CREB-induced transcriptional activation depends on mGluR6 in rod bipolar cells

To investigate the molecular mechanisms of stimuli-induced transcriptional activation in neuronal cells, we have investigated the light-induced gene expression in the neural retina of rats. The immunoreactivity for phosphorylated cAMP responsive element binding protein (PCREB-IR) was expressed in the outer half of the inner nuclear layer (INL) and the ganglion cell layer (GCL) after 5 min exposure to steady light also in mice. In addition to these cells, PCREB-IR was also detected in the inner border of the INL after 5 min exposure to flashing light. Both steady and flashing lights induced c-fos mRNA in the same types of cells as the PCREB-IR-positive cells. Majority of PCREB immunoreactive nuclei in the outer half of the INL were also immunopositive for anti-protein kinase C alpha (PKC alpha), a marker of rod bipolar cells, while CaM kinase IV immunoreactivity was not detected in these cells. PCREB-IR and c-fos gene expression in the PKC alpha positive rod bipolar cells were lost in mice lacking metabotropic glutamate receptor 6 (mGluR6). Thus, we propose that the transcriptional response of CREB to light stimulation in rod bipolar cells is regulated via mGluR6.