Differential distribution of three members of a gene family encoding low voltage-activated (T-type) calcium channels

Low voltage-activated (T-type) calcium currents are observed in many centra l and peripheral neurons and display distinct physiological and functional properties. Using in situ hybridization, we have localized central and peri pheral nervous system expression of three transcripts (alpha 1G, alpha 1H, and alpha 1I) of the T-type calcium channel family (CavT). Each mRNA demons trated a unique distribution, and expression of the three genes was largely complementary. We found high levels of expression of these transcripts in regions associated with prominent T-type currents, including inferior oliva ry and thalamic relay neurons (which expressed alpha 1G), sensory ganglia, pituitary, and dentate gyrus granule neurons (alpha 1H), and thalamic retic ular neurons (alpha 1I and alpha 1H). Other regions of high expression incl uded the Purkinje cell layer of the cerebellum, the bed nucleus of the stri a terminalis, the claustrum (alpha 1G), the olfactory tubercles (alpha 1H a nd alpha 1I), and the subthalamic nucleus (alpha 1I and alpha 1G). Some neu rons expressed high levels of all three genes, including hippocampal pyrami dal neurons and olfactory granule cells. Many brain regions showed a predom inance of labeling for alpha 1G, including the amygdala, cerebral cortex, r ostral hypothalamus, brainstem, and spinal cord. Exceptions included the ba sal ganglia, which showed more prominent labeling for alpha 1H and alpha 1I , and the olfactory bulb, the hippocampus, and the caudal hypothalamus, whi ch showed more even levels of all three transcripts. Our results are consis tent with the hypothesis that differential gene expression underlies pharma cological and physiological heterogeneity observed in neuronal T-type calci um currents, and they provide a molecular basis for the study of T-type cha nnels in particular neurons.