GASOTRANSMITTER MODULATION OF HYPOGLOSSAL MOTONEURON ACTIVITY

Obstructive sleep apnea (OSA) is characterized by sporadic collapse of the upper airway leading to periodic disruptions in breathing. Upper airway patency governed by genioglossal nerve activity originates from the hypoglossal motor nucleus. Mice with targeted deletion of the gene Hmox2, encoding the carbon monoxide (CO) producing enzyme, heme oxygenase-2 (HO-2), exhibit severe OSA, yet the contribution of central HO-2 dysregulation to the phenomenon is unknown. Using the rhythmic brainstem slice preparation, which contains the preBötzinger complex (preBötC) and the hypoglossal nucleus, we tested the hypothesis that central HO-2 dysregulation weakens hypoglossal motoneuron output. Disrupting HO-2 activity increased transmission failure as determined by the intermittent inability of the preBötC rhythm to trigger output from the hypoglossal nucleus. Failed transmission was associated with a reduced input-output relationship between the preBötC and the motor nucleus. These network phenomena were related to smaller inspiratory drive currents and reduced intrinsic excitability among hypoglossal neurons. In addition to HO-2, hypoglossal neurons also expressed the CO-regulated H ₂ S producing enzyme cystathionine □-lyase (CSE). H ₂ S abundance was higher in hypoglossal neurons of HO-2 null mice than wild-type controls. Disrupting CSE function normalized transmission in HO-2 null mice and an H ₂ S donor mimicked the effects of HO-2 dysregulation. These findings demonstrate a hitherto uncharacterized modulation of hypoglossal activity through the interaction of HO-2 and CSE-derived H ₂ S, and supports the perspective that centrally derived HO-2 activity plays an important role regulating upper airway control.