Effects of p-chlorophenylalanine on thermoregulation and sleep in rats

Abstract

sleep/waking and body temperature (Tb) were recorded in male rats in a 12:12 light-dark photoperiod at one of 3 ambient temperatures (Ta's): 20, 30, or 32°C. After adaptation to the sleep recording chamber for at least 48 h, the rats were injected with saline at the beginning of lights-on (day S1). Twenty-four hours later (day P1), they were injected with PCPA (300 mg/kg, i.p.) and recordings continued for 4 more days (P2–P5). At these Ta's, hypothalamic 5-HT was depleted by 66–75% 30 h post-PCPA. Changes in both amplitude and acrophase of Tb depended on Ta. Compared to S1, amplitude was reduced on P2–P4 at 20°C and on P3–P4 at 30°C. Acrophase was advanced on P1–P3 at Ta 20°C only. Sleep variables were generally independent of Ta and largely unchanged in the dark. In the light, amounts of slow-wave sleep (SWS) were depressed on P2–P4, number of bouts decreased on P3–P5 and percent nocturnality decreased on P2–P5. Bout length was depressed on P2 and lengthened on P4–P5. Acrophase was delayed on P2–P4 at Ta 30°C. Amounts of rapid-eye-movement sleep (REMS) were depressed on P1–P3. REMS bout length decreased on P1–P3. The decreases in number of REMS bouts seen on P1–P3 depended on Ta. Changes in percent nocturnality and acrophase of REMS were minor. Waking→SWS transitions decreased on P3–P5 while SWS→REMS transitions were reduced on P1–P2. These results suggest that PCPA affects circadian aspects of both Tb and sleep, that 5-HT is important in the initiation of SWS bouts, and finally that the mechanisms by which 5-HT depletion affects Tb, SWS and REMS are different.