Involvement of endocannabinoids in antidepressant and anti-compulsive effect of fluoxetine in mice

Endocannabinoid analogues exhibit antidepressant and anti-compulsive like effects similar to that of serotonin selective reuptake inhibitors (SSRIs) indicating a parallelism between the effects of serotonin and endocannabinoids. Therefore, the present study was designed to investigate the role of endocannabinoids in the antidepressant and anti-compulsive like effect of fluoxetine using mice model of forced swim test (FST) and marble-burying behavior (MBB). The results revealed that intracerebroventricular injections of endocannabinoid analogues, anandamide, a CB₁ agonist (AEA: 1-20 μg/mouse); AM404, an anandamide transport inhibitor (0.1-10 μg/mouse); and URB597, a fatty acid amide hydrolase inhibitor (0.05-10 μg/mouse) produced antidepressant-like effect dose-dependently, whereas influenced the MBB in a biphasic manner (produced a U-shaped dose-response curve). Fluoxetine (2.5-20 mg/kg, i.p.) dose dependently decreased the immobility time as well as burying behavior. Co-administration of sub-effective dose of fluoxetine (2.5 mg/kg, i.p.) potentiated the effect of sub-effective dose of AEA (0.5 μg/mouse, i.c.v.), AM404 (0.05 μg/mouse, i.c.v) or URB597 (0.01 μg/mouse, i.c.v) in both the paradigms. Interestingly, pretreatment with AM251, a CB₁ antagonist, blocked the effect of fluoxetine in FST and MBB at a dose (1 μg/mouse, i.c.v) that per se had no effect on either parameter. Similar effects were obtained with endocannabinoid analogues in AM251 pretreated mice. However, AM251 increased the burying behavior in MBB at a highest dose tested (5 μg/mouse). None of the treatments had any influence on locomotor activity. Thus, the study indicates an interaction between endocannabinoid and serotonergic system in regulation of depressive and compulsive-like behavior.     

Antidepressant-like effect of the novel thiadiazolidinone NP031115 in mice

Glycogen synthase kinase-3beta (GSK-3beta) is an enzyme that phosphorylates glycogen synthase, thereby inhibiting glycogen synthesis. Besides this role, it is now believed that this enzyme plays an important role in the pathophysiology of many brain diseases including depression. Some inhibitors of this enzyme have shown antidepressant effects in animal models. This study investigated the effects of a novel thiadiazolidinone NP031115, a putative GSK-3beta inhibitor, and the well-established GSK-3beta inhibitor AR-A014418 in the mouse forced swimming test (FST), a model widely used to evaluate antidepressant activity. We found that NP031115 had an IC50 of 1.23 and 6.5 microM for GSK-3beta and GSK-3alpha, respectively. NP031115 (0.5 and 5 mg/kg, i.p.), in a way similar to imipramine (15 mg/kg, i.p), fluoxetine (32 mg/kg, i.p), AR-A014418 (9 mg/kg, i.p.), and rosiglitazone (5 microg/site, i.c.v.), significantly reduced immobility time in the FST. NP031115 at the higher dose and AR-A014418 (9 mg/kg, i.p.) reduced locomotion in the open-field test. Rosiglitazone (30 microM), AR-A014418 (1 microM), PG(J2) (10 microM), and NP031115 (1, 10 and 25 microM) activate PPARgamma in CHO transfected cells. GW-9662 (10 microg/site, i.c.v, a PPARgamma antagonist) administered 15 min before NP03115 (5 mg/kg, i.p.) or co-administered with rosiglitazone (5 microg/site, i.c.v.) prevented the antidepressant-like effect of these drugs in the FST. The results of this study show that NP031115 can exhibit an antidepressant effect, likely by inhibiting GSK-3beta and enhancing PPARgamma activity.     

