Experimental reorganization of the cerebellar cortex. 3. Regeneration of the external germinal layer and granule cell ectopia

Opiate Drugs with Abuse Liability Hijack the Endogenous Opioid System to Disrupt Neuronal and Glial Maturation in the Central Nervous System

The endogenous opioid system, comprised of multiple opioid neuropeptide and receptor gene families, is highly expressed by developing neural cells and can significantly influence neuronal and glial maturation. In many central nervous system (CNS) regions, the expression of opioid peptides and receptors occurs only transiently during development, effectively disappearing with subsequent maturation only to reemerge under pathologic conditions, such as with inflammation or injury. Opiate drugs with abuse liability act to modify growth and development by mimicking the actions of endogenous opioids. Although typically mediated by μ-opioid receptors, opiate drugs can also act through δ- and κ-opioid receptors to modulate growth in a cell-type, region-specific, and developmentally regulated manner. Opioids act as biological response modifiers and their actions are highly contextual, plastic, modifiable, and influenced by other physiological processes or pathophysiological conditions, such as neuro-acquired immunodeficiency syndrome. To date, most studies have considered the acute effects of opiates on cellular maturation. For example, activating opioid receptors typically results in acute growth inhibition in both neurons and glia. However, with sustained opioid exposure, compensatory factors become operative, a concept that has been largely overlooked during CNS maturation. Accordingly, this article surveys prior studies on the effects of opiates on CNS maturation, and also suggests new directions for future research in this area. Identifying the cellular and molecular mechanisms underlying the adaptive responses to chronic opiate exposure (e.g., tolerance) during maturation is crucial toward understanding the consequences of perinatal opiate exposure on the CNS.

Developing central nervous system and vulnerability to platinum compounds

Comparative studies on the effects of the platinum complexes in use or in clinical trials are carried out in order to discover differences in the neurotoxic potential and the reversibility of neurotoxicity. In this paper, we summarized the current literature on neurotoxicity and chemoresistance of cisplatin (cisPt) and discussed our recent efforts on the interference of cisPt and a new platinum compound [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS), with high specific reactivity with sulphur ligands instead of nucleobases as cisPt, on some crucial events of rat postnatal cerebellum development. The acute effects of drug treatments on cell proliferation and death in the external granular layer and granule cell migration and the late effects on the dendrite growth of Purkinje cells were evaluated. Together with the demonstrated antineoplastic effectiveness in vitro, compared with cisPt, data suggest a lower neurotoxicity of PtAcacDMS, in spite of its presence in the brain that involves considerations on the blood brain barrier permeability.

Radiation damage increases Purkinje neuron heterokaryons in neonatal cerebellum

OBJECTIVE

Recent studies have shown that in radiated and bone marrow transplanted mice, bone marrow-derived cells (BMDCs) fuse with Purkinje neurons resulting in the formation of binucleated heterokaryons. Here we investigated whether radiation plays a role in the formation of Purkinje neuron heterokaryons.

METHODS

Fused cells were identified by reporter gene expression in mice, carrying floxed LacZ (R26R-LacZ) in all cells and Cre in hematopoietic-derived cells. Cell fusion was confirmed by the presence of two nuclei. The number of fused Purkinje neurons was studied in: 1) whole-body radiated newborn and adult R26R-LacZ mice, transplanted with bone marrow cells expressing Cre; 2) in newborn and adult mice that received different doses of radiation to the head; and 3) in radiated and non-radiated newborns treated with a myeloablative drug before bone marrow transplantation.

RESULTS

In neonatal, but not in adult cerebelleum, radiation-in a dose-dependent manner-induces a dramatic increase in the number of fused Purkinje neurons.

INTERPRETATION

Increase recruitment of BMDCs into the cerebellum, radiation damage to cerebellar cells, or both, increase the formation of fused Purkinje cells. BMDC-Purkinje heterokaryons formation may reflect an endogeneous neuronal repair mechanism, or it could be a by-product of radiation-induced inflammation. In either case, fused Purkinje neurons increase following radiation damage in the developing cerebellum. The above observations reveal a novel consequence of head radiation in neonatal rodents. It will be interesting to determine if similar increase in the number of binucleated Purkinje neurons, occurs in children that receive radiation during early development. Ann Neurol 2009;66:100-109.

Reorganization of the rat cerebellar cortex during postnatal development following cisplatin treatment

We examined the effects of the antitumor agent cisplatin on the development and plasticity of cerebellar cytoarchitecture. Since knowledge of the parallel and climbing fiber-Purkinje cell system is important in order to determine the architectural basis of cerebellar function, we used immunofluorescence for vesicular glutamate transporters (VGluT1 and VGluT2) to evaluate the trend of synaptogenesis of parallel and climbing fibers on Purkinje cells in the cerebellum vermis after a single injection of cisplatin to 10-day-old rats, i.e., during a crucial period of cerebellar development. The temporal and spatial patterns of VGluT1 and VGluT2 immunoreactivity after the early cisplatin injury provided evidence that remodeling of excitatory afferents and Purkinje cell dendrites occurs. After an early slow down of Purkinje cell dendrite growth, 7 days following the treatment, the extension of the molecular layer was reduced, as was parallel fiber innervation, but VGluT1 immunoreactive fibers contacted Purkinje cell dendrite branches extending within the external granular layer. VGluT2 immunopositive climbing fiber varicosities were still largely present on the soma and stem dendrites of Purkinje cells. Twenty days after the cisplatin injection, the thickness of the VGluT1 immunopositive molecular layer was reduced. VGluT2 climbing fiber varicosities were found on the remodeled Purkinje cell dendrites, as in controls, although at a lower density. Alterations in the immunoreactivity for polysialic acid neural cell adhesion molecule (PSA-NCAM) during the recovery phase suggest that this molecule plays a fundamental role not only during development, but also in the reorganization of neuroarchitecture. The changes were restricted to the neocerebellar vermis and were likely dependent on the different timing of lobule formation. The results of these investigations reveal the existence of vulnerability windows of the cerebellum to exposure to experimental or environmental cytotoxic agents during a critical period in development.

