Ultrastructural observations of efferent terminals in the crista Ampullaris of the toadfish, opsanus tau

Abstract

The present study was conducted to visualize the ultrastructural features of vestibular efferent boutons in the oyster toadfish, Opsanus tau. The crista ampullaris of the horizontal semicircular canal was processed for and examined by routine transmission electron microscopy. The results demonstrate that such boutons vary in size and shape, and contain a heterogeneous population of lucent vesicles with scattered dense core vesicles. Efferent contacts with hair cells are characterized by local vesicle accumulations in the presynaptic terminal and a subsynaptic cistern in the postsynaptic region of the hair cell. Serial efferent to hair cell to afferent synaptic arrangements are common, particularly in the central portion of the crista. However, direct contacts between efferent terminals and afferent neurites were not observed in our specimens. The existence of serial synaptic contacts, often with a row of vesicles in the efferent boutons lining the efferent-afferent membrane apposition, suggests that the efferent influence on the crista may involve both synaptic and nonsynaptic, secretory mechanisms. Further, it is suggested that differences in more subtle aspects of synaptic architecture and/or transmitter and receptor localization and interaction may render the efferent innervation of the peripheral crista less effective in influencing sensory processing.

Determinants of Spatial and Temporal Coding by Semicircular Canal Afferents

“…It is evident from Fig. 8B that the range of the phases re: velocity seen in the hair cell voltage-clamp records falls far short of the wide range of afferent nerve response phases (Holstein et al 2004a; also cf. Figs.…”

“…The flat gain and phase of hair cells over the bandwidth tested is somewhat surprising, but is notable because our experiments have been conducted in vivo and the stimuli are restricted to naturally occurring physiological levels and rates. Hair cells hardly adapt, whereas afferent adaptation spans several orders of magnitude (Holstein et al 2004a). Previous data indicate that the extent of slow adaptation in hair cells may be reduced as the stimulus magnitude is decreased to the physiological range (Holt et al 1997;Corey 1992, 1994).…”

Diverse Synaptic Terminals on Rat Stapedius Motoneurons

“…Apparently, those on spinal α-motoneurons arise from a cholinergic source in the spinal cord (McLaughlin 1972). A similar Cist (C) terminal type has been identified on other motoneuron types within the CNS Saxon et al 1996;Ichiyama et al 2006) as well as in the periphery-efferent terminals on auditory and vestibular hair cells (Jones and Eslami 1983;Holstein et al 2004). Whether Cist terminals on SMNs are excitatory or inhibitory is unknown.…”

“…Cist terminals, if they are similar to terminals on spinal α-motoneurons, may arise from a source in the spinal cord (McLaughlin 1972;Conradi et al 1979). A cistern-containing synapse appears in the periphery-efferent terminals on auditory and vestibular hair cells (Jones and Eslami 1983;Holstein et al 2004). In the auditory periphery, the subsynaptic cistern and associated elements in synapses onto outer hair cells may generate slow effects associated with calcium release (Sridhar et al 1997).…”

A comparison of the external morphology of the membranous inner ear in elasmobranchs

“…Group: Mean ratio of organ height and width of the species comprising each of the new groupings. canals and putative differences in the cupula mechanics within the ampulla are all variables that may affect canal responses (Bernacsek and Carroll, 1981;Holstein et al, 2004;Hullar, 2006). Therefore, it would be premature and possibly misleading to infer any functional significance of differences based only on the length and diameter of the canals in different species.…”