Histamine immunoreactivity changes in vestibular-lesioned and histaminergic-treated cats

Abstract

Histamine is likely involved in vestibular function recovery since histaminergic medications are effective in vestibular-related syndromes. We investigated the histamine immunoreactivity changes after unilateral vestibular neurectomy and the effects of betahistine (a partial histamine H 1 receptor agonist and an histamine H 3 receptor antagonist) and thioperamide (a pure histamine H 3 receptor antagonist) treatment in cats. Histamine staining was analyzed in the tuberomammillary and vestibular nuclei through immunohistochemical methods and quantification techniques in light microscopy. Unilateral vestibular neurectomy induced a strong bilateral decrease in histamine immunoreactivity in the vestibular nuclei and a smaller reduction in the tuberomammillary nuclei in both acute (1 week) and compensated (3 weeks, 1 year) cats. One-week thioperamide or betahistine treatment led to a near-total lack of staining in these structures in both lesioned and control cats. One-month 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 tuberomammillary nuclei, promoting vestibular functions recovery, and betahistine could contribute to this process by acting on both the presynaptic histamine H 3 and postsynaptic histamine H 1 receptors.