Auditory Pathway of the Epileptic Waltzing Mouse I. A COMPARISON OF THE ACOUSTIC PATHWAYS OF THE NORMAL MOUSE WITH THOSE OF THE TOTALLY DEAF EPILEPTIC WALTZER MURIEL D. ROSS Department of Anatomy, Medical Center, University of Michigan, Ann Arbor, Michigan Waltzing and epilepsy are hereditary cisms of this paper, and to Dr. Edward traits which appear independently or to- Lauer for his suggestions and his assist- gether in various stocks of mice of the ance in matters of technique. She is also genus Peromyscus. They are inherited in grateful to Dr. Lee R. Dice and the Labo- general as Mendelian recessives (Dice, '35; ratory of Vertebrate Biology for making Watson, '39 j. Young members of the par- the mice and the testing equipment avail- ticular stock of Peromyscus rnnniculatus able to her for this study, and to Dr. Eliza- artemisiae to be described in this study ex- beth Barto, who tested the mice for range hibit both waltzing and epilepsy when of hearing. Assistance was obtained from stimulated by sounds of various kinds. a grant from the Alfonso Morton Clover At the sound of jingling keys, or of certain Scholarship and Research Fund to the pure tones, the young epileptic waltzer Laboratory of Comparative Neurology for whirls in circles and then dashes wildly the preparation of the material for micro- about the enclosure. After a few seconds, scopic examination. Aid in testing the he falls upon his side in an epileptic responses of the experimental animals seizure. His body becomes rigid, his fore- used in this study was supplied through legs are flexed and his hind legs are ex- a grant (MH 375 j to Dr. Lee R. Dice from tended. The animal resumes his circus the National Institute of Mental Health, movements after recovering from the seiz- of the National Institutes of Health, Pub- ure but whirls in a graceful manner, not lic Health Service. wildly as before. As the mouse grows older, it is more and more difficult to in- MATERIALS AND METHODS duce the waltzing and epileptic attack. A total of 26 animals was obtained from Finally, the animal appears to become the Laboratory of Vertebrate Biology for deaf, for he gives no visible sign that he use in this study. Of this number eight hears the sound stimulus. His ears do not animals were normal controls taken from a twitch and he shows no uneasiness. stock of Peromyscus maniculatus blandus This study represents an attempt to as- from Tularosa, New Mexico. They showed sess possible nervous system changes re- neither waltzing nor convulsive behavior lated to the loss of hearing exhibited by when exposed to the stimulus of jingling these mice. In Part I of this report, the keys for 90 seconds. The rest of the ani- central relations of the auditory systems mals were epileptic waltzers, hybrids be- in older, deaf epileptic waltzers will be tween several subspecies of mice. Nine of compared with those in normal controls the epileptic waltzers were considered deaf of the genus Peromyscus. The auditory because they did not twitch their ears in centers of young, partially deaf, epileptic response to a tap on glass, to a squeak, or waltzing mice will be considered separately to keys jingling, and the last procedure did in Part 11. not cause waltzing or a seizure. Six ani- The author is deeply indebted to Dr. mals were young, possessed acute hearing, Elizabeth C. Crosby €or her helpful criti- and both waltzed and had a convulsive 317 318 MURIEL D. ROSS scizure when exposed to the sound of the medulla oblongata dorsolateral to the resti- jingling keys. Three animals had less form body. The posterior end of the acute hearing than the young mice; they tubercle lies at the level of the lateral re- suffered less violent reactions to key jin- cesses of the fourth ventricle. As it is gling, as evidenced by a weak dash or ear followed forward, the dorsal cochlear nu- twitching. One deaf and one young mouse cleus increases in size ventrolaterally and, died of natural causes, leaving 24 animals to a lesser degree, in thickness, reaching which were actually prepared for study. its greatest development in its middle At the end of the experimental testing, third. In these sections it lies dorsolateral all of the animals were sacrificed and per- to the ventral cochlear nucleus and to the fused. Seventeen of these animals were restiform body. Rostra1 to a plane through perfused with 10% formalin; seven with a the caudal part of the genu of VII, the dor- special modification of the Zenker-formol sal cochlear nucleus shortens dorsoven- solution described by Guild ('19). Then, trally and gradually flattens into a narrow the skull cap was opened and the lower band of granular cells which still covers jaw and muscles of the head were cut off. the dorsolateral surface of the ventral The