Somato-dendritic distribution of 5-HT(1A) and 5-HT(1B) autoreceptors in the BDNF- and cAMP-differentiated RN46A serotoninergic raphe cell line

The rapid differentiating effects of brain-derived neurotrophic factor (BDNF) or dibutyryl-cAMP (dBcAMP) were characterized on RN46A, a rat raphe-derived neuronal cell line. After BDNF treatment, RN46A cells were serotonin-immunopositive and bipolar, and expressed the microtubule-associated-protein 2 (Map2). After dBcAMP treatment, the cells often became multipolar, bearing very long processes strongly immunopositive for serotonin and Map2. Under both conditions, the expression and distribution of 5-HT(1A) and 5-HT(1B) autoreceptors remained identical. 5-HT(1A) and Map2 immunolabelings were superimposable, as expected of their somato-dendritic targeting. Surprisingly, the distribution of 5-HT(1B) immunoreactivity was similar, in contrast with its usual localization in axons and nerve terminals in the brain. In conclusion, both BDNF and cAMP-differentiated RN46A cells towards a neuronal serotoninergic-like phenotype without the typical differential targeting of the 5-HT(1) autoreceptors, an interesting model to study the molecular mechanisms ensuing the targeting of 5-HT(1) autoreceptors to somas and dendrites.     

Antidepressant-like action of the ethanolic extract from Tabebuia avellanedae in mice: Evidence for the involvement of the monoaminergic system

The antidepressant-like effect of the ethanolic extract obtained from barks of Tabebuia avellanedae, a plant widely employed in folk medicine, was investigated in two predictive models of depression: forced swimming test (FST) and tail suspension test (TST) in mice. Additionally, the mechanisms involved in this antidepressant-like action and the effects of the association of the extract with the antidepressants fluoxetine, desipramine and bupropion in the TST were investigated. The extract from T. avellanedae produced an antidepressant-like effect, in the FST (100 mg/kg, p.o.) and in the TST (10–300 mg/kg, p.o.), without accompanying changes in ambulation when assessed in the open-field test. The anti-immobility effect of the extract (30 mg/kg, p.o.) in the TST was prevented by pre-treatment of mice with ketanserin (5 mg/kg, i.p., a preferential 5-HT_2A receptor antagonist), prazosin (1 mg/kg, i.p., an α₁-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α₂-adrenoceptor antagonist), propranolol (2 mg/kg, i.p., a β-adrenoceptor antagonist), sulpiride (50 mg/kg, i.p., a dopamine D₂ receptor antagonist) and SCH23390 (0.05 mg/kg, s.c., a dopamine D₁ receptor antagonist). The combined administration of a subeffective dose of WAY100635 (0.1 mg/kg, s.c., a selective 5-HT_1A receptor antagonist) and a subeffective dose of the extract (1 mg/kg, p.o.) produced a significant reduction in the immobility time in the TST. In addition, the combination of fluoxetine (1 mg/kg, p.o.), desipramine (0.1 mg/kg, p.o.), or bupropion (1 mg/kg, p.o.) with a subeffective dose of the extract (1 mg/kg, p.o.) produced a synergistic antidepressant-like effect in the TST, without causing hyperlocomotion in the open-field test. It may be concluded that the extract from T. avellanedae produces an antidepressant-like effect in the FST and in the TST that is dependent on the monoaminergic system. Taken together, our results suggest that T. avellanedae deserves further investigation as a putative alternative therapeutic tool that could help the conventional pharmacotherapy of depression.     

I(4), a new synthetic sulfonylurea compound, inhibits the action of TXA(2)in vivo and in vitro on platelets and aorta vascular smooth muscle

Introduction

1-[4-[2-(4-Bromobenzene-sulfonamino)ethyl]phenylsulfonyl]-3-(trans-4-methylcy-clohexyl)urea(I₄, CAS865483-06-3); a totally synthetic new sulfonylurea compound, combining the hypoglycemic active structure of Glimepiride (CAS 93479-97-1) and anti-TXA₂ receptor (TP) active structure of BM-531(CAS 284464-46-6), was designed and synthesized. Its effects on TXA₂ synthesis and TP have not been reported yet.

Aim

To study the inhibitory effects of I₄ and its mechanisms of action on TXA₂ and TP.

Methods

Platelet aggregation studies were performed on human platelet, rat whole blood platelet and rabbit platelet, platelets aggregation was induced by TP agonist U-46619(stable analog of TXA₂, CAS 56985-40-1). Plasma TXB₂ and 6-keto-prostaglandin F_1α (6-keto-PGF_1α) were used as markers to determine the effect of I₄ on thromboxane synthesis. Fluo-3-AM was used to measure the cytosolic Ca^2 + concentrations ([Ca^2 +]_i) in rabbit platelet. Aorta rings with and without endothelium were prepared and aorta contraction was induced by U-46619. A model of type 2 diabetes mellitus was established by intraperitoneal injection of low dose of streptozocin to rats fed a high-calorie diet. Both normal rats and type 2 diabetic rats were used to assay the inhibitory effect of I₄ on platelet aggregation induced by U-46619.

