Involvement of the adenosine A1 and A2A receptors in the antidepressant-like effect of zinc in the forced swimming test

Exploring the contribution of the dopaminergic and noradrenergic systems in the antidepressant-like action of 1-(2-(4-(4-ethylphenyl)-1H-1,2,3-triazol-1-yl)phenyl)ethanone in mice

1-(2-(4-(4-ethylphenyl)-1H-1,2,3-triazol-1-yl)phenyl)ethanone (ETAP) is a novel hybrid compound containing 1,2,3-triazole and acetophenone. It exhibits antidepressant-like effects in male mice, linked to modulation of serotonergic receptors and monoamine oxidase A (MAO-A) inhibition. This study aimed to evaluate the involvement of the dopaminergic and noradrenergic systems, as well as MAO-B activity inhibition, in the antidepressant-like effect of ETAP in male mice, and to evaluate the antidepressant-like effect of ETAP in female mice. Male mice were treated with different dopaminergic and noradrenergic receptors antagonists 15 min before administering ETAP (1 mg/kg, intragastrically, i.g.). The tail suspension test (TST) was performed 30 minutes later. Different male mice were treated with ETAP (1 mg/kg, i.g.), and 30 minutes later, were euthanized to assess MAO-B activity in the prefrontal cortex and hippocampus. To evaluate the antidepressant-like of ETAP in female mice, ETAP (1 mg/kg, i.g.) was administered, followed by the TST and the forced swimming test (FST) 30 minutes later. The dopaminergic antagonists haloperidol (0.05 mg/kg, intraperitoneally, i.p.), SCH23390 (0.01 mg/kg, subcutaneously, s.c.), and sulpiride (50 mg/kg, i.p.), as well the noradrenergic antagonists prazosin (1 mg/kg, i.p.), yohimbine (1 mg/kg, i.p.), and propranolol (2 mg/kg, i.p.), prevented the antidepressant-like effect of ETAP in the TST. MAO-B activity was unaffected by ETAP in both the prefrontal cortex and hippocampus. ETAP (1 mg/kg, i.g.) induced a significant antidepressant-like effect in female mice in the TST and FST. These findings provide valuable insights into the antidepressant-like effect of ETAP, highlighting its potential for developing more effective depression treatments.

1-(Phenylselanyl)-2-(p-tolyl)indolizine: A selenoindolizine with potential antidepressant-like activity in mice mediated by the modulation of dopaminergic and noradrenergic systems

1-(Phenylselanyl)-2-(p-tolyl)indolizine (MeSeI) is a selenoindolizine with an antidepressant-like effect in mice by regulation of the serotonergic system. This study investigated the involvement of dopaminergic and noradrenergic systems in the antidepressant-like action of MeSeI. For this purpose, Swiss male mice were pretreated with different antagonists, after 15 min, the MeSeI was administrated by intragastric (i.g.) via; after 30 min, the mouse behavior was assessed in the forced swimming test (FST). The action of MeSeI on the activity of monoamine oxidase (MAO) was determined. The pretreatment of mice with haloperidol (0.05 mg/kg, intraperitoneally, i.p.; non-selective dopamine receptor antagonist), sulpiride (50 mg/kg, i.p.; D2 receptor antagonist), yohimbine (1 mg/kg, i.p.; α2 receptor antagonist), and propranolol (2 mg/kg, i.p.; non-selective β receptor antagonist), inhibited the anti-immobility action of MeSeI (50 mg/kg, i.g.) in the FST. This blocking effect was not observed when SCH23390 (0.01 mg/kg, i.p.; D1 receptor antagonist), and prazosin (1 mg/kg, i.p.; α1 receptor antagonist) were administered. The coadministration of subeffective doses of bupropion (3 mg/kg. i.g.; dopamine and noradrenaline reuptake inhibitor) and MeSeI (0.5 mg/kg. i.g.) reduced the immobility time in the FST. Furthermore, MeSeI inhibited MAO-A and B activities in vitro and ex vivo tests. These results suggest that MeSeI exerts its antidepressant-like effect via regulation of the D2, α2, and β1 receptors and the inhibition of MAO-A and B activities. Molecular docking investigations corroborated these results. This study provides comprehensive insights into the antidepressant-like mechanism of MeSeI in mice, suggesting its potential as a novel antidepressant candidate.

In vivo phenotypic validation of adenosine receptor-dependent activity of non-adenosine drugs

Some non-adenosinergic drugs are reported to also act through adenosine receptors (ARs). We used mouse hypothermia, which can be induced by agonism at any of the four ARs, as an in vivo screen for adenosinergic effects. An AR contribution was identified when a drug caused hypothermia in wild type mice that was diminished in mice lacking all four ARs (quadruple knockout, QKO). Alternatively, an adenosinergic effect was identified if a drug potentiated adenosine-induced hypothermia. Four drugs (dipyridamole, nimodipine, cilostazol, cyclosporin A) increased the hypothermia caused by adenosine. Dipyridamole and nimodipine probably achieved this by inhibition of adenosine clearance via ENT1. Two drugs (cannabidiol, canrenoate) did not cause hypothermia in wild type mice. Four other drugs (nifedipine, ranolazine, ketamine, ethanol) caused hypothermia, but the hypothermia was unchanged in QKO mice indicating non-adenosinergic mechanisms. Zinc chloride caused hypothermia and hypoactivity; the hypoactivity was blunted in the QKO mice. Interestingly, the antidepressant amitriptyline caused hypothermia in wild type mice that was amplified in the QKO mice. Thus, we have identified adenosine-related effects for some drugs, while other candidates do not affect adenosine signaling by this in vivo assay. The adenosine-modulating drugs could be considered for repurposing based on predicted effects on AR activation.

The antidepressant-like effect of guanosine involves the modulation of adenosine A1 and A2A receptors

Guanosine has been considered a promising candidate for antidepressant responses, but if this nucleoside could modulate adenosine A₁ (A₁R) and A_2A (A_2AR) receptors to exert antidepressant-like actions remains to be elucidated. This study investigated the role of A₁R and A_2AR in the antidepressant-like response of guanosine in the mouse tail suspension test and molecular interactions between guanosine and A₁R and A₂AR by docking analysis. The acute (60 min) administration of guanosine (0.05 mg/kg, p.o.) significantly decreased the immobility time in the tail suspension test, without affecting the locomotor performance in the open-field test, suggesting an antidepressant-like effect. This behavioral response was paralleled with increased A₁R and reduced A_2AR immunocontent in the hippocampus, but not in the prefrontal cortex, of mice. Guanosine-mediated antidepressant-like effect was not altered by the pretreatment with caffeine (3 mg/kg, i.p., a non-selective adenosine A₁R/A_2AR antagonist), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX - 2 mg/kg, i.p., a selective adenosine A₁R antagonist), or 4-(2-[7-amino-2-{2-furyl}{1,2,4}triazolo-{2,3-a}{1,3,5}triazin-5-yl-amino]ethyl)-phenol (ZM241385 - 1 mg/kg, i.p., a selective adenosine A_2AR antagonist). However, the antidepressant-like response of guanosine was completely abolished by adenosine (0.5 mg/kg, i.p., a non-selective adenosine A₁R/A_2AR agonist), N-6-cyclohexyladenosine (CHA - 0.05 mg/kg, i.p., a selective adenosine A₁ receptor agonist), and N-6-[2-(3,5-dimethoxyphenyl)-2-(methylphenyl)ethyl]adenosine (DPMA - 0.1 mg/kg, i.p., a selective adenosine A_2A receptor agonist). Finally, docking analysis also indicated that guanosine might interact with A₁R and A_2AR at the adenosine binding site. Overall, this study reinforces the antidepressant-like of guanosine and unveils a previously unexplored modulation of the modulation of A₁R and A_2AR in its antidepressant-like effect.

