Requirement of hippocampal DG nNOS-CAPON dissociation for the anxiolytic and antidepressant effects of fluoxetine.

Background: Adult hippocampal neurogenesis and synaptic plasticity are necessary for the behavioral response to the selective serotonin reuptake inhibitor (SSRI) fluoxetine, but the molecular mechanisms underlying these effects are only partially understood. Methods: Anxiety and depressive-like behaviors in mice were developed by chronic mild stress (CMS) or chronic corticosterone (CORT) treatment. Pharmacological and genetic approaches were used to investigate the role of the neuronal nitric oxide synthase (nNOS)-carboxy-terminal PDZ ligand of nNOS (CAPON) interaction in behavioral and neuroplasticity effects of serotoninergic system. Molecular biological and morphological studies were performed to examine the mechanisms underlying the behavioral effects of nNOS-CAPON interaction that modulated by 5-HT1A receptor (5-HT1AR). Results: Fluoxetine prevented chronic stress-induced nNOS-CAPON upregulation and coupling in the dentate gyrus (DG), and promoting nNOS-CAPON association weakened the anxiolytic and antidepressant effects of fluoxetine in stressed mice. The chronic fluoxetine elevated 5-HT and 5HT1AR agonist 8-OH-DPAT decreased the expression and binding of nNOS with CAPON, whereas 5-HT1AR antagonist NAN-190 had the opposite effects. Importantly, augmenting nNOS-CAPON binding neutralized 8-OH-DPAT-upregulated spine density of DG granule cells and well-characterized synaptic-related proteins, including brain-derived neurotrophic factor (BDNF) and phosphorylation of extracellular signal regulated kinase (ERK), cAMP-response element binding protein (CREB), and synapsin in the DG and abolished the anxiolytic and antidepressant-like effects of 8-OH-DPAT. In contrast, dissociation of nNOS from CAPON rescued the effects of NAN-190 on behavior and neuroplasticity. Conclusion: Taken together, our results indicated that fluoxetine modifies mood behaviors and hippocampal neuroplasticity by disrupting the nNOS-CAPON interaction that links postsynaptic 5-HT1AR activation.

Hippocampal nuclear factor kappa B accounts for stress-induced anxiety behaviors via enhancing neuronal nitric oxide synthase (nNOS)-carboxy-terminal PDZ ligand of nNOS-Dexras1 coupling.

Anxiety disorders are associated with a high social burden worldwide. Recently, increasing evidence suggests that nuclear factor kappa B (NF-κB) has significant implications for psychiatric diseases, including anxiety and depressive disorders. However, the molecular mechanisms underlying the role of NF-κB in stress-induced anxiety behaviors are poorly understood. In this study, we show that chronic mild stress (CMS) and glucocorticoids dramatically increased the expression of NF-κB subunits p50 and p65, phosphorylation and acetylation of p65, and the level of nuclear p65 in vivo and in vitro, implicating activation of NF-κB signaling in chronic stress-induced pathological processes. Using the novelty-suppressed feeding (NSF) and elevated-plus maze (EPM) tests, we found that treatment with pyrrolidine dithiocarbamate (PDTC; intra-hippocampal infusion), an inhibitor of NF-κB, rescued the CMS- or glucocorticoid-induced anxiogenic behaviors in mice. Microinjection of PDTC into the hippocampus reversed CMS-induced up-regulation of neuronal nitric oxide synthase (nNOS), carboxy-terminal PDZ ligand of nNOS (CAPON), and dexamethasone-induced ras protein 1 (Dexras1) and dendritic spine loss of dentate gyrus (DG) granule cells. Moreover, over-expression of CAPON by infusing LV-CAPON-L-GFP into the hippocampus induced nNOS-Dexras1 interaction and anxiety-like behaviors, and inhibition of NF-κB by PDTC reduced the LV-CAPON-L-GFP-induced increases in nNOS-Dexras1 complex and anxiogenic-like effects in mice. These findings indicate that hippocampal NF-κB mediates anxiogenic behaviors, probably via regulating the association of nNOS-CAPON-Dexras1, and uncover a novel approach to the treatment of anxiety disorders.

L-Tetrahydropalmatine alleviates mechanical hyperalgesia in models of chronic inflammatory and neuropathic pain in mice.

Chronic pain is categorized as inflammatory and neuropathic, and there are common mechanisms underlying the generation of each pain state. Such pain is difficult to treat and the treatment at present is inadequate. Corydalis yanhusuo is a traditional Chinese medicine with demonstrated analgesic efficacy in humans. The potential antihyperalgesic effect of its active component is L-tetrahydropalmatine (L-THP). L-THP has been used for the treatment of headache and other mild pain. However, little is known about its analgesic effect on chronic pain and its mechanism. Here, we report that L-THP exerts remarkable antihyperalgesic effects on neuropathic and inflammatory pain in animal models. Neuropathic hypersensitivity was induced by segmental spinal nerve ligation and inflammatory hypersensitivity was induced by an intraplantar injection of complete Freund's adjuvant. To determine the receptor mechanism underlying the antihyperalgesic actions of L-THP, we used SCH23390, an antagonist of a dopamine D1 receptor, in an attempt to block the antihyperalgesic effects of L-THP. We found that L-THP (1-4 mg/kg, i.p.) produced a dose-dependent antihyperalgesic effect in spinal nerve ligation and complete Freund's adjuvant models. The antihyperalgesic effects of L-THP were abolished by a dopamine D1 receptor antagonist SCH23390 (0.02 mg/kg). Furthermore, L-THP (4 mg/kg, i.p.) did not influence motor function. These findings suggest that L-THP may ameliorate mechanical hyperalgesia by enhancing dopamine D1 receptor-mediated dopaminergic transmission.

