Rate of climbing fiber degeneration in rabbit cerebellum following parafloccular stalk and...

Rate of Climbing Fiber Degeneration in Rabbit Cerebellum Following Parafloccular Stalk and Medullopontine Lesions

HUGO MEJIA Washington University School of Medicine, Department of Neurology and Neurological Surgery (Neurology), 660 South Euclid, Box 81 11, St. Louis, Missouri 631 3 0

ABSTRACT To resolve inconsistencies in experimental studies which use reduced silver methods to detect cerebellar climbing fiber sources within the brain stem, an evaluation of the temporal course of degeneration was under- taken. The paraflocculus of the rabbit is uniquely situated within the temporal bone and connects with the corpus cerebelli via a stalk passing through a bony foramen. A unilateral electrolytic lesion deafferented the paraflocculus without disturbing blood supply or causing other damage (18 animals). Comparatively, another group of unilateral lesions was placed at the dorsolateral pontomedullary junction, adding significantly to the cortical area dederented (12 animals). Animals of each group were killed at successively longer intervals commencing a t 18 hours, and a modified Fink-Heimer impregnation process was applied to the cerebellar cortex and opposite-sided controls.

In parafloccular lesions, degeneration was detected at 24 hours in the climbing fibers of the molecular layer. At successively longer intervals, degeneration became increasingly evident in granule layer and white matter. Subsequent to dorsolateral pontomedullary lesions, climbing fiber degeneration was first observed in the molecular layer a t 24 hours and was clearly evident there at 36 hours. By 72 hours degeneration had reached the white matter, meanwhile disappearing in the molecular layer where it was first seen.

Using techniques of Nauta-Fink-Heimer to display secondary climbing fiber degeneration in cerebellar cortex, it was found that too long post-operative intervals could preclude its detection, since in both groups of animals it com- menced earlier and disappeared sooner in the molecular layer.

Silver impregnation techniques for degenerating axon terminals and for tracing tracts to their termini within the central nervous system were described as early as 1932 by Hoff ('32), Foerster et al. ('33), Gibson ('371, Lawrentjew ('34), and gained increased application after Glees ('46), Nauta ('50), Nauta and Gygax ('51), and Fink and Heimer ('67). Yet, for whatever reason, i t has been especially difficult to demonstrate the secondary degeneration of cerebellar climbing fibers subsequent to appropriate lesions involving their cells or origin. These terminals, ramifying lin- early along the arborizations of the Pur- kinje dendrites of the cerebellar molecular layer, stand in contrast to the larger com- pact mossy terminals of the granule layer which leave more lasting clues of their secondary degeneration. If the fine caliber

J. COMP. NEUR., 165; 433-456.

of the climbing fiber does permit speedier degeneration, removal of the products of disintegration could significantly precede corresponding changes in mossy terminals, thus explaining the variable results of Mis- kolczy ('34), Carrea et al. ('47), Szenta- gothai and Rajkovits ('59), O'Leary et al. ('70), all of whom sought evidence of climbing fiber degeneration.

In the effort to determine if the time factor is of prime importance in demon- strating secondary climbing fiber degeneration, the stalk of the rabbit paraflocculus was selected as a site for making unilateral electrolytic lesions. That cerebellar adnexa is uniquely situated within a fossa of the temporal bone and is con-

' This study was supported by Grant NS045 from the National Institutes of Health, United States Public Health Services.

433

434 HUGO MEJIA

nected with the corpus cerebelli via a stalk passing through an intervening foramen. An electrolytic lesion there severs its en- tering afferents at a short distance from their terminus without disturbing the parafloccular blood supply or doing direct damage to either its cortex or white matter. Further confirmation was sought by con- ducting a second experiment at a greater distance effected by destruction of the dorsolateral quadrant of the medulla at the medullopontine junction. The post-operative interval required for initial detection of terminal cerebellar degeneration ranged from 24 hours for the shorter as compared with 36 hours for the longer distance along the path involved.

MATERIALS A N D METHODS

1. Parafloccular stalk lesions (Group I)

Healthy rabbits four months old were used. Animals were excluded in the event of anesthetic complications such as respi- ratory arrest or shock developing during surgery, or where late complications en- sued such as vascular occlusion compli- cated by cerebellar infarction. A total of 19 animals was suitable for histological study. All had been alert and able to hop about immediately after the procedure and remained in good health throughout the post-operative period.

