EM-Autoradiography of cerebellar nucleocortical terminals in the cat

Summary The findings from the present EM-autoradiography experiments identify the cerebellar nucleocortical projection as a mossy fiber-type pathway. In these studies orthogradely labelled axons and terminals were observed in the folial white matter and granule cell layer, with only background levels of silver grains over the Purkinje cell and molecular layers. Most nucleocortical axons synapsed within cerebellar glomeruli either at en passant contacts along dilated segments of unmyelinated axons or at multilobulated (terminal) expansions of the axons. Typically these synaptic junctions were of the asymmetrical type containing clear round vesicles. Usually, each labelled mossy fiber rosette synapsed on a large number of small terminal dendrites of granule cells; however, occasionally a series of 4–8 asymmetric contacts were noted on a single large dendrite. Labelled nucleocortical terminals were occasionally present in the nonglomerular neuropil between granule cell bodies where they contacted large dendrites of Golgi cells.This work was supported in part by U.S. Public Health Service Grants BRSG 410 and NIH fellowship NS0557. Preliminary reports of this work have been presented at the 9th Society for Neuroscience meeting and at the Fogarty International Center Conference on The Cerebellum: New Vistas, Bethesda, Maryland, May 1980     

The cerebellar corticonuclear projection from lobule Vb/c of the cat anterior lobe: a combined electrophysiological and autoradiographic study

Summary The present study examines the projection to the cerebellar nuclei of Purkinje cells in particular sagittal zones within the intermediate region of the cerebellar cortex. The boundaries between the zones were delimited electrophysiologically on the basis of their climbing fibre input so that a small volume (10–120 nl) of ³H-leucine could be injected into the centre of a chosen zone. The subsequent uptake and orthograde transport of labelled material by the Purkinje cells was studied autoradiographically. It was found that the smallest injections resulted in injection sites restricted to a single cortical zone and extremely reproducible results could be obtained using such a combined electrophysiological/autoradiographic technique. Larger injections sometimes spread to a neighbouring zone but the resultant terminal labelling within the deep nuclei was invariably consistent with the results obtained from smaller injections. The c₁ and c₃ olivocerebellar zones, which are known to receive climbing fibre input transmitted from the ipsilateral forelimb via a dorsal funiculus spino-olivo-cerebellar pathway (DF-SOCP), were found to project to partially overlapping regions within nucleus interpositus anterior (NIA). No projection to nucleus interpositus posterior (NIP) was demonstrated for either zone. No distinction could be seen between the terminal fields for the medial and lateral halves of the c₁ zone which are, however, known to receive their climbing fibre input from quite separate regions within the inferior olive. The c₂ zone, which was delimited on the basis of its climbing fibre input which is transmitted from both forelimbs via a lateral funiculus SOCP, was found to project exclusively to interpositus posterior. The hemispheral d₁ zone was found to project to the transitional region where interpositus anterior and the dentate nucleus adjoin.     

Arrested granule cells and their synapses with mossy fibers in the molecular layer of the cerebellar cortex

Summary Foci of undescended and arrested granule cells occur beneath the pial surface in the normal cerebellar cortex. The dendrites of the cells participate in synaptic glomeruli with mossy fibers and axons of stellate or basket cells that have been isolated in the foci. Thus, ectopic masses of granular layer are present at these sites in the molecular layer. These granule cells are probably among the last cells to proliferate in the external granular layer. It is proposed that because they may have been late in this phase of their development they were arrested prior to or during migration. Maturation and synapse formation, however, occur because of the arrival of mossy fibers from the internal granular layer. These observations exemplify the specificity of neuronal interaction during development. In addition, the data suggest that neurons may mature and form synapses with their proper partners despite having missed the migratory phase imposed on similar neurons in the normal state.Supported in part by U.S. Public Health Service Research Grant NS 03659 and Training Grant NS 05591 from the National Institute of Neurological Diseases and Stroke.     

