Olivocerebellar projections modify hereditary Purkinje cell degeneration

Autophagy precedes apoptosis among at risk cerebellar Purkinje cells in the shaker mutant rat: an ultrastructural study

Cerebellar Purkinje cell (PC) death has been shown to occur in essential tremor, ataxia, and many other neurodegenerative diseases in humans. Shaker mutant rats have an X-linked recessive mutation that causes hereditary degeneration of "at risk" cerebellar PCs. This defect can occur in the restricted anterior (ADC) and posterior (PDC) vermal degeneration compartments postnatally within 7 to 14 weeks of age as a natural phenotype in the shaker mutant rat. "Secure" PCs persist in a flocculonodular survival compartment (FNSC). Because we have previously shown that "at risk" PCs die due to apoptosis in the shaker mutant rat, we hypothesized that the PC death observed in the hereditary shaker mutant rat may be due to the activation of more than one type of death pathway. This ultrastructural investigation suggests that "at risk" PCs die due to apoptosis as a result of autophagic activation. Moreover, our data suggest that both apoptosis and autophagy must be simultaneously inhibited to rescue "at risk" PCs from death.

Activation of the maternal immune system alters cerebellar development in the offspring

A common pathological finding in autism is a localized deficit in Purkinje cells (PCs). Cerebellar abnormalities have also been reported in schizophrenia. Using a mouse model that exploits a known risk factor for these disorders, maternal infection, we asked if the offspring of pregnant mice given a mid-gestation respiratory infection have cerebellar pathology resembling that seen in these disorders. We also tested the effects of maternal immune activation in the absence of virus by injection of the synthetic dsRNA, poly(I:C). We infected pregnant mice with influenza on embryonic day 9.5 (E9.5), or injected poly(I:C) i.p. on E12.5, and assessed the linear density of PCs in the cerebellum of adult or postnatal day 11 (P11) offspring. To study granule cell migration, we also injected BrdU on P11. Adult offspring of influenza- or poly(I:C)-exposed mice display a localized deficit in PCs in lobule VII of the cerebellum, as do P11 offspring. Coincident with this are heterotopic PCs, as well as delayed migration of granule cells in lobules VI and VII. The cerebellar pathology observed in the offspring of influenza- or poly(I:C)-exposed mice is strikingly similar to that observed in autism. The poly(I:C) findings indicate that deficits are likely caused by the activation of the maternal immune system. Finally, our data suggest that cerebellar abnormalities occur during embryonic development, and may be an early deficit in autism and schizophrenia.

Don't get too excited: mechanisms of glutamate-mediated Purkinje cell death

Purkinje cells (PCs) present a unique cellular profile in both the cerebellum and the brain. Because they represent the only output cell of the cerebellar cortex, they play a vital role in the normal function of the cerebellum. Interestingly, PCs are highly susceptible to a variety of pathological conditions that may involve glutamate-mediated 'excitotoxicity', a term coined to describe an excessive release of glutamate, and a subsequent over-activation of excitatory amino acid (NMDA, AMPA, and kainite) receptors. Mature PCs, however, lack functional NMDA receptors, the means by which Ca(2+) enters the cell in classic hippocampal and cortical models of excitotoxicity. In PCs, glutamate predominantly mediates its effects, first via a rapid influx of Ca(2+)through voltage-gated calcium channels, caused by the depolarization of the membrane after AMPA receptor activation (and through Ca(2+)-permeable AMPA receptors themselves), and second, via a delayed release of Ca(2+) from intracellular stores. Although physiological levels of intracellular free Ca(2+) initiate vital second messenger signaling pathways in PCs, excessive Ca(2+) influx can detrimentally alter dendritic spine morphology via interactions with the neuronal cytoskeleton, and thus can perturb normal synaptic function. PCs possess various calcium-binding proteins, such as calbindin-D28K and parvalbumin, and glutamate transporters, in order to prevent glutamate from exerting deleterious effects. Bergmann glia are gaining recognition as key players in the clearance of extracellular glutamate; these cells are also high in S-100beta, a protein with both neurodegenerative and neuroprotective abilities. In this review, we discuss PC-specific mechanisms of glutamate-mediated excitotoxic cell death, the relationship between Ca(2+) and cytoskeleton, and the implications of glutamate, and S-100beta for pathological conditions, such as traumatic brain injury.

