Aggression-associated changes in murine olfactory tubercle bioamines

Aggression in Group-Housed Male Mice: A Systematic Review

Aggression among group-housed male mice is a major animal welfare concern often observed at animal facilities. Studies designed to understand the causes of male mice aggression have used different methodological approaches and have been heterogeneous, using different strains, environmental enrichments, housing conditions, group formations and durations. By conducting a systematic literature review based on 198 observed conclusions from 90 articles, we showed that the methodological approach used to study aggression was relevant for the outcome and suggested that home cage observations were better when studying home cage aggression than tests provoking aggression outside the home cage. The study further revealed that aggression is a complex problem; one solution will not be appropriate for all animal facilities and all research projects. Recommendations were provided on promising tools to minimize aggression, based on the results, which included what type of environmental enrichments could be appropriate and which strains of male mice were less likely to be aggressive.

Acute Air Pollution Exposure and the Risk of Violent Behavior in the United States

BACKGROUND

Violence is a leading cause of death and an important public health threat, particularly among adolescents and young adults. However, the environmental causes of violent behavior are not well understood. Emerging evidence suggests exposure to air pollution may be associated with aggressive or impulsive reactions in people.

METHODS

We applied a two-stage hierarchical time-series model to estimate change in risk of violent and nonviolent criminal behavior associated with short-term air pollution in U.S. counties (2000-2013). We used daily monitoring data for ozone and fine particulate matter (PM2.5) from the Environmental Protection Agency and daily crime counts from the Federal Bureau of Investigation. We evaluated the exposure-response relation and assessed differences in risk by community characteristics of poverty, urbanicity, race, and age.

RESULTS

Our analysis spans 301 counties in 34 states, representing 86.1 million people and 721,674 days. Each 10 µg/m change in daily PM2.5 was associated with a 1.17% (95% confidence interval [CI] = 0.90, 1.43) and a 10 ppb change in ozone with a 0.59% (95% CI = 0.41, 0.78) relative risk increase (RRI) for violent crime. However, we observed no risk increase for nonviolent property crime due to PM2.5 (RRI: 0.11%; 95% CI = -0.09, 0.31) or ozone (RRI: -0.05%; 95% CI = -0.22, 0.12). Our results were robust across all community types, except rural regions. Exposure-response curves indicated increased violent crime risk at concentrations below regulatory standards.

CONCLUSIONS

Our results suggest that short-term changes in ambient air pollution may be associated with a greater risk of violent behavior, regardless of community type.

Neurochemical organization of the ventral striatum's olfactory tubercle

The ventral striatum is a collection of brain structures, including the nucleus accumbens, ventral pallidum and the olfactory tubercle (OT). While much attention has been devoted to the nucleus accumbens, a comprehensive understanding of the ventral striatum and its contributions to neurological diseases requires an appreciation for the complex neurochemical makeup of the ventral striatum's other components. This review summarizes the rich neurochemical composition of the OT, including the neurotransmitters, neuromodulators and hormones present. We also address the receptors and transporters involved in each system as well as their putative functional roles. Finally, we end with briefly reviewing select literature regarding neurochemical changes in the OT in the context of neurological disorders, specifically neurodegenerative disorders. By overviewing the vast literature on the neurochemical composition of the OT, this review will serve to aid future research into the neurobiology of the ventral striatum.

Developmental exposure to concentrated ambient ultrafine particulate matter air pollution in mice results in persistent and sex-dependent behavioral neurotoxicity and glial activation