Purinergic transmission in depressive disorders

Purinergic signaling involves the actions of purine nucleotides and nucleosides (such as adenosine) at P1 (adenosine), P2X, and P2Y receptors. Here, we present recent data contributing to a comprehensive overview of the association between purinergic signaling and depression. We start with background information on adenosine production and metabolism, followed by a detailed characterization of P1 and P2 receptors, with an emphasis on their expression and function in the brain as well as on their ligands. We provide data suggestive of altered metabolism of adenosine in depressed patients, which might be regarded as a disease biomarker. We then turn to considerable amount of preclinical/behavioral data obtained with the aid of the forced swim test, tail suspension test, learned helplessness model, or unpredictable chronic mild stress model and genetic activation/inactivation of P1 or P2 receptors as well as nonselective or selective ligands of P1 or P2 receptors. We also aimed to discuss the reason underlying discrepancies observed in such studies.

The Interaction of Selective A1 and A2A Adenosine Receptor Antagonists with Magnesium and Zinc Ions in Mice: Behavioural, Biochemical and Molecular Studies

The purpose of the study was to investigate whether the co-administration of Mg²⁺ and Zn²⁺ with selective A1 and A2A receptor antagonists might be an interesting antidepressant strategy. Forced swim, tail suspension, and spontaneous locomotor motility tests in mice were performed. Further, biochemical and molecular studies were conducted. The obtained results indicate the interaction of DPCPX and istradefylline with Mg²⁺ and Zn²⁺ manifested in an antidepressant-like effect. The reduction of the BDNF serum level after co-administration of DPCPX and istradefylline with Mg²⁺ and Zn²⁺ was noted. Additionally, Mg²⁺ or Zn²⁺, both alone and in combination with DPCPX or istradefylline, causes changes in Adora1 expression, DPCPX or istradefylline co-administered with Zn²⁺ increases Slc6a15 expression as compared to a single-drug treatment, co-administration of tested agents does not have a more favourable effect on Comt expression. Moreover, the changes obtained in Ogg1, MsrA, Nrf2 expression show that DPCPX-Mg²⁺, DPCPX-Zn²⁺, istradefylline-Mg²⁺ and istradefylline-Zn²⁺ co-treatment may have greater antioxidant capacity benefits than administration of DPCPX and istradefylline alone. It seems plausible that a combination of selective A1 as well as an A2A receptor antagonist and magnesium or zinc may be a new antidepressant therapeutic strategy.

Of adenosine and the blues: The adenosinergic system in the pathophysiology and treatment of major depressive disorder

Major depressive disorder (MDD) is the foremost cause of global disability, being responsible for enormous personal, societal, and economical costs. Importantly, existing pharmacological treatments for MDD are partially or totally ineffective in a large segment of patients. As such, the search for novel antidepressant drug targets, anchored on a clear understanding of the etiological and pathophysiological mechanisms underpinning MDD, becomes of the utmost importance. The adenosinergic system, a highly conserved neuromodulatory system, appears as a promising novel target, given both its regulatory actions over many MDD-affected systems and processes. With this goal in mind, we herein review the evidence concerning the role of adenosine as a potential player in pathophysiology and treatment of MDD, combining data from both human and animal studies. Altogether, evidence supports the assertions that the adenosinergic system is altered in both MDD patients and animal models, and that drugs targeting this system have considerable potential as putative antidepressants. Furthermore, evidence also suggests that modifications in adenosine signaling may have a key role in the effects of several pharmacological and non-pharmacological antidepressant treatments with demonstrated efficacy, such as electroconvulsive shock, sleep deprivation, and deep brain stimulation. Lastly, it becomes clear from the available literature that there is yet much to study regarding the role of the adenosinergic system in the pathophysiology and treatment of MDD, and we suggest several avenues of research that are likely to prove fruitful.

The sex-dependent anti-depressant-like effects of zeatin in rat behavioral despair model as a candidate A2A receptor ligand

Zeatin, an adenine-derivative cytokinin has well-established functions in plants. It is also suggested to activate A2A receptors in animals, however, there is limited knowledge of its effects. The main objective of this study is to evaluate the possible effects of zeatin on depression, and our hypothesis is that zeatin might induce an anti-depressant effect via A2A receptor-linked pathways. The forced swim test was used to create a depression-like model on female and male rats. A balanced zeatin isomer mixture (80 % trans-zeatin (tZ), 20 % cis-zeatin (cZ)) was administered intraperitoneally to analyze the effects. Caffeine with a suboptimal dose (2 mg/kg) was used as a known ligand of A2A receptor. Finally, a molecular docking study was also implemented to compare caffeine and tZ in the ligand binding site of A2A receptor. We demonstrate that (1) there is a clear sex-dependent difference in the susceptibility to depression-like symptoms, where female rats in the metestrus phase display higher depressive-like behavior and lower responses to the anti-depressant-like effects of pharmacological applications; (2) 10 mg/kg zeatin exerts an anti-depressant-like effect for both females and males without affecting locomotor activity; (3) 8 mg/kg tZ alone replicates this effect for both sexes, (4) the effect of zeatin is also differential for either sex and (5) the similar effect of caffeine and zeatin implies that the effect might be exerted via A2A receptor mediated pathways. Computational analysis further yielded similar binding patterns for both ligands. In conclusion, zeatin might have a potential therapeutic use in depression, acting via adenosinergic pathways.

Antidepressant-Like Effect of Terpineol in an Inflammatory Model of Depression: Involvement of the Cannabinoid System and D2 Dopamine Receptor

Depression has a multifactorial etiology that arises from environmental, psychological, genetic, and biological factors. Environmental stress and genetic factors acting through immunological and endocrine responses generate structural and functional changes in the brain, inducing neurogenesis and neurotransmission dysfunction. Terpineol, monoterpenoid alcohol, has shown immunomodulatory and neuroprotective effects, but there is no report about its antidepressant potential. Herein, we used a single lipopolysaccharide (LPS) injection to induce a depressive-like effect in the tail suspension test (TST) and the splash test (ST) for a preventive and therapeutic experimental schedule. Furthermore, we investigated the antidepressant-like mechanism of action of terpineol while using molecular and pharmacological approaches. Terpineol showed a coherent predicted binding mode mainly against CB1 and CB2 receptors and also against the D2 receptor during docking modeling analyses. The acute administration of terpineol produced the antidepressant-like effect, since it significantly reduced the immobility time in TST (100-200 mg/kg, p.o.) as compared to the control group. Moreover, terpineol showed an antidepressant-like effect in the preventive treatment that was blocked by a nonselective dopaminergic receptor antagonist (haloperidol), a selective dopamine D2 receptor antagonist (sulpiride), a selective CB1 cannabinoid receptor antagonist/inverse agonist (AM281), and a potent and selective CB2 cannabinoid receptor inverse agonist (AM630), but it was not blocked by a nonselective adenosine receptor antagonist (caffeine) or a β-adrenoceptor antagonist (propranolol). In summary, molecular docking suggests that CB1 and CB2 receptors are the most promising targets of terpineol action. Our data showed terpineol antidepressant-like modulation by CB1 and CB2 cannabinoid receptors and D2-dopaminergic receptors to further corroborate our molecular evidence.