Hippocampal nitric oxide contributes to sex difference in affective behaviors.

Mechanisms underlying the female preponderance in affective disorders are poorly understood. Here we show that hippocampal nitric oxide (NO) plays a role in the sex difference of depression-like behaviors in rodents. Female mice had substantially lower NO production in the hippocampus and were significantly more likely to display negative affective behaviors than their male littermates. Eliminating the difference in the basal hippocampal NO level between male and female mice mended the sex gap of affective behaviors. Estradiol exerted a positive control on hippocampal NO production via estrogen receptor-ß-mediated neuronal NO synthase expression. Thus, low estrogen in the female hippocampus accounts for lower local NO than in the male hippocampus. Although estrogen has important significance in modulating affective behaviors, it is not estrogen but NO in the hippocampus that mediates the sex difference of affective behaviors directly, because hippocampal NO was necessary for the behavioral effects of estradiol, and NO was an independent factor in modulating behaviors. Stress promoted hippocampal NO production in males because of glucocorticoid release, thus leading to local NO excess. In contrast, stress suppressed NO production in females because of decreased estrogen, thereby resulting in hippocampal NO shortage. Whereas activating cAMP response element binding protein (CREB) rescued the depression-like effects of the intrahippocampal NO donor diethylenetriamine/nitric oxide adduct (DETA/NONOate), inactivating CREB abolished the antidepressant-like effects of the intrahippocampal NO donor DETA/NONOate. Our findings suggest a molecular mechanism underlying the sex difference of affective behaviors.

Hippocampal telomerase is involved in the modulation of depressive behaviors.

Telomere and telomerase alterations have been reported in mood disorders. However, the role of telomerase in depression remains unclear. Here we show that chronic mild stress (CMS) led to a significant decrease in telomerase reverse transcriptase (TERT) level and telomerase activity in the hippocampus. Treatment with antidepressant fluoxetine reversed the CMS-induced TERT and telomerase activity changes. Inhibiting telomerase by systemic administration (100 mg · kg(-1) · d(-1), i.p., for 14 d), intrahippocampal microinjection (0.7 µmol, 2 µl), or infusion (using an osmotic minipump, 0.134 µg/µl, 0.25 µl/h) of 3'-azido-deoxythymidine (AZT) resulted in depression-like behaviors and impaired hippocampal neurogenesis in mice. In contrast, overexpressing telomerase by intrahippocampal infusion of recombinant adenovirus vector expressing mouse TERT (Ad-mTERT-GFP) led to neurogenesis upregulation, produced antidepressant-like behaviors, and prevented the CMS-induced behavioral modifications. Disrupting neurogenesis in the dentate gyrus by X-irradiation (15 Gy) of a restricted region of mouse brain containing the hippocampus abolished the antidepressant-like effect of Ad-mTERT-GFP. Additionally, AZT had no effect on DNA polymerase activity and did not cause cell damage in vitro and in vivo. Microinjection of AZT into the subventricular zone of lateral ventricle (0.7 µmol, 2 µl) inhibited local neurogenesis but had no behavioral effect. These results suggest that hippocampal telomerase is involved in the modulation of depression-related behaviors, possibly by regulating adult neurogenesis.

Neuronal nitric oxide synthase alteration accounts for the role of 5-HT1A receptor in modulating anxiety-related behaviors.

Increasing evidence suggests that 5-HT(1A) receptor (5-HT(1A)R) is implicated in anxiety disorders. However, the mechanism underlying the role of 5-HT(1A)R in these diseases remains unknown. Here, we show that 5-HT(1A)R-selective agonist 8-OH-DPAT and selective serotonin reuptake inhibitor (SSRI) fluoxetine downregulated hippocampal neuronal nitric oxide synthase (nNOS) expression, whereas 5-HT(1A)R-selective antagonist NAN-190 upregulated hippocampal nNOS expression. By assessing anxiety-related behaviors using the novelty suppressed feeding, open-field, and elevated plus maze tests, we show that mice lacking nNOS gene [knock-out (KO)] or treated with nNOS-selective inhibitor 7-nitroindazole (7-NI; i.p., 30 mg/kg/d for 28 d; or intrahippocampal microinjection, 16.31 microg/1.0 microl) displayed an anxiolytic-like phenotype, implicating nNOS in anxiety. We also show that, in wild-type (WT) mice, administrations of 8-OH-DPAT (i.p., 0.1 mg/kg/d) or fluoxetine (i.p., 10 mg/kg/d) for 28 d caused anxiolytic-like effects, whereas NAN-190 (i.p., 0.3 mg/kg/d for 28 d) caused anxiogenic-like effects. In KO mice, however, these drugs were ineffective. Moreover, intrahippocampal infusion of 8-OH-DPAT (45.963 microg/100 microl) using 14 d osmotic minipump produced anxiolytic effects. Intrahippocampal microinjection of 7-NI (16.31 microg/1.0 microl) abolished the anxiogenic-like effects of intrahippocampal NAN-190 (4.74 microg/1.0 microl). Additionally, NAN-190 decreased and 8-OH-DPAT increased phosphorylated cAMP response element-binding protein (CREB) levels in WT mice but not in KO mice. Blockade of hippocampal CREB phosphorylation by microinjection of H89 (5.19 microg/1.0 microl), a PKA (protein kinase A) inhibitor, abolished the anxiolytic-like effects of 7-NI (i.p., 30 mg/kg/d for 21 d). These findings indicate that both hippocampal nNOS and CREB activity mediate the anxiolytic effects of 5-HT(1A)R agonists and SSRIs.