Connections of Purkinje cell axons of lobule X with vestibulocerebellar neurons projecting to lobule X or IX in the rat

Connections of Purkinje cell axons of lobule X (nodulus) with vestibulocerebellar neurons projecting to lobule X or IX (uvula) were revealed in the rat. Purkinje cell axons were anterogradely labeled with biotinylated dextran (BD) injected into sublobule Xa while vestibular neurons were retrogradely labeled with cholera toxin subunit B (CTB) injected into sublobule Xa or IXc. Labeled terminals of Purkinje cell axons of lobule X were numerous in the superior vestibular nucleus (SV), medial parts of the parvocellular (MVpc) and the caudal part (MVc) of the medial vestibular nucleus (MV), and group y. These subdivisions of the vestibular nuclei contained many neurons projecting to lobule X or IX. Lobule-X-projecting and lobule-IX-projecting neurons were in contact with terminals of Purkinje cell axons of lobule X in the MVpc and MVc. They were distributed dorsally to medially in medial parts of the MVpc and MVc. The present study suggests that Purkinje cells in lobule X regulate the output of a population of lobule-X-projecting or lobule-IX-projecting neurons of the MVpc and MVc.     

Developmentally regulated changes of glutamate binding sites in mouse deep cerebellar nuclei

The expression of L-[³H]glutamate binding sites of different ionic and pharmacological sensitivities was studied in mouse deep cerebellar nuclei during early postnatal development by means of in vitro autoradiography. Ca²⁺/Cl⁻-dependent, quisqualate/AMPA/ibotenate-sensitive, and APB-insensitive binding sites are present at high density in the deep cerebellar nuclei of young animals, but greatly decrease between the 10th and 25th postnatal day and remain low in the adult. The density of Ca²⁺/Cl⁻-independent binding sites remains low and constant during the whole of postnatal development. The possible involvement of the Ca²⁺/Cl⁻-dependent binding sites in brain development is discussed.     

Process of differentiation of cerebellar Purkinje neurons in the chick embryo

Summary The microscopic and ultrastructural differentiation of Purkinje neurons has been studied in 40 chicken embryo cerebella, from the 10th incubation day to hatching, and the transverse diameter of the cell body measured, for each developmental stage, on 30 electron micrographs of sagittally cut Purkinje cells. The developing Purkinje cell bodies, bipolar, at first, given the presence of two processes emerging from the opposite poles of the oval perikaryon, grow progressively in size. After the 12th incubation day, they develop a branched dendritic tree, and, shortly before hatching time, the cells acquire the characteristic flask or pear-shaped configuration. On the 10th incubation day, microtubules are already detectable together with Golgi complexes and a few vesicles of rough endoplasmic reticulum; on the 14th incubation day, RER cisterns are recognizable in the supranuclear cytoplasm, later extending into the whole perikaryon, and attaining their definitive distribution by the 18th incubation day. Pinocytotic and coated vesicles, as well as subsurface cisterns are seen during the whole embryonic life. In the earliest stages of development, three distinct types of junctional contacts between Purkinje cells and surrounding axons are described, and their functional role in relation to synaptogenetic processes is discussed. Beginning with the 16th incubation day, some Purkinje neurons undergo degenerative changes similar to those described in other types of neurons of the central and peripheral nervous system.     

The lobulus petrosus of the paraflocculus relays cortical visual inputs to the posterior interposed and lateral cerebellar nuclei: an anterograde and retrograde tracing study in the monkey

