Hypertrophy of neurons in the inferior olive after cerebellar ablations in the cat

Neuroscience Letters, 61 (1985) 49-54

49

Elsevier Scientific Publishers Ireland Ltd.

NSL 03569

H Y P E R T R O P H Y OF N E U R O N S IN T H E I N F E R I O R OLIVE AFTER CEREBELLAR ABLATIONS IN T H E CAT

A.J.P. BOESTEN L* and J. VOOGD 2

lElisabeth Hospital, Department of Neurology, 2353 GA Leiderdorp, and :Department of Anatomy, Leiden University, Wassenaarseweg62, 2333 A L Leiden (The Netherlands) (Received March 22nd, 1985; Revised version received July 15th, 1985; Accepted July 17th, 1985)

Key words." inferior olive - hypertrophy - cat

Olivary hypertrophy, a combined retrograde and transneuronal reaction, is found in cells of the inferior olive after cerebellar ablation in the cat. Its chief features are central chromatolysis and hypertrophy o f the peripherally located granular endoplasmatic reticulum with accumulation of electron-dense material in its often vacuolarly distended cisterns. Hypertrophy is restricted to subdivisions o f the inferior olive included in recurrent cerebello-mesencephalic-olivary circuits.

Usually neuronal cell bodies react to axotomy with complex changes (axonal reaction) [11]; most conspicuously with a redistribution and depletion of their Nissl substance (chromatolysis). In neurons whose axons are contained within the peripheral nervous system, chromatolysis reaches its peak within days or weeks after axotomy. Subsequently, they may recover their normal appearance concomitant with the reestablishment of functional connections of the axon [20]. In central neurons both the axonal reaction and the reaction on interruption of their afferent fibers (antegrade transneuronal reaction) often take the form of a rapid atrophy or degeneration, sometimes preceded by a phase of chromatolysis. The features and the time-course of these reactions vary with the kind of animal used, its age and the part of the nervous system under consideration [4, 12, 19]. A quite different type of neuronal reaction, characterized by a long-standing neuronal hypertrophy, has been described in the inferior olive (IO) of man [1] as an accidental finding after lesions of either the contralateral dentate nucleus or the ipsilateral pontine tegmentum. Olivary hypertrophy in man is considered as an antegrade transneuronal reaction consequent to the interruption of a postulated crossed connection between the dentate nucleus and the IO [10]. Clinically, hypertrophy of the IO has been related to myoclonus of the palate [3]. Olivary hypertrophy regularly occurs in certain parts of the IO in chronic cerebellectomized cats [21]. In experimentally induced olivary hypertrophy the histological changes can be studied in more detail than in human cases. Moreover, for the cat *Author for correspondence. 0304-3940/85/$ 03.30 © 1985 Elsevier Scientific Publishers Ireland Ltd.

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sufficient data are available on the connections between the IO arid the cerebellum for an interpretation of olivary hypertrophy in terms of connectivity. In this report a description is given of the hypertrophic changes in cell bodies of the IO after total or hemi-cerebellectomies in adult, healthy cats with survival times of 15, 26, 49, 89, 126, 139, 147, 244, 254, 345 and 524 days. The cats with survival times of 26, 126 and 254 days were studied with light microscopy only. For the other cats cresyl violet-stained Vibratome (R) sections, semithin, Epon-embedded toluidine-stained sections and ultrathin sections stained with uranyl acetate and lead citrate from material fixed according to Rinvik and Grofova [15] were studied. Olivary cells in cresyl violet-stained preparations of normal cats are medium sized, have a slightly eccentrically located nucleus with a distinct nucleolus and small dispersed Nissl bodies (Fig. 2). Except for a larger size of the cells of the medial accessory olive (MAO), no obvious regional differences in cell morphology have been observed in the IO. After ablation of one half of the cerebellum, hypertrophic changes are only present in the contralateral IO. Hypertrophic cells are always found in the rostral part of the MAO (Fig. 3), and in cats with the longest survival times of 139, 244, 254 and 524 days also in the dorsal lamella of the principal olive (PDL). With these longer survival times, hypertrophy in the rostral half of the MAO extend more caudally. Between hypertrophic cells no normal cells are found. There are no signs of a considerable cell loss from the hypertrophic parts. Atrophic changes, with disappearance of the cells, are mainly found in the dorsal accessory olive (DAO) and the dorsomedial cell column. In other parts of the IO virtually normal cells remain present after

Fig. 1. Transverse section through rostral IO 147 days after cerebellectomy. Hypertrophic cells restricted to rostrolateral part of medial accessory olive (MAO). Numerous normal cells are present in dorsal leaf of principal olive (PDL) and dorsal accessory olive (DAO). Vibratome section, cresyl violet. Fig. 2. Normal cells from rostrolateral MAO. Vibratome section, cresyl violet. Fig. 3. Hypertrophic cell from MAO. Note nucleus with prominent nucleolus, chromatolytic center (c) and peripheral vacuolization (arrow). 139 days. Vibratome section, cresyl violet. Same magnification as Fig. 2. Fig. 4. Hypertrophic cell of rostrolateral MAO. Note peripheral ring of confluent Nissl bodies, nucleus with prominent nucleolus and central chromatolysis (c). 147 days. Vibratome section, cresyl violet. Same magnification as Fig. 2. Fig. 5. Hypertrophic cells of rostrolateral MAO. Note large vacuole (v) and darkly staining inclusions (di) and nucleus with prominent nucleolus (n). 139 days; I/am Epon section, toluidine blue. Fig. 6. Electron micrograph of Nissl body (N) in periphery of hypertrophic cell from the MAO. Note distended cisterns containing electron-dense inclusions with more translucent parts (di). Cell membrane indicated by arrows. 139 days. Uranyl acetate-lead citrate staining.

