Behavioral effects following subacute inhalation exposure to m-xylene or trimethylbenzene in the rat - A comparative study

Trimethylbenzene (TMB), like xylene (dimethylbenzene), is a significant con stituent of some industrial solvent mixtures. In earlier studies, we found that in the rat a subacute low-level inhalation exposure to some of the TMB isomers may result in behavioral alterations detectable weeks after the ex posure [Neurotoxicol Teratol 19;1997:327; Int J Occup Med Environ Health 11 ;1998:319]. The propose of the present study was to compare m-xylene (XYL) and each of the TMB isomers: 1,2,3-TMB (heminzellitene - HM), 1,2,4-TMB (ps eudocumene - PS), and 1,3,5-TMB (mesitylene - MES) with respect to the abil ity for inducing behavior-al effects in the rat. The rats (10-11 animals pe r group) were exposed repeatedly for 4 weeks (6 h per day, 5 days per week) to XYL (XYL group), HM (HM group), PS (PS group) or MES (MES group) at 100 ppm, or sham exposed (C group) in 1.3 cu/m dynamic inhalation chambers. St arting 2 weeks after exposure the following forms of rat's behavior were as sessed: radial maze performance, spontaneous activity in an open field, lea rning and retention of passive and active (two-way) avoidance response, and heat-induced paw licking before and after a 2 min footshack (a test for as sessment of the stress response). None of the solvent-exposed groups differ ed considerably from the control one,vith respect to the radial maze perfor mance. Compared to control mts, the rats of the XYL, PS and MES groups, but not those of HM group, showed a significantly higher spontaneous locomotor activity in the open field, an impaired passive avoidance learning and sig nificantly longer paw-lick latencies 24 h after footshock. Acquisition, but not retention of the the two-way active avoidance response was significant ly impaired in all solvent-exposed groups. The XYL group did not differ sig nificantly from PS, MES of HM group in any of the behavioral parameters. Th e above results show that a short-term exposure to any of the TMB isomers o r m-xylene at concentration as lo,v as 100 ppm may induce persistent behavi oral alterations in the vat. (C) 2001 Elsevier Science Inc. All lights rese rved.