Variations of histamine concentration in sleep and arousal hemodialysates (seasonal, thalamic and reticular influences).

In hemodialysates of cerebral venous blood from rabbits kept asleep by electrical stimulation of the somnogenic intralaminar thalamus, a seasonal correlation was found between the histamine (H) concentration and the external daily temperature, with a minimum in winter and a maximum in summer. By contrast, in dialysates of rabbits aroused by electrical stimulation of the midtrain reticular formation, the H concentration reached in winter the same high level as in summer. During the winter, stimulation of the waking midbrain reticular system increased the H-level of the cerebral blood dialysate, whereas that of the somnogenic intralaminar thalamus did not enhance, sometimes even lowered, the H-concentration. This suggests that the mechanism of H release in blood might be associated with the midbrain activating reticular system and moderated by the intralaminar thalamus.