Proliferation and migration of granule cells in the developing rat cerebellum: cisplatin effects

We evaluated the relationship among proliferation, death and migration of granule cells in lobules VI-VIII of vermis, in comparison with lobule III, during cerebellar development. To this aim, a single injection of cisplatin, i.e., a cytostatic agent that is known to induce death of proliferating granule cells, was given to 10-day-old rats. Histochemical markers of proliferating (PCNA immunoreaction) and apoptotic (TUNEL staining) cells were used; the variations of the external granular layer (EGL) thickness were evaluated in parallel. After PCNA and TUNEL reactions, evident changes of the whole EGL were found on PD11 (1 day after treatment), when a reduction of the thickness of this layer was found in treated rats, mainly in consequence of the high number of apoptotic cells in all the cerebellar lobules. On PD17 (7 days after treatment), a thick layer of proliferating cells was observed in lobules VI-VIII of treated rats, while the peculiar pattern of the normal development showed a thin EGL. At the same time, in treated rats, the number of apoptotic cells in EGL was low. In all developmental stages of treated rats, after GFAP immunoreaction, glial fibers appeared twisted, thickened, and with an irregular course; intensely labeled end-feet were present. The damage of radial glia suggests an alteration of migratory processes of granule cells, which is also evidenced by the decreased thickness of the premigratory zone of the EGL. Injured radial glia fibers were restricted to lobules VI-VIII and they persisted at PD30, leading to the presence of ectopic granule cells in the molecular layer, as we previously described.

Developmental plasticity of rat cerebellar cortex after cisplatin injury: inhibitory synapses and differentiating Purkinje neurons

A single injection of cisplatin, a cytostatic agent, (5 microg/g body weight) in 10-day old rats leads later to the reorganization of the cerebellar cortex in lobules VI-VIII of the vermis. Double immunofluorescence reaction for glutamate receptor (GluR)2/3, a ionotropic glutamate receptor that labels postsynaptically Purkinje neurons, and glutamic acid decarboxylase (GAD)65, an isoform of the GABA synthesis enzyme that labels presynaptically inhibitory terminals in the molecular layer, were employed. Less-differentiated Purkinje cells were present in rats treated on postnatal day (PD)11 at the top of lobule VI and in lobules VII-VIII, in comparison with the deep zones of the same lobules and lobule III. The changes were interpreted as due to loss of trophic factors of Purkinje cell growth, e.g. signaling molecules and granule cells. However, we have shown that a remodelling of Purkinje cell dendrites occurred on PD30 (20 days after cisplatin). In fact, despite of the GluR2/3 labeling of the entire Purkinje cell dendrites, the GAD65 immunofluorescent terminals were adjacent to the proximal parts of the dendrite, while they were scarce in the distal dendritic branchlets. The findings were discussed in relation to the changed cytoarchitecture of the cerebellar cortex, which from PD17 to PD30 includes regeneration of the external germinal layer, reorientation of the main dendritic branches and of the Purkinje cell branchlets, and the presence of ectopic cells.

Analysis of cerebellar development in math1 null embryos and chimeras

The cerebellar granule cell is the most numerous neuron in the nervous system and likely the source of the most common childhood brain tumor, medulloblastoma. The earliest known gene to be expressed in the development of these cells is math1. In the math1 null mouse, neuroblasts never populate the external germinal layer (EGL) that gives rise to granule cells. In this study, we examined the embryonic development of the math1 null cerebellum and analyzed experimental mouse chimeras made from math1 null embryos. We find that the anterior rhombic lip gives rise to more than one cell type, indicating that the rhombic lip does not consist of a homogeneous population of cells. Furthermore, we demonstrate that math1 null granule cells are absent in the math1 null chimeric cerebellum, from the onset of their genesis in the mouse anterior rhombic lip. This finding indicates a vital cell intrinsic role for Math1 in the granule cell lineage. In addition, we show that wild-type cells are unable to compensate for the loss of mutant cells. Finally, the colonization of the EGL by wild-type cells and the presence of acellular gaps provides evidence that EGL neuroblasts undergo active migration and likely have a predetermined spatial address in the rhombic lip.

CXC chemokine receptors in the central nervous system: Role in cerebellar neuromodulation and development

Chemokines and their receptors are constitutively present in the central nervous system (CNS), expressed in neurons and glial cells. Much evidence suggests that, beyond their involvement in neuroinflammation, these proteins play a role in neurodevelopment and neurophysiological signaling. The goal of this review is to summarize recent information concerning expression, signaling, and function of CXC chemokine receptor in the CNS, with the main focus on the developmental and neuromodulatory actions of chemokines in the cerebellum.

Developmental pattern of expression of the alpha chemokine stromal cell-derived factor 1 in the rat central nervous system

Stromal cell-derived factor 1 (SDF-1) is an alpha-chemokine that stimulates migration of haematopoietic progenitor cells and development of the immune system. SDF-1 is also abundantly and selectively expressed in the developing and mature CNS, as we show here. At embryonic day 15, SDF-1 transcripts were detected in the germinal periventricular zone and in the deep layer of the forming cerebral cortex. At birth, granule cells in the cerebellum and glial cells of the olfactory bulb outer layer showed an SDF-1 in situ hybridization signal that decreased progressively within the next 2 weeks. In other regions such as cortex, thalamus and hippocampus, SDF-1 transcripts detected at birth progressively increased in abundance during the postnatal period. SDF-1 protein was identified by immunoblot and/or immunocytochemistry in most brain regions where these transcripts were detected. SDF-1 was selectively localized in some thalamic nuclei and neurons of the fifth cortical layer as well as in pontine and brainstem nuclei which relay the nociceptive response. The presence of SDF-1 transcripts in cerebellar granule cells was correlated with their migration from the external to the inner granular layers with disappearance of the signal when migration was completed. In contrast, SDF1 mRNA signal increased during formation of the hippocampal dentate gyrus and stayed high in this region throughout life. The selective and regulated expression of SDF-1 in these regions suggests a role in precursor migration, neurogenesis and, possibly, synaptogenesis. Thus this alpha chemokine may be as essential to nervous system function as it is to the immune system.

Differential development of the human cerebellar vermis: immunohistochemical and morphometrical evaluation

Differential development of regions of the human cerebellar vermis was evaluated immunohistochemically and morphometrically between 18 weeks of gestation and 10 years of age. The density of Purkinje cells in the cerebellar vermis decreased rapidly until 38 weeks of gestation and slowly thereafter. At all stages of development, the density was higher in the posterior (lobules VI-IX) than the anterior vermis (lobules I-V). The area of cut sections of the anterior and posterior vermis in the mid-sagittal section increased rapidly before 40 weeks of gestation and gradually after birth, whereas growth was slower in the nodules. These developmental characteristics may be related to the selective susceptibility of cerebellar regions to environmental insults.

