Nitric oxide modulates elicitation of reflex swallowing from the pharynx in rats

Abstract

. Nitric oxide modulates elicitation of reflex swallowing from the pharynx in rats. Am J Physiol Regul Integr Comp Physiol 291: R651-R656, 2006. First published April 6, 2006 doi:10.1152/ajpregu.00646.2005.-The pharynx is very important for elicitation of reflex swallowing. The region of the pharynx is innervated by the pharyngeal branch of the glossopharyngeal nerve (GPNph). Nitric oxide (NO) plays an important role in various physiological functions. The purpose of this study is to investigate the contribution of NO to reflex swallowing evoked by electrical stimulation of the GPN-ph. Swallowing was evoked in urethane-anesthetized rats by application of repetitive electrical stimulation (10-to 20-A amplitude, 10-to 20-Hz frequency, 1.0-ms duration) to the central cut end of the GPN-ph or superior laryngeal nerve. Swallowing was identified by electromyographic activity of the mylohyoid muscle. Latency to the first swallow and the interval between swallows were measured. Intravenous administration of N G -nitro-L-arginine (L-NNA, 0.6 mg/ kg), a nonselective inhibitor of NO synthase (NOS), extremely prolonged latency to the first swallow and the interval between swallows evoked by the GPN-ph. Intraperitoneal administration of 7-nitroindazole (5.0 mg/kg), a selective inhibitor of neuronal NOS, significantly prolonged latency to the first swallow and the interval between swallows evoked by the GPN-ph. Administration of L-arginine (an NO donor, 500 mg/kg) and sodium nitroprusside (an NO releaser, 0.6 mg/kg) restored the suppression of swallowing induced by the NOS inhibitor. Superior laryngeal nerve-evoked swallowing was suppressed by administration of a higher dose of L-NNA (6.0 mg/kg). Swallowing evoked by water stimulation of the pharynx was also suppressed by L-NNA (0.6 mg/kg). These results suggest that NO plays an important role in signal processing for initiation of reflex swallowing from the pharynx. nitric oxide synthase; pharyngeal branch; glossopharyngeal nerve; superior laryngeal nerve; L-arginine THE PHARYNX IS VERY IMPORTANT for elicitation of reflex swallowing. The regions of the pharynx involved in initiation of reflex swallowing have been analyzed in many studies (5-7, 15, 17, 21, 24 -28). One study showed that, in the cat, the posterior pillars are the most reflexogenic to mechanical stimulation, and the posterior pharyngeal wall is slightly less sensitive (27). Recently, Kitagawa et al. (17) examined the receptive regions for swallowing in the rat and reported that the palatopharyngeal arches, the posterior pharyngeal wall, the edge of the soft palate, the epiglottis, and the aryepiglottic fold are the most sensitive areas for reflex swallowing. On the basis of a study by Pommerenke (24), the receptive regions for swallowing in humans are considered to be essentially similar to those in animals.The effective regions for elicitation of reflex swallowing are innervated by the glossopharyngeal nerve (GPN) and the superior laryngeal nerve (SLN) (6,14,20,21,26,28,30). The SLN has been well known as ...

Modular and functionally-different descending recto-anal motor pathways in a rat model

“…The recto-anal function in the discrimination of gut content is mainly attributed to the enteric recto-anal reflex, which consists of rectal contraction and the internal relaxation of the anal sphincter. This demonstrates the importance of propulsion generated by the internal anal sphincter [11][12][13]. However, according to Bharucha (2006) both the internal and external anal sphincters are responsible for evacuative motion in the anal canal [14].…”

Facilitation of reflex swallowing from the pharynx and larynx

“…The trachea of the animal was cannulated to maintain respiration. Bipolar enamel-coated stainless steel wire electrodes (5 mm in diameter) were inserted into the left mylohyoid muscle, recognized as "obligate muscle" involved in swallowing movements, to record its electromyographic (EMG) activity (10,11,21). Swallowing was identified by the EMG activity of the mylohyoid muscle and by visual observation of laryngeal movement.…”

“…The superior laryngeal nerve (SLN), innervating the laryngeal region, is well known to be the most important afferent nerve for initiation of reflex swallowing (2)(3)(4)(5)(6)(7)(8). Animal studies have shown that electrical stimulation of the SLN elicits reflex swallowing (7)(8)(9)(10)(11)(12)(13). On the other hand, the role of the glossopharyngeal nerve (GPN) in reflex swallowing is less well understood (2,7).…”

Voluntary Versus Spontaneous Swallowing in Man

“…Some cues for the modulation of SS were obtained from the ''fetal swallowing'' studies in human and nonhuman fetuses [69][70][71]. Fetal swallowing that may be considered like SS develops in utero and occurs at much higher rates in comparison to adult spontaneous drinking activities [51,69,70].…”

“…NO, neural NO synthetase (NOS), angiotensin-II, and glutamate NMDA receptors are essential components in the pathways that mediate the high rate of swallowing. It is likely that other neurotransmitters (i.e., cholinergic and adrenergic) contribute to the regulation of SS in the fetus [70,71]. It was also proposed that the NMDA-NO pathway is involved in the central nervous system mechanism underlying the initiation of reflex swallow or SS [69,71,73].…”