REVERSIBLE INHIBITION OF THE OLFACTORY BULB REDUCES MK801‑ENHACED HIGH‑FREQUENCY OSCILLATIONS (130‑180 HZ) IN THE PIRIFORM CORTEX

In rodents, NMDAR antagonists enhance high frequency oscillations (HFO) 130-180 Hz measured in LFP in many brain regions. The olfactory bulb (OB), a strong generator of HFO, sends excitatory projections to the piriform cortex (PCtx). Here, we examined whether systemic injection of MK801 also enhances HFO in the PCtx and if reversible inhibition of the OB influences this activity. LFP from the OB and PCtx were recorded after systemic injection of 0.15 mg/kg MK801 in freely moving rats. Thirty minutes after injection rats received microinfusion of muscimol (0.5 µg) or saline to the OB or PCtx. Systemic injection of MK801 increased the HFO power in both structures. HFO power was significantly higher in the OB compared to the PCtx. Microinfusion of muscimol to the OB produced an immediate reduction in HFO power in the OB and PCtx. By contrast, muscimol infusion to the PCtx produced a gradual reduction in HFO power in the PCtx without affecting the OB. These findings suggest that OB efferent activity plays a critical role in the generation of HFO post NMDAR antagonists in downstream targets. The OB appears to play a crucial role in broadcasting this activity to other brain areas.