Adenosine-Related Mechanisms in Non-Adenosine Receptor Drugs

Many ligands directly target adenosine receptors (ARs). Here we review the effects of noncanonical AR drugs on adenosinergic signaling. Non-AR mechanisms include raising adenosine levels by inhibiting adenosine transport (e.g., ticagrelor, ethanol, and cannabidiol), affecting intracellular metabolic pathways (e.g., methotrexate, nicotinamide riboside, salicylate, and 5-aminoimidazole-4-carboxamide riboside), or undetermined means (e.g., acupuncture). However, other compounds bind ARs in addition to their canonical ‘on-target’ activity (e.g., mefloquine). The strength of experimental support for an adenosine-related role in a drug’s effects varies widely. AR knockout mice are the ‘gold standard’ method for investigating an AR role, but few drugs have been tested on these mice. Given the interest in AR modulation for treatment of cancer, CNS, immune, metabolic, cardiovascular, and musculoskeletal conditions, it is informative to consider AR and non-AR adenosinergic effects of approved drugs and conventional treatments.

Electroacupuncture inhibits visceral pain via adenosine receptors in mice with inflammatory bowel disease

To investigate the involvement of peripheral adenosine receptors in the effect of electroacupuncture (EA) on visceral pain in mice with inflammatory bowel disease (IBD). 2,4,6-Trinitrobenzene sulfonic acid (TNBS) was used to induce the visceral pain model. EA (1 mA, 2 Hz, 30 min) treatment was applied to bilateral acupoints "Dachangshu" (BL25) 1 day after TNBS injection once daily for 7 consecutive days. Von Frey filaments were used to measure the mechanical pain threshold. Western blot was used to detect the protein expression levels of adenosine 1 receptor (A1R), adenosine 2a receptor (A2aR), adenosine 2b receptor (A2bR), adenosine 3 receptor (A3R), substance P (SP), and interleukin 1 beta (IL-1β) in colon tissue. EA significantly ameliorated the disease-related indices and reduced the expression of SP and IL-1β in the colon tissues of mice with IBD. EA increased the expression of A1R, A2aR, and A3R and decreased the expression of A2bR in the colon tissue. Furthermore, the administration of adenosine receptor antagonists influenced the effect of EA. EA can inhibit the expression of the inflammatory factors SP and IL-1β by regulating peripheral A1, A2a, A2b, and A3 receptors, thus inhibiting visceral pain in IBD mice.

Involvement of glutamatergic neurotransmission in the antidepressant-like effect of zinc in the chronic unpredictable stress model of depression

Stress and excessive glutamatergic neurotransmission have been implicated in the pathophysiology of depression. Therefore, this study was aimed at investigating the influence of zinc on depressive-like behavior induced by chronic unpredictable stress (CUS), on alterations in glutamate-induced toxicity and immunocontent of proteins involved in the control of glutamatergic neurotransmission in the hippocampus of mice. Mice were subjected to CUS procedure for 14 days. From the 8th to the 14th day, mice received zinc chloride (ZnCl2) (10 mg/kg) or fluoxetine (10 mg/kg, positive control) once a day by oral route. CUS caused a depressive-like behavior evidenced by the increased immobility time in the tail suspension test (TST), which was prevented by treatment with ZnCl2 or fluoxetine. Ex vivo exposure of hippocampal slices to glutamate (10 mM) resulted in a significant decrease on cell viability; however, neither CUS procedure nor drug treatments altered this reduction. No alterations in the immunocontents of GLT-1 and GFAP or p-Akt were observed in any experimental group. The ratio of p-Akt/AKT was also not altered in any group. However, Akt immunocontent was increased in stressed mice and in animals treated with ZnCl2 (stressed or non-stressed mice) and EAAC1 immunocontent was increased in stressed mice treated with ZnCl2, fluoxetine or vehicle and in non-stressed mice treated with ZnCl2 and fluoxetine. These findings indicate a robust effect of zinc in reversing behavioral alteration induced by CUS in mice, through a possible modulation of the glutamatergic neurotransmission, extending literature data regarding the mechanisms underlying its antidepressant-like action.

The effect of imipramine, ketamine, and zinc in the mouse model of depression

Relationship between the chronic and excessive exposure to glucocorticoids and the development of psychiatric disorders, including depression, has been described in the literature. We decided to investigate whether a combination of agents with antidepressant activity (i.e., imipramine, ketamine, and Zn(2+)) may influence/reverse the depressogenic effect of dexamethasone therapy. The antidepressant-like effect was assessed by the forced swim test in adult mice. The inhibitory activity of dexamethasone was dose-dependent: only the highest tested dose of the glucocorticoid (i.e., 64 μg/kg) given as a single injection increased immobility time, whereas 16 μg/kg/day of dexamethasone administered repeatedly (for 14 days) induced a significant alteration in animal behavior. Both the acute or sub-chronic administration of the active doses of imipramine (10 mg/kg), Zn(2+) (30 mg/kg), and ketamine (30 mg/kg), and the combinations of their per se inactive doses reversed the inhibitory activity of dexamethasone (16 μg/kg/day) administered for 14 consecutive days. Whereas a single injection of an inhibitory dose of dexamethasone (64 μg/kg) was not able to abolish the antidepressant effect of imipramine (5 mg/kg), Zn(2+) (10 mg/kg), and imipramine-Zn(2+) combination (2.5 and 5 mg/kg, respectively) given once a day for 14 consecutive days. Our findings indicate that the chronic dexamethasone injection procedure has some potential as an animal model of depression and they further support the theory of interplay between glutamatergic neurotransmission and the chronic or excessive exposition to glucocorticoids.

Synergistic antidepressant-like effect of the joint administration of caffeine and NMDA receptor ligands in the forced swim test in mice

The optimal treatment of depressed patients remains one of the most important challenges concerning depression. The identification of the best treatment strategies and development of new, safer, and more effective agents are crucial. The glutamatergic system seems to be a promising drug target, and consequently the use of the NMDA receptor ligands, particularly in co-administration with other substances exerting the antidepressant activity, has emerged among the new ideas. The objective of this study was to examine the effect of caffeine on the performance of mice treated with various NMDA modulators in the forced swim test. We demonstrated a significant interaction between caffeine (5 mg/kg) and the following NMDA receptor ligands: MK-801 (an antagonist binding in the ion channel, 0.05 mg/kg), CGP 37849 (an antagonist of the glutamate site, 0.312 mg/kg), L-701,324 (an antagonist of the glycine site, 1 mg/kg), and d-cycloserine (a high-efficacy partial agonist of the glycine site, 2.5 mg/kg), while the interaction between caffeine and the inorganic modulators, i.e., Zn²⁺ (2.5 mg/kg) and Mg²⁺ (10 mg/kg), was not considered as significant. Based on the obtained results, the simultaneous blockage of the adenosine and NMDA receptors may be a promising target in the development of new antidepressants.