The afferent and efferent projections of the lobulus petrosus (LP) of the paraflocculus were examined by retrograde tracing with cholera toxin subunit B (CTB) and anterograde tracing with CTB or biotinylated dextran (BD) in the macaque. Following injections of the tracers into the LP, labeled neurons were seen mainly in the lateral, dorsal, paramedian and dorsolateral parts of the contralateral pontine nuclei (Pn) and in the ventromedial part of the principal olivary nucleus and the lateral pole of the medial accessory olivary nucleus at the rostral levels. Labeled terminals were seen ipsilaterally in the ventrolateral part of the posterior interposed nucleus and the basal interstitial nucleus of the cerebellum at their rostral levels, and in the ventromedial part of the lateral cerebellar nucleus. To reveal the connections between the LP-projecting pontine neurons and the corticopontine axons, BD was injected into the left prearcuate region or extrastriate visual areas, and CTB into the right LP. Labeled terminals from the prearcuate region were seen mainly in the left dorsal, medial and paramedian Pn, whereas those from the extrastriate visual areas were seen in the lateral and dorsolateral Pn. The distribution of the LP-projecting neurons overlapped that of the terminals from the extrastriate visual areas but did not overlap that of the terminals from the prearcuate region. The present study demonstrates that the LP of the monkey receives cortical visual inputs and projects to the posterior interposed and lateral cerebellar nuclei, suggesting that the LP may be involved in the control of voluntary eye movements. Electronic Publication     

Connections of Purkinje cell axons of lobule X with vestibulospinal neurons projecting to the cervical cord in the rat

Connections of Purkinje cell axons of lobule X (nodulus vermis) with vestibulospinal neurons have been demonstrated in the rat, by anterograde labeling of axons with biotinylated dextran (BD) injected into sublobule Xa and by retrograde labeling of neurons with cholera toxin subunit B (CTB) injected into cervical segments. Labeled terminals of Purkinje cell axons were numerous in the superior vestibular nucleus, the parvocellular (MVpc) and the caudal part (MVc) of the medial vestibular nucleus (MV), and group y. A limited number of labeled terminals were seen in the caudal part of the descending vestibular nucleus (DV). Occasional labeled terminals were seen in the lateral part of the lateral vestibular nucleus (LV) whereas few labeled terminals were seen in the magnocellular part of the MV (MVmc). Vestibulospinal neurons labeled from the C2 and C3 segments were seen bilaterally in the MVmc, MVpc, MVc, and DV, and ipsilaterally in the LV. CTB-labeled vestibulospinal neurons in contact with BD-labeled terminals of Purkinje cell axons were identified in the lateral part of the MVpc, near the border between the MVpc and MVmc, or close to the dorsal acoustic stria, and in the middle part of the MVc at its rostral level. The present study suggests that Purkinje cells of lobule X regulate the output of cervical-projecting vestibulospinal neurons in the MVpc and MVc.     

Responses of Purkinje cells in the cerebellar anterior vermis to off-vertical axis rotation

Responses of 67 Purkinje cells (P-cells) and 44 unidentified neurons (U-cells) located in the cerebellar anterior vermis were recorded in decerebrate cats during off-vertical axis rotation (OVAR). This stimulus consisted of a slow constant velocity (9.4°/s) rotation in the clockwise (CW) and counterclockwise (CCW) directions around an axis inclined by 5° with respect to the vertical. OVAR imposes on the animal head a 5° tilt, whose direction changes continuously over the horizontal plane, thus eliciting a selective stimulation of macular receptors. A total of 27/67 P-cells (40%) and 24/44 U-cells (55%) responded to both CW and CCW rotations. For these bidirectional units, the direction of maximum sensitivity to tilt (S_max) could be identified. S_max directions were distributed over the whole horizontal plane of stimulation. Among bidirectional neurons, 48% of the P-cells and 33% of the U-cells displayed an equal amplitude of modulation during CW and CCW rotations, indicating a cosinetuned behaviour. In these instances, the temporal phase of the unit response to a given direction of tilt remained constant, while the sensitivity was maximal along the S_max direction and declined with the cosine of the angle between S_max and the tilt direction. The remaining bidirectional units displayed unequal amplitudes of modulation during CW and CCW rotations. For these neurons, a nonzero sensitivity along the null direction was expected and the response phase varied as a function of stimulus direction. Finally, 31% and 23% of P-cells and U-cells, respectively, responded during OVAR in one direction only (unidirectional units). This behaviour predicts equal sensitivities along any tilt direction in the horizontal plane and a response phase that changes linearly with the stimulus direction. The possibility that the tested neurons formed a population which coded the direction of head tilt in space was also investigated. The data from the whole population of cells were analysed using a modified version of vectorial analysis. This model assumes that for a particular tilt each cell makes vectorial contributions; the vectorial sum of these contributions represent the outcome of the population code and points in the direction of head tilt in space. Thus, a dynamic head tilt along four representative directions was simulated. For each of the four directions, 12 population vectors were calculated at regular time intervals so as to cover an entire cycle of head tilt. The results indicate that for each selected time in the cycle the direction of the population vector closely corresponded to that of the head tilt, while its amplitude was related to the amount of head tilt. These data were particularly obtained for the P-cells. In view of their efferent connections, the cerebellar anterior vermis may provide a framework for the spatial organization of vestibulospinal reflexes induced by stimulation of otolith receptors.     