Diazepam,z 0.5 mg/kg/body weight and a commercial mixture of Fentonyl, 0.5 mg/ ml with Droperidol,3 2.5 mglml, at a dose of 2 ml/kg body weight, were injected intra- venously in divided doses. Via an occipital craniectomy and under a dissecting microscope the left parafloccular stalk was exposed (fig. 1). A 24-gauge needle electrode, insulated to within 2 mm of the tip, was advanced into the stalk (fig. 2). Using a Grass radio-frequency lesion maker (model LN-3), a lesion 3 mm in diameter was produced. There was no bleeding in the majority of animals, and the cerebellum contin- ued to pulsate normally. Penicillin, 600,000 units, was given routinely during the post- operative period. Eighteen animals produced histologically successful results.

2. Dorsolateral medullopontine lesions

The same criteria for anesthetic and post-operative complications were followed.

( ~ r o u p rr)

Twelve preparations were satisfactory for study.

Through a midline occipital craniec tomy, the left side of the medulla to the cervico- medullary junction was exposed. With the aid of a micrometrically controlled ad- vance mechanism, an electrode, similar to that used for the first group, was intro- duced in the dorsolateral aspect of the medulla at the level of the obex, and advanced 10 mm rostro-ventrally at a rostro-caudal angle of about 30" in relation to the surface. Three radio-frequency lesions were made, one at a depth of 10 mm, a second at 6 mm, and a third at 3 mm, respectively. They invariably became con- fluent, forming a corresponding longitudi- nal defect in the dorsolateral lower pons and upper third of the medulla.

Post-operatively, a majority of the animals developed rotational ataxic body move- ments, conjugate deviation of head and trunk toward the side of the lesion, and rotational nystagmus. Each animal was placed in a hammock-like support and hung from the inside of the cage to pre- vent self-injury. Penicillin, 600,000 units, was given during the immediate post-operative period.

3. Sacrifice and tissue preparation

Animals of Group I were sacrificed at 24 hours, and at two, three, four, and seven days after surgery. Two to four animals were available for each interval. Using the same anesthesia as for the original surgery, through a left thoracotomy, a Foley catheter was placed in the left ven- tricle and the ascending aorta was can- nulated as described elsewhere (Mejia, '74). A total of three liters of 10% formalin in normal saline at 34°C was de- livered by a Mayo roller pump operating at a rate of 150 mumin.

After the perfusion, the cerebellum and brain stem of each animal were removed in toto under the dissecting microscope and stored in 10% formalin from two to six weeks. Following albumin embedding (Snodgrass and Dorsey, '63), 25 micra frozen sections were cut serially in the

2 Available from Roche Laboratories under the trade

3 Available from McNeil Laboratories under the trade name of Valium.

nameof Innovar.

RATE OF CLIMBING FIBER DEGENERATION 435

transverse plane and stored in 1% formalin at 34°C.

Sections were impregnated using different variations of the original Nauta ('50), the Nauta-Gygax ('51) and finally with the Fink-Heimer Procedure I (Fink and Heimer, '67), modified slightly (Nauta and Heimer, '71; personal communication) in the following steps:

Step 2: 0.1% Potassium Permanga- nate solution for 15 to 20 minutes was used.

Step 6: Solution A for 45 minutes. Step 7 : Solution B for 45 minutes. Step 8:

Step 9:

Rinse in distilled water, three changes, for a total of five minutes.

Solution C is made of 1.0 cc of base mixture in each 10 cc of 2.5% AgN03, stirring until dissolved. Base mixture is made of nine parts of 2.5% NaOH and six parts of concentrated NH3. Solu- tion C is used within ten minutes and tissue is kept in this solution for two and one-half minutes. Minimal increases in the amount of base mixture in solution C made sections proportionally lighter, an effect that eventually reached the point where it interfered with the impregnation of degenerating fibers. Decreases of base mixture had the reverse effect. Other effects occasioned by duration of exposure of section to solutions, variation on pH, and ratio between solutions, have been described by Heimer ('70).

Animals of Group I1 were sacrificed at 18, 24, 36 hours, and at two, three and four days after surgery. Except for s e p arate sectioning of the brain stem in a transverse plane and the cerebellum in a sagittal plane, and the staining by the Weil-Weigert method of the brain stem frozen sections, other procedures were iden- tical with those used on Group I animals.

