Distribution of TRPC1 receptors in dendrites of rat substantia nigra: a confocal and electron microscopy study.

Transient receptor potential channels (TRPC) are plasma membrane, non-selective cationic channels and have been proposed as candidates involved in the regulation of cellular Ca2+ influx. The expression, at mRNA level, of several TRPCs has been demonstrated recently in dopaminergic neurons of the substantia nigra (SN). The aim of the present study was to characterize the expression of TRPC1, at a protein level, in the substantia nigra neurons and non-excitable cells of Wistar rats. Single-label immunohistochemistry and double-label immunofluorescence were used to study the expression of TRPC1 among substantia nigra dopamine neurons and cellular processes using antibodies against tyrosine hydroxylase (TH), substance P (SP), enkephalin, synaptophysin, vesicular glutamate transporter-2 (Vglut-2), microtubule associated protein-2 and metabotropic glutamate receptor 1 (mGluR1). Moreover, the ultrastructural localization of TRPC1 was investigated by means of electron microscopy. A set of dual label experiments was also performed to investigate the presence of TRPC1 among glial cells. Our results showed that TRPC1 is localized mainly in dendritic processes of dopamine neurons, whereas a relatively small percentage of neuronal somata display a light TRPC1 immunoreactivity. Such results were confirmed by our electron microscopy observations. Our study demonstrates, for the first time, a coexpression of TRPC1 and mGluR1 receptors in dendrites of the substantia nigra dopaminergic neurons. Such observation reinforces the concept of an involvement of TRPC1 in mGluR1-mediated excitatory inputs in rat dopamine neurons.