Interaction between spontaneous and electrically induced convulsions and their short- and long-term effects in the abstinence after chronic barbital treatment in the rat.

Male rats were treated with barbital supplied in their drinking water (daily dose around 200 mg/kg) for 50 weeks. When the treatment was stopped (day 0) spontaneous convulsions were monitored for the first 3 days of the abstinence. On day 3 a convulsion was induced by electricity in half of the rats (controls and barbital-treated) and 1 h later the sensitivity to hexobarbital was determined with a threshold test. Sensitivity to hexobarbital was then tested in the same manner at approximately weekly intervals for the first 110 days of the abstinence. On day 3 of the abstinence a tolerance to hexobarbital (48% increase in threshold above controls) and a reduced threshold to induce convulsions with electricity (-27% compared with controls) was seen in previously barbital-treated animals. Spontaneous or induced convulsions occurring prior to the hexobarbital threshold determination decreased the tolerance to the same extent (-22 to -28%). On day 28 rats with no convulsions up to day 3 had a marked renewal of tolerance to hexobarbital (29% increase above controls), while rats with convulsions recorded up to day 3 had less or no such tolerance. There was a positive correlation (r = 0.63) between the hexobarbital thresholds in barbital-treated rats recorded on day 3 and on day 28. Later in the abstinence, barbital-treated rats with convulsions prior to day 3 tended to have a hexobarbital threshold slightly but significantly elevated compared with the controls (10-15%). This change could be a sign of a long-lasting increased excitation.