Spasmodic Dysphonia Bulletin Board

D1 and D2 Receptors and What Role They May Play in Spasmodic Dysphonia

In our most current issue of Our Voice, there was a reference to a research study which provided some important insight into the brain pathways of people living with focal dystonia. In the summary article “The direct basal ganglia pathway is hyperfunctional in focal dystonia” published in Brain, A Journal of Neurology, (BRAIN 2017: 140; 3179–3190) Kristina Simonyan, Hyun Cho, Azadeh Hamzehei Sichani, Estee Rubien-Thomas and Mark Hallett discussed their findings.

The study used high-resolution research tomography to compare D1 and D2 receptors in two dystonias (writers’s cramp and laryngeal dysphonia) to a control group who did not have a dystonia. What they found was that in patients who had either focal dystonia also had increased D1 receptors as compared to the control group. This receptor functions to produce the excitability of the ganglia pathways that control movement. They also found a corresponding under production in D2 receptors. This functions to counteract the D1 receptor.

We are not brain scientists like the smart people who performed this study, so we created an analogy that helps to put this into perspective. When you have acid indigestion, you have an imbalance in your stomach where your pH level is too low. So you take a Tums or Rolaids which has a higher pH. This combination levels out the pH in your stomach and makes you feel better. Too much D1 and not enough D2 receptors is like that. Heightened D1 is responsible for too much movement and D2 is the counteracting receptor that helps balance everything out, however it was too low in those with the focal dysphonias that they studied as compared to the control groups.

In addition, they found that the imbalance in the D1 and D2 receptors was localized to the portion of the brain that controlled the target movements. The subjects that were living with laryngeal dysphonia had the D1 increase appeared in the larynx area of right putamen and caudate nucleus of the brain. This is the area that controls the movement in the larynx, while the subjects with writer’s cramp, a dysphonia that affects the hand, had an increase in the hand area of bilateral putamen, the area of the brain which controls hand movement.

This study was groundbreaking because it provided a clearer understanding of how D1 and D2 receptors affected the basal ganglia pathways that control focal dystonias. Hopefully, this exciting information leads to treatment options in the future that help control these receptors.

A copy of the article along with a scientific commentary can be downloaded here . Be warned, you might need to be a brain surgeon to understand it, (or at least have a dictionary nearby).