Results

I₄ exhibited a higher inhibitory potency than Glimepiride on U-46619 induced platelet aggregation in vitro and in vivo. I₄ increased the ratio of plasma PGI₂/TXA₂ and decreased [Ca^2 +]_i release from platelet internal stores. In addition, I₄ presented a vasorelaxant activity on isolated rat aorta contraction induced by U-46619.Oral administration of I₄ (1 ~ 10 mg/kg) markedly and dose-dependently inhibited platelet aggregation in both normal rats and type 2 diabetic rats.

Conclusion

I₄ significantly inhibited platelet aggregation induced by U-46619 in vitro and in vivo, and rat aorta contraction. It probably acts by partly blocking TXA₂ action, decreasing the platelet intracellular Ca^2 +, and increasing the PGI₂/TXA₂ ratio.     

Effects of additional treatment of sarpogrelate to aspirin therapy on platelet aggregation and plasma plasminogen activator inhibitor activity in patients with stable effort angina

Introduction

Serotonin is secreted from platelets at sites of endothelial injury, where it promotes thrombogenic reactions. Serotonin is reported to be associated with not only coronary artery disease but also cardiac events.

Materials and Methods

We studied 33 patients with stable effort angina (SEA) (11 patients with multivessel disease (MVD) and 22 patients with singlevessel disease (SVD)) and 25 patients with chest pain syndrome (CPS). Sarpogrelate was administered to 22 of 33 patients with SEA in addition to aspirin therapy, and platelet aggregation, plasma serotonin concentration, and plasma plasminogen activator inhibitor (PAI) activity were measured before and 1 week after administration.

Results and Conclusions

Serotonin level was higher in patients with MVD than in those with SVD (p < 0.05) and in those with CPS (p < 0.001). The formation of small-sized platelet aggregates was significantly higher in the high serotonin group than in the low serotonin group of SEA patients. The formation of large-sized platelet aggregates was significantly decreased by administration of sarpogrelate (P < 0.05). The formation of small- or medium-sized aggregates was not significantly decreased. Plasma PAI activity decreased significantly (P < 0.05) although the plasma serotonin concentration did not show significant change by administration of sarpogrelate. Plasma serotonin level is increased in relation to severity of coronary artery disease and plasma serotonin level is associated with increased platelet aggregation. Administration of sarpogrelate in addition to aspirin therapy reduces the increased platelet aggregation and PAI activity, and it may indicate that additional administration of sarpogrelate is useful for patients with SEA.     

AMPA receptor involvement in 5-hydroxytryptamine2A receptor-mediated pre-frontal cortical excitatory synaptic currents and DOI-induced head shakes

Glutamate plays an important role in the psychotomimetic effects of both channel blocking N-methyl D-aspartate (NMDA) receptor antagonists and hallucinogenic drugs which activate 5-hydroxytryptamine2A (5-HT2A) receptors. Previous work suggested that activation of non-NMDA ionotropic glutamate receptors mediates the effects of 5-HT-induced excitatory post-synaptic potentials/currents (EPSPs/EPSCs) when recording from layer V pyramidal cells in the rat medial pre-frontal cortex (mPFC). However, those effects are mediated by either alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) or kainate receptors of the iGluk5 subtype. To test whether activation of AMPA receptors is sufficient to mediate 5-HT-induced EPSCs, a 2,3-benzodiazepine that selectively blocks AMPA receptors was assessed. This selective AMPA receptor antagonist potently suppressed 5-HT-induced EPSCs. Since phenethylamine hallucinogens induce head shakes by activating 5-HT2A receptors in the mPFC and this action is modulated by glutamate, we also examined whether selective blockade of AMPA receptors would suppress DOI-induced head shakes. As predicted, we found that selective blockade of AMPA receptors suppressed DOI-induced head shakes. Given evidence that activation of AMPA receptors is an important downstream effect for both channel blocking NMDA receptor antagonists and phenethylamine hallucinogens, we also tested multiple doses of DOI with a sub-anesthetic dose of MK-801. Synergistic action between these two classes of psychotomimetic drugs was demonstrated by MK-801 enhancing DOI-induced head shakes and locomotor activity. These findings expand the dependence of both channel blocking NMDA receptor antagonists and phenethylamine hallucinogens on enhancing extracellular glutamate.     

