Digastric muscle activities in anoxic infant rats

Abstract

The digastric muscle acts for both feeding (including mastication and swallowing) and respiration. In this study, we examined whether or not the muscle activity is detectable during anoxia in developing rats. Rats at 4 different ages, days 5, 10, 16, and 24, were exposed to 100% N2 under pentobarbital or ketamine-xylazine anesthesia, and the electromyograms of digastric muscles (dEMG) and the diaphragm (diaEMG) were examined simultaneously. Prior to the anoxic exposure, at all ages, the dEMG was similar to or less apparent than the diaEMG, which was detected at each inspiratory movement. In anoxia, we first observed dEMG activity, mostly sporadic (days 5 and 10) or mostly tonic (days 16 and 24), when diaEMG activity was temporarily suppressed (we termed it Phase 1). Second, synchronous phasic or tonic dEMG and phasic diaEMG were recorded temporarily before terminal apnea (we termed it Phase 2). These phenomena were also obtained in vagotomized rats (all ages) or in rats injected with the N-methyl-D-aspartate receptor antagonist MK-801 (dizocilpine (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate) (days 16 and 24). In conclusion, our results suggest that in anoxia, dEMG activity is detectable during diaEMG suppression in early anoxia, irrespective of the developmental age, the anesthetic (pentobarbital or ketamine-xylazine), vagotomy, or MK-801 injections.

Active expiratory oscillator regulates nasofacial and oral motor activities in rats

“…It is possible that in the in situ decerebrated preparation the pathway that exists allowing the MhN to be incorporated into events that require synchronization with inspiratory breathing, such as gasping and hypoxia, is being utilized to transmit this signal in the absence of cortical control. However, it has been reported previously that neonatal and juvenile rats present inspiratory‐related activity in digastric muscle during basal breathing (Saiki & Matsumoto, ), suggesting that the observed pre‐I and inspiratory modulation of MhN in normocapnia is an essential component of the respiratory control of oropharyngeal resistance, at least in juvenile rats.…”

“…The same is true for the glottal control of laryngeal airway resistance during pre‐I and inspiratory phases (Paton & Dutschmann, ; Richter & Smith, ). On the other hand, oral breathing associated with jaw movements is presumed to be a transient behaviour that appears during airway obstruction or high chemical drive (Carlo et al., ; Saiki & Matsumoto, ). In this regards, previous studies reported inspiratory‐related activity in jaw‐opening submandibular muscles (including digastric) during asphyxia and apnoea (Carlo et al., ).…”

“…A restriction of lung expansion, airway obstruction or high chemical drive all induce oral breathing associated with jaw movements (Bartlett & St John, ; Carlo et al., ; Saiki & Matsumoto, ; Song & Pae, ). Oral breathing is produced by trigeminal motoneurons, which consist of the jaw‐opening motoneurons, innervating the anterior digastric and mylohyoid muscles, and the jaw‐closing motoneurons innervating the masseter, temporal and pterygoid muscles (Oka et al., ).…”

“…Oral breathing, associated with jaw movements, is presumed to be a survival skill during airway obstruction or high chemical drive (Carlo, Miller, & Martin, ; Saiki & Matsumoto, ), but also gasping (St‐John et al., ). Jaw movements are produced mainly by trigeminal motoneurons, which cause jaw opening, driven by motoneurons located in the ventromedial division of the trigeminal nucleus, and jaw closing mediated by motoneurons in the dorsolateral division (Mizuno, Konishi, & Sato, ; Oka et al., ).…”

Population calcium imaging of spontaneous respiratory and novel motor activity in the facial nucleus and ventral brainstem in newborn mice

“…Activation of ala nasi muscles results in a decrease in nasal and total respiratory resistance (Mathew, 1984). The platysma and digastric muscles show respiratory‐modulated activity under high respiratory drive (De et al 1986; Saiki & Matsumoto, 2004), the mentalis muscle under quiet breathing (Dutra et al 2006). Thus, we surmise that the brainstem of newborn mice already has in place the pattern forming circuits that are necessary to activate the parts of the facial nucleus needed to maintain airway patency.…”