Impairment of olfactory discrimination by blockade of nitric oxide activity in the terrestrial slug Limax valentianus.

The terrestrial slug Limax readily associates an innately preferred food odor with the aversive taste of quinidine. We investigated slugs' olfactory discrimination capability among structurally similar alcohols and the effects of inhibition of nitric oxide (NO) synthesis to the olfactory discrimination behavior, using an olfactory discriminatory learning task. Limax could discriminate among the odor of 1-octanol (OT), 3-methylcyclohexanol (MC) and 1-hexanol (HX). OT was perceptually more similar to HX than was MC for them. When NO synthesis was inhibited by injecting N-nitro-L-arginine methyl ester (l-NAME) shortly before the discrimination test, slugs could not discriminate between OT and HX whereas the retrieval of olfactory memory and the discrimination between OT and MC remained intact. These results indicate that the NO cascade plays a crucial role for fine olfactory discrimination in Limax.