Effect of histamine depletion on the circadian amplitude of the sleep-wakefulness cycle.
Behavioral states of rats were automatically classified with a newly developed computer program into three sleep stages (awake, slow-wave sleep and REM sleep) from continuous long-term EEG and EMG recordings for several circadian cycles under entrained circumstances (L:D = 12:12). Histamine was depleted by 100 mg/kg intraperitoneal administration of a specific inhibitor of its synthesis, alpha-fluoromethylhistidine, in the mid-light period. This treatment had no effect on the amount of each sleep stage in the total 24-h period or in the light period, but caused significant increases in slow-wave sleep and REM sleep in the dark period. Equivalent decrease in the awake stage during the dark period was also observed. As a result, histamine depletion decreased the light:dark ratio of slow-wave sleep. These findings suggest that decrease of the histamine content of the brain attenuated the circadian amplitude of sleep-wakefulness by suppressing the surge of wakefulness during the dark period. From these results, histamine is suggested to modulate the circadian amplitude of the sleep-wakefulness cycle.
Itowi
N
N
Department of Pharmacology II, Faculty of Medicine, Osaka University, Japan.
Yamatodani
A
A
Kiyono
S
S
Hiraiwa
M L
ML
Wada
H
H
D000818:Animals; D001921:Brain / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D006632:Histamine / Q000502:physiology*; D008297:Male; D051381:Rats; D012894:Sleep Stages / Q000502:physiology*; D012895:Sleep, REM / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D014851:Wakefulness / Q000502:physiology*
D006632:Histamine