The brain appears to be a target of air pollution. This study aimed to further ascertain behavioral and neurobiological mechanisms of our previously observed preference for immediate reward (Allen, J. L., Conrad, K., Oberdorster, G., Johnston, C. J., Sleezer, B., and Cory-Slechta, D. A. (2013). Developmental exposure to concentrated ambient particles and preference for immediate reward in mice. Environ. Health Perspect. 121, 32-38), a phenotype consistent with impulsivity, in mice developmentally exposed to inhaled ultrafine particles. It examined the impact of postnatal and/or adult concentrated ambient ultrafine particles (CAPS) or filtered air on another behavior thought to reflect impulsivity, Fixed interval (FI) schedule-controlled performance, and extended the assessment to learning/memory (novel object recognition (NOR)), and locomotor activity to assist in understanding behavioral mechanisms of action. In addition, levels of brain monoamines and amino acids, and markers of glial presence and activation (GFAP, IBA-1) were assessed in mesocorticolimbic brain regions mediating these cognitive functions. This design produced four treatment groups/sex of postnatal/adult exposure: Air/Air, Air/CAPS, CAPS/Air, and CAPS/CAPS. FI performance was adversely influenced by CAPS/Air in males, but by Air/CAPS in females, effects that appeared to reflect corresponding changes in brain mesocorticolimbic dopamine/glutamate systems that mediate FI performance. Both sexes showed impaired short-term memory on the NOR. Mechanistically, cortical and hippocampal changes in amino acids raised the potential for excitotoxicity, and persistent glial activation was seen in frontal cortex and corpus callosum of both sexes. Collectively, neurodevelopment and/or adulthood CAPS can produce enduring and sex-dependent neurotoxicity. Although mechanisms of these effects remain to be fully elucidated, findings suggest that neurodevelopment and/or adulthood air pollution exposure may represent a significant underexplored risk factor for central nervous system diseases/disorders and thus a significant public health threat even beyond current appreciation.

Iron deficiency: Differential effects on monoamine transporters

In this study, we extend previous work on iron deficiency and dopamine (DA) transporters to include an examination of central serotonin (5-HT) and noradrenergic (NE) transporters. Rats were fed either iron deficient (ID) or iron adequate (CN) diets from weaning until adulthood. In males, an additional group of iron deficient animals (IR) were given iron supplementation. DA, 5-HT, and NE transporter binding was done in situ on thin sections. ID males, but not females, decreased DA transporter binding in the nucleus accumbens, caudate putamen and substantia nigra by 20-40%. ID males also had a 20-30% reduction in 5-HT transporter binding in several areas (nucleus accumbens, olfactory tubercle, colliculus) while in ID females there was 15-25% increased serotonin transporter binding in the olfactory tubercle, zona incerta, anteroventral thalamic nucleus and vestibular nucleus. Iron deficiency reduced 3H-nisoxetine binding to the NE transporter in locus ceruleus and anteroventral thalamic nucleus in males but not females. Only some of the changes observed in DA, serotonin and NE transporter binding were reversible by iron supplementation. These findings show that iron deficiency affects monoamine systems related to homeostasis and in most cases males appear to be more vulnerable than females.

GluA3-deficiency in mice is associated with increased social and aggressive behavior and elevated dopamine in striatum

Glutamate signaling has been implicated in the regulation of social behavior. AMPA-glutamate receptors are assembled from four subunits (GluA1-4) of mainly GluA1/2 and GluA2/3 tetramers that form ion channels of distinct functional properties. Mice lacking GluA1 showed a reduced anxiety and male aggression. To understand the role of GluA3 in modulating social behavior, we investigated GluA3-deficient mice (Gria3-/Y) on C57BL/6J background. Compared to wild type (WT) littermates (n=14), Gria3-/Y mice (n=13) showed an increase in isolation-induced male aggression (p=0.011) in home cage resident-intruder test; an increase in sociability (p=0.01), and increase in male-male social interactions in neutral arena (p=0.005); an increase in peripheral activities in open field test (p=0.037) with normal anxiety levels in elevated plus maze and light-dark box; and minor deficits in motor and balance function in accelerating rotarod test (p=0.016) with normal grip strength. Gria3-/Y mice showed no significant deficit in spatial memory function in Morris-water maze and Y-maze tests, and normal levels of testosterone. Increased dopamine concentrations in stratum (p=0.034) and reduced serotonin turnover in olfactory bulb (p=0.002) were documented in Gria3-/Y mice. These results support a role of GluA3 in the modulation of social behavior through brain dopamine and/or serotonin signaling and different AMPA receptor subunits affect social behavior through distinct mechanisms.

