REM sleep: a sensitive index of fear conditioning in rats

Abstract

To examine the influence of conditioned fear stimuli on sleep-wake states, we recorded sleep in Sprague-Dawley rats after exposure to tones previously paired with footshock. After habituation to a recording chamber and the recording procedure, a baseline sleep recording was obtained the next day. One day later, experimental animals were exposed to shock training designed to induce conditioned fear (FC), consisting of five tone-footshock pairings. The 5-s tones (conditioned stimuli; CS) co-terminated with 1-s footshocks (unconditioned stimuli; US). The next day sleep was recorded for 4 h in the recording chamber after presentation of five CSs alone. Sleep efficiency (total sleep time/recording period) and REM sleep (REM) and non-REM (NREM) measures were determined. While sleep efficiency was not significantly changed after CS presentation, the percentage of total sleep time spent in REM (REM percentage) was reduced in the FC animals. The reduction in REM percentage in the FC animals was due to a decrease in the number of REM bouts. In a separate experiment, we repeated the procedures, except the tones and shocks were presented in an explicitly unpaired (UP) fashion. The next day, presentation of the tones increased REM percentage in the UP group. Results are discussed in terms of the decreases in REM as a response to conditioned fear, and the relevance of these findings to the sleep changes seen in post-traumatic stress disorder (PTSD).

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

“…The rodent model is also frequently employed to measure the changes in sleep-wake architecture after experimental manipulation (Ho et al, 2002;Jha et al, 2005;Tang et al, 2005). Classical fear conditioning, the most common paradigm, utilizes an unconditioned footshock presented with a conditioned stimulus to measure the acquisition, expression and/or extinction of fear Pawlyk et al, 2005;Tang et al, 2005).…”

Learning not to Fear: Neural Correlates of Learned Safety

“…When contrasting learned safety and learned fear, several important insights about the neurobiology of learned safety can also be drawn from a host of studies in which explicitly unpaired 'control' groups had been studied. Important examples include the assessment of generalization described above (Bang et al, 2008;Ito et al, 2009;Laxmi et al, 2003), the effect on sleep (Jha et al, 2005;Madan et al, 2008), and investigations on the role of the amygdala (Choi et al, 2001;Maren, 2000;Maren et al, 2001). …”

Sleep alterations in mammals: Did aquatic conditions inhibit rapid eye movement sleep?

“…Merely keeping an animal in such a condition suppresseses REM sleep. However, keeping an animal over water could be stressful and/or fear-inducing, and it is known that stress/fear suppresses REM sleep [70] . …”