Activation of mTOR dependent signaling pathway is a necessary mechanism of antidepressant-like activity of zinc

The rapid antidepressant response to the N-methyl-D-aspartate (NMDA) receptor antagonists is mediated by activation of the mammalian target of the rapamycin (mTOR) signaling pathway, an increase in the synthesis of synaptic proteins and formation of new synapses in the prefrontal cortex (PFC) of rats. Zinc (Zn), which is a potent NMDA receptor antagonist, exerts antidepressant-like effects in screening tests and models of depression. We focused these studies in investigating whether activation of the mTOR signaling pathway is also a necessary mechanism of the antidepressant-like activity of Zn. We observed that a single injection of Zn (5 mg/kg) induced an increase in the phosphorylation of mTOR and p70S6K 30 min and 3 h after Zn treatment at time points when Zn produced also an antidepressant-like effect in the forced swim test (FST). Furthermore, Zn administered 3 h before the decapitation increased the level of brain derived neurotrophic factor (BDNF), GluA1 and synapsin I. An elevated level of GluA1 and synapsin I was still observed 24 h after the Zn treatment, although Zn did not produce any effects in the FST at that time point. We also observed that pretreatment with rapamycin (mTORC1 inhibitor), LY294002 (PI3K inhibitor), H-89 (PKA inhibitor) and GF109203X (PKC inhibitor) blocked the antidepressant-like effect of Zn in FST in rats and blocks Zn-induced activation of mTOR signaling proteins (analyzed 30 min after Zn administration). These studies indicated that the antidepressant-like activity of Zn depends on the activation of mTOR signaling and other signaling pathways related to neuroplasticity, which can indirectly modulate mTOR function.

Antidepressant-like effect of zinc is dependent on signaling pathways implicated in BDNF modulation

Considering that intracellular signaling pathways that modulate brain BDNF are implicated in antidepressant responses, this study investigated whether signaling pathway inhibitors upstream to BDNF might influence the antidepressant-like effect of zinc, a metal that has been shown to display antidepressant properties. To this end, the influence of i.c.v. administration of H-89 (1μg/site, PKA inhibitor), KN-62 (1μg/site, CAMKII inhibitor), chelerythrine (1μg/site, PKC inhibitor), PD98059 (5μg/site, MEK1/2 inhibitor), U0126 (5μg/site, MEK1/2 inhibitor), LY294002 (10nmol/site, PI3K inhibitor) on the reduction of immobility time in the tail suspension test (TST) elicited by ZnCl2 (10mg/kg, p.o.) was investigated. Moreover, the effect of the combination of sub-effective doses of ZnCl2 (1mg/kg, p.o.) and AR-A014418 (0.001μg/site, GSK-3β inhibitor) was evaluated. The occurrence of changes in CREB phosphorylation and BDNF immunocontent in the hippocampus and prefrontal cortex of mice following ZnCl2 treatment was also investigated. The anti-immobility effect of ZnCl2 in the TST was prevented by treatment with PKA, PKC, CAMKII, MEK1/2 or PI3K inhibitors. Furthermore, ZnCl2 in combination with AR-A014418 caused a synergistic anti-immobility effect in the TST. None of the treatments altered locomotor activity of mice. ZnCl2 treatment caused no alteration in CREB phosphorylation and BDNF immunocontent. The results extend literature data regarding the mechanisms underlying the antidepressant-like action of zinc by indicating that its antidepressant-like effect may be dependent on the activation of PKA, CAMKII, PKC, ERK, and PI3K/GSK-3β pathways. However, zinc is not able to acutely increase BDNF in the hippocampus and prefrontal cortex.

Creatine, similarly to ketamine, affords antidepressant-like effects in the tail suspension test via adenosine A₁ and A2A receptor activation

The benefits of creatine supplementation have been reported in a broad range of central nervous systems diseases, including depression. A previous study from our group demonstrated that creatine produces an antidepressant-like effect in the tail suspension test (TST), a predictive model of antidepressant activity. Since depression is associated with a dysfunction of the adenosinergic system, we investigated the involvement of adenosine A1 and A2A receptors in the antidepressant-like effect of creatine in the TST. The anti-immobility effect of creatine (1 mg/kg, po) or ketamine (a fast-acting antidepressant, 1 mg/kg, ip) in the TST was prevented by pretreatment of mice with caffeine (3 mg/kg, ip, nonselective adenosine receptor antagonist), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (2 mg/kg, ip, selective adenosine A1 receptor antagonist), and 4-(2-[7-amino-2-{2-furyl}{1,2,4}triazolo-{2,3-a}{1,3,5}triazin-5-yl-amino]ethyl)-phenol (ZM241385) (1 mg/kg, ip, selective adenosine A2A receptor antagonist). In addition, the combined administration of subeffective doses of creatine and adenosine (0.1 mg/kg, ip, nonselective adenosine receptor agonist) or inosine (0.1 mg/kg, ip, nucleoside formed by the breakdown of adenosine) reduced immobility time in the TST. Moreover, the administration of subeffective doses of creatine or ketamine combined with N-6-cyclohexyladenosine (CHA) (0.05 mg/kg, ip, selective adenosine A1 receptor agonist), N-6-[2-(3,5-dimethoxyphenyl)-2-(methylphenyl)ethyl]adenosine (DPMA) (0.1 mg/kg, ip, selective adenosine A2A receptor agonist), or dipyridamole (0.1 μg/mouse, icv, adenosine transporter inhibitor) produced a synergistic antidepressant-like effect in the TST. These results indicate that creatine, similarly to ketamine, exhibits antidepressant-like effect in the TST probably mediated by the activation of both adenosine A1 and A2A receptors, further reinforcing the potential of targeting the purinergic system to the management of mood disorders.

The role of NMDA receptors in the pathophysiology and treatment of mood disorders

Mood disorders such as major depressive disorder and bipolar disorder are chronic and recurrent illnesses that cause significant disability and affect approximately 350 million people worldwide. Currently available biogenic amine treatments provide relief for many and yet fail to ameliorate symptoms for others, highlighting the need to diversify the search for new therapeutic strategies. Here we present recent evidence implicating the role of N-methyl-D-aspartate receptor (NMDAR) signaling in the pathophysiology of mood disorders. The possible role of NMDARs in mood disorders has been supported by evidence demonstrating that: (i) both BPD and MDD are characterized by altered levels of central excitatory neurotransmitters; (ii) NMDAR expression, distribution, and function are atypical in patients with mood disorders; (iii) NMDAR modulators show positive therapeutic effects in BPD and MDD patients; and (iv) conventional antidepressants/mood stabilizers can modulate NMDAR function. Taken together, this evidence suggests the NMDAR system holds considerable promise as a therapeutic target for developing next generation drugs that may provide more rapid onset relief of symptoms. Identifying the subcircuits involved in mood and elucidating the role of NMDARs subtypes in specific brain circuits would constitute an important step toward the development of more effective therapies with fewer side effects.

Overexpression of Adenosine A2A Receptors in Rats: Effects on Depression, Locomotion, and Anxiety

Adenosine A2A receptors (A2AR) are a sub-type of receptors enriched in basal ganglia, activated by the neuromodulator adenosine, which interact with dopamine D2 receptors. Although this reciprocal antagonistic interaction is well-established in motor function, the outcome in dopamine-related behaviors remains uncertain, in particular in depression and anxiety. We have demonstrated an upsurge of A2AR associated to aging and chronic stress. Furthermore, Alzheimer's disease patients present A2AR accumulation in cortical areas together with depressive signs. We now tested the impact of overexpressing A2AR in forebrain neurons on dopamine-related behavior, namely depression. Adult male rats overexpressing human A2AR under the control of CaMKII promoter [Tg(CaMKII-hA2AR)] and aged-matched wild-types (WT) of the same strain (Sprague-Dawley) were studied. The forced swimming test (FST), sucrose preference test (SPT), and the open-field test (OFT) were performed to evaluate behavioral despair, anhedonia, locomotion, and anxiety. Tg(CaMKII-hA2AR) animals spent more time floating and less time swimming in the FST and presented a decreased sucrose preference at 48 h in the SPT. They also covered higher distances in the OFT and spent more time in the central zone than the WT. The results indicate that Tg(CaMKII-hA2AR) rats exhibit depressive-like behavior, hyperlocomotion, and altered exploratory behavior. This A2AR overexpression may explain the depressive signs found in aging, chronic stress, and Alzheimer's disease.

