Nrf2 activation rescues stress-induced depression-like behaviour and inflammatory responses in male but not female rats

BACKGROUND

Major depressive disorder (MDD) is a recurring affective disorder that is two times more prevalent in females than males. Evidence supports immune system dysfunction as a major contributing factor to MDD, notably in a sexually dimorphic manner. Nuclear factor erythroid 2-related factor 2 (Nrf2), a regulator of antioxidant signalling during inflammation, is dysregulated in many chronic inflammatory disorders; however, its role in depression and the associated sex differences have yet to be explored. Here, we investigated the sex-specific antidepressant and immunomodulatory effects of the potent Nrf2 activator dimethyl fumarate (DMF), as well as the associated gene expression profiles.

METHODS

Male and female rats were treated with vehicle or DMF (25 mg/kg) whilst subjected to 8 weeks of chronic unpredictable stress. The effect of DMF treatment on stress-induced depression- and anxiety-like behaviours, as well as deficits in recognition and spatial learning and memory were then assessed. Sex differences in hippocampal (HIP) microglial activation and gene expression response were also evaluated.

RESULTS

DMF treatment during stress exposure had antidepressant effects in male but not female rats, with no anxiolytic effects in either sex. Recognition learning and memory and spatial learning and memory were impaired in chronically stressed males and females, respectively, and DMF treatment rescued these deficits. DMF treatment also prevented stress-induced HIP microglial activation in males. Conversely, females displayed no HIP microglial activation associated with stress exposure. Last, chronic stress elicited sex-specific alterations in HIP gene expression, many of which were normalized in animals treated with DMF. Of note, most of the differentially expressed genes in males normalized by DMF were related to antioxidant, inflammatory or immune responses.

CONCLUSIONS

Collectively, these findings support a greater role of immune processes in males than females in a rodent model of depression. This suggests that pharmacotherapies that target Nrf2 have the potential to be an effective sex-specific treatment for depression.

A journey with psychedelic mushrooms: From historical relevance to biology, cultivation, medicinal uses, biotechnology, and beyond

Psychedelic mushrooms containing psilocybin and related tryptamines have long been used for ethnomycological purposes, but emerging evidence points to the potential therapeutic value of these mushrooms to address modern neurological, psychiatric health, and related disorders. As a result, psilocybin containing mushrooms represent a re-emerging frontier for mycological, biochemical, neuroscience, and pharmacology research. This work presents crucial information related to traditional use of psychedelic mushrooms, as well as research trends and knowledge gaps related to their diversity and distribution, technologies for quantification of tryptamines and other tryptophan-derived metabolites, as well as biosynthetic mechanisms for their production within mushrooms. In addition, we explore the current state of knowledge for how psilocybin and related tryptamines are metabolized in humans and their pharmacological effects, including beneficial and hazardous human health implications. Finally, we describe opportunities and challenges for investigating the production of psychedelic mushrooms and metabolic engineering approaches to alter secondary metabolite profiles using biotechnology integrated with machine learning. Ultimately, this critical review of all aspects related to psychedelic mushrooms represents a roadmap for future research efforts that will pave the way to new applications and refined protocols.

Beyond the Binary: Gender Inclusivity in Schizophrenia Research

Schizophrenia is a severe neuropsychiatric disorder with significant differences in the incidence and symptomology between cisgender men and women. In recent years, considerably more attention has been on the inclusion of sex and gender in schizophrenia research. However, the majority of this research has failed to consider gender outside of the socially constructed binary of men and women. As a result, little is known about schizophrenia in transgender and gender-nonconforming populations. In this review, we present evidence showing that transgender and gender-nonconforming individuals have elevated risk of developing schizophrenia, and we discuss minority stress theory and other potential factors that may contribute to this risk. The need for inclusion of transgender and gender-nonconforming communities in schizophrenia research is emphasized, alongside a discussion on considerations and challenges associated with this type of research. Finally, we offer specific strategies to make research on schizophrenia, and research on other neuropsychiatric disorders, more inclusive of those populations that do not fall within the socially constructed gender binary. If we are to succeed in the development of more personalized therapeutic approaches for all, a better understanding of the variability of the human brain is needed.

A Simple, Lightweight, and Low-Cost Customizable Multielectrode Array for Local Field Potential Recordings

Local field potential (LFP) recording is a valuable method for assessing brain systems communication. Multiple methods have been developed to collect LFP data to study the rhythmic activity of the brain. These methods range from the use of single or bundled metal electrodes to electrode arrays that can target multiple brain regions. Although these electrodes are efficient in collecting LFP activity, they can be expensive, difficult to build, and less adaptable to different applications, which may include targeting multiple brain regions simultaneously. Here, the building process for a 16-channel customizable multielectrode array (CMEA) that can be used to collect LFP data from different brain regions simultaneously in rats is described. These CMEA electrode arrays are lightweight (<1 g), take little time to build (<1 h), and are affordable ($15 Canadian). The CMEA can also be modified to record single-unit and multiunit activity in addition to LFP activity using both wired and wireless neural data acquisition systems. Moreover, these CMEAs can be used to explore neural activity (LFP and single-unit/multiunit activity) in preliminary studies, before purchasing more expensive electrodes for targeted studies. Together, these characteristics make the described CMEA a competitive alternative to the commercially available multielectrode arrays for its simplicity, low cost, and efficiency in collecting LFP data in freely behaving animals.

Cortical dopamine D5 receptors regulate neuronal circuit oscillatory activity and memory in rats

INTRODUCTION

The dopamine D5 receptor (D5R) shows high expression in cortical regions, yet the role of the receptor in learning and memory remains poorly understood. This study evaluated the impact of prefrontal cortical (PFC) D5R knockdown in rats on learning and memory and assessed the role of the D5R in the regulation of neuronal oscillatory activity and glycogen synthase kinase-3 (GSK-3β), processes integral to cognitive function.

MATERIALS AND METHODS

Using an adeno-associated viral (AAV) vector, male rats were infused with shRNA to the D5R bilaterally into the PFC. Local field potential recordings were taken from freely moving animals and spectral power and coherence were evaluated in, and between, the PFC, orbitofrontal cortex (OFC), hippocampus (HIP), and thalamus. Animals were then assessed in object recognition, object location, and object in place tasks. The activity of PFC GSK-3β, a downstream effector of the D5R, was evaluated.

RESULTS

AAV-mediated knockdown of the D5R in the PFC induced learning and memory deficits. These changes were accompanied by elevations in PFC, OFC, and HIP theta spectral power and PFC-OFC coherence, reduced PFC-thalamus gamma coherence, and increased PFC GSK-3β activity.

CONCLUSION

This work demonstrates a role for PFC D5Rs in the regulation of neuronal oscillatory activity and learning and memory. As elevated GSK-3β activity has been implicated in numerous disorders of cognitive dysfunction, this work also highlights the potential of the D5R as a novel therapeutic target via suppression of GSK-3β.

