Abstract Characterization of the expression pattern of connexins in neural tissue is a necessary prerequisite for understanding the functional relevance of the corresponding gap junction channels in brain. Here we describe the cell type-specific expression of connexin45 in the CNS and the spatiotemporal expression pattern from embryonic day 19.5 to adult brain using a recently described connexin45 LacZ-reporter mouse. The connexin45 gene is highly expressed during embryogenesis and up to 2 weeks after birth in nearly all brain regions. Afterward its expression is restricted to the thalamus, the CA3 region of hippocampus and the cerebellum. In adult mouse brain, the pattern of LacZ-staining in combination with the analysis of different neuronal and glial marker proteins strongly suggests that connexin45 is expressed in neurons, but presumably not in astrocytes or mature oligodendrocytes. Expression of the LacZ/connexin45 reporter gene in subsets of neurons, such as cerebral cortical, hippocampal and thalamic neurons as well as basket and stellate cells of cerebellum should be corroborated by functional investigations of connexin45 protein in electrical synapses. Based on its expression pattern during development, we suggest that the connexin45-containing gap junction channels have a rather ubiquitous role during brain development and may contribute to functional specification in certain subsets of neurons in the adult brain.