Network and synaptic mechanisms underlying high frequency oscillations in the rat and cat olfactory bulb under ketamine-xylazine anesthesia.

Abstract

High frequency oscillations (HFO) are receiving increased attention for their role in health and disease. Ketamine-dependent HFO have been identified in cortical and subcortical regions in rodents, however, the mechanisms underlying their generation and whether they occur in higher mammals is unclear. Here, we show under ketamine-xylazine anesthesia, classical gamma oscillations diminish and a prominent > 80 Hz oscillation emerges in the olfactory bulb of rats and cats. In cats negligible HFO was observed in the thamalus and visual cortex indicating the OB was a suitable site for further investigation. Simultaneous local field potential and thermocouple recordings demonstrated HFO was dependent on nasal airflow. Silicon probe mapping studies spanning almost the entire dorsal ventral aspect of the OB revealed this rhythm was strongest in ventral areas of the bulb and associated with microcurrent sources about the mitral layer. Pharmacological microinfusion studies revealed HFO was dependent on excitatory-inhibitory synaptic activity, but not gap junctions. Finally, we showed HFO was preserved despite surgical removal of the piriform cortex. We conclude that ketamine-dependent HFO in the OB are driven by nasal airflow and local dendrodendritic interactions. The relevance of our findings to ketamines model of psychosis in awake state are also discussed.