Optogenetic control of motor coordination by Gi/o protein-coupled vertebrate rhodopsin in cerebellar Purkinje cells.

G protein-coupled receptors are involved in the modulation of complex neuronal networks in the brain. To investigate the impact of a cell-specific G(i/o) protein-mediated signaling pathway on brain function, we created a new optogenetic mouse model in which the G(i/o) protein-coupled receptor vertebrate rhodopsin can be cell-specifically expressed with the aid of Cre recombinase. Here we use this mouse model to study the functional impact of G(i/o) modulation in cerebellar Purkinje cells (PCs). We show that in vivo light activation of vertebrate rhodopsin specifically expressed in PCs reduces simple spike firing that is comparable with the reduction in firing observed for the activation of cerebellar G(i/o)-coupled GABA(B) receptors. Notably, the light exposure of the cerebellar vermis in freely moving mice changes the motor behavior. Thus, our studies directly demonstrate that spike modulation via G(i/o)-mediated signaling in cerebellar PCs affects motor coordination and show a new promising approach for studying the physiological function of G protein-coupled receptor-mediated signaling in a cell type-specific manner.

Delayed postnatal loss of P/Q-type calcium channels recapitulates the absence epilepsy, dyskinesia, and ataxia phenotypes of genomic Cacna1a mutations.

Inherited loss of P/Q-type calcium channel function causes human absence epilepsy, episodic dyskinesia, and ataxia, but the molecular "birthdate" of the neurological syndrome and its dependence on prenatal pathophysiology is unknown. Since these channels mediate transmitter release at synapses throughout the brain and are expressed early in embryonic development, delineating the critical circuitry and onset underlying each of the emergent phenotypes requires targeted control of gene expression. To visualize P/Q-type Ca(2+) channels and dissect their role in neuronal networks at distinct developmental stages, we created a novel conditional Cacna1a knock-in mouse by inserting the floxed green fluorescent protein derivative Citrine into the first exon of Cacna1a and then crossed it with a postnatally expressing PCP2-Cre line for delayed Purkinje cell (PC) gene deletion within the cerebellum and sparsely in forebrain (purky). PCs in purky mice lacked P/Q-type calcium channel protein and currents within the first month after birth, displayed altered spontaneous firing, and showed impaired neurotransmission. Unexpectedly, adult purky mice exhibited the full spectrum of neurological deficits seen in mice with genomic Cacna1a ablation. Our results show that the ataxia, dyskinesia, and absence epilepsy caused by inherited disorders of the P/Q-type channel arise from signaling defects beginning in late infancy, revealing an early window of opportunity for therapeutic intervention.