Pterin-4α-carbinolamine dehydratase in rat brain I.: Patterns of co-localization with tyrosine hydroxylase

The bifunctional protein, PCD/DCoH, is both a pterin-4 alpha-carbinolamine dehydratase (PCD) and a dimerization cofactor of the hepatic nuclear factor 1 alpha (DCoH). In association with brain tyrosine hydroxylase (TH), which is required for dopamine synthesis, PCD catalyses dehydration and thus recycling of the cofactor tetrahydrobiopterin (BP4). PCD immunoreactivity in the catecholaminergic system of the rat brain was studied using a rabbit polyclonal antibody. Double immunofluorescence was performed to establish intracellular co-localization with TH. PCD immunoreactivity was found to be high and consistently present in all the neuron groups expressing TH. More than 90% the TH + cells were also expressing PCD. The highest co-expression (99-100% of TH + cells) was observed in pontine catecholaminergic cell groups including locus coeruleus. Lower co-expression was observed in substantia nigra (17% of TH + cells without PCD) and particularly in arcuate nucleus (41% of TH + cells without PCD). Our results argue in favor of a generalized recycling of BH4 in catecholaminergic neurons except when the neuron terminal field is located outside the blood-brain barrier. The respective roles of synthesis and recycling of BH4 in the control of TH activity are discussed, (C) 2000 Elsevier Science B.V. All rights reserved.