Heterogeneous spindle- and theta-phase preference of supragranular regular spiking interneurons (RSIs) during non-REM and REM sleep: comparison with fast spiking interneurons (FSIs)
01/29/2020
János Horváth1, Róbert Averkin1, Sándor Bordé1, Vitalii Dashkovskyi1, Viktor Szemenyei1, Gábor Tamás1
1 Research Group for Cortical Microcircuits of the Hungarian Academy of Sciences Department of Physiology, Anatomy and Neuroscience, University of Szeged
Neocortical FSIs show temporally structured firing relative to rhythmic population activity during non-REM sleep, but our understanding of the activity of RSIs is less clear. We applied the technique of juxtacellular recording and labelling of supragranular RSIs in the parietal cortex during natural sleep in Wistar rats. Action potentials of RSIs were wider compared to FSIs and their average firing frequency was lower in non-REM sleep. Rhythmic activity was observed in 21 out of 26 RSIs during spindle episodes with firing locked to different phases of spindle cycles: 12 cells increased firing near the trough, two cells near the peak, four cells at the descending phase and three cells at the ascending phase, respectively. Each cell recorded in REM sleep (n=14) showed elevated firing during theta activity in comparison to non-REM episodes either without significant phase preference (n=8) or with sustained phase-locked activity near the peak (n=2) or the trough (n=4) of the ongoing theta oscillation. Interestingly, REM theta phase relatedness was preserved during awake theta in each cell (n=14). The majority of RSIs (n=20) were differentially recruited to spindle and theta oscillations, however, similar and rhythmic firing behavior during spindle versus theta activity was in n=3 cells and phase unrelated firing during spindles and theta was observed in n=3 cells. In conclusion, RSIs heterogeneously contribute to network activity during non-REM and REM sleep, partly in cooperation with FSIs during the trough of spindle oscillations. However, RSIs have additional contribution to network rhythms during theta periods when FSIs do not appear to be phase-locked. Supported by: GINOP, HAS