006 The effect of sodium oxybate on cataplexy in orexin knockout mice

Abstract

Abstract Introduction Narcolepsy is a neurological disorder that is characterized by the loss of orexin neurons in the lateral hypothalamus. Cataplexy is a symptom of narcolepsy and is identified by a sudden loss of muscle tone during wakefulness. Cataplexy abruptly interrupts day-to-day activities, and makes activities like driving dangerous and potentially fatal. It is hypothesized that cataplexy occurs due to the intrusion of REM sleep muscle atonia during wakefulness. It has been demonstrated that a GABAergic mechanism is responsible for silencing the REM sleep atonia circuit and preventing REM sleep muscle atonia from occurring during wakefulness. Sodium oxybate (SXB), a low affinity agonist of GABAB receptors, is currently an approved treatment for narcolepsy; however, its mechanism of action in the brain remains unknown. Here, we investigate the hypothesis that SXB prevents cataplexy through a GABAB mediated mechanism by potentially suppressing the REM sleep atonia circuit. Methods We intraperitoneally (IP) injected orexin-/- mice with one of five treatments; either Lactated Ringers Solution, SXB at 50, 100, or 200 mg/kg, or Phaclophen at 10 mg/kg followed by SXB at 100 mg/kg. Cataplexy was assessed by video recordings. We gathered and analyzed data at three distinct chronological time points (i.e, at baseline, after three consecutive weeks of daily dosing with a treatment, and after one week of no treatment). These experiments were designed and conducted to determine whether; 1) SXB reduces cataplexy, 2) the cessation of SXB administration has an effect on cataplexy, 3) SXB is mediated through a GABAB mechanism. Results We first confirmed that mice used were indeed orexin-/- using immunohistochemical analysis to show that no orexin-a expressing neurons were located in the lateral hypothalamus. Then, we determined that: 1) SXB reduces cataplexy compared to time matched controls (unpaired t-test, p=0.0027, n=18); 2) When we stopped administering SXB IP injections, cataplexy levels increased towards control levels (paired t-test, p=0.0024, n=18); 3) it remains unclear if SXB’s effect is solely mediated through a GABAB mechanism. Conclusion Our findings demonstrate that SXB effectively reduces cataplexy in orexin-/- mice. Support (if any) This research was funded by Jazz Pharmaceuticals