Mice heterozygous for both targeted mutations are viable and fertile. Dopamine-deficient (DA-deficient, DA-/-, or DD) mice are homozygous for the TH mutant allele and heterozygous for the DBH-TH mutant allele (Th-/-; DbhTh/+). While no expression from the TH mutant allele is observed in any tissues (resulting in deficiency of both dopamine (DA) and norepinephrine (NE)), the DBH-TH mutant allele contains the TH coding sequence under the control of the endogenous DBH promoter region and restores TH expression in noradrenergic neurons. DD mice become hypoactive and hypophagic around two weeks of age and usually die before four weeks of age. Treatment with L-DOPA, the product of TH enzymatic activity, rescues size, feeding, and life span. These DD mice may be useful in studying dopaminergic neurobiology (including neurotransmitters, addiction, feeding, learning and memory, catecholamines, and Parkinsonian phenotypes).
NOTE: Th-/-; DbhTh/+ mice congenic on a C57BL/6 genetic background may exhibit declining birth rates and increased mortality (Hnasko et al 2007 J Neurosci 27:12484-8).
