Discrimination between the enantiomers of carvone and terpinen-4-ol in normal rats and those with olfactory bulb lesions

We assessed (1) whether the enantiomers of terpinen-4-ol, odorants that activate nearly identical areas of the olfactory bulb, are more difficult to discriminate than those of carvone, odorants that activate different areas of the olfactory bulb, and (2) whether olfactory bulb lesions that disrupt the pattern of bulbar activation produced by these enantiomers degraded the ability of rats to discriminate between them. In psychophysical tests, normal rats discriminated between the enantiomers of terpinen-4-ol and of carvone equally well. Surgical lesions that removed the majority of bulbar glomeruli activated by these odorants (As demonstrated in prior olfactory bulb studies using optical imaging and 2-deoxyglucose [2-DG]) resulted in increased detection thresholds but few or no deficits in discriminating between supra threshold concentrations of enantiomers. These results fail to confirm prior predictions based on 2-DG maps of bulbar activity that enantiomers of terpinen-4-ol should be more difficult to discriminate than those of carvone and that the ability to discriminate between enantiomers of an odorant are based on differences in patterns of bulbar activation revealed in such maps.