Odor information is processed by several olfactory cortical regions, all receiving direct input from the olfactory bulb. While much attention has been focused on some of these, others remain largely unexplored. The nucleus of the lateral olfactory tract (nLot) is one such brain region that has been very little studied and the function it serves in olfactory processing is unknown. It is located at the rostral end of the lateral olfactory tract, medially to piriform cortex, and has a 3 layered organization. The nLot contains about 5000 pyramidal neurons in the mouse and anatomical studies show that it is interconnected with several olfactory brain regions. The physiological properties of nLot neurons and its synaptic organization are currently completely unknown and revealing them may shed light on potential functions it serves.
We analyzed the biophysical properties of nLot pyramidal neurons, and the properties of various synaptic inputs onto them. We show that nLot neurons are bursters and that this burstiness stems from voltage activated calcium channels that are activated below the threshold for somatic action potentials. Olfactory bulb inputs make synaptic connections with distal dendrites of layer 2 nLot neurons and these manifest at the soma as very small EPSCs that do not reach threshold for action potential generation. Occasionally, activation of the mitral and tufted cell axons elicited dendritic regenerative responses that were able to evoke somatic action potentials. Associative inputs into nLot terminate within layer 2 and their activation evokes much larger EPSCs that can reach threshold without requiring dendritic spikes.
The increased responsivity to associative inputs compared to olfactory bulb inputs, indicates that the nLot is a high-level node in the olfactory circuit.