Toluene and toluene-containing volatile substances are the most commonly abused solvents with a demonstrative addictive potential in humans. Numerous clinical and experimental data indicate that long-term exposure to toluene vapors leads to diverse outcomes at the levels ranging from the cell to the whole organism. The central nervous system is one of the main targets: as a result of chronic toluene exposure a number of long-lasting neurological and behavioral impairments, as well as various neurochemical, molecular and diffuse changes in the white and gray matter of organisms of different ages were described. In the present study, we evaluated and compared toluene chronic exposure provokes immediate and/or persistent effect on spatial memory function assessed in one day water maze paradigm and hippocampal structure in rats. The behavioral changes, based on Escape Latency and Long Term Memory were evaluated. For the study the escape latency and long-term memory the one-day MWM training protocol with eight training trials was used. We used the adult male Wistar rats of (P150–165, weight 160–175 g). Each rat was placed separately in the glass cylindrical chamber (45 cm height × 35 cm diameter) and was exposed to toluene vapor at the concentration 2000 ppm, or clean air (control animals), for 3–5 min/d, during 20 d. Immediate effect of toluene chronic exposure was evaluated immediately after the end of toluene inhalation, while persisting effect–90 days after the end of toluene exposure. Nissl staining of hippocampal sections showed that the pyramidal cell loss in the CA1 and CA3 experimental group is significantly higher than that in the control group. The results of behavioral experiments showed that effect of chronic toluene exposure affects learning process and short-term spatial memory but induced impairment in spatial long-term memory assessed in probe test performance 24 h after training. 24 hours after training, a probe test (60 s) with the platform removed was performed to assess long-term spatial memory. The comparisons for factor group within Sector 1 (S opp) showed no significant difference (P = 0.829) but revealed such difference (P < 0.001) within Sector 4 (S test) (P = 0.025). This fact indicates that in toluene-treated animals the long-term memory is worsened. Long-term spatial memory was assessed using a Morris water maze, according the test proposed by Ge et al. [4]. The changes in behavior were based on the evaluation of (i) Escape Latency and (ii) Long-term memory. Statistical analysis of quantitative data was made using Post-hoc (Tukey test) and three-way ANOVA. In the present study we show that chronic toluene exposure to 2000 ppm significantly alters the behavior of rats in MWM also. Such behavior comprised the acquisition and spatial localization of relevant visual cues that are subsequently processed, consolidated, retained and finally retrieved in order to successfully navigate and thereby to find the hidden platform and to escape water. Staistical analysis of quantitative data showed significant difference between toluene-treated and control animals. The hippocampus is known as a key structure for place learning, and the water maze procedures have been considered as a hippocampus-dependent. Toluene chronic exposure-induced spatial memory impairment may be attributed to the hippocampal cell death.

References

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