microRNA-146a modulates behavioural activity, neuroinflammation, and oxidative stress in adult mice.

Small non-coding miRNA act as key regulators of several physiological processes due to their ability to interact with numerous target mRNA within a network. Whilst several miRNA can act in concert to regulate target mRNA expression, miR-146a has emerged as a critical modulator of inflammation by targeting key upstream signalling proteins of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway and reductions in this miRNA have been observed in several neurological and neurodegenerative disorders. However, a targeted assessment of behaviour and neural tissues following the loss of miR-146a has not been documented. In this study, we examined the behavioural and neuroinflammatory phenotype of mice lacking miR-146a to determine the role of this miRNA in neurological function. Adult miR-146a-/- mice displayed no overt developmental phenotype with the exception of enlarged spleens. Behavioural testing revealed a mild but significant reduction in exploratory locomotor activity and increase in anxiety-like behaviour, with no changes in short-term spatial memory, fear conditioning, or sensorimotor gating. In the brain, the lack of miR-146a resulted in a significant compensatory miR-155 expression with no significant changes in expression of the target Interleukin 1 Receptor Associated Kinase (Irak) gene family. Despite these effects on upstream NF-κB mediators, downstream expression of cytokine and chemokine messengers was significantly elevated in miR-146a-/- mice compared to wild-type controls. Moreover, this increase in inflammatory cytokines was observed alongside an induction of oxidative stress, driven in part by nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase, and included reduced thiol antioxidant concentrations and increased oxidised protein carbonyl concentrations. In female miR-146a mice, this increase in oxidative stress resulted in an increased expression of superoxide dismutase 1 (SOD1). Together, this suggests miR-146a plays a key role in regulating inflammation even in the absence of inflammatory stimuli and reduced levels of this miRNA have the capacity to induce limited behavioural effects whilst exacerbating both inflammation and oxidative stress in the brain.

Impaired fear memory in a rat model of the brain-derived neurotrophic factor Val66Met polymorphism is reversed by chronic exercise.

The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with reduced activity-dependent BDNF release in the brain and has been implicated in fear and anxiety disorders, including post-traumatic stress disorder. Exercise has been shown to have benefits in affective disorders but the role of BDNF Val66Met remains unclear. Male and female BDNF Val66Met rats were housed in automated running-wheel cages from weaning while controls were housed in standard cages. During adulthood, all rats underwent standard three-day fear conditioning testing, with three tone/shock pairings on day 1 (acquisition), and extinction learning and memory (40 tones/session) on day 2 and day 3. Expression of BDNF and stress-related genes were measured in the frontal cortex. Extinction testing on day 2 revealed significantly lower freezing in response to initial cue exposure in control Met/Met rats, reflecting impaired fear memory. This deficit was reversed in both male and female Met/Met rats exposed to exercise. There were no genotype effects on acquisition or extinction of fear, however chronic exercise increased freezing in all groups at every stage of testing. Exercise furthermore led to increased expression of Bdnf in the prefrontal cortex of females and its isoforms in both sexes, as well as increased expression of FK506 binding protein 51 (Fkpb5) in females and decreased expression of Serum/glucocorticoid-regulated kinase (Sgk1) in males independent of genotype. These results show that the Met/Met genotype of the Val66Met polymorphism affects fear memory, and that chronic exercise selectively reverses this genotype effect. Chronic exercise also led to an overall increase in freezing in all genotypes which may contribute to results.

Methamphetamine-induced locomotor sensitization in mice is not associated with deficits in a range of cognitive, affective and social behaviours: interaction with brain-derived neurotrophic factor Val66Met genotype.