Disruption of the vasopressin 1b receptor gene impairs the attack component of aggressive behavior in mice

Vasopressin affects behavior via its two brain receptors, the vasopressin 1a and vasopressin 1b receptors (Avpr1b). Recent work from our laboratory has shown that disruption of the Avpr1b gene reduces intermale aggression and reduces social motivation. Here, we further characterized the aggressive phenotype in Avpr1b -/- (knockout) mice. We tested maternal aggression and predatory behavior. We also analyzed the extent to which food deprivation and competition over food increases intermale aggression. We quantified defensive behavior in Avpr1b -/- mice and later tested offensive aggression in these same mice. Our results show that attack behavior toward a conspecific is consistently reduced in Avpr1b -/- mice. Predatory behavior is normal, suggesting that the deficit is not because of a global inability to detect and attack stimuli. Food deprivation, competition for food and previous experience increase aggression in both Avpr1b +/+ and -/- mice. However, in these circumstances, the level of aggression seen in knockout mice is still less than that observed in wild-type mice. Defensive avoidance behaviors, such as boxing and fleeing, are largely intact in knockout mice. Avpr1b -/- mice do not display as many 'retaliatory' attacks as the Avpr1b +/+ mice. Interestingly, when territorial aggression was measured following the defensive behavior testing, Avpr1b -/- mice typically show less initial aggressive behavior than wild-type mice, but do show a significant increase in aggression with repeated testing. These studies confirm that deficits in aggression in Avpr1b -/- mice are limited to aggressive behavior involving the attack of a conspecific. We hypothesize that Avpr1b plays an important role in the central processing that couples the detection and perception of social cues (which appears normal) with the appropriate behavioral response.

Early signs of neuronal apoptosis in the substantia nigra pars compacta of the progressive neurodegenerative mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model of Parkinson’s disease

Parkinson's disease is associated with a progressive loss of substantia nigra pars compacta dopaminergic neurons. The cellular and molecular mechanisms underlying Parkinson's disease neurodegeneration have not been fully determined. Clinical investigations and subacute in vivo studies using the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine have generated some observations suggesting that apoptosis is involved in neurodegeneration; however, this view remains equivocal. In this study, the substantia nigra pars compacta neurodegenerative process was examined in the chronic mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model of Parkinson's disease treated with 10 doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (25 mg/kg) and probenecid (250 mg/kg) over five weeks. One day after chronic treatment, numerous terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells were detected specifically in the substantia nigra pars compacta displaying shrunken volume, chromatin condensation, and DNA fragmentation. The number of apoptotic cells declined over time. No terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells were found in untreated or probenecid-treated control animals. Cytomorphometric analysis of substantia nigra pars compacta nuclear loci revealed eccentric nucleoli dislocation and vesicular degranulation in all of the apoptotic neurons for the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model for Parkinson's disease. The terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells phenotypically showed neuronal origin (NeuN-positive) with a loss of tyrosine hydroxylase immunoreactivity. While the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells were not co-localized with astroglial (GFAP-positive) cells, some apoptotic cells were clearly associated with the activated microglial (macrophage antigen complex-1 and isolectin B(4)-positive) cells suggesting an active process of dead cell removal. In the one-day and seven-day post-treated mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model for Parkinson's disease, marked depression of tyrosine hydroxylase immunoreactivity in the substantia nigra pars compacta and striatum was observed, which was correlated with significant reductions of striatal dopamine content and uptake. These results suggest that initial neuronal apoptosis and morphological changes are involved, at least in part, in the chronic neurodegeneration of mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model for Parkinson's disease.

5-HT1A and 5-HT1B receptor agonists and aggression: a pharmacological challenge of the serotonin deficiency hypothesis

