ACHE-STAINING OF TYPE-II GANGLION-CELLS, PROCESSES AND TERMINALS IN THE COCHLEA OF THE MOUSTACHED BAT

There have been a number of reports showing that ganglion cells of sen sory neurons may be stained by traditional acetylcholinesterase (AChE) histochemical techniques commonly used to demonstrate efferent nerve fibers and terminals. AChE-staining has been described for cell bodies in the vestibular and spiral ganglia; staining of peripheral and cent ral processes, however, is rare and the presence of reaction product i n afferent terminals has not been reported. The outer hair cells of mu stached bats, Pteronotus parnellii, differ from those of most mammals in that they typically have a single, large efferent terminal surround ed by 5-7 small, afferent terminals. In this animal an AChE-positive r eaction was found not only in efferent fibers and terminals but also i n type II ganglion cells, their peripheral and central processes and i n outer hair cell terminals. The stained cell bodies were smaller than the unstained type I ganglion cells and they were much fewer in numbe r. The processes of the stained cells could be followed from the soma. The central processes were dispersed throughout the VIIIth nerve trun k. Stained peripheral processes were evident in the osseous spiral lam ina, floor of the tunnel of Corti and first space of Nuel and in the o uter spiral plexus along the sides of the outer phalangeal (Deiters') cells. AChE-stained afferent terminals were easy to identify after tra nsection of the crossed olivocochlear bundle (COCB) and subsequent deg eneration of large efferent terminals. These results are of interest i n that assessments of efferent nerve histochemistry after COCB transec tion need to recognize the potential contribution of AChE reaction pro duct in afferent terminals. The functional significance of AChE-positi ve sensory nerves is not known; the positive reaction of the type II n eurons does not mean that they are cholinergic.