Chronic methamphetamine (Meth) abuse may induce psychosis similar to that observed in schizophrenia. Brain-derived neurotrophic factor (BDNF) has been implicated in the development of psychosis. We have previously shown long-term protein expression changes in mice treated chronically with Meth depending on BDNF Val66Met genotype. The aim of this study was to investigate if these protein expression changes were associated with differential changes in a range of behavioural paradigms for cognition, anxiety, social and other behaviours. Male and female Val/Val, Val/Met and Met/Met mice were treated with an escalating Meth dose protocol from 6 to 9 weeks of age, with controls receiving saline injections. Several overlapping cohorts were tested in the Y-maze for short-term spatial memory, novel-object recognition test, context and cued fear conditioning, sociability and social preference, elevated plus maze for anxiety-like behaviour and prepulse inhibition (PPI) of acoustic startle. Finally, the animals were assessed for spontaneous exploratory locomotor activity and acute Meth-induced locomotor hyperactivity. Acute Meth caused significantly greater locomotor hyperactivity in mice previously treated with the drug than in saline-pretreated controls. Meth-pretreated female mice showed a mild increase in spontaneous locomotor activity. There were no Meth-induced deficits in any of the other behavioural tests. Val/Met mice showed higher overall social investigation time and lower PPI compared with the Val/Val genotype independent of pretreatment. These results show limited long-term effects of chronic Meth on a range of cognitive, affective and social behaviours despite marked drug-induced locomotor sensitization in mice. There was no interaction with BDNF Val66Met genotype.

Chronic running-wheel exercise from adolescence leads to increased anxiety and depression-like phenotypes in adulthood in rats: Effects on stress markers and interaction with BDNF Val66Met genotype.

Exercise has been shown to be beneficial in reducing symptoms of affective disorders and to increase the expression of brain-derived neurotrophic factor (BDNF). The BDNF Val66Met polymorphism is associated with reduced activity-dependent BDNF release and increased risk for anxiety and depression. Male and female Val66Met rats were given access to running wheels from 3 weeks of age and compared to sedentary controls. Anxiety- and depression-like behaviors were measured in adulthood using the elevated plus maze (EPM), open field (OF), and forced swim test (FST). Expression of BDNF and a number of stress-related genes, the glucocorticoid receptor (Nr3c1), serum/glucocorticoid-regulated kinase 1 (Sgk1), and FK506 binding protein 51 (Fkbp5) in the hippocampus were also measured. Rats given access to running wheels developed high levels of voluntary exercise, decreased open-arm time on the EPM and center-field time in the OF, reduced overall exploratory activity in the open field, and increased immobility time in the FST with no differences between genotypes. Chronic exercise induced a significant increase in Bdnf mRNA and BDNF protein levels in the hippocampus with some of these effects being genotype specific. Exercise decreased the expression of Nr3c1 and Sgk1, but increased the expression of Fkbp5. These results suggest that chronic running-wheel exercise from adolescence increased anxiety and depression-like phenotypes in adulthood, independent of BDNF Val66Met genotype. Further studies are required to confirm that increased indices of anxiety-like behavior are independent from reduced overall locomotor activity.

Short-Term Environmental Enrichment is a Stronger Modulator of Brain Glial Cells and Cervical Lymph Node T Cell Subtypes than Exercise or Combined Exercise and Enrichment.

Physical exercise (PE) and environmental enrichment (EE) can modulate immunity. However, the differential effects of short-term PE, EE, and PE + EE on neuroimmune mechanisms during normal aging has not been elucidated. Hence, a cohort of 3-, 8-, and 13-month-old immunologically unchallenged C57BL/6 wild-type mice were randomly assigned to either Control, PE, EE, or PE + EE groups and provided with either no treatment, a running wheel, a variety of plastic and wooden objects alone or in combination with a running wheel for seven weeks, respectively. Immunohistochemistry and 8-color flow cytometry were used to determine the numbers of dentate gyrus glial cells, and the proportions of CD4+ and CD8+ T cell numbers and their subsets from cervical lymph nodes, respectively. An increase in the number of IBA1+ microglia in the dentate gyrus at 5 and 10 months was observed after EE, while PE and PE + EE increased it only at 10 months. No change in astroglia number in comparison to controls were observed in any of the treatment groups. Also, all treatments induced significant differences in the proportion of specific T cell subsets, i.e., CD4+ and CD8+ T naïve (TN), central memory (TCM), and effector memory (TEM) cells. Our results suggest that in the short-term, EE is a stronger modulator of microglial and peripheral T cell subset numbers than PE and PE + EE, and the combination of short-term PE and EE has no additive effects.

Maternal immune activation targeted to a window of parvalbumin interneuron development improves spatial working memory: Implications for autism.

