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  • Title: Acute 5-HT₁A autoreceptor knockdown increases antidepressant responses and serotonin release in stressful conditions.
    Author: Ferrés-Coy A, Santana N, Castañé A, Cortés R, Carmona MC, Toth M, Montefeltro A, Artigas F, Bortolozzi A.
    Journal: Psychopharmacology (Berl); 2013 Jan; 225(1):61-74. PubMed ID: 22820867.
    Abstract:
    RATIONALE: Identifying the etiological factors in anxiety and depression is critical to develop more efficacious therapies. The inhibitory serotonin(1A) receptors (5-HT(1A)R) located on 5-HT neurons (autoreceptors) limit antidepressant responses and their expression may be increased in treatment-resistant depressed patients. OBJECTIVES: Recently, we reported that intranasal administration of modified small interference RNA (siRNA) molecules targeting 5-HT(1A)R in serotonergic neurons evoked antidepressant-like effects. Here we extended this finding using marketed siRNAs against 5-HT(1A)R (1A-siRNA) to reduce directly the 5-HT(1A) autoreceptor expression and evaluate its biological consequences under basal conditions and in response to stressful situations. METHODS: Adult mice were locally infused with vehicle, nonsense siRNA, and 1A-siRNA into dorsal raphe nucleus (DR). 5-HT(1A)R knockout mice (1A-KO) were also used. Histological approaches, in vivo microdialysis, and stress-related behaviors were performed to assess the effects of 5-HT(1A) autoreceptor knockdown. RESULTS: Intra-DR 1A-siRNA infusion selectively reduced 5-HT(1A)R mRNA and binding levels and canceled 8-OH-DPAT-induced hypothermia. Basal extracellular 5-HT in medial prefrontal cortex (mPFC) did not differ among treatments. However, 1A-siRNA-treated mice displayed less immobility in the tail suspension and forced swim tests, as did 1A-KO mice. This was accompanied by a greater increase in prefrontal 5-HT release during tail suspension test. Moreover, intra-DR 1A-siRNA infusion augmented the increase of extracellular 5-HT in mPFC evoked by fluoxetine, up to the level in 1A-KO mice. CONCLUSION: Together with our previous report, the present results indicate that acute suppression of 5-HT(1A) autoreceptor expression evokes robust antidepressant-like effects, likely mediated by an increased capacity of serotonergic neurons to release 5-HT in stressful conditions.
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