52 all survival time~ (Fig. l). In one experiment with a survival time of 345 days only morphologically normal cells were found in areas containing the hypertrophic cells in other cases. In all experiments cells in the rostrolateral MAO are considerably enlarged. The nucleus is located in the extreme periphery of the cell body, and the nucleolus is larger than in normal cells. In the periphery of the cell body a prominent ring of often confluent Nissl bodies is found. The chromatolytic center of the cell body shows a granular basophilia or a homogeneous, lightly staining substance (Fig. 4). At all survival times vacuoles can be found in the periphery of the cell body. In semithin toluidine blue-stained sections the features of the hypertrophic cells are essentially the same. The peripherally located nucleus is often flattened and indented. In many cells vacuoles of different size replace the peripherally located Nissl bodies. They contain a vaguely staining substance and/or dense globular inclusions of various size (Fig. 5). In some of these gluboles translucent patches can be observed. Their almost spherical shape distinguishes the inclusions from lipofuscin granules. In electron micrographs of normal cells none of the organelles are abundantly present, and the granular endoplasmatic reticulum (GER) is dispersed in small aggregations throughout the cytoplasm. In hypertrophic cells the ultrastructure is changed dramatically. The nucleus is located in the extreme periphery. The chromatolytic center of the cell is studded with mitochondria, microtubules, small clear vacuoles and membrane-bound dense bodies of varying size. Free ribosomes, polysomes and short fragments of GER, the latter with a moderate electron-dense content, are found and accumulate towards the periphery. The most conspicuous features of the hypertrophic cells are found in the periphery of the cell body. Here a well-developed GER, together with free ribosomes and polysomes, and a large, more centrally located Golgi apparatus are found. Parts of the GER are distended and sometimes have an almost globular appearance. Sometimes one vacuolated cistern, its membrane studded with ribosomes, occupies half the cell body. Often these distended cisterns can be seen in direct continuity with parts of the parallel arrays of GER or with each other. In the G E R fibrillary material with a varying electron density is found. It can condense in small irregular patches or in electron-dense globules with a bristled contour. In these globules electron-lucent patches with a fibrillary structure can be found (Fig. 6). The cell border is often irregular. In the cat with a survival time of 345 days the cells in the IO have a normal appearance, but in the MAO a number of cells is partially myelinated. Since direct projections from the central cerebellar nuclei to the IO are known to exist [6, 18] and the termination of fibers from the IO as climbing fibers in the molecular layer of the cerebellum and the central cerebellar nuclei is well documented [5, 7], the reaction of the cells in the IO on cerebellar ablation can be considered to be either axonal or antegrade transneuronal. This, however, does not explain the hypertrophy in itself nor its localization in specific parts of the IO. The cytological features in experimental hypertrophy of the IO in the cat are very similar to the changes described in the human IO in cases of palatal myoclonus [1]. Distension of the G E R is a prominent'finding in both humans and cat, neurofilamen-

