Bull. Environ. Contam. Toxicol. (1994)52:i63-170 ~Environmental 9 1994 Springer-Verlag New York Inc. ~Conllgamination |and Toxicology Brain Met-Enkephalin Immunostaining after Subacute and Subchronic Exposure to Benzene J. M. de Gandarias, 1 E. Echevarrfa, 1 F. Martfnez-Garcia, 2 L. Martfnez-Mill~.n, 1 and L. Casis 1 ~Departmentsof Physiologyand Neurosciences,School of Medicine, University of the Basque Country, Bilbao, Spain and 2Departmentof Animal Biology, School of Biological Sciences, Universityof Valencia, Spain Benzene is used in a wide variety of domestic and occupational activities, and due to its lipophilic nature, it accumulates in lipid-rich tissues like the brain. In this sense, neurotoxic action has long been associated with organic solvent exposure and it has been shown that benzene, injected in a single dose or during a prolongued administration, modifies the content of dopamine, noradrenaline (Paradowski et al. 1985), serotonin and its main metabolite 5-hydroxy indolacetic acid (Paradowski et al. 1984), in several brain regions of the rat, then revealing a stimulating action on brain monoamine synthesis and turnover (Hsieh et al. 1989). However, information concerning neurotoxic action of benzene exposure in vivo on peptidergic neuromodulatory systems is still lacking. Nevertheless, it has been recently described that subacute benzene exposure in rats generates regional changes in brain aminopeptidase activity (Gandarias et al. 1992). These proteolytic enzymes have been widely associated with metabolic control of neuropeptides (Turner 1987) and it has been suggested that they could play a role in benzene neurotoxic mechanism by hypothetically changing regional neuropeptide levels (Gandarias et al. 1992). This being the case, we focused on analyzing met-enkephalin immunostaining in different brain regions of the rat after subacute and subchronic administration of benzene. Send reprint request to Dr. L. Casis at Dpt. Physiology, Medical School, Univ. Basque Country, P.O. Box 699, Bilbao (Spain). 163