Targeted disruption of inducible nitric oxide synthase protects against obesity-linked insulin resistance in muscle

Inducible nitric oxide synthase (iNOS) is induced by inflammatory cytokines in skeletal muscle and fat. It has been proposed that chronic iNOS induction may cause muscle insulin resistance. Here we show that iNOS expression is increased in muscle and fat of genetic and dietary models of obesity. Moreover, mice in which the gene encoding iNOS was disrupted (Nos2-/- mice) are protected from high-fat-induced insulin resistance. Whereas both wild-type and Nos2-/- mice developed obesity on the high-fat diet, obese Nos2-/- mice exhibited improved glucose tolerance, normal insulin sensitivity in vivo and normal insulin-stimulated glucose uptake in muscles. iNOS induction in obese wild-type mice was associated with impairments in phosphatidylinositol 3-kinase and Akt activation by insulin in muscle. These defects were fully prevented in obese Nos2-/- mice. These findings provide genetic evidence that iNOS is involved in the development of muscle insulin resistance in diet-induced obesity.

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.

Psychosis pathways converge via D2high dopamine receptors

The objective of this review is to identify a target or biomarker of altered neurochemical sensitivity that is common to the many animal models of human psychoses associated with street drugs, brain injury, steroid use, birth injury, and gene alterations. Psychosis in humans can be caused by amphetamine, phencyclidine, steroids, ethanol, and brain lesions such as hippocampal, cortical, and entorhinal lesions. Strikingly, all of these drugs and lesions in rats lead to dopamine supersensitivity and increase the high-affinity states of dopamine D2 receptors, or D2High, by 200-400% in striata. Similar supersensitivity and D2High elevations occur in rats born by Caesarian section and in rats treated with corticosterone or antipsychotics such as reserpine, risperidone, haloperidol, olanzapine, quetiapine, and clozapine, with the latter two inducing elevated D2High states less than that caused by haloperidol or olanzapine. Mice born with gene knockouts of some possible schizophrenia susceptibility genes are dopamine supersensitive, and their striata reveal markedly elevated D2High states; suchgenes include dopamine-beta-hydroxylase, dopamine D4 receptors, G protein receptor kinase 6, tyrosine hydroxylase, catechol-O-methyltransferase, the trace amine-1 receptor, regulator of G protein signaling RGS9, and the RIIbeta form of cAMP-dependent protein kinase (PKA). Striata from mice that are not dopamine supersensitive did not reveal elevated D2High states; these include mice with knockouts of adenosine A2A receptors, glycogen synthase kinase GSK3beta, metabotropic glutamate receptor 5, dopamine D1 or D3 receptors, histamine H1, H2, or H3 receptors, and rats treated with ketanserin or aD1 antagonist. The evidence suggests that there are multiple pathways that convergetoelevate the D2High state in brain regions and that this elevation may elicit psychosis. This proposition is supported by the dopamine supersensitivity that is a common feature of schizophrenia and that also occurs in many types of genetically altered, drug-altered, and lesion-altered animals. Dopamine supersensitivity, in turn, correlates with D2High states. The finding that all antipsychotics, traditional and recent ones, act on D2High dopamine receptors further supports the proposition.

Activation of p38 mitogen-activated protein kinase alpha and beta by insulin and contraction in rat skeletal muscle: potential role in the stimulation of glucose transport

The stress-activated p38 mitogen-activated protein kinase (MAPK) was recently shown to be activated by insulin in muscle and adipose cells in culture. Here, we explore whether such stimulation is observed in rat skeletal muscle and whether muscle contraction can also affect the enzyme. Insulin injection (2 U over 3.5 min) resulted in increases in p38 MAPK phosphorylation measured in soleus (3.2-fold) and quadriceps (2.2-fold) muscles. Increased phosphorylation (3.5-fold) of an endogenous substrate of p38 MAPK, cAMP response element binder (CREB), was also observed. After in vivo insulin treatment, p38 MAPKalpha and p38 MAPKbeta isoforms were found to be activated (2.1- and 2.4-fold, respectively), using an in vitro kinase assay, in immunoprecipitates from quadriceps muscle extracts. In vitro insulin treatment (1 nmol/l over 4 min) and electrically-induced contraction of isolated extensor digitorum longus (EDL) muscle also doubled the kinase activity of p38 MAPKalpha and p38 MAPKbeta. The activity of both isoforms was inhibited in vitro by 10 micromol/l SB203580 in all muscles. To explore the possible participation of p38 MAPK in the stimulation of glucose uptake, EDL and soleus muscles were exposed to increasing doses of SB203580 before and during stimulation by insulin or contraction. SB203580 caused a significant reduction in the insulin- or contraction-stimulated 2-deoxyglucose uptake. Maximal inhibition (50-60%) occurred with 10 micromol/l SB203580. These results show that p38 MAPKalpha and -beta isoforms are activated by insulin and contraction in skeletal muscle. The data further suggest that activation of p38 MAPK may participate in the stimulation of glucose uptake by both stimuli in rat skeletal muscle.

