Atropine in the abstinence after chronic barbital treatment in the rat.

Since cholinergic mechanisms seem to be involved in the changes induced by chronic barbital treatments in male rats, various treatments with atropine were given during the abstinence after 32--33 weeks of exposure to barbital (200 mg/kg/day). The effects of the atropine treatment were recorded as a tolerance towards a hexobarbital anaesthesia threshold. In Experiment 1, 1.5 mg/kg/day of atropine was given on Days 23--29 after the end of the barbital treatment. Two weeks after the end of the atropine treatment a significant tolerance (+ 16%, Fig. 1A) was seen in barbital-treated animals given the atropine treatment (group BA), but not in the corresponding control groups (group BS, CA and CS). In Experiment 2, the atropine dose was 4 mg/kg/day and the treatment was given on Days 29--44. A tolerance (+ 20%, Fig. 4) with maximum 2 weeks after the end of the atropine treatment was recorded in the animals given the combined treatment (group BA). In both experiments a single dose of atropine given on Day 3 reduced this tolerance. In Experiment 3 the atropine treatment was 4 mg/kg/day on Days 3--12. A tolerance above that induced by the barbital treatment (+ 16%, Fig. 5) was recorded three weeks after the end of the atropine treatment (group BA). In this group there was also recorded a new tolerance much later (Day 80). Since a tolerance was induced by atropine, only in previously barbital-treated animals, a carry-over of some change in cholinergic mechanisms is probably involved.