Arman Sheybani and John Caprio, Biological Sciences

A Study of Synergism in Vertebrate Olfaction

Electrophysiological experiments indicated that channel catfish (Ictalurus punctatus) and goldfish (Carassius auratus) detect a variety of odorants, such as bile salts, amino acids, polyamines, and nucleotides. While previous experiments investigated olfactory receptor responses to specific compounds representing each of these odorant classes, few studies have combined odorants from different odorant classes to determine possible synergistic effects. In the present investigation, the fish were adapted to mixtures of polyamines and nucleotides, respectively, while mixtures representing the different classes of odorants were tested to determine if an enhancement of responses occurred. The underwater electro-olfactogram (EOG), a slow negative potential change in response to odorant stimulation that is comprised of olfactory generator current, was recorded in vivo with calomel electrodes from the water that continuously bathed the olfactory organ (4 mls/min). Test stimuli were presented at varying concentrations that provided similar EOG response magnitudes. The fish were immobilized with an injection of Flaxedil (0.1mg/100g body weight), and the gills of the fish were irrigated using water which contained the anesthetic MS-222 (0.005%). Synergism was determined to occur if the peak EOG response to a stimulus under a particular adapting regime was greater than its response under control water. The EOG responses were recorded on both tape and chart recorders. The results indicated that synergistic odorant responses occurred in catfish between ATP (adapting regime) and polyamines (test stimulus). For goldfish, synergistic responses occurred between ATP (adapting regime) and amino acids and polyamines as test stimuli.