The role of glutamate on the action of antidepressants

Major depressive disorder (MDD) is a common, chronic, recurrent mental illness that affects millions of individuals worldwide. Currently available antidepressants are known to affect the monoaminergic (e.g., serotonin, norepinephrine, and dopamine) systems in the brain. Accumulating evidence suggests that the glutamatergic neurotransmission via the excitatory amino acid glutamate also plays an important role in the neurobiology and treatment of this disease. Clinical studies have demonstrated that the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist ketamine has rapid antidepressant effects in treatment-resistant patients with MDD, suggesting the role of glutamate in the pathophysiology of treatment-resistant MDD. Furthermore, a number of preclinical studies demonstrated that the agents which act at glutamate receptors such as NMDA receptors, α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors and metabotropic glutamate receptors (mGluRs) might have antidepressant-like activities in animal models of depression. In this article, the author reviews the role of glutamate in the neuron-glia communication induced by potential antidepressants.     

Developments in harmine pharmacology — Implications for ayahuasca use and drug-dependence treatment

Ayahuasca is a hallucinogenic botanical mixture originating in the Amazon area where it is used ritually, but is now being taken globally. The 2 main constituents of ayahuasca are N,N-dimethyltryptamine (DMT), a hallucinogen, and harmine, a monoamine oxidase inhibitor (MAOI) which attenuates the breakdown of DMT, which would otherwise be broken down very quickly after oral consumption. Recent developments in ayahuasca use include the sale of these compounds on the internet and the substitution of related botanical (anahuasca) or synthetic (pharmahuasca) compounds to achieve the same desired hallucinogenic effects. One intriguing result of ayahuasca use appears to be improved mental health and a reduction in recidivism to alternate (alcohol, cocaine) drug use. In this review we discuss the pharmacology of ayahuasca, with a focus on harmine, and suggest pharmacological mechanisms for the putative reduction in recidivism to alcohol and cocaine misuse. These pharmacological mechanisms include MAOI, effects at 5-HT_2A and imidazoline receptors and inhibition of dual-specificity tyrosine-phosphorylation regulated kinase 1A (DYRK1A) and the dopamine transporter. We also speculate on the therapeutic potential of harmine in other CNS conditions.     

Decreased kainate receptors in the hippocampus of apolipoprotein D knockout mice

Apolipoprotein D (ApoD) has many actions critical to maintaining mammalian CNS function. It is therefore significant that levels of ApoD have been shown to be altered in the CNS of subjects with schizophrenia, suggesting a role for ApoD in the pathophysiology of the disorder. There is also a large body of evidence that cortical and hippocampal glutamatergic, serotonergic and cholinergic systems are affected by the pathophysiology of schizophrenia. Thus, we decided to use in vitro radioligand binding and autoradiography to measure levels of ionotropic glutamate, some muscarinic and serotonin 2A receptors in the CNS of ApoD^-/- and isogenic wild-type mice. These studies revealed a 20% decrease (mean ± SEM: 104 ± 10.2 vs. 130 ± 10.4 fmol/mg ETE) in the density of kainate receptors in the CA 2–3 of the ApoD^-/- mice. In addition there was a global decrease in AMPA receptors (F_1,214 = 4.67, p < 0.05) and a global increase in muscarinic M2/M4 receptors (F_1,208 = 22.77, p < 0.0001) in the ApoD^-/- mice that did not reach significance in any single cytoarchitectural region. We conclude that glutamatergic pathways seem to be particularly affected in ApoD^-/- mice and this may contribute to the changes in learning and memory, motor tasks and orientation-based tasks observed in these animals, all of which involve glutamatergic neurotransmission.     