Nutritional strategies for dealing with depression

Depression is a highly recurrent and debilitating psychiatric disorder associated with multicausal origins. Impairments in the monoaminergic transmission, increased glutamatergic excitotoxicity, neuroinflammation, oxidative stress and deficits in neurotrophic factors are the main hypothesis raised in order to explain the etiological basis of depression. Although the current antidepressant therapy usually alleviates symptoms and prevents recurrence of episodes, the delay in the onset of the therapeutic effect and the refractory or intolerant responses exhibited by a large number of patients are the main drawbacks of the current therapy. For these reasons, several studies have dealt with the investigation of alternative therapeutic approaches or adjunctive strategies which could improve clinical outcomes. One potential adjunctive treatment with conventional antidepressants involves the use of nutraceuticals (a food, a part of a food, a vitamin, a mineral, or a herb that provides health benefits). In this review, we will focus on the main nutrients, phytochemicals and food that have been shown to have beneficial effects against depression.

Psychological stress-induced lower serum zinc and zinc redistribution in rats

In humans, long-term exposure to uncontrollable and unpredictable life stressors is a major precipitant in the development of depressive disorders. There are strong evidences that depression is accompanied by lower serum zinc. The aim of present study is to assess the effects of repeated psychological stress (PS) on the zinc metabolism in rat. The rats were divided into control group and PS group which were subdivided into three subgroups: 7-day group, 14-day group, and recovery group (ten rats in each subgroup). PS model was created by a communication box which contains room A and room B. Rats in room A were only exposed to the responses of rats which were randomly given electrical shock for 30 min in room B. PS was given to rats for 30 min every morning for 14 days. The serum corticosterone (CORT), zinc in serum and tissues, and zinc apparent absorption after PS exposure were investigated. The results showed that the serum CORT increased and serum zinc decreased after 7 and 14 days of PS treatment. The zinc concentration in the liver was increased by 14 days PS exposure, whereas its concentration in the hippocampus was decreased by 7 and 14 days of PS exposure. There were no significant changes in zinc concentration in the heart, spleen, kidney, duodenum, cortex, and cerebellum. A decrease in the zinc apparent absorption was observed in the 7- and 14-day PS groups. The increased serum CORT and liver zinc concentrations and decreased serum zinc and apparent absorption of zinc recovered to normal concentrations 7 days away from PS exposure. The results suggest that PS could induce lower serum zinc, which might be correlated with decreased zinc absorption in the small intestine and increased liver zinc accumulation after PS exposure. The consequent effects of decreased hippocampal and serum zinc and increased CORT concentration after PS exposure on stress-related diseases await further research.

The antidepressant-like effect of inosine in the FST is associated with both adenosine A1 and A 2A receptors

Inosine is an endogenous purine nucleoside, which is formed during the breakdown of adenosine. The adenosinergic system was already described as capable of modulating mood in preclinical models; we now explored the effects of inosine in two predictive models of depression: the forced swim test (FST) and tail suspension test (TST). Mice treated with inosine displayed higher anti-immobility in the FST (5 and 50 mg/kg, intraperitoneal route (i.p.)) and in the TST (1 and 10 mg/kg, i.p.) when compared to vehicle-treated groups. These antidepressant-like effects started 30 min and lasted for 2 h after intraperitoneal administration of inosine and were not accompanied by any changes in the ambulatory activity in the open-field test. Both adenosine A1 and A2A receptor antagonists prevented the antidepressant-like effect of inosine in the FST. In addition, the administration of an adenosine deaminase inhibitor (1 and 10 mg/kg, i.p.) also caused an antidepressant-like effect in the FST. These results indicate that inosine possesses an antidepressant-like effect in the FST and TST probably through the activation of adenosine A1 and A2A receptors, further reinforcing the potential of targeting the purinergic system to the management of mood disorders.

Effect of curcumin against pentylenetetrazol-induced seizure threshold in mice: possible involvement of adenosine A1 receptors

Curcumin, obtained from Curcuma longa, has been in use for manifold human disorders. The present study explores the effect of curcumin against pentylenetetrazol (PTZ) seizure threshold in mice. The possible involvement of adenosine receptor(s) mechanism was also investigated. Minimal dose of PTZ (i.v., mg/kg) needed to induce different phases of convulsions were recorded as an index of seizure threshold. Curcumin (20-120 mg/kg, p.o.) produced an increase in seizure threshold for convulsions induced by PTZ i.v. infusion. The anticonvulsant effect of curcumin (80 mg/kg) was prevented by 8-phenyltheophylline (0.5 mg/kg, i.p., non-selective adenosine receptor antagonist) and 8-cyclopentyl-1,3-dipropylxanthine (5 mg/kg, i.p., adenosine A1 receptor antagonist) but not by 8-(3-cholorostryl)caffeine (4 mg/kg, i.p., adenosine A2A receptor antagonist). Further, 5'-N-ethylcarboxamidoadenosine (0.005 mg/kg, i.p., non-selective A1 /A2 receptor agonist), or N(6) -cyclohexyladenosine (0.2 mg/kg, i.p., adenosine A1 receptor agonist), was able to potentiate the anticonvulsant action of curcumin. In contrast, 5'-(N-cyclopropyl) carboxamidoadenosine (0.1 mg/kg, i.p., adenosine A2A receptor agonist) failed to potentiate the effect of curcumin. This study demonstrated the anticonvulsant effect of curcumin against PTZ i.v. seizure threshold via a direct or indirect activation of adenosine A1 but not A2A receptors in mice. Thus, curcumin may prove to be an effective adjunct in treatment of convulsions.

Potential roles of zinc in the pathophysiology and treatment of major depressive disorder

Incomplete response to monoaminergic antidepressants in major depressive disorder (MDD), and the phenomenon of neuroprogression, suggests a need for additional pathophysiological markers and pharmacological targets. Neuronal zinc is concentrated exclusively within glutamatergic neurons, acting as an allosteric modulator of the N-methyl D-aspartate and other receptors that regulate excitatory neurotransmission and neuroplasticity. Zinc-containing neurons form extensive associational circuitry throughout the cortex, amygdala and hippocampus, which subserve mood regulation and cognitive functions. In animal models of depression, zinc is reduced in these circuits, zinc treatment has antidepressant-like effects and dietary zinc insufficiency induces depressive behaviors. Clinically, serum zinc is lower in MDD, which may constitute a state-marker of illness and a risk factor for treatment-resistance. Marginal zinc deficiency in MDD may relate to multiple putative mechanisms underlying core symptomatology and neuroprogression (e.g. immune dysfunction, monoamine metabolism, stress response dysregulation, oxidative/nitrosative stress, neurotrophic deficits, transcriptional/epigenetic regulation of neural networks). Initial randomized trials suggest a benefit of zinc supplementation. In summary, molecular and animal behavioral data support the clinical significance of zinc in the setting of MDD.

