The role of gonadal hormones in the hypoglossal discharge activity of rats exposed to chronic intermittent hypoxia

Combination of acute intermittent hypoxia and intermittent transcutaneous electrical stimulation in obstructive sleep apnea: a randomized controlled crossover trial

Intermittent hypoxia (IH) and intermittent transcutaneous electrical stimulation (ITES) might benefit patients with obstructive sleep apnea (OSA). However, the therapeutic value of combined IH and ITES in OSA is unknown. In this prospective, randomized, controlled crossover study, normoxia (air exposure for 50 min before sleep and sham stimulation for 6 h during sleep), IH (5 repeats of 5 min 10-12 % O2 alternating with 5 min air for 50 min, and sham stimulation for 6 h), ITES (air exposure for 50 min and 6 repeats of 30 min transcutaneous electrical stimulation alternating with 30 min of sham stimulation for 6 h), and IH&ITES (10-12 % O2 alternating with air for 50 min and transcutaneous electrical stimulation alternating with sham stimulation for 6 h) were administered to patients with OSA over four single-night sessions. The primary endpoint was difference in OSA severity between the interventions according to apnea-hypopnea index (AHI) and oxygen desaturation index (ODI). The efficacy was response to IH, ITES, IH&ITES defined as a ≥50 % reduction in AHI compared with normoxia. Twenty participants (17 male, 3 female) completed the trial. The median (IQR) AHI decreased from 14.5 (10.8, 17.5) events/h with normoxia to 6.9 (3.9, 14.8) events/h with IH (p=0.020), 5.7 (3.4, 9.1) events/h with ITES (p=0.001), and 3.5 (1.8, 6.4) events/h with IH&ITES (p=0.001). AHI was significantly different between IH and IH&ITES (p=0.042) but not between ITES and IH&ITES (p=0.850). For mild-moderate OSA (n=17), IH, ITES, and IH&ITES had a significant effect on AHI (p=0.013, p=0.001, p=0.001, respectively) compared with normoxia, but there were no differences in post hoc pairwise comparisons between intervention groups. No serious adverse events were observed. In conclusion, IH, ITES, and IH&ITES significantly reduced OSA severity. IH&ITES showed better efficacy in mild-moderate OSA than IH and was comparable to ITES. Our data do not support recommending IH&ITES over ITES for OSA.

Sex-dependent effects of chronic intermittent hypoxia: implication for obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) affects 10-26% of adults in the United States with known sex differences in prevalence and severity. OSA is characterized by elevated inflammation, oxidative stress (OS), and cognitive dysfunction. However, there is a paucity of data regarding the role of sex in the OSA phenotype. Prior findings suggest women exhibit different OSA phenotypes than men, which could result in under-reported OSA prevalence in women. To examine the relationship between OSA and sex, we used chronic intermittent hypoxia (CIH) to model OSA in rats. We hypothesized that CIH would produce sex-dependent phenotypes of inflammation, OS, and cognitive dysfunction, and these sex differences would be dependent on mitochondrial oxidative stress (mtOS).

METHODS

Adult male and female Sprague Dawley rats were exposed to CIH or normoxia for 14 days to examine the impact of sex on CIH-associated circulating inflammation (IL-1β, IL-6, IL-10, TNF-α), circulating steroid hormones, circulating OS, and behavior (recollective and spatial memory; gross and fine motor function; anxiety-like behaviors; and compulsive behaviors). Rats were implanted with osmotic minipumps containing either a mitochondria-targeting antioxidant (MitoTEMPOL) or saline vehicle 1 week prior to CIH initiation to examine how inhibiting mtOS would affect the CIH phenotype.

RESULTS

Sex-specific differences in CIH-induced inflammation, OS, motor function, and compulsive behavior were observed. In female rats, CIH increased inflammation (plasma IL-6 and IL-6/IL-10 ratio) and impaired fine motor function. Conversely, CIH elevated circulating OS and compulsivity in males. These sex-dependent effects of CIH were blocked by inhibiting mtOS. Interestingly, CIH impaired recollective memory in both sexes but these effects were not mediated by mtOS. No effects of CIH were observed on spatial memory, gross motor function, or anxiety-like behavior, regardless of sex.

