Trimethyltin (TMT) intoxication is considered a suitable experimental model to study the molecular basis of selective hippocampal neurodegeneration as that occurring in several neurodegenerative diseases. We have previously shown that rat hippocampal neurons expressing the Ca2+‐binding protein calretinin (CR) are spared by the neurotoxic action of TMT hypothetically owing to their ability to buffer intracellular Ca2+ overload. The present study was aimed at determining whether intracellular Ca2+ homeostasis dysregulation is involved in the TMT‐induced neurodegeneration and if intracellular Ca2+‐buffering mechanisms may exert a protective action in this experimental model of neurodegeneration. In cultured rat hippocampal neurons, TMT produced time‐ and concentration‐dependent [Ca2+]i increases that were primarily due to Ca2+ release from intracellular stores although Ca2+ entry through Cav1 channels also contributed to [Ca2+]i increases in the early phase of TMT action. Cell pre‐treatment with the Ca2+ chelator, 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid tetrakis(acetoxymethyl ester) (2 μM) significantly reduced the TMT‐induced neuronal death. Moreover, CR+ neurons responded to TMT with smaller [Ca2+]i increases. Collectively, these data suggest that the neurotoxic action of TMT is mediated by Ca2+ homeostasis dysregulation, and the resistance of hippocampal neurons to TMT (including CR+ neurons) is not homogeneous among different neuron populations and is related to their ability to buffer intracellular Ca2+ overload.

Magnetic resonance imaging (MRI) is the only noninvasive technique that provides structural information on both cell loss and metabolic changes. After reviewing all the results obtained in clinical studies, reliable biomarkers in neurological diseases are still lacking. Diffusional MRI, MR spectroscopy, and the assessment of regional atrophy are promising approaches, but they cannot be simultaneously used on a single patient. Thus, for further research progress, reliable animal models are needed. To this aim, we have used the clinical MRI to assess neurodegenerative processes in the hSOD-1 G93A ALS rat model and in the trimethyltin (TMT)-treated model of Alzheimer's-like disease. T2-weighted (T2W) hyperintensive neurodegenerative foci were found in the brainstem of the ALS rat with apparent lateral ventricle dilation (T1W-hypointensity vs. T2W-hyperintensity). Degenerative processes in these areas were also confirmed by confocal images of GFAP-positive astrogliosis. MRI after i.v.i. of magnetic anti-CD4 antibodies indicated an accumulation of inflammatory cells near dilated ventricles. TMTtreated rats also revealed the dilation of lateral ventricles. Expected deterioration in the hippocampus was not observed by clinical MRI, but immunocytochemistry could reveal significant redistribution of macroand microglia in this structure. In both models, Gd-DTPA contrast revealed a compromised blood brain barrier that may serve as the passage for inflammatory immune cells in the vicinity of dilated lateral ventricles. Moreover, in both models the midbrain region of the dorsal hippocampus was the target of BBB compromise, thus revealing a potentially vulnerable point that can be the primary target of neurodegeneration in the central nervous system.

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To more clearly elucidate the complete network of molecular mechanisms induced by trimethyltin (TMT) toxicity, we used a homogeneous cell culture model represented by PC12 cells treated with 1 and 5 lmol/L TMT for 24 h. The gene expression profile was performed by microarray analysis, enabling us to identify 189 genes that were significantly modulated in treated cells, compared with controls. The main effects of TMT on gene expression seem to be related to the activation of metabolic processes (glycolysis and lipogenesis) along with cell death pathways, membrane remodeling and intracellular biomolecules trafficking. These alterations are triggered by the neurotoxicant earlier than a strong decrease in cell viability, which occurs at higher TMT concentrations or at later time points. Some aspects of the transcriptional modulation observed in this study resemble the gene activation known to occur during cell response to hypoxia. Other cell toxicants have also been reported to exert similar effects on gene expression. Therefore, our data help to delineate general basic adaptive mechanisms possibly shared by cells responding to different death-inducing noxae, such as TMT.

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