Cellular Diversity and Differential Subcellular Localization of the G-Protein G Subunit in the Mouse Cerebellum.

Heterotrimeric guanine nucleotide-binding proteins (G proteins) transduce signals from G protein-coupled receptors (GPCRs) to effector ion channels and enzymes G, a member of the pertussis toxin-sensitive G family, is widely expressed in the brain, although its role within a neuronal context remains largely unknown. Using immunohistochemical and quantitative immunoelectron microscopy techniques, we have investigated the expression, cellular and subcellular localization of G in the cerebellar cortex. Histoblot revealed that G is expressed in many brain regions, including the cerebellum. At the cellular level, G protein was distributed in Purkinje cells, basket cells, stellate cells, granule cells and Golgi cells. At the subcellular level, pre-embedding immunoelectron microscopy revealed mainly a postsynaptic localization of G along the extrasynaptic plasma membrane of Purkinje cell dendritic shafts and spines, and dendrites of basket, stellate and granule cells. To a lesser extent, immunolabeling for G was localized in different types of axon terminals establishing excitatory synapses. Moreover, post-embedding immunoelectron microscopy revealed the synaptic localization of G on PSDs of glutamatergic synapses between Purkinje cell spines and parallel fiber terminals and its co-localization with GABA in the same spines. Quantitative analysis of G immunoparticles revealed they preferentially localized on the cytoplasmic face of the plasma membrane. Furthermore, the analysis revealed a high concentration of G around excitatory synapses on Purkinje cell dendritic spines, but a uniform distribution in granule cell dendrites. These molecular-anatomical findings suggest that G is a major signal transducer of specific GPCRs in different neuronal populations in the cerebellum.