Maternal immune activation (MIA) increases risk for neuropsychiatric disorders such as autism spectrum disorder (ASD) in offspring later in life through unknown causal mechanisms. Growing evidence implicates parvalbumin-containing GABAergic interneurons as a key target in rodent MIA models. We targeted a specific neurodevelopmental window of parvalbumin interneurons in a mouse MIA model to examine effects on spatial working memory, a key domain in ASD that can manifest as either impairments or improvements both clinically and in animal models. Pregnant dams received three consecutive intraperitoneal injections of Polyinosinic:polycytidylic acid (poly(I:C), 5 mg/kg) at gestational days 13, 14 and 15. Spatial working memory was assessed in young adult offspring using touchscreen operant chambers and the Trial-Unique Non-matching to Location (TUNL) task. Anxiety, novelty seeking and short-term memory were assessed using Elevated Plus Maze (EPM) and Y-maze novelty preference tasks. Fluorescent immunohistochemistry was used to assess hippocampal parvalbumin cell density, intensity and co-expression with perineuronal nets. qPCR was used to assess the expression of putatively implicated gene pathways. MIA targeting a window of parvalbumin interneuron development increased spatial working memory performance on the TUNL touchscreen task which was not influenced by anxiety or novelty seeking behaviour. The model reduced fetal mRNA levels of Gad1 and adult hippocampal mRNA levels of Pvalb and the distribution of low intensity parvalbumin interneurons was altered. We speculate a specific timing window for parvalbumin interneuron development underpins the apparently paradoxical improved spatial working memory phenotype found both across several rodent models of autism and clinically in ASD.

TrkB agonist 7,8-dihydroxyflavone reverses an induced prepulse inhibition deficit selectively in maternal immune activation offspring: implications for schizophrenia.

Reduced brain-derived neurotrophic factor (BDNF) signalling has been implicated in schizophrenia endophenotypes, including deficits in prepulse inhibition (PPI). Maternal immune activation (MIA) is a widely used neurodevelopmental animal model for schizophrenia but it is unclear if BDNF and its receptor, tropomyosin receptor kinase B (TrkB), are involved in PPI regulation in this model. Pregnant Long Evans rats were treated with the viral mimetic, polyinosinic-polycytidylic acid (poly I:C; 4 mg/kg i.v.), and nine male offspring from these dams were compared in adulthood to 11 male Long Evans controls. Offspring underwent PPI testing following injection with the TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF) (10 mg/kg i.p.), with or without the dopamine receptor agonist, apomorphine (APO; 1 mg/kg s.c.), or the dopamine releasing drug, methamphetamine (METH; 2 mg/kg s.c.). Acute administration of APO and METH caused the expected significant reduction of PPI. Acute administration of 7,8-DHF did not alter PPI on its own; however, it significantly reversed the effect of APO on PPI in poly I:C rats, but not in controls. A similar trend was observed in combination with METH. Western blot analysis of frontal cortex revealed significantly increased levels of BDNF protein, but not TrkB or phosphorylated TrkB/TrkB levels, in poly I:C rats. These findings suggest that, selectively in MIA offspring, 7,8-DHF has the ability to reverse PPI deficits caused by dopaminergic stimulation. This effect could be associated with increased BDNF expression in the frontal cortex. These data suggest that targeting BDNF signalling may have therapeutic potential for the treatment of certain symptoms of schizophrenia.

Short-term environmental enrichment, and not physical exercise, alleviate cognitive decline and anxiety from middle age onwards without affecting hippocampal gene expression.

