G_αq/11 mediates neurotensin excitation of substantia nigra dopaminergic neurons

Using acutely dissociated substantia nigra pars compacta (SNC) dopaminergic (DA) neurons, our previous studies indicated that neurotensin (NT) excites SNC DA neurons by increasing the cationic conductance and reducing the inwardly rectifying K⁺ conductance. Further investigation also revealed that pertussis toxin (PTX)-insensitive G-proteins mediate neurotensin modulation of cation and potassium channels. G_αq and G_α11 are widely distributed in various tissues including the brain and likely to mediate PTX-insensitive signal transductions in the nervous system. In this study, two different experiments were conducted to test the hypothesis that G_αq/11 mediates neurotensin regulation of the cationic and K⁺ conductances. First, we investigated the expression of G_αq and G_α11 mRNAs in NT-responsive SNC DA neurons by combining whole-cell patch-clamp recordings with single-cell reverse transcriptase-polymerase chain reaction (RT-PCR) assay. After recording NT-evoked membrane currents, the cellular content was harvested from single neurons and used as the template for the subsequent RT-PCR analysis. Both G_αq and G_α11 mRNAs were present in all SNC DA neurons that responded to neurotensin. SNC DA neurons were also internally dialyzed with an antibody directed against the common C-terminus of G_αq and G_α11 during whole-cell recordings. In DA neurons perfused with the anti-G_αq/11 antiserum, neurotensin failed to evoke inward currents resulting from the opening of cation channels and the closure of inward rectifier K⁺ channels. It is concluded that NT modulation of cation and inward rectifier K⁺ channels in SNC DA neurons is transduced by G_αq and/or G_α11.