HISTAMINE IMMUNOREACTIVITY CHANGES IN VESTIBULAR-LESIONED AND HISTAMINERGIC-TREATED CATS

Histamine is likely involved in vestibular function recovery since his taminergic medications are effective in vestibular-related syndromes. We investigated the histamine immunoreactivity changes after unilatera l vestibular neurectomy and the effects of betahistine (a partial hist amine H-1 receptor agonist and an histamine H-3 receptor antagonist) a nd thioperamide (a pure histamine H-3 receptor antagonist) treatment i n cats. Histamine staining was analyzed in the tuberomammillary and ve stibular nuclei through immunohistochemical methods and quantification techniques in light microscopy. Unilateral vestibular neurectomy indu ced a strong bilateral decrease in histamine immunoreactivity in the v estibular nuclei and a smaller reduction in the tuberomammillary nucle i in both acute (1 week) and compensated (3 weeks, 1 year) cats. One-w eek thioperamide or betahistine treatment led to a near-total lack of staining in these structures in both lesioned and control cats. One-mo nth betahistine treatment had weaker effects in the compensated cats. We conclude that vestibular lesions reduce histamine staining because of an increase in histamine release in the vestibular and tuberomammil lary nuclei, promoting vestibular functions recovery, and betahistine, could contribute to this process by acting on both the presynaptic his tamine H-3 and postsynaptic histamine H-1 receptors. (C) 1997 Elsevier Science B.V.