Influence of thyroxine and steroid hormones on spontaneous and evoked unitary activity in the olfactory bulb of goldfish

Three different types of discharge patterns of single cells were observed in the glomerular and subglomerular layers of the olfactory bulbs of normal goldfish, and these patterns were studied also in hormone-treated fish. The Type I pattern is a series of small spikes of relatively higher discharge rate seen in control and thyroxine-treated fishes with the recording electrode in the subglomerular layers of the bulb. Thyroxine treatment elicited a remarkable increase in the “spontaneous” Type I firing rate. Type B, also recorded from the subglomerular zone, a discharge pattern characterized by bursts of spikes, was obtained mostly after sex steroid treatment. Type G is a pattern of somewhat large action potentials, regularly firing, recorded from cells in the glomerular layer of all animals studied. Observations were made of the changes in rate and pattern of firing during infusion of 0.06 M NaCl into the olfactory sac. Estradiol pretreatment produced a strong facilitatory effect on the NaCl response of cells exhibiting the Type G pattern, but it did not alter the responses of cells of the Type B pattern. In contrast, testosterone did not affect the responsiveness of cells of the Type G pattern, but it facilitated NaCl-evoked changes in the firing rate of cells initially presenting the type B pattern. Progesterone and thyroxine were similar in their tendency to inhibit NaCl-evoked changes in rates of these single unit discharges. However, there was a pattern difference in the altered Type I and B firing, after NaCl infusion, between the progesterone and the thyroxine-treated fishes.