The relationship between anxiety and sleep–wake behavior after stressor exposure in the rat

Disturbed sleep is a common subjective complaint among individuals diagnosed with anxiety disorders. In rodents, sleep is often recorded after exposure to various foot-shock paradigms designed to induce an anxiety state. Although differences in sleep–wake architecture are noted, the relationship to specific level of anxiety is often assumed or absent. Utilizing the elevated plus-maze (EPM) after exposure to escapable shock (ES), inescapable shock (IS) or fear conditioning (FC), resulting differences in sleep architecture were compared to an objective measure of anxiety. Male Wistar rats were implanted with EEG, EMG and hippocampal theta electrodes to record sleep–wake behavior. After recovery and recording of baseline sleep, rats were exposed to one of five manipulations: ES, IS, FC or control (CES or CIS; utilizing either chamber with no shock exposure). Shortly after experimental manipulation, the EPM was employed to quantify traditional and ethological measures of anxiety and polygraphic signs of sleep–wake behavior were recorded continuously for 6 h. Although no significance was observed in EPM measurements across groups, profound differences in sleep architecture were present. Individual correlation analysis revealed no differences in anxiety level and total percentage of time spent in sleep–wake states. These results indicate that differences in sleep architecture after foot-shock exposure may not be simply due to increased anxiety. Rather, individual anxiety may be exacerbated by disrupted sleep. To fully understand the relationship between anxiety and sleep–wake behavior, a more objective analysis of anxiety after stressor exposure is mandated.