The cerebellar projection from the raphe nuclei in the cat as studied with the method of retrograde transport of horseradish peroxidase

Summary Following injections of horseradish peroxidase (HRP) in the cerebellar cortex and nuclei of the cat, the distribution of labeled cells in the raphe nuclei was mapped. The findings confirm those made previously in studies of retrograde cell degeneration following cerebellar ablations (Brodal et al., 1960a), and in addition reveal new details in the projection of the raphe nuclei onto the cerebellar cortex and nuclei.All the raphe nuclei except nucleus linearis intermedius and nucleus linearis rostralis project onto the cerebellar cortex. The nuclei raphe obscurus and pontis contribute the greatest number of afferents to the cerebellum.With the exception of lobule VI which probably is the recipient of a weak projection, all parts of the cerebellar cortex receive afferents from the raphe nuclei. The heaviest projection is to the vermis of lobules VIIA and X, and to crus II. The afferents to the cerebellar nuclei are few in number (Tables 2–6).The observations indicate that each raphe neuron probably projects to more than one terminal site in the cerebellum.The findings are discussed with reference to other efferent and afferent studies of the raphe nuclei. All these studies indicate that the raphe nuclei have widespread efferent and afferent connections, making them capable to participate in a variety of regulatory functions.List of abbreviations f.apm. Ansoparamedian fissure - f.icul. Intraculminate fissure - f.in.cr. Intercrural fissure - fl. Flocculus - f.pc. Preculminate fissure - f.pfl. parafloccular fissure - f.ppd. Prepyramidal fissure - f.pr. Fissura prima - f.prc. Precentral fissure - f.prc.a Precentral fissure a - f.p.l. Posterolateral fissure - f.p.s. Posterior superior fissure - f.sec. Fissura secunda - HII–HX Hemispheral lobules II–X - HVIIA cr.I, cr. II Crus I and II of lobule HVIIA - HVIIIA,B Sublobules A and B of lobule HVIII - Li Nucleus linearis intermedius - Lr Nucleus linearis rostralis - l.ans. Ansiform lobule - N.f. Nucleus fastigii - N.i.a. Nucleus interpositus anterior - N.i.p. Nucleus interpositus posterior - N.l. Nucleus lateralis - pfl.d. Dorsal paraflocculus - pfl.v. Ventral paraflocculus - Rd Nucleus raphe dorsalis - Rm Nucleus raphe magnus - Rob Nucleus raphe obscurus - Rpa Nucleus raphe pallidus - Rpo Nucleus raphe pontis - Sc Nucleus raphe centralis superior - s.int.cr.1 Intracrural sulcus 1 - s.int.cr.2 Intracrural sulcus 2 - I–VI Vermian lobules I–VI - VIIA,B Anterior and posterior sublobule of lobule VII - VIIIA,B Anterior and posterior sublobule of lobule VIII     

