- Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology
- Published about 6 years ago
Adult neurogenesis in the hippocampal subgranular zone (SGZ) and the anterior subventricular zone (SVZ) is regulated by multiple factors, including neurotransmitters, hormones, stress, aging, voluntary exercise, environmental enrichment, learning, and ischemia. Chronic treatment with selective serotonin reuptake inhibitors (SSRIs) modulates adult neurogenesis in the SGZ, the neuronal area that is hypothesized to mediate the antidepressant effects of these substances. Layer 1 inhibitory neuron progenitor cells (L1-INP cells) were recently identified in the adult cortex, but it remains unclear what factors other than ischemia affect the neurogenesis of L1-INP cells. Here, we show that chronic treatment with an SSRI, fluoxetine (FLX), stimulated the neurogenesis of gamma-aminobutyric acid (GABA)ergic interneurons from L1-INP cells in the cortex of adult mice. Immunofluorescence and genetic analyses revealed that FLX treatment increased the number of L1-INP cells in all examined cortical regions in a dose-dependent manner. Furthermore, enhanced Venus reporter expression driven by the synapsin I promoter demonstrated that GABAergic interneurons were derived from retrovirally labeled L1-INP cells. In order to assess if these new GABAergic interneurons possess physiological function, we examined the their effect on apoptosis surrounding areas following ischemia. Intriguingly, the number of neurons expressing the apoptotic marker, active caspase-3, was significantly lower in adult mice pretreated with FLX. Our findings indicate that FLX stimulates the neurogenesis of cortical GABAergic interneurons, which might have, at least, some functions, including a suppressive effect on apoptosis induced by ischemia.Neuropsychopharmacology accepted article preview online, 4 January 2013; doi:10.1038/npp.2013.2.
Current antidepressants used to treat pediatric patients have the disadvantage of limited efficacy and potentially serious side effects. The purpose of this study was to assess the efficacy of vitamin C as an adjuvant agent in the treatment of pediatric major depressive disorder in a six-month, double-blind, placebo-controlled pilot trial.
Antidepressant drugs such as selective serotonin re-uptake inhibitors (SSRIs) remediate negative biases in emotional processing in depressed patients in both behavioural and neural outcome measures. However, it is not clear if these effects occur before, or as a consequence of, changes in clinical state. Method In the present study, we investigated the effects of short-term SSRI treatment in depressed patients on the neural response to fearful faces prior to clinical improvement in mood. Altogether, 42 unmedicated depressed patients received SSRI treatment (10 mg escitalopram daily) or placebo in a randomised, parallel-group design. The neural response to fearful and happy faces was measured on day 7 of treatment using functional magnetic resonance imaging. A group of healthy controls was imaged in the same way.
The melanocortin-4 receptor (MC4R) is well recognized as an important mediator of body weight homeostasis. Activation of MC4R causes dramatic weight loss in rodent models, and mutations in human are associated with obesity. This makes MC4R a logical target for pharmacological therapy for the treatment of obesity. However, previous studies in rodents and humans have observed a broad array of side effects caused by acute treatment with MC4R agonists, including increased heart rate and blood pressure. We demonstrate that treatment with a highly-selective novel MC4R agonist (BIM-22493 or RM-493) resulted in transient decreases in food intake (35%), with persistent weight loss over 8 weeks of treatment (13.5%) in a diet-induced obese nonhuman primate model. Consistent with weight loss, these animals significantly decreased adiposity and improved glucose tolerance. Importantly, we observed no increases in blood pressure or heart rate with BIM-22493 treatment. In contrast, treatment with LY2112688, an MC4R agonist previously shown to increase blood pressure and heart rate in humans, caused increases in blood pressure and heart rate, while modestly decreasing food intake. These studies demonstrate that distinct melanocortin peptide drugs can have widely different efficacies and side effects.