1. Paraflocculus ipsilateral to stalk lesion

Of the several silver impregnation techniques used on the cerebellum the modified Fink-Heimer procedure gave the best results. In animals studied 24 hours after making a lesion, the climbing fiber degeneration was discretely localized (figs. 3, 4) in the cortical depth. Climbing fibers showing the characteristic Indian file beaded appearance of fine axons during secondary degeneration were confined initially to the

RESULTS

molecular layer. There the climbing fiber traces could be followed continuously along the P shaft dendrite, dividing in tandem with secondary and tertiary dendrites, and ending short of the pial investment. The entire thickness of the molecular layer was free of signs of degeneration other than those involving climbing fibers. Nor was degeneration of any sort seen in the granule layer or white matter at this time.

In the 2-day survival group (fig. 5) the density of degenerating climbing fibers had decreased in the molecular layer when compared with the 24-hour animals. There was also minor degeneration in the granule layer but none in the white matter. In animals surviving three days (fig. 6) only occasional and ill-defined degenerating climbing fibers were impregnated. None could be seen after four days, and the molecular layer showed only the charac- tersitics of the control silver impregnated preparation.

In all animals with survivals of three or more days (figs. 6, 7) degenerating fibers could be followed from the white matter into the granule layer. Some of the latter showed terminal clusters of fine silver precipitate having the shape of mossy terminals (fig. 6). Degenerating fibers were most evident in the white matter of 4- to 7-day animals (fig. 7). In all of these animals the paraflocculus opposite to the side of the lesion was included in the same impregnated tissue section as a histological control. The parafloccular cortex and white matter contralateral to stalk lesions had no evidence of fiber degeneration at any survival intervals (fig. 9).

2. DOTSOkZteTUl p o n t o m e d u h r y lesions Eighteen-hour animals showed no de-

generating climbing fibers. At 24 hours, occasional ill-defined climbing fibers were encountered in the molecular layer of the paravermian region (fig. 10). Otherwise, both cortex and white matter appeared normal at that stage. However, at 36 hours, there was marked evidence of molecular layer climbing degeneration, comparable with that observed in parafloccular stalk lesions. All involved fibers showed the typi- cal beaded pattern traceable along a dendritic arbor to the tertiary dendrites. There was still no degeneration evident in either granule layer or white matter (figs. 11,

436 HUGO MEJIA

12, 13). By contrast, no climbing fibers were seen in the molecular layers of animals with post-operative survival times of two days or longer, nor did the molecular layer of the experimental side differ in any other way from the controls. However, degeneration was evident in the granule layer of the lesioned side at two days, a minimal scatter also being evident in the white matter (fig. 14). A s survival time lengthened, the locus of maximal fiber degeneration shifted markedly toward the white matter. At three days (fig. 15) characteristic degenerating mossy terminals could be seen in the granule layer. Sec- tions from the control side were negative in all animals.

Brain stem sections on Group I1 animals showed destruction of 90% of the dorse lateral medulla in its upper third involving restiform body, cochlear nuclei, trigeminal nuclei and spinal root, and lateral part of the vestibular nucleus complex (fig. 9). In most of the animals, the rostra1 extent of the lesion encroached on the ipsilateral pontine peduncle as well.

3. Purhinje dendrite degeneration, Group 1 animals; possible confusion with

degenerating climbing fibers In some preparations of Group I animals,

areas adjoining the lesion and suspect of direct trauma showed trellis-like structures presenting an irregularly granular or beaded texture. Viewed in a plane paralleling the cerebellar folia they took the shape of columns of scattered dots radiating from the P cell level toward the periphery. Seen perpendicular to the axis of a folium, the trellis-like structures were readily identi- fied as shrunken P cell dendritic arbors (figs. 16-19). Their massive destruction leaves the related climbing fibers without an anchorage, probably causing them to degenerate after this receptor surface has been drastically altered.

DISCUSSION

According to Ramon y Cajal ('28) there is a direct relationship between fiber diameter and onset of degeneration, the larger fibers showing the earlier onset. This gen- eralization has been shown to apply to peripheral and spinal cord axons, but rel- ative onset of degeneration between cerebellar mossy and climbing fibers would

appear unsupported. In climbing fibers the earliest terminal degeneration is seen in the fine superficial rami. Only later do larger caliber mossy terminals also show degenerative changes. The evidence strong- ly suggests, but is insufficient to demonstrate conclusively, that degeneration occurs first in the distal reaches of the climbing fibers and moves proximally. A series having shorter time gaps extending throughout the 7-day period would be required for support of such an assumption.

