Anatomy and development of the meso-diencephalic dopaminergic neurons.
A. Sagittal (left) and coronal (right) sections of the adult human brain are shown. The location of the coronal section is indicated by a dashed yellow line on the sagittal section.
The dopaminergic neurons in the adult ventral midbrain are mainly categorized as: (1) the 'A9' group neurons, which are located in the substantia nigra pars compacta (SNC). These neurons send their axons to the dorsal striatum (caudate and putamen) and thus form the 'nigro-striatal pathway' and (2) the 'A10' group neurons, which are located in the ventral tegmental area (VTA) and send their axons to the ventral striatum (nucleus accumbens), the limbic cortex (forming the ‘meso-limbic’ pathway) and the prefrontal cortex (forming the 'meso-cortical' pathway).
B. Top: Meso-diencephalic dopaminergic precursor cells originate in the floor plate and basal plate of the mesencephalon (M) and the caudal diencephalon (P1/2/3=prosomers 1/2/3). A sagittal section of the E9.5-E12.5 mouse brain is shown.
Middle: A coronal section through the mesencephalon shows the location of the floor plate (FP), basal plate (BP) and alar plate (AP). The region surrounding the cerebral aqueduct (Aq) is called the ventricular zone (VZ). The locations of the intermediate zone (IZ), marginal zone (MZ), and the presumptive SNC/VTA are also indicated. The location of the coronal section is indicated by a dashed yellow line on the sagittal section.
Bottom: An enlargement of the coronal section above is shown, and the locations of the developing dopaminergic neurons are indicated. Meso-diencephalic dopaminergic neurons are born and proliferate in the ventricular zone between E9.5 and E12.5. Then, they start to migrate towards the intermediate zone, exit the cell cycle and begin to express Ddc and Nr4a2. In the next stage, they arrive at their final location in the marginal zone of the mesencephalic floor and basal plate, and start to express TH and Pitx3 and to extend axons towards the telencephalon.
Abbreviations: SNC, substantia nigra pars compacta; VTA, ventral tegmental area; M, mesencephalon; P1/2/3, prosomers 1/2/3; FP, floor plate; BP, basal plate; AP, alar plate; Aq, cerebral aqueduct; VZ, ventricular zone; IZ, intermediate zone; MZ, marginal zone;