Book - Anatomical and physiological studies on the growth of the inner ear of the albino rat (1923)

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Wada T. Anatomical and physiological studies on the growth of the inner ear of the albino rat. (1923) Memoirs of the Wistar Institute of Anatomy and Biology, No. 10, Philadelphia.

Rat Inner Ear (1923): I. Cochlea growth | II. Inception of hearing and cochlea growth | III. Growth of largest nerve cells in ganglion vestibulare | Final Summary | Literature Cited

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Anatomical and Physiological Studies on the Growth of the Inner Ear of the Albino Rat

Tokujiro Wada

Wistar Institute Of Anatomy And Biology

Contents

Introduction

Material

Technique

I. On the growth of the cochlea

A. On the growth of the radial distance between the two spiral ligaments

B. On the growth of the tympanic wall of the ductus cochlearis

1. Membrana tectoria

2. Membrana basilaris

3. The radial distance between the habenula perforata and the inner corner of the inner pillar cell at base

4. The radial distance between the habenula perforata and the outer corner of the inner pillar cell (resp., the inner corner of the outer pillar cell) at base

5. The radial basal breadth of the outer pillar cell (including the outer pillar)

6. The radial distance between the habenula perforata and the outer border of the foot of the outer pillar cell

7. The greatest height of the greater epithelial ridge (dem grossen Epithelwulst Bottcher's s. Organon Kollikeri) resp. of the inner supporting cells

8. The radial distance between the labium vestibulare and the habenula perforata

9. The radial distance between the labium vestibulare and the inner edge of the head of the inner pillar cell

10. Vertical distance from the membrana basilaris to the summit of the pillar cells

11. The greatest height of the tunnel of Corti

12. The height of the papilla spiralis at the third series of the outer hair cells

13. The greatest height of Hensen's supporting cells

14. The angle subtended by the extension of the surface of the lamina reticularis with the extended plane of the membrana basilaris

15. Lengths of the inner and outer pillar cells

16. Inner and outer hair cells

17. Deiter's cells

18. Summary and discussion

C. On the growth of the largest nerve cells in the ganglion spirale

Observations

Discussion

Conclusions

II. Correlation between the inception of hearing and the growth of the cochlea

Observation 146

Discussion 152

Conclusions 155

III. On the growth of the largest nerve cells in the ganglion vestibulare

Material and technique 156

Observations 156

Discussion 165

Conclusions 168

Final Summary

Literature Cited

Introduction

Since Alphonse Corti, in 1851, published his famous work on the cochlea of mammals, studies on this organ have been made by many authors and have produced fairly concordant results. Concerning the postnatal growth of the internal ear, however, systematic studies are lacking. Especially is there no investigation, so far as I know, on the growth of the nerve cells in the ganglion spiral, not even in the great work of Retzius. ('84).

It was the special object of these studies, therefore, to follow the growth of the cells forming the spiral ganglion from birth to maturity and to correlate the changes in them with the appearance of the functional responses and with the structural changes in the membranous cochlea. In the course of this investigation studies were made also on the cells of the ganglion vestibulare, in order to see whether these cells differed in their growth from the cells in the spiral ganglion. Both of these ganglia are situated in the course of nervus acusticus, but have, as is well known, entirely different functions.

Thus determinations have been made on the diameters of the cells of the ganglion spirale and of their nuclei at different ages; of the nucleus-plasma ratios and of then* growth in relation to those of other portions of the membranous cochlea. For the cells of the vestibular ganglion similar determinations were also made. Finally, these results have been compared with those obtained from the study of other craniospinal ganglia in the albino rat.

In presenting my results I shall begin with a description of the changes in the larger portions of the membranous cochlea and pass from these to the cell elements themselves, and then to the observations on the ganglion cells and to the correlation between hearing and the growth of the cochlea.


Material

For the present studies forty male and thirty female albino rats were used, representing every phase of postnatal growth and having approximately standard body weights. These were all from the colony of The Wistar Institute, and were sometimes from the same, and sometimes from different litters.

At first all these rats were tested for their ability to hear and their equilibrium, and it was ascertained that after about twelve days of age, or somewhat earlier, they responded positively to the test for hearing. Such examinations were deemed necessary, to make certain that the rats used were normal.

I have arranged the animals thus tested in fourteen groups according to age, each group having five individuals in it. Serial sections from all these cochleas were made by methods to be given later. Most of them were in the plane of the vertical axis of the cochlea, but some were at right angles to it.

From the former I selected four ears in each group for the study of the growth of the cochlea. For the study of the growth of the ganglion vestibulare, I have used for the most part the same specimens. For the study of the sections at right angles to the vertical axis of the cochlea, sections from one ear of each group were used.

Technique

In order to obtain good preparations of this delicate organ, the method of vital fixation (injection under anaesthesia) was used. The method employed, and which proved almost ideal, was that introduced by Metzner and Yoshii ('09), Siebenmann and Yoshii ('08) and somewhat improved by Sato ('17). After the animals had been tested to make sure that they were quite normal, the fixing solution was injected through the aorta under ether. The brain was then carefully removed, care being taken not to drag the trunk of the nervus acusticus, as noted by Nager ('05), and the bulla tympanica was opened to allow the further penetration of the fluid.