brains were allowed to harden in situ cochlear nucleus. Both ventral and dorsal in 10% formalin for several days and then cochlear nuclei extend rostrally to a plane the temporal bones and/or the brains were through the motor nucleus of the trigemi- removed. nal nerve. None of the cochleae were suitable for The internal organization of the acous- study and will not be considered further tic tubercle differs at various levels. Cau- here. Of the 16 brains which were re- dally, it is composed of a few delicate moved, three were fixed, cleared, and em- fibers and numerous cells; the latter are bedded according to the Huber-Guild pyri- either small in size, fusiform or round, dine-silver method. The tissue became and darkly staining, or they are of me- very hard and shattered when cut at a dium-size, spherical and pale staining. No thickness of 20 p. The 13 remaining pattern of distribution of the cells or of brains were fixed, cleared, and embedded the fibers is observed at this level. As the in paraffin according to the usual methods. acoustic tubercle broadens, the fibers with- Seven paraffin blocks were cut on a rotary in it become thicker and more numerous microtome in sections 25 LI thick, mounted and the cells increase in number. A dis- serially, and stained after the Weil method tinct lamination of the tubercle, involving for fibers. Two brains were cut at 15 cr, both the cells and the fibers, begins at the mounted in serial sections, and stained level of the facial nucleus and ends ros- with cresyl-echt-violet. The remaining four trally in sections through the genu and brains were cut at 25 u, mounted serially, roots of VII. The distance between the and stained with toluidin blue. All of the caudal pole of the acoustic tubercle and brains were cut transversely. the onset of lamination within it is very The first part of this report is based upon short. a study of the acoustic pathway in four Among the observers who have de- series of brains. Brain no. 87932 (nor- scribed the lamination of the acoustic mal, female) and brain no. 85842 (deaf, tubercle in mammals are Ram6n y Cajal female) were stained according to the ('09), Winkler and Potter ('11, '14), and, Weil method. Brain no. 87120 (normal, more recently, Lorente de N6 ('33). Each male) and brain no. 85836 (deaf, male) of the these workers recognized four were stained with cresyl-echt-violet. fundamental layers, although the lami- nae described by each include different DESCRIPTION OF THE NORMAL MATERIAL elements and the nomenclature varies. Lorente de N6, working with Golgi prepa- Primary auditory centers rations of mouse and cat brains, sub- Dorsal cochlear nucleus. The acoustic divided the acoustic tubercle still further. tubercle of the mouse (figs. 1, 2, 3) is In addition to the four laminae, he found comparable with the dorsal cochlear nu- several other distinct areas. In the pri- cleus of higher forms. It is located in the mary acoustic nuclei as a group, he de- NORMAL AND ABNORMAL AUDITORY PATH 319 fined at least 13 different regions and 40 toward the midline as dorsal secondary to 50 types of neurons. cochlear fibers. In the acoustic tubercle of the mouse In addition to the lamination just de- material studied for this paper, four layers scribed, some authors have recognized fur- are distinguishable lying in a lateromedial ther cell groupings within the acoustic direction; these will be described from the tubercle. Thus, Winkler and Potter have surface toward the restiform body. The described a nucleus proprius, which rep- most superficial lamina, Layer I, is poor resents the central unlaminated core of in fibers and cells (fig. 2). Beneath the the tubercle. In mouse brain no. 87120, pia there are small, round or fusiform, stained for cells, nucleus proprius begins dark staining cells intermingled with in sections at the level of the facial nu- others medium in size, round or ovoid, and cleus, just caudal to the beginning of lami- pale staining. This lamina I corresponds nation of the acoustic tubercle. Some of to both the surface (“epithelial”) and the its cells can be traced rostrally to sections “superficial plexiform” layers of Itam6n y through the caudal end of the gem of VII. Cajal, and to the “stratum griseum super- At this level, with an increase of similar ficiale” of Winkler and Potter (’11). cells within the rest of the acoustic tu- Winkler and Potter employed “lamina bercle, the nucleus proprius can no longer cellularis” for the second layer, which is be distinguished. rich in cells as the terminology suggests. Nucleus proprius (figs. 1, 2, 3) varies This lamina is Ram6n y Cajal’s “zone of considerably in size from level to level, granule and large fusiform cells.” Layer but small, round, dark staining cells arc I1 (fig.