Vestibular compensation in the cat: the role of the histaminergic system.

Histamine is thought to be involved in the recovery of vestibular function as histaminergic medications are effective in vestibular-related syndromes. We conducted studies in the cat to assess the effects of betahistine (a histamine-like substance) on the behavioural recovery process after unilateral vestibular neurectomy (UVN). We also investigated histamine immunoreactivity changes in the vestibular and tuberomammillary nuclei of betahistine-treated lesioned cats compared with untreated and unlesioned cats. Betahistine strongly accelerated the behavioural recovery process after UVN, with a time benefit of approximately 2 weeks for both static posture (support surface) and dynamic equilibrium function (locomotor balance) compared with untreated animals. A bilateral decrease in histamine immunoreactivity was seen in both acute and compensated UVN cats; this effect was strongly accentuated with betahistine treatment. In conclusion, the results indicate that vestibular lesion reduces histamine staining due to an increase in histamine release in the vestibular and tuberomammillary nuclei that promote vestibular recovery. Betahistine dihydrochloride should contribute to this process by acting on both the presynaptic histamine H3 and postsynaptic histamine H1 receptors.