The drug 4-methylmethcathinone (4-MMC; aka, mephedrone, MMCAT, “plant food”, “bath salts”) is a recent addition to the list of popular recreational psychomotor-stimulant compounds. Relatively little information about this drug is available in the scientific literature, but popular media reports have driven recent drug control actions in the UK and several US States. Online user reports of subjective similarity to 3,4-methylenedioxymethamphetamine (MDMA, “Ecstasy”) prompted the current investigation of the thermoregulatory and locomotor effects of 4-MMC. Male Wistar and Sprague-Dawley rats were monitored after subcutaneous administration of 4-MMC (1-10 mg/kg ) using an implantable radiotelemetry system under conditions of low (23°C) and high (27°C) ambient temperature. A reliable reduction of body temperature was produced by 4-MMC in Wistar rats at 23°C or 27°C with only minimal effect in Sprague-Dawley rats. Increased locomotor activity was observed after 4-MMC administration in both strains with significantly more activity produced in the Sprague-Dawley strain. The 10 mg/kg s.c. dose evoked greater increase in extracellular serotonin, compared with dopamine, in the nucleus accumbens. Follow-up studies confirmed that the degree of locomotor stimulation produced by 10 mg/kg 4-MMC was nearly identical to that produced by 1 mg/kg d-methamphetamine in each strain. Furthermore, hypothermia produced by the serotonin 1(A/7) receptor agonist 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) was similar in each strain. These results show that the cathinone analog 4-MMC exhibits thermoregulatory and locomotor properties that are distinct from those established for methamphetamine or MDMA in prior work, despite recent evidence of neuropharmacological similarity with MDMA.
To investigate the proposed synergistic teratogenic effect of use of selective serotonin receptor inhibitors (SSRI) together with sedatives or hypnotics, primarily benzodiazepines, during pregnancy.
Reversal of dopamine d2 agonist-induced inhibition of ventral tegmental area neurons by gq-linked neurotransmitters is dependent on protein kinase C, g protein-coupled receptor kinase, and dynamin
- The Journal of pharmacology and experimental therapeutics
- Published over 6 years ago
Dopaminergic neurons of the ventral tegmental area are important components of brain pathways related to addiction. Prolonged exposure of these neurons to moderate concentrations of dopamine (DA) decreases their sensitivity to inhibition by DA, a process called DA-inhibition reversal (DIR). DIR is mediated by phospholipase C and conventional subtype of protein kinase C (cPKC) through concurrent stimulation of D2 and D1-like DA receptors, or by D2 stimulation concurrent with activation of 5-HT(2) or neurotensin receptors. In the present study, we further characterized this phenomenon by use of extracellular recordings in brain slices to examine whether DIR is linked to G protein-coupled receptor kinase-2 (GRK2) or dynamin by assessing DIR in the presence of antagonists of these enzymes. DIR was blocked by β-ARK1 inhibitor, which inhibits GRK2, and by dynasore, which blocks dynamin. Reversal of inhibition by D2 agonist quinpirole was produced by serotonin (50 µM) and by neurotensin (5-10 nM). Serotonin-induced or neurotensin-induced reversal was blocked by β-ARK1 inhibitor, dynasore, or cPKC antagonist 5,6,7,13-tetrahydro-13-methyl-5-oxo-12H-indolo[2,3-a]pyrrolo[3,4c]carbazole-12-propanenitrile (Gö6976). This further characterization of DIR indicates that cPKC, GRK2, and dynamin play important roles in the desensitization of D2 receptors. As drugs of abuse produce persistent increases in DA concentration in the ventral tegmental area, reduction of D2 receptor sensitivity as a result of drug abuse may be a critical factor in the processes of addiction.
Selective serotonin reuptake inhibitors (SSRIs) are antidepressants used for the treatment of mood and anxiety disorders. Here we demonstrate that incubation (2 h) of murine islets or Min6 β cell line with the SSRIs paroxetine, fluoxetine or sertraline inhibited insulin-induced Tyr phosphorylation of insulin receptor substrate (IRS)-2 protein and the activation of its downstream targets Akt and S6K1. Inhibition was dose-dependent with half-maximal effects at ~15-20 μM. It correlated with a rapid phosphorylation and activation of the IRS kinase GSK3β. Introduction of GSK3β-siRNAs eliminated the inhibitory effects of the SSRIs. Inhibition of IRS-2 action by 30 μM SSRIs was associated with a marked inhibition of glucose-stimulated insulin secretion from murine and human pancreatic islets. Secretion induced by basic secretagogues (KCl and Arg) was not affected by these drugs. Prolonged treatment (16h) of Min6 cells with sertraline resulted in the induction of iNOS; activation of an ER stress and the initiation of the Unfolded Protein Response (UPR), manifested by enhanced transcription of ATF4 and CHOP. This triggered an apoptotic process, manifested by enhanced caspase 3/7 activity, that resulted in beta cell death. These findings implicate SSRIs as inhibitors of IRS protein function and insulin action through the activation of GSK3β. They further suggest that SSRIs inhibit insulin secretion; induce the UPR; activate an apoptotic process and trigger beta cell death. Given that SSRIs promote insulin resistance while inhibiting insulin secretion, these drugs might accelerate the transition from an insulin resistant state to overt diabetes.
