EFFECTS OF VERAPAMIL ON TWITCH POTENTIATION INDUCED BY INDIRECT CONDITIONING STIMULATION IN MOUSE PHRENIC NERVE-DIAPHRAGM MUSCLE PREPARATION

In aging Fischer 344 rats, phrenic motor neuron loss, neuromuscular junction abnormalities, and diaphragm muscle (DIAm) sarcopenia are present by 24 mo of age, with larger fast-twitch fatigue-intermediate (type FInt) and fast-twitch fatigable (type FF) motor units particularly vulnerable. We hypothesize that in old rats, DIAm neuromuscular transmission deficits are specific to type FInt and/or FF units. In phrenic nerve/DIAm preparations from rats at 6 and 24 mo of age, the phrenic nerve was supramaximally stimulated at 10, 40, or 75 Hz. Every 15 s, the DIAm was directly stimulated, and the difference in forces evoked by nerve and muscle stimulation was used to estimate neuromuscular transmission failure. Neuromuscular transmission failure in the DIAm was observed at each stimulation frequency. In the initial stimulus trains, the forces evoked by phrenic nerve stimulation at 40 and 75 Hz were significantly less than those evoked by direct muscle stimulation, and this difference was markedly greater in 24-mo-old rats. During repetitive nerve stimulation, neuromuscular transmission failure at 40 and 75 Hz worsened to a greater extent in 24-mo-old rats compared with younger animals. Because type IIx and/or IIb DIAm fibers (type FInt and/or FF motor units) display greater susceptibility to neuromuscular transmission failure at higher frequencies of stimulation, these data suggest that the age-related loss of larger phrenic motor neurons impacts nerve conduction to muscle at higher frequencies and may contribute to DIAm sarcopenia in old rats. NEW & NOTEWORTHY Diaphragm muscle (DIAm) sarcopenia, phrenic motor neuron loss, and perturbations of neuromuscular junctions (NMJs) are well described in aged rodents and selectively affect FInt and FF motor units. Less attention has been paid to the motor unit-specific aspects of nerve-muscle conduction. In old rats, increased neuromuscular transmission failure occurred at stimulation frequencies where FInt and FF motor units exhibit conduction failures, along with decreased apposition of pre- and postsynaptic domains of DIAm NMJs of these units.

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Anatomical variations of the phrenic nerve: an actualized review

Journal of Morphological Sciences ◽

10.4322/jms.070114 ◽

2015 ◽

Vol 32 (01) ◽

pp. 053-056 ◽

Cited By ~ 5

Author(s):

A. Prates Júnior ◽

L. Vasques ◽

L. Bordoni

Keyword(s):

Subclavian Artery ◽

Phrenic Nerve ◽

Subclavian Vein ◽

Internal Thoracic Artery ◽

Anatomical Variations ◽

Surgical Anatomy ◽

Diaphragm Muscle ◽

Normal Anatomy ◽

The Subject ◽

Superior Portion

Abstract Introduction: The phrenic nerve normally arises from ventral rami of C3, C4 and C5. It emerges laterally to the superior portion oflateral border of scalenus anterior muscle and presents a descendent course between subclavian artery and vein. It crosses anterior to internal thoracic artery and descends through the mediastinum, until the diaphragm muscle, to supply it with motor and sensitive fibers. Matherials and Methods: A bibliographic review was conducted, based on anatomy, neuroanatomy and surgical anatomy textbooks, published in Brazil and abroad, as well as a review of scientific articles, published over the last 20 years, available on research databases PubMed, Scielo, LILACS and MEDLINE, from keywords phrenic nerve, variation and anomaly. Results: Variations of the phrenic nerve are frequent, but they are not often discussed. Thus, we aimed to conduct an actualized review over the subject. Regarding the variations in the origin of the phrenic nerve, textbooks vaguely inform that it is mainly formed by C4, but the recent cadaveric studies pointed the segments C4 and C5 as the most common origin. About the variations in its course, the most described is its passage anterior to the subclavian vein, before reaching the thorax. However, the presence of accessory phrenic nerve represents the greatestvariation, mostly arising from nerve to subclavian. There are few reports in literature about the complications associated to these variations, but some are suggested, as the possibility of causing its damage during the puncture of the subclavian vein, when the nerve descends anterior to it, which may lead to a hemidiaphragmatic paresis. When variations are present, even simple procedures may cause injuries. Conclusion: Therefore it is fundamental to know the normal anatomy and the possible variations of the phrenic nerve, in order to perform safe procedures in its topography, as well as to enable a timely recognition of complications.

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