Brain histamine levels and neocortical slow-wave activity in rats with portacaval anastomosis

To determine whether the increased histamine levels in the brain of rats with portacaval anastomosis (PCA) are associated with the development of sleep disturbances during the light phase, the neocortical slow-wave activity of PCA-operated rats was examined with electroencephalography (EEG) 1 month and 6 months after the surgery. The tissue levels of histamine, tele-methylhistamine, 5-hydroxytryptamine (5-HT) (serotonin), and 5-hydroxyindole-3-acetic acid (5-HIAA) in frontal cortex were assayed by high-performance liquid chromatography 6 months after the surgery. PCA surgery led to changes in the synchronized, low-frequency, high-amplitude frontal cortex EEG activity recorded during the light phase. Delta-wave amplitude but not delta time was significantly decreased, whereas both spindle amplitude and spindling time were significantly decreased. There were also significant age-related changes, presented as increases in the duration of spindles and the amplitude of both delta waves and spindles. PCA-operated rats showed a change in the pattern of EEG activity with increasing age similar to sham-operated rats. This suggests that once established, the resetting of the systems regulating the sleep-waking behavior is being maintained with time. The tissue levels of both histamine and metabolite in the frontal cortex were increased, whereas the serotonin system showed only an increase in the level of the metabolite. There was a significant negative correlation between the spindling time and the tissue histamine levels. We suggest that histamine, which participates in the control of vigilance, sleep, and wakefulness, as well as in the modulation of circadian rhythmicity, may play a role in the development of sleep disturbances in rats with PCA.