Postnatal maturation of phrenic nerve in children

The phrenic nerve at the pericardial level was examined postmortem in 17 children, ages 3 days to 8 years. Detailed macroscopic and histologic examination of the central nervous system in all patients disclosed no abnormalities. Quantitative developmental studies demonstrated that myelinated axons doubled in number from birth to age 1 year when a plateau was reached. The main period of growth in diameter of myelinated axons also corresponded to the first year when median diameters increased from 1.75 microns at 3 days of age to 3.0 microns by 8 months of age. Unmyelinated axons also grew significantly in the first 11 months when median diameters reached 1.4 microns. There was no significant increase in axonal diameter at later ages. The slope of the regression line for the number of myelin lamellae on axonal diameters increased with age until 6 months of age, whereas the dispersion around the regression lines decreased in the same period. This finding suggests a direct relationship between myelination and axonal growth. Significant maturation of the phrenic nerve occurs during the first year of life.

Identification of the axon pathways which mediate functional recovery of a paralyzed hemidiaphragm following spinal cord hemisection in the adult rat

Despite extensive neurophysiological work carried out to characterize the crossed phrenic phenomenon, relatively little is known about the morphological substrate of this reflex which restores function to a hemidiaphragm paralyzed by spinal cord injury. In the present study WGA-HRP was injected into normal and functionally recovered hemidiaphragm muscle in rats during the crossed phrenic phenomenon. The retrograde transynaptic transport characteristics of WGA-HRP was utilized to delineate the source of the neurons which mediate the crossed phrenic phenomenon. The results indicated that the neurons which drive phrenic motoneurons in spinal hemisected rats during the crossed phrenic phenomenon are located bilaterally in the rostral ventral respiratory group (rVRG) of the medulla. No transneuronal labeling of propriospinal neurons was noted in either normal or spinal-hemisected rats. Thus, propriospinal neurons do not relay respiratory drive to phrenic motoneurons. The neurons of the rVRG project monosynaptically to phrenic motoneurons. The present results suggest that both crossed and uncrossed bulbospinal pathways from the rVRG collateralize to both the left and right phrenic nucleic and functional recovery of a hemidiaphragm paralyzed by ipsilateral spinal cord hemisection is mediated by supraspinal neurons from both sides of the brain stem. These results are important to our complete understanding of the mechanisms which govern motor recovery in mammals following spinal cord injury.

[Number and thickness of myelinic fibres of the phrenic nerve of young and aged rats]

The phrenic nerve of albino rats was studied for age changes in number of fibres, myelin sheath thickness and axon calibre. There is no significant morphological differences between nerves from young and aged rats and no difference with age was found in the number of fibres, myelin sheath thickness and axon calibre.

The suprascapular nerve as re-interpreted by its communication with the phrenic nerve

A particular nerve bundle which may be called phrenicosuprascapular communication is, although only rarely, met with in various forms in man. By teasing, fibres of this communication are revealed to belong to the most anterior components of the brachial plexus, being closely associated with anterior nerves such as the phrenic, accessory phrenic, subclavius and even pectoralis. It is, therefore, obvious that the nervus suprascapularis conveys anterior fibres. It may be interpreted that the anteriormost nerve fibres may be separated from the main cord(s) and form an irregular network or plexus for themselves. It should be stressed that the n. suprascapularis consists of all the anterior components of the brachial plexus and that this is an anterior nerve.

Tumours involving the intrathoracic vagus and phrenic nerves demonstrated by computed tomography: anatomical features

Four cases of mediastinal tumours involving the intrathoracic vagus and phrenic nerves are presented and their computed tomographic (CT) features are described with particular attention to the intrathoracic course of these nerves. One case of mediastinal plexiform neurofibromatosis appeared as a series of low attenuation masses along the intrathoracic course of the nerves. Three examples of neurilemmomas of the vagus nerve appeared as masses with central low attenuation; one in the retrocaval area, one to the left of the aortic arch, and one in the right paraoesophageal area. Familiarity with the CT anatomy of the vagus and phrenic nerves will greatly assist in the diagnosis of mediastinal tumours.

Normal anatomy of the thoracic inlet as seen on transaxial MR images

The thoracic inlet can now be studied with high-resolution MR imaging. Recent advances in fold-over suppression (antialiasing software) allow for small fields of view without the usual problems of aliasing from the shoulders. This pictorial assay shows the normal anatomy that can be seen in this area on transaxial MR images. The vagus, phrenic, and recurrent laryngeal nerves can be seen as discrete entities. MR imaging can be used more often for pathologic conditions involving the lower portion of the neck and the thoracic inlet.

Morphology and innervation of the diaphragma of Myrmecophaga tridactyla

The diaphragma of 4 "Myrmecophaga tridactyla" was described. The diaphragma follows the general pattern of EDENTATA, but it has special features which make it possible to differentiate it from that of "Bradypus tridactylus.

