Histology of 5-HT neurons studied by juxtacellular recordings in medulla and midbrain. A, Labeled medullary raphe 5-HT cell recorded juxtacellularly, stained for tryptophan hydroxylase (TPOH) in A1, Neurobiotin (NBiotin) in A2, and merge in A3. B, Labeled midbrain dorsal raphe 5-HT cell recorded juxtacellularly, stained for TPOH in B1, Neurobiotin in B2, and merge in B3. Scale bars, 10 μm. C, Locations of all recorded 5-HT neurons in the medulla (n = 8). Identified 5-HT neurons were located in regions of raphe magnus and raphe pallidus. D, Locations of all recorded 5-HT neurons in the midbrain (n = 10). Identified 5-HT neurons were located in the following regions of the dorsal raphe dorsal, ventral, and caudal subnuclei. Coronal section schematics reproduced with permission from Paxinos and Watson (1998).