Physical exercise (PE) and environmental enrichment (EE) have consistently been shown to modulate behavior and neurobiological mechanisms. The current literature lacks evidence to confirm the relationship between PE and EE, if any, and whether short-term treatment with PE, EE, or PE+EE could be considered to correct age-related behavioral deficits. Three-, 8-, and 13-month-old C57BL/6 mice were assigned to either PE, EE, or PE+EE treatment groups (n = 12-16/group) for 4 weeks before behavioral testing and were compared to controls. Differential effects of the treatments on various behaviors and hippocampal gene expression were measured using an established behavioral battery and high-throughput qPCR respectively. Short-term EE enhanced locomotor activity at 9 and 14 months of age, whereas the combination of PE and EE reduced locomotor activity in the home cage at 14 months. Short-term EE also was found to reverse the age-related increase in anxiety at 9 months and spatial memory deficits at 14 months of age. Conversely, short-term PE induced spatial learning impairment and depressive-like behavior at four months but showed no effects in 9- and 14-month-old mice. PE and PE+EE, but not EE, modified the expression of several hippocampal genes at 9 months of age compared with control mice. In conclusion, short-term EE may help to alleviate age-related cognitive decline and increase in anxiety, without altering hippocampal gene expression. On the contrary, PE is detrimental at a young age for both affective-like behaviors and spatial learning and memory but showed no effects at middle and late middle age despite hippocampal gene expression alterations.

GAL3 receptor knockout mice exhibit an alcohol-preferring phenotype.

Galanin is a neuropeptide which mediates its effects via three G-protein coupled receptors (GAL1-3 ). Administration of a GAL3 antagonist reduces alcohol self-administration in animal models while allelic variation in the GAL3 gene has been associated with an increased risk of alcohol use disorders in diverse human populations. Based on the association of GAL3 with alcoholism, we sought to characterize drug-seeking behavior in GAL3 -deficient mice for the first time. In the two-bottle free choice paradigm, GAL3 -KO mice consistently showed a significantly increased preference for ethanol over water when compared to wildtype littermates. Furthermore, male GAL3 -KO mice displayed significantly increased responding for ethanol under operant conditions. These differences in alcohol seeking behavior in GAL3 -KO mice did not result from altered ethanol metabolism. In contrast to ethanol, GAL3 -KO mice exhibited similar preference for saccharin and sucrose over water, and a similar preference for a high fat diet over a low fat diet as wildtype littermates. No differences in cognitive and locomotor behaviors were observed in GAL3 -KO mice to account for increased alcohol seeking behavior. Overall, these findings suggest genetic ablation of GAL3 in mice increases alcohol consumption.

Extensive phenotyping of two ARX polyalanine expansion mutation mouse models that span clinical spectrum of intellectual disability and epilepsy.

The Aristaless-related homeobox gene (ARX) is a known intellectual disability (ID) gene that frequently presents with X-linked infantile spasm syndrome as a comorbidity. ID with epilepsy in children is a chronic and devastating disorder that has poor treatment options and disease outcomes. To gain a better understanding of the role that mutations in ARX play in ID and epilepsy, we investigate ARX patient mutations modelled in mice. Over half of all ARX mutations result from expansions of the first two polyalanine (PA1 and PA2 respectively) tracts. However, phenotypic data for the mouse modelling the more frequent ARX PA2 dup24 mutation in patients has not been reported and constitutes a barrier to understanding the molecular mechanisms involved. Here we report the first comprehensive analysis of postnatal outcomes for mice modelling disease-causing expansions to both PA1 and PA2 tracts. Both strains were found to have impaired learning and memory, reduced activity, increased anxiety and reduced sociability; with PA1 mice generally displaying greater behavioural deficits in keeping with the more severe phenotype reported in patients. In agreement with previous reports, 70% of PA1 males exhibit myoclonic seizures by two months of age, with the first observed at P18. In this report, we show 80% of PA2 males also display myoclonic seizures, with the first observed at P19. Consistent with patient phenotypes, we observe large variations in seizure progression and severity for both PA1 and PA2 individual mice. The generation of this comprehensive baseline data is a necessary step on the path to the development of therapies to improve patient outcomes.

Administering a Behavioral Test Battery in Rodents.

Although animal models cannot broadly represent uniquely human psychiatric or psychological syndromes such as anxiety, depression, or schizophrenia, behavioral testing in rodents can be extremely helpful to investigate specific disease aspects and symptoms. Animal behavioral test batteries allow researchers to reveal specific behavioral changes in genetically modified mice or following targeted treatments or in response to environmental interventions. Examples of types of behaviors that can be combined in a test battery include anxiety-like behavior, learning and memory, depression-relevant behavior, social interaction, and locomotor hyperactivity. Here, we describe several commonly used and relatively simple behavioral tests which can be combined in the same cohort of animals.