Earlier workers who searched for the origin of cerebellar afferents seem to have been influenced by Cajal's estimates of degeneration, and thus might have inad- vertently ignored the fine climbing fibers. Among the students of the cerebellar paths involved in presumptions based on Cajal's studies were Miskolczy ('3 1, '34), Snider ('36), Mettler and Lubin ('42), Carrea et al. ('47), Grant ('62), Brodal and Grant ('62), and Brodal and H~ivik ('64). In most such studies, utilizing intervals of 48 hours or more, little, if any, climbing fiber degeneration could be shown to exist. Carrea et al. ('47) also produced intracerebellar lesions involving the deep nuclei and white matter with variable results. Only Szenta- gothai and Rajkovits ('59), after inferior olivary lesions, found climbing fiber degeneration in the lower part of the molecular layer.

Desclin ('74) has recently detected early climbing fiber degeneration in the cere- bellums of rats following systemic administration of 3-acetylpyridine intraperitone- ally. He concluded that the inferior olive was the major and probably the only source of climbing fibers because of the extensive degeneration also seen in the inferior olives of his preparations. However, that anti- metabolite produces widespread cellular changes perhaps related to anoxia. Des- clin and Escubi ('74), for example, cite other workers who have described changes in the hippocampus, basal ganglia, and several brain stem nuclei besides the inferior olive (Coggeshall and McLean, '58; Denk et al., '68; Herken, '68; Hicks, '55; Kiokegami and Fuse, '61; and Lierse, '65).

The cerebellar substance as well as its exogenous axons would also seem directly involved in Desclin's study as evident from the numerous degenerating Purkinje's dendritic arbors he reports and illustrates in

RATE OF CLIMBING FIBER DEGENERATION 437

his figure 8 (Desclin, '74). Such massive dendritic involvement is similar to that reported adjoining electrolytic lesions in the present work (figs. 16, 19). Therefore one may question his inference that the climbing fiber degeneration he describes is due to inferior olivary nuclear involvement and that alone.

Past failures to demonstrate climbing fiber degeneration from extra-olivary sources known to project to the cerebellum may well have been due to technical inadequa- cies. There is also neurophysiological evidence of extra-olivary sources of evoked climbing fiber potentials (Oscarsson, '69a,b; Sasaki, '69; Batini and Pumain, '68; Lli- nas and Bloedel, '66/'67; Llina's et al., '67). The entire subject of the origin of climbing fibers deserves re-examination using modified Fink-Heimer ('67) techniques, shorter survival times, and giving detailed attention to the tertiary P dendrite ramifications as the earliest detect- able site of climbing fiber degeneration.

ACKNOWLEDGMENTS

I am indebted to Dr. James L. O'Leary for his critical guidance and suggestions throughout the course of this study, and to Dr. William M. Landau for his precise editorial help. Also I want to extend my thanks to Dr. W. J. H. Nauta for his advice in the use of silver impregnating techniques.

LITERATURE CITED

Batini, C., and R. Pumain 1968 Activation of Purkinje neurons through climbing fibers after chronic lesions of the olivo-cerebellar pathway. Experientia (Basel), 24: 914-916.

Brodal, A. 1943 Eksperimentelle Undersekelser over de ponto-cerebellare Forbindelser hos Katt og Kanin. Norske Vid. Akad., I. Math-Naturv.

1946 The ponto-cerebellar projection in the rabbit and cat. J. Comp. Neur., 84: 31-118.

Brodal, A,, and G. Grant 1962 Morphology and temporal course of degeneration in cerebellar mossy fibers following transection of spinocere- bellar tracts in the cat. Exp. Neur., 5: 67-87.

Brodal, A,, and B. Hgivik 1964 Site and mode of termination of primary vestibulocerebellar fi- bres in the cat. Arch. I ta l . Biol., 102: 1-21.

Brodal, A,, and J. Jansen 1941 Beitrag zur Kenntnis der spino-cerebellaren Bahnen beim Menschen. Anat. Anz., 91: 185-195.