Human cerebral spheroids undergo 4-aminopyridine-induced, activity associated changes in cellular composition and microrna expression

Activity-induced neurogenesis has been extensively studied in rodents but the lack of ante mortem accessibility to human brain at the cellular and molecular levels limits studies of the process in humans. Using cerebral spheroids derived from human induced pluripotent stem cells (iPSCs), we investigated the effects of 4-aminopyridine (4AP) on neuronal activity and associated neurogenesis. Our studies demonstrate that 4AP increases neuronal activity in 3-month-old cerebral spheroids while increasing numbers of new neurons and decreasing the population of new glial cells. We also observed a significant decrease in the expression of miR-135a, which has previously been shown to be decreased in exercise-induced neurogenesis. Predicted targets of miR-135a include key participants in the SMAD2/3 and BDNF pathways. Together, our results suggest that iPSC-derived cerebral spheroids are an attractive model to study several aspects of activity-induced neurogenesis.

Cannabis Vapor Exposure Alters Neural Circuit Oscillatory Activity in a Neurodevelopmental Model of Schizophrenia: Exploring the Differential Impact of Cannabis Constituents

Cannabis use is highly prevalent in patients with schizophrenia and worsens the course of the disorder. To understand how exposure to cannabis changes schizophrenia-related oscillatory disruptions, we investigated the impact of administering cannabis vapor containing either Δ9-tetrahydrocannabinol (THC) or balanced THC/cannabidiol (CBD) on oscillatory activity in the neonatal ventral hippocampal lesion (NVHL) rat model of schizophrenia. Male Sprague Dawley rats underwent lesion or sham surgeries on postnatal day 7. In adulthood, electrodes were implanted targeting the cingulate cortex (Cg), the prelimbic cortex (PrLC), the hippocampus (HIP), and the nucleus accumbens (NAc). Local field potential recordings were obtained after rats were administered either the "THC-only" cannabis vapor (8-18% THC/0% CBD) or the "Balanced THC:CBD" cannabis vapor (4-11% THC/8.5-15.5% CBD) in a cross-over design with a 2-week wash-out period between exposures. Compared to controls, NVHL rats had reduced baseline gamma power in the Cg, HIP, and NAc, and reduced HIP-Cg high-gamma coherence. THC-only vapor exposure broadly suppressed oscillatory power and coherence, even beyond the baseline reductions observed in NHVL rats. Balanced THC:CBD vapor, however, did not suppress oscillatory power and coherence, and in some instances enhanced power. For NVHL rats, THC-only vapor normalized the baseline HIP-Cg high-gamma coherence deficits. NHVL rats demonstrated a 20 ms delay in HIP theta to high-gamma phase coupling, which was not apparent in the PrLC and NAc after both exposures. In conclusion, cannabis vapor exposure has varying impacts on oscillatory activity in NVHL rats, and the relative composition of naturally occurring cannabinoids may contribute to this variability.

Sex differences in neuronal systems function and behaviour: beyond a single diagnosis in autism spectrum disorders

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that is associated with functional brain alterations that underlie the expression of behaviour. Males are diagnosed up to four times more than females, and sex differences have been identified in memory, cognitive flexibility, verbal fluency, and social communication. Unfortunately, there exists a lack of information on the sex-dependent mechanisms of ASD, as well as biological markers to distinguish sex-specific symptoms in ASD. This can often result in a standardized diagnosis for individuals across the spectrum, despite significant differences in the various ASD subtypes. Alterations in neuronal connectivity and oscillatory activity, such as is observed in ASD, are highly coupled to behavioural states. Yet, despite the well-identified sexual dimorphisms that exist in ASD, these functional patterns have rarely been analyzed in the context of sex differences or symptomology. This review summarizes alterations in neuronal oscillatory function in ASD, discusses the age, region, symptom and sex-specific differences that are currently observed across the spectrum, and potential targets for regulating neuronal oscillatory activity in ASD. The need to identify sex-specific biomarkers, in order to facilitate specific diagnostic criteria and allow for more targeted therapeutic approaches for ASD will also be discussed.

Glycogen Synthase Kinase-3: A Focal Point for Advancing Pathogenic Inflammation in Depression

Increasing evidence indicates that the host immune response has a monumental role in the etiology of major depressive disorder (MDD), motivating the development of the inflammatory hypothesis of depression. Central to the involvement of chronic inflammation in MDD is a wide range of signaling deficits induced by the excessive secretion of pro-inflammatory cytokines and imbalanced T cell differentiation. Such signaling deficits include the glutamatergic, cholinergic, insulin, and neurotrophin systems, which work in concert to initiate and advance the neuropathology. Fundamental to the communication between such systems is the protein kinase glycogen synthase kinase-3 (GSK-3), a multifaceted protein critically linked to the etiology of MDD and an emerging target to treat pathogenic inflammation. Here, a consolidated overview of the widespread multi-system involvement of GSK-3 in contributing to the neuropathology of MDD will be discussed, with the feed-forward mechanistic links between all major neuronal signaling pathways highlighted.

The Antidepressant-Like and Analgesic Effects of Kratom Alkaloids are accompanied by Changes in Low Frequency Oscillations but not ΔFosB Accumulation

Mitragyna speciosa (“kratom”), employed as a traditional medicine to improve mood and relieve pain, has shown increased use in Europe and North America. Here, the dose-dependent effects of a purified alkaloid kratom extract on neuronal oscillatory systems function, analgesia, and antidepressant-like behaviour were evaluated and kratom-induced changes in ΔFosB expression determined. Male rats were administered a low or high dose of kratom (containing 0.5 or 1 mg/kg of mitragynine, respectively) for seven days. Acute or repeated low dose kratom suppressed ventral tegmental area (VTA) theta oscillatory power whereas acute or repeated high dose kratom increased delta power, and reduced theta power, in the nucleus accumbens (NAc), prefrontal cortex (PFC), cingulate cortex (Cg) and VTA. The repeated administration of low dose kratom additionally elevated delta power in PFC, decreased theta power in NAc and PFC, and suppressed beta and low gamma power in Cg. Suppressed high gamma power in NAc and PFC was seen selectively following repeated high dose kratom. Both doses of kratom elevated NAc-PFC, VTA-NAc, and VTA-Cg coherence. Low dose kratom had antidepressant-like properties whereas both doses produced analgesia. No kratom-induced changes in ΔFosB expression were evident. These results support a role for kratom as having both antidepressant and analgesic properties that are accompanied by specific changes in neuronal circuit function. However, the absence of drug-induced changes in ΔFosB expression suggest that the drug may circumvent this cellular signaling pathway, a pathway known for its significant role in addiction.

