Structural and functional cellular alterations underlying the toxicity of methamphetamine in rat retina and prefrontal cortex.

The consumption of illicit drugs is an increasing problem in contemporary societies, and is one of the major causes of death and illness all over the world. Methamphetamine is among the drugs more widely used. Although evidence for a role of reactive species--especially reactive oxygen species (ROS) and apoptotic events--has been shown, the mechanism(s) underlying the cellular toxicity induced by this drug is not yet fully identified. In this context the elucidation of the cytotoxic effects induced by methamphetamine in rat frontal cortex and retina, which compromise cell viability and ultimately result in cell death, can further contribute to the understanding of its mechanism of action. This knowledge may provide new insights into the development of new therapeutic approaches to prevent or ameliorate deleterious alterations of the nervous system. The use of epifluorescence microscopy associated with different fluorescent probes, markers of structural and/or functional cell parameters, can be used as a powerful tool to carry out those studies, in particular, the viability probes propidium iodide (PI) to assess plasma membrane integrity and fluorescein diacetate (FDA), which can monitor intracellular esterase activity and/or pH. In a preliminary study, the kinetic assessment of cellular changes induced by different drug concentrations (0, 1.2, 3, and 6 mM) allowed detection of dose-dependent alterations that are observed earlier in the retina. In fact, in the retina it was possible to monitor alterations (at 4 h of incubation) both in plasma membrane integrity and in esterase activity and/or pH for the lowest drug concentration (1.2 mM). In the prefrontal cortex these changes were only visible for drug concentrations > or = 3 mM. This work is a novel approach to the mechanisms of action of illicit drugs in the central nervous system and will provide the foundations and guidelines for further investigations in the context of tolerance, dependence, and addiction.