DMSO potentiates the suppressive effect of dronabinol on sleep apnea and REM sleep in rats

INTRODUCTION: Dimethyl sulfoxide (DMSO) is an amphipathic molecule with innate biological activity that also is used to dissolve both polar and nonpolar compounds in preclinical and clinical studies. Recent investigations of dronabinol, a cannabinoid, dissolved in DMSO demonstrated decreased sleep apnea frequency and time spent in REM sleep in rats. Here, we tested the effects of dronabinol dissolved in 25% DMSO diluted in phosphate-buffered saline (PBS) to rule out potentiating effects of DMSO. METHODS: Sprague–Dawley rats were anesthetized and implanted with bilateral stainless steel screws into the skull for electroencephalogram recording and bilateral wire electrodes into the nuchal muscles for electromyogram recording. Each animal was recorded by polysomnography. The study was a fully nested, repeated measures crossover design, such that each rat was recorded following each of 8 intraperitoneal injections separated by three days: vehicle (25% DMSO/PBS); vehicle and CB(1) antagonist (AM 251); vehicle and CB(2) antagonist (AM 630); vehicle and CB(1)/CB(2) antagonist; dronabinol (CB(1)/CB(2) agonist); dronabinol and CB(1) antagonist; dronabinol and CB(2) antagonist; and dronabinol and CB(1)/CB(2) antagonists. Sleep was manually scored into NREM and REM stages, and sleep apneas were quantified. RESULTS: Dronabinol dissolved in 25% DMSO did not suppress sleep apneas or modify sleep efficiency compared to vehicle controls, in contrast to previously published results. However, dronabinol did suppress REM sleep, which is in line with previously published results. CONCLUSIONS: Dronabinol in 25% DMSO partially potentiated dronabinol’s effects, suggesting a concomitant biological effect of DMSO on breathing during sleep.