FIGURE 3.

Diurnal PNN Rhythms Coincide with Rhythms in CHSY1 Expression and Memory Consolidation Processes. Diurnal rhythms in the numerical density of WFA+ PNNs decreases during the day as mice sleep, reaching the lowest density in WFA+ PNN numbers between ZT 4-ZT 10 (red curved line). This coincides with decreased expression of CHSY1 PNNs (green curved line) and the reported daytime decrease in LTP [blue circles, (Chaudhury et al., 2005)]. This decrease in PNNs also coincides with reported broad synaptic downscaling in this region (Spano et al., 2019; Gisabella et al., 2020). In comparison, the numerical density of WFA+ and CHSY1 immunoreactive PNNs peaks during the dark at ∼ZT 20 during the active period for nocturnal mice, coinciding with the reported increase in LTP at night in mice [pink circles, (Chaudhury et al., 2005)]. These results suggest that decreases in PNN composition during sleep coinciding with synaptic downscaling and decreased LTP, potentially allowing for memory consolidation. PNN composition is restored during the active wake periods, in part through CHSY1 expression.