Pathological and functional changes following hemisection of the lateral ampullary nerve

Expression of brain-derived neurotrophic factor and its receptor mRNA in the vestibuloauditory system of the bullfrog

Brain-derived neurotrophic factor (BDNF) is a neurotrophin which has been suggested to play a crucial role in the development and maintenance of the inner ear. In the present study, we investigated the expression of mRNAs of BDNF and its high-affinity receptor trkB in the vestibuloauditory system of the adult bullfrog. In situ hybridization was performed using riboprobes transcribed from Xenopus BDNF and trkB cDNA clones. BDNF mRNA was expressed in the sensory epithelia of the ampullary cristae, utricular and saccular maculae, lagena, and amphibian and basilar papillae. Strong hybridization for BDNF mRNA was also found in neuron somata of the vestibuloauditory nuclear complex. trkB mRNA was detected in the sensory epithelia of all vestibular and auditory endorgans. High levels of both BDNF and trkB mRNAs were found in vestibuloauditory ganglion cells. These results support the hypothesis that BDNF participates in the maintenance of vestibuloauditory neurons and may be important for the trophic regulation of vestibular and auditory sensory epithelia in this animal model.

Effect of different vestibular lesions upon body equilibrium function in squirrel monkeys

By utilizing the squirrel monkey rail test, postoperative compensation status after unilateral saccular macula destruction, unilateral utricular nerve section and unilateral lateral ampullary nerve section, were studied in a quantitative fashion and the results were statistically compared. First, it was confirmed that the preoperative random assignments of subjects were evenly distributed among different experimental categories and therefore inter-categoric statistical comparisons of postoperative status were valid. Minimal effect after the unilateral saccular macula ablation toward the maintenance of body equilibrium was reconfirmed. The utricular input is probably the most important for the maintenance of body equilibrium function, inasmuch as slightly less equilibrium disturbance was found after unilateral lateral ampullary nerve cut even though the difference was not significant.

Experimental studies on the nerve--sensory cell relationship during degeneration and regeneration in ampullar nerves of the frog labyrinth

The degeneration and regeneration of afferent and efferent nerves to the crista ampullaris in the frog were studied after transsection of the ampullar nerves. In some experiments one or both rostral ampullar nerves were simply divided and left in place. In other experiments the ampullar nerves to the horizontal and to the anterior vertical crista were divided and the branch to the former was brought into contact with the distal stump of the anterior vertical ampullar nerve. Sensory cells in the labyrinth survived total denervation for 1-2 weeks without regular signs of ultrastructural damage. The afferent synaptic structures in these cells were often preserved in the denervated stage. The afferent nerve fibres degenerated earlier than the efferent ones. Both type of fibres reinnervated the vestibular epithelium after division of the ampullar nerve. The fibres from a horizontal ampullar nerve could reinnervate a denervated anterior vertical crista, resulting in misdirected reflexes. About 40 days after division both function and morphological organization had been restored to normal.