EXPRESSION OF TYROSINE-HYDROXYLASE IN MAGNOCELLULAR HYPOTHALAMIC NEURONS OF OBESE (FA FA) AND LEAN HETEROZYGOUS (FA/FA) ZUCKER RATS/

In the magnocellular hypothalamic neurons (MCN) of normal rats, tyrosi ne hydroxylase (TH) is expressed in response to hyperosmotic stimulati on and co-exists with vasopressin. The present study shows that both Z ucker obese (fa/fa) and heterozygous lean (Fa/fa) rats express TH in M CN independently of an osmotic challenge, The lack of L-DOPA and aroma tic-L-aminoacid decarboxylase in the MCN showed the absence of mechani sms necessary for catecholamine synthesis in these cells. Therefore, T H in MCN seems to be functionally inactive and is not involved in cate cholamine abnormalities observed in these rats. All TH-immunoreactive MCN co-expressed vasopressin mRNA while a part of them co-expressed ox ytocin mRNA. This suggests a mechanism of regulation of TH expression in MCN which is different in Zucker rats and in dehydrated normal rats . (C) 1997 Elsevier Science B.V.