This suggests that specific β2-AR agonists like clenbuterol may be beneficial therapeutics in PD, whereas our data with the β1-AR agonist xamoterol indicates that β1-AR activation is associated with increased dopaminergic neuron degeneration in the SN, suggesting that the use of β1-AR agonists in PD patients may not be warranted. This evidence concerns the gene ADRB2 and Parkinson disease.