The bony labyrinth with its surrounding bones was then placed in the fixing solution for two weeks, the fluid being renewed every day.

The fixing solution which I used consists, according to Yoshii ('09), of

10 per cent formol 74 parts

M tiller's fluid 24 parts

Glacial acetic acid 2 parts

According to Tadokoro and Watanabe ('20), this solution is one of the best, ranking with that of Wittmaack ( '04, '06) and that of Nakamura ('14).

This injection method is sometimes difficult to apply to very young rats on account of the small size and the delicacy of the vessels. When injection failed in very young animals, then immediately the head was cut off and put directly in the fixing fluid. Owing to the incomplete calcification of the very young cochlea, the fixing solution enters rapidly and fixes the deepseated organs in good condition. Since the parts of the internal ear are not yet well developed in the very young rats, they do not suffer from this method of fixation as do the older cochleas.

Indeed, no differences are to be seen between the sections prepared by vital fixation and by decapitation in very young rats.

For decalcification I have employed the following solution during three days, renewing it every day.

Decalcifying fluid

5 per cent aqueous nitric acid 49 parts

10 per cent formol 49 parts

Glacial acetic acid 2 parts

After the specimens had been washed in running water for three days, they were passed through the alcohols from 50 to 97 per cent. For the imbedding I have used 'parlodion' with good results. Here it is to be mentioned that all the cochleas were treated in the same way, even unossified cochlea being passed through the decalcifying fluid, so that there should be absolutely no differences in treatment.


The next important matter is the determination of the plane of the section. For the measurement of growth changes it was necessary to obtain corresponding sections from the several cochleas. In an organ like that of Corti, which changes in its details from one end to the other, however, it is very difficult to accomplish this, but I believe that I have overcome most of the difficulties.

After much testing, I found that a section parallel to the under surface of os occipitale in the fronto-occipital direction runs nearly exactly parallel to the axis of the modiolus of the cochlea. In order to get the same direction from right to left, I have taken as the standard the transverse plane of the under surface of the os occipitale, controlling the direction of the section with a magnifying glass. Thus nearly the same radial direction and nearly corresponding places in the cochlea were obtained in the several series of sections. This makes possible a trustworthy comparison of the measurements and drawings.

The cross-section of the cochlea was gotten by making the plane of the cut transverse to the axis of the modiolus. To get the corresponding levels is difficult. At first I divided all the serial sections by 2^, which is the number of complete turns in the cochlea of the albino rat. Next, from the number of the slides representing each turn, I determined nearly the corresponding level in the cochlea according to age.

All the sections were 10;x in thickness. The sections were stained for the most part with haematoxylin and eosin, but sometimes by Heidenhain's iron haematoxylin or the iron haematoxylin and Van Gieson's stain. For the measurements, however, only the sections stained with haematoxylin and eosin were used.

For the examination of the larger parts of the cochlea and their relations, the sections were projected on a sheet of paper by the Leitz-Edinger projection apparatus, at a magnification of exactly a hundred diameters, and the outline of the image accurately traced. The remaining measurements of the ganglion cells and the smaller portions of the cochlea were made directly under the microscope. The measurements made on the tympanic wall of the cochlea are somewhat complicated, but by the aid of figures 1 and 2 they may be explained. In figure 1 lines 1-1, 1-1'. 2-2, 3-3 indicate, respectively, the height of the arch of Corti, of the tunnel of Corti, of the papilla spiralis (Huschke) at the third series of outer hair cells, and of Hensen's supporting cells, respectively, above the plane of the membrana basilaris.

Lines 4-4' which are the extensions of the surface of the lamina reticularis and of the membrana basilaris, subtend the angle 8.

To get the exact measurements of the radial breadth of the membrana tectoria is very difficult, if not impossible, because it is sinuous in its course; moreover, it differs in thickness from point to point. Therefore, it has been variously described by different authors. Intra vitam fixation tends to prevent distortion. We divide the membrana tectoria, figure 1, into two portions, the first or inner (7-7'-9-9') and the second or outer (5-5 '-7-7') or outer zones of Retzius; each of these is again divided in two at 6-6' and 8-8', as shown in figure 1.

I have measured the radial distance of each portion and added all four together. This total approximates the natural radial breadth of this membrane, and since the sections have all been prepared in the same way and examined by the same method, the relations during growth can be followed.

In figure 2, 1-1 and 2-2, mark the length of the inner and outer pillar cells, respectively, from base to the point, which is situated just under their junction. It is to be noted here that the term ' pillar cell ' here applies to the pillars in the strict sense and does not include the associated cells.

