RESUMO
It has long been a concern that performance measures of species distribution models react to attributes of the modeled entity arising from the input data structure rather than to model performance. Thus, the study of Allouche et al. (Journal of Applied Ecology, 43, 1223, 2006) identifying the true skill statistics (TSS) as being independent of prevalence had a great impact. However, empirical experience questioned the validity of the statement. We searched for technical reasons behind these observations. We explored possible sources of prevalence dependence in TSS including sampling constraints and species characteristics, which influence the calculation of TSS. We also examined whether the widespread solution of using the maximum of TSS for comparison among species introduces a prevalence effect. We found that the design of Allouche et al. (Journal of Applied Ecology, 43, 1223, 2006) was flawed, but TSS is indeed independent of prevalence if model predictions are binary and under the strict set of assumptions methodological studies usually apply. However, if we take realistic sources of prevalence dependence, effects appear even in binary calculations. Furthermore, in the widespread approach of using maximum TSS for continuous predictions, the use of the maximum alone induces prevalence dependence for small, but realistic samples. Thus, prevalence differences need to be taken into account when model comparisons are carried out based on discrimination capacity. The sources we identified can serve as a checklist to safely control comparisons, so that true discrimination capacity is compared as opposed to artefacts arising from data structure, species characteristics, or the calculation of the comparison measure (here TSS).
RESUMO
The designer drug of cathinone family, methylenedioxypyrovalerone (MDPV), is a cheap and frequently used psychoactive drug of abuse. However, its mechanism of action, particularly its potential detrimental effect on the developing brain, is largely unknown, despite the fact that pregnant females may occur among the users. The objective of our study was to identify the brain areas sensitive for a possible apoptotic effect of the widely abused MDPV on the developing brain. To this end, we used a mouse model which can be compared with the human fetus of third trimester, considering the developmental stage of the brain. Litters of 7-day-old C57BL/6J mice were treated either with i.p. injection of 10mg/kg b.wt.of MDPV or vehicle (saline), and sacrificed after 24h. Similar dose of MDPV enhanced locomotor activity of pups. The brains were processed for anti-caspase 3 (Casp3) immunohistochemistry and the apoptotic cells were identified and counted. We found prominent increase in the number of apoptotic cells in the piriform cortex, retrosplenial area, hippocampus CA1 and nucleus accumbens, whereas the overall density of cells did not change significantly in these regions. The neurons of the nucleus accumbens appeared to be especially sensitive to MDPV: Casp3-immunoreactive cells marked out the core and shell regions of the accumbens. Highest percentage of apoptotic cells as compared to total cell density was also found in the nucleus accumbens. However, we did not observe the same effect on the brain of adult mice. Thus, MDPV did not seem to increase apoptosis in the mature nervous system. The results are in agreement with the assumption that cathinones (in particular MDPV) may adversely affect neural integrity in the developing CNS.
