Sleep and respiratory patterns in the Djungarian hamster

Djungarian hamsters adapted to a 12/12-h L/D photoperiod at 28 +/- 1 degrees C Tamb, implanted with electroencephalogram and electromyogram electrodes and fitted with pneumomanometers were monitored for 4 h on 5 consecutive days to obtain baseline sleep stages and respiration in the nontorpid hamster. Fifty-seven percent of recording time was spent in the sleep state with rapid eye movement (REM) sleep occupying 11% of the total sleep time. An analysis of successive 30-min epochs revealed that REM percentage and REM period (REMP) frequency in the first 30 min were significantly (p less than 0.0001) lower compared to the last 150 min, while REMP duration remained unchanged throughout the recording session. Respiratory frequency was significantly higher (p less than 0.01) by 24% in REM sleep as compared to Non-REM sleep. The euthermic sleep pattern in the non-torpid Djungarian hamster, adapted to a steady-state photoperiod, contained alternating periods of non-rapid eye movement (Non-REM) and REM sleep, similar to that seen in other rodents. REM sleep pattern regulation became steady after the initial 90-min transition period during which REM frequency but not duration increased. This transition to a steady REM sleep pattern might allow flexibility in entering the torpor state during the presence of unfavorable environmental stimuli.