Low-voltage-activated (LVA) Ca2+ channels play a critical role in the generation of burst firing in the thalamus. Recently, three LVA Ca2+ channel isoforms (Cav3.1, Cav3.2, Cav3.3) have been identified in the reticular thalamic nucleus (RE). Previous electrophysiological and modelling studies have suggested that kinetically different T-type channels might be expressed in a compartmentalized manner in RE cells. However, their precise subcellular distribution has not been fully elucidated. Using light and electron microscopic (EM) immunocytochemistry, we investigated the subcellular expression pattern of Cav3.1 and Cav3.3 channel subunits in RE neurons of the cat. Fluorescent and peroxidase labelling demonstrated the presence of Cav3.1 channel predominantly on the somata and proximal dendrites and Cav3.3 channels on cell bodies. Quantitative immunogold localization disclosed that Cav3.1 and Cav3.3 isoforms showed 5.8- and 8.7-fold higher density, respectively, in the cytoplasm compared with somatic plasma membrane. Density of Cav3.1 isoform in the somatic plasma membrane was 2.21-fold higher compared with Cav3.3 subunit. In the dendritic plasma membrane, Cav3.1 channel isoform was expressed throughout the entire dendritic tree. In contrast, Cav3.3 isoform was absent from large-caliber, presumably proximal dendritic segments. Quantitative comparison showed that the relative density of immunogold particles compared with dendritic surface was 8.9- and 14.8-fold higher for Cav3.1 and Cav3.3, respectively, in small-diameter dendrites than in large proximal dendritic segments or somata. Our results demonstrate a higher density of low-threshold Ca2+ channels in distal dendrites and provide further evidence of the role of RE neuron dendrites in the generation of prolonged, low-threshold spike bursts. © 2009 Wiley-Liss, Inc.