ADRB2 and Tremor: We reasoned that examining the effects of propranolol in these β1-AR−/−;β2-AR−/−;Car8wdl/wdl triple mutant mice would provide further evidence of propranolol acting through β1 and β2 receptors to reduce tremor, since these mice persist with the pathophysiological Car8wdl/wdl tremor.