Kappa-opioid receptors mediate the antidepressant-like activity of hesperidin in the mouse forced swimming test

The opioid system has been implicated as a contributing factor for major depression and is thought to play a role in the mechanism of action of antidepressants. This study investigated the involvement of the opioid system in the antidepressant-like effect of hesperidin in the mouse forced swimming test. Our results demonstrate that hesperidin (0.1, 0.3 and 1 mg/kg; intraperitoneal) decreased the immobility time in the forced swimming test without affecting locomotor activity in the open field test. The antidepressant-like effect of hesperidin (0.3 mg/kg) in the forced swimming test was prevented by pretreating mice with naloxone (1 mg/kg, a nonselective opioid receptor antagonist) and 2-(3,4-dichlorophenyl)-Nmethyl-N-[(1S)-1-(3-isothiocyanatophenyl)-2-(1-pyrrolidinyl)ethyl] acetamide (DIPPA (1 mg/kg), a selective κ-opioid receptor antagonist), but not with naloxone methiodide (1 mg/kg, a peripherally acting opioid receptor antagonist), naltrindole (3 mg/kg, a selective δ-opioid receptor antagonist), clocinnamox (1 mg/kg, a selective μ-opioid receptor antagonist) or caffeine (3 mg/kg, a nonselective adenosine receptor antagonist). In addition, a sub-effective dose of hesperidin (0.01 mg/kg) produced a synergistic antidepressant-like effect in the forced swimming test when combined with a sub-effective dose of morphine (1 mg/kg). The antidepressant-like effect of hesperidin in the forced swimming test on mice was dependent on its interaction with the κ-opioid receptor, but not with the δ-opioid, μ-opioid or adenosinergic receptors. Taken together, these results suggest that hesperidin possesses antidepressant-like properties and may be of interest as a therapeutic agent for the treatment of depressive disorders.

Effect of zinc in animal models of anxiety, depression and psychosis

The role of zinc (Zn) in anxiety, depression and psychosis was studied in rodents. Zn was administered at doses of 15 and 20 mg/kg intraperitoneally for 7 days. Both doses of Zn reduced the immobility time and increased the swimming time in the modified forced swim test. In the elevated plus maze test, increases in the number of open arm entries and time spent in the open arms were observed with both doses of Zn. In the amphetamine (1 and 2 mg/kg subcutaneously) induced locomotor activity test both doses of Zn produced reduction in the total movement time, mean velocity and stereotypic movements. Extrapyramidal symptoms such as catalepsy in animals are usually observed with conventional antipsychotic agents; but in the present study, Zn at doses of 15 and 20 mg/kg did not produce any cataleptic state in mice. The results of the present study demonstrated the anxiolytic, antidepressant and antipsychotic-like effects of Zn metal ion, which may be due to its N-methyl d-aspartate receptor antagonistic activity. Concurrent administration of a lower dose of Zn with standard existing anxiolytic and antidepressant drugs in this study showed potentiating effect, suggesting that Zn could exert beneficial role when prescribed as add-on medicine in the psychiatric illnesses. The results obtained in this study are preliminary, as further research is required to confirm the exact role of Zn metal in the investigated central nervous system disorders.

In vitro antioxidant activity and in vivo antidepressant-like effect of α-(phenylselanyl) acetophenone in mice

In this study, the antioxidant and antidepressant-like effects of α-(phenylselanyl) acetophenone (PSAP), an organoselenium compound, were investigated. To assess the in vitro antioxidant properties, PSAP was evaluated in four test systems (DPPH, ABTS, FRAP and inhibition of lipid peroxidation). PSAP (100-500 μM) showed potent antioxidant activity and protected against lipid peroxidation. Additionally, we investigated whether PSAP, when administered in mice (100, 200 and 400mg/kg, per oral, p.o.), could cause acute toxicity. Our results demonstrated that PSAP did not cause the death of any animal, significantly reduce body weight or cause any oxidative tissue stress following treatment. This study also evaluated the effect of PSAP (0.1-10 mg/kg, p.o) on mice in a forced swim test (FST) and tail suspension test (TST), assays that are predictive of depressant activity and motor activity in the open-field. PSAP (5-10 mg/kg) significantly reduced immobility time in the FST and TST without affecting motor activity. In addition, the antidepressant-like effect caused by PSAP (5m/kg, p.o) in mice during the TST was dependent on an interaction with the serotonergic system (5-HT(1A) receptors), but not with the noradrenergic, dopaminergic or adenosinergic system. Together, these results suggest that PSAP possesses antioxidant and antidepressant-like properties and may be of interest as a therapeutic agent for the treatment of depressive disorders.

Sex-Specific Regulation of Depression, Anxiety-Like Behaviors and Alcohol Drinking in Mice Lacking ENT1

OBJECTIVES: Adenosine signaling has been implicated in the pathophysiology of several psychiatric disorders including alcoholism, depression, and anxiety. Adenosine levels are controlled in part by transport across the cell membrane by equilibrative nucleoside transporters (ENTs). Recent evidence showed that a polymorphism in the gene encoding ENT1 is associated with comorbid depression and alcoholism in women. We have previously shown that deletion of ENT1 reduces ethanol intoxication and elevates alcohol intake in mice. Interestingly, ENT1 null mice display decreased anxiety-like behavior compared to wild-type littermates. However, our behavioral studies were performed only in male mice. Here, we extend our research to include female mice, and test the effect of ENT1 knockout on other behavioral correlates of alcohol drinking, including depressive and compulsive behavior, in mice. METHODS: To assess depression-like behavior, we used a forced swim test modified for mice. We examined anxiety-like behavior and locomotor activity in open field chambers, and perseverant behavior using the marble-burying test. Finally, we investigated alcohol consumption and preference in female mice using a two-bottle choice paradigm. RESULTS: ENT1 null mice of both sexes showed reduced immobility time in the forced swim test and increased time in the center of the open field compared to wild-type littermates. ENT1 null mice of both sexes showed similar locomotor activity levels and habituation to the open field chambers. Female ENT1 null mice displayed increased marble-burying compared to female wild-types, but no genotype difference was evident in males. Female ENT1 null mice showed increased ethanol consumption and preference compared to female wild-types. CONCLUSIONS: Our findings suggest that ENT1 contributes to several important behaviors involved in psychiatric disorders. Inhibition of ENT1 may be beneficial in treating depression and anxiety, while enhancement of ENT1 function may reduce compulsive behavior and drinking, particularly in females.

Stimulant effects of adenosine antagonists on operant behavior: differential actions of selective A2A and A1 antagonists

RATIONALE

Adenosine A(2A) antagonists can reverse many of the behavioral effects of dopamine antagonists, including actions on instrumental behavior. However, little is known about the effects of selective adenosine antagonists on operant behavior when these drugs are administered alone.

OBJECTIVE

The present studies were undertaken to investigate the potential for rate-dependent stimulant effects of both selective and nonselective adenosine antagonists.

METHODS

Six drugs were tested: two nonselective adenosine antagonists (caffeine and theophylline), two adenosine A(1) antagonists (DPCPX and CPT), and two adenosine A(2A) antagonists (istradefylline (KW6002) and MSX-3). Two schedules of reinforcement were employed; a fixed interval 240-s (FI-240 sec) schedule was used to generate low baseline rates of responding and a fixed ratio 20 (FR20) schedule generated high rates.

