Episodic blockade of cranial nerve VIII provokes asymmetric changes in lobule X of the rat.

Although debilitating syndromes like Ménière's disease are in part characterized by recurrent or episodic vestibular disturbance the study of episodic vestibular disruption has only recently been possible with the introduction of a new model utilizing tetrodotoxin (TTX). In the present study, serial unilateral transtympanic administration of TTX produced behavioral symptoms indicative of transient vestibular disruption and novel patterns of Fos activity in the brainstem and cerebellum. Following two or three serial injections of TTX and a final survival time of 2 h, Fos immunocytochemistry revealed a distinct pattern of labeling in the brainstem that differed temporally from that observed following a single unilateral TTX injection. Specifically there was protracted expression of Fos in the beta subdivision of the inferior olive (IO) on the side ipsilateral to TTX treatment. In the cerebellum, the hallmark of episodic vestibular blockade was an asymmetric pattern of Fos labeling that involved all three layers of the cortex. In particular, there was prominent Fos labeling of Purkinje cells in the contra-TTX half of lobule X. In view of the fact that Fos labeling is not found in Purkinje cells following a single transient event or following peripheral vestibular ablation, it is suggested that Fos expression in Purkinje cells is a unique feature of episodic vestibular disruption and may represent a novel plastic response by a select population of Purkinje cells to episodic functional deafferentation.