Circadian periodicity of brain activity and urinary excretion in the epileptic baboon.

A 24-H rhythm in the proclivity of the baboon Papio papio to exhibit a seizure response to intermittent light stimulation (ILS) has been uncovered. Seizure response to ILS was found to be greatest in the morning at about 0900 h, 2 h after lights on, and least severe in the evening at about 2000 h 1 h after lights off. Urine cortisol and potassium excretion rhythms followed the same pattern as seizure susceptibility and sodium rhythms were 3 or 4 delayed. Mean values for urine cortisol per 4 h ranged from 25 microgram/4 h at the maxima (0400 to 0800 h) to 2 microgram/4 h at the minima (2000 to 2400 h). Electrolyte rhythms ranged from 13 to 3 meq/4 h for potassium and 1 to 5 meq/4 h for sodium. Changes in electroencephalographic (EEG) activity also accompanied the change in urine cortisol and potassium, and seizure sensitivity, Changes in the EEG at the diurnal minima (2000 h) consisted of a decrease in slow waves concomitant with an increase in fast activity in the 18-25 Hz range,