Fig. 5. Recue of α3 expression in defined neuronal cell types. (A ) An α3KO mouse is crossed with a DBH-iCre mouse to obtain DBH-iCre Rescue mice (in our studies hemizygous males) containing both the α3 knockout allele and the DBH-iCre transgene. The artificial exon 5 in the α3 KO allele functions as a “STOP” signal, resulting in messenger RNA degradation.18In noradrenergic neurons of the Rescue mouse, this “STOP” signal is removed by cre-lox  P-mediated recombination. Thus, in the Rescue mice, the α3 subunit is expressed only in the noradrenergic neurons. Similar considerations apply to the generation of the DAT-Rescue mice using the DAT-iCre transgene expressing iCre specifically in dopaminergic neurons. (B ) Neuron-specific rescue of α3 subunit expression in the locus coeruleus: Immunofluorescence double-labeling of the α3 subunit (red ) and tyrosine hydroxylase (green ) shows that the α3 subunit is highly expressed in the LC in WT mice. In α3KO mice expressing the iCre recombinase selectively in noradrenergic neurons (DBH-Rescue) α3 subunit expression is restricted to noradrenergic neurons. It is not detectable in the locus coeruleus of α3KO mice expressing the iCre recombinase exclusively in dopaminergic neurons (DAT-Rescue), nor in α3KO mice. Scale bar: 50 µm. (C ) Neuron-specific rescue of α3 subunit expression in the SNpc: Immunofluorescence double-labeling of the α3 subunit (red ) and tyrosine hydroxylase (green ) shows that α3 subunit expression is found in dopaminergic neurons of the SNpc of WT mice and in α3KO mice expressing the iCre recombinase selectively in dopaminergic neurons (DAT-Rescue). It is not detectable in the SNpc of α3KO mice expressing the iCre recombinase selectively in noradrenergic neurons (DBH-Rescue), nor in α3KO mice. Scale bar: 50 µm. DBH-iCre = dopamine β hydroxylase impoved Cre; DAT = dopamine transporter; WT = wild type; LC, locus coeruleus; SNpc = substantia nigra pars compacta.