Acute sleep deprivation enhances avoidance learning and spatial memory and induces delayed alterations in neurochemical expression of GR, TH, DRD1, pCREB and Ki67 in rats.

The current study investigated the effects of acute versus repeated periods of sleep deprivation on avoidance learning and spatial memory and on the expression of discrete biochemical brain signals involved in stress regulation, motivation and brain plasticity. Male Long-Evans rats were sleep deprived using the platform-over-water method for a single 4 h period (ASD) or for daily 4h RSD period on five consecutive days (CSD). The Y maze passive avoidance task (YM-PAT) and the Morris water maze (MWM) were used to determine learning and memory 1h following the last SD period. Region-specific changes in glucocorticoid receptors (GR), tyrosine hydroxylase (TH), dopamine 1 receptors (DRD1), phospho-CREB (pCREB) and Ki-67 expression were assessed in the hippocampal formation, hypothalamus and mesolimbic regions 72 h following RSD. Behaviorally, our findings revealed increased latency to re-enter the aversive arm in the YM-PAT and reduced distance traveled and latency to reach the platform in the MWM in ASD rats compared to all other groups, indicative of improved avoidance learning and spatial memory, respectively. Acute SD enhanced TH expression in the ventral tegmental area, nucleus accumbens and A11 neurons of the hypothalamus and DRD1 expression in the lateral hypothalamus. Cell proliferation in the subventricular zone and pCREB expression in the dentate gyrus and CA3 regions was also enhanced following acute SD. In contrast, repeated SD significantly elevated GR-ir at the hypothalamic paraventricular nucleus and CA1 and CA3 layers of the hippocampus compared to all other groups. Our study supports that a brief 4h sleep deprivation period is sufficient to induce delayed neurochemical changes.