Expression and distribution of vanilloid receptor 1 (TRPV1) in the adult rat brain.

The vanilloid receptor (TRPV1 or VR1) is a molecular integrator of various painful stimuli, including capsaicin, acid, and high temperature. It can also be activated by endogenous ligands, like the cannabinoid 1 receptor (CB1) agonist anandamide. TRPV1 is well characterized at the terminals of sensory nerves involved in the pain pathway. There is also evidence that TRPV1 is expressed in the brain but little is known about its function. Here, using commercially available specific antibodies to investigate the localization of TRPV1 in the brain of the rat, we report that TRPV1 was expressed in hippocampus, cortex, cerebellum, olfactory bulb, mesencephalon and hindbrain. Immunohistochemical analyses showed high expression in the cell bodies and dendrites of neurons in the hippocampus and in the cortex. To address the question of subcellular localization, immunoelectronmicroscopy was used. TRPV1-like staining was detected in the synapses (mostly, but not exclusively in post-synaptic dendritic spines), on the end feet of astrocytes and in pericytes. In summary, TRPV1 expression shows wide distribution in the brain of the rat, being found in astrocytes and pericytes as well as in neurons. Its localization is consistent with multiple functions within the central nervous system, including the regulation of brain vasculature.