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C Sotelo

Publications and source records attributed to C Sotelo.

At least 91 records · Page 5Linked to original sources
PubMed1990

Early development of the rat precerebellar system: migratory routes, selective aggregation and neuritic differentiation of the inferior olive and lateral reticular nucleus neurons. An overview.

The migration, cytoarchitectonic segregation and neuritogenesis of the inferior olive (ION) and lateral reticular (LRN) neurons are described in the rat. Generated in the same primary precerebellar neuroepithelium, at embryonic days 12-13 (E12-E13) for the ION and E12-E14 for the LRN, the postmitotic cells take either the intraparenchymal (smms, for ION neurons) or the subpial migratory streams (mms, for LRN neurons and other populations, as those of the external cuneate nucleus, ECN). The ION neurons settle in their ultimate domain from E16 to E18, ipsilaterally to their proliferation side. The LRN (and ECN) neurons cross the midline at the "floor plate" (FP) level, and settle contralaterally to their birthplace between E17 and E19. In both cases, the acquisition of a mature dendritic tree is a late event when compared to the precocious axonogenesis. The FP structure may play a major role in i) attracting the axons of the precerebellar neurons, and ii) instructing these neurons whether to cross the midline or not. Thus, ultimately the FP may govern the pattern (crossed or uncrossed) of the projections of the ION and LRN to their common cerebellar target.

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PubMed1989

Synaptology of the cerebello-olivary pathway. Double labelling with anterograde axonal tracing and GABA immunocytochemistry in the rat.

The dentato-olivary projection has been ultrastructurally studied in rats that received a wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) injection in the nucleus lateralis. Ultrathin sections containing the inferior olive have been double-labelled with the GABA-immunogold method. About 97% of the WGA-HRP labelled axon terminals are GABA-immunopositive. Most of them belong to a single type consisting of small boutons establishing symmetrical synapses on dendrites. Nevertheless, there is some morphological and neurochemical diversity among the labelled terminals, and particularly, a small contingent are GABA-immunonegative. Of the GABAergic dentato-olivary boutons, 4% occupy a privileged position, with synaptic contacts straddling two dendritic profiles linked by gap junctions. The strategic location of these inhibitory dentato-olivary synapses suggests that they can modulate the electrotonic coupling rate between sets of inferior olivary neurons.

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PubMed1989

Proximal trajectory of the brachium conjunctivum in rat fetuses and its early association with the parabrachial nucleus. A study combining in vitro HRP anterograde axonal tracing and immunocytochemistry.

The proximal course of the developing brachium conjunctivum (BC) in the rat described from embryonic day 16 (E16) to one day postnatal (P1). Axons of the cerebellar deep nuclear neurons entering this bundle were identified by anterograde axonal tracing after in vitro horseradish peroxidase (HRP) injections in the cerebellar plate. At all ages, the main ascending limb of the BC can be followed from its emergence, dorsal to the cerebellar plate where it assumes an almost vertical course, up to its decussation. Close to the ventricle at E16, the decussating fibers are progressively displaced ventrally probably because of the fusion, on the midline, of bilaterally produced raphe neurons. In E16 and E17 embryos, labeled BC fibers extend beyond the decussation in the caudal part of the red nucleus. Decussating BC axons, in some E16 early embryos, end with large and complicated growth cones, as described previously in 'decision regions' for chick embryo motoneurons. Growth cones were never observed in this region in older embryos. In addition to the main ascending limb of the BC, we also traced its ipsilateral descending limb and the cerebello-olivary projections. In parallel, the development of a nucleus immunoreactive for the vitamin D-dependent calcium-binding protein (CaBP) is reported. By E16, its neurons migrate rostrally and settle in the region where the BC is demonstrated by tracing experiments. At E17 and thereafter this isthmic nucleus is composed of a shell of CaBP-immunoreactive neurons ensheathing an immunonegative cylinder. Between E17 and birth, in spite of the profound modifications of the isthmic region, this CaBP-immunoreactive nucleus remains in close proximity to the BC. This nucleus is identified as the marginal nucleus of the BC or parabrachial nucleus, by double-labeling experiments combining the visualization of the retrogradely labeled axons and neurons of the deep cerebellar nuclei inside the CaBP immunofluorescently labeled parabrachial nucleus. Subsequently the deep cerebellar neurons translocate caudoventrally moving away from the parabrachial nucleus inside which their axons become visible. This pattern of migration could indicate that a few neurons of the deep nuclei remain ectopic, wedged between the restiform body and the BC while receiving an appropriate Purkinje cell (PC) projection.