Sex-Specific Cannabidiol- and Iloperidone-Induced Neuronal Activity Changes in an In Vitro MAM Model System of Schizophrenia

Cortical circuit dysfunction is thought to be an underlying mechanism of schizophrenia (SZ) pathophysiology with normalization of aberrant circuit activity proposed as a biomarker for antipsychotic efficacy. Cannabidiol (CBD) shows potential as an adjunctive antipsychotic therapy; however, potential sex effects in these drug interactions remain unknown. In the present study, we sought to elucidate sex effects of CBD coadministration with the atypical antipsychotic iloperidone (ILO) on the activity of primary cortical neuron cultures derived from the rat methylazoxymethanol acetate (MAM) model used for the study of SZ. Spontaneous network activity measurements were obtained using a multielectrode array at baseline and following administration of CBD or ILO alone, or combined. At baseline, MAM male neurons displayed increased bursting activity whereas MAM female neurons exhibited no difference in bursting activity compared to sex-matched controls. CBD administered alone showed a rapid but transient increase in neuronal activity in the MAM networks, an effect more pronounced in females. Furthermore, ILO had an additive effect on CBD-induced elevations in activity in the MAM male neurons. In the MAM female neurons, CBD or ILO administration resulted in time-dependent elevations in neuronal activity, but the short-term CBD-induced increases in activity were lost when CBD and ILO were combined. Our findings indicate that CBD induces rapid increases in cortical neuronal activity, with sex-specific drug interactions upon ILO coadministration. This suggests that sex should be a consideration when implementing adjunct therapy for treatment of SZ.

Sex differences in innate and adaptive neural oscillatory patterns link resilience and susceptibility to chronic stress in rats

BACKGROUND

Major depressive disorder is a chronic illness with a higher incidence in women. Dysregulated neural oscillatory activity is an emerging mechanism thought to underlie major depressive disorder, but whether sex differences in these rhythms contribute to the development of symptoms is unknown.

METHODS

We exposed male and female rats to chronic unpredictable stress and characterized them as stress-resilient or stress-susceptible based on behavioural output in the forced swim test and the sucrose preference test. To identify sex-specific neural oscillatory patterns associated with stress response, we recorded local field potentials from the prefrontal cortex, cingulate cortex, nucleus accumbens and dorsal hippocampus throughout stress exposure.

RESULTS

At baseline, female stress-resilient rats innately exhibited higher theta coherence in hippocampal connections compared with stress-susceptible female rats. Following stress exposure, additional oscillatory changes manifested: stress-resilient females were characterized by increased dorsal hippocampal theta power and cortical gamma power, and stress-resilient males were characterized by a widespread increase in high gamma coherence. In stress-susceptible animals, we observed a pattern of increased delta and reduced theta power; the changes were restricted to the cingulate cortex and dorsal hippocampus in males but occurred globally in females. Finally, stress exposure was accompanied by the time-dependent recruitment of specific neural pathways, which culminated in system-wide changes that temporally coincided with the onset of depression-like behaviour.

LIMITATIONS

We could not establish causality between the electrophysiological changes and behaviours with the methodology we employed.

CONCLUSION

Sex-specific neurophysiological patterns can function as early markers for stress vulnerability and the onset of depression-like behaviours in rats.

GSK-3β Disrupts Neuronal Oscillatory Function to Inhibit Learning and Memory in Male Rats

Alterations in glycogen synthase kinase-3β (GSK-3β) activity have been implicated in disorders of cognitive impairment, including Alzheimer's disease and schizophrenia. Cognitive dysfunction is also characterized by the dysregulation of neuronal oscillatory activity, macroscopic electrical rhythms in brain that are critical to systems communication. A direct functional relationship between GSK-3β and neuronal oscillations has not been elucidated. Therefore, in the present study, using an adeno-associated viral vector containing a persistently active mutant form of GSK-3β, GSK-3β(S9A), the impact of elevated kinase activity in prefrontal cortex (PFC) or ventral hippocampus (vHIP) of rats on neuronal oscillatory activity was evaluated. GSK-3β(S9A)-induced changes in learning and memory were also assessed and the phosphorylation status of tau protein, a substrate of GSK-3β, examined. It was demonstrated that increasing GSK-3β(S9A) activity in either the PFC or vHIP had similar effects on neuronal oscillatory activity, enhancing theta and/or gamma spectral power in one or both regions. Increasing PFC GSK-3β(S9A) activity additionally suppressed high gamma PFC-vHIP coherence. These changes were accompanied by deficits in recognition memory, spatial learning, and/or reversal learning. Elevated pathogenic tau phosphorylation was also evident in regions where GSK-3β(S9A) activity was upregulated. The neurophysiological and learning and memory deficits induced by GSK-3β(S9A) suggest that aberrant GSK-3β signalling may not only play an early role in cognitive decline in Alzheimer's disease but may also have a more central involvement in disorders of cognitive dysfunction through the regulation of neurophysiological network function.

Acute mitragynine administration suppresses cortical oscillatory power and systems theta coherence in rats

BACKGROUND

Mitragynine is the major alkaloid of Mitragyna speciosa (kratom) with potential as a therapeutic in pain management and in depression. There has been debate over the potential side effects of the drug including addiction risk and cognitive decline.

AIMS

To evaluate the effects of mitragynine on neurophysiological systems function in the prefrontal cortex (PFC), cingulate cortex (Cg), orbitofrontal cortex, nucleus accumbens (NAc), hippocampus (HIP), thalamus (THAL), basolateral amygdala (BLA) and ventral tegmental area of rats.

METHODS

Local field potential recordings were taken from animals at baseline and for 45 min following mitragynine administration (10 mg/kg, intraperitoneally). Drug-induced changes in spectral power and coherence between regions at specific frequencies were evaluated. Mitragynine-induced changes in c-fos expression were also analyzed.

RESULTS

Mitragynine increased delta power and reduced theta power in all three cortical regions that were accompanied by increased c-fos expression. A transient suppression of gamma power in PFC and Cg was also evident. There were no effects of mitragynine on spectral power in any of the other regions. Mitragynine induced a widespread reduction in theta coherence (7-9 Hz) that involved disruptions in cortical and NAc connectivity with the BLA, HIP and THAL.

CONCLUSIONS

These findings show that mitragynine induces frequency-specific changes in cortical neural oscillatory activity that could potentially impact cognitive functioning. However, the absence of drug effects within regions of the mesolimbic pathway may suggest either a lack of addiction potential, or an underlying mechanism of addiction that is distinct from other opioid analgesic agents.

Transient Dose-dependent Effects of Ketamine on Neural Oscillatory Activity in Wistar-Kyoto Rats

Ketamine is a promising therapeutic for treatment-resistant depression (TRD) but is associated with an array of short-term psychomimetic side-effects. These disparate drug effects may be elicited through the modulation of neural circuit activity. The purpose of this study was to therefore delineate dose- and time-dependent changes in ketamine-induced neural oscillatory patterns in regions of the brain implicated in depression. Wistar-Kyoto rats were used as a model system to study these aspects of TRD neuropathology whereas Wistar rats were used as a control strain. Animals received a low (10 mg/kg) or high (30 mg/kg) dose of ketamine and temporal changes in neural oscillatory activity recorded from the prefrontal cortex (PFC), cingulate cortex (Cg), and nucleus accumbens (NAc) for ninety minutes. Effects of each dose of ketamine on immobility in the forced swim test were also evaluated. High dose ketamine induced a transient increase in theta power in the PFC and Cg, as well as a dose-dependent increase in gamma power in these regions 10-min, but not 90-min, post-administration. In contrast, only low dose ketamine normalized innate deficits in fast gamma coherence between the NAc-Cg and PFC-Cg, an effect that persisted at 90-min post-injection. These low dose ketamine-induced oscillatory alterations were accompanied by a reduction in immobility time in the forced swim test. These results show that ketamine induces time-dependent effects on neural oscillations at specific frequencies. These drug-induced changes may differentially contribute to the psychomimetic and therapeutic effects of the drug.

