Patterns of intracellular potentials in salamander mitral/tufted cells in response to odor stimulation

1. Changes in membrane potential and temporal patterns of spikes were analyzed in 30 output cells in the salamander olfactory bulb in response to stimulation with 1-s pulses of the odorants isoamyl acetate, cineole, and camphor. The odor responses were more complex than responses to electrical stimulation of the olfactory nerve or olfactory tracts, with which they were compared. Most began with hyperpolarization and contained prolonged hyperpolarizing and depolarizing potentials that appeared to be compound postsynaptic potentials. These potentials were related to periods of spike inhibition and excitation. The temporal patterns of the responses resembled S-type (for suppression) and E-type (for excitation) patterns described previously in extracellular-unit studies. 2. In single cells, graded but nonmonotonic changes in the responses were observed with increases in the odor concentration from 10(-3) to 10(-1) vapor-phase saturation. Abrupt changes from one category of temporal response pattern to another were generally not observed in response to different concentrations of a single odorant but were frequently observed when the stimulus was changed from one odorant to another. 3. In S-type patterns, the first event was always membrane hyperpolarization and spike inhibition, regardless of the odor concentration. At all concentrations, simple S-type responses were observed in which a single period of hyperpolarization and inhibition lasted several seconds. At moderate to high concentrations, complex S-type responses were observed in which a period of excitation followed an initial period of hyperpolarization and inhibition. In these responses, spikes were often elicited near the termination of the odor pulse, occasionally as early as 300-400 ms after pulse onset. A prolonged period of inhibition followed the period of excitation. 4. In E-type patterns, the first event depended on the odor concentration. At all concentrations, complex responses were observed in which a period of excitation occurred with short latency, followed by a period of inhibition. At low to moderate concentrations, a brief initial period of hyperpolarization preceded the excitation. This initial period of hyperpolarization was always shorter than those in complex S-type responses to equivalent concentrations. However, the range of spike latencies overlapped that of S-type responses to high concentrations. With increasing odor concentration, spike latencies in the E-type responses decreased relative to the onset and peak of the initial hyperpolarization. At high concentrations. spikes were frequently elicited preceding a single period of hyperpolarization and inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)