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PubMed1988

Organization of spinocerebellar projection map in three types of agranular cerebellum: Purkinje cells vs. granule cells as organizer element.

The organization of the spinocerebellar projection was analysed by the anterograde axonal WGA-HRP (horseradish peroxidase-wheat germ agglutinin conjugate) tracing method in three different types of agranular cerebellar cortex either induced experimentally by X-irradiation or occurring spontaneously in weaver (wv/wv) and staggerer (sg/sg) mutant mice. The results of this study show that in the X-irradiated rat and weaver mouse, in both of which the granule cells are directly affected and die early in development, the spinal axons reproduce, with few differences, the normal spinocerebellar pattern. Conversely, in staggerer mouse, in which the Purkinje cells are intrinsically affected and granule neurons do not seem to be primarily perturbed by the staggerer gene action, the spinocerebellar organization is severely modified. These findings appear somewhat paradoxical because if granule cells, the synaptic targets of mossy spinocerebellar fibers, were necessary for the organization of spinocerebellar projection, the staggerer cerebellum would exhibit a much more normal projectional map than the weaver and the X-irradiated cerebella. It is, therefore, obvious that granule cells, and even specific synaptogenesis, are not essential for the establishment of the normal spinocerebellar topography. On the other hand, the fact that the Purkinje cells are primarily affected in the unique agranular cortex in which the spinocerebellar organization is severely modified suggests that these neurons could be the main element in the organization of the spinocerebellar projection map. This hypothesis is discussed in correlation with already-reported findings on the zonation of the cerebellar cortex by biochemically different clusters of Purkinje cells.

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PubMed1988

Migratory pathways and neuritic differentiation of inferior olivary neurons in the rat embryo. Axonal tracing study using the in vitro slab technique.

The use of the HRP retrograde tracing method, applied in vitro to embryonic (E15-E20) cerebellum-brainstem slabs, has allowed the identification of single young postmitotic olivary neurons. Labeled neurons move within two migratory streams: one superficial, under the pia (the marginal stream), and the other, of earlier onset, deeper in the medullary parenchyma (the submarginal stream). All neurons in the latter converge to the inferior olive ipsilaterally to their proliferation site; whereas, most neurons within the marginal stream cross the midline and bypass the olivary domain. Only a few HRP-labeled neurons leave the marginal stream towards the olivary territory, on their proliferation side. Hence, contrary to previous reports, the submarginal stream provides almost all the olivary neurons (95% at least), while the contribution of the marginal stream is very small (5% at the most). Axonogenesis is the earliest event in neuritic differentiation. By E15, 48 h after proliferation, the axons at the front of the migrating neurons have already crossed the interolivary commissure, and reached at least the site of HRP application, while the cell bodies have not yet penetrated their terminal domain. An ipsilateral component of this axonal tract was never detected. Hence, the olivocerebellar projection is formed very early, and is entirely crossed from its onset. Dendritogenesis was also analyzed during intra-uterine life; olivary neurons evolve from a fusiform shape (typical of migrating neurons) to a stellate form, with long and straight dendrites (once arrived at their ultimate location). Thus the acquisition of their mature spherical 'ball of wool' shape is a postnatal event, most probably concomitant with the major synaptogenetic phase.

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PubMed1988

Electrophysiological demonstration of a synaptic integration of transplanted Purkinje cells into the cerebellum of the adult Purkinje cell degeneration mutant mouse.

