Nasal respiration entrains delta-frequency oscillations in the prefrontal cortex and hippocampus of rodents

2018-01

Nasal respiration - rodents

Delta-frequency oscillations - rodents

Hippocampus

Interestingly, rodents breathe at the delta-frequency range (~ 0.5–4 Hz) during anesthesia (Clement et al. 2008), therefore, at overlapping frequencies with the oscillations described by Roy et al. (2017). Rhythmic airflow is known to activate receptors in the nasal cavity and drive a prominent respiration-coupled LFP rhythm (RR) in olfactory brain areas such as the olfactory bulb and piriform cortex (Adrian 1942; Fontanini et al. 2003). The piriform cortex projects directly to the PFC (Clugnet and Price 1987) and indirectly to the hippocampus, after a relay in the entorhinal cortex (Wilson and Steward 1978). We have recently characterized three different types of low-frequency oscillations < 6 Hz in LFPs from the olfactory bulb, hippocampus, and PFC of urethane-anesthetized rats (Lockmann et al. 2016), the same experimental preparation as in Roy et al. (2017). By simultaneously assessing air pressure in the nasal cavity of these animals, we could demonstrate that one of the three oscillations actually corresponded to RR: it had the same frequency as and phase-locked to the breathing cycles (the other two oscillations corresponded to up-and-down state transitions and theta oscillations; Lockmann et al. 2016). We further showed that respiration-entrained LFP oscillations were abolished by tracheostomy and restored by rhythmic air puffing into the nasal cavity; moreover, in the hippocampus, RR had the maximum amplitude in the dentate gyrus hilus, the anatomical site where olfactory inputs impinge (Lockmann et al. 2016).