Toluene, styrene and methyl-ethyl-ketone inhalation: Effects on the power of cortical oscillations in rats

Exposure to volatile organic solvents, in both industrial workers and animal models, has a depressant effect on the central nervous system and alters behavior. However, the specific impact on brain activity during acute exposure has not been extensively studied. Here, we assessed how acute exposure to three common industrial solvents - toluene, styrene and methyl-ethyl-ketone (MEK) - affected the power of brain oscillations in rats. Rats (n = 14/group) were implanted with cortical electrodes which were connected to a removable headstage during exposure, to wirelessly transmit digitized electrocorticographic (ECoG) signals. Signals were continuously recorded while the rats inhaled solvent vapors (1000 ppm) for 6 h, with a 1-h control period before and after (breathing filtered air). Experiments were repeated for four successive days. In addition to brain oscillations, post-rotatory nystagmus (PRN) and sensory-motor coordination were tested following air/solvent exposure. MEK had no significant effects on the parameters tested. Styrene decreased the power of overall brain activity, but had no effect on motor activity. Toluene increased the power of fast oscillations (30-90 Hz) within minutes and further over time; concomitantly, the power of slow waves (2-12 Hz) decreased. Motor activity was slightly increased by toluene. Both toluene and styrene increased the number and duration of saccades measured by PRN. Dose-response experiments with styrene (n = 16 rats) revealed significant changes in oscillation power even at 50 ppm. These findings suggest that ECoG can be used to assess solvent effects on brain activity in real-time, surpassing the sensitivity of traditional sensorimotor tests.