GABAergic synaptic communication in the GABAergic and non-GABAergic cells in the deep cerebellar nuclei

The deep cerebellar nuclei (DCN) are the final integrative units of the cerebellar network. The strongest single afferent to the DCN is formed by GABAergic Purkinje neuron axons whose synapses constitute the majority of all synapses in the DCN, with their action strongly regulating the intrinsic activity of their target neurons. Although this is well established, it remains unclear whether all DCN cell groups receive a functionally similar inhibitory input. We previously characterized three types of mouse DCN neurons based on the expression of glutamic acid decarboxylase isoform 67 (GAD67), their active membrane properties and morphological features. Here we describe the GABAergic synapses in these cell groups and show that spontaneous GABAergic synaptic activity can be seen in all three cell types. Since the majority of DCN neurons fire action potentials spontaneously at high frequencies both in vivo and in vitro, we expected that spontaneous GABAergic synaptic activities mediated by intra-DCN synaptic connections could be uncovered by their sensitivity to TTX. However, TTX had little effect on spontaneous synaptic activity. It seems, therefore that functional GABAergic connectivity within the DCN is sparse and/or weak at least under our experimental conditions. Even though present in all cell types, the spontaneous GABAergic events showed significant differences between the cell types. The synaptic currents in GABAergic cells had lower amplitude, lower frequency and slower kinetics than those of non-GABAergic cells. These differences could not be sufficiently explained by considering only cell size differences or a differential GABA(A)-receptor alpha-subunit composition. Rather, the main differentiating factor appears to be the dendritic localization of GABAergic synapses in the GABAergic cells.     

Suppression of GABA input by A1 adenosine receptor activation in rat cerebellar granule cells

Synaptic transmission has been shown to be modulated by purinergic receptors. In the cerebellum, spontaneous inhibitory input to Purkinje neurons is enhanced by ATP via P2 receptors, while evoked excitatory input via the granule cell parallel fibers is reduced by presynaptic P1 (A1) adenosine receptors. We have now studied the modulation of the complex GABAergic input to granule cells by the purinergic receptor agonists ATP and adenosine in acute rat cerebellar tissue slices using the whole-cell patch-clamp technique. Our experiments indicate that ATP and adenosine substantially reduce the bicuculline- and gabazine-sensitive GABAergic input to granule cells. Both phasic and tonic inhibitory components were reduced leading to an increased excitability of granule cells. The effect of ATP and adenosine could be blocked by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), but not by other P1 and P2 receptor antagonists, indicating that it was mediated by activation of A1 adenosine receptors. Our results suggest that, in the cerebellar network, A1 receptor activation, known to decrease the excitatory output of granule cells, also increases their excitability by reducing their complex GABAergic input. These findings extend our knowledge on purinergic receptors, mediating multiple modulations at both inhibitory and excitatory input and output sites in the cerebellar network.     

Two types of GABA-containing axon terminals in cerebellar glomeruli of cat: An immunogold-EM study

Summary Immunogold demonstration of GABA was used in ultrathin sections of cerebellar cortex of cat to identify GABA(+) profiles in cerebellar glomeruli. In addition to small, GABA-containing axonal varicosities found at the periphery of all glomeruli, a few complex glomeruli were found to contain a second type of GABA(+) terminal, with a mossy ending appearance. GABA(+) type I axon terminals, which were identified as the axonal arborization of local Golgi cells, contained ovoid, small synaptic vesicles. GABA(+) type II terminals, however, exhibited large, spheroid synaptic vesicles. Experimental evidence is provided that type II GABA(+) mossy like terminals are the endings of nucleocortical fibers.     