Glycogen synthase kinase-3: The missing link to aberrant circuit function in disorders of cognitive dysfunction?

Elevated GSK-3 activity has been implicated in cognitive dysfunction associated with various disorders including Alzheimer's disease, schizophrenia, type 2 diabetes, traumatic brain injury, major depressive disorder and bipolar disorder. Further, aberrant neural oscillatory activity in, and between, cortical regions and the hippocampus is consistently present within these same cognitive disorders. In this review, we will put forth the idea that increased GSK-3 activity serves as a pathological convergence point across cognitive disorders, inducing similar consequent impacts on downstream signaling mechanisms implicated in the maintenance of processes critical to brain systems communication and normal cognitive functioning. In this regard we suggest that increased activation of GSK-3 and neuronal oscillatory dysfunction are early pathological changes that may be functionally linked. Mechanistic commonalities between these disorders of cognitive dysfunction will be discussed and potential downstream targets of GSK-3 that may contribute to neuronal oscillatory dysfunction identified.

Sex difference in dopamine D1-D2 receptor complex expression and signaling affects depression- and anxiety-like behaviors

Depression and anxiety are more common among females than males and represent a leading cause of disease-related disability in women. Since the dopamine D1-D2 heteromer is involved in depression- and anxiety-like behavior, the possibility that the receptor complex may have a role in mediating sex differences in such behaviors and related biochemical signaling was explored.

In non-human primate caudate nucleus and in rat striatum, females expressed higher density of D1-D2 heteromer complexes and a greater number of D1-D2 expressing neurons compared to males. In rat, the sex difference in D1-D2 expression levels occurred even though D1 receptor expression was lower in female than in male with no difference in D2 receptor expression. In behavioral tests, female rats showed faster latency to depressive-like behavior and a greater susceptibility to the pro-depressive and anxiogenic-like effects of D1-D2 heteromer activation by low doses of SKF 83959, all of which were ameliorated by the selective heteromer disrupting peptide, TAT-D1. The sex difference observed in the anxiety test correlated with differences in low-frequency delta and theta oscillations in the nucleus accumbens. Analysis of signaling pathways revealed that the sex difference in D1-D2 heteromer expression led to differences in basal and heteromer-stimulated activities of two important signaling pathways, BDNF/TrkB and Akt/GSK3/β-catenin.

These results suggest that the higher D1-D2 heteromer expression in female may significantly increase predisposition to depressive-like and anxiety-like behavior in female animals.

Asenapine maleate normalizes low frequency oscillatory deficits in a neurodevelopmental model of schizophrenia

Asenapine maleate (AM) is an atypical antipsychotic that, unlike many other antipsychotics, shows some efficacy in treating cognitive dysfunction in schizophrenia. Normal cognitive function has long since been associated with high frequency neuronal oscillations. However, recent research has highlighted the potential importance of low frequency oscillations. Here, the impact of AM on low frequency neural oscillatory activity was evaluated in the methylazoxymethanol acetate (MAM) rat model system used for the study schizophrenia, and the oscillatory signatures compared to those of haloperidol (HAL) and clozapine (CLZ). AM and CLZ normalized low frequency spectral power deficits in the prefrontal cortex, while HAL and AM reversed corticostriatal and corticocortical delta coherence deficits. However, only chronic AM administration normalized corticostriatal and corticocortical delta coherence deficits between 3-4 Hz. These findings support the idea that antipsychotic-induced amelioration of both delta coherence and power may be important for therapeutic efficacy in treating the cognitive deficits inherent in schizophrenia.

Hormonal regulation of circuit function: sex, systems and depression

Major depressive disorder (MDD) is a debilitating chronic illness that is two times more prevalent in women than in men. The mechanisms associated with the increased female susceptibility to depression remain poorly characterized. Aberrant neuronal oscillatory activity within the putative depression network is an emerging mechanism underlying MDD. However, innate sex differences in network activity and its contribution to depression vulnerability have not been well described. In this review, current evidence of sex differences in neuronal oscillatory activity, including the influence of sex hormones and female cycling, will first be described followed by evidence of disrupted neuronal circuit function in MDD and the effects of antidepressant treatment. Lastly, current knowledge of sex differences in MDD-associated aberrant circuit function and oscillatory activity will be highlighted, with an emphasis on the role of sex steroids and female cycling. Collectively, it is clear that there are significant gaps in the literature regarding innate and pathologically associated sex differences in network activity and that the elucidation of these differences is invaluable to our understanding of sex-specific vulnerabilities and therapies for MDD.

Pathogenic Feed-Forward Mechanisms in Alzheimer's and Parkinson's Disease Converge on GSK-3

Alzheimer's disease (AD) and Parkinson's disease (PD) share many commonalities ranging from signaling deficits such as altered cholinergic activity, neurotrophin and insulin signaling to cell stress cascades that result in proteinopathy, mitochondrial dysfunction and neuronal cell death. These pathological processes are not unidirectional, but are intertwined, resulting in a series of feed-forward loops that worsen symptoms and advance disease progression. At the center of these loops is glycogen synthase kinase-3 (GSK-3), a keystone protein involved in many of the multidirectional biological processes that contribute to AD and PD neuropathology. Here, a unified overview of the involvement of GSK-3 in the major processes involved in these diseases will be presented. The mechanisms by which these processes are linked will be discussed and the feed-forward pathways identified. In this regard, this review will put forth the notion that combination therapy, targeting these multiple facets of AD or PD neuropathology is a necessary next step in the search for effective therapies.

Disparate Effects of Lithium and a GSK-3 Inhibitor on Neuronal Oscillatory Activity in Prefrontal Cortex and Hippocampus

Glycogen synthase kinase-3 (GSK-3) plays a critical role in cognitive dysfunction associated with Alzheimer’s disease (AD), yet the mechanism by which GSK-3 alters cognitive processes in other disorders, such as schizophrenia, remains unknown. In the present study, we demonstrated a role for GSK-3 in the direct regulation of neuronal oscillations in hippocampus (HIP) and prelimbic cortex (PL). A comparison of the GSK-3 inhibitors SB 216763 and lithium demonstrated disparate effects of the drugs on spatial memory and neural oscillatory activity in HIP and PL. SB 216763 administration improved spatial memory whereas lithium treatment had no effect. Analysis of neuronal local field potentials in anesthetized animals revealed that whereas both repeated SB 216763 (2.5 mg/kg) and lithium (100 mg/kg) induced a theta frequency spike in HIP at approximately 10 Hz, only SB 216763 treatment induced an overall increase in theta power (4–12 Hz) compared to vehicle. Acute administration of either drug suppressed slow (32–59 Hz) and fast (61–100 Hz) gamma power. In PL, both drugs induced an increase in theta power. Repeated SB 216763 increased HIP–PL coherence across all frequencies except delta, whereas lithium selectively suppressed delta coherence. These findings demonstrate that GSK-3 plays a direct role in the regulation of theta oscillations in regions critically involved in cognition, and highlight a potential mechanism by which GSK-3 may contribute to cognitive decline in disorders of cognitive dysfunction.

