Odor representation in the olfactory bulb under different brain states revealed by intrinsic optical signals imaging

Effect of Xylazine-Tiletamine-Zolazepam on the Local Field Potential of the Rat Olfactory Bulb

Neural oscillations of the mammalian olfactory system have been studied for decades. This research suggests they are linked to various processes involved in odor information analysis, depending on the vigilance state and presentation of stimuli. In addition, the effects of various anesthetics, including commonly used ones like chloral hydrate, pentobarbital, ketamine, and urethane, on the local field potential (LFP) in the olfactory bulb (OB) have been studied. In particular, the combination of xylazine and tiletamine-zolazepam has been shown to produce steady anesthesia for an extended period and relatively few adverse effects; however, their effects on the LFP in the OB remain unknown. To study those effects, we recorded the LFP in the OB of rats under xylazine-tiletamine-zolazepam anesthesia. During the period of anesthesia, the spectral powers of the 1-4, 9-16, 31-64, 65-90 frequency bands increased significantly, and that of 91-170 Hz frequency band decreased significantly, whereas no significant changes were observed in the 5-8 and 17-30 Hz ranges. These results reveal dynamic changes in the time and frequency characteristics of the LFP in the OB of rats under xylazine-tiletamine- zolazepam anesthesia and suggest that this combination of anesthetics could be used for studying oscillatory processes in the OB of rats.

Brain-state dependent uncoupling of BOLD and local field potentials in laminar olfactory bulb

The neural activities of the olfactory bulb (OB) can be modulated significantly by internal brain states. While blood oxygenation level dependent functional MRI (BOLD-fMRI) has been extensively applied to study OB in small animals, the relationship between BOLD signals and electrophysiological signals remains to be elucidated. Our recent study has revealed a complex relationship between BOLD and local field potentials (LFP) signals in different OB layers during odor stimulation. However, no study has been performed to compare these two types of signals under global brain states. Here, the changes of BOLD and LFP signals in the glomerular, mitral cell, and granular cell layers of the OB under different brain states, which were induced by different concentrations of isoflurane, were sequentially acquired using electrode array and high-resolution MRI. It was found that under deeper anesthesia, the LFP powers in all layers were decreased but the BOLD signals were unexpectedly increased. Furthermore, the decreases of LFP powers were layer-independent, but the increases of BOLD signal were layer-specific, with the order of glomerular>mitral cell>granular cell layer. The results provide new evidence that the direct neural activity levels might not be correlated well with BOLD signals in some cases, and remind us that cautions should be taken to use BOLD signals as the index of neural activities.