53 tous hyperplasia is less distinct in experimental hypertrophy. Contrary to the reactions of IO neurons after cerebellectomy, the neurons in the ventrobasal complex of the thalamus [12] react to cortical lesions, which combined deafferentation with axotomy, with rapid atrophy and degeneration. Hypertrophy of neurons in the lateral geniculate body has been described after lesions of the striate cortex in infant monkeys [8]. Hypertrophy with distension of the G E R has been described in retinal ganglion cells of the goldfish after lesions of the optic nerve. This hypertrophy subsides, and the cells regain their normal appearance after functional contacts of the regenerated nerve have been made [13]. Hypertrophy with distension of the G E R has been observed as a stage in the development of neurons [14]. Dendro-dendritic and dendro-somatic synaptic contacts appear in the neuropil of the hypertrophic part of the IO (unpublished observations). These contacts are normally absent [2, 9, 17]. This may indicate that the hypertrophic cell reaction in the IO also is the expression of an attempt of the cell at establishing new functional contacts. Ablation of the cerebellum removes the terminations of the axons of all olivary cells and interrupts the reciprocal cerebello-olivary connections. However, hypertrophy is limited to the rostral M A O and the PDL. These parts of the IO are distinguished by being included in recurrent cerebeilo-mesencephalic-olivary circuits, consisting of, respectively, rostral MAO-posterior interposed nucleus-Darkschewitsch' nucleus and PDL-dentate nucleus-parvocellular red nucleus [16]. This indicates that hypertrophy in the IO of the cat is not determined exclusively by the interruption of direct cerebello-olivary connections, as maintained for human cases, or by a retrograde cellular reaction. It appears that recurrent cerebello-mesencephalic-olivary circuits, more specifically the mesencephalic olivary connections which remain intact after cerebellar ablation, may be implicated in eliciting the hypertrophic reaction. This hypothesis is open to further experimentation. Therefore olivary hypertrophy can be considered as the expression of a functional differentiation within the IO complex based on differences in the olivo-cerebellar relations. Morphologically, experimental hypertrophy of the IO seems to be a promising model to study the relations between neuronal hypertrophy and function. 1 Barron, K.D., Dentinger, M.P. and Koeppen, A.H., Fine structure of neurons of the hypertrophied human inferior olive, J. Neuropath., Exp. Neurol., 41 (1982) 186-203. 2 Boesten, A.J.P., Systemes afferents et ultrastructure de la parolive externe chez le chat, C.R. Assoc. Anat., 152 (1971) 459-463. 3 Bonduelle,M., The myoclonias.In P.J. Vinken and G.W. Bruyn (Eds.), Handbook of Clinical Neurology, Vol. 6, Elsevier, Amsterdam, 1968, pp. 772-795. 4 Cowan, W.M., Anterograde and retrograde transneuronal degeneration in the central and peripheral nervous system. In W.J.H. Nauta and S.O.E. Ebbeson (Eds.), Contemporary Research Methods in Neuroanatomy, Springer Verlag, Berlin, Heidelberg, New York, 1970, pp. 217-249. 5 Desclin, J.C., Histological evidence supporting the inferior olive as the major source of cerebellar climbing fibers in the rat, Brain Res., 77 (1974) 365-384. 6 Graybiel, A.M., Nauta, HA.W, Lasek, R.J. and Nauta, W.J.H., A cerebello-olivarypathway in the cat: an experimental study using autoradiographictracing techniques, Brain Res., 58 (1973) 205-211. 7 Groenewegen,H.J., Freedman, S.L. and Voogd,J., The parasagittal zonation within the olivio-cerebellar projection. II. Climbingfiber distribution in the intermediate and hemispheric parts of cat cerebellum, J. Comp. Neurol., 183 (1979) 551-602.

54 8 Hendrickson, A.A. and Dineen, J.T., Hypertrophy of neurons in dorsal lateral geniculate nucleus following striate cortex lesions in infant monkeys, Neurosci. Lett., 30 (1982) 217-222. 9 King, J.S., Synaptic organization of the inferior olivary complex. In J. Courville, C. de Montigny and Y. Lamarre (Eds., The Inferior Olivary Nucleus, Raven Press, New York, 1980, pp. 1-33. 10 Lapresle, J. and Ben Hamida, M., The dentato-olivary pathway. Somatotopic relationship between the dentate nucleus and the con tralateral inferior olive, Arch. Neurol., 22 (1970) 135-143. 11 Liebermann, A.R., The axon reaction: a review of the principal features of perikaryal responses to axon injury, Int. Rev, Neurobiol., 14 (1971) 49-124. 12 Matthews, M.M., Death of the central neuron: an electron microscopic study of thalamic retrograde degeneration following cortical ablation, J. Neurocytol., 2 (1973) 265-288. 13 Murray, M. and Forman, D.S., Fine structural changes in goldfish retinal ganglion cells during axonal degeneration, Brain Res., 32 (1971) 287-298. 14 Parnavelas, J.G. and Liebermann, A.R., An ultrastructural study of the maturation of neuronal somata in the visual cortex of the rat, Anat. Embryol., 157 (1979) 311-328. 15 Rinvik, E. and Grofova, I., Observation on the fine structure of the substantia nigra in the cat, Exp. Brain Res., 11 (1970) 229 248. 16 Saint Cyr, J.A. and Couville, J., Descending projections to the inferior olive from the mesencephalon and superior colliculus in the cat. An autoradiographic study, Exp. Brain Res., 45 (1982) 33 348. 17 Sotelo, C., Llinas, R. and Baker, R., Structural study of inferior olivary nucleus of the cat; morphological correlates of electrotonic coupling, J. Neurophysiol., 37 (1974) 514-549. 18 Tolbert, D.L., Massopust, L.C., Murphy, M.G. and Young, P.A., The anatomical organization of the cerebello-olivary projection in the cat, J. Comp. Neurol., 170 (1976) 525-544. 19 Torvik, A., Transneuronal changes in the inferior olive and pontine nuclei in kittens, J. Neuropath., 15(1956) 119 145. 20 Torvik, A. and Skj6rten, F., Electron microscopic observations on nerve cell regeneration and degeneration after axon lesions. I. Changes in the nerve cell cytoplasm, Acta Neuropath. (Bed.), 17 (1971) 248-264. 21 Verhaart, W.J.C. and Voogd, J., Hypertrophy of the inferior olives in the cat, Neuropath. Exp. Neurol., 21 (1962) 9~104.