Odor- and state-dependent olfactory tubercle local field potential dynamics in awake rats

Abstract

The olfactory tubercle (OT), a trilaminar structure located in the basal forebrain of mammals, is thought to play an important role in olfaction. While evidence has accumulated regarding the contributions of the OT to odor information processing, studies exploring the role of the OT in olfaction in awake animals remain unavailable. In the present study, we begin to address this void through multiday recordings of local field potential (LFP) activity within the OT of awake, freely exploring Long-Evans rats. We observed spontaneous OT LFP activity consisting of theta- (2-12 Hz), beta- (15-35 Hz) and gamma- (40-80 Hz) band activity, characteristic of previous reports of LFPs in other principle olfactory structures. Beta- and gamma-band powers were enhanced upon odor presentation. Simultaneous recordings of OT and upstream olfactory bulb (OB) LFPs revealed odor-evoked LFP power at statistically similar levels in both structures. Strong spectral coherence was observed between the OT and OB during both spontaneous and odor-evoked states. Furthermore, the OB theta rhythm more strongly cohered with the respiratory rhythm, and respiratory-coupled theta cycles in the OT occurred following theta cycles in the OB. Finally, we found that the animal's internal state modulated LFP activity in the OT. Together, these data provide initial insights into the network activity of the OT in the awake rat, including spontaneous rhythmicity, odor-evoked modulation, connectivity with upstream sensory input, and state-dependent modulation.