Carrea, R. M. E., M. Reissig and F. A. Mettler 1947 The climbing fibers of the simian and feline cerebellum. Experimental inquiry into their origins by lesions of the inferior olives and deep cerebellar nuclei. J. Comp. Neur., 87: 321-366.

KI., 10: 1-27.

Coggeshall, R. E., and P. D. McLean 1958 Hip- pocampal lesions following administration of 3- acetylpyridine. Proc. SOC. Exp. Biol. Med., 98: 687-688.

Denk, H., M. Haider, W. Kovak und G. Studynka 1968 Verhaltensanderung and Neuropathologie bei der 3-Acetylpyridinvergiftung der Ratte. Acta Neuropath., 10: 34-44.

De Olmos, J. S. 1969 A cupric-silver method for impregnation of terminal axon degeneration and its further use i n staining granular argyrophilic neurons. Brain, Behav. and Evol., 2: 213-237.

De Olmos, J. S., and W. R. Ingram 1971 An improved cupric-silver method for impregnation of axonal and terminal degeneration. Brain Res., 33: 523-529.

Desclin, J. C. 1974 Histological evidence sup- porting the inferior olive as the major source of cerebellar climbing fibers in the rat. J. Comp. Neur., 77: 3 6 M 8 4 .

Desclin, J. C., and J. Escubi 1974 Effects of 3-acetylpyridine on the central nervous system of the rat, as demonstrated by silver methods. Brain Res., 77: 349-364.

Fink, R. P., and L. Heimer 1967 Two methods for selective silver impregnation of degenerating axons and their synaptic endings in the central nervous system. Brain Res., 4: 369-374.

Foerster, O., 0. Gagel and D. Sheehan 1933 Veranderungen an dem Endosen im Riicken- mark des Affen nach Hinterwurzeldurchschneid- ~~

ung. Z . ges. Anat. 1, 2. Anat. Entwgesch., 101: 553--565. _ _ ~

Gibson, W. C. 1937 Degeneration of the boutons terminaux in the spinal cord. Arch. Neur. Psy- chiat., 38: 1145-1157.

Glees, P. 1946 Terminal degeneration within the central nervous system as studied by a new silver method. J . Neuropath. Exp. Neur., 5: 54- 59.

Grant, G. 1962 Projection of the external cu- neate nucleus onto the cerebellum in the cat: an experimental study using silver methods. Exp. Neur., 5: 179-195.

Heimer, L. 1970 Contemporary Research Meth- ods in Neuroanatomy. W. J. H. Nauta and S. 0. E. Ebesson, eds. Springer-Verlag, New York, pp. 106129.

Herken, J. 1968 Functional disorders of the brain induced by synthesis of nucleotides containing 3-acetylpyridine. Z. Klin. Chem., 6: 357-367.

Hicks, S. P. 1955 Pathologic effects of anti- metabolites. I. Acute lesions in the hypothala- mus, peripheral ganglia and adrenal medulla caused by 3-acetylpyridine and prevented by nicotinamide. Amer. J. Path., 31: 189-197.

Hoff, E. C. 1932 The distribution of the spinal terminals (boutons) of the pyramidal tract, de- termined by experimental degeneration. Proc. Roy. SOC., 1 1 1 : 226-237.

Koikegami, H., and S. Fuse 1961 Degeneration of hippocampus and other brain structures by administration of 3-acetylpyridine. Acta Anat., 36: 33CL331.

Lawrentjew, B. J. 1934 Experimentell-morphol- ogische Studien iiber den feineren Bau des au- tonomen Nervensystems: IV. Weitere Untersuch- ungen iiber die Degeneration und Regeneration der Synapsen. Arch. mikr. Anat. Forsch., 35. 71-118.

438 HUGO MEJIA

Lierse, W. 1965 Ultrastrukturelle Hirnverhder- ungen der Ratte nach Gaben von 3-acetylpyridin. Z . Zellforsch., 67: 8 6 9 5 .

Llinas, R., and J. Bloedel 1966/67 The climbing fiber activation of Purkinje cells in the f?og cerebellum. Brain Res., 3: 299-302.

Llinas, R., W. Precht and S. T. Kitai 1967 Climb- ing fiber activation of Purkinje cell following primary vestibular afferent stimulation in the frog. Brain Res., 6 : 371-375.

