Effects of Cannabinoid Agonists and Antagonists on Sleep and Breathing in Sprague-Dawley Rats

Abstract

Study objectives: There are no pharmacological treatments for obstructive sleep apnea syndrome, but dronabinol showed promise in a small pilot study. In anesthetized rats, dronabinol attenuates reflex apnea via activation of cannabinoid (CB) receptors located on vagal afferents; an effect blocked by cannabinoid type 1 (CB1) and/or type 2 (CB2) receptor antagonists. Here, using a natural model of central sleep apnea, we examine the effects of dronabinol, alone and in combination with selective antagonists in conscious rats chronically instrumented to stage sleep and measure cessation of breathing.

Methods: Adult male 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 on multiple occasions separated by at least 3 days. The study was a fully nested, repeated measures crossover design, such that each rat was recorded following each of 8 intraperitoneal injections: vehicle; vehicle and CB1 antagonist (AM 251); vehicle and CB2 antagonist (AM 630); vehicle and CB1/CB2 antagonist; dronabinol; dronabinol and CB1 antagonist; dronabinol and CB2 antagonist; and dronabinol and CB1/CB2 antagonist.

Results: Dronabinol decreased the percent time spent in rapid eye movement (REM) sleep. CB receptor antagonists did not reverse this effect. Dronabinol also decreased apneas during sleep, and this apnea suppression was reversed by CB1 or CB1/CB2 receptor antagonism.

Conclusions: Dronabinol's effects on apneas were dependent on CB1 receptor activation, while dronabinol's effects on REM sleep were CB receptor-independent.

Keywords: cannabinoid receptors; cannabinoids; dronabinol; obstructive sleep apnea; rat.

Figure 1

Sleep efficiency quantified as a percentage of time spent asleep from 6-hour recordings of conscious chronically instrumented rat experiments. Vehicle (DMSO) 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 (shaded bars). There was a significant agonist main effect; there was a decrease in sleep efficiency in the dronabinol treat rats. Data (mean ± SEM) were analyzed using 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 < .05.

Figure 2

Awake time (left), and NREM (center), and REM (right) sleep as a percentage of total recording time quantified from 6-hour recordings of conscious chronically instrumented rat experiments. Vehicle (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 (shaded bars). Dronabinol and a combination of dronabinol and CB₂ antagonist significantly reduced REM sleep. CB₁ or combination of CB₁/CB₂ antagonists also significantly decreased REM sleep compared to CB₂ antagonist alone. Data (mean ± SEM) were analyzed using 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 < .05.

Figure 3

Apnea (A), spontaneous apnea (B), post-sigh apnea (C), and NREM apnea (D) indices quantified from 6-hour recordings of conscious chronically instrumented rat experiments. Indices were quantified as events/hour during sleep. Vehicle (DMSO) 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 (shaded bars). Dronabinol significantly decreased the apnea post-sigh, and NREM apnea indices; CB₁ antagonism reversed dronabinol’s effect. Data (mean ± SEM) were analyzed using 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 < .05.