After implantation of solid pieces of cerebellar primordia from 12-day-old C57BL embryos into the cerebellar parenchyma of 3- to 4-month-old "Purkinje cell degeneration" mutant mice, Purkinje cells from the donor leave the implant and differentiate while migrating into the host molecular layer. Electrophysiological studies were performed using in vitro cerebellar slice preparations from "Purkinje cell degeneration" mutants 1-2 months after grafting, when grafted Purkinje cells have reached their final location in the host molecular layer and have completed their morphological differentiation. Intracellular recordings obtained from 45 Purkinje cells in mutant mice demonstrated that such grafted neurons have normal bioelectrical properties including sodium and calcium conductances and inward rectification. Moreover, all grafted Purkinje cells responded to electrical white matter stimulation by a typical all-or-none climbing fiber response. Responses mediated through the activation of mossy and parallel fibers, as well as inhibitory postsynaptic potentials, were also recorded in a significant number of grafted Purkinje cells. On the whole, all these excitatory and inhibitory responses in grafted "Purkinje cell degeneration" mutant mice have characteristics comparable to those in control mice. After electrophysiological studies, Purkinje cells were further characterized by their positive staining by calbindin antibody. Neurons of this class were dispersed throughout the molecular layer of the host folia in which the electrophysiological recordings had been performed. The ectopic location of their perikarya, the presence of dendritic trees spanning most of the molecular layer (without entering the granular layer), and the occasional presence of axons emerging from the ectopic neurons and forming loose bundles at the white matter axis of the folia, corroborate the grafted nature of the Purkinje cells studied. Therefore, these experiments demonstrate that embryonic Purkinje cells from the graft can complete differentiation in the adult host cerebellum, and establish specific synaptic contacts with the presynaptic elements previously impinging on the missing neurons of "Purkinje cell degeneration" mutants. This process leads to a qualitative functional synaptic restoration of the cortical cerebellar network.

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PubMed1988

Pathologic changes in the CNS of dystonia musculorum mutant mouse: an animal model for human spinocerebellar ataxia.

This paper examines the topography of neuronal degeneration in the central nervous system of the dystonia musculorum (dt) mutant mouse, revealed by selective silver impregnation, specific histochemical staining and electron microscopy. Neuronal lesions have been observed exclusively in the spinal cord, the medulla and the anterior lobe of the vermis. In the spinal cord, axonal degeneration was maximal among large and medium-sized primary sensory fibers, whereas thin caliber primary afferents were unaffected, with the exception of those containing acid phosphatase activity. In regions of laminae VI to VIII that receive numerous degenerative primary afferents, neurons undergoing different phases of degeneration (chromatolysis, lipid accumulation, dark shrunken necrosis) were constantly found. Most of the latter belonged to spinocerebellar neurons, owing to the presence of fiber degeneration in both spinocerebellar tracts and mossy fiber degeneration in the anterior vermal lobe. In the medulla only axonal degeneration was observed and was confined to three fiber systems: the dorsal column pathway, the sensory trigeminal fibers (both from the trigeminal ganglion and from the mesencephalic trigeminal nucleus), and the spinocerebellar fibers entering the cerebellum through the inferior and superior cerebellar peduncles. This study also suggests a simple pathophysiological mechanism for the onset and the progression of the degeneration: dystonic gene action would affect perinatally specific classes of sensory receptors, producing the degeneration of the nerve terminals and, progressively, the cell death of the sensory ganglion cells at their origin. This retrograde death, which results in the massive and early deafferentation of spinocerebellar neurons, would provoke, trans-neuronally, the impairment of these second order sensory neurons and the progressive degeneration of the spinocerebellar system. The close resemblance of the neuropathology of the mutant mouse to Friedreich's ataxia (the commonest form of human degenerative ataxic disorders) allows one to suppose that the dystonic mouse may be an optimal animal model for studying the genetic basis and the pathophysiological mechanisms of this form of human ataxia.

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PubMed1987

The dentato-olivary projection in the rat as a presumptive GABAergic link in the olivo-cerebello-olivary loop. An ultrastructural study.

