The following were inserted, in order, between the promoter and coding sequences of the endogenous gene: tTA-pA-STOP-"PF" [TetO-tTA] cassette-pA-loxP-Neo-loxP. The PF (positive feedback) amplification cassette enhances tTA expression following the removal of the STOP. Cre-mediated recombination removed the downstream floxed neo cassette. Transgene expression is eight-fold higher than endogenous alpha-synuclein expression in dopaminergic neurons.