Rat brain amines, blood histamine and glucose levels in relationship to circadian changes in sleep induced by pentobarbitone sodium.

1. The circadian patterns for onset and duration of sleep after the administration of a constant dose of pentobarbitone sodium have been measured in rats adapted to and maintained under a fixed illumination cycle. The relationship of these patterns to others for rectal temperature and motor activity as well as for noradrenaline (NA), 5-hydroxytryptamine (5-HT) and histamine in mid-brain and caudate nucleus, and histamine and glucose in blood serum, has been examined.2. The onset of sleep is longest and duration shortest during the phase of the illumination cycle when motor activity and rectal temperature are maximal. An inverse relationship for these parameters is found during the light phase of the illumination cycle.3. In untreated rats, mid-brain NA and histamine and caudate nucleus histamine levels are maximal and 5-HT minimal during the dark phase of the illumination cycle. An inverse relationship for these parameters is found during the light phase of the illumination cycle.4. Pentobarbitone sodium treatment significantly elevates mid-brain NA and histamine and caudate nucleus histamine levels during the dark phase of the illumination cycle. Although 5-HT levels are reduced over the entire circadian cycle this change is significant only during the light phase of the illumination cycle.5. Pentobarbitone sodium treatment reverses the circadian pattern for body temperature, producing a mirror image of the control pattern.6. The circadian pattern for blood serum histamine levels differs from the C.N.S. pattern for histamine. Peak levels occur at the end of the light phase of the illumination cycle. After pentobarbitone sodium these levels are reduced, although the circadian pattern is similar to the control.7. Circadian blood glucose patterns have bimodal peaks; a primary peak at the end of the dark phase, a secondary peak at the end of the light phase of the illumination cycle. Pentobarbitone sodium did not significantly alter the pattern. The relationship between this pattern and C.N.S. and peripheral histamine and catechol amines is discussed.