Response of epilithic diatom communities to environmental gradients along an Ecuadorian Andean River.

Epilithic diatom communities are particularly suitable for the evaluation of freshwater quality. In Ecuador, however, no water quality index includes this biotic parameter. This work is the first attempt in the country to determine the composition of epilithic diatom communities associated with different degrees of eutrophication. This was accomplished by measuring physical, chemical and microbiological variables at five sampling sites along the Pita River, Ecuador, from August to December 2016. The results indicate a clear gradient of eutrophication from sampling sites P1 (good water) in the upper reaches to P5 (bad water) located in the lower reaches. Concerning diatom analyses, the results indicated a high diversity for tropical areas in terms of species richness, varying from S=34 in headwaters to S=42 downstream. Moreover, the results obtained suggest a lack of concordance with the trophic values given to some of the epilithic diatoms in the literature. There were also species that seem to be sensitive to downstream nutrient increases that were not considered as bioindicators in previous studies. We concluded that the trophic values of diatom species available in the scientific literature are not directly applicable to their sites in the Pita River. Hence, it is necessary to establish a trophic diatom index for the Andean region of Ecuador.

Impaired retention in AßPP Swedish mice six months after oral exposure to chlorpyrifos.

Chlorpyrifos (CPF) is an organophosphate pesticide. This pesticide induces cognitive impairments, oxidative stress and neuronal damage, which suggests a possible relationship between CPF exposure and Alzheimer's disease. In this study we examined long-term changes in behavior and brain levels of the amyloid beta (Aß) protein after repeated CPF exposure in a mouse model of Alzheimer's disease. Tg2576 male mice between four and six months of age carrying the human Swedish mutation for Alzheimer's disease were exposed to eight doses of 25 mg/kg of CPF distributed over four weeks. Five months after exposure, general activity was measured in an open-field, while learning and memory were assessed in a Morris water maze task six months after treatment with CPF. Levels of the Aß fragments (1-40 and 1-42) were also measured in the frontal cortex and hippocampal brain regions. Motor activity was increased in CPF-exposed mice. Although acquisition learning in a water maze task was not affected, retention was worsened in CPF-exposed mice. There were no significant increases of Aß levels in the brains of CPF-treated mice six months after exposure. These findings raise concerns about the risk of developing neurodegenerative diseases in vulnerable subjects following repeated exposure to CPF.

Amyloid ß peptide levels increase in brain of AßPP Swedish mice after exposure to chlorpyrifos.

Chlorpyrifos (CPF) is an organophosphate pesticide widely used in intensive agriculture. Various studies have demonstrated delayed neurotoxic effects in adult mammals after acute CPF exposure. This pesticide induces oxidative stress and neuronal damage, which suggests a possible relationship between CPF exposure and Alzheimer's disease (AD). In the present study, we examined in a mice model of AD, long-term changes in the behavior and brain levels of amyloid ß after acute CPF exposure. Fifty mg/kg of CPF were subcutaneously injected to Tg2576 (Tg) mice carrying the Swedish amyloid-ß protein precursor (AßPP) mutation for AD. General status, body weight, acetyl cholinesterase (AChE) inhibition, and behavioral changes were assessed. Amyloid ß fragment (1-40 and 1-42) levels were also measured in the cortical and hippocampal brain regions. A significant and transient decrease in body weight was observed 72 hr after treatment, while no autonomic effects were noted. Motor activity was decreased in Tg mice seven months after CPF treatment. Acquisition learning in a water maze task was not affected, but retention was ameliorated in CPF-exposed Tg mice. Amyloid ß levels increased in the brains of treated Tg mice eight months after CPF exposure. The results of this study show that some behavioral changes persisted or emerged months after acute CPF exposure, while amyloid ß levels increased. These findings raise concern about the risk of developing neurodegenerative diseases following moderate exposure to CPF in vulnerable subjects.