Propranolol Modulates Cerebellar Circuit Activity and Reduces Tremor

Tremor is the most common movement disorder. Several drugs reduce tremor severity, but no cures are available. Propranolol, a β-adrenergic receptor blocker, is the leading treatment for tremor. However, the in vivo circuit mechanisms by which propranolol decreases tremor remain unclear. Here, we test whether propranolol modulates activity in the cerebellum, a key node in the tremor network. We investigated the effects of propranolol in healthy control mice and Car8(wdl/wdl) mice, which exhibit pathophysiological tremor and ataxia due to cerebellar dysfunction. Propranolol reduced physiological tremor in control mice and reduced pathophysiological tremor in Car8(wdl/wdl) mice to control levels. Open field and footprinting assays showed that propranolol did not correct ataxia in Car8(wdl/wdl) mice. In vivo recordings in awake mice revealed that propranolol modulates the spiking activity of control and Car8(wdl/wdl) Purkinje cells. Recordings in cerebellar nuclei neurons, the targets of Purkinje cells, also revealed altered activity in propranolol-treated control and Car8(wdl/wdl) mice. Next, we tested whether propranolol reduces tremor through β(1) and β(2) adrenergic receptors. Propranolol did not change tremor amplitude or cerebellar nuclei activity in β(1) and β(2) null mice or Car8(wdl/wdl) mice lacking β(1) and β(2) receptor function. These data show that propranolol can modulate cerebellar circuit activity through β-adrenergic receptors and may contribute to tremor therapeutics.