Effects induced by cannabinoids on monoaminergic systems in the brain and their implications for psychiatric disorders

The endocannabinoid system and CB(1) receptors participate in the control of emotional behavior and mood through a functional coupling with the classic monoaminergic systems. In general, the acute stimulation of CB(1) receptors increases the activity (spontaneous firing rate) of noradrenergic (NE), serotonergic (5-HT) and dopaminergic (DA) neurons as well as the synthesis and/or release of the corresponding neurotransmitter in specific brain regions. Notably, the antagonist/inverse agonist rimonabant (SR141617A) can decrease the basal activity of NE and 5-HT neurons, suggesting a tonic/constitutive regulation of these neuronal systems by endocannabinoids acting at CB(1) receptors. Monoaminergic systems are modulated via CB(1) receptors by direct or indirect effects depending on the localization of this inhibitory receptor, which can be present on monoaminergic neurons themselves and/or inhibitory (GABAergic) and/or excitatory (glutamatergic) regulatory neurons. The repeated stimulation of CB(1) receptors is not associated with the induction of tolerance (receptor desensitization) on the activity of NE, 5-HT and DA neurons, in contrast to chronic agonist effects on neurotransmitter synthesis and/or release in some brain regions. CB(1) receptor desensitization may alter the direct and/or indirect effects of cannabinoid drugs modulating the functionality of monoaminergic systems. The sustained activation of monoaminergic neurons by cannabinoid drugs can also be related to changes in the function of presynaptic inhibitory α(2)-adrenoceptors or 5-HT(1A) receptors (autoreceptors and heteroreceptors), whose sensitivity is downregulated or upregulated upon chronic CB(1) agonist exposure. The functional interactions between endocannabinoids and monoaminergic systems in the brain indicate a potential role for CB(1) receptor signaling in the neurobiology of various psychiatric disorders, including major depression and schizophrenia as the major syndromes.     

Evidence for the involvement of the monoaminergic system in the antidepressant-like action of two 4-amine derivatives of 10,11-dihydro-5H-dibenzo [a,d] cycloheptane in mice evaluated in the tail suspension test

Our previous study described the synthesis of 4-amine derivatives of 10,11-dihydro-5H-dibenzo-alkylamine-cycloheptane, 4-amine (3-N,N-dimethylpropylamine)-10,11-dihydro-5H-dibenzo[a,d] cycloheptane-5-one (ADDCH1), and 1,2,3,4,8,9-hexahydro-dibenzocycloheptane[4,4a,5-ef]1,4-diazepin (ADDCH2), and the characterization of their antidepressant-like effect in the forced swimming test in mice. This study investigated the involvement of monoaminergic pathways in the antidepressant-like effect of these compounds in mice evaluated in the tail suspension test (TST), another animal model to screen antidepressant drugs. Our results show that the immobility time in the TST was significantly reduced by ADDCH1 (15 to 50 mg/kg, i.p.) or ADDCH2 (30 and 50 mg/kg, i.p.). The antidepressant-like effect of ADDCH1 (30 mg/kg, i.p.) in the TST was prevented by pre-treatment of mice with methysergide (2 mg/kg, i.p.), a non-selective serotonin receptor antagonist, p-chlorophenylalanine methylester (pCPA, 100 mg/kg, i.p.), an inhibitor of serotonin synthesis, prazosin (62.5 microg/kg, i.p.), an alpha1-adrenoceptor antagonist, or yohimbine (1 mg/kg, i.p.), an alpha2-adrenoceptor antagonist. In contrast, the antidepressant-like effect of ADDCH2 was antagonized only by yohimbine (1 mg/kg) or haloperidol (50 microg/kg, i.p.), a dopamine D2/D3/D4 receptor antagonist, and was not affected by methysergide, pCPA or prazosin. Altogether, the present results strongly suggest the differential involvement of monoaminergic systems, serotonin/noradrenaline (ADDCH1) and noradrenaline/dopamine (ADDCH2) pathways, respectively, in the antidepressant-like effect of dibenzosuberone compounds.     

Effects of perinatal exposure to low dose of bisphenol A on anxiety like behavior and dopamine metabolites in brain

Bisphenol A (BPA), an endocrine-disrupting chemical, is widely present in the environment. It has been reported that perinatal exposure to low doses of BPA that are less than the tolerable daily intake level (50 μg/kg/day) affects anxiety-like behavior and dopamine levels in the brain. Although the dopaminergic system in the brain is considered to be related to anxiety, no study has reported the effects of low-dose BPA exposure on the dopaminergic system in the brain and on anxiety-like behavior using the same methods of BPA exposure.     