RESULTS

Caffeine and theophylline produced rate-dependent effects on lever pressing, increasing responding on the FI-240 sec schedule but decreasing responding on the FR20 schedule. The A(2A) antagonists MSX-3 and istradefylline increased FI-240 sec lever pressing but did not suppress FR20 lever pressing in the dose range tested. In fact, there was a tendency for istradefylline to increase FR20 responding at a moderate dose. A(1) antagonists failed to increase lever pressing rate, but DPCPX decreased FR20 responding at higher doses.

CONCLUSIONS

These results suggest that adenosine A(2A) antagonists enhance operant response rates, but A(1) antagonists do not. The involvement of adenosine A(2A) receptors in regulating aspects of instrumental response output and behavioral activation may have implications for the treatment of effort-related psychiatric dysfunctions, such as psychomotor slowing and anergia in depression.

Antidepressant drugs transactivate TrkB neurotrophin receptors in the adult rodent brain independently of BDNF and monoamine transporter blockade

Background

Antidepressant drugs (ADs) have been shown to activate BDNF (brain-derived neurotrophic factor) receptor TrkB in the rodent brain but the mechanism underlying this phenomenon remains unclear. ADs act as monoamine reuptake inhibitors and after prolonged treatments regulate brain bdnf mRNA levels indicating that monoamine-BDNF signaling regulate AD-induced TrkB activation in vivo. However, recent findings demonstrate that Trk receptors can be transactivated independently of their neurotrophin ligands.

Methodology

In this study we examined the role of BDNF, TrkB kinase activity and monoamine reuptake in the AD-induced TrkB activation in vivo and in vitro by employing several transgenic mouse models, cultured neurons and TrkB-expressing cell lines.

Principal Findings

Using a chemical-genetic TrkB^F616A mutant and TrkB overexpressing mice, we demonstrate that ADs specifically activate both the maturely and immaturely glycosylated forms of TrkB receptors in the brain in a TrkB kinase dependent manner. However, the tricyclic AD imipramine readily induced the phosphorylation of TrkB receptors in conditional bdnf^−/− knock-out mice (132.4±8.5% of control; P = 0.01), indicating that BDNF is not required for the TrkB activation. Moreover, using serotonin transporter (SERT) deficient mice and chemical lesions of monoaminergic neurons we show that neither a functional SERT nor monoamines are required for the TrkB phosphorylation response induced by the serotonin selective reuptake inhibitors fluoxetine or citalopram, or norepinephrine selective reuptake inhibitor reboxetine. However, neither ADs nor monoamine transmitters activated TrkB in cultured neurons or cell lines expressing TrkB receptors, arguing that ADs do not directly bind to TrkB.

Conclusions

The present findings suggest that ADs transactivate brain TrkB receptors independently of BDNF and monoamine reuptake blockade and emphasize the need of an intact tissue context for the ability of ADs to induce TrkB activity in brain.

Role of zinc in the development and treatment of mood disorders

PURPOSE OF REVIEW

The present review is a critical examination of the most recent published work on the role of zinc in the development and treatment of mood disorders.

RECENT FINDINGS

Clinical studies and experimental work using animal models have both revealed a link between zinc status and neuropsychological disorders such as depression and anxiety. Not only has zinc deficiency been shown to induce depression-like and anxiety-like behaviors, supplementation has been used as a treatment for major depression. Zinc administration improves the efficacy of antidepressant drugs in depressed patients and may have a particular role to play in treatment-resistant patients. Recent investigations into the molecular mechanisms responsible for these observations suggest a role for zinc in the regulation of neurotransmitter systems, antioxidant mechanisms, neurotrophic factors, and neuronal precursor cells.

SUMMARY

The data reviewed here not only indicate a role for zinc deficiency in the development of mood disorders, but also show that zinc may also be important in their treatment. Given the prevalence of zinc deficiency in human populations, this work has the potential to influence strategies to prevent and treat these disorders.

Differential effects of selective adenosine antagonists on the effort-related impairments induced by dopamine D1 and D2 antagonism

Mesolimbic dopamine (DA) is a critical component of the brain circuitry regulating behavioral activation and effort-related processes. Rats with impaired DA transmission reallocate their instrumental behavior away from food-reinforced tasks with high response requirements, and instead select less effortful food-seeking behaviors. Previous work showed that adenosine A(2A) antagonists can reverse the effects of DA D(2) antagonists on effort-related choice. However, less is known about the effects of adenosine A(1) antagonists. Despite anatomical data showing that A(1) and D(1) receptors are co-localized on the same striatal neurons, it is uncertain if A(1) antagonists can reverse the effects DA D(1) antagonists. The present work systematically compared the ability of adenosine A(1) and A(2A) receptor antagonists to reverse the effects of DA D(1) and D(2) antagonists on a concurrent lever pressing/feeding choice task. With this procedure, rats can choose between responding on a fixed ratio 5 lever-pressing schedule for a highly preferred food (i.e. high carbohydrate pellets) vs. approaching and consuming a less preferred rodent chow. The D(1) antagonist ecopipam (0.2 mg/kg i.p.) and the D(2) antagonist eticlopride (0.08 mg/kg i.p.) altered choice behavior, reducing lever pressing and increasing lab chow intake. Co-administration of the adenosine A(1) receptor antagonists 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.375, 0.75, and 1.5 mg/kg i.p.), and 8-cyclopentyltheophylline (CPT; 3.0, 6.0, 12.0 mg/kg i.p.) failed to reverse the effects of either the D(1) or D(2) antagonist. In contrast, the adenosine A(2A) antagonist KW-6002 (0.125, 0.25 and 0.5 mg/kg i.p.) was able to produce a robust reversal of the effects of eticlopride, as well as a mild partial reversal of the effects of ecopipam. Adenosine A(2A) and DA D(2) receptors interact to regulate effort-related choice behavior, which may have implications for the treatment of psychiatric symptoms such as psychomotor slowing, fatigue or anergia that can be observed in depression and other disorders.

Oral tremor induced by the muscarinic agonist pilocarpine is suppressed by the adenosine A2A antagonists MSX-3 and SCH58261, but not the adenosine A1 antagonist DPCPX

Tremulous jaw movements in rats, which can be induced by dopamine (DA) antagonists, DA depletion, and cholinomimetics, have served as a useful model for studies of tremor. Although adenosine A(2A) antagonists can reduce the tremulous jaw movements induced by DA antagonists and DA depletion, there are conflicting reports about the interaction between adenosine antagonists and cholinomimetic drugs. The present studies investigated the ability of adenosine antagonists to reverse the tremorogenic effect of the muscarinic agonist pilocarpine. While the adenosine A(2A) antagonist MSX-3 was incapable of reversing the tremulous jaw movements induced by the 4.0mg/kg dose of pilocarpine, both MSX-3 and the adenosine A(2A) antagonist SCH58261 reversed the tremulous jaw movements elicited by 0.5mg/kg pilocarpine. Systemic administration of the adenosine A(1) antagonist DPCPX failed to reverse the tremulous jaw movements induced by either an acute 0.5mg/kg dose of the cholinomimetic pilocarpine or the DA D2 antagonist pimozide, indicating that the tremorolytic effects of adenosine antagonists may be receptor subtype specific. Behaviorally active doses of MSX-3 and SCH 58261 showed substantial in vivo occupancy of A(2A) receptors, but DPCPX did not. The results of these studies support the use of adenosine A(2A) antagonists for the treatment of tremor.

