Morphological characteristics of the A10 catecholaminergic group of neurons in the human midbrain

The authors examined ten serially sectioned human midbrains stained with luxol fast blue and/or cresyl violet. They found the neuromelanin-containing neurons in the central (CL) and rostral (RL) linear nuclei, the interfascicular (IF), the paranigral (PN), and the parabrachial pigmented (PB) nuclei, as well as in the medial longitudinal fasciculus and the dorsal nucleus of the raphe. The CL nucleus measured 4.7 mm x 1.9 mm, the RL 2.9 mm x 0.6 mm, the IF 2.8 mm x 0.6 mm, the PN 1.3 mm x 0.8 mm, and the PB 4.4 mm x 0.7 mm. The number of pigmented neurons per section was 9.4 in the CL, 13.5 in the RL, 51.7 in the IF, 41.8 in the PN, and 33.1 in the PB nucleus. The pigmented neurons, which were fusiform, oval or multipolar, ranged from 9.3 microns x 9.0 microns to 62.0 microns x 25.0 microns in size. Clustering of the cells was most prominent in the IF and PN nuclei, as well as in the lateral parts of the PB and RL nuclei. The authors concluded that: 1. the CL and PB were the largest nuclei; 2. the greatest cellular density was in the IF and PN nuclei; 3. the largest pigmented neurons were present in the RL and PB nuclei, and 4. the CL and RL nuclei were more complex than the other nuclei of the A10 catecholaminergic group.