Characterisation of functional deficits induced by AAV overexpression of alpha-synuclein in rats.

Background: In the last decades different preclinical animal models of Parkinson's disease (PD) have been generated, aiming to mimic the progressive neuronal loss of midbrain dopaminergic (DA) cells as well as motor and non-motor impairment. Among all the available models, AAV-based models of human alpha-synuclein (h-aSYN) overexpression are promising tools for investigation of disease progression and therapeutic interventions. Objectives: The goal with this work was to characterise the impairment in motor and non-motor domains following nigrostriatal overexpression of h-aSYN and correlate the behavioural deficits with histological assessment of associated pathology. Methods: Intranigral injection of an AAV9 expressing h-aSYN was compared with untreated animals, 6-OHDA and AAV9 expressing either no transgene or GFP. The animals were assessed on a series of simple and complex behavioural tasks probing motor and non-motor domains. Post-mortem neuropathology was analysed using immunohistochemical methods. Results: Overexpression of h-aSYN led to progressive degeneration of DA neurons of the SN and axonal terminals in the striatum (STR). We observed extensive nigral and striatal pathology, resembling that of human PD brain, as well as the development of stable progressive deficit in simple motor tasks and in non-motor domains such as deficits in motivation and lateralised neglect. Conclusions: In the present work we characterized a rat model of PD that closely resembles human PD pathology at the histological and behavioural level. The correlation of cell loss with behavioural performance enables the selection of rats which can be used in neuroprotective or neurorestorative therapies.

Lateralized deficits after unilateral AAV-vector based overexpression of alpha-synuclein in the midbrain of rats on drug-free behavioral tests.

BACKGROUND: Preclinical rodent models of Parkinson's aim to recapitulate some of the hallmarks of the disease as it presents in humans, including the progressive neuronal loss of dopaminergic neurons in the midbrain as well as the development of a behavioral phenotype. AAV vector-based models of alpha-synuclein overexpression are a promising tool to achieve such animal models with high face and predictive validity. OBJECTIVE: We have developed a preclinical rodent model of Parkinson's disease using an AAV-vector based overexpression of human alpha-synuclein. In the present work we characterize this model on a behavioral and histopathological level. METHODS: We use a AAV9 vector for transgene delivery to overexpress human alpha-synuclein under a CBA promoter. We compare the behavioral and histopathological changes to a AAV vector control group where the transgene was omitted and to that of a 6-OHDA lesion control. We assessed the behavioral performance of these three groups on a series of tests (Cylinder, Stepping, Corridor) at baseline and up to 22 weeks post-injection at which point we performed electrochemical recordings of dopamine kinetics. RESULTS: The overexpression of human alpha-synuclein led to the progressive manifestation of behavioral deficits on all three behavioral tests. This was accompanied with impaired dopamine release and reuptake kinetics as demonstrated by electrochemical detection methods. Histopathological quantifications corroborated the findings that we induced a moderate cell loss with remaining cells displaying pathological markers which are abundant in the brains of human PD patients. CONCLUSIONS: In the present work we developed a characterized a rat model of PD that closely mimics human disease development and pathology. Such model will be of great use for investigation of disease mechanisms and early therapeutic interventions.

Optimal conditions for assay of cytochrome-c-oxidase activity in human skeletal muscle tissue.

Conditions for the assay of cytochrome-c-oxidase in human skeletal muscle tissue were studied, including an evaluation of the optimal conditions during the in vitro assay as well as the optimal conditions for storage and treatment of the tissue before the assay. The activity of cytochrome-c-oxidase was assayed polarographically with a Clark oxygen electrode. Optimal oxygen consumption rates were obtained at a cytochrome-c-concentration above 0.2 mmol/l, in the presence of TMPD, 2.2 mmol/l and ascorbic acid, 4.4 mmol/l as reducing agents. Enzyme proportionality was obtained after correction of the oxygen consumption rates for a blank reaction according to one of three alternatives presented. Variations in the homogenizing technique and the degree of dilution of the homogenate (1:11-1:88) had only moderate effects on the enzyme activity. Optimal storage conditions were evaluated by comparing the enzyme activities measured in fresh muscles, frozen muscles and homogenates prepared from fresh muscles. During all storage conditions significantly higher activities were obtained when sucrose buffer (0.25 mol/l) was used as homogenizing medium as compared to phosphate buffer (0.1 mol/l). Freezing and thawing of the muscle tissue before the assay caused an average decrease in the enzyme activity of 50% (P less than 0.005) as compared to the activity obtained in fresh tissue. This untoward effect of the freezing and thawing was reduced when the enzyme activity was analysed in frozen homogenates prepared from fresh muscles. Thus, an average decrease in the enzyme activity of 15% (P less than 0.05) was found in frozen homogenates prepared in sucrose buffer as compared to the activity obtained in the fresh tissue. These findings emphasize the importance of evaluating the effects of the tissue treatment for comparative studies of maximum enzyme activities in vitro.