Researchers from Northwestern University have discovered three distinct subtypes of dopamine-reactive neurons in the substantia nigra pars compacta (SNc) region of the brain. These neurons have unique functions related to satisfying experiences, unpleasant stimuli, and speed changes, challenging the conventional view that dopamine neurons only reinforce pleasurable and reward behaviour.
The substantia nigra is a key area implicated in Parkinson's disease, where the loss of dopamine-sensitive neurons leads to symptoms like rigidity, slowness, and tremors. Interestingly, despite the loss of these neurons, rewarding feelings following successful or joyful tasks are still experienced. This raised questions about whether dopamine-reactive neurons serve multiple functions or if distinct neurons are responsible for different roles.
To investigate this, the researchers focused on three genes found in these neurons: Slc17a6, Calb1, and Anxa1. They tagged transgenic mouse neurons to observe their activity when these genes were active. Around 30 per cent of dopamine-reactive neurons were active during mouse movement, leaving the remaining neurons responsible for aversive or rewarding behaviours.
These accelerator-specific dopamine neurons might play a role in the imbalance associated with Parkinson's shaking movements. Loss of these neurons, which govern acceleration, could lead to a dominance of deceleration neurons, causing muscle movements to stop abruptly.
Further research is required to understand the specific functions of each subtype of dopamine nerve cell and why some are more vulnerable to damage than others. This discovery challenges the traditional view of dopamine neurons and provides new insights into the mechanisms underlying Parkinson's disease.
The findings open new avenues for studying Parkinson's disease and could help develop targeted therapies to address the specific neuronal subtypes affected by the condition. This research is a crucial step toward understanding the complexities of the brain and its role in neurological disorders like Parkinson's.