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

Abstract

Goldfish are ideal vertebrates for the study of regeneration within the peripheral and the central olfactory system. The present behavioural investigations studied the effects of bilateral lesions on the animals' ability to qualitatively discriminate two amino acids (107 -6 M) and their performance in two more difficult tasks: (i) rewarded amino acid applied in a lower concentration, and (ii) rewarded stimulus contaminated. A 50 and 85% reduction of the olfactory epithelium resulted in no recordable behavioural deficit. After axotomy of olfactory nerves and lateral olfactory tractotomy, fishes were anosmic 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. After three surgical modifications of the olfactory bulbs' position, (i) crossing olfactory tracts and bulbs, (ii) crossing tracts and turning bulbs, and (iii) turning bulbs upside down, a full functional recovery was recorded for amino-acid discrimination in a similar concentration. A permanent, and similar slight deficit was, however, found during application of different concentrations, and of contaminated stimuli when medial lateral halves of the bulb were in ‘incorrect’ position (i) and (iii), or olfactory bulbs were positioned in the vicinity of the contralateral epithelium (i) and (ii).