquire nesting sites display high rates of sexual and agonistic behavior. Past studies show that mu and delta opioid receptors regulate behaviors associated with social ascension or defeat. Opioids also act at kappa receptors, with dynorphin binding with the highest affinity; however, the role of these opioids in social behavior has not been well studied. We observed flocks of male starlings during the breeding season and ran quantitative real-time polymerase chain reaction (qPCR) to measure expression of kappa opioid receptors (OPRK1) and prodynorphin (PDYN) in brain regions involved in social behavior and motivation (ventral tegmental area [VTA], medial preoptic nucleus [mPOA]) and vocal behavior (Area X). Males with nesting territories displayed more sexual/agonistic behavior than males without nesting territories. They also had lower OPRK1 expression in VTA and mPOA. OPRK1 expression in VTA correlated negatively with sexual/agonistic behaviors, consistent with past studies showing kappa receptors in VTA to inhibit sociosexual behaviors. PDYN in mPOA correlated negatively with a measure of nesting behavior that may also reflect sexual motivation. PDYN in Area X related positively to song. Distinct patterns of OPRK1 and PDYN expression in VTA, mPOA, and Area X related to gonad volume, suggesting that breeding condition may modify (or be modified by) OPRK1 and PDYN expression. Studies are now needed to further characterize the role of OPRK1 and PDYN in status-appropriate social behaviors.

Is there a shared neurobiology between aggression and Internet addiction disorder?

PURPOSE

Evidences indicate that Internet addiction disorder (IAD) has a higher risk of developing aggression and violent behavior. A few correlation studies between IAD and aggression have implicated a common biological mechanism. However, neurobiological approaches to IAD and aggression have not yet been studied.

METHODS

A literature search for studies for Internet addiction disorder or aggression was performed in the PubMed database and we selected articles about neurobiology of IAD or aggression.

RESULTS

This review includes (a) common neural substrates such as the prefrontal cortex and the limbic system between aggression and IAD; (b) common neuromodulators such as dopamine, norepinephrine, serotonin, opiate and nicotine between aggression and IAD.

CONCLUSIONS

Through reviewing the relevant literature, we suggested the possibility of common neurobiology between the two psychiatric phenomena and direction of research on aggression in IAD.

Downregulation of serotonergic gene expression in the Raphe nuclei of the midbrain under chronic social defeat stress in male mice

There is ample experimental evidence supporting the hypothesis that the brain serotonergic system is involved in the control of chronic social defeat stress (CSDS), depression, and anxiety. The study aimed to analyze mRNA levels of the serotonergic genes in the raphe nuclei of midbrain that may be associated with chronic social defeats consistently shown by male mice in special experimental settings. The serotonergic genes were the Tph2, Sert, Maoa, and Htr1a. The Bdnf and Creb genes were also studied. The experimental groups were composed of male mice with experience of defeats in 21 daily encounters and male mice with the same track record of defeats followed by a no-defeat period without agonistic interactions (relative rest for 14 days). It has been shown that mRNA levels of the Tph2, Maoa, Sert, Htr1a, Bdnf, and Creb genes in the raphe nuclei of defeated mice are decreased as compared with the controls. The expression of the serotonergic genes as well as the Creb gene is not restored to the control level after the 2 weeks of relative rest. mRNA levels of Bdnf gene are not recovered to the control levels, although some upregulation was observed in rested losers. CSDS experience inducing the development of mixed anxiety/depression-like state in male mice downregulates the expression of serotonergic genes associated with the synthesis, inactivation, and reception of serotonin. The Bdnf and Creb genes in the midbrain raphe nuclei are also downregulated under CSDS. Period of relative rest is not enough for most serotonergic genes to recover expression to the control levels.

Snca and Bdnf gene expression in the VTA and raphe nuclei of midbrain in chronically victorious and defeated male mice

Background

Alpha-synuclein (α-Syn) is a small neuronal protein that has been found to be expressed throughout the brain. It has been shown that α-Syn regulates the homeostasis of monoamine neurotransmitters and is involved in various degenerative and affective disorders. There is indication that α-Syn may regulate expression of the brain-derived neurotropic factor (BDNF) which plays an important role in the mood disorders.

Methodology/Principal Findings

The study aimed to analyze the mRNA levels of Snca and Bdnf genes in the ventral tegmental area (VTA) and raphe nuclei of the midbrain in male mice that had each won or defeated 20 encounters (20-time winners and 20-time losers, respectively) in daily agonistic interactions. Groups of animals that had the same winning and losing track record followed by a no-fight period for 14 days (no-fighting winners and no-fighting losers) were also studied. Snca mRNA levels were increased in the raphe nuclei in the 20-time losers and in the VTA of the 20-time winners. After no-fight period Snca mRNA levels decreased in both groups. Snca mRNA levels were similar to the control level in the VTA of the 20-time losers and in the raphe nuclei of the 20-time winners. However Snca gene expression increased in these areas in the no-fighting winners and no-fighting losers in comparison with respective mRNA levels in animals before no-fight period. Bdnf mRNA levels increased in VTA of 20-time winners. Significant positive correlations were found between the mRNA levels of Snca and Bdnf genes in the raphe nuclei.

Conclusions/Significance

Social experience affects Snca gene expression depending on brain areas and functional activity of monoaminergic systems in chronically victorious or defeated mice. These findings may be useful for understanding the mechanisms of forming different alpha-synucleinopathies.

Molecular implications of repeated aggression: Th, Dat1, Snca and Bdnf gene expression in the VTA of victorious male mice

Background

It is generally recognized that recurrent aggression can be the result of various psychiatric disorders. The aim of our study was to analyze the mRNA levels, in the ventral tegmental area (VTA) of the midbrain, of the genes that may possibly be associated with aggression consistently shown by male mice in special experimental settings.

Methodology/Principal Findings

The genes were Th, Dat1, Snca and Bdnf; the male mice were a group of animals that had each won 20 daily encounters in succession and a group of animals that had the same winning track record followed by a no-fight period for 14 days. Increased Th, Dat1 and Snca mRNA levels were in the fresh-from-the-fight group as compared to the controls. Increased Th and Dat1 mRNA levels were in the no-fight winners as compared to the controls. Significant positive correlations were found between the level of aggression and Th and Snca mRNA levels.

Conclusions

Repeated positive fighting experience enhances the expression of the Th, Dat1 and Snca genes, which are associated with brain dopaminergic systems. The expression of the Th and Dat1 genes stays enhanced for a long time.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).