Development and characterisation of a novel rat model of Parkinson's disease induced by sequential intranigral administration of AAV-α-synuclein and the pesticide, rotenone.

Modeling Parkinson's disease remains a major challenge for preclinical researchers, as existing models fail to reliably recapitulate all of the classic features of the disease, namely, the progressive emergence of a bradykinetic motor syndrome with underlying nigrostriatal α-synuclein protein accumulation and nigrostriatal neurodegeneration. One limitation of the existing models is that they are normally induced by a single neuropathological insult, whereas the human disease is thought to be multifactorial with genetic and environmental factors contributing to the disease pathogenesis. Thus, in order to develop a more relevant model, we sought to determine if administration of the Parkinson's disease-associated pesticide, rotenone, into the substantia nigra of rats overexpressing the Parkinson's disease-associated protein, α-synuclein, could reliably model the triad of classic features of the human disease. To do so, rats underwent stereotaxic surgery for unilateral delivery of the adeno-associated virus (AAV)-α-synuclein into the substantia nigra. This was followed 13 weeks later by delivery of rotenone into the same site. The effect of the genetic and environmental insults alone or in combination on lateralised motor performance (Corridor, Stepping, and Whisker Tests), nigrostriatal integrity (tyrosine hydroxylase immunohistochemistry), and α-synucleinopathy (α-synuclein immunohistochemistry) was assessed. We found that rats treated with either AAV-α-synuclein or rotenone developed significant motor dysfunction with underlying nigrostriatal neurodegeneration. However, when the genetic and environmental insults were sequentially administered, the detrimental impact of the combined insults on motor performance and nigrostriatal integrity was significantly greater than the impact of either insult alone. This indicates that sequential exposure to relevant genetic and environmental insults is a valid approach to modeling human Parkinson's disease in the rat.

Characterisation of a novel model of Parkinson's disease by intra-striatal infusion of the pesticide rotenone.

One of the most promising models of Parkinson's disease to have emerged in recent years is one in which the pesticide, rotenone, is administered systemically to laboratory rats. However, this model is associated with peripheral toxicity and high mortality rates which impede its widespread application in preclinical drug discovery research. This study sought to determine if administration of rotenone directly into the rat striatum could also mimic the motor dysfunction and neuropathological features of the human condition while overcoming the toxicity associated with systemic administration. Male Sprague-Dawley rats were infused with control or rotenone solutions into the striatum. The effect of the pesticide on body weight and spontaneous motor function (Corridor, Stepping and Whisker Tests) was assessed ante mortem, and its effect on nigrostriatal integrity (quantitative tyrosine hydroxylase immunohistochemistry), α-synuclein expression (quantitative α-synuclein immunohistochemistry), and striatal neurotransmitter content (HLPC for dopamine, GABA and noradrenaline) was assessed post mortem. Intra-striatal infusion of rotenone had no detrimental effect on the rats' body weight but caused significant impairments in contralateral motor function. Neuropathologically, rotenone caused significant nigrostriatal degeneration and selective loss of dopamine from the striatum but there was no evidence of any change in α-synuclein expression in the rotenone-infused rats. This study shows intra-striatal rotenone to be capable of modelling some of the main behavioural and neuropathological features of human Parkinsonism, while being less toxic than its systemic counterpart. Thus, this model may prove to be useful in future Parkinson's disease drug discovery programmes.

Contrasting patterns of Bim induction and neuroprotection in Bim-deficient mice between hippocampus and neocortex after status epilepticus.

Prolonged seizures (status epilepticus) are associated with brain region-specific regulation of apoptosis-associated signaling pathways. Bcl-2 homology domain 3-only (BH3) members of the Bcl-2 gene family are of interest as possible initiators of mitochondrial dysfunction and release of apoptogenic molecules after seizures. Previously, we showed that expression of the BH3-only protein, Bcl-2 interacting mediator of cell death (Bim), increased in the rat hippocampus but not in the neocortex after focal-onset status epilepticus. In this study, we examined Bim expression in mice and compared seizure damage between wild-type and Bim-deficient animals. Status epilepticus induced by intra-amygdala kainic acid (KA) caused extensive neuronal death within the ipsilateral hippocampal CA3 region. Hippocampal activation of factors associated with transcriptional and posttranslational activation of Bim, such as CHOP and c-Jun NH(2)-terminal kinases, was significant within 1 h. Upregulation of bim mRNA was evident after 2 h and Bim protein increased between 4 and 24 h. Hippocampal CA3 neurodegeneration was reduced in Bim-deficient mice compared with wild-type animals after seizures in vivo, and short interfering RNA molecules targeting bim reduced cell death after KA treatment of hippocampal organotypic cultures. In contrast, neocortical Bim expression declined after status epilepticus, and neocortex damage in Bim-deficient mice was comparable with that in wild-type animals. These results show region-specific differential contributions of Bim to seizure-induced neuronal death.