It is here shown that autoradiographically labelled axon terminals of the dentato-olivary projection form a heterogeneous population. However, a majority of them constitute an even class of synapses, characterized by their small axonal size, their content in pleimorphic vesicles, and the establishment of symmetric synapses on small dendrites, about 5% of which are linked through a gap junction. The same material, used for immunocytochemistry of GABA with the postembedding technique, discloses that a majority of boutons with cytological features similar to the dentato-olivary terminals are GABA-immunoreactive, especially those synapsing on dendrites linked by gap junctions. The cerebello-olivary projection, despite its heterogeneity, thus appears as part of the GABAergic system which governs the synaptic modulation of the electrotonic coupling between olivary neurons.

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PubMed1987

Postnatal development of the inferior olivary complex in the rat: IV. Synaptogenesis of GABAergic afferents, analyzed by glutamic acid decarboxylase immunocytochemistry.

The postnatal maturation of the GABAergic innervation of the rat inferior olive was studied with an antiserum to glutamic acid decarboxylase (GAD), the GABA-synthesizing enzyme. GAD-positive axons were present at a very low density in the periolivary and interlamellar regions of newborn rats, as well as in certain precise areas of the lamellae, at the mediodorsal limit. The immature distribution indicates that the GABAergic projections reach the inferior olive shortly before birth and that the greater part of synaptogenesis and the establishment of the adult organization occurs postnatally. Light and electron microscopic analyses disclosed that the maturation of this system of olivary afferents passes through three well-defined stages: (1) During the first, or immature stage (from PO to P5), GAD immunoreactivity is not confined to axon terminals, as in adult rats. The labeled fibers penetrate progressively into the periphery of the lamellae and reach their centers in an irregular manner by the end of the immature stage. This staggered invasion of the lamellae accentuates intraregional olivary differences and begins to take the adult configuration. As fiber penetration advances, the density of labeled axons establishing synaptic contacts increases, while the number of completely immunostained fibers decreases. This distribution prevails until the end of the immature stage and suggests that the GABAergic afferent projections remain in a "waiting compartment" from their prenatal arrival until the moment they invade the olivary parenchyma. (2). The second stage is designated as an intermediate stage of maturation and lasts from P7 to P10. During this period, GAD axoplasmic compartmentation occurs, and henceforth only axon terminals exhibit GAD immunoreactivity. Concomitantly, intraregional differences in the pattern of innervation become more marked, because of the continuing irregular distribution of the growing labeled axons. This intermediate maturational stage is also characterized by a rapid increase in labeled axon terminals bearing synaptic complexes and by the formation of complex synaptic arrangements, the protoglomeruli. From the beginning of protoglomeruli formation, GAD-positive axon terminals are one of their constituents, and they are systematically localized at the periphery of the incipient dendritic protrusions. (3) The final stage of maturation takes place from P10 to P15. During this stage, the adultlike pattern of GABAergic innervation of the inferior olive is attained. Toward P15, intraregional differences in GAD immunoreactivity are similar to those of the adult rat.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1987

Localization of benzodiazepine-like molecules in the rat brain. A light and electron microscopy immunocytochemistry study with an anti-benzodiazepine monoclonal antibody.

The anti-benzodiazepine (BZD) monoclonal antibody 21-7F9 was used with light and electron microscopy immunocytochemistry techniques for studying the distribution of BZD-like molecules in the rat brain. With light microscopy, BZD-like immunoreactivity was found throughout the brain, mainly in neurons and occasionally in some glial cells (in periventricular areas, as well as in some perivascular astrocytes). Despite the fact that in the cerebellum the GABAergic neurons exhibit BZD-like immunoreactivity, co-localization of these two molecules is not exact, since there are also BZD-like positive neurons that are non-GABAergic (e.g., cerebellar granule cells, some neocortical and hippocampal pyramidal cells). Ultrastructural study of the cerebellar cortex disclosed that all neuronal categories were immunoreactive, as were some astrocytes within the granular layer. The reaction product was concentrated in neuronal perikarya and dendritic processes. Axons and axon terminals remained mostly unlabeled. The absence of immunoprecipitate within cytoplasmic organelles (Golgi apparatus, mitochondria, lumen of endoplasmic reticulum) and its presence at the cytoplasmic face of the cell membranes strongly suggests that endogenous BZD-like molecules are present in both the soluble cytoplasm (hyatoplasm), and also in association with both external and internal cell membranes. The results suggest that the brain BZD-like molecules might be functionally involved in either the modulation of GABA neurotransmission and/or the biotransformation, accumulation and elimination of benzodiazepines and benzodiazepine-like molecules in the brain.