Activation of Dopamine D1-D2 Receptor Complex Attenuates Cocaine Reward and Reinstatement of Cocaine-Seeking through Inhibition of DARPP-32, ERK, and ΔFosB

A significant subpopulation of neurons in rat nucleus accumbens (NAc) coexpress dopamine D1 and D2 receptors, which can form a D1-D2 receptor complex, but their relevance in addiction is not known. The existence of the D1-D2 heteromer in the striatum of rat and monkey was established using in situ PLA, in situ FRET and co-immunoprecipitation. In rat, D1-D2 receptor heteromer activation led to place aversion and abolished cocaine CPP and locomotor sensitization, cocaine intravenous self-administration and reinstatement of cocaine seeking, as well as inhibited sucrose preference and abolished the motivation to seek palatable food. Selective disruption of this heteromer by a specific interfering peptide induced reward-like effects and enhanced the above cocaine-induced effects, including at a subthreshold dose of cocaine. The D1-D2 heteromer activated Cdk5/Thr75-DARPP-32 and attenuated cocaine-induced pERK and ΔFosB accumulation, together with inhibition of cocaine-enhanced local field potentials in NAc, blocking thus the signaling pathway activated by cocaine: D1R/cAMP/PKA/Thr34-DARPP-32/pERK with ΔFosB accumulation. In conclusion, our results show that the D1-D2 heteromer exerted tonic inhibitory control of basal natural and cocaine reward, and therefore initiates a fundamental physiologic function that limits the liability to develop cocaine addiction.

The atypical dopamine receptor agonist SKF 83959 enhances hippocampal and prefrontal cortical neuronal network activity in a rat model of cognitive dysfunction

Deficits in neuronal network synchrony in hippocampus and prefrontal cortex have been widely demonstrated in disorders of cognitive dysfunction, including schizophrenia and Alzheimer's disease. The atypical dopamine agonist SKF 83959 has been shown to increase brain-derived neurotrophic factor signalling and suppress activity of glycogen synthase kinase-3 in PFC, two processes important to learning and memory. The purpose of this study was to therefore evaluate the impact of SKF 83959 on oscillatory deficits in methylazoxymethanol acetate (MAM) rat model of schizophrenia. To achieve this, local field potentials were recorded simultaneously from the hippocampus and prefrontal cortex of anesthetized rats at 15 and 90 min following both acute and repeated administration of SKF 83959 (0.4 mg/kg). In MAM rats, but not controls, repeated SKF 83959 treatment increased signal amplitude in hippocampus and enhanced the spectral power of low frequency delta and theta oscillations in this region. In PFC, SKF 83959 increased delta, theta and gamma spectral power. Increased HIP-PFC theta coherence was also evident following acute and repeated SKF 83959. In apparent contradiction to these oscillatory effects, in MAM rats, SKF 83959 inhibited spatial learning and induced a significant increase in thigmotactic behaviour. These findings have uncovered a previously unknown role for SKF 83959 in the positive regulation of hippocampal-prefrontal cortical oscillatory network activity. As SKF 83959 is known to have affinity for a number of receptors, delineating the receptor mechanisms that mediate the positive drug effects on neuronal oscillations could have significant future implications in disorders associated with cognitive dysfunction.

Disruption of a dopamine receptor complex amplifies the actions of cocaine

Cocaine-induced increases in dopamine signaling in nucleus accumbens (NAc) play a significant role in cocaine seeking behavior. The majority of cocaine addiction research has focused on neuroanatomically segregated dopamine D1 and D2 receptor-expressing neurons, yet an involvement for those NAc neurons coexpressing D1 and D2 receptors in cocaine addiction has never been explored. In situ proximity ligation assay, confocal fluorescence resonance energy transfer and coimmunoprecipitation were used to show native D1 and D2 receptors formed a heteromeric complex in D1/D2 receptor-coexpressing neurons in rat and non-human primate NAc. D1-D2 heteromer expression was lower in NAc of adolescent rats compared to their adult counterparts. Functional disruption of the dopamine D1-D2 receptor heteromer, using a peptide targeting the site of interaction between the D1 and D2 receptor, induced conditioned place preference and increased NAc expression of ∆FosB. D1-D2 heteromer disruption also resulted in the promotion, exacerbation and acceleration of the locomotor activating and incentive motivational effects of cocaine in the self-administration paradigm. These findings support a model for tonic inhibition of basal and cocaine-induced reward processes by the D1-D2 heteromer thus highlighting its potential value as a novel target for drug discovery in cocaine addiction. Given that adolescents show increased drug abuse susceptibility, an involvement for reduced D1-D2 heteromer function in the heightened sensitivity to the rewarding effects of cocaine in adolescence is also implicated.

Rapid anti-depressant and anxiolytic actions following dopamine D1-D2 receptor heteromer inactivation

A role for the mesolimbic dopaminergic system in the pathophysiology of depression has become increasingly evident. Specifically, brain-derived neurotrophic factor (BDNF) has been shown to be elevated in the nucleus accumbens of depressed patients and to positively contribute to depression-like behaviour in rodents. The dopamine D1-D2 receptor heteromer exhibits significant expression in NAc and has also been shown to enhance BDNF expression and signalling in this region. We therefore examined the effects of D1-D2 heteromer stimulation in rats by SKF 83959, or its inactivation by a selective heteromer-disrupting TAT-D1 peptide on depression- and anxiety-like behaviours in non-stressed animals and in animals exposed to chronic unpredictable stress. SKF 83959 treatment significantly enhanced the latency to immobility in the forced swim test, increased the latency to drink condensed milk and reduced total milk consumption in the novelty-induced hypophagia test, and additionally reduced the total time spent in the open arms in the elevated plus maze test. These pro-depressant and anxiogenic effects of SKF 83959 were consistently abolished or attenuated by TAT-D1 peptide pre-treatment, signifying the behaviours were mediated by the D1-D2 heteromer. More importantly, in animals exposed to chronic unpredictable stress (CUS), TAT-D1 peptide treatment alone induced significant and rapid anxiolytic and antidepressant-like effects in two tests for CUS-induced anhedonia-like reactivity and in the novelty-suppressed feeding test. Together these findings indicate a positive role for the D1-D2 heteromer in mediating depression- and anxiety-like behaviours and suggest its possible value as a novel therapeutic target.

