In goldfish the discriminative ability for odours persists after reductionof the olfactory epithelium, and rapidly returns after olfactory nerve axotomy and crossing bulbs

Goldfish are ideal vertebrates for the study of regeneration within the per ipheral and the central olfactory system. The present behavioural investiga tion studied the effects of bilateral lesions on the animals' ability to qu alitatively discriminate two amino acids (10(-6)M) and their performance in two more difficult tasks: (i) rewarded amino acid applied in a lower conce ntration, and (ii) rewarded stimulus contaminated. A 50 and 85% reduction o f the olfactory epithelium resulted is no recordable behavioural deficit. A fter axotomy of olfactory nerves and lateral olfactory tractotomy, fishes w ere anosomic for seven to ten days. Following replacement of sensory cells in the epithelium, and after regeneration of olfactory tract fibres a full functional recovery, i.e a highly specific regeneration, was recorded. Afte r three surgical modifications of the olfactory bulbs' position, (i) crossi ng olfactory tracts and bulbs, (ii) crossing tracts and turning bulbs, and (iii) turning bulbs upside down, a full functional recovery was recorded fo r amino-acid discrimination in a similar concentration. A permanent and sim ilar slight deficit was, however, found during application of different con centrations, and of contaminated stimuli when medical lateral halves of bul b were in 'incorrect' position (i) and (iii), or olfactory bulbs were posit ioned in the vicinity of the contralateral epithelium (i) and (ii).