Evaluation of oxidative status and depression-like responses in Brown Norway rats with acute myeloid leukemia

It has been proved that oxidative stress increases when leukemia is accompanied by depression. This fact may indicate the role of oxidative stress in the development of depression in cancer patients. The aim of this study was to determine whether the acute myeloid leukemia of Brown Norway rats, which is accompanied by oxidative stress, evoked behavioral and receptor changes resembling alterations characteristic of rat models of depression. The rats were divided into two groups: leukemic rats and healthy control. Leukemia was induced through intraperitoneal injection of 10⁷ promyelocytic leukemia cells to the Brown Norway rats. Depression-like behavior was evaluated in the forced swim test at 30 or 34 days after leukemic cells injection. The rats were killed after the evaluation and the spleen, brain cortex and hippocampus were excised. The red–ox state was assessed in homogenates of tissues by measuring total glutathione (GSH) content, the ferric ion reducing ability of plasma (FRAP) level, expression of heme oxygenase-1 (HO-1), biliverdin reductase (BvR) and ferritin mRNA, superoxide dismutase (SOD) activity, as well as malondialdehyde (MDA) concentration. Radioligand binding assay was used to assess of the effect of leukemia on cortical receptors. Leukemic cells were identified using RM-124 antibody by FACS Calibur flow cytometry. Leukemia influenced locomotory activity as well as forced swim test behavior in a 34-day series of experiments. Signs of oxidative stress in leukemic rats were observed in each examined stage of leukemia development. The FRAP values and glutathione contents, were significantly lowered whereas HO-1 mRNA expression, and malonodialdehyde concentrations were significantly increased in the spleen and brain structures of leukemic rats in comparison with the healthy controls. A significant increase in the potency of glycine to displace [³H]L-689,560 from the strychnine-insensitive glycine site of the N-methyl-D-aspartic (NMDA) receptors receptor complex in cortical homogenates of the leukemic rats in 30- and 34-day experimental series was observed in comparison with the control. Upregulation of 5-HT_2A receptors was observed in rat cortex after 30 days of leukemia development but not in 34-days series compared with the control. It is concluded that disturbances in antioxidant system in brain cortex were accompanied by an activation of glycine sites of the NMDA receptor complex, regardless of stage of leukemia development, which are characteristic of model of depression. Findings of our study demonstrate the link between glutamatergic activity, oxidative stress and leukemia.     

Association of alpha2A-adrenergic receptor gene polymorphism with susceptibility to suicide in Japanese females

OBJECTIVES: It has been suggested that noradrenergic system abnormalities are involved in suicide. Postmortem brain studies have shown that molecular and functional alterations in alpha2A-adrenergic receptor-induced signal transduction are associated with suicide and depression. Recently, a single nucleotide polymorphism (SNP) within a coding region of the alpha2A-adrenergic receptor gene (ADRA2A), which results in an Asn-to-Lys change at amino acid 251 (N251K), has been implicated in susceptibility to suicide in Caucasians. The aim of our study is to determine whether genetic variants of the ADRA2A gene are also associated with suicide in a Japanese population. METHODS: Three SNPs, C-1291G, N251K and rs3750625C/A, and one insertion/deletion polymorphism in the ADRA2A gene were genotyped in 184 completed suicides and 221 control subjects with the polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method. RESULTS: Neither variation of the N251K SNP nor the insertion/deletion polymorphism was found in our Japanese samples. The C-1291G SNP in the promoter region was found to be significantly associated with suicide in females (P=0.043 and 0.013 for genotypic and allelic comparisons, respectively). One of the common haplotypes, CC of C-1291G and rs3750625C/A, was also associated with suicide in females (P=0.015). These associations were also significant in the female violent suicide victims (P=0.009 and 0.009 for allelic and CC haplotypic comparisons, respectively). Although the significance was nominal, it was maintained even after correction for multiple comparisons. By contrast, neither of these two SNPs showed any association with violent and/or non-violent suicide in males. CONCLUSION: Our results raise the possibility that promoter genetic variation in the ADRA2A gene is associated with either suicide or violent suicide in females.     

D-arginine action against neurotoxicity induced by glucocorticoids in the brain

Glucocorticoids (GC) are necessary for normal life but elevated levels of GC have been implicated in the development of several neurological diseases and psychiatric disorders. Nowadays, it is well known that high levels of GC in the central nervous system (CNS) generate an increase in the production of reactive oxygen species (ROS), derived mainly from the nitric oxide (NO) pathway. Accordingly, there is an increase of l-arginine (l-Arg.) availability. This report reviews the evidence that d-arginine (d-Arg.) induces normalization of l-Arg. resulting in protection against GC neurotoxic actions in the hippocampus. It is important to highlight that this D-amino acid does not interfere with the expected peripheral effects of GC such as suppression of the hypothalamic-pituitary-adrenal axis (HPA axis) and the immune response, commonly used in clinical practice.     

