Relationship between brain norepinephrine and barbital activity in stressed and nonstressed rats

Chronic and acute stress is known to affect barbiturate activity. The effects of 14 day restriction-of-movement stress and hindleg ligation stress, singly and in combination, were observed on the duration of hypnosis of barbital (200 mg/kg, I.P.). Tolerance to barbital was observed when it was administered beginning at 26, 50, 74 hours after removal from chronic stress(without acute stress, however, it was significant only in males). Administration of acute stress at 50 hours after removal from chronic stress resulted in elimination of tolerance to barbital. A subsequent injection 24 hours later produced tolerance to barbital, Proadifen (50 mg/kg, IP) prolonged sleeping time with the second dose of barbital, but had no effect on the first dose in chronically and acutely stressed animals. Proadifen did lengthen sleeping time when the first dose of barbital was administered 50 hours after stress in chronically stressed rats. The stress changes in barbital activity were studied by determination of the whole brain norepinephrine concentration. Chronic stress resulted in a greater brain concentration of norepinephrine than that seen in non-stressed rats. Barbital hypnosis increased the brain norepinephrine concentration in non-stressed rats, but not in stressed rats, stressed animals exhibited a shorter sleeping time than non-stressed animals.