Olfaction and peripheral olfactory connections in methimazole-treated rats

Methimazole has been reported to produce extensive degenerative changes in olfactory epithelium and a severe deficit in odor detection [Genter BM, Owe ns DM, Carlone HE, Crofton KM. Fundam. Appl. Toxicol. 1996;29:71-77; Genter BM, Owens DM, Deamer NJ, Blake BL, Wesley DS, Levi PE. Toxicol. Pathol. 19 95;23:477-486.]. To examine this further, rats were tested on olfactory det ection and discrimination problems before and after intraperitoneal injecti on of 300 mg/kg methimazole. In the first 2 days after treatment, experimen tal rats had nasal congestion and a modest decrement on odor detection and odor mixture discrimination tasks. They performed almost as well as control rats on the third post injection day. In a separate group of rats, anterog rade transport of horseradish peroxidase from olfactory epithelium to the b ulb was examined 1, 2, 3, and 5 days after administration of methimazole. T he treatment produced a modest but progressive disruption of bulbar input: 2 days after administration only approximately 10% of bulbar glomeruli had reduced levels of reaction product while 30-40% of glomeruli had little or no reaction product in 3-5 day survival rats. These results indicate that m ethimazole is not a particularly effective olfactotoxin and does not produc e anosmia or even a severe hyposmia. (C) 1999 Elsevier Science B.V. All rig hts reserved.