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.

Insulin stimulation of glucose uptake in skeletal muscles and adipose tissues in vivo is NO dependent

The purpose of this study was to investigate whether in vivo nitric oxide synthase (NOS) inhibition influences insulin-mediated glucose disposal in rat peripheral tissues. The NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) or saline was infused constantly during a hyperinsulinemic-euglycemic clamp in normal rats. Glucose utilization rates of insulin-sensitive tissues (individual muscles, heart, and adipose tissues) were simultaneously determined using tracer infusion of 2-deoxy-D-[3H]glucose (2-[3H]DG). NOS blockade with L-NAME resulted in significant (P < 0.05) reduction in both whole body glucose disposal (-16%, P < 0.01) and plasma 2-[3H]DG disappearance rate (-30%, P < 0.05) during hyper-insulinemic-euglycemic clamp. L-NAME significantly decreased insulin-stimulated glucose uptake in heart (-62%, P = 0.01), soleus (-42%, P = 0.05), red (-53%, P < 0.001) and white (-62%, P < 0.001) gastrocnemius, tibialis (-57%, P < 0.01), and quadriceps (-33%, P < 0.05) muscles. The NOS inhibitor also decreased insulin action in brown interscapular (-47%, P < 0.01), retroperitoneal (-52%, P = 0.07), and gonadal (-66%, P = 0.06) adipose tissues. In contrast to in vivo NOS blockade, L-NAME failed to affect basal or insulin-stimulated 2-[3H]DG transport in isolated soleus or extensor digitorum longus muscles in vitro. These results support the hypothesis that the action of insulin to augment glucose uptake by skeletal muscles and other peripheral insulin-sensitive tissues in vivo is NO dependent.

Heteromeric dopamine receptor signaling complexes: emerging neurobiology and disease relevance

The pharmacological modification of dopamine transmission has long been employed as a therapeutic tool in the treatment of many mental health disorders. However, as many of the pharmacotherapies today are not without significant side effects, or they alleviate only a particular subset of symptoms, the identification of novel therapeutic targets is imperative. In light of these challenges, the recognition that dopamine receptors can form heteromers has significantly expanded the range of physiologically relevant signaling complexes as well as potential drug targets. Furthermore, as the physiology and disease relevance of these receptor heteromers is further understood, their ability to exhibit pharmacological and functional properties distinct from their constituent receptors, or modulate the function of endogenous homomeric receptor complexes, may allow for the development of alternate therapeutic strategies and provide new avenues for drug design. In this review, we describe the emerging neurobiology of the known dopamine receptor heteromers, their physiological relevance in brain, and discuss the potential role of these receptor complexes in neuropsychiatric disease. We highlight their value as targets for future drug development and discuss innovative research strategies designed to selectively target these dopamine receptor heteromers in the search for novel and clinically efficacious pharmacotherapies.

Resistance to the orexigenic effect of ghrelin in dietary-induced obesity in mice: reversal upon weight loss

BACKGROUND

Ghrelin, an endogenous ligand for growth hormone secretagogue receptor (GHS-R), is known to increase food intake in lean humans and rodents. In addition, ghrelin levels are increased by fasting in lean rodents and are elevated before meals in humans, suggesting an important role for ghrelin in meal initiation. However, in obese human, circulating ghrelin levels were found to be significantly reduced as compared to lean individuals.

OBJECTIVES

To evaluate whether circulating ghrelin levels, as well as ghrelin sensitivity, are decreased in obese individuals in order to limit its effect on food intake.

DESIGN

: Lean C57BL/6J mice fed a chow, a low- (LFD) or a high-fat diet (HFD) were used to determine ghrelin regulation and secretion as well as ghrelin sensitivity.

MEASUREMENTS

Plasma ghrelin levels were measured in low- and high-fat fed mice. Ghrelin-induced food intake was measured in chow, low- and high-fat fed mice.

RESULTS

We measured ghrelin levels in lean and diet-induced obese mice, fed on an LFD or an HFD, respectively. We observed that not only ghrelin secretion was reduced in obese mice but its diurnal regulation was also lost. In addition, we failed to observe any change in ghrelin secretion upon fasting and refeeding. Moreover, we observed that the sensitivity to the orexigenic effects of exogenous ghrelin was reduced in obese mice when compared to lean mice fed a chow or a LFD. The insensitivity of obese mice to ghrelin was improved upon weigh loss.

