Early N-acetylaspartate depletion is a marker of neuronal dysfunction in rats and primates chronically treated with the mitochondrial toxin 3-nitropropionic acid.

N-acetylaspartate (NAA) quantification by 1H-magnetic resonance spectroscopy has been commonly used to assess in vivo neuronal loss in neurodegenerative disorders. Here. the authors used ex vivo and in vivo 1H-magnetic resonance spectroscopy in rat and primate models of progressive striatal degeneration induced by the mitochondrial toxin 3-nitropropionate (3NP) to determine whether early NAA depletions could also be associated with neuronal dysfunction. In rats that were treated for 3 days with 3NP and had motor symptoms, the authors found a significant decrease in NAA concentrations, specifically restricted to the striatum. No cell loss or dying cells were found at this stage in these animals. After 5 days of 3NP treatment, a further decrease in striatal NAA concentrations was observed in association with the occurrence of dying neurons in the dorsolateral striatum. In 3NP-treated primates, a similar striatal-selective and early decrease in NAA concentrations was observed after only a few weeks of neurotoxic treatment, without any sign of ongoing cell death. This early decrease in striatal NAA was partially reversed after 4 weeks of 3NP withdrawal. These results demonstrate that early NAA depletions reflect a reversible state of neuronal dysfunction preceding cell degeneration and suggest that in vivo quantification of NAA 1H-magnetic resonance spectroscopy may become a valuable tool for assessing early neuronal dysfunction and the effects of potential neuroprotective therapies in neurodegenerative disorders.

Major strain differences in response to chronic systemic administration of the mitochondrial toxin 3-nitropropionic acid in rats: implications for neuroprotection studies.

Chronic systemic treatment with 3-nitropropionic acid in rats produces persistent dystonia and bradykinesia, and striatal lesions reminiscent of Huntington's disease. However, the interpretation of results obtained with this model are complicated by a heterogeneous distribution of the response to a given toxic dose of 3-nitropropionic acid: approximately half of the animals develop selective striatal lesions, which in certain cases are associated with extrastriatal lesions, and the other half are apparently spared. Thus, the chronic 3-nitropropionic acid lesion model can be difficult for neuroprotection studies in which a consistent response to neurotoxic treatment is prerequisite. We hypothesized that some of the variability in the model was related to the use of Sprague-Dawley rats, since inter-individual variability in response to various stressful conditions has been described previously in this rat strain. We therefore compared 3-nitropropionic acid toxicity in rat strains known to be highly (Fisher 344) or poorly (Lewis) responsive to stress and compared the distribution of responses to that of Sprague-Dawley rats. In a protocol of intraperitoneal injection, toxicity of 3-nitropropionic acid was highest in Fisher rats, intermediate in Sprague-Dawley rats and lowest in Lewis rats. In addition, survival curves showed a more heterogeneous response to 3-nitropropionic acid toxicity in Sprague-Dawley rats than that observed in Lewis and Fisher rats. These differences between Sprague-Dawley and Lewis rats were confirmed in a protocol of subcutaneous 3-nitropropionic acid intoxication using osmotic minipumps, where doses up to 36-45mg/kg per day for five days were necessary to induce striatal lesions in Lewis rats as compared to 12-14mg/kg per day for five days in Sprague-Dawley rats. The selectivity of the striatum to lesions, and homogeneous progression of symptoms and neurodegeneration, were more consistently observed in Lewis as compared to Sprague-Dawley rats. These results suggest that vulnerability to 3-nitropropionic acid may depend on genetic factors, which could also influence the physiological response to stress. The present findings also establish an improved model of progressive striatal degeneration in the rat adapted for the testing of new neuroprotective strategies.

Differentiation of dialects and courtship strategies in allopatric populations of Drosophila teissieri.

Intra-specific differentiation has been investigated between two geographically isolated populations of D. teissieri, one from Brazzaville (Congo) and the other from Silinda (Zimbabwe). Courtship songs were analyzed on 23 parameters. In addition, certain parameters related to sexual activity (five) and wing morphology (five) were also examined. As in other Drosophilidae, there are two types of courtship songs resulting from wing vibration: the love song, and the sine song. Love songs from Brazzaville are longer than those from Silinda (334ms vs. 216) with a tendency to smaller and more regular inter-pulse intervals (24.56ms vs. 25.5). The sine songs (SS) are about six times longer than the love songs in each population, with an adaptation of their duration according to the receptivity of the female in Brazzaville. All the LS temporal parameters, except the interpulse interval mean, are significantly different between the two populations. The Brazzaville flies show a greater acoustic activity and have higher mating success than the Silinda ones (53.3% vs. 27.7%). Their wings are slightly shorter and wider than those from Silinda. The role of acoustic parameters, sexual activity and wing physical constraints are discussed in the perspective of incipient speciation.