CONCLUSIONS

Our results indicate that the impact of CIH is dependent on sex, such as an inflammatory response and OS response in females and males, respectively, that are mediated by mtOS. Interestingly, there was no effect of sex or mtOS in CIH-induced impairment of recollective memory. These results indicate that mtOS is involved in the sex differences observed in CIH, but a different mechanism underlies CIH-induced memory impairments.

The combination of intermittent electrical stimulation with acute intermittent hypoxia strengthens genioglossus muscle discharge in chronic intermittent hypoxia-pretreated rats

OBJECTIVE

Exploring whether the genioglossus discharge in chronic intermittent hypoxia(CIH) - pretreated rats could be enhanced by intermittent electrical stimulation combined with acute intermittent hypoxia(AIH).

METHODS

Rats were pretreated with CIH for 4 weeks and then were randomly divided into 6 groups: time control, intermittent electric stimulation, AIH, intermittent electric stimulation + AIH, continuous electric stimulation and continuous hypoxia exposure. The genioglossus discharges were recorded and compared before and after stimulation. Normoxic-treated rats were grouped and treated with the same stimulation protocols.

RESULTS

Intermittent electrical stimulation or AIH temporarily increased the activity of the genioglossus discharge, in which the degree of the increase was significantly higher in CIH-pretreated rats than in normoxic rats.After intermittent electrical stimulation, AIH evoked a sustained elevation of genioglossus discharge activities in CIH-pretreated rats, in which the degree of the increase was significantly higher than in rats induced by a single intermittent electric stimulation.

CONCLUSION

Intermittent electrical stimulation combined with AIH strengthens the genioglossus plasticity in CIH-pretreated rats.

Chronic intermittent hypoxia increases excitability and synaptic excitation of protrudor and retractor hypoglossal motoneurones

KEY POINTS

Dysfunctions in the hypoglossal control of tongue extrinsic muscles are implicated in obstructive sleep apnoea (OSA) syndrome. Chronic intermittent hypoxia (CIH), an important feature of OSA syndrome, produces deleterious effects on the motor control of oropharyngeal resistance, but whether the hypoglossal motoneurones innervating the tongue extrinsic muscles are affected by CIH is unknown. We show that CIH enhanced the respiratory-related activity of rat hypoglossal nerve innervating the protrudor and retractor tongue extrinsic muscles. Intracellular recordings revealed increases in respiratory-related firing frequency and synaptic excitation of inspiratory protrudor and retractor hypoglossal motoneurones after CIH. CIH also increased their intrinsic excitability, depolarised resting membrane potential and reduced K⁺ -dominated leak conductance. CIH affected the breathing-related synaptic control and intrinsic electrophysiological properties of protrudor and retractor hypoglossal motoneurones to optimise the neural control of oropharyngeal function.

ABSTRACT

Inspiratory-related tongue movements and oropharyngeal motor actions are controlled mainly by the protrudor and retractor extrinsic tongue muscles, which are innervated by the hypoglossal motoneurones. Chronic intermittent hypoxia (CIH), an important feature of obstructive sleep apnoea syndrome, produces detrimental effects on the contractile function of the tongue extrinsic muscles and the medullary inspiratory network of rodents. However, the impact of the CIH on the electrophysiological properties of protrudor and retractor hypoglossal motoneurones has not been described before. Using nerves and intracellular recordings in in situ preparation of rats (5 weeks old), we tested the hypothesis that CIH (FiO₂ of 0.06, SaO₂ 74%, during 30-40 s, every 9 min, 8 h/day for 10 days) increases the intrinsic excitability of protrudor and retractor motoneurones from the hypoglossal motor nucleus of rats. Recordings of hypoglossal nerve, before its bifurcation to innervate the tongue protrudor and retractor muscles, revealed that CIH enhances its pre-inspiratory, simultaneously with the presence of active expiration, and inspiratory activities. These changes were mediated by increases in the respiratory-related firing frequency and synaptic excitation of inspiratory protrudor and retractor hypoglossal motoneurones. Besides, CIH increases their intrinsic excitability and depolarises resting membrane potential by reducing a K⁺ -dominated leak conductance. In conclusion, CIH enhances the respiratory-related neural control of oropharyngeal function of rats by increasing the synaptic excitation, intrinsic excitability, and reducing leak conductance in both protrudor and retractor hypoglossal motoneurones. We propose that these network and cellular changes are important to optimise the oropharyngeal resistance in conditions related to intermittent hypoxia.