Activity pattern and convulsions in the abstinence period after barbital treatment in the rat

Barbital solution was given as the only drinking fluid to male rats for 50 weeks (daily dose around 200 mg/kg). During the treatment and in the abstinence period activity and convulsive episodes were recorded with jiggle cages. Sensitivity to hexobarbital was tested with a threshold method. A 12:12 HR L:D schedule was used. During the barbital treatment the activity of the treated rats started earlier (prior to light off) and ended earlier (prior to light on) compared with controls. A clear 24-hr pattern remained and the total activity was same as in the controls. In the first part of the abstinence period there was a large increase in activity with loss of the 24-hr pattern. Later in the abstinence period the activity was still increased both during light and darkness but a 24-hr pattern influenced by the L:D cycle was re-established. The changes in activity seemed to occur in a least two phases with the second phase lasting between abstinent Days 20-60. A similar two phase pattern was seen also in the changes of the hexobarbital thresholds. The convulsive episodes had several maxima during the abstinence period. The first one occurred around abstinent Days 3--4 and the second one was seen around Day 12. After Day 37 no convulsions were seen. All recorded changes can tentatively be explained by a common increased excitation in the central nervous system.