The olfactory glomerulus is an important module for processing odor information. Patterns of activated glomeruli encode odor identity and intensity, while each glomerulus consists of multiple intrinsic juxtaglomerular (JG) cells and circuits that modulate transfer of sensory input to principal neurons. External tufted (ET) cells are principal neurons at the deep border of the glomerulus that may synchronize processing within a glomerular unit via plateau potential firing and extensive interconnections. This thesis regards two critical questions, employing in vitro olfactory bulb slice preparations. First, what ionic mechanisms underlie ET plateau potentials? Second, what is the functional impact of a single ET cell on glomerular circuits?

Pharmacology of the plateau potential mechanism in current clamp supported that low threshold-like calcium currents are critical for generation. Voltage clamp analysis of calcium current in ET cells revealed a transient, low threshold-like current, I_Ca,T, that had voltage dependence, kinetics, and pharmacology similar to the plateau potential. A sustained calcium current as well one transient and one sustained potassium current were also characterized. Simulation of these four currents, with an established fast sodium current, generated a single compartment model that reconstructed plateau potential firing and demonstrated that I_Ca,T was necessary for plateau potential generation.

ET cell functional influence was assessed on multiple levels. Single cell calcium imaging demonstrated that plateau potentials drive significantly more calcium into ET cell dendrites than single spikes, even with Na ⁺ conductances blocked. Paired recordings revealed that an ET plateau potential can elicit large, long duration EPSPs in JG cells with monosynaptic delay and high probability. Though a single spike robustly drove transmitter release, spike train output depressed significantly. Contrastingly, plateau potentials could create large EPSPs in the absence of Na⁺ conductances. Multi-cell calcium imaging demonstrated that a single plateau potential elicits spiking in multiple JG cells simultaneously, and that such synchrony is specifically enhanced by plateau potential firing mode.

In sum, a single ET cell plateau potential, generated by low threshold-like calcium current, can have significant functional impact on glomerular unit circuits by directly driving synchronous activity in JG cell populations.