INVOLVEMENT OF NGF IN THE INDUCTION OF INCREASED NORADRENERGIC INNERVATION OF THE URETER IN NEONATALLY CAPSAICIN-TREATED RATS

Neonatal denervation of primary afferents with capsaicin leads to incr eased sympathetic innervation of the rat ureter. In the present study the development and the immunohistochemical characterization of this s ympathetic hyperinnervation as well as the specific involvement of ner ve growth factor (NGF) was investigated. Noradrenaline levels were fou nd elevated in neonatally capsaicin-treated rats by 2 weeks of age and remained at that high level into adulthood. Injections of an anti-NGF antiserum during postnatal days (PN) PN 8-14, PN 13-19 or during PN 1 7-23 counteracted the capsaicin effect and reduced noradrenaline towar ds control levels. Immunohistochemical localization of tyrosine hydrox ylase (TH), a marker for sympathetic nerve fibres, revealed that the c apsaicin-induced hyperinnervation was mainly represented by fibres in deeper muscle layers and to a smaller extent by fibres in the submucos a. In control animals and in rats treated with capsaicin and anti-NGF antiserum fibres were mainly distributed in the adventitia and in the outer part of the smooth muscle layer. These results show that NGF is responsible for the development of an increased noradrenergic innervat ion in the rat ureter after neonatal capsaicin treatment. (C) 1998 Els evier Science B.V. All rights reserved.