Testing Prepulse Inhibition of Acoustic Startle in Rodents.

Prepulse inhibition (PPI) is a measure of sensorimotor gating which is widely used in rodents to study information processing and attention dysfunction. PPI is commonly measured in rats and mice using automated equipment. Here, we present details of a PPI testing protocol extensively used in previous studies. The protocol includes a set pulse-alone startle level and prepulse-pulse combinations with varying interval and intensity. Variations of this protocol can be used depending on the experimental aim or equipment and software version.

Interaction of Brain-derived Neurotrophic Factor, Exercise, and Fear Extinction: Implications for Post-traumatic Stress Disorder.

Brain-Derived Neurotrophic Factor (BDNF) plays an important role in brain development, neural plasticity, and learning and memory. The Val66Met single-nucleotide polymorphism is a common genetic variant that results in deficient activity-dependent release of BDNF. This polymorphism and its impact on fear conditioning and extinction, as well as on symptoms of post-traumatic stress disorder (PTSD), have been of increasing research interest over the last two decades. More recently, it has been demonstrated that regular physical activity may ameliorate impairments in fear extinction and alleviate symptoms in individuals with PTSD via an action on BDNF levels and that there are differential responses to exercise between the Val66Met genotypes. This narrative literature review first describes the theoretical underpinnings of the development and persistence of intrusive and hypervigilance symptoms commonly seen in PTSD and their treatment. It then discusses recent literature on the involvement of BDNF and the Val66Met polymorphism in fear conditioning and extinction and its involvement in PTSD diagnosis and severity. Finally, it investigates research on the impact of physical activity on BDNF secretion, the differences between the Val66Met genotypes, and the effect on fear extinction learning and memory and symptoms of PTSD.

Interaction of Brain-Derived Neurotrophic Factor with the Effects of Chronic Methamphetamine on Prepulse Inhibition in Mice Is Independent of Dopamine D3 Receptors.

The aim of the present study was to gain a better understanding of the role of brain-derived neurotrophic factor (BDNF) and dopamine D3 receptors in the effects of chronic methamphetamine (METH) on prepulse inhibition (PPI), an endophenotype of psychosis. We compared the effect of a three-week adolescent METH treatment protocol on the regulation of PPI in wildtype mice, BDNF heterozygous mice (HET), D3 receptor knockout mice (D3KO), and double-mutant mice (DM) with both BDNF heterozygosity and D3 receptor knockout. Chronic METH induced disruption of PPI regulation in male mice with BDNF haploinsufficiency (HET and DM), independent of D3 receptor knockout. Specifically, these mice showed reduced baseline PPI, as well as attenuated disruption of PPI induced by acute treatment with the dopamine receptor agonist, apomorphine (APO), or the glutamate NMDA receptor antagonist, MK-801. In contrast, there were no effects of BDNF heterozygosity or D3 knockout on PPI regulation in female mice. Chronic METH pretreatment induced the expected locomotor hyperactivity sensitisation, where female HET and DM mice also showed endogenous sensitisation. Differential sex-specific effects of genotype and METH pretreatment were observed on dopamine receptor and dopamine transporter gene expression in the striatum and frontal cortex. Taken together, these results show a significant involvement of BDNF in the long-term effects of METH on PPI, particularly in male mice, but these effects appear independent of D3 receptors. The role of this receptor in psychosis endophenotypes therefore remains unclear.

A Rat Model of the Brain-Derived Neurotrophic Factor Val66Met Polymorphism Shows Attenuated Motivation for Alcohol Self-Administration and Diminished Propensity for Cue-Induced Relapse in Females.

