Catherine A. Smith

The structure and innervation of the pigeon's basilar papilla

Sensory cells in the pigeons basilar papilla can be divided into three groups on the basis of shape, cuticular plate dimensions, and innervation. Tall hair cells are columnar with deep cuticular plates and are found over the superior cartilaginous plate from proximal to distal end of papilla; they cover the entire papilla at distal tip. Large cochlear and small efferent nerve endings terminate on their basal ends. Short hair cells are pitcher-shaped, with flattened cuticular plates and are found only on the proximal two-thirds of the free basilar membrane. They have small cochlear and large efferent nerve terminals. Transitional cells are present in between. The efferent nerve fibers, as revealed by the AChE stain, form extensive networks from which many branches are given off to the hair cells. The cochlear nerve fibers, as revealed by the Holmes silver stain, take transverse courses across the papilla with few branches before terminal ramification. Supported by N.I.H. grants Nos. NB 00966-13 and NS 08813-01.

The Delayed Effects of Ethacrynic Acid on the Stria Vascularis of the Guinea Pig

Guinea pigs were administered 40 mg ethacrynic acid per kg b.wt. and sacrificed at 30-48 minutes, 3-4 hours, 2 or 7 days post-drug. Cochlear potentials (EP and CP) were monitored before sacrifice. At 30-48 minutes, the potentials had decreased considerably, and a marked edema plus cytological changes were visible in the stria vascularis. The potentials had recovered to about 75% of their original value at 3-4 hours; some cell recovery was visible, but the edema was still present. Potentials recorded from the basal turn were normal at 2 and 7 days, although some strial cells showed deterioration.

Structure of the Avian Tectorial Membrane

The avian tectorial membrane is a thick massive-appearing structure permeated by cavities, which probably facilitate the diffusion of endolymph. As revealed by scanning and transmission electron microscopy, the cavities are arranged in a characteristic honeycomb-like pattern and each hair bundle is enclosed in an alveolus. The open ends of the alveoli show the impressions of sensory hairs on one side. The rims about the cavities are attached to the microvilli of the supporting cells by means of fibrous material. These morphological aspects are compared with those of reptiles and mammals, and the functional significance of the fibrillar anchors is discussed.

Golgi Stains On The Guinea Pig Organ Of Corti

The Golgi stain has been used to study branching of cochlear and efferent nerve fibers within the organ of Corti of the guinea pig. Impregnations of the fibers of the olivo-cochlear tract was obtained more often than of the cochlear nerve fibers. Some cochlear nerve fibers showed branching limited to the terminal end of their spiral traverse.

Auditory Receptor Organs of Reptiles, Birds, and Mammals

Publisher Summary This chapter describes the auditory receptor organs of reptiles, birds, and mammals. Although reptiles have poor conduction of sound because of the low-grade sensitivity to their ears, some of them have great variations in their middle-ear structure. Birds have a more stable middle-ear structure but still have the columellar apparatus and the lagena that are found in reptiles. The ears of monotremes represent an intermediate stage between reptiles and mammals. They retain the lagena as well as the stapes with the single shaft. The reptilian papillae are all small and, except for the alligator, have a receptor cell population that is composed of nondifferentiated hair cells. The pigeon displays two populations of differentiated hair cells with a distinctive distribution of afferent and efferent nerve fibers. The location of tall and short hair cells is similar in part to that of inner and outer hair cells in the organ of Corti of mammals.

Stereo-kinociliar bonds in mammalian vestibular organs.

The ultrastructure of the apical end of the hair bundle of the vestibular hair cell in the guinea pig was studied by transmission electron microscopy using osmium and aldehyde-osmium fixed specimens. Stereo-kinociliar bonds were a regular finding in both cristae and maculae. The bond unit consisted of two parts: extracellular, interciliar filaments of macromolecular size and an intracellular structure, bound to the plasma membrane within the kinocilia. In the cristae, the stereo-kinociliar bonding was usually effected by only one bond unit between a single stereocilium and the kinocilium; in the maculae the units were generally paired and several stereocilia were coupled to each kinocilium.

Golgi Stains of the Cochlear Nerve Fibers

The terminal branching of the cochlear nerve dendrites within the organ of Corti of the guinea pig has been studied by means of the Golgi impregnation methods. Under fortuitous conditions, only a few nerve fibers are stained, so that the ramifications of a single nerve fiber can be studied. There appears to be some difference between the branching of the outer spiral nerve fibers in the basal coil and those in the upper coils. The cochlear nerve fibers which have been found in the basal coil either exclusively or predominantly supply a single row of outer hair cells. The nerve fibers in the upper coils generally supply two, and often all three rows of outer hair cells. In a previous report [Acta Oto‐Laryngol. 75, 203 (1973)] we were uncertain if the latter were cochlear nerve dendrites or efferent olivo‐cochlear axons. Electron microscopy has now supplied evidence that our previous assumption was correct, and that these nerve fibers are cochlear. The outer spirals studied thus far all course for some dist...

The Auditory Receptor Organs of Birds

Birds have retained at least two reptilian features; one, the compact arrangement of sensory and sustentacular cells on the basilar membrane, and two. a kinocilium in many, if not all, of the hair bundles. The cytoarchitecture of the avian papilla Seems to be quite consistent between families. All the birds thus far examined (pigeon, chicken, parakeet, and sparrow) have two major types of sensory cells: tall hair cells and short hair cells. Each type has a characteristic distribution along the papilla, and a distinctive pattern of efferent and afferent nerve endings. The tectorial membrane is thick and bulky but highly cavitated. Only the tallest of the cilia appear to penetrate into its mass. It is also attached to all the sustentacular cells on the papilla. It appears that both birds and mammals eventually developed stabilized auditory receptor organs, but with a different organization. Even the most primitive of existing mammals (the monotremes) clearly point toward the direction of the organ of Corti and the cochlear duct which is found in the multitude of other living mammals. [Supported by NIH Grant No. 08813.]

The Effects of Low Dose Ethacrynic Acid on the Guinea Pig Cochlea with Special Reference to Normal Variations in the Stria Vascularis

A controlled study of the effects of ethacrynic acid (5 mg/kg/day) vs. saline for 7 days on the guinea pig cochlea is described. The a.c. cochlear potential, d.c. endocochlear potential, Preyer pinna reflex, number of hair cells and ultrastructure of the cochlear duct were studied as indices of cochlear integrity. There were no differences between control and experimental groups in any of these indices. An unexpectedly wide variation in the histologic and cytologic appearance of the normal stria vascularis at the light and electron microscopic levels is described.

Function and structure of the avian peripheral auditory system

Studies of the function of the avian peripheral auditory system originated with cochlear microphonic recordings from pigeon by Wever and Bray in 1936. More recently, there have been several studies of the response properties of avian auditory‐nerve fibers; these will form the basis of our review of the function of the avian periphery. In many respects, the characteristics of avian auditory‐nerve fibers are quite comparable as is the precision of phase‐locking to low‐frequency tones. On the other hand, there do appear to be significant differences. For example, tuning curves of avian auditory‐nerve fibers seem to lack the low‐frequency tails found in tuning curves of mammalian fibers. Rates of driven and spontaneous activity are higher in birds than in mammals. Spontaneous activity of many avian fibers can be suppressed by appropriate single tones, whereas single‐tone suppression has rarely been reported in mammalian auditory‐nerve fibers. In light of these similarities and differences in function, it is i...