The characteristics of the electro-olfactogram (EOG): its loss and recovery following olfactory nerve section in rainbow trout (Salmo gairdneri).

Electro-olfactograms (EOGs) were recorded from both sensory and non-sensory epithelia on the olfactory lamellae and from other areas within the rosette of rainbow trout (Salmo gairdneri). The trout EOG induced by amino acids was a monophasic negative voltage composed of a phasic component which declined to a steady level (tonic component) that was maintained throughout stimulus duration. The time period (2 min) for complete recovery of the EOG was obtained by applying two identical stimuli (10(-5) mol/liter L-serine for 5 s) successively at increasing intervals. EOG response to amino acids increased nearly exponentially with concentration and no saturation was reached. Gradual deterioration of olfactory receptor cells occurred within 14 days after olfactory nerve section (axotomy) as indicated by phospholipid staining. Regeneration of the receptor cells started at 56 days postaxotomy, reached approximately normal density and the elongate form of mature neurons at 84 days. In axotomized fish the magnitude of EOG response decreased relative to the controls at 7 days with minimal sensitivity between 14 and 28 days postaxotomy. EOGs were not evoked by L-serine nor L-leucine in most fish 17-22 days postaxotomy. Restoration of the EOG response coincided with morphological repopulation of receptor neurons after 84 days. EOG recovery was only 50% of the control values at 230 days. The EOG responses evoked by HCl in sensory and non-sensory epithelia were indistinguishable from each other, indicating that receptor neurons are not likely to be their primary origin.