A new study in Annals of Neurology shows that propranolol, an antagonist of beta-adrenergic receptors, may help Parkinson's disease (PD) patients with resting tremor. The study sheds fresh light on the involvement of stress and the brain's motor control networks in tremor amplification.

Resting tremor, a hallmark sign of Parkinson's disease, is thought to originate in the basal ganglia and spread via the cerebello-thalamo-cortical circuit. While stress has long been known to aggravate tremors, the noradrenergic system's function in this process was previously unknown. To find out what effects propranolol has under different types of stress, a crossover, double-blind study was done with 27 Parkinson's disease patients who had noticeable resting tremors.

Participants received either a single 40 mg propranolol dose or a placebo on different days. Accelerometry and functional magnetic resonance imaging (fMRI) were used to measure the severity of tremors in people who were doing a mentally demanding task that turned on the noradrenergic system. The study looked at medication effects, stress levels, and tremor-related brain activity.

The study provided important insights into the dynamics of Parkinson's disease (PD) tremors and the therapeutic potential of propranolol. Researchers discovered that tremors get a lot worse when people have to do mentally demanding tasks. This suggests that stress makes the brain activity that causes tremors stronger (p=0.001). However, as compared to placebo, propranolol significantly reduced tremor severity (p=0.02). Notably, this effect happened regardless of stress levels. This suggests that propranolol's effects go beyond tremors caused by stress and include treating all tremors.

The study also revealed propranolol's potential to modify brain activity in the primary motor cortex, a critical location for motor control. This drop in brain activity related to tremors happened even when the brain was under a lot of cognitive load. This shows that propranolol has a direct effect on the motor system instead of just lowering stress responses. These findings imply that propranolol acts on the motor cortex to diminish tremor, making it a promising option for controlling Parkinson's disease tremors regardless of external stressors.

The results show that the motor cortex mediates propranolol's tremor-reducing effects, which are not exclusive to stressful situations.

This study shows that propranolol can effectively reduce PD tremors in the general population. This suggests that propranolol could be a beneficial option for treating PD patients whose symptoms are not getting better with their current medications. Propranolol, which works on the motor cortex, may be able to help manage tremors in a way that doesn't involve changing how stress responses work directly.

The long-term effectiveness and safety of propranolol for Parkinson's disease patients require further research. However, these findings are a positive step forward in improving quality of life for those living with PD.