Genioglossus premotoneurons and the negative pressure reflex in rats

• Published in: The Journal of physiology Vol. 579; no. 2; pp. 515 - 526
• Main Authors: Chamberlin, Nancy L., Eikermann, Matthias, Fassbender, Philipp, White, David P., Malhotra, Atul
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01-03-2007; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Animals; Disease Models, Animal; Electromyography; GABA Agonists - pharmacology; Hypoglossal Nerve - physiology; Male; Motor Neurons - drug effects; Motor Neurons - physiology; Muscimol - pharmacology; Muscle, Smooth - innervation; Muscle, Smooth - physiology; Rats; Rats, Sprague-Dawley; Reflex - physiology; Respiratory; Respiratory Mechanics - physiology; Sleep Apnea Syndromes - etiology; Sleep Apnea Syndromes - physiopathology; Tongue - innervation; Tongue - physiology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2006.121889

Reflex increases in genioglossus (GG) muscle activity in response to negative pharyngeal pressure are important for maintenance
of upper airway patency in humans. However, little is known of the central circuitry that mediates this negative pressure
reflex (NPR). We used two approaches to determine which GG premotoneurons relay negative pressure-related information to the
hypoglossal motor nucleus. First, to identify GG premotoneurons, we injected pseudorabies virus (PRV152) into the GG muscle.
We found that medullary GG premotoneurons were concentrated mainly in the reticular formation adjacent to the hypoglossal
motor nucleus. Second, in order to determine whether these perihypoglossal neurons were involved in the NPR, we quantified
GG EMG responses to negative pressure applied to the isolated upper airway in anaesthetized rats before and after microinjection
of muscimol (9 nl; 0.25 m m ), a GABA-A receptor agonist, into the perihypoglossal premotor field. Pressures as low as −4 cmH 2 O increased inspiratory phase-related GG activity. The NPR was abolished following bilateral injections of muscimol into the
perihypoglossal premotor field at and up to 500 μm rostral to the obex. Muscimol in this location also increased the amplitude
of basal, unstimulated phasic GG activity. By contrast, inhibition of neurons caudal to the obex decreased phasic GG activity
but had no impact on the NPR. These results suggest that perihypoglossal GG premotoneurons near the obex mediate the NPR and
those caudal to the obex are important mediators of respiratory-related GG activity but are not involved in the NPR.