GROWTH-HORMONE INHIBITS THE HYPOPHYSECTOMY-INDUCED EXPRESSION OF GALANIN IN HYPOTHALAMIC NEURONS OF THE TOAD (BUFO-ARENARUM HENSEL)

The expression of the neuropeptide galanin was analyzed by immunohisto chemistry in magnocellular and preoptic hypothalamic neurons of toads following hypophysectomy (HPX) and pars distalectomy (PDX). There was a marked increase in the galanin-like immunoreactive expression in mag nocellular hypothalamic cells 3 days after HPX, followed by a decrease to normal levels after 7 days. No changes in the expression of galani n were detected after PDX in these neurons when compared to controls. Moreover, 7 days after HPX or PDX the number of cells expressing galan in was significantly increased in the preoptic area, where numerous in traependymal cells were intensely immunoreactive. The hypophysis graft s into the hind limb in HPX or PDX animals prevented increased galanin -like immunoreactivity in preoptic cells but not in magnocellular neur ons. Similarly, PDX toads given growth hormone showed no GAL-LI in the intraependymal preoptic cells. These results suggest the presence of a regional regulation of galanin expression in the preoptic area by hy pophyseal hormones, in particular growth hormone. (C) 1997 Academic Pr ess.