Olivocerebellar projections are necessary for exogenous trophic factors to delay heredo-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.

GDNF-induced cerebellar toxicity: A brief review

Recombinant-methionyl human glial cell line-derived neurotrophic factor (GDNF) is known for its neurorestorative and neuroprotective effects in rodent and primate models of Parkinson's disease (PD). When administered locally into the putamen of Parkinsonian subjects, early clinical studies showed its potential promise as a disease-modifying agent. However, the development of GDNF for the treatment of PD has been significantly clouded by findings of cerebellar toxicity after continuous intraputamenal high-dose administration in a 6-month treatment/3-month recovery toxicology study in rhesus monkeys. Specifically, multifocal cerebellar Purkinje cell loss affecting 1-21% of the cerebellar cortex was observed in 4 of 15 (26.7%; 95% confidence interval [CI]: 10.5-52.4%) animals treated at the highest dose level tested (3000μg/month). No cerebellar toxicity was observed at lower doses (450 and 900μg/month) in the same study, or at similar or higher doses (up to 10,000μg/month) in subchronic or chronic toxicology studies testing intermittent intracerebroventricular administration. While seemingly associated with the use of GDNF, the pathogenesis of the cerebellar lesions has not been fully understood to date. This review integrates available information to evaluate potential pathogenic mechanisms and provide a consolidated assessment of the findings. While other explanations are considered, the existing evidence is most consistent with the hypothesis that leakage of GDNF into cerebrospinal fluid during chronic infusions into the putamen down-regulates GDNF receptors on Purkinje cells, and that subsequent acute withdrawal of GDNF generates the observed lesions. The implications of these findings for clinical studies with GDNF are discussed.