Distribution of cholinergic neuronal differentiation factor/leukemia inhibitory factor binding sites in the developing and adult rat nervous system in vivo

Cholinergic neuronal differentiation factor/leukemia inhibitory factor (CDF/LIF) is a multifunctional cytokine that affects neurons as well as many other cell types. Toward elucidating its neural functions in vivo, we previously investigated the distribution of CDF/LIF binding sites with iodinated native CDF/LIF in embryonic to postnatal day 0 (P0) rats. In the present study, we have extended our examination to postnatal ages and find that specific CDF/LIF binding sites are present at defined developmental stages in additional brain regions not previously exhibiting binding by P0. High levels of binding are detected in all P7 sensory and autonomic ganglia examined, but only in restricted postnatal central nervous system structures. Cranial motor and mesencephalic trigeminal neurons maintain high levels throughout, while binding to spinal motor neurons, which decreases to low levels at P0, reappears by P14 and increases with age. Most other structures, which show detectable binding by P0, exhibit higher levels at postnatal ages, including the red, deep, ventral cochlear, trapezoid, superior olivary, vestibular, ventral tegmental, and ventral posterior thalamic nuclei as well as the glomerular layer of the olfactory bulb. High levels are also detected in several structures for the first time after P0, including the cerebellar cortex (molecular and Purkinje cell layers), lateral reticular nucleus of the medulla and reticular formation, as well as the reticulotegmental, medial geniculate, solitary (rostral, dorsomedial, and commissural regions), medial septal, lateral mammillary, and lateral habenular nuclei. These results not only identify regions of potential CDF/LIF-responsive neurons and glia throughout development but suggest new CDF/LIF roles in the nervous system.

Neuroanatomical and functional alterations resulting from early postnatal cerebellar insults in rodents

This review examines neuroanatomical and functional alterations in rodents resulting from postnatal insults during cerebellar development. Treatments such as irradiation and methylazoxymethanol (MAM) administration produced near birth (< postnatal day 8 for irradiation treatment and < postnatal day 4 for MAM administration) result in more severe cerebellar damage than do similar treatments administered several days after birth. Prominent among the more severe alterations are foliation abnormalities, misalignment of Purkinje cells and continued multiple innervation of climbing fibers; few or none of these occur as a result of later treatments (> postnatal day 8 for irradiation treatment and > postnatal day 4 for MAM treatment). The functional alterations also differ: insults produced near birth result in hypoactivity, ataxia, tremor and accompanying learning deficits, whereas those produced later result in hyperactivity and few learning deficits. This hyperactivity may have relevance to human disorders. Brief discussions of cerebellar and functional alterations (e.g., hyperactivity) resulting from neonatal infection with the Borna disease virus and induction of hypo- and hyperthyroidism during the preweaning period are also presented.

Cerebellar granule cell differentiation in mutant and X-irradiated rodents revealed by the neural adhesion molecule TAG-1

In the external granular layer of the cerebellum, the granule cell precursors express the transient axonal glycoprotein TAG-1, a molecule involved in adhesion and neurite outgrowth. Granule cells express TAG-1 transiently, just as they extend neurites before migrating over the radial glia. The present study aims to investigate whether the expression pattern of TAG-1 is altered when granule cells develop abnormally. We studied in vivo models in which Purkinje and/or granule cell defects occur during postnatal development. These include the cerebellar mutant mice staggerer and lurcher as well as rats irradiated during postnatal development. Neither alterations in Purkinje cell differentiation nor the related granule cell loss in the mouse mutants impairs the ability of the surviving granule cell precursors to express TAG-1. Also, early granule cell loss in the X-irradiated rats do not disturb the TAG-1 expression phase in the patches of surviving granule cell precursors. Ectopic granule cells found in the adult cerebellum of X-irradiated rats do not bear the molecule, although they are located in the most superficial part of the molecular layer, occupied by the immunopositive cells a few days earlier. Thus, TAG-1 marks a very precise stage of granule cell differentiation, and the inward migration process itself is not required for the cessation of the expression. We postulate that TAG-1 may be involved in local differentiation steps restricted to the deep external granular layer such as parallel migratory routes or synchrony of axonal growth.

Further evidence for a unique developmental compartment in the cerebellum of the meander tail mutant mouse as revealed by the quantitative analysis of Purkinje cells

The cerebellum of the meander tail mutant mouse (mea/mea) is characterized by a relatively normal cytoarchitecture posteriorly with an abrupt transition to an anterior region in which there is abnormal foliation, agranularity, and Purkinje cell (PC) ectopia. This study presents the results of a qualitative and quantitative analysis of the PC in the mea/mea cerebellum. Developmental and morphological analyses reveal that the PC in the anterior region of the mea/mea cerebellum do not form a monolayer during the first week of postnatal development as they do in the wild type mouse. In the adult mea/mea, the dendrites of these ectopic cells are atrophic and disoriented. Quantitative studies in adult animals reveal that while the total number of PC is normal, the number of PC in the affected anterior region of the mea/mea cerebellum is greater than the number of PC in the anterior lobe, as classically defined by the primary fissure, of the normal animal. These data suggest that 1) the developmental morphology of the PC in the anterior region is abnormal, probably due to the lack of granule cells at early postnatal times; 2) the total number of PC in the cerebellum is normal, and 3) the defect is not restricted to the anterior lobe but involves a portion of the posterior lobe. The latter supports the notion that the mutant gene affects a unique developmental compartment in the cerebellum which does not coincide with the classic adult boundary, the primary fissure, between the anterior and posterior lobes.