Distances 3 and 7 in figure 2 show the basal breadth of the inner and outer pillars, respectively. The former is identical with the distance between the habenula perforata and the outer corner of the inner pillar after the inner corner of the pillar has reached the habenula perforata, but there is some difference between the two distances in very young rats. Distance 4 is that between the habenula perforata and the inner corner of the outer pillar; distance 5 is that between the habenula perforata and the outer corner of the outer pillar. The latter represents at the same time the radial breadth of the zona arcuata of the membrana basilaris.



Fig. 1 Showing the localities for the measurement of each part of the tympanic wall of ductus cochlearis in the albino rat, 100 days old radial vertical section. 1-1, height from the basal plane to the surface of pillar cells; 1-1', greatest height of the tunnel of Corti; 2-2, height of papilla spiralis at the third series of the outer hair cells; 3-3, height of Hensen's supporting cells; 4~4', 4 indicates the extension of the membrana basilaris and 4' the extension of the lamina reticularis. The two lines subtend the angle 0. The radial breadth of the membrana tectoria is taken as the sum of the four segments between the lines 5-5' and 9-9'.

Fig. 2 Showing the method of measurement for several parts of the tympanic wall of the ductus cochlearis in the albino rat, 100 days old. 1-1, length of inner pillar cell without head; 2-2, length of outer pillar cell without head Distance 3 shows radial distance between habenula perforata and the outer corner of inner pillar at base after twelve days of age this equals the radial basal breadth of inner pillar. Distance 4, radial distance between habenula perforata and the inner corner of outer pillar at base. Distance 5, radial breadth of the zona arcuata (Deiters') of membrana basilaris, and at the same time it indicates radial distance between habenula perforata and the outer corner of outer pillar at base. Distance 6, radial distance between the outer corner of inner pillar and the inner corner of outer pillar at base. Distance 7, radial basal breadth of outer pillar. Distance 8, radial distance between the habenula perforata and outer corner of inner pillar cell at base. Distance 9, radial basal breadth of the outer pillar cell. Distance 10, radial breadth of zona pectinata of the membrana basilaris. Distance 11, radial breadth of entire membrana basilaris.

Fig. 3 Showing the general outline of the cochlea in the radial vertical section albino rat, 100 days of age.



Abbreviations

Line 1, 1, distance between two basal L.L.S., limbus laminae spiralis

spiral ligaments L.S., ligamentum spirale

Line 2, 2, distance between two apical L.S.O., lamina spiralis ossea

spiral ligaments M.T., membrana tectoria

7, first turn N.C., nervus cochlearis

II, second turn O., bone

///, third turn P.S., papilla spiralis

IV, fourth turn S., stria vascularis

D.C., ductus cochlearis S.T., scala tympani

G.S., ganglion spirale S.V., scala vestibuli G.V., ganglion vestibulare


Distance 6 is that between the outer corner of the inner pillar and the inner corner of the outer pillar. Distance 8 is that between the habenula perforata and the outer corner of the inner pillar cell. Distance 9 shows the radial basal breadth of the outer pillar cell plus the outer pillar. Distance 11 shows the radial breadth of the membrane basilaris comprising distance 5 (zona arcuata) and 10, which is the radial breadth of the zona pectinata of the membrana basilaris.

Final summary

This study is concerned with the age changes in the organ of Corti and the associated structures. The changes in the largest nerve cells which constitute the spiral ganglion and the vestibular ganglion, respectively, have also been followed from birth to maturity. On pages 116 to 124 are given the summary and discussion of the observations on the growth of the tympanic wall of the ductus cochlearis.

The conclusions reached from the study of the largest nerve cells in the ganglion spirale appear on pages 143 to 145. On pages 155 and 156 are presented the results of the study on the correlation between the response to sound and to the conditions of the cochlea.

Finally, the observations on the growth of the largest cells in the ganglion vestibu'are are summarized on pages 168 and 169.

It is not necessary to again state in detail the conclusions reached in the various parts of this study.

At the same time, if we endeavor to obtain a very general picture of the events and changes thus described, this may be sketched as follows:


170 ANATOMICAL AND PHYSIOLOGICAL STUDIES ON

Within the membranous cochlea there occurs a wave of growth passing from the axis to the periphery as shown in figures 4 to 13. The crest or highest point of the tissue mass appears at birth near the axis, in the greater epithelial ridge, and then progressively shifts toward the periphery, so that at maturity it is in the region of the Hensen cells. With advancing age the hair cells come to lie more and more under the tectorial membrane and the pillar cells seem to shift toward the axis.

At from 9 to 12 days the tunnel of Corti appears and the rat can hear.

All of these changes occur first in the basal turn and progress toward the apex. The mature relations are established at about twenty days. There are thus two waves of change in the membranous cochlea, from the axis to the periphery and the other from the base to the apex. The rat can usually hear at twelve days of age or about three days before the eyes open.

The largest cells in the ganglion spirale are very immature at birth, reach their maximum at twenty days, and after that diminish in size, slightly but steadily. The rat hears, therefore, before these cells have reached their full size.

The largest cells in the vestibular ganglion are precocious and remarkably developed, even at birth. They cease their rapid growth at about fifteen days of age, but increase very slightly though steadily throughout life.