CONCLUSION

: Altogether, these results indicate that ghrelin secretion and regulation is impaired in dietary-induced obesity in mice and suggest that ghrelin inhibition could prevent weight regain after weight loss.

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.

Adaptation of parents in relation to their 6-month-old infant's type of disability

The adaptation of parents to a disabled infant was studied in relation to the type of disability presented by the baby. Participants were divided according to three types of disability and one control group: patents of infants with (1) Down's syndrome (DS), (2) congenital heart disease (CHD), (3) a cleft lip and/or palate (CLP), and (4) no disability (ND). The data were collected using a self-administered questionnaire given to each parent 6 months after the birth of their baby. The measures included parenting stress, stress appraisal, and psychological distress. Overall, the results indicate that parents of infants with DS and parents of infants with CHD report greater levels of parenting stress and psychological distress than parents of babies with CLP or non-disabled infants. Mothers were found to report greater levels of stress and distress overall, but differences across diagnostic groups were similar for mothers and fathers. The implications of the findings for theory and clinical intervention are discussed.

[Validation of an eating attitude scale in a French-speaking Quebec population]

The Eating Attitudes Test (EAT-26) is one of the most frequently used screening questionnaires for anorexia and bulimia nervosa for use with clinical and general populations. Although the psychometric qualities of the instrument have been reported for the English version, little has been done to date to validate a French version. A french version of the EAT-26 was distributed to anglophone students and francophone students, as well as anglophone and francophone patients. Overall, the results demonstrated that the authors' French version has the same psychometric characteristics as the English version when used with clinical and non clinical populations. The overall test and its subscales differentiated between patients and non patients similarly in both linguistic groups. The internal consistency of the two versions, as assessed by Cronbach's alpha, was comparable. Among female high-school students, 14.1% of the anglophone students and 14.3% of the francophone students scored above the cutoff score for significant eating disorders behaviour.

Longitudinal effects of an early family intervention programme on the adaptation of parents of children with a disability

This study assesses the longitudinal effects of an original early intervention programme on the adaptation of parents of children with a disability (Down syndrome and cleft lip/palate, i.e. DS and CLP). Variations in the effects of the programme according to the time of measurement, the type of disability and parent's gender are also examined. Globally, the results show a better adaptation among parents who participated in the intervention programme compared to those who did not participated in the programme. These parents had lower levels of parental stress, they had more positive perceptions and attitudes concerning their child's disability and their parental situation, they were more confident in their own resources and the help they could receive from others, they had lower levels of emotional distress, anxiety and depression and they perceived more emotional support from their spouse. In general, these gains were maintained throughout the year when the children were between six and 18 months of age, they were relatively similar for parents of children with DS and parents of children with CLP, as well as for mothers and fathers.

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.

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.

Profiling serum bile acid glucuronides in humans: gender divergences, genetic determinants, and response to fenofibrate

Glucuronidation, catalyzed by UDP-glucuronosyltransferase (UGT) enzymes detoxifies cholestatic bile acids (BAs). We aimed at i) characterizing the circulating BA-glucuronide (-G) pool composition in humans, ii) evaluating how sex and UGT polymorphisms influence this composition, and iii) analyzing the effects of lipid-lowering drug fenofibrate on the circulating BA-G profile in 300 volunteers and 5 cholestatic patients. Eleven BA-Gs were determined in pre- and post-fenofibrate samples. Men exhibited higher BA-G concentrations, and various genotype/BA-G associations were discovered in relevant UGT genes. The chenodeoxycholic acid-3G concentration was associated with the UGT2B7 802C>T polymorphism. Glucuronidation assays confirmed the predominant role of UGT2B7 and UGT1A4 in CDCA-3G formation. Fenofibrate exposure increased the serum levels of 5 BA-G species, including CDCA-3G, and up-regulated expression of UGT1A4, but not UGT2B7, in hepatic cells. This study demonstrates that fenofibrate stimulates BA glucuronidation in humans, and thus reduces bile acid toxicity in the liver.

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.

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.

Patients' requests and satisfaction with services in an outpatient psychiatric setting

OBJECTIVE

Patients in four major diagnostic categories were compared to determine if their satisfaction with outpatient services varied. Both overall satisfaction and the degree to which clients and therapists agreed on the importance of 16 aspects of treatment were examined.