GABAA/benzodiazepine receptor alpha 6 subunit mRNA in granule cells of the cerebellar cortex and cochlear nuclei: expression in developing and mutant mice

The gamma aminobutyric acidA/benzodiazepine (GABAA/BZ) receptor is a multisubunit (alpha, beta, gamma, delta, and rho) ligand-gated chloride channel; there are several variants of the alpha, beta, and gamma subunits, each of which has been localized throughout the central nervous system. A large number of GABAA/BZ subunit variants are expressed within the cerebellar cortex. In previous studies from other laboratories, alpha 6 subunit mRNA has been reported to be present exclusively in cerebellar granule cells. The developmental expression of alpha 6 mRNA in cerebellar and cochlear granule cells is of interest because it has been suggested that each of these cell types is derived from a common precursor pool. The polymerase chain reaction was used to generate a cDNA fragment encoding a portion of the M3-M4 intracellular loop of the alpha 6 subunit of the GABAA/BZ receptor. A [35S] riboprobe, transcribed from this cDNA fragment, was used to examine the expression of the alpha 6 subunit mRNA by in situ hybridization in developing normal mice and in adult mutant mice with known deficits in synaptic circuitry. A strong hybridization signal was observed over the granule cell layers of both the cerebellum and cochlear nuclei in adult mice. The signal over the cochlear nuclei appeared after birth toward the end of postnatal week 1, coinciding with the appearance of labeling in the cerebellar cortex. The intensity of the hybridization signal in both regions increased rapidly until postnatal day 14, after which it increased more gradually, reaching adult levels during postnatal week 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental analysis of the external granular layer in the meander tail mutant mouse: do cerebellar microneurons have independent progenitors?

The cerebellum of the meander tail mutant mouse (mea/mea) is characterized by an apparently normal cytoarchitecture posteriorly with an abrupt transition to an abnormal anterior region. Anteriorly, there is abnormal foliation, a drastic reduction in the granule cells (GC) population, disorganization of the Purkinje cells (PC), and a virtual absence of Bergmann glial processes. In this paper we analyze the prenatal and postnatal development of the cerebellum in the mea/mea and attempt to determine the phenotypic onset of the mutation in the anterior region. Hematoxylin and eosin stained sections reveal a morphological difference in the cerebellum of the mea/mea as early as embryonic day 16 characterized by a reduction in the external granule cell layer (EGL). The reduction in the EGL becomes increasingly apparent as development proceeds. This deficit in the EGL most probably results in the absence of GC, but it is unclear at this point whether reduced migration, proliferation, and/or increased cell death is the major factor. Interestingly, immunohistochemical staining with a monoclonal antibody against parvalbumin reveals that the basket and stellate cells, which are also thought to arise from the EGL, are present in the anterior region of the mea/mea cerebellum. These results suggest that the lack of GC in the meander tail is due to an early expressed abnormality of the EGL. However, the presence of the basket and/or stellate cells raises some interesting questions concerning the lineage of the cerebellar microneurons.

Regional differences in the timing of dendritic outgrowth of Purkinje cells in the vermal cerebellum demonstrated by MAP2 immunocytochemistry

Detailed, within-subjects Golgi analyses of regional differences in cerebellar Purkinje cell dendritic development are impractical due to the capriciousness of that technique. Immunocytochemical labeling of microtubule-associated protein 2 (MAP2) was used to reveal the dendritic development of Purkinje cells, and indicated marked differences in the timing of initial outgrowth of Purkinje cell dendrites for different lobules in the developing rat cerebellar vermis. In particular, an early maturing region of Purkinje cell dendritic outgrowth (lobules I, II, IX and X and along the primary fissure), and a late maturing region (distal lobule VI, lobule VII and dorsal lobule VIII) were documented.

Developmental neurotoxicology

Some injuries to the developing nervous system can be detected with traditional evaluation for morphologic pathology, but many early injuries differ in character from those that are produced later in life. Such injuries arise from interference with developmental processes, rather than destruction of tissue. For example, an injury which kills neurons in the mature CNS leads to gliosis and a reduction in neuronal density, but a reduction in the number of neurons produced during development is not likely to lead to gliosis, and typically affects tissue volume rather than cell density. Some effects of developmental insults, such as misplaced and misoriented neurons, are never seen after adult injury. Functional effects reflect the role of the CNS in physiological regulation as well as in behavior. To evaluate CNS for developmental injury, it is necessary to know something about the structural and functional outcomes already recognized to result from teratogens and how these effects are related to time of exposure and time of testing.

Developmental factors related to abnormal cerebellar foliation induced by methylazoxymethanol acetate (MAM)

Quantitation of mid-sagittal sections of the molecular layer, and both the external and internal granular layers between control and methylazoxymethanol acetate (MAM)-treated rats, at various stages of cerebellar development revealed a much smaller area of these layers in sagittal profile, however, the fiber core was not significantly affected by the drug. The expansion of the pial surface length was parallel to the length of the Purkinje cell layer, although comparison of a fissure index revealed hypofissuration in the experimental group. In histological examination, there was perforation, patching, and agenesis of the external granular layer. Mushroom expansion of the external granular layer occurred at patches producing a gyrating folial pattern rather than parallel ones. The number of lobules and their basic pattern remained normal. We conclude that the deficits in the external granular layer interrupted the growth force that produces the normal rostrocaudal organization of parallel coronal foliation and this resulted in shallow periodic fissuration along the sagittal extent. Fissurations forming lobules arose largely independent of the external granular layer by directed expansion of the central fiber core while normal parallel foliation is an elaboration of the lobular surface controlled by growth forces defined by both distribution of the external granular layer and the underlying fiber core with associated Purkinje cells.

Perinatal methylazoxymethanol acetate uncouples coincidence of orientation of cerebellar folia and parallel fibers

Perinatal administration of methylazoxymethanol acetate in the rat, as a one time injection on gestational day 21, postnatal days 0, 1 or 2, altered the parallel orientation of cerebellar folia. The effect persisted into adulthood. In animals injected on one of the postnatal days 3, 4 or 5, the folial pattern was not altered. Even when the injection was repeated for three days on postnatal days 3, 4 and 5, changes in the cerebellar surface were not found. However, in animals receiving a low protein diet during the last five days of gestation, the three injection regimen produced a distortion of the folial pattern. The surface of cerebella of animals injected on gestational day 21 through postnatal day 2 was covered with small blebs resembling the surface of a cauliflower head. In sagittal sections, islands of cortical laminae appeared to be isolated from the arbor vitae. However, serial reconstruction of the granular layer from sections revealed that these pieces were continuous with the arbor vitae. Surprisingly, cerebella having malaligned folia also had varying degrees of Purkinje cell somas distributed throughout the granule cell layer rather than in a single layer. This occurred even when the granule cell layer approached normal thickness. Analysis of cerebellar weight from the group injected on the day of birth revealed three levels of weight reduction: severe (greater than 40%), moderate (20-40%) and mild (less than 20%). The granule cell deficit was directly related to the weight reduction of the cerebella. In the severely-affected cerebella, areas of the cortex were virtually devoid of granule cells. The moderately-affected cerebella had a continuous granular layer which was thick and thin. In the mild type, the layer was relatively normal in thickness but, nevertheless, the cerebellar surface was highly distorted. In all animals treated with methylazoxymethanol acetate on days G21 through P5, parallel fibers were disoriented. This occurred even though the folia appeared normal in the G20, P3, P4, P5 and P3-5 injected groups. Bundles of parallel fibers crisscrossed in the plane of the cerebellar surface in all areas where a molecular layer was found.(ABSTRACT TRUNCATED AT 400 WORDS)

Meningeal cells influence cerebellar development over a critical period

We have investigated the influence of meningeal cells on the development of the cerebellum by destroying these cells with 6-hydroxydopamine in hamsters of different ages. The ensuing foliation and lamination disruption in the cerebellar vermis is attributed to a disintegration of the cerebellar surface and a disorganization of the glial scaffold of the cerebellar cortex due to a loss of meningeal-glial interaction in stabilizing the extracellular matrix at the glia limitans superficialis (v. Knebel Doeberitz et al. 1986, Neuroscience 17:409-426). The severity of these cerebellar defects is correlated with the ontogenetic stage at which meningeal cells are destroyed, being greatest after treatment at postnatal day 1 and decreasing thereafter until day 5 and beyond, when no abnormalities occur, although all meningeal cells are destroyed throughout. The absence of cerebellar defects after destruction of meningeal cells at day 5 or later is associated firstly with the end of the period of branching morphogenesis of the cerebellum when all folial primordia are established, and, secondly, with the maturation of the glia limitans superficialis. These findings indicate that meningeal cells stabilize the cerebellar surface and glial scaffold over a critical period that ends, when the pattern of cerebellar foliation is established, and when the glia limitans superficialis has reached a mature state. Beyond this stage glial end-feet alone are sufficient to maintain the epithelial integrity of the cerebellum.

Long-term effects of parallel fiber loss in the cerebellar cortex of the adult and weanling rat

Short- and long-term effects of parallel fiber deafferentation of adult and weanling cerebellar cortex were investigated following parasagittal transections of the lateral cerebellar hemisphere. Short-term electron microscopic examination revealed that parallel fibers undergo rapid electron-dense degeneration within 5 days of axotomy. These axons were the only neuronal elements immediately affected by the lesion. The continued maintenance of Purkinje cell terminal branchlets and stellate cell dendrites is dependent upon the presence of an adequate parallel fiber milieu. Morphological evidence is provided which suggests that Purkinje cell dendritic spines may be phagocytically removed by Bergmann glial cells following parallel fiber loss. Although a marked decrease was reported in the number of spines projecting from terminal branchlets following deafferentation of both adult and weanling rats, these data suggest that some spines are capable of increasing their length. The elongation of these spines may represent a form of dendritic plasticity. No evidence was found to suggest that deafferentated terminal branchlets are receptive to forming heterologous synaptic contacts. The primary response to parallel fiber deafferentation for both the adult and weanling cerebellum therefore appears to be transneuronal degeneration.

Neurogenesis and gliogenesis in the human brain

The primary germinal neural epithelium lines the ventricular system of the brain and shows intense mitotic activity. Neuroblasts migrate from a juxtaluminal position to establish neural centres and, when this task is completed, the definitive ependymal epithelial lining of the ventricles develops, shifting the remnants of the germinal epithelium to a subendymal location. The subendymal layer continues to proliferate giving rise to glia in the postnatal brain. Premature arrest of migration of neuroblasts leads to the accumulation of heterotopic nests anywhere along the migratory path. Within such ectopia, neurons may make normal connections or they may remain undifferentiated and later become tumorigenic. The subependymal layer has long been considered the site of original of periventricular gliomas. Some migrating neuroblasts establish secondary germinal centres far removed from the ventricular system. An example of this is the external granular layer of the cerebellum which, in man, persists for the first 6 months of life. Cerebellar neuroblastomas could originate directly from this layer in the neonate, or from remnants of this layer in older individuals.

Histochemical distribution of acid glycosaminoglycans in rat cerebellum during postnatal development: neuropile

Developmentally regulated modifications of glycosaminoglycans (GAGs) in the central nervous system (CNS) have suggested that also in the CNS, these compounds might participate in morphogenesis and nerve cell differentiation. However very few studies have been reported concerning the regional distribution of these compounds by histochemical techniques. We have used the Alcian Blue staining method also in conjunction with enzymatic digestion and with a technique which allowed the measurement of the degree of GAG sulphatation. The combination of the three techniques showed that during the first week GAGs, presumed to be hyaluronic acid, are localized throughout the neuropile of the entire cerebellum and especially in the medullary region. Sulphated glycans appear later in the medullary region (particularly at the border between the medullary region and the internal granular layer) and in all the layers of cerebellum (in particular around the Purkinje and deep cerebellar nuclei neurons and possibly in the cerebellar glomeruli). Sulphated glycans in the medullary region disappear around the 12th day when myelination starts. The transient presence of glycoproteins in the molecular layer was also detected.

Meningeal cells are involved in foliation, lamination, and neurogenesis of the cerebellum: evidence from 6-hydroxydopamine-induced destruction of meningeal cells

In the present paper we report on experiments conducted to find out if there is a positive correlation between the destruction of meningeal cells over the newborn rat cerebellum by 6-hydroxydopamine (6-OHDA) and the subsequent development of abnormalities in cerebellar fissuration, lamination, and granule cell number. Both destruction of meningeal cells and quality and magnitude of 6-OHDA-induced cerebellar defects show the same threshold sensitivity without further dose responsiveness. Blockade of neuronal uptake 1 for catecholamines with nomifensine prevents neither destruction of meningeal cells nor the development of abnormalities in cerebellar structure after 6-OHDA treatment. Blockade of extraneuronal uptake 2 for catecholamines with normetanephrine prevents both destruction of meningeal cells and the development of typical cerebellar abnormalities after 6-OHDA treatment. All three parallel experiments suggest that there is a positive correlation between the destruction of meningeal cells and the development of abnormal cerebellar structure, indicating that meningeal cells are involved in these defective morphogenetic processes, i.e., fissuration, lamination, and cell proliferation in the external granular layer. The preferential localization of defects in cerebellar fissures indicates that, in analogy to the mesenchyme surrounding other epithelia with a branching morphogenesis, the role of meningeal cells could be the production of interstitial collagen which is necessary to stabilize the epithelial basal lamina in the fissures.

Purkinje cell growth beyond the twenty-third postnatal day

Purkinje cell dendritic trees from adult and weanling cerebella were analyzed with an image analysis system following Golgi-Cox impregnation. Measurements of the mean length, number and total length of primary trunks, smooth branches and spiny branchlets were taken to assess the amount of growth between postnatal days 23 and 150. These results revealed a significant post-weanling growth in the length and number of smooth branches and spiny branchlets.

Subcortical projections from ectopic neocortical neurons

There is a high degree of specificity in the efferent connections of the cerebral cortex. In the rodent neocortex, the characteristic band of corticospinal neurons within layer V is present at birth even though changes still occur in the areal distribution of these neurons. Disruption of neocortical development with ionizing radiation before, during, or after the production of neurons destined for layer V results in abnormally located corticospinal neurons. One abnormal location in which corticospinal neurons are found is in ectopic cell clusters beneath the cortical white matter bordering the dorso-medial aspect of the lateral ventricle. Corticospinal neurons only occur in these periventricular ectopias in adult rats irradiated on or before embryonic day 17. A second abnormal location of corticospinal neurons is between layer V and the pial surface. These scattered supragranular corticospinal neurons occur in all adult animals irradiated on embryonic days 16, 17, 18, or 19. The fact that neurons having an unusual position project to a subcortical target appropriate for one neocortical sublayer indicates that neither migratory path nor final position is essential to specifying a subcortical target. In addition, the fact that labeled corticospinal neurons are located in periventricular ectopias only when irradiation occurs on or before embryonic day 17 suggests that the initial projections of corticospinal neurons are determined early in their individual ontogeny prior to migration.

Early development of the granule cell in the cerebellum of the chick embryo

The sequence of differentiation of the cerebellar granule cell in chick embryos from the eighth to the 15th days of incubation has been studied in Golgi-stained celloidin sections. In the germinal-cell phase, the presumptive granule cell sends out one or two horizontal processes which may originate either in the body of the cell or in the extension which attaches it to the pial surface. Thus the germinal cell may be converted into either a monopolar or a bipolar presumptive granular cell. Bipolar cells may have two processes of the same length (symmetrical cells) or of unequal length (asymmetrical cells). In the symmetrical as well as asymmetrical bipolar cells the leading process is formed, by means of which the perikaryon emigrates until it situates itself definitely in the internal granular layer. Thus, symmetrical and asymmetrical bipolar cells give rise to a granule cell with parallel fibers of equal or different lengths. The monopolar element may originate a second process or may remain in the monopolar phase until it reaches the internal granular layer. Once there, it completes the formation of the parallel fibers.

Alterations in cerebellar germinal cell division induced by graft-versus-host disease

A systemic immunological syndrome, graft-versus-host disease (GVHD), which does not cause inflammation or cell death in the cerebellum, is shown to retard granule cell production by decreasing the rate of DNA synthesis (S phase) and prolonging mitosis (M), at metaphase. The rate of cell production in diseased animals at postnatal day 14, quantitated by analysis of the rate of labeling of DNA with 3H-thymidine (3H-Tdr), revealed decreased ability to synthesize new DNA. The number of cells taking up 3H-Tdr label per mm2, as detected by autoradiography, was similar in 14-day-old GVHD and control tissue as was the area of the germinal matrix zone and the number of mitotically active germinal cells per mm2 in sagittal sections near the midline. However, because the total volume of the cerebellum was less, the total number of mitotically active cells in the whole cerebellum of 11-, 14-, and 17-day-old diseased animals was less than in littermate controls. Furthermore, DNA synthesis per mitotically active germinal cell was less in diseased animals at each age examined. The mitotic index was unaffected until late in the disease (day 17), suggesting that a prolongation of the cell cycle was responsible for this GVHD-induced decrease in DNA synthesis. Consistent with a prolongation of the cell cycle was the finding that the mitotic figures in 14-day-old GVHD cerebella were mostly metaphase figures, whereas those in control cerebella were, as predicted, mostly prophase. Prolongation of the cerebellar cell cycle in 11- and 14-day-old diseased animals may explain the dramatic decrease in the mitotic index, the thickness of the germinal matrix zone, and the number of germinal cells at postnatal day 17.

Generation of the ocular motor nuclei and their cell types in the rabbit

Autoradiography of 3H-thymidine incorporation was combined with horseradish peroxidase (HRP) transport to distinguish the birthdates of motoneurons and internuclear neurons of the abducens nucleus, and of specific motor pools within the oculomotor nucleus. Motoneurons were identified by their retrograde transport of HRP from the extraocular muscles. In other experiments, internuclear neurons of the abducens nucleus were identified by their retrograde transport of HRP from the oculomotor nucleus. We found that motoneurons and internuclear neurons are generated simultaneously in the abducens nucleus, and suggest that the differentiation of these two neuron types may be controlled by the local environment. The motor pools of the oculomotor nucleus are generated sequentially. This may reflect the mechanism whereby nuclei are constructed.

Redirected perforant and commissural of connections of eutopic and ectopic neurons in the hippocampus of methylazoxymethanol-acetate treated rats

In an earlier study, it was reported that clusters of ectopic neurons developed postnatally in the hippocampus of rats which were exposed to Methylazoxymethanol acetate (MAMac) during fetal development (Singh, 1977b). This paper describes the perforant tract and commissural connections of hippocampal eutopic and ectopic neurons. These connections were traced with a reduced-silver method (Eager, 1970). Two observations of significance were made: (i) Ectopic neurons misplaced in stratum radiatum received terminals from axons in the perforant tract. The upper boundary for these redirected fibers was stratum pyramidale--approximately 350 mu outside the normal boundary which is situated near the hippocampal fissure. (ii) Ectopic neurons received a dramatically reduced commissural projection, compared with eutopic pyramidal neurons in Ammon's horn. Eutopic neurons in the hippocampus were found to receive afferent perforant tract and commissural fibers in the same way--i.e., density and distribution, as in control rats.

Quantitative effects of methylzoxymethanol acetate on Purkinje cell dendritic growth

A quantitative analysis was made of alterations in the dendritic organisation of Purkinje cells in the cerebellum of the rat following the administration of the degranulating agent, methylazoxymethanol acetate (MAM). This drug depleted the granule cell population of the cerebellar cortex and disturbed Purkinje cell alignment such that a number of Purkinje cells became inverted and grew in the white matter. The quantitative changes that occurred in the dendritic trees of these cells (increase in segment length, decrease in segment numbers, trichotomy and branching probability) were similar to those seen following other degranulation procedures. The size of the Purkinje cell dendritic tree was found to be related to the number of parallel fibres present in the molecular layer. These results were discussed in relation to current theories of neuronal development and were shown to lend further support to the filopodial attachment hypothesis of dendritic growth.

The effect of ethanol chronically administered to preweanling rats on cerebellar development: a morphological study

The effects of ethanol on body, brain and cerebellar growth of the postnatal rat have been studied. Vapor inhalation, the procedure used to administer ethanol directly to preweanling (3-20-day-old) rats, produced maximal blood ethanol levels that averaged 239 mg/100 ml. Weight determinations indicated that brain but not body growth was significantly stunted by exposure to ethanol. Moreover, cerebellar growth, which occurred largely but not wholly during the period of ethanol treatment, was inhibited twice as much as the rest of the brain. Arrested brain and cerebellar growth appeared shortly after ethanol treatment was begun and persisted into adulthood following a postweaning rehabilitation period. Ethanol treatment diminished the growth of both the anterior and posterior lobes and of all layers of the cerebellar vermis. However, the effect of ethanol was larger in the anterior lobe than the posterior lobe, and the medullary layer was more retarded than the others. Some compensatory growth occurred in the molecular and granular layers of the experimental rats during a postweaning rehabilitation period. The effects of ethanol on 2 major neuronal populations of the cerebellar cortex -- the large, prenatally-formed Purkinje cells and the small, postnatally-formed granule cells -- were assessed via light microscopy. After 2 days of ethanol treatment the number of Purkinje cells in all 10 vermal lobules was reduced; neither additional exposure to ethanol nor a postweaning rehabilitation period subsequently altered cell number. The possibility that the regional magnitude of the Purkinje cell loss was related to the chronology of lobular development was discussed; Purkinje cells in the latest maturing lobules being least affected. The morphological development of surviving Purkinje cells proceeded normally. An autoradiographic study indicated the pattern of granule cell neurogenesis in cerebella of ethanol-treated rats and of control rats did not differ, although the experimental animals had consistently fewer cells in all stages of development. The ultimate loss of 20-25% of their granule cells was accounted for by an early diminution of the stem cell population of the external germinal layer by about 10%. The results suggest the initial targets of ethanol were the immature Purkinje cells, which were reduced in number before the onset of granule cell formation. A complex age-dependent interaction between blood ethanol levels and vulnerable periods in Purkinje cell development was suggested. Mechanisms for the subsequent correlative reduction in the granule cell population were also discussed.

Effects of low-level x-irradiation on cat cerebella at different postnatal intervals. I. Quantitative evaluation of morphological changes

Whole head fractionated doses of 200 r and 150 r were initiated postnatally in five experimental age groups (birth, 1-week, 2-week, 3-week and 4-week) and continued over a period of 14 or 20 days to prevent reconstitution of the external granular layer. Animals irradiated at birth displayed minor deficits in behavior, which included ataxia, tremor, hypertonus and dysmetria, while animals irradiated at 1-week showed only mild symptoms of hypermetria. All other animals displayed no motor deficits. Animals irradiated at birth had smaller eyes and ears, a reduction in the size of the entire head and were susceptible to seizures. All animals were sacrified at 70 days of age. The cerebellum was found to be reduced in size and weight, the greatest deficit being seen in animals x-irradiated at the very early ages. Newborn condition animals were found to have large compliments of interneurons in the molecular layer, an established internal granular layer, and Purkinje cells were found to have a normal orientation, position, and to be unreduced in number or size. Total granule cell deficits were found to range from 83% at birth to 29% at four weeks. Quantitative changes for the molecular layer, internal granular layer, medullary layer, Purkinje cell to granule cell ratio, and granule cell density, all depicted the greatest changes in the newborn, 1-week and 2-week conditions. This experiment confirmed that the critical period in the development at which damage would result in behavioral abnormalities was from birth to five days, while for neuroanatomical abnormalities, this critical period was from birth to 18 days.

Postnatal development of the cerebellar cortex in the rat. V. Spatial organization of purkinje cell perikarya

The development of the spatial organization of Purkinje cell perikarya was examined in the rat cerebellum from birth to adulthood. Dispersion of the perikarya following birth is made possible by the rapid expansion of the cortical surface. Their subsequent regular monocellular alignment is ensured by mechanical factors, the pressure exerted from below by the expanding granular layer and the barrier formed above by the pile of parallel fibers which prevent the penetration of the bulky perikarya into the molecular layer. The perikarya remain in this position even after the slender stem dendrite pierces the molecular layer along the descending axons of basket cells. The increase in interperikaryal distance between Purkinje cells is rapid up to day 12, then declines. This is temporally associated with the growth of the basket cell plexus and glial envelope around the perikaryon. The increase in perikaryal size continues up to day 30. This may be temporally associated with the growth of the Purkinje cell dendritic arbor as reflected by the expansion of the molecular layer up to day 30. The spatial arrangement of Purkinje cells within the monocellular sheet was graphically displayed with computer aid. In the adult cerebellum a hexagonal arrangement could be recognized in a proportion of "near-neighborhoods," consisting of about six Purkinje cells and their neighbors. When the neighborhoods were extended with fixed orientation with respect to the axis of the folium, the hexagonal arrangement disappeared. When orientation was ignored, the superimposed near-neighborhoods could be rotated to produce a hexagonal pattern. In the infant cerebellum the hexagonal arrangement could not be demonstrated before the alignment of Purkinje cells in a monolayer. Thereafter there appeared to be an increase with age in the proportion of hexagonally arranged near-neighborhoods. It was concluded that in the monocellular ganglionic layer Purkinje cells are not aligned in regular rows with respect to the geometrically arranged elements of the supraganglionic layer. The formation of an imprecise hexagonal pattern, like the alignment of Purkinje cells in a monolayer, was attributed to mechanical factors.

