Electrophysiology of interneurons in the glomerular layer of the rat olfactory bulb

In the mammalian olfactory bulb, glomeruli are surrounded by a heterogeneou s population of interneurons called juxtaglomerular neurons. As they receiv e direct input from olfactory receptor neurons and connect with mitral cell s, they are involved in the initial stages of olfactory information process ing, but little is known about their detailed physiological properties. Usi ng whole cell patch-clamp techniques, we recorded from juxtaglomerular neur ons in rat olfactory bulb slices. Based on their response to depolarizing p ulses, juxtaglomerular neurons could be divided into two physiological clas ses: bursting and standard firing. When depolarized, the standard firing ne urons exhibited a range of responses: accommodating, nonaccommodating, irre gular firing, and delayed to firing patterns of action potentials. Although the ring pattern was not rigorously predictive of a particular neuronal mo rphology, most short axon cells fired accommodating trains of action potent ials, while most delayed to firing cells were external tufted cells. In con trast to the standard firing neurons, bursting neurons produced a calcium-c hannel-dependent low-threshold spike when depolarized either by current inj ection or by spontaneous or evoked postsynaptic potentials. Bursting neuron s also could oscillate spontaneously. Most bursting cells were either perig lomerular cells or external tufted cells. Based on their mode of firing and placement in the bulb circuit, these bursting cells are well situated to d rive synchronous oscillations in the olfactory bulb.