Methylene blue alters retention of inhibitory avoidance responses

These experiments examined the effects of methylene blue on retention, by rats and mice, of an inhibitory avoidance response. The studies using mice investigated the effects of graded doses of methylene blue administered shortly before or after training. A 500-mg/kg dose impaired retention in mice (tested 3 days after training) if administered 15 min, but not 30 or 5 min, prior to training. Further studies with rats indicated that retention was enhanced by a low dose (1.0 mg/kg) administered immediately after training (tested 1 day after training). Retention in rats was not affected by a 1.0-mg/kg dose given 15 min before training, 6 h after training, or 15 min before testing. These results are interpreted in the light of methylene blue’s actions on blood hemoglobin and carbohydrate metabolism.