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

Abstract

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 CB₁ antagonist (AM 251); vehicle and CB₂ antagonist (AM 630); vehicle and CB₁/CB₂ antagonist; dronabinol (CB₁/CB₂ agonist); dronabinol and CB₁ antagonist; dronabinol and CB₂ antagonist; and dronabinol and CB₁/CB₂ 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.

Keywords: Cannabinoids; DMSO; Dronabinol; REM sleep; Sleep apnea.

Fig. 1

Sleep efficiency quantified as a percentage of time spent asleep from 6 h recordings of conscious chronically-instrumented rat experiments. Vehicle (25% DMSO in PBS) or dronabinol (10 mg/kg) was injected IP in combination with vehicle or CB₁ receptor (AM 251, 5 mg/kg) or CB₂ receptor (AM 630, 5 mg/kg) antagonist, or both. There were no significant main effects. Data (mean ± SEM) were analyzed using linear mixed model analysis with repeated/fixed measures (CB agonist and CB antagonist)

Fig. 2

Sleep apnea (A), spontaneous sleep apnea (B), post-sigh sleep apnea (C) and NREM sleep apnea (D) indices quantified from 6 h recordings of conscious chronically-instrumented rat experiments. Indices were quantified as events/hr. Vehicle (25% DMSO in PBS) or dronabinol (10 mg/kg) was injected IP in combination with vehicle (solid bars) or CB₁ receptor (AM 251, 5 mg/kg) or CB₂ receptor (AM 630, 5 mg/kg) antagonist, or both. There were no significant main effects. Data (mean ± SEM) were analyzed using linear mixed model analysis with repeated/fixed measures (CB agonist and CB antagonist)

Fig. 3

Awake time (left), and NREM (center) and REM (right) sleep as a percentage of total recording time quantified from 6 h recordings of conscious chronically-instrumented rat experiments.. Vehicle (25% DMSO in PBS) or dronabinol (10 mg/kg) was injected IP in combination with vehicle or CB₁ receptor (AM 251, 5 mg/kg) or CB₂ receptor (AM 630, 5 mg/kg) antagonist, or both. Dronabinol and a combination of dronabinol and CB₂ antagonist significantly reduced REM sleep. Data (mean ± SEM) were analyzed using linear mixed model analysis with repeated/fixed measures (CB agonist and CB antagonist) followed by post hoc multiple comparison tests with Sidak’s correction if there were significant main effects or a significant interaction of main effects. *p < 0.05