Differential expression of neuronal and inducible nitric oxide synthase in rat brain after subchronic administration of 3-monochloro-1,2-propanediol

The compound 3-monochloro-1,2-propanediol (3-MCPD) is a contaminant of acid-hydrolyzed vegetable protein foodstuffs. Several reports have suggested that chronic exposure to 3-MCPD can produce neurotoxicity or neurobehavioral effects in experimental animals. We sought to further explore the neurotoxic effects of 3-MCPD (10 or 30 mg/kg) administered for 13 weeks on the expression of two forms of nitric oxide synthase (NOS), neuronal NOS (nNOS), and inducible NOS (iNOS), in rat cerebral cortex and striatum. Using immunocytochemistry, the number of nNOS-expressing neurons or the optical density of iNOS staining in sections from three coronal levels (bregma 1.0, −0.4, and −2.3 mm) were compared between 3-MCPD-treated and control rats. At bregma level 1.0 mm, the number of nNOS-expressing neurons was significantly decreased in the 10 and 30 mg/kg groups. At bregma level −0.4 mm, nNOS expression was significantly decreased only in the 30 mg/kg group, in the cortex and striatum. However, at bregma level −2.3 mm, 3-MCPD administration produced no significant difference in the number of nNOS-expressing neurons in the cortex or striatum. In contrast, iNOS expression was significantly increased in the neocortex and striatum at all three rostrocaudal levels following subchronic 3-MCPD administration. These data suggest that subchronic 3-MCPD exposure may involve compensatory mechanisms acting on nNOS and iNOS expression to maintain nitric oxide homeostasis in the rostral part of the neocortex and striatum. However, in the caudal brain, increased iNOS expression did not profoundly suppress nNOS expression. Thus, the present study suggests that 3-MCPD-induced neurotoxicity is mediated, at least in part, through disturbances in the nitric oxide signaling pathway and exhibits a rostrocaudal difference, through differential expression of nNOS and iNOS in the neocortex and striatum.