Development of spontaneous, age-related nonconvulsive seizure electrocortical activity and radial-maze learning after exposure to m-xylene in rats.

It has been hypothesized that exposure to neurotoxins may result in accelerated ageing of the central nervous system (CNS). The present study investigated the effects of a 3-month (6 hr daily, 5 days/week) inhalation exposure of rats to m-xylene, at concentrations of 100 and 1000 ppm, on the spontaneous neocortical spike and wave discharges (SWD) and spatial learning in an eight-arm radial maze. According to the literature, the SWD activity increases and the ability to solve spatial problems worsens as the animal gets older. The testing in the maze (one trial daily for five days) was performed two months after the exposure. The SWD activity was assessed on the basis of the number and duration of SWD bursts in one-hour EEG recordings performed before the exposure, on day 28, 56 and 84 of exposure, and then on day 14, 28, 42, and 84 after the exposure. In rats exposed to 1000 ppm m-xylene, unlike in the controls, neither decrease in the number of omission errors nor decrease in response speed was noted in the course of training in the radial maze, which suggested a learning deficit. However, the development of the age-related SWD activity was significantly retarded in these rats when compared with the controls. In rats exposed to 100 ppm m-xylene, the effects on maze behaviour and the SWD activity were similar as in rats exposed to 1000 ppm m-xylene but they were less pronounced. The study has provided an experimental evidence for persistent changes in the CNS functions, resulting from a subchronic exposure to m-xylene. The changes, however, cannot be interpreted simply as an accelerated brain ageing.