Brain-derived neurotrophic factor (BDNF) has been implicated in alcohol use disorder. The Val66Met polymorphism is a common variant of the BDNF gene (rs6265) which reduces activity-dependent BDNF release, and has been suggested as a risk factor for psychiatric disorders and substance use. Using an operant self-administration paradigm, this study aimed to investigate ethanol preference and ethanol seeking in a novel rat model of the BDNF Val66Met polymorphism, Val68Met rats. Male and female BDNF Val68Met rats of three genotypes (Val/Val, Val/Met and Met/Met) were trained to lever press for a 10% ethanol solution. There was no effect of Val68Met genotype on acquisition of stable response to ethanol or its extinction. Met/Met rats of both sexes had a slight, but significantly lower breakpoint during progressive ratio sessions while female rats with the Met/Met genotype demonstrated a lower propensity for reinstatement of responding to cues. There were no effects of Val68Met genotype on anxiety-like behaviour or locomotor activity. In conclusion, Met/Met rats showed lower motivation to continue to press for a reward, and also a decreased propensity to relapse, suggesting a possible protective effect of the Met/Met genotype against alcohol use disorder, at least in females.

Enhanced methamphetamine sensitisation in a rat model of the brain-derived neurotrophic factor Val66Met variant: Sex differences and dopamine receptor gene expression.

Brain-derived neurotrophic factor (BDNF) and the Val66Met polymorphism may play a role in the development of psychosis and schizophrenia. The aim of this study was to investigate long-term effects of methamphetamine (Meth) on psychosis-like behaviour and dopamine receptor and dopamine transporter gene expression in a novel rat model of the BDNF Val66Met polymorphism. At the end of a 7-day subchronic Meth treatment, female rats with the Met/Met genotype selectively showed locomotor hyperactivity sensitisation to the acute effect of Meth. Male rats showed tolerance to Meth irrespective of Val66Met genotype. Two weeks later, female Met/Met rats showed increased locomotor activity following both saline treatment or a low dose of Meth, a hyperactivity which was not observed in other genotypes or in males. Baseline PPI did not differ between the groups but the disruption of PPI by acute treatment with apomorphine was absent in Meth-pretreated Met/Met rats. Female Met/Met rats selectively showed down-regulation of dopamine D2 receptor gene expression in striatum. Behavioural effects of MK-801 or its locomotor sensitisation by prior Meth pretreatment were not influenced by genotype. These data suggest a selective vulnerability of female Met/Met rats to short-term and long-term effects of Meth, which could model increased vulnerability to psychosis development associated with the BDNF Val66Met polymorphism.

Metergoline Shares Properties with Atypical Antipsychotic Drugs Identified by Gene Expression Signature Screen.

Novel approaches are required to find new treatments for schizophrenia and other neuropsychiatric disorders. This study utilised a combination of in vitro transcriptomics and in silico analysis with the BROAD Institute's Connectivity Map to identify drugs that can be repurposed to treat psychiatric disorders. Human neuronal (NT2-N) cells were treated with a combination of atypical antipsychotic drugs commonly used to treat psychiatric disorders (such as schizophrenia, bipolar disorder, and major depressive disorder), and differential gene expression was analysed. Biological pathways with an increased gene expression included circadian rhythm and vascular endothelial growth factor signalling, while the adherens junction and cell cycle pathways were transcriptionally downregulated. The Connectivity Map (CMap) analysis screen highlighted drugs that affect global gene expression in a similar manner to these psychiatric disorder treatments, including several other antipsychotic drugs, confirming the utility of this approach. The CMap screen specifically identified metergoline, an ergot alkaloid currently used to treat seasonal affective disorder, as a drug of interest. In mice, metergoline dose-dependently reduced MK-801- or methamphetamine-induced locomotor hyperactivity confirming the potential of metergoline to treat positive symptoms of schizophrenia in an animal model. Metergoline had no effects on prepulse inhibition deficits induced by MK-801 or methamphetamine. Taken together, metergoline appears a promising drug for further studies to be repurposed as a treatment for schizophrenia and possibly other psychiatric disorders.

The Role of Dorsal Raphe Nucleus Serotonergic Systems in Emotional Learning and Memory in Male BALB/c Mice.

