Vestibular Sympathetic Nervous System in Guinea Pig

Abstract

The vestibular sympathetic fibers were examined in 20 guinea pigs by immunohistochemical demonstration of tyrosine hydroxylase and dopamine β-hydroxylase. The vestibular sympathetics originated in the ipsilateral superior cervical ganglion and entered the internal auditory meatus along the labyrinthine artery. At the Schwannglial border, some of the sympathetic fibers left the artery and went into both the superior and inferior divisions of the vestibular nerves and made a loose mesh-work among the Scarpa's ganglion cells while other fibers followed the labyrinthine artery. Both types of fibers entered the crista ampularis and otoconial macula after several bifurcations in the cribrosa and terminated either near the capillaries beneath the sensory epithelia or among the vestibular nerve fibers. These fibers traveled freely in the vestibular labyrinth and were not restricted to following blood vessels or vestibular nerve fibers. Some sympathetic fibers made direct contact with the vestibular efferent fibers or the vestibular afferent fibers at the node of Ranvier. Sympathetic fibers were not observed in the sensory epithelia and semicircular canals and were rarely found in the vicinity of the dark cells; however, they were found to be distributed in the endolymphatic sac.

Key Words:

• tyrosine hydroxylase
• immunohisto-chemistry
• vestibular labyrinth
• endolymphatic sac