Differential expression of catecholamine synthetic enzymes in the caudal ventral pons

The analysis of colocalization of multiple catecholamine biosynthetic enzym es within the ventrolateral part of the medulla oblongata of the rat reveal ed distinct subpopulations. of neurons within the C1 region (Phillips et al ., J Comp Neurol 2001, 432:20-34). In extending this study to include the c audal pons, it was shown for the first time that the A5 cell group could be distinguished by the presence of immunoreactivity to tyrosine hydroxylase (TH), aromatic I-amino acid decarboxylase (AADC), and dopamine beta hydroxy lase (DBH). A novel cell group was also identified. The cells within this n ew group were immunoreactive to DBH but not TH, AADC, or phenylethanolamine N-methyltransferase (PNMT) and will be referred to as the TH-, DBH+ cell g roup. The TH-, DBH+ neurons were not immunoreactive for either the dopamine or noradrenaline transporters, suggesting that these neurons do not take u p these transmitters. A5 neurons were immunoreactive for the noradrenaline transporter but not the dopamine transporter (as previously shown). Retrogr ade tracing with cholera toxin B revealed that the TH-, DBH+ neurons do not project to the thoracic spinal cord or to the rostral ventrolateral medull a, but A5 neurons do. A calbindin immunoreactive cell group is located in a region overlapping TH-, DBH+ cell group. However, only a few neurons were immunoreactive for both markers. The physiological role of the TH-, DBH+ ce ll group remains to be determined. J. Comp. Neurol. 438:457-467, 2001. (C) 2001 Wiley-Liss, Inc.