0027 Reciprocal Modulation of Cortical Excitatory and Inhibitory Synapses by Wake-Sleep Homeostatic State

Abstract

Abstract Introduction A widely debated function of sleep involves a homeostatic program of down-regulation of excitatory synaptic strength following an overall increase during the preceding waking period, preserving however the previously existing synaptic weights associated with newly acquired memories. We tested this hypothesis by applying thorough statistical analysis of parameters of excitatory and inhibitory miniature postsynaptic currents (mEPSC/mIPSC) recorded ex vivo in mouse cortical pyramidal neurons at three characteristic wake/sleep stages. Methods Cingulate cortex coronal slices were obtained at fixed Zeitgeber time (ZT6, to control for circadian clock) from control C57BL6 (MEF2C f/f) mice subjected to 6h acute sleep deprivation (SD), recovery sleep =4hSD+2h(RS), or 6h control sleep (CS). mEPSCs and mIPSCs were recorded from functionally identified whole-cell patch-clamped pyramidal neurons in cortical layer 2/3 (L2/3). Statistical analysis of frequencies, amplitudes, and charge transfer rates of mEPSCs and mIPSCs was done using non-parametric Kruskal-Wallis multiple comparison test and K-means clustering test. Results mEPSC frequency (F) and charge transfer (CT) were significantly reduced for RS and CS compared to SD (F: -57%, -47%; CT: -64%, -55%). mEPSC amplitude (A) was significantly reduced for CS compared to SD (-15%). Two-centroid clustering test revealed that analyzed parameters of F, A and CT for SD condition were approximately evenly split between upper and lower range clusters, while the same parameters for RS and CS conditions revealed a pronounced redistribution (>75% lower-, <25% upper ranges). Wake/sleep state related changes of mIPSC parameters showed opposite pattern compared to excitatory synapses. All three parameters were increased in RS vs. SD (F: +63%, A: +7%, CT: +42%) and this difference reached significance levels in CS vs. SD (F: +88%, A: +24%, CT: +109%). Clustering analysis of mIPSC parameters revealed mostly stable distribution pattern between upper and lower ranges for all wake/sleep states. Conclusion Significant changes in excitatory/inhibitory balance in the frontal cortex is part of the homeostatic response upon transition from wakefulness to various phases of sleep. The excitatory component prevails during wakefulness, while the inhibitory component peaks during sleep. Support (If Any) NIH grant R01 NS103422 to RWG.