Intermittent hypoxic exposure during light phase induces changes in cAMP response element binding protein activity in the rat CA1 hippocampal region: water maze performance correlates.
Intermittent hypoxia (IH) during sleep, a characteristic feature of sleep-disordered breathing (SDB) is associated with time-dependent apoptosis and spatial learning deficits in the adult rat. The mechanisms underlying such neurocognitive deficits remain unclear. Activation of the cAMP-response element binding protein (CREB) transcription factor mediates critical components of neuronal survival and memory consolidation in mammals. CREB phosphorylation and DNA binding, as well as the presence of apoptosis in the CA1 region of the hippocampus were examined in Sprague-Dawley male rats exposed to IH. Spatial reference task learning was assessed with the Morris water maze. IH induced significant decreases in Ser-133 phosphorylated CREB (pCREB) without changes in total CREB, starting as early as 1 h IH, peaking at 6 h-3 days, and returning toward normoxic levels by 14-30 days. Double-labeling immunohistochemistry for pCREB and Neu-N (a neuronal marker) confirmed these findings. The expression of cleaved caspase 3 (cC3) in the CA1, a marker of apoptosis, peaked at 3 days and returned to normoxic values at 14 days. Initial IH-induced impairments in spatial learning were followed by partial functional recovery starting at 14 days of IH exposure. We postulate that IH elicits time-dependent changes in CREB phosphorylation and nuclear binding that may account for decreased neuronal survival and spatial learning deficits in the adult rat. We suggest that CREB changes play an important role in the neurocognitive morbidity of SDB patients.