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PubMed1987

Cerebellar mutations affecting the postnatal survival of Purkinje cells in the mouse disclose a longitudinal pattern of differentially sensitive cells.

The pattern of surviving Purkinje cells (PCs) was investigated in three cerebellar mutant mice with severe postnatal PC death. Two of these mutations, nervous (nr) and Purkinje cell degeneration (pcd) mutations are already well characterized. The third mutation is a new one, which appeared spontaneously in DW/J-Pas mice and was called tambaleante (tbl). PCs were identified by immunocytochemistry using an antibody against vitamin D-dependent calcium-binding protein which labels all the PCs in adult control mice. In each of the three mutations, surviving PCs are arranged according to a different and reproducible pattern which is symmetric relative to the midline. In NR and young PCD mutants, PCs are closely packed in broad sagittal bands. In TBL, they are more loosely arranged in a rather patchy pattern. In PCD and in TBL mutants the death of resistant PCs is only shortly delayed but in NR there is little change in the number of surviving PCs after 3 months. The differential sensitivity of subsets of PCs to the effect of nr, pcd, and tbl mutations is topographically determined. These results provide a new evidence of the PC heterogeneity which has been previously demonstrated by histochemical and immunohistochemical techniques. Moreover, in the anterior vermis of control mice, three thin sagittal bands of PCs are labeled by the Q113 monoclonal antibody. Similarly, in the anterior lobe of the NR cerebellum, the thin longitudinal strips of missing PCs coincide with the absence of Q113 immunoreactivity: in this region the nr mutation affects specifically the survival of Q113 positive cells. However, other clusters of Q113 immunoreactive PCs do survive in NR mice suggesting that susceptibility to the nr mutation and Q113 positivity are two independent markers of the underlying PC compartmentalization.

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PubMed1987

Reconstruction of the defective cerebellar circuitry in adult Purkinje cell degeneration mutant mice by Purkinje cell replacement through transplantation of solid embryonic implants.

Solid pieces of cerebellar primordia taken from 12-day-old C57BL embryos were implanted into the cerebellar parenchyma of 3- to 4-month-old "Purkinje cell degeneration" mutant mice and analysed 2-3 months later. Purkinje cell replacement was followed by means of immunocytochemistry with antisera against either cyclic guanosine monophosphate-dependent protein kinase or vitamin D-dependent calcium-binding protein, which allows the complete staining of these neurons. Although all solid graft implants survived, their fate within the mutant cerebellum varied in three ways: Often, a more or less large fragment of the solid graft remained in the white matter, close to the cortex or even partially replacing it. These remnants contained a few distorted Purkinje cells and a region corresponding to the transplanted deep nuclei, composed of numerous immunostained axons and axon terminals surrounding immunonegative neurons. Less frequently remnants of the graft were extruded to an extracerebellar location, between two adjacent folia. They contained a few Purkinje cells intermixed with granule cells and other neurons. In a few cases corresponding to superficial deposition, the implants developed lobulated and trilaminated minicerebella which were located outside the mutant cerebellum but integrated into it. In all three situations, a large number of grafted Purkinje cells succeeded in moving out of the implants and in invading the host molecular layer. These Purkinje cells develop flattened dendritic trees perpendicular to host bundles of parallel fibres. Ultrastructural examination of the synaptic investment of Purkinje cells which have reached the host molecular layer revealed that they acquire normal synaptic inputs although complex pericellular baskets and pinceau formation do not develop. Axons from molecular layer interneurons synapse on perikaryal and smooth dendritic membranes, climbing fibres synapse on stubby spines emerging from thick dendritic branches, and parallel fibres contact almost exclusively the long-necked spines of the distal spiny branchlets. Finally, Purkinje cells which succeed in migrating to molecular layer regions no further than 0.6 mm from the host deep nuclei are able to grow axons which reach appropriate target areas and establish synaptic connections on nuclear neurons. The results obtained from this series of long-term survival cerebellar transplantations point to the possibility of fulfilling most of the conditions necessary for functional restoration of neural grafts in systems in which neurons are connected in a point-to-point manner.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1986

Non-Purkinje cell GABAergic innervation of the deep cerebellar nuclei: a quantitative immunocytochemical study in C57BL and in Purkinje cell degeneration mutant mice.