On the identification of the afferent axon terminals in the nucleus lateralis of the cerebellum an electron microscope study

Summary Axon terminals in the neuropil of the lateral nucleus can be divided into six classes, each with a specific constellation of characteristics that consistently occur together. Two of these classes have synaptic varicosities with elliptical synaptic vesicles, one in a dense, the other in a sparse matrix, and both make axosomatic and axodendritic synapses. The remaining four classes all have round synaptic vesicles and do not make axosomatic synapses. In the first of these four, the vesicles are tightly packed in a dense matrix, in another they are loosely dispersed, and in the third they are clustered. In the fourth, large granular vesicles predominate. Of these six classes, the most numerous belong to the axons of the Purkinje cell terminal arborization. These boutons resemble their counterparts in the cerebellar cortex, the recurrent collaterals of the Purkinje axon. They have elliptical and flat synaptic vesicles in a dark matrix. The varicosities terminate on somata and dendrites of large and small neurons and constitute the majority of their input. Purkinje axons constitute 86% of the total population of terminals on large neuronal perikarya and 50% of those on their dendrites, but only 78% on the somata of small neurons and 31% on their dendrites. The terminals of climbing fiber collaterals are recognized by their resemblance in electron micrographs to the terminals of the climbing fiber arborization in the cerebellar cortex. They bear round synaptic vesicles packed into a dense axoplasmic matrix and make Gray's type 1 axodendritic synapses with large and small neurons. These axons are restricted to the lateral and ventral aspects of the nucleus and constitute 5% of the terminals on large cell dendrites and 6% of those on small neurons. The axons tentatively identified as collaterals of mossy fibers are myelinated fibers with a light axoplasm containing round synaptic vesicles, dispersed throughout their varicosities. They make Gray's type 1 synapses and constitute a fair percentage of the total axodendritic contacts in the neuropil, 22% on large neurons and 28% on small neurons. The bases for these tentative identifications are discussed in detail, as are the various synaptic relationships undertaken by each class of axon. The remaining 4 classes of axons of the neuropil will be described in subsequent papers.Supported in part by U.S. Public Health Service grants NS 10536 and NS 03659, Training grant NS 05591 from the National Institute of Neurological Diseases and Stroke, and a William F. Milton Fund Award from Harvard University.     

The fine structure of the cerebellar central nuclei in the cat I. Neurons and neuroglial cells

Summary The four deep cerebellar nuclei exhibit a similar pattern of organization. They consist of isodendritic neurons of different sizes. The dendritic fields of the neurons display the characteristics of noyaux fermés. The medium sized neurons contain small Nissl bodies anastomosed by threads of the same material giving rise to a tridimensional network; the large majority of the polyribosomes are free and suspended among the cisterns of the Nissl substance. Peculiar inclusions, resembling laminated inclusion bodies, are occasionally present in the perikarya. The origin of such inclusions from the endoplasmic reticulum has been proved, since intermediary steps in the transformation of endoplasmic reticular cisterns into laminated bodies have been disclosed. Rarely, annulate lamellae occur in the perinuclear region. The smaller neurons contain a large nucleus, almost 2/3 of the somatal volume, and in their cytoplasm Nissl bodies are practically absent. The Golgi impregnation and the electron microscopic observations have revealed the existence of large dendritic varicosities, giving rise to long slender filopodia localized in distal segments of some dendrites. The varicosities are filled with mitochondria and some glycogen particles. These features are characteristics of growing tips of dendrites (Sotelo and Palay, 1968). The immediate environment of medium sized neurons consists of axon terminals and astrocytic processes, in a near similar proportion. On the other hand, smaller neurons are in intimate contact with satellite oligodendrocytes, astrocytic processes, myelinated fibers and very few axon terminals. Close appositions, resembling gap junctions have been disclosed between perikarya of interfascicular oligodendrocytes.     

