Cellular localization of dopamine D2 receptor messenger RNA in the rat trigeminal ganglion.

The actions of dopamine are mediated by specific, high-affinity, G protein-coupled receptors. Multiple subtypes of dopamine receptors have been characterized, including the D2 subtype (D2R). Cells within the dorsal root and petrosal ganglia of the rat express D2R messenger RNA (mRNA) consistent with D2R expression by primary sensory neurons. We hypothesized that neurons of the trigeminal ganglion express D2R mRNA. Total cellular RNA from rat trigeminal ganglia was analyzed on Northern blots under high stringency conditions. Hybridization of trigeminal ganglion RNA resulted in a signal which comigrated with striatal, pituitary, and hypothalamic D2R mRNA. To determine the distribution of D2R expressing cells in the trigeminal ganglion, cryostat sections were analyzed by in situ hybridization followed by emulsion autoradiography. We identified a population of clustered cells labeled with dense grain concentrations over their cytoplasms. These findings demonstrate the expression of D2 dopamine receptor mRNA in discrete subpopulations of neurons in the rat trigeminal ganglion. Our observations suggest that drugs active at dopamine receptors of the D2 subtype are potential modulators of sensory activity of neurons whose cell bodies reside in the trigeminal ganglion. D2 dopamine receptors may thus have a role in clinical pain syndromes involving the head and neck.