A, A Pcp2 BAC-Cre transgenic line produces Cre expression that is restricted to the cerebellum localized to Purkinje cell neurons as seen in a sagittal brain section. B, A Cmtm5 BAC-Cre transgenic line produces Cre expression in oligodendrocyte cells throughout the brain. Bi, Labeled cells in a forebrain area including the cerebral cortex, underlying white matter, and striatum are seen to have the morphology of oligodendrocytes. C, Inducible Cre expression occurs in a serotonin transporter (Slca4) BAC-ER-Cre transgenic line. Mice treated with saline show no Cre expression, whereas a single treatment with tamoxifen (6 mg/kg, i.p.) produces Cre expression in serotonin neurons in the dorsal raphe.