Cannabidiol ameliorates cognitive and motor impairments in mice with bile duct ligation

BACKGROUND/AIMS

The endocannabinoid system in mice plays a role in models of human cirrhosis and hepatic encephalopathy (HE), induced by a hepatotoxin. We report now the therapeutic effects of cannabidiol (CBD), a non-psychoactive constituent of Cannabis sativa, on HE caused by bile duct ligation (BDL), a model of chronic liver disease.

METHODS

CBD (5mg/kg; i.p.) was administered over 4weeks to mice that had undergone BDL.

RESULTS

Cognitive function in the eight arm maze and the T-maze tests, as well as locomotor function in the open field test were impaired by the ligation and were improved by CBD. BDL raised hippocampal expression of the TNF-alpha-receptor 1 gene, which was reduced by CBD. However, BDL reduced expression of the brain-derived neurotrophic factor (BDNF) gene, which was increased by CBD. The effects of CBD on cognition, locomotion and on TNF-alpha receptor 1 expression were blocked by ZM241385, an A(2)A adenosine receptor antagonist. BDL lowers the expression of this receptor.

CONCLUSIONS

The effects of BDL apparently result in part from down-regulation of A(2)A adenosine receptor. CBD reverses these effects through activation of this receptor, leading to compensation of the ligation effect.

Differential actions of adenosine A1 and A2A antagonists on the effort-related effects of dopamine D2 antagonism

Adenosine and dopamine receptors in striatal areas interact to regulate a number of different functions, including aspects of motor control and motivation. Recent studies indicate that adenosine A(2A) receptor antagonists can reverse the effects of dopamine (DA) D(2) antagonists on instrumental tasks that provide measures of effort-related choice behavior. The present experiments compared the ability of the adenosine A(2A) antagonist KW6002, the nonselective adenosine antagonist caffeine, and the adenosine A(1) receptor selective antagonist DPCPX, to reverse the behavioral effects of the DA D(2) antagonist haloperidol. For these studies, a concurrent choice procedure was used in which rats could select between lever pressing on a fixed ratio 5 schedule for a preferred food or approaching and consuming a less preferred lab chow that was concurrently available in the chamber. Under baseline or control conditions, rats show a strong preference for lever pressing, and eat little of the chow; IP injections of 0.1 mg/kg haloperidol significantly reduced lever pressing and substantially increased chow intake. The adenosine A(2A) antagonist KW6002 (0.125-0.5 mg/kg IP) and the nonselective adenosine antagonist caffeine (5.0-20.0 mg/kg) significantly reversed the effects of haloperidol. However, the adenosine A(1) antagonist DPCPX (0.1875-0.75 mg/kg IP) failed to reverse the effects of the D(2) antagonist. The rank order of effect sizes in the reversal experiments was KW6002>caffeine>DPCPX. None of these drugs had any effect on behavior when they were injected in the absence of haloperidol. These results indicate that the ability of an adenosine antagonist to reverse the effort-related effects of a D(2) antagonist depends upon the subtype of adenosine receptor being blocked. Together with other recent results, these experiments indicate that there is a specific interaction between DA D(2) and adenosine A(2A) receptors, which could be related to the co-localization of these receptors on the same population of striatal neurons.

The adenosine A2A antagonist MSX-3 reverses the effects of the dopamine antagonist haloperidol on effort-related decision making in a T-maze cost/benefit procedure

RATIONALE

Mesolimbic dopamine (DA) is a critical component of the brain circuitry regulating behavioral activation and effort-related processes. Research involving choice tasks has shown that rats with impaired DA transmission reallocate their instrumental behavior away from food-reinforced tasks with high response requirements and instead select less effortful food-seeking behaviors.

OBJECTIVE

Previous work showed that adenosine A(2A) antagonism can reverse the effects of the DA antagonist haloperidol in an operant task that assesses effort-related choice. The present work used a T-maze choice procedure to assess the effects of adenosine A(2A) and A(1) antagonism.

MATERIALS AND METHODS

With this task, the two arms of the maze have different reinforcement densities (four vs. two food pellets), and a vertical 44 cm barrier is positioned in the arm with the higher density, presenting the animal with an effort-related challenge. Untreated rats strongly prefer the arm with the high density of food reward and climb the barrier in order to obtain the food.

RESULTS

Haloperidol produced a dose-related (0.05-0.15 mg/kg i.p.) reduction in the number of trials in which the rats chose the high-barrier arm. Co-administration of the adenosine A(2A) receptor antagonist MSX-3 (0.75, 1.5, and 3.0 mg/kg i.p.), but not the A(1) antagonist 8-cyclopentyl-1,3-dipropylxanthine (0.75, 1.5, and 3.0 mg/kg i.p.), reversed the effects of haloperidol on effort-related choice and latency.

CONCLUSIONS

Adenosine A(2A) and D2 receptors interact to regulate effort-related decision making, which may have implications for the treatment of psychiatric symptoms such as psychomotor slowing or anergia that can be observed in depression, parkinsonism, and other disorders.

The involvement of serotonergic system in the antidepressant effect of zinc in the forced swim test

Recent preclinical data indicated the antidepressant-like activity of zinc in different tests and models of depression. The present study investigates the involvement of the serotonergic system in zinc activity in the forced swim test (FST) in mice and rats. The combined treatment of sub-effective doses of zinc (hydroaspartate, 2.5 mg Zn/kg) and citalopram (15 mg/kg), fluoxetine (5 mg/kg) but not with reboxetine (2.5 mg/kg) significantly reduces the immobility time in the FST in mice. These treatments had no influence on the spontaneous locomotor activity. Moreover, while the antidepressant-like effect of zinc (5 mg/kg) in the FST was significantly blocked by pretreatment with inhibitor of serotonin synthesis, p-chlorophenylalanine (pCPA, 3x200 mg/kg), 5HT-2(A/C) receptor antagonist, ritanserin (4 mg/kg) or 5HT-1A receptor antagonist, WAY 1006335 (0.1 mg/kg), the zinc-induced reduction in the locomotor activity was not affected by these serotonin modulator agents. These results indicate the specific involvement of the serotonergic system in antidepressant but not the motion behavior of zinc in mice. Also, an increase in the swimming but not climbing parameter of the rat FST observed following zinc administration (2.5 and 5 mg Zn/kg) indicates the serotonin pathway participation. This present data indicates that the antidepressant-like activity of zinc observed in the FST involves interaction with the serotonergic system.

Role of zinc in maternal and child mental health

Mental health problems in women, children, and adolescents are a significant public health issue. Given current barriers to the effective treatment of these problems, researchers are looking to the field of nutrition for potential alternatives to better understand and address mental health issues. The purpose of this article was to review current evidence on the relation between zinc and mental health disorders with a focus on 2 mental health problems that commonly affect women and children: depression and attention-deficit hyperactivity disorder (ADHD). A literature search of the databases Medline and PsychInfo was conducted with the use of key terms. The review included articles from 1975 to May 2008, but focused on articles published in recent years. Relations between zinc concentrations and behavior in animals; the relation between zinc deficiency, depression, and ADHD in patient and community samples; and the potential biological mechanisms for these relations were explored. The data support a relation between low concentrations of zinc and mental health problems, especially in at-risk populations. Evidence for the potential use of zinc in treating mental health problems comes mainly from patient populations and is strongest when zinc is given in combination with pharmacologic treatment. Less conclusive evidence exists for the effectiveness of zinc alone or in general community samples. Recommendations for further research in this area are provided.