Purinergic signaling contributes significantly to pain mechanisms, and the nociceptor-specific P2X3 ATP receptor channel is considered a target in pain therapeutics. Recent evidence for co-expression of metabotropic P2Y receptors with P2X3 suggests that ATP release triggers the activation of both ionotropic and metabotropic purinoceptors, with strong potential for functional interaction. Modulation of native P2X3 function by P2Y receptor activation was investigated in rat dorsal root ganglia (DRG) neurons using whole-cell patch-clamp recordings. Application of the selective P2Y receptor agonist UTP decreased peak amplitudes of α,β-meATP-evoked homomeric P2X3-mediated currents, but had no effect on heteromeric P2X2/3-mediated currents. Treatment with phospholipase C (PLC) inhibitor U73122 significantly reversed P2X3 current inhibition induced by UTP-sensitive P2Y receptor activation. We previously reported the modulation of P2X receptors by phospholipids in DRG neurons and injection of exogenous phosphatidylinositol-4,5-bisphosphate (PIP2) fully reverses UTP-mediated regulation of P2X3 channel activity. Pharmacological as well as functional screening of P2Y receptor subtypes indicates the predominant involvement of P2Y2 receptor in P2X3 inhibition and immunolocalization confirms a significant cellular co-expression of P2X3 and P2Y2 in rat DRG neurons. In summary, the function of P2X3 ATP receptor can be inhibited by P2Y2-mediated depletion of PIP2. We propose that expression of P2Y2 purinoceptor in nociceptive sensory neurons provides an homeostatic mechanism to prevent excessive ATP signaling through P2X3 receptor channels.
BACKGROUND: Brazilin, isolated from the heartwood of Caesalpinia sappan L., has been shown to possess multiple pharmacological properties. METHODS: In this study, platelet aggregation, flow cytometry, immunoblotting analysis, and electron spin resonance (ESR) spectrometry were used to investigate the effects of brazilin on platelet activation ex vivo. Moreover, fluorescein sodium-induced platelet thrombi of mesenteric microvessels was also used in in vivo study. RESULTS: We demonstrated that relatively low concentrations of brazilin (1 to 10 muM) potentiated platelet aggregation induced by collagen (0.1 mug/ml) in washed human platelets. Higher concentrations of brazilin (20 to 50 muM) directly triggered platelet aggregation. Brazilin-mediated platelet aggregation was slightly inhibited by ATP (an antagonist of ADP). It was not inhibited by yohimbine (an antagonist of epinephrine), by SCH79797 (an antagonist of thrombin protease-activated receptor [PAR] 1), or by tcY-NH2 (an antagonist of PAR 4). Brazilin did not significantly affect FITC-triflavin binding to the integrin alphaIIbbeta3 in platelet suspensions. Pretreatment of the platelets with caffeic acid phenethyl ester (an antagonist of collagen receptors) or JAQ1 and Sam.Q4 monoclonal antibodies raised against collagen receptor glycoprotein VI and integrin alpha2beta1, respectively, abolished platelet aggregation stimulated by collagen or brazilin. The immunoblotting analysis showed that brazilin stimulated the phosphorylation of phospholipase C (PLC)gamma2 and Lyn, which were significantly attenuated in the presence of JAQ1 and Sam.Q4. In addition, brazilin did not significantly trigger hydroxyl radical formation in ESR analysis. An in vivo mouse study showed that brazilin treatment (2 and 4 mg/kg) significantly shortened the occlusion time for platelet plug formation in mesenteric venules. CONCLUSION: To the best of our knowledge, this study provides the first evidence that brazilin acts a novel collagen receptor agonist. Brazilin is a plant-based natural product, may offer therapeutic potential as intended anti-thrombotic agents for targeting of collagen receptors or to be used a useful tool for the study of detailed mechanisms in collagen receptors-mediated platelet activation.