Field potentials in the olfactory bulb of the rainbow trout (Salmo gairdneri): evidence for a dendrodendritic inhibitory pathway.

Field potentials have been recorded from the olfactory bulb of the teleost fish, Salmo gairdneri. Stimulation of the olfactory nerve generates a complex wave pattern, which when recorded near the surface in the centre of the bulb consists of one positive and three negative components, P, N1, N2 and N3. The N1 has been attributed to depolarization of mitral cell dendrites, N2 to depolarization of the superficial dendrites of granules cells, and P to subsequent hyperpolarization of mitral cells. Possible origins of the N3 wave are discussed. Spikes from single units recorded in the mitral cell layer usually occur superimposed on the N1 wave, and single units recorded in the region of granule cells are usually found coincident with the trailling edge of the deep positive wave. With the exception of N3 the patterns of activity observed are very similar to previously published results obtained from other vertebrates. It is suggested that the dendrodendritic inhibitory pathway proposed for the mammalian olfactory bulb (Rall et al., 1966; Rall and Shepherd, 1968) is common to all vertebrates.