Convergence of directional vestibular and neck signals on cerebellar Purkinje cells

 Convergence of spatially oriented vestibular and neck signals within the cerebellar anterior vermis in decerebrate cats was studied by recording the simple spike discharge of Purkinje (P) cells during wobble either of the whole animal (vestibular input) or of the body under a fixed head (neck input) at 0.156 Hz, 5° and 2.5°, respectively. Both clockwise (CW) and counterclockwise (CCW) rotations were performed. Units that had equal response amplitudes to CW and CCW rotations (narrowly tuned neurons) were described by a single vector (S _max), characterized by a gain, a direction and a temporal phase. Units with different response amplitudes to CW and CCW rotation (broadly tuned neurons) were described by two vectors (S _max and S _min). In addition to these bidirectional units, there were also unidirectional units which responded either to CW or CCW rotation; in these cases the gain of S _max equals that of S _min. On the whole, 77% and 63% of the P cells responding to vestibular and neck stimulation, respectively, showed a bidirectional broadly tuned or unidirectional behavior. These response patterns were attributed to the convergence of signals with different spatial and temporal properties. About 50% of the P cells from which recordings were made responded to stimulation of both sensory systems. However, the gains of the S _max vectors of the neck responses were much greater than those of the vestibular responses, at least for small amplitudes of rotation, and were positively correlated with them. Usually the differences in the orientation components of the neck and vestibular S _max vectors were larger, while the differences in temporal phases were smaller than 90°. These findings suggest that periodic changes in the phase difference and gain ratio of the neck to the vestibular response may occur during dynamic displacement of the head over the body, depending on the stimulus direction. As a result of these data, the P cells of the cerebellar vermis are expected to show prominent responses to head rotation, which could affect the spatially organized postural responses by utilizing vestibular and reticular targets. Received: 10 June 1997 / Received after revision: 23 October 1997 / Accepted: 25 November 1997     

Ultrastructure of Purkinje cell perikarya and their dendritic processes in the rat cerebellar cortex in experimental encephalopathy induced by chronic application of valproate

Long-term intragastric administration of the antiepileptic drug sodium valproate (Vuprol Polfa) to rats for 1, 3, 6, 9 and 12 months, once daily at the effective dose of 200 mg/kg body weight showed morphological evidence of encephalopathy, manifested by numerous nonspecific changes within Purkinje cell perikarya and their dendritic processes. The first ultrastructural abnormalities appeared after 3 months. They became more severe in animals with longer survival and were most pronounced after 12 months. The changes were maintained both 1 and 3 months after drug withdrawal. Mitochondria of Purkinje cell perikarya were most severely affected. Damage to mitochondria was accompanied by disintegration and fragmentation of granular endoplasmic reticulum, dilation of channels and cisterns of Golgi apparatus, enlargement of smooth endoplasmic reticulum elements including submembranous cisterns, and accumulation of profuse lipofuscin deposits. Frequently, Purkinje cells appeared as dark ischemic neurones, with focally damaged cellular membrane and features of disintegration. Swollen Bergmann's astrocytes were seen among damaged Purkinje cells or at the site of their loss. The general pattern of submicroscopic alterations of Purkinje cell perikarya suggested severe disorders in several intercellular biochemical extents, including inhibition of oxidative phosphorylation and abnormal protein synthesis, both of which could lead to lethal damage. Ultrastructural abnormalities within dendrites were characterized by damage to elements of smooth endoplasmic reticulum, which was considerably enlarged, with formation of large vacuolar structures situated deep in the dendroplasm. Mitochondrial lesions and alterations in cytoskeletal elements--disintegration of microtubules or even their complete loss--were also observed. The general pattern of abnormalities within the organelles and cytoskeletal elements of dendritic processes in Purkinje cells in the VPA chronic experimental model imply that there are disturbances in detoxication processes. Furthermore these changes were irreversible, as they were maintained after drug withdrawal.     