Mejia, H. 1974 Foley catheter i n intracardiac perfusion. Stain Technol., 49; 411-412.

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Miskolczy, D. 1931 Uber die Endigungsweise der spino-cerebellaren Bahnen. Z. Ges. Anat., 96: 537-542.

1934 Die Endigungsweise der olivo-cerebellaren Faserung. Arch. Psychiat. Nervenkr.,

Nauta, W. J. H. 1950 Uber die sogenannte ter- minale Degeneration im Zentralnervensystem und ihre Darstellung durch Silberimpragnation. Arch. New. Psychiat., 66: 35S376.

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the olivo-cerebellar system in the cat. Arch. Neur. (Chicago), 22. 19S206 .

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The sagittal organization of the cerebellar anterior lobe a s revealed by the projection patterns of the climbing fiber system. In: Neurobiology of Cerebellar Evolution and Development. R. Llinas, ed. American Medical Association, Chicago, pp. 525-537.

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1969b

3 8 ; 149-155.

PLATE 1

EXPLANATION OF FIGURES

1 Dorsal view of rabbit cerebellum and medulla. Arrow points to stalk of paraflocculus. X 2.

2 Transverse section of rabbit cerebellum and upper medulla. Arrow indicates site of lesion in stalk of paraflocculus. x 2.

RATE OF CLIMBING FIBER DEGENERATION Hugo Mejia

PLATE 1

439

PLATE 2


3,4 Parafloccular stalk, lesions, 24-hour survival showing climbing fiber degeneration in the molecular layer. No degeneration is evident in granular layer or white matter. Fink-Heimer X 200.

440


PLATE 2

44 I

PLATE 3


5 Left parailoccular stalk lesion. Forty-eight-hour survival. Infinitesimal degeneration is seen in the molecular layer, and a light amount of degeneration is seen in the granular layer. (Arrows). Fink-Heimer x 200.

Left parafloccular stalk lesion. Seventy-two-hour survival. Degeneration has shifted toward granular layer and is beginning to appear in the white matter. (Arrows). Fink-Heimer X 200.

6

442


PLATE 3

443

PLATE 4


7 Left parafioccular stalk lesion (7-day survival). No degeneration re- mains in the molecular layer. Less degeneration is evident in the granular layer than is shown in figure 6. White matter shows abun- dance of degenerating fibers. Fink-Heimer X 200.

Right parafloccular control in a 24-hour survival with a left parafloccular stalk lesion. No evidence of degeneration is seen. Fink-Heimer x 200.

8

444


PLATE 4

445

PLATE 5

EXPLANATION O F FIGURE

9 Weil-Weigert sections at the level of lower pons, upper medulla and lower medulla. Lesion is seen in the left dorsolateral quadrants of upper two sections. (Arrows). Lowest section shows edema on same side as lesion. X 4.

446


PLATE 5

44 7

PLATE 6

EXPLANATION O F FIGURES

10 Left dorsolateral pontomedullary lesion. Twenty-four-hour survival. Suggestive degeneration of climbing fibers is present. (Arrows). Fink- Heimer X 200.

1 1 Idem. Thirty-six-hour survival, shows marked climbing fiber degeneration in molecular layer with no involvement as yet in deeper layers. Fink-Heimer X 200.

448


PLATE 6

449

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14 Left dorsolateral pontomedullary lesion. Forty-eight-hour survival. No degeneration is apparent in molecular layer. Some is seen in granule cell layer. Fink-Heimer X 200.

15 Idem. Seventy-two-hour survival. Degeneration is only seen in granule cell layer and white matter. Fink-Heimer X 200.

452


PLATE 8

453

PLATE 9


Different views and stages of Purkinje cell dendritic degeneration (Fink- Heimer) i n cerebellar cortex adjacent to injured region.

16 (25 X Oil) Tangential view of early degeneration of Purkinje cell dendritic tree. Fink-Heimer x 200.

17 (10 X ) Multiple degenerating Purkinje cell dendrites. Fink-Heimer X 80.

18 Shows a more advanced stage of degeneration with darker impregnation of dendrites. Fink-Heimer X 200.

19 Perpendicular view of another degenerating Purkinje dendritic tree. Fink-Heimer X 200.

454


PLATE 9

455

Rate of climbing fiber degeneration in rabbit cerebellum following parafloccular stalk and...

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