The dopamine D1-D2 receptor heteromer exerts a tonic inhibitory effect on the expression of amphetamine-induced locomotor sensitization

A role for the dopamine D1-D2 receptor heteromer in the regulation of reward and addiction-related processes has been previously implicated. In the present study, we examined the effects of D1-D2 heteromer stimulation by the agonist SKF 83959 and its disruption by a selective TAT-D1 peptide on amphetamine-induced locomotor sensitization, a behavioral model widely used to study the neuroadaptations associated with psychostimulant addiction. D1-D2 heteromer activation by SKF 83959 did not alter the acute locomotor effects of amphetamine but significantly inhibited amphetamine-induced locomotor responding across the 5day treatment regimen. In addition, a single injection of SKF 83959 was sufficient to abolish the expression of locomotor sensitization induced by a priming injection of amphetamine after a 72-hour withdrawal. Conversely, inhibition of D1-D2 heteromer activity by the TAT-D1 peptide enhanced subchronic amphetamine-induced locomotion and the expression of amphetamine locomotor sensitization. Treatment solely with the TAT-D1 disrupting peptide during the initial 5day treatment phase was sufficient to induce a sensitized locomotor phenotype in response to the priming injection of amphetamine. Together these findings demonstrate that the dopamine D1-D2 receptor heteromer exerts a tonic inhibitory control on neurobiological processes involved in sensitization to amphetamine, indicating that the dopamine D1-D2 receptor heteromer may be a novel molecular substrate in addiction processes involving psychostimulants.

Regulation of c-fos expression by the dopamine D1-D2 receptor heteromer

The dopamine D1 and D2 receptors form the D1-D2 receptor heteromer in a subset of neurons and couple to the Gq protein to regulate intracellular calcium signaling. In the present study the effect of D1-D2 heteromer activation and disruption on neuronal activation in the rat brain was mapped. This was accomplished using the dopamine agonist SKF 83959 to activate the D1-D2 heteromer in combination with a TAT-D1 disrupting peptide we developed, and which has been shown to disrupt the D1/D2 receptor interaction and antagonize D1-D2 heteromer-induced cell signaling and behavior. Acute SKF 83959 administration to rats induced significant c-fos expression in the nucleus accumbens that was significantly inhibited by TAT-D1 pretreatment. No effects of SKF 83959 were seen in caudate putamen. D1-D2 heteromer disruption by TAT-D1 did not have any effects in any striatal subregions, but induced significant c-fos immunoreactivity in a number of cortical regions including the orbitofrontal cortex, prelimbic and infralimbic cortices and piriform cortex. The induction of c-fos by TAT-D1 was also evident in the anterior olfactory nucleus, as well as the lateral habenula and thalamic nuclei. These findings show for the first time that the D1-D2 heteromer can differentially regulate c-fos expression in a region-dependent manner either through its activation or through tonic inhibition of neuronal activity.

A peptide targeting an interaction interface disrupts the dopamine D1-D2 receptor heteromer to block signaling and function in vitro and in vivo: effective selective antagonism

Although the dopamine D1-D2 receptor heteromer has emerging physiological relevance and a postulated role in different neuropsychiatric disorders, such as drug addiction, depression, and schizophrenia, there is a need for pharmacological tools that selectively target such receptor complexes in order to analyze their biological and pathophysiological functions. Since no selective antagonists for the D1-D2 heteromer are available, serial deletions and point mutations were used to precisely identify the amino acids involved in an interaction interface between the receptors, residing within the carboxyl tail of the D1 receptor that interacted with the D2 receptor to form the D1-D2 receptor heteromer. It was determined that D1 receptor carboxyl tail residues (404)Glu and (405)Glu were critical in mediating the interaction with the D2 receptor. Isolated mutation of these residues in the D1 receptor resulted in the loss of agonist activation of the calcium signaling pathway mediated through the D1-D2 receptor heteromer. The physical interaction between the D1 and D2 receptor could be disrupted, as shown by coimmunoprecipitation and BRET analysis, by a small peptide generated from the D1 receptor sequence that contained these amino acids, leading to a switch in G-protein affinities and loss of calcium signaling, resulting in the inhibition of D1-D2 heteromer function. The use of the D1-D2 heteromer-disrupting peptide in vivo revealed a pathophysiological role for the D1-D2 heteromer in the modulation of behavioral despair. This peptide may represent a novel pharmacological tool with potential therapeutic benefits in depression treatment.

Enhanced brain-derived neurotrophic factor signaling in the nucleus accumbens of juvenile rats

Brain-derived neurotrophic factor (BDNF) signaling through its receptor, tropomyosin receptor kinase B (TrkB), plays a critical role in neural plasticity and its dysregulation in striatum and prefrontal cortex (PFC) has been implicated in the etiology of mental health disorders such schizophrenia and drug addiction. In the present study, we characterized age-dependent differences in BDNF signaling and TrkB expression within the nucleus accumbens (NAc), caudate putamen (CP) and PFC in rats and determined the effects of administration of the dopamine agonist, SKF 83959, which activates the Gq-coupled dopamine receptors, the dopamine D5 receptor and the D1-D2 receptor heteromer. As proBDNF binds with high affinity to the p75 neurotrophin receptor (p75NTR), expression levels of these proteins were also assessed. The present findings showed that juvenile rats (aged 26-28 days) exhibited significantly elevated basal BDNF expression and activation of full-length TrkB (TrkBfull) in NAc compared to their adult counterparts, as evidenced by increased TrkBfull phosphorylation. These changes were concomitant with an increase in the relative expression of TrkBfull compared to the truncated isoform, TrkB.T1, in NAc and CP. Conversely, in PFC the basal expression of BDNF in juvenile rats was significantly lower than in adult rats with an elevated relative expression of TrkBfull. Acute administration of SKF 83959 to juvenile rats abolished the age-dependent differences in BDNF expression in NAc and PFC, and in the relative expression of TrkBfull in NAc and CP. Together these findings indicate that the expression and/or signaling of BDNF and TrkB in striatum and PFC of juvenile rats is fundamentally different from that of adult rats, a finding that may have implications in neuropsychiatric disorders that exhibit age-dependent susceptibility such as schizophrenia and drug addiction.

Reduced striatal dopamine D1-D2 receptor heteromer expression and behavioural subsensitivity in juvenile rats

In adult rat striatum the dopamine D1-D2 receptor heteromer is expressed selectively in a subset of medium spiny neurons (MSNs) that coexpress the dopamine D1 and D2 receptors (D1R and D2R) as well as dynorphin (DYN) and enkephalin (ENK), with higher coexpression in nucleus accumbens (NAc) and much lower in the caudate putamen (CP). In the present study we showed that in neonatal striatal cultured neurons >90% exhibited the D1R/D2R-DYN/ENK phenotype. Similarly, in the striatum of juvenile rats (age 26-28 days) coexpression of D1R and D2R was also coincident with the expression of both DYN and ENK. Quantification of the number of striatal MSNs exhibiting coexpression of D1R and D2R in juvenile rats revealed significantly lower coexpression in NAc shell, but not core, and CP than in adult rats. However, within MSNs that coexpressed D1R and D2R, the propensity to form the D1-D2 receptor heteromer did not differ between age groups. Consistent with reduced coexpression of the D1R and D2R, juvenile rats exhibited subsensitivity to D1-D2 receptor heteromer-induced grooming following activation by SKF 83959. Given the proposed role of D1R/D2R-coexpressing MSNs in the regulation of thalamic output, and the recent discovery that these MSNs exhibit both inhibitory and excitatory capabilities, these findings suggest that the functional regulation of neurotransmission by the dopamine D1-D2 receptor heteromer within the juvenile striatum may be significantly different than in the adult.

