Resumo

INTRODUCTION: It has been suggested that sleep loss interferes with a wide range of learning and memory processes but it is still unclear how sleep is involved in extinction. The aim of this study was to evaluate if paradoxical sleep deprivation (PSD) prior to prolonged and repeated re-exposure to a previously aversive context has an impact on conditioned fear memory extinction. METHODS: Wistar male rats were exposed to the contextual fear conditioning which was consisted of inescapable foot shocks (5 shocks, 1 s each, 0.8 mA). PSD was performed using the multiple platform method for ninety-six hour. Sleep rebound group (SR) was allowed to sleep for 48h after PSD. The control group remained in their homecages and had normal sleep opportunity throught the experimental period. Recall was assessed by freezing behaviour during 5 min re-exposure to the conditioning chamber immediately after PSD or SR. Extra 25 min of re-exposure served as extinction procedure in the first session. The second session test was performed one week lately to evaluate memory reinstatement. RESULTS: Upon 5 min re-exposure, PSD group spent significantly less time in freezing behaviour compared to control group (p<.05). During the subsequent 25 min in the first test session, control group gradually decreased freezing reaching minimum scores at the end of the session, which we considered to reflect fear extinction. No significant changes were observed in freezing performance throughout the first test session for the PSD group. Control and PSD groups maintained low freezing rates throughout the second session. PARCIAL DISCUSSION: Our results suggest that PSD may have caused the increase in locomotor activity in animals, affecting the expression os fear response. However, PSD did not appear to affect the learning of extinction memory. In this case, the freezing time presented by the animals would be much higher in test 2.