The α1 adrenoceptor antagonist prazosin enhances sleep continuity in fear-conditioned Wistar-Kyoto rats

Abstract

Fragmentation of rapid eye movement sleep (REMS) is well described in individuals with posttraumatic stress disorder (PTSD) and likely has significant functional consequences. Fear-conditioned rodents may offer an attractive model of the changes in sleep that characterize PTSD. Following fear conditioning (FC), Wistar-Kyoto (WKY) rats, a strain known to be particularly stress-sensitive, have increased REMS fragmentation that can be quantified as a shift in the distribution of REMS episodes towards the more frequent occurrence of sequential REMS (inter-REMS episode interval≤3 min) vs. single REMS (interval>3 min). The α1 adrenoceptor antagonist prazosin has demonstrated efficacy in normalizing sleep in PTSD. To determine the utility of fear-conditioned WKY rats as a model of sleep disturbances typical of PTSD and as a platform for the development of new treatments, we tested the hypothesis that prazosin would reduce REMS fragmentation in fear-conditioned WKY rats. Sleep parameters and freezing (a standard measure of anxiety in rodents) were quantified at baseline and on Days 1, 7, and 14 following FC, with either prazosin (0.01mg/kg, i.p.) or vehicle injections administered prior to testing in a between-group design. Fear conditioning was achieved by pairing tones with a mild electric foot shock (1.0mA, 0.5s). One, 7, and 14 days following FC, prazosin or vehicle was injected, the tone was presented, freezing was measured, and then sleep was recorded from 11 AM to 3 PM. WKY rats given prazosin, compared to those given vehicle, had a lower amount of seq-REMS relative to total REMS time 14 days after FC. They also had a shorter non-REMS latency and fewer non-REMS arousals at baseline and on Days 1 and 7 after FC. Thus, in FC rats, prazosin reduced both REMS fragmentation and non-REMS discontinuity.

Keywords: BLA; BNST; CNA; CS; ECG; EEG; EMG; FC; Fear conditioning; LA; NE; Norepinephrine; PTSD; Posttraumatic stress disorder; REM sleep; REMS; VLPO; WKY; Wistar–Kyoto; Wistar–Kyoto rats; basolateral nucleus of the amygdala; bed nucleus of the stria terminalis; central nucleus of the amygdala; conditioning stimulus; electrocardiogram; electroencephalogram; electromyogram; fear-conditioned or fear conditioning; lateral nucleus of the amygdala; norepinephrine; posttraumatic stress disorder; rapid eye movement sleep; seq-REMS; sequential rapid eye movement sleep; si-REMS; single rapid eye movement sleep; ventrolateral preoptic nucleus.

Fig. 1

Timeline of the experimental procedures. F/S - Entry into recording chamber followed by 5-min freezing assessment and 4-h sleep recording; T/F/S - Entry into recording chamber followed by 3 tone presentations, 5-min freezing assessment, and 4-h sleep recording.

Fig. 2

Cortical EEG and nuchal EMG traces with an example of a transient arousal during non-REMS. A transient arousal occurs in the framed portion of the record, with the EEG changing to a low voltage/high frequency pattern and a concurrent nuchal EMG activation.

Fig. 3

Stability of the power spectra of the cortical EEG between Baseline and Day 14, and comparison of the characteristic features of cortical power spectra between a vehicle-treated (left) and a prazosin-treated (right) rat. Cortical power in the delta frequency range (0.5–4.0 Hz) is consistently lower in the prazosin-treated rat than in the vehicle-treated rat in all three behavioral states. Also, there is the characteristic increase of relative power in the 12–18 Hz range during non-REMS in the prazosin-treated rat (arrow). For this comparison, cortical power spectra were calculated for continuous 10-min periods of waking prior to the first non-REMS episode in each recording session (top graphs), 2-min periods of the first sufficiently long non-REMS episode in each recording (middle row), and 1-min periods of the first sufficiently long REMS episode in each recording. The graphs show relative powers in 0.4883 Hz bins normalized by the total power of each spectrogram over the 0–50 Hz range.

Fig. 4

Comparison of selected non-REMS and REMS parameters in prazosin- and vehicle-treated rats. (A) non-REMS latency (± SEM) in rats receiving prazosin (n=7) compared to rats receiving vehicle (n=6). Significance level for between-group comparisons: *P<0.05, ***P<0.02. (B) non-REMS arousal frequency (± SEM) in the same groups of prazosin- and vehicle-treated rats. Significance level for between-group comparisons: ****P<0.002. Significance level for within-group comparisons (Vehicle/Day 1 vs. Baseline and Day 7): ^#P<0.006. (C) Seq-REMS% (seq-REMS time/total REMS time; ± SEM) in the same groups of prazosin- and vehicle-treated rats. Significance level for the between-group comparison: ***P<0.02.

Fig. 4

Comparison of selected non-REMS and REMS parameters in prazosin- and vehicle-treated rats. (A) non-REMS latency (± SEM) in rats receiving prazosin (n=7) compared to rats receiving vehicle (n=6). Significance level for between-group comparisons: *P<0.05, ***P<0.02. (B) non-REMS arousal frequency (± SEM) in the same groups of prazosin- and vehicle-treated rats. Significance level for between-group comparisons: ****P<0.002. Significance level for within-group comparisons (Vehicle/Day 1 vs. Baseline and Day 7): ^#P<0.006. (C) Seq-REMS% (seq-REMS time/total REMS time; ± SEM) in the same groups of prazosin- and vehicle-treated rats. Significance level for the between-group comparison: ***P<0.02.