Neuronal Nitric Oxide Synthase Alteration Accounts for the Role of 5-HT1A Receptor in Modulating Anxiety-Related Behaviors

Increasing evidence suggests that 5-HT1A receptor (5-HT1AR) is implicated in anxiety disorders. However, the mechanism underlying the role of 5-HT1AR in these diseases remains unknown. Here, we show that 5-HT1AR-selective agonist 8-OH-DPAT and selective serotonin reuptake inhibitor (SSRI) fluoxetine downregulated hippocampal neuronal nitric oxide synthase (nNOS) expression, whereas 5-HT1AR-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 mu g/1.0 mu l) 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 mu g/100 mu l) using 14 d osmotic minipump produced anxiolytic effects. Intrahippocampal microinjection of 7-NI (16.31 mu g/1.0 mu l) abolished the anxiogenic-like effects of intrahippocampal NAN-190 (4.74 mu g/1.0 mu l). 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 mu g/1.0 mu l), 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-HT1AR agonists and SSRIs.