More than any other brain neurotransmitter system, the indolamine serotonin (5-HT) has been linked to aggression in a wide and diverse range of species, including humans. The nature of this linkage, however, is not simple and it has proven difficult to unravel the precise role of this amine in the predisposition for and execution of aggressive behavior. The dogmatic view that 5-HT inhibits aggression has dominated both pharmacological research strategies to develop specific and effective novel drug treatments that reduce aggressive behavior and the pharmacological mechanistic interpretation of putative serenic drug effects. Our studies on brain serotonin and aggression in feral wild-type rats using the resident-intruder paradigm have challenged this so-called serotonin deficiency hypothesis of aggressive behavior. The well-known fact that certain 5-HT(1A/1B) receptor agonists potently and specifically reduce aggressive behavior without motor slowing and sedative effects is only consistent with this hypothesis under the assumption that the agonist mainly acts on the postsynaptic 5-HT(1A/1B) receptor sites. However, systemic injections of anti-aggressive doses of 5-HT(1A) and (1B) agonists robustly decrease brain 5-HT release due to their inhibitory actions at somatodendritic and terminal autoreceptors, respectively. The availability of the novel benzodioxopiperazine compound S-15535, which acts in vivo as a preferential agonist of the somatodendritic 5-HT(1A) auto-receptor and as an antagonist (weak partial agonist) at postsynaptic 5-HT(1A) receptors, allows for a pharmacological analysis of the exact site of action of this anti-aggressive effect. It was found that, similar to other prototypical full and partial 5-HT(1A) and/or 5-HT(1B) receptor agonists like repinotan, 8-OHDPAT, ipsapirone, buspirone, alnespirone, eltoprazine, CGS-12066B and CP-93129, also S-15535 very effectively reduced offensive aggressive behavior. Unlike the other ligands, however, a remarkable degree of behavioral specificity was observed after treatment with S-15535, in that the anti-aggressive effects were not accompanied by inhibiting (like other 5-HT(1A) receptor agonist with moderate to high efficacy at postsynaptic 5-HT(1A) receptors) or enhancing (like agonists with activity at 5-HT(1B) receptors and alnespirone) non-aggressive motor behaviors (e.g., social exploration, ambulation, rearing, and grooming) beyond the range of undrugged animals with corresponding levels of aggression. The involvement of 5-HT(1A) and/or 5-HT(1B) receptors in the anti-aggressive actions of these drugs was convincingly confirmed by showing that the selective 5-HT(1A) receptor antagonist WAY-100635 and/or the 5-HT(1B) receptor antagonist GR-127935, while inactive when given alone, effectively attenuated/prevented these actions. Furthermore, combined administration of S-15535 with either alnespirone or CGS-42066B elicited a clear additive effect, indicated by a left-ward shift in their dose-effect curves, providing further support for presynaptic sites of action (i.e., inhibitory somatodendritic 5-HT(1A) and terminal 5-HT(1B) autoreceptors). These findings strongly suggest that the specific anti-aggressive effects of 5-HT(1A) and 5-HT(1B) receptor agonists are predominantly based on reduction rather than enhancement of 5-HT neurotransmission during the combative social interaction. Apparently, normal display of offensive aggressive behavior is positively related to brief spikes in serotonergic activity, whereas an inverse relationship probably exists between tonic 5-HT activity and abnormal forms of aggression only.

Reduced aggression in AMPA-type glutamate receptor GluR-A subunit-deficient mice

The importance of AMPA-type glutamate receptors has been demonstrated in neuronal plasticity and in adaptation to drugs of abuse. We studied the involvement of AMPA receptors in social interaction and anxiety and found that in several paradigms of agonistic behavior naïve male mice deficient for the GluR-A subunit- containing AMPA receptors are less aggressive than wild-type littermates. GluR-A deficient mice and wild-type littermates exhibited similar basic behavior and reflexes as monitored by observational Irwin's test, but they tended to be less anxious in elevated plus-maze and light-dark tests. Maternal aggression or male-female encounters were not affected which suggests that male hormones are involved in the expression of suppressed aggressiveness. However, testosterone levels and brain monoamines can be excluded and found to be similar between GluR-A deficient and wild-type littermates. The reduced AMPA receptor levels caused by the lack of the GluR-A subunit, and measured by a 30% reduction in hippocampal [3H]-S-AMPA binding, seem to be the reason for suppressed male aggressiveness. When we analyzed mice with reduced number of functional AMPA receptors mediated by the genomic introduced GluR-A(Q582R) channel mutation, we observed again male-specific suppressed aggression, providing additional evidence for GluR-A subunit-containing AMPA receptor involvement in aggression.