Normative data of dopaminergic neurotransmission functions in substantia nigra measured with MRI and PET: Neuromelanin, dopamine synthesis, dopamine transporters, and dopamine D2 receptors

- Neuromelanin-sensitive (NM) MRI compared to dopaminergic neurotransmission function.
- Positive correlation between dopamine D2 receptor and neuromelanin accumulation.
- Dopamine transporter binding is not correlated with neuromelanin accumulation.
- Dopamine synthesis is not correlated with neuromelanin accumulation.
- Regional mismatch between NM MRI and dopaminergic transmission indices in sub. nigra.

The central dopaminergic system is of major importance in the pathophysiology of Parkinson's disease, schizophrenia, and other neuropsychiatric disorders. In the present study, the normative data of dopaminergic neurotransmission functions in the midbrain, consisting of neuromelanin, dopamine synthesis, dopamine transporters and dopamine D2 receptors, were constructed using magnetic resonance (MR) imaging and positron emission tomography (PET). PET studies with L-[β-11C]DOPA, [18F]FE-PE2I and [11C]FLB457 and MRI studies were performed on healthy young men. Neuromelanin accumulation measured by MRI was compared with dopaminergic functions, dopamine synthesis capacity, dopamine transporter binding and dopamine D2 receptor binding measured by PET in the substantia nigra. Although neuromelanin is synthesized from DOPA and dopamine in dopaminergic neurons, neuromelanin accumulation did not correlate with dopamine synthesis capacity in young healthy subjects. The role of dopamine transporters in the substantia nigra is considered to be the transport of dopamine into neurons, and therefore dopamine transporter binding might be related to neuromelanin accumulation; however, no significant correlation was observed between them. A positive correlation between dopamine D2 receptor binding and neuromelanin accumulation was observed, indicating a feedback mechanism by dopaminergic autoreceptors. Discrepancies in regional distribution between neuromelanin accumulation and dopamine synthesis capacity, dopamine transporter binding or dopamine D2 receptor binding were observed in the substantia nigra.

The neuromelanin accumulation in the substantia nigra measured with MRI was compared the indicators of dopaminergic neurotransmission functions such as dopamine synthesis capacity, dopamine transporter binding, and dopamine D2 receptor binding measured with PET.192