Coordinated Respiratory Motor Activity in Nerves Innervating the Upper Airway Muscles in Rats

Responses evoked by electrical stimulation of the brainstem reticular formation in the jaw-opening and hypoglossal motor nerves of an arterially perfused rat preparation

The interneuronal system in the brainstem reticular formation plays an important role in elaborate muscle coordination during various orofacial motor behaviors. In this study, we examined the distribution in the brainstem reticular formation of the sites that induce monosynaptic motor activity in the mylohyoid (jaw-opening) and hypoglossal nerves using an arterially perfused rat preparation. Electrical stimulation applied to 286 and 247 of the 309 sites in the brainstem evoked neural activity in the mylohyoid and hypoglossal nerves, respectively. The mean latency of the first component in the mylohyoid nerve response was significantly shorter than that in the hypoglossal nerve response. Moreover, the latency histogram of the first component in the hypoglossal nerve responses was bimodal, which was separated by 4.0 ms. The sites that induced short-latency (<4.0 ms) motor activity in the mylohyoid nerve and the hypoglossal nerve were frequently distributed in the rostral portion and the caudal portion of the brainstem reticular formation, respectively. Such difference in distributions of short-latency sites for mylohyoid and hypoglossal nerve responses likely corresponds to the distribution of excitatory premotor neurons targeting mylohyoid and hypoglossal motoneurons.

Pathophysiology of Neuromuscular Respiratory Diseases

Gas exchange between the atmosphere and the human body depends on the lungs and the function of the respiratory pump. The respiratory pump consists of the respiratory control center located in the brain, bony rib cage, diaphragm, and intercostal, accessory, and abdominal muscles. A variety of muscles serve to fine-tune adjustments of ventilation to metabolic demands. Appropriate evaluation and interventions can prevent respiratory complications and prolong life in individuals with neuromuscular diseases. This article discusses normal function of the respiratory pump, general pathophysiologic issues, and abnormalities in more common neuromuscular diseases.

Recovery of respiratory function and autonomic diaphragm movement following unilateral recurrent laryngeal nerve to phrenic nerve anastomosis in rabbits

The authors studied restoration of respiratory function in rabbits, using the recurrent laryngeal nerve to restore function after the phrenic nerve had been severed. The results of this animal study are encouraging and suggest that a similar technique could possibly be used to help patients with severe cervical spinal cord injuries.

Coordinated control of the tongue during suckling-like activity and respiration

The tongue can move freely and is important in oral motor functions. Tongue movement must be coordinated with movement of the hyoid, mandible, and pharyngeal wall, to which it is attached. Our previous study using isolated brainstem-spinal cord preparations showed that application of N-methyl-D-aspartate induces rhythmic activity in the hypoglossal nerve that is coincident with rhythmic activity in the ipsilateral trigeminal motor nerve. Partial or complete midline transection of the preparation only abolishes activity in the trigeminal motor nerve; therefore, the neuronal network contributing to coordinated activity of the jaw/tongue muscles is located on both sides of the preparation and sends motor commands to contralateral trigeminal motoneurons. Arterially perfused decerebrate rat preparations exhibit stable inspiratory activity in the phrenic nerve, with efferent nerves innervating the upper airway muscles (the hypoglossal nerve, a branch of the cervical spinal nerve, the external branch of the superior laryngeal nerve, and the recurrent laryngeal nerve) under normocapnic conditions (5% CO₂). During hypercapnia (8% CO₂), pre-inspiratory discharges appear in all nerves innervating upper airway muscles. Such coordinated activity in the pre-inspiratory phase contributes to dilation of the upper airway and improves hypercapnia.