Phrenic nerve paralysis following neck dissection

One of the complications of neck dissection to control regional metastatic disease in cancer of the head and neck is phrenic nerve paralysis. The resulting elevation of the ipsilateral diaphragm can be diagnosed on a postoperative chest X-ray and confirmed by fluoroscopy. Symptoms can be respiratory, cardiac or gastrointestinal. In a retrospective study, unilateral phrenic nerve paralysis was observed in 14 (8%) of 176 consecutive neck dissections. None of the patients with postoperative phrenic nerve paralysis displayed severe symptoms, although a significantly higher number sustained atelectasis with or without pulmonary infiltrates to complicate the postoperative course.

Ventral respiratory group projections to phrenic motoneurons: electron microscopic evidence for monosynaptic connections

The hypothesis that excitatory drive is transmitted monosynaptically from bulbospinal medullary respiratory neurons to spinal respiratory motoneurons was tested by an ultrastructural analysis of the phrenic motoneuronal pool in the rat. Combined anterograde labeling of the principal inspiratory bulbospinal neuron population (ventral respiratory group) and retrograde labeling of the phrenic motoneuron pool demonstrated the presence of labeled synaptic profiles, indicating that at least some bulbospinal inspiratory neurons make monosynaptic contacts with phrenic motoneurons. The synaptic boutons of ventral respiratory group neurons that were labeled in the phrenic nucleus had asymmetrical membrane densities at sites of synaptic contact with labeled phrenic somal or dendritic profiles, supporting the notion that this bulbospinal pathway has excitatory contacts with phrenic motoneurons. The morphological types of labeled boutons included three of the eight previously identified bouton types in the phrenic nucleus (Goshgarian and Rafols: Journal of Neurocytology 13:85-109, 1984), including the "S"-terminal, the "NFs"-terminal, and the "F"-terminal. There was no conclusive evidence of labeled double synapses, indicating that this type of synaptic contact is not common in the intact bulbospinal pathway.

[Respiratory neurons in medullary reticular formation which directly project to hypoglossal motoneurons in cats]

The present study was carried out to determine the location of the excitatory premotor neurons projecting to the hypoglossal motoneurons (XII MNs) that show respiratory activities in pentobarbital-anesthetized cats. Projections from these hypoglossal premotor neurons to the phrenic motoneurons were also investigated. The following results were obtained. (1) Injection of a fluorescent dye (Fast Blue, FB) into the hypoglossal nucleus and another fluorescent dye (Nuclear Yellow, NY) into the phrenic nucleus the cells in the medullary reticular formation labelled retrogradely with FB and/or NY mainly in the region ventrolateral to the nucleus of the tractus soritarius (vl-NTS) and dorsomedial to the nucleus ambiguus (dm-AMB). (2) There were respiratory neurons in the region vl-NTS and dm-AMB which antidromically responded to the stimulation of the hypoglossal nucleus. Some of them antidromically responded also to the stimulation of the phrenic nucleus. (3) Averaging of the hypoglossal and phrenic nerve discharges by spontaneous spikes of single respiratory neurons in the region vl-NTS and dm-AMB revealed a facilitation in the hypoglossal nerve discharge. In some of these excitatory hypoglossal premotor neurons, a facilitation was also revealed in the phrenic nerve discharge. It was concluded that there were respiratory neurons in the region vl-NTS and dm-AMB which were excitatory premotor neurons projecting to the XII MNs showing respiratory activities. Some of them had excitatory projections to both the hypoglossal and phrenic motoneurons via the bifurcating axons.

Retrophrenic location of the internal mammary artery graft

A technique of locating the internal mammary artery behind the phrenic nerve is described, which extends the application of internal mammary artery grafting to the lateral wall of the left ventricle. The technique also facilitates the performance of the posterolateral anastomosis between the internal mammary and circumflex coronary arteries.

[Detection of the pericardial branch of the phrenic nerve by silver impregnation method]

The pericardial branch (R. pericardiacus) of the phrenic nerve (N. phrenicus) was examined in 14 pericardia of 8 male and 6 female adult Japanese cadavers. Specimens were impregnated with silver nitrate, and cleared and mounted in lactic acid. A pericardial branch was detected in the right side of one specimen (No. 273, male). This branch arose from the phrenic nerve at approximately the same level as the root of lung. The branch ran from the cervical plexus together with the proper phrenic nerve. The distribution of this branch to the pericardium could not be determined as the branch was accidentally cut near the above mentioned arising point during the anatomical practice. Even by this impregnation method, the pericardial branch of the phrenic nerve could not be detected in any other specimens.

Right phrenic nerve: anatomy, CT appearance, and differentiation from the pulmonary ligament

The pulmonary ligament appears on computed tomographic (CT) sections as a thin, high-attenuation line, frequently seen above or at the level of the diaphragm and usually extending from the region of the esophagus. However, another line coursing laterally from the midportion of the inferior vena cava has also been identified as the pulmonary ligament. The authors examined sections from eight cadavers and 80 chest CT examinations to more clearly delineate the pulmonary ligