Long-term effect of mossy fiber degeneration in the rat

Neogenesis of cerebellar Purkinje neurons from gene-marked bone marrow cells in vivo

The versatility of stem cells has only recently been fully recognized. There is evidence that upon adoptive bone marrow (BM) transplantation (BMT), donor-derived cells can give rise to neuronal phenotypes in the brains of recipient mice. Yet only few cells with the characteristic shape of neurons were detected 1-6 mo post-BMT using transgenic or newborn mutant mice. To evaluate the potential of BM to generate mature neurons in adult C57BL/6 mice, we transferred the enhanced green fluorescent protein (GFP) gene into BM cells using a murine stem cell virus-based retroviral vector. Stable and high level long-term GFP expression was observed in mice transplanted with the transduced BM. Engraftment of GFP-expressing cells in the brain was monitored by intravital microscopy. In a long-term follow up of 15 mo post-BMT, fully developed Purkinje neurons were found to express GFP in both cerebellar hemispheres and in all chimeric mice. GFP-positive Purkinje cells were also detected in BM chimeras from transgenic mice that ubiquitously express GFP. Based on morphologic criteria and the expression of glutamic acid decarboxylase, the newly generated Purkinje cells were functional.

Afferent innervation influences the development of dendritic branches and spines via both activity-dependent and non-activity-dependent mechanisms

The present investigation uses an in vitro co-culture system to study the role of afferent innervation in early development and differentiation of hippocampal neurons. Our experiments indicate that the formation of two key morphological features, dendritic branches and dendritic spines, is induced by afferent innervation. Hippocampal neurons develop multiple dendritic branches and spines only when extensively innervated by living axonal afferents. No morphological changes occurred when hippocampal neurons were plated on other cell surfaces such as fixed axons or astrocytes. Furthermore, afferents exerted their effect locally on individual dendrites that they contacted. When one portion of the dendritic arbor of a neuron was contacted by afferents and the other portion was not, morphological effects were restricted to the innervated dendrites. Innervation of some of the dendrites on a neuron did not produce global effects throughout the neuron. Afferent-induced dendritic branching is independent of activity, since branch induction was unaffected by chronic application of TTX or glutamate receptor blockers. In contrast, the formation of dendritic spines is influenced by activity. The number of developing spines was reduced when TTX or a cocktail of three glutamate receptor blockers was applied. Blockade of individual AMPA, NMDA, or metabotropic glutamate receptors did not affect the number of spines. These results, taken together, demonstrate that afferents can have a prominent influence on the development of postsynaptic target cells via both activity-dependent and non-activity-dependent mechanisms, indicating the presence of multiple signals. Accordingly, this suggests an important interplay between pre- and postsynaptic elements early in development.

The Purkinje cell in olivopontocerebellar atrophy. A Golgi and immunocytochemical study

Purkinje cells were examined in three familial cases of olivopontocerebellar atrophy (OPCA) by means of the Golgi method, and neurofilament and calcium-binding protein immunocytochemistry. Reduced dendritic arborizations, as seen with different techniques, early formation of axonal spheroids, and abnormal accumulation of phosphorylated neurofilament epitopes in dendrites, somata and axonal spheroids, together with limited formation of proximal spine-like protrusions were the main changes in Purkinje cells. These lesions are unlikely to be the consequence of anterograde degeneration secondary to olivary atrophy, as postulated by some investigators, but probably represent primary damage to Purkinje cells in patients with OPCA. Reduced dendritic arborizations result in a decrease of receptor sites for parallel fibres and deprive granule cells of their main targets. Abnormal accumulation of neurofilaments in somata, dendrites and axonal spheroids may contribute to an abnormal transport and may impair protein turnover in the distal regions of Purkinje cells.

Repeated changes of dendritic morphology in the hippocampus of ground squirrels in the course of hibernation

Quantitative Golgi study of hippocampal pyramidal neurons of ground squirrels showed rapid and profound transformation of their apical dendrites in the course of hibernation. The dendrites were significantly shorter, less branched and had fewer dendritic spines in the middle of hibernation bout than in the active euthermic ground squirrels between bouts. After arousal from torpor, within 2 h dendrites completely restored their structure. During hibernation, season remodelling of the hippocampal dendrites occurs repeatedly during each torpor-activity cycle.