Selective participation of the bed nucleus of the stria terminalis and CRF in sustained anxiety-like versus phasic fear-like responses

The medial division of the central nucleus of the amygdala (CeA_M) and the lateral division of the bed nucleus of the stria terminalis (BNST_L) are closely related. Both receive projections from the basolateral amygdala (BLA) and both project to brain areas that mediate fear-influenced behaviors. In contrast to CeA_M however, initial attempts to implicate the BNST in conditioned fear responses were largely unsuccessful. More recent studies have shown that the BNST does participate in some types of anxiety and stress responses. Here, we review evidence suggesting that the CeA_M and BNST_L are functionally complementary, with CeA_M mediating short- but not long-duration threat responses (i.e., phasic fear) and BNST_L mediating long- but not short-duration responses (sustained fear or ‘anxiety’). We also review findings implicating the stress-related peptide corticotropin-releasing factor (CRF) in sustained but not phasic threat responses, and attempt to integrate these findings into a neural circuit model which accounts for these and related observations.     

Behavioral effects of elevated expression of human equilibrative nucleoside transporter 1 in mice

Adenosine concentrations are regulated by purinergic enzymes and nucleoside transporters. Transgenic mice with neuronal expression of human equilibrative nucleoside transporter 1 (hENT1) have been generated (Parkinson et al., 2009 [7]). The present study tested the hypothesis that mice homozygous and heterozygous for the transgene exhibit differences in hENT1 mRNA and protein expression, and in behavioral responses to caffeine and ethanol, two drugs with adenosine-dependent actions. Real time polymerase chain reaction (PCR) was used to identify mice heterozygous and homozygous for the transgene. Gene expression, determined by real time PCR of cDNA reverse transcribed from cerebral cortex RNA, was 3.8-fold greater in homozygous mice. Protein abundance, determined by radioligand binding assays using 0.14 nM [³H]S-(4-nitrobenzyl)-6-thioinosine ([³H]NBTI), was up to 84% greater in cortex synaptosome membranes from homozygous than from heterozygous mice. In western blots with an antibody specific for hENT1, a protein of approximately 40 kDa was strongly labelled in cortex samples from homozygous mice, weakly labelled in samples from heterozygous mice and absent from samples from wild type mice. In behavioral assays, transgenic mice showed a greater response to ethanol and a reduced response to caffeine than wild type littermates; however, no significant differences between heterozygous and homozygous mice were detected. These data indicate that the difference in ENT1 function between wild type and heterozygous mice was greater than that between heterozygous and homozygous mice. Therefore, either heterozygous or homozygous hENT1 transgenic mice can be used in studies of ENT1 regulation of adenosine levels and adenosine dependent behaviors.     

Low affinity binding of the classical D1 antagonist SCH23390 in rodent brain: potential interaction with A2A and D2-like receptors

Whereas structurally dissimilar D(1) antagonists competing for [(3)H]-SCH23390 binding recognize primarily one site in striatum, two distinct affinity states are observed in both amygdala and hippocampus. The binding profile of SCH23390 is similar in both of these regions, with the high affinity site (K(D) approximately 0.4 nM) consistent with D(1)/D(5) receptors. The appearance of the low affinity site (K(D) approximately 300 nM) is dependent upon the absence of MgCl(2), but independent of D(1) expression (i.e., still present in D(1) knockout mice). Although the density of high affinity state receptor is lower in hippocampus or amygdala of D(1) knockout mice, some residual binding remains, consistent with the known expression of D(5) receptors in these regions. Remarkably, in hippocampus, the affinity of the low affinity site is shifted rightward in the presence of the D(2) antagonist domperidone and is largely absent in the hippocampus of D(2) knockout animals. Additionally, this site is also shifted rightward in the presence of the A(2A) ligands SCH58261, CSC, or NECA, or in the absence of A(2A) receptors. The affinity of SCH23390 for this low affinity site is greater than seen for SCH23390 binding to D(2) receptors in heterologous expression systems, consistent with the hypothesis that both D(2) and A(2A) receptors are involved in the low affinity binding site. Therefore, we suggest that the heteromerization of D(2) and A(2A) receptors reported previously in vitro also may occur in the brain of both rats and mice.