Maturation of the cerebellar Purkinje cells

Summary The postnatal evolution of the Purkinje cell spontaneous firing (simple spikes) has been studied in the white Rat from 3 days after birth until adulthood using the following parameters: modal interspike interval, mean interspike interval, and ratio of the modal over the mean interspike interval of the discharge. Furthermore, two experimental conditions have been used: rats anaesthetized with Nembutal and rats only locally analgesied, the two preparations being curarized. It is shown that:1) Between 3 and 5 days after birth, the spontaneous activity of many Purkinje cells is only formed by brief bursts of several spike potentials occuring more or less frequently. Evidence is given that some of these bursts are climbing fiber responses, the others being presumably elicited in Purkinje cells by parallel fibers activation. 2) After 5 days, the firing pattern (simple spikes) of Purkinje cells become more subtained and is formed by a more or less regular succession of spikes. Experimental conditions significantly change for all ages studied this firing pattern, and also change the time course of the evolution of all the considered parameters excepted for the modal interspike interval. 3) As a whole, Purkinje cells look immature until 8 days after birth. They rapidly mature between days 10 and 20. After the end of the 3rd postnatal week they show no significant differences when compared to the spontaneous firing of adult Purkinje cells, at least for the unanaesthetized preparations.At all ages a good correlation exist between Purkinje cells spontaneous firing (simple spikes) and data from the litterature concerning synaptogenesis in the cerebellum (parallel fibers Purkinje cells synapses).     

Demonstration of axonal branching of fibres from certain precerebellar nuclei to the cerebellar cortex and nuclei: a retrograde fluorescent double-labelling study in the cat

Summary The projections from certain brain stem precerebellar nuclei to the cerebellar cortex and nuclei have been examined in the cat by using the retrograde fluorescent double-labelling technique. Crystalline Fluoro-Gold was implanted into the left cerebellar nuclei from the contralateral side and rhodamine-B-isothiocyanate was injected into the overlying cerebellar cortex. The inferior olive, the lateral reticular nucleus, and the reticular tegmental pontine nucleus all contained double- as well as single-labelled neurons, and it was concluded that these nuclei have a high number of neurons whose axons branch to both the cerebellar cortex and nuclei. The neurons in the paramedian reticular nucleus and the pontine nuclei proper appear to project only to the cerebellar cortex.     

Saccade-related Purkinje cells in the cerebellar hemispheres of the monkey

Summary Extracellular single unit discharges of cerebellar Purkinje cells (P-cells) were recorded from the cerebellar hemispheres of two Japanese monkeys (Macaca fuscata) during spontaneous and visually guided eye movements. We found that saccade-related P-cells, whose simple-spike (SS) discharge rates were modulated in close correlation with saccadic eye movements, were localized in fairly restricted areas in the hemisphere, mostly in Crus IIa with some in the deep folia of Crus I. P-cells located in simple lobules, superficial folia of Crus I or in Crus IIp did not change their discharge rate during voluntary eye movements. Fifty-five saccade-related P-cells recorded from Crus I and II showed modulation of SS discharge rate related to both spontaneous and visually triggered saccades, with the modulation closely time-locked to the saccades. Two thirds (37/55) of saccade-related P-cells began to change their SS discharge rate 20–100 ms prior to the onset of saccades. The remaining one third (18/55) changed their activity approximately at the same time as the saccade onset. These saccade-related P-cells did not show changes in activity during smooth pursuit eye movements, and we did not find any P-cells in the cerebellar hemisphere which showed changes of activity preferentially during smooth pursuit eye movements. In about half (26/55) of the saccade-related P-cells, the pattern of modulation prior to and during saccades was biphasic: increase-decrease or decrease-increase. The other half (29/55) showed monophasic increases or decreases. For a given P-cell, the discharge pattern during saccades was similar for saccades of all directions, though there was a preferred direction in the amount of discharge rate modulation. The present findings suggest that the cerebellar hemisphere (Crus I and IIa) plays an important role in the control of voluntary saccadic eye movements, in addition to other cerebellar cortical areas (flocculus and posterior vermis) which are known to participate in the control of saccades.