The growth of the dendritic trees of Purkinje cells in irradiated agranular cerebellar cortex

The heads of noenatal Wistar rats were irradiated with 200 rads daily from birth to the 10th day post-partum. Ten litters each containing 5 animals were killed at 30 days post-partum and their brains treated by the Golgi-Cox technique. The dendritic trees of 24 Purkinje cells were analysed using the quantitative technique of network analysis, and comparisons made between parameters obtained from 20 normal Purkinje cells. All dendritic trees in agranular irradiated cortex were markedly reduced in size (as indicated by total dendritic length and total number of segments) although mean path lengths were normal. Segment lengths were normal over proximal branches, but uniformly increased over distal branches. Abnormal appendages, called 'giant spines' were observed on many dendrites. They were often some 10 mum in length and their presence effectively reduced segment lengths, increased the frequency of trichotomy and deviated growth from the normal random terminal pattern so that long collateral branching topologies were formed. Nevertheless, trichotomy was uniformly reduced in those trees without 'giant spines' and the distribution of branching patterns suggested that growth had proceeded by random terminal dichotomy. These results demonstrate that the development of dendritic trees is retarded in the agranular irradiated cerebellum, where synaptogenesis is very greatly reduced below normal. The quantitative changes in segment lengths, size of trees, and trichotomy accord with those predicted by the filopodial synaptogenic hypothesis of dendritic growth formulated by Vaughn et al. 99, whilst the results of the topological analysis suggest that branching is established by a degree of non-random interaction between growing dendrites and their substrate. 'Claw-like' dendritic complexes within some Purkinje cell trees may have been induced by aberrent fibre bundles of few surviving granule cells.

The development of the cerebellar cortex of the Syrian hamster, Mesocricetus auratus. Foliation, cytoarchitectonic, Golgi, and electron microscopic studies

Although a number of investigations of abnormalities of cerebellar development have been carried out in the hamster, no detailed Golgi or ultrastructural studies of cerebellar development in this species have been reported. This report describes the development of the hamster cerebellar cortex from birth (day 0) through postnatal day 78, as studied by light, Golgi, and electron microscopic methods. Foliation patterns correlate with the expansion of the cerebellar layers and of total cerebellar area. Cytologic and morphologic development of the major cerebellar cell types--Purkinje, Golgi, basket, stellate, granule, and Bergmann glial cells--correlate with those of other species, such as the rat and mouse. Electron microscopic observations at selected developmental ages allow identification and classification of synapses in the early postnatal hamster. Parallel fiber and climbing fiber synapses are already present at birth. Although synaptogenesis probably continues through the first two postnatal months, all major cell types have developed initial synapses by postnatal day 6, at a time when little cellular maturation has occurred. By using gestational rather than natal age, close developmental correlations between hamsters and rat and mouse are possible. Since the gestational period of the hamster is only 16 days, the hamster cerebellum is less mature at birth than that of either the rat or mouse. Thus, the hamster is a convenient animal in which to investigate the effects of various procedures on early cerebellar development.

The effects of reduced climbing and parallel fibre input on Purkinje cell dendritic growth

The effects of afferent fibre depletion on the development of the dendritic trees of Purkinje cells in the cerbellum were investigated. Parallel fibres were reduced by postnatal administration of a schedule of low level X-irradiation. Climbing fibers were prevented from innervating the cerebellum by lesioning the olivo-cerebellar tract. Network analysis was performed on Purkinje cells in Golgi-Cox preparations of the vermis of 30-day-old animals. tin the irradiated cerebella Purkinje cells with a 'weeping willow' type morphology predominated. Purkinje cells devoid of their climbing fibre contact exhibited large spines on their main dendritic trunks. In both experimental situations the size of the dendritic tree was reduced. This diminution was the result of a decrease in the total number of dendritic segemnts. Individual segment lengths were largely unalteral. Topological type analysis revealed that the trees had arisen in a manner indistinguishable from terminal dichotomous branching and that the 'weep-willow' pattern was produced by a deviation of branching from a purely random form. The interaction of intrinsic and extrinsic factors in the formation of segments and on the nature of branching were discussed.

Behavioral correlates of focal hippocampal x-irradiation in rats

A study presenting findings of focal hippocampal x-irradiation in early infancy and late behavior at two ages was carried out using Long-Evans hooded rats (Rattus norvegicus). Animals from eleven litters received 150-R irradiation treatments for 5 or 15 consecutive days and were then tested in an open field situation and in a two-way active avoidance apparatus. The results indicated that the behavioral deficits paralleled those seen in animals with classical hippocampal lesions. The results were offered in support of a response suppression model for hippocampal functioning.

Experimental reorganization of the cerebellar cortex. VII. Effects of late x-irradiation schedules that interfere with cell acquisition after stellate cells are formed

In Long-Evans rats the area of the cerebellum was irradiated with multiple doses of low-level X-ray beginning on day 12 after the bulk of stellate cells were acquired. The treatment spared basket, stellate and early-forming granule cells but led to a substantial reduction in the total granule cell population and a correlated miniaturization of the cerebellar cortex. Nevertheless most Purkinje cells had normally shaped planar dendritic arbors, with an upward directed stem dendrite, several smooth branches and a multitude of spiny branchlets. The frequency piling up of spiny branchlets near the surface was attributed to the truncation of the bed of parallel fibers by this radiation schedule. In this last paper of the series the accumulated results are summarized and evaluated. The hypothesis is offered that while the growth of the Purkinje cell perikaryon is an autonomous process, the oriented perpendicular growth of a single stem dendrite depends on the presence of basket cell axons, the outgrowth of smooth branches on the presence of stellate cell axons, and the proliferation of spiny branchlets on interaction with parallel fibers. The parallel fibers are responsible for the orthogonal, planar growth of the dendritic arbor and a hypothesis is offered about the mechanisms involved.