The dopamine d1-d2 receptor heteromer in striatal medium spiny neurons: evidence for a third distinct neuronal pathway in Basal Ganglia

Dopaminergic signaling within the basal ganglia has classically been thought to occur within two distinct neuronal pathways; the direct striatonigral pathway which contains the dopamine D1 receptor and the neuropeptides dynorphin (DYN) and substance P, and the indirect striatopallidal pathway which expresses the dopamine D2 receptor and enkephalin (ENK). A number of studies have also shown, however, that D1 and D2 receptors can co-exist within the same medium spiny neuron and emerging evidence indicates that these D1/D2-coexpressing neurons, which also express DYN and ENK, may comprise a third neuronal pathway, with representation in both the striatonigral and striatopallidal projections of the basal ganglia. Furthermore, within these coexpressing neurons it has been shown that the dopamine D1 and D2 receptor can form a novel and pharmacologically distinct receptor complex, the dopamine D1–D2 receptor heteromer, with unique signaling properties. This is indicative of a functionally unique role for these neurons in brain. The aim of this review is to discuss the evidence in support of a novel third pathway coexpressing the D1 and D2 receptor, to discuss the potential relevance of this pathway to basal ganglia signaling, and to address its potential value, and that of the dopamine D1–D2 receptor heteromer, in the search for new therapeutic strategies for disorders involving dopamine neurotransmission.

Dopamine receptor homooligomers and heterooligomers in schizophrenia

Over the past two decades the dopamine D2 receptor has been undoubtedly the most widely studied dopamine receptor for the therapeutic treatment of schizophrenia, as the majority of antipsychotics exhibit antagonism at this receptor. However, the cognitive symptoms of the disorder are mostly resistant to the majority of available antipsychotic treatments and, as a result, there is a critical need to develop novel therapies that ameliorate all symptoms. The recognition that dopamine receptors, such as all G protein-coupled receptors (GPCRs), exist as oligomeric complexes has provided new avenues for drug design in the search for novel therapies. Furthermore, that it is now known that dopamine receptors can form heteromers, such as the dopamine D1-D2 receptor heteromer, with pharmacology and function distinct from its constituent receptors, has significantly expanded the range of potential drug targets. The aim of this review is to discuss the therapeutic relevance of these dopamine receptor oligomers to schizophrenia and to address the potential value of dopamine receptor heteromers in the search for new therapeutic strategies.

The dopamine D1-D2 receptor heteromer localizes in dynorphin/enkephalin neurons: increased high affinity state following amphetamine and in schizophrenia

The distribution and function of neurons coexpressing the dopamine D1 and D2 receptors in the basal ganglia and mesolimbic system are unknown. We found a subset of medium spiny neurons coexpressing D1 and D2 receptors in varying densities throughout the basal ganglia, with the highest incidence in nucleus accumbens and globus pallidus and the lowest incidence in caudate putamen. These receptors formed D1-D2 receptor heteromers that were localized to cell bodies and presynaptic terminals. In rats, selective activation of D1-D2 heteromers increased grooming behavior and attenuated AMPA receptor GluR1 phosphorylation by calcium/calmodulin kinase IIα in nucleus accumbens, implying a role in reward pathways. D1-D2 heteromer sensitivity and functional activity was up-regulated in rat striatum by chronic amphetamine treatment and in globus pallidus from schizophrenia patients, indicating that the dopamine D1-D2 heteromer may contribute to psychopathologies of drug abuse, schizophrenia, or other disorders involving elevated dopamine transmission.

Cotreatment with the kappa opioid agonist U69593 enhances locomotor sensitization to the D2/D3 dopamine agonist quinpirole and alters dopamine D2 receptor and prodynorphin mRNA expression in rats

RATIONALE

The repeated coadministration of the kappa opioid receptor agonist U69593 with the D2/D3 dopamine (DA) agonist quinpirole (QNP) potentiates locomotor sensitization induced by QNP. Behavioral evidence has implicated both pre- and postsynaptic changes as being involved in this augmentation.

OBJECTIVES

The objectives of this study were to obtain supporting molecular evidence of pre- and/or postsynaptic alterations in the DA system with U69593/QNP cotreatment and to examine the relationship of such changes to locomotor sensitization.

MATERIALS AND METHODS

Gene expression of D1 and D2 receptors (D1R and D2R), the DA transporter, as well as the endogenous opioid prodynorphin (DYN), in the basal ganglia was examined by in situ hybridization in rats after one or ten drug injections.

RESULTS

After one injection, changes that were specific to U69593/QNP cotreatment were decreased D1R and D2R messenger RNA (mRNA) in the nucleus accumbens (Acb) shell and increased DYN mRNA in the dorsal striatum (STR). After ten injections, U69593/QNP-specific changes were decreased D2R mRNA in substantia nigra (SN) and increased DYN mRNA in STR and Acb core. Only in U69593/QNP rats was the sensitized locomotor performance on injection ten positively correlated with DYN mRNA levels in Acb and STR.

CONCLUSIONS

Distinct alterations of D2R and DYN mRNA levels in SN and Acb/STR, respectively, strengthen the evidence implicating pre- and postsynaptic changes in augmented locomotor sensitization to U69593/QNP cotreatment. It is suggested that repeated U69593/QNP cotreatment may augment locomotor sensitization to QNP by activating D1R-expressing DYN neurons and attenuating presynaptic D2R function.

Kappa-opioid receptor stimulation quickens pathogenesis of compulsive checking in the quinpirole sensitization model of obsessive-compulsive disorder (OCD)

Repeated injections of the D2/D3 dopamine agonist, quinpirole, induce locomotor sensitization and compulsive checking behavior in rats, a phenomenon that may constitute an animal model of obsessive- compulsive disorder (OCD). Considering that the co-joint treatment with quinpirole and the kappa opioid receptor agonist U69593 potentiates locomotor sensitization to quinpirole, the present study examined whether such co-stimulation of kappa and dopamine receptors also enhances compulsive checking and whether dopamine receptor supersensitivity mediates the augmentation effects. Results showed that co-treatment of quinpirole and U69593 had a robust accelerating effect on the acquisition of sensitized locomotion and compulsive checking but that the effects on the expression of quinpirole sensitization were behavior dependent, with increased magnitude of locomotion but not of compulsive checking. Quinpirole and even U69593, which by itself did not induce sensitization, increased the proportion of dopamine D2 receptors in the high-affinity state (D2(High)) in the nucleus accumbens and striatum, indicating that elevation of D2(High) is not sufficient to account for sensitization or compulsive checking. The animal model findings point to a potential role of kappa opioid systems in hastening the pathogenesis of OCD and to the possibility that distinct brain regions may mediate the development and the expression of compulsive checking.