Purkinje cell degeneration (pcd) mutant mice, 3-4 months old, were used to identify and quantify the non-Purkinje cell GABAergic innervation of deep cerebellar nuclei. Glutamic acid decarboxylase (GAD) immunoreactive structures appeared as dark dots throughout the 4 nuclei. Ultrastructural examination confirmed that each dot corresponded to an axon terminal. GAD-labeled boutons were large, contained tightly packed flattened vesicles and established Gray type II synapses with all nuclear neuronal populations. Thus, cytological criteria did not distinguish between Purkinje cell and non-Purkinje cell GAD-positive nerve terminals, since they shared many common features. The number of GAD-immunoreactive axon terminals in the deep nuclei of pcd cerebella was compared to that of normal C57BL mice. Despite an almost complete disappearance of Purkinje cells in the pcd mouse (less than 0.05% of these neurons remained in the mutants), the surface density of GAD-positive nerve terminals in the deep nuclear region was 37% of control value. Taking into account a volumetric decrease of 58% for the deep nuclei of the mutant cerebellum, we estimated the percentage of GAD-positive boutons innervating these nuclei to be 15% of normal values. This important residual innervation of the deep nuclei might arise from local GABAergic neurons, which were identified in the normal and mutant cerebella by immunostaining with an anti-GABA antibody.

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PubMed1986

Localization of glutamic-acid-decarboxylase-immunoreactive axon terminals in the inferior olive of the rat, with special emphasis on anatomical relations between GABAergic synapses and dendrodendritic gap junctions.

Immunocytochemical and electron microscopic methods were used to examine the GABAergic innervation of the inferior olivary nucleus in adult rats. This neuronal system was visualized with an antibody against glutamic acid decarboxylase (GAD, EC 4.1.1.15), the GABA-synthesizing enzyme. A GAD-positive reaction product was encountered only in short segments of preterminal axons and in axon terminals. Their relative number per unit area of neuropil was very similar in all olivary subnuclei. Despite this homogeneity in density, obvious intraregional differences existed. Some regions were strongly immunoreactive (the "c" subgroup, the beta nucleus, and the mediolateral outgrowth of the medial accessory olive), whereas others were weakly labeled (the dorsomedial cell column and the central zones of the medial accessory and principal olives). The strongly immunoreactive areas contained the largest and most intensively labeled axon terminals. Areas of weak labeling were filled with small, weakly immunoreactive nerve terminals. Thus, variations in size and in intensity of labeling create a specific pattern of GABA innervation, revealed by an almost continuous gradient between the above-mentioned extremes. The GAD-positive axon terminals established conventional synapses with dendrites (94% of the samples) or with cell bodies (6%). The vast majority of these synapses were type II (84%) and only a small proportion formed type I synaptic contacts (16%), regardless of the nature of the postsynaptic element. Immunoreactive terminals were also involved in the complex synaptic arrangements--the glomeruli, which characterize the olivary neuropil. Within these formations, olivary neurons were electrotonically coupled through dendrodendritic gap junctions. There was a constant association between GAD-positive axon terminals and small dendritic appendages linked by gap junctions. This association was revealed not only by the systematic presence of immunolabeled terminals directly apposed to the dendritic appendages but, more importantly, by the frequent presence of type II synapses straddling both elements. These synapses were in close proximity to the low-resistance pathways represented by the gap junctions. The strategic location of these GABA synapses is discussed in relation to recent findings indicating the possibility of a synaptic modulation of the electrical coupling: the release of GABA, by increasing nonjunctional membrane conductance, could shunt the coupling between olivary neurons. The functional decoupling of selected gap junctions would be responsible for the spatial organization of the olivary electrotonic coupling.

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