Expression of the Transient Receptor Potential Vanilloid 1 ion channel in the supramammillary nucleus and the antidepressant effects of its antagonist AMG9810 in mice.

The Transient Receptor Potential Vanilloid 1 (TRPV1) non-selective cation channel predominantly expressed in primary sensory neurons of the dorsal root and trigeminal ganglia mediates pain and neurogenic inflammation. TRPV1 mRNA and immunoreactivity were described in the central nervous system (CNS), but its precise expression pattern and function have not been clarified. Here we investigated Trpv1 mRNA expression in the mouse brain using ultrasensitive RNAScope in situ hybridization. The role of TRPV1 in anxiety, depression-like behaviors and memory functions was investigated by TRPV1-deficient mice and pharmacological antagonism by AMG9810. Trpv1 mRNA is selectively expressed in the supramammillary nucleus (SuM) co-localized with Vglut2 mRNA, but not with tyrosine hydroxylase immunopositivity demonstrating its presence in glutamatergic, but not dopaminergic neurons. TRPV1-deleted mice exhibited significantly reduced anxiety in the Light-Dark box and depression-like behaviors in the Forced Swim Test, but their performance in the Elevated Plus Maze as well as their spontaneous locomotor activity, memory and learning function in the Radial Arm Maze, Y-maze and Novel Object Recognition test were not different from WTs. AMG9810 (intraperitoneal injection 50 mg/kg) induced anti-depressant, but not anxiolytic effects. It is concluded that TRPV1 in the SuM might have functional relevance in mood regulation and TRPV1 antagonism could be a novel perspective for anti-depressant drugs.