Patterned Purkinje cell death in the cerebellum

The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.

Olivocerebellar projections are necessary for exogenous trophic factors to delay heredo-Purkinje cell degeneration

The temporally protracted heredodegeneration of cerebellar Purkinje cells in shaker mutant rats can be modified: ablation of the inferior olive accelerates their degeneration whereas chronic intraventricular infusion of trophic factors extends their survival. The present study sought to determine if chronic trophic factor infusion could block the accelerated degeneration of Purkinje cells due to inferior olivary chemoablation thereby focusing on possible mechanisms for the amelioration of heredo-Purkinje cell death. When the inferior olive was chemically ablated with 3-acetylpyridine at the midpoint of 2 weeks of conjoint intraventricular infusion of glial cell line-derived trophic factor (GDNF) and insulin like growth factor type I (IGF-1) Purkinje cells were not protected by the exogenous trophic factors, but rather degenerated prematurely consistent with chemoablation alone. These findings support the conclusion that when the inferior olive is ablated, Purkinje cell heredodegeneration progresses through a mechanism not significantly affected by the action of these trophic factors.

GDNF and IGF-I trophic factors delay hereditary Purkinje cell degeneration and the progression of gait ataxia

Neurotrophic factors GDNF and/or IGF-I were chronically infused into shaker mutant rats to rescue cerebellar Purkinje neurons from adult-onset heredodegeneration. The natural expression of the shaker mutation is characterized by spatially restricted degeneration of Purkinje cells that occurs earlier and faster in an anterior vermal compartment and slightly later and more slowly in a posterior vermal compartment. Gait ataxia and whole body tremor develop concomitant with the degeneration of Purkinje neurons. The number and spatial distribution of surviving Purkinje neurons, identified by cell-specific calbindin immunoreactivity, were quantitatively analyzed in mid-sagittal sections and correlated with quantitative movement analysis of hindlimb gait patterns. Compared to the number of surviving Purkinje cells in age-matched, non-infused, or saline-infused control mutants, 4 weeks of infusion of GDNF or IGF-I rescued many anterior compartment Purkinje cells from early degeneration. However, 2 and 4 weeks after cessation of GDNF or IGF-I infusion, respectively, the number and spatial distribution of surviving Purkinje cells was comparable to that observed in age-matched controls. Eight weeks of infusion of trophic factors did not support the continued survival of most anterior compartment Purkinje cells and was partially, and probably only transiently, neuroprotective for some posterior compartment Purkinje cells. When GDNF and IGF-I were infused together for 4 weeks the number of surviving Purkinje cells was additively greater than with either factor alone. Behaviorally, 4 weeks of infusion of trophic factors delayed the development of gait ataxia. Infused GDNF appeared to preserve hip stability, whereas IGF-I stabilized step length. Tremor was attenuated with 8 weeks of infusion of GDNF or IGF-I. GDNF-infused animals showed low power tremor frequencies, whereas IGF-I infusion resulted in a single large power peak with decreased numbers of low-amplitude frequencies. Collectively these findings indicate that exogenous trophic factors can delay the onset of hereditary Purkinje cell degeneration and gait ataxia. Quite surprisingly, GDNF and IGF-I appeared to act on disparate populations of mutant Purkinje cells, whose differential survival affected different aspects of locomotion.

