Peripheral acting muscle relaxants alter the effects of baclofen on the electrocorticograms in the rat

The effects of intraperitoneally administered baclofen on behavior and electrocorticograms (ECoG) were studied in freely moving and paralyzed rats. In the freely moving rats, 10 mg/kg of baclofen suppressed ECoGs with behavioral sedation, and 20 mg/kg caused whole body twitching accompanied with spike discharges in low voltage slow waves background. In the freely moving rats, baclofen acted as depressant in low dose and convulsant in high dose. In the paralyzed rat, 10 mg/kg of baclofen first suppressed ECoGs. Though fast waves components recovered with slow waves background in the ECoGs of rats paralyzed with gallamine (50 mg/kg) 3 hours after the baclofen injection, fast waves activities were not observed in the ECoG of rats paralyzed with succinylcholine (50 mg/kg), d-tubocurarine (3 mg/kg) or pancuronium (1 mg/kg). Under paralysis with d-tubocurarine, baclofen suppressed ECoG first, and then spike discharges started 90 min after the injection. These results suggest that the effects of baclofen on ECoG were different depending on the muscle relaxant used.