METHODS

The Patient Request Form (PRF) and the Client Satisfaction Questionnaire were used to interview 464 outpatients. The professional who was the primary contact for each patient filled out a therapist version of the PRF. Diagnoses were grouped into four major categories: anxiety disorders, affective disorders, schizophrenia, and other psychotic disorders.

RESULTS

The diagnostic groups differed in overall satisfaction with treatment, treatment characteristics, patients' reasons for coming to the clinic, therapists' descriptions of treatment, and patient-therapist agreement on the importance of different aspects of treatment. Agreement between patients and providers was associated with higher levels of patients' satisfaction. Patients with schizophrenia or with other psychotic disorders had the lowest level of agreement with their therapists and also were the least satisfied. In all patient categories, therapists underestimated the importance to patients of having a reliable source of help.

CONCLUSIONS

The greater dissatisfaction expressed by patients with schizophrenia and other psychotic disorders may be related to their therapists' undervaluing the nonbiological aspects of treatment such as social support. Combining medication with psychosocial approaches that have been adapted for patients with psychotic disorders is likely to improve the patients' satisfaction and compliance and increase the overall effectiveness of treatment.

Nitric oxide: a new player in the modulation of energy metabolism

Nitric oxide (NO) is a key messenger molecule in several cell types. NO formation is catalyzed by a family of NO synthases (NOS) that use L-arginine as a substrate. Rat adipose tissue expresses the inducible, macrophage-type, nitric oxide (NO) synthase isoform (iNOS). Systemic administration of the bacterial endotoxin lipopolysaccharide (LPS) markedly increases the expression and activity of iNOS in both white and brown adipose tissues, as well as in skeletal muscle. iNOS induction can be reproduced in vitro by treatment of cultured white or brown adipocytes or L6 myocytes with LPS and inflammatory cytokines (TNFalpha, IFNgamma). The physiological role of NO in adipose tissues and skeletal muscle is still obscure. Recent evidence suggests that NO may be implicated in the regulation of energy metabolism. Using both pharmacological and genetic models of iNOS invalidation, we have recently begun to uncover a role for NO in the modulation of glucose transport and lipoprotein hydrolysis. These studies support the emerging concept that NO may fulfill the dual role of modulating energy metabolism in both physiological and pathological conditions as well as contributing to local immune defense during inflammatory processes.

Mechanism of impaired nitric oxide synthase activity in skeletal muscle of streptozotocin-induced diabetic rats

AIMS/HYPOTHESIS

The aims of our study were to investigate whether nitric oxide synthase (NOS) activity is impaired in skeletal muscle of insulin-deficient [Type I (insulin-dependent)] diabetic rats and if the case, to determine the mechanism of NOS dysregulation in this disorder.

METHODS

Rats were rendered diabetic by streptozotocin injection (65 mg/kg, i.v.) and NOS activity and expression in gastrocnemius muscles were studied 1, 2, 3 or 4 weeks after diabetes induction.

RESULTS

The diabetic state was associated with a progressive reduction (down to 42 % of control values after 4 weeks) in muscle NOS activity compared with control rats. Using reverse transcriptase-polymerase chain reaction, we could not detect statistically significant changes in the expression of either neuronal NOS (nNOS) or endothelial NOS (eNOS) mRNAs in diabetic muscle. The contents of nNOS and eNOS protein were, however, progressively reduced in muscle homogenates of diabetic rats and these alterations were prevented by insulin treatment. Subcellular fractionation of skeletal muscle showed that both nNOS and eNOS proteins are mainly localised to the plasma membrane with lower abundance in T-tubules and not detectable in sarcoplasmic reticulum-enriched fractions. After 1 week of diabetes, eNOS protein content was decreased only in the plasma membrane whereas nNOS protein abundance was not affected at this time. Neither the expression nor the interaction of caveolin-1 and caveolin-3 with NOS enzymes was found to be altered in muscle of diabetic rats.

CONCLUSION/INTERPRETATION

These results show that skeletal muscle NOS activity is impaired during the progression of insulin-deficient diabetes and reduced NOS activity is associated with a decreased abundance of both nNOS and eNOS proteins, which appears to involve post-transcriptional mechanisms.

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.

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.

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.

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.

Predictors of psychological distress in family caregivers of persons with psychiatric disabilities

The purpose of the study was to determine the relationships of primary and secondary stressors, and informal and formal supports, to psychological distress in 154 family caregivers of persons with psychiatric disabilities. All caregivers were members of self-help groups located in the Province of Quebec in Canada. Psychological distress was significantly lower among older caregivers, those working full time, and those experiencing lower objective and subjective burdens. Contrary to the hypotheses, caregivers who perceived more support from friends and had more contacts with their relatives' primary mental health providers experienced a higher level of psychological distress.