TRPV1 channels facilitate glutamate transmission in the striatum

Transient receptor potential vanilloid 1 (TRPV1) channels participate in the modulation of synaptic transmission in the periphery and in central structures. Here, we investigated the role of TRPV1 channels in the control of both excitatory and inhibitory transmission in the striatum. Pharmacological stimulation of TRPV1 channels with capsaicin (10 nM) selectively enhanced the frequency of glutamate-mediated spontaneous (sEPSCs) and miniature excitatory postsynaptic currents (mEPSCs) recorded from putative striatal medium spiny neurons. Capsaicin-mediated response underwent a rapid rundown, and was no longer detected in the majority of the neurons when the concentration of the drug was in the micromolar range, possibly due to receptor desensitization. Consistently, the totality of striatal neurons responded to capsaicin (10 nM or 10 microM) after prevention of desensitization of TRPV1 channels with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA). PMA was able per se to increase sEPSC frequency. The effects of capsaicin and of PMA were absent after pharmacological or genetic inactivation of TRPV1 channels. Finally, we provided evidence for anandamide as an endovanilloid substance in the striatum, since genetic inhibition of anandamide degradation resulted in a tonic activation of TRPV1 channels modulating glutamate but not GABA release. TRPV1-mediated regulation of excitatory transmission in the striatum might be important for the final output to other basal ganglia structures, and might play a role in several physiological and pathological processes.