Creutzfeldt-Jakob disease with severe involvement of cerebral white matter and cerebellum

We describe a patient with Creutzfeldt-Jakob disease (CJD) of the ataxic and panencephalopathic type. Postmortem examination revealed the characteristic lesions of CJD in the grey matter and profound white matter involvement was seen with immunocytochemical techniques. Ultrastructural white matter lesions were identical to those described in experimentally transmitted CJD. There was marked loss of cerebellar granule cells with virtual disappearance of parallel fibres, but Purkinje cells were only slightly reduced. Electron microscopic studies revealed extensive degenerative changes including cytoplasmic vacuoles in both cell types. Silver methods disclosed massive impregnation of white matter and striking abnormalities of Purkinje cells consisting of hypertrophy and flattening of thick dendritic branches, reduction in the number of terminal branchlets, segmentary loss of spines and polymorphic spines. These findings show the extensive involvement of all three cerebellar cortical layers and the reactive plasticity of Purkinje cells to deafferentiation. They favour the hypothesis that demyelination represents a primary lesion of the white matter.

Rapid changes in ultrastructure during deafferentation-induced dendritic atrophy

This study describes qualitative and quantitative changes in dendritic ultrastructure during the rapid atrophy of nucleus laminaris (NL) dendrites following deafferentation. The dendrites of n. laminaris neurons in the chick auditory system are segregated into dorsal and ventral dendritic tufts, which receive spatially separated innervation from the ipsilateral and contralateral nucleus magnocellularis, respectively. We have previously shown that removing the input to the ventral side of NL results in the rapid atrophy of the ventral dendrites, whereas the nondeafferented dorsal dendrites of the same cells do not change in length. The ultrastructure of NL was examined in normal animals and after deafferentation. Changes in dendritic ultrastructure were not qualitatively apparent 4 hours after deafferentation. Between 12 and 48 hours the cytoplasm of the ventral dendrites became progressively more lucent, and a gap formed in the transition between the soma and ventral dendritic cytoplasm. Many of the dendrite tips, however, appeared normal even 2 days after deafferentation. Degeneration of dendrite plasma membrane was not visible until 2 days after deafferentation. On the other hand, quantitative measurements revealed a 30% decrease in microtubule density in the initial portion of the ventral dendrite by 4 hours, and a 50-60% decrease from 12 to 48 hours after deafferentation. Neurofilament density in the initial ventral dendrites decreased 50% by 12 hours, and 70% by 2 days after deafferentation. Many of the terminals of the severed afferents remained attached to the atrophying dendrite until 2 days after surgery, when they were in advanced stages of degeneration. Glia apparently were not involved in dendrite loss. The implications of these results on the role of cytoskeleton in the production and maintenance of dendritic shape are discussed.

Quantitative study of the Purkinje cell dendritic spines in the rat cerebellum

The number of spines on an individual Purkinje cell in the cerebellar cortex of the rat was determined by stereological methods. Investigations were based on thin section electron micrographs, freeze fracture replicas, and horseradish peroxidase labeled cells. Purkinje cell dendritic spines in our embedded material had a mean length of 1.4 +/- 0.05 micron and mean neck and head diameters of 0.22 +/- 0.01 micron and 0.45 +/- 0.02 micron, respectively. From these dimensions, an estimate of spine volume in embedded material of 0.132 micron 3 was obtained. The density of dendritic spines in our fixed material was 8.15 x 10(8) or 7.24 x 10(8) per microliters of molecular layer from volume fraction and density per mm2, respectively. The number of spines per linear micron of Purkinje cell spiny branchlet was 17.2 from freeze fracture and 17.6 from horseradish peroxidase labeled dendrites. These all indicate that there are between 154,000 and 175,000 spines on the dendritic tree of each Purkinje cell, considerably more than previously reported for the rat.