Selective serotonin reuptake inhibitors (SSRIs) are the first-line pharmacological treatment for a variety of anxiety-, trauma- and stressor-related disorders. Although they are efficacious, therapeutic improvements require several weeks of treatment and are often associated with an initial exacerbation of symptoms. The dorsal raphe nucleus (DR) has been proposed as an important target for the modulation of emotional responses and the therapeutic effects of SSRIs. Using a fear-conditioning paradigm we aimed to understand how SSRIs affect emotional learning and memory, and their effects on serotonergic circuitry. Adult male BALB/c mice were treated with vehicle (n = 16) or the SSRI fluoxetine (18 mg/kg/d) acutely (n = 16), or chronically (21d, n = 16), prior to fear conditioning. Treatment was stopped, and half of the mice (n = 8/treatment group) were exposed to cued fear memory recall 72 h later. Activation of DR serotonergic neurons during fear conditioning (Experiment 1) or fear memory recall (Experiment 2), was measured using dual-label immunohistochemistry for Tph2 and c-Fos. Acute and chronic fluoxetine treatment reduced associative fear learning without affecting memory recall and had opposite effects on anxiety-like behaviour. Acute fluoxetine decreased serotonergic activity in the DR, while chronic treatment led to serotonergic activity that was indistinguishable from that of control levels in DRD and DRV subpopulations. Chronic fluoxetine facilitated fear extinction, which was associated with rostral DRD inhibition. These findings provide further evidence that SSRIs can alter aspects of learning and memory processes and are consistent with a role for discrete populations of DR serotonergic neurons in regulating fear- and anxiety-related behaviours.

Analysis of striatum and brain levels reveals sex differences in conversion of methamphetamine to amphetamine in mice.

The aim of this study was to compare methamphetamine (Meth) and amphetamine (Amph) levels in the brain of male and female mice. Meth and Amph levels were significantly higher at 30 min after systemic administration of 2 mg/kg of Meth than at 120 min. Meth levels were similar in striatum as in the rest of the brain and there was no sex difference. However, females showed significantly higher levels of Amph compared to males in both regions. The ratio of Amph to Meth levels was significantly higher in female mice than in males at 120 min after Meth administration. In a separate cohort of mice, treatment with 3 mg/kg of Meth induced significant locomotor hyperactivity which was maximum in the first 60 min after injection and not different between male and female mice. Treatment with 1 mg/kg Meth induced mild hyperactivation in female, but not male mice at 60-120 min post-injection. These data show sex differences in conversion of Meth to Amph in mice, which could play a role in sex differences in the behavioural, addictive and neurotoxic properties of Meth in rodents as well as in humans.

Differential effects of chronic adolescent glucocorticoid or methamphetamine on drug-induced locomotor hyperactivity and disruption of prepulse inhibition in adulthood in mice.

Sensitization of dopaminergic activity has been suggested as an underlying mechanism in the psychotic symptoms of schizophrenia. Adolescent stress and chronic abuse of methamphetamine (Meth) are well-known risk factors for psychosis and schizophrenia; however it remains unknown how these factors compare in terms of dopaminergic behavioural sensitization in adulthood. In addition, while Brain-Derived Neurotrophic Factor (BDNF) has been implicated in dopaminergic activity and schizophrenia, its role in behavioural sensitization remains unclear. In this study we therefore compared the effect of chronic adolescent treatment with the stress hormone, corticosterone (Cort), or with Meth, on drug-induced locomotor hyperactivity and disruption of prepulse inhibition in adulthood in BDNF heterozygous mice and their wild-type controls, as well as on dopamine receptor gene expression. Between 6 and 9 weeks of age, the animals either received Cort in the drinking water or were treated with an escalating Meth dose protocol. In adulthood, Cort-pretreated mice showed significantly reduced Meth-induced locomotor hyperactivity compared to vehicle-pretreated mice. In contrast, Meth hyperlocomotion was significantly enhanced in animals pretreated with the drug in adolescence. There were no effects of either pretreatment on prepulse inhibition. BDNF Het mice showed greater Meth-induced hyperlocomotion and lower prepulse inhibition than WT mice. There were no effects of either pretreatment on D1 or D2 gene expression in either the dorsal or ventral striatum, while D3 mRNA was shown to be reduced in male mice only irrespective of genotype. These results suggest that in adolescence, chronically elevated glucocorticoid levels, a component of chronic stress, do not cause dopaminergic sensitization adulthood, in contrast to the effect of chronic Meth treatment in the same age period. BDNF does not appear to be involved in the effects of chronic Cort or chronic Meth.