Features of cell death in brain and liver, the target tissues of progressive neuronal degeneration of childhood with liver disease (Alpers-Huttenlocher disease)

Alpers-Huttenlocher disease (AHD) is a rare encephalopathy of infancy and childhood characterized by myoclonic seizures and progressive neurological deterioration, usually associated with signs and symptoms of liver dysfunction. There is no biological marker of the disease, and ultimate diagnosis still relies on pathological examination. Features of clinical progression and pathological findings suggest AHD to be secondary to a genetically determined disorder of mitochondrial function. We report on four AHD patients and focus on their pathological features in brain, liver and muscle. Liver and muscle biopsy specimens were examined using histochemical markers of the oxidative pathways, probes to immunodetect molecules of the apoptotic cascades and electron microscopy. In liver (but not in muscle) biopsy samples, activated caspases were detected by immunohistochemistry: foci of caspase-9-positive cells were seen in a child affected with chronic, progressive fibrosis. In an 18-year-old boy, who suffered from valproic acid-associated acute hepatitis, caspase-3 cells were clustered among the necrotic foci and the foamy cells. In both patients electron microscopy revealed apoptotic nuclei. Normal muscle biopsy specimens were observed in two children, 2 and 8 years-old respectively; in the 18-year-old patient cytochrome oxidase-negative fibers as well as ultrastructural findings of mitochondrial abnormalities were observed. In no patient was there biochemical evidence of impaired oxidative metabolism. Neuropathological examination of the brains of two patients (13 months and 19 years old, respectively) showed focal distribution of the lesions affecting the telencephalic cortex and, to a lesser extent, subcortical gray nuclei. Along with the necrotizing lesions, characterized by neuronal loss, neuropil microcysts and newly formed vessels, we also observed acutely shrunken neurons and features of apoptotic cell death in the cerebral cortex only. Severe neuronal loss without necrotizing features was observed in the cerebellar cortex. The presence of both anoxic and apoptotic nuclei in brain and liver, the target tissues of the disease, is consistent with the hypothesis that abnormal activation of mitochondrion-related cell death pathways might be involved in the pathogenesis of AHD.

Localization of ataxin-2 within the cerebellar cortex of the rat

Spinocerebellar ataxia type 2 is caused by a polyglutamine stretch in the protein ataxin-2 that is due to an expansion of a CAG repeat in the spinocerebellar ataxia-2 gene. The function of wild-type ataxin-2 has not been clarified. A widespread distribution of this protein throughout the brain has been reported. We examined the expression of ataxin-2 in cortical cerebellar cells of the adult rat. We performed a single label immunohistochemical study of ataxin-2 and a single label immunofluorescence study of ataxin-2 and zebrin on adjacent sections, to compare the distribution of the observed parasagittal band pattern. We also performed a double label immunofluorescence study of ataxin-2 and one of each parvalbumin, calbindin, and calretinin. Single label studies revealed that between 50% and 70% of the Purkinje cells express ataxin-2. The abundance of ataxin-2 was different between hemisphere and vermis, with a clear prevalence for the former. Furthermore, the distribution of ataxin-2-positive Purkinje cells showed a peculiar alternating parasagittal band pattern. Among the other cortical cerebellar cells only basket and granule cells showed ataxin-2 staining. Our dual label studies showed that about 50% of calbindin and more than 70% of parvalbumin-immunoreactive Purkinje cells were also labeled for ataxin-2. The uneven distribution of ataxin-2 expression in the Purkinje cell layer does not support the hypothesized link between ataxin-2 content and cell vulnerability. The differences in ataxin-2 expression among the cell types of cerebellar cortex, on the other hand, suggest a possible correlation between ataxin-2 content and cell function.

Chronic intraventricular infusion of glial cell line-derived neurotrophic factor (GDNF) rescues some cerebellar Purkinje cells from heredodegeneration

Cerebellar Purkinje cells degenerate in shaker mutant rats. Glia cell line-derived neurotrophic factor (GDNF) was chronically infused intraventricularly in an attempt to rescue mutant Purkinje cells from dying. Four weeks of chronic GDNF infusion delayed the degeneration of many but not all Purkinje cells. Surviving Purkinje cells formed spatially related groups interrupted by other groups of degenerated Purkinje cells. There was a positive correlation in GDNF-supported Purkinje cell survival and persistence of normal motor behaviors.