Kappa-opioid agonist U69593 potentiates locomotor sensitization to the D2/D3 agonist quinpirole: pre- and postsynaptic mechanisms

To assess whether the development and expression of behavioral sensitization to the dopamine D2/D3 agonist quinpirole (QNP) is influenced by coadministration of the kappa opioid receptor agonist U69593, rats received every 3-4 days for a total of 10 treatments an injection of U69593 (0.3 mg/kg) together with an injection of either a postsynaptic (0.5 mg/kg) or a presynaptic dose of QNP (0.05 mg/kg); locomotor activity was measured after each treatment. Control rats were injected as appropriate with QNP, U69593, and vehicle/saline. Following chronic treatment, dose-response profiles to QNP were obtained to assess the expression of sensitization; the effect of U69593 on locomotor activity in animals already sensitized to QNP was also assessed. Results showed that cotreatment of U69593 with a postsynaptic dose of QNP doubled the speed and magnitude of sensitization to QNP, while U69593 cotreatment with a presynaptic dose of QNP switched the effects of QNP from locomotor depression to locomotor sensitization. However, U69593 cotreatment with a presynaptic dose of QNP changed a different set of measures of sensitization than did cotreatment with a postsynaptic dose of the dopamine agonist. Together, findings suggest that sensitization to QNP is not a unitary phenomenon but has components that are relatively independent, mediated by distinct pre- and postsynaptic mechanisms and modulated by kappa receptor activity.

Development and temporal organization of compulsive checking induced by repeated injections of the dopamine agonist quinpirole in an animal model of obsessive-compulsive disorder

Rats treated chronically with the dopamine D2/D3 receptor agonist quinpirole develop locomotor sensitization and exhibit compulsive checking of specific places in an open-field arena, a behavioral profile that may represent an animal model of obsessive-compulsive disorder. However, it is not known how compulsive checking develops across quinpirole injections nor whether checking behavior possesses a particular temporal structure. Male rats received quinpirole (0.5mg/kg, twice weekly x 10) or an equivalent regimen of saline and were placed in a large open field for 55 min where their behavior was digitally tracked for subsequent analysis of checking behavior using existing and newly developed computer software. Results showed that the measures of compulsive checking did not follow a singular profile across injections: some remained constant and others changed monotonically reaching their near-maximum levels after about 5-7 quinpirole injections. Moreover, results showed that checking behavior was organized into bouts of checking, with the number of bouts, as well as the rate of checking within a bout, increasing across injections to reach near maximal levels after about 5-7 administrations of quinpirole. Finally, quinpirole-treated rats showed a paucity of long inter-bout intervals. These results suggest that (a) compulsive checking emerges from the operation of at least two underlying processes: a regulated process and a process of sensitization that intensifies the performance of checking behavior; and (b) quinpirole treatment may attenuate a sense of satiety that could underlie the compulsive nature of checking. Finally, because key variables measured using the newly developed algorithms showed the expected profile, the present study provides validation for the use of this methodology for the analysis of checking behavior.

Dopamine supersensitivity correlates with D2High states, implying many paths to psychosis

Dopamine supersensitivity occurs in schizophrenia and other psychoses, and after hippocampal lesions, antipsychotics, ethanol, amphetamine, phencyclidine, gene knockouts of Dbh (dopamine beta-hydroxylase), Drd4 receptors, Gprk6 (G protein-coupled receptor kinase 6), Comt (catechol-O-methyltransferase), or Th-/-, DbhTh/+ (tyrosine hydroxylase), and in rats born by Cesarean-section. The functional state of D2, or the high-affinity state for dopamine (D2High), was measured in these supersensitive animal brain striata. Increased levels and higher proportions (40-900%) for D2High were found in all these tissues. If many types of brain impairment cause dopamine behavioral supersensitivity and a common increase in D2High states, it suggests that there are many pathways to psychosis, any one of which can be disrupted.

Thermoregulation of transgenic growth hormone mice

Transgenic growth hormone (TG) mice (Mus musculus L., 1758) obtain enhanced growth via compensatory feeding at intermediate sizes and via higher growth efficiency. The latter involves diverting resources from other functions such as locomotion and wakefulness. Thermogenesis is a major expense for small mammals, so we explored whether TG mice express a trade-off between growth and thermoregulation. TG mice are hypothermic and cannot maintain their body temperature under cold stress. TG mice showed initial enlargement of brown adipose tissue and subsequent age-related decreases not seen in controls. Some TG mice became torpid after fasting durations not known to affect other mice. On a high-calorie diet, TG mice had higher body temperatures even though controls did not. Our background strain developed obesity on a high-protein and high-fat diet, and on a diet supplemented with carbohydrates, whereas TG mice never developed obesity. White adipose tissue deposits of TG females were relatively larger, but those of TG males were relatively smaller, than those of controls fed standard food. We also found significant effects of the three experimental diets, as well as gender, age, body mass, ambient temperature, and behavioural activity, on rectal temperatures of TG mice and controls in a large breeding colony. Thermogenesis of TG mice fed standard food appears energetically constrained, likely contributing to enhanced growth efficiency.

Transgenic growth hormone mice exposed to lifetime constant illumination: gender-specific effects

Photoperiod affects most of the features altered in transgenic growth hormone (TG) mice, and laboratory rats and mice retain some sensitivity to photoperiod. We examined growth, feeding, longevity, and reproduction of TG mice and normal control mice (Mus musculus L., 1758) in 12 h light : 12 h dark (LD) and 24 h light (LL) photoperiods. Sexual dichotomy in growth and hepatic gene expression are considered to require gender-specific patterns of growth hormone secretion that are absent in TG mice. Regardless, in the LD photoperiod mature TG females were 82.8% (46.8 g) of the mass of TG males (56.5 g, p < 0.05), whereas control mice showed no size dichotomy (≈33 g). Mature masses of TG males and of control mice of either gender were unaffected by the LL photoperiod. TG females, however, reached a mature mass 92% (50.9 g) of that of mature TG males in the LL photoperiod, attenuating the sexual size dichotomy expressed in the LD photoperiod. Growth of females was slower than that of males, even in the control group. TG females in the LL photoperiod expressed faster growth, higher reproduction, and greater mean longevity than TG females in the LD photoperiod. Differences in age-related feeding associated with gender and photoperiod reflected differential growth rates. Females grew more slowly and ate more than males of similar age because they were smaller (i.e., had lower growth efficiencies). The LL photoperiod improved the energy balance of TG females. Possible mechanisms mediating such gender-specific effects are explored.