Dopamine, often referred to as the brain’s reward neurotransmitter, is responsible for the feeling of accomplishment and pleasure. Whether it’s winning a game of cards or savoring a favorite treat, dopamine activates specific neurons that generate feelings of joy. Researchers from Northwestern University in the US have now made a breakthrough by identifying three distinct subtypes of dopamine-reactive neurons within a brain region called the substantia nigra pars compacta (SNc). This discovery challenges the conventional understanding of dopamine neurons solely associated with reward responses and sheds light on their potential involvement in various functions beyond pleasure.

The substantia nigra plays a critical role in both movement processing and reward responses, making it a pivotal area to investigate. Interestingly, Parkinson’s disease originates in this region, where the loss of dopamine-sensitive neurons results in symptoms like tremors, slowness, and rigidity.

The recent study, led by neurobiologist Daniel Dombeck and his team, focused on three specific genes – Slc17a6, Calb1, and Anxa1 – known to operate within dopamine-reactive neurons. By tagging these genes in transgenic mice, the researchers observed that approximately 30% of these neurons lit up in response to movement, while other nerve cells were responsible for aversive or rewarding behaviors.

One of the most intriguing findings was a subtype of dopamine neurons associated with acceleration, a function that had not been previously linked to dopamine. Surprisingly, these neurons were located precisely where dopamine neurons are susceptible to degradation in Parkinson’s disease. This correlation suggests a potential genetic susceptibility to degeneration over time as individuals age.

While researchers had previously assumed that dopamine neurons related to movement were also involved in reward responses, this study challenges that assumption by revealing distinct neuronal subtypes. Further research is needed to fully understand the functions of each subclass of dopamine nerve cells and why some are more susceptible to damage than others.

Co-lead author Rajeshwar Awatramani explains that this discovery is a starting point in understanding the intricate workings of the brain, particularly in the context of Parkinson’s disease. As researchers delve deeper into this newfound diversity of dopamine neurons, it could open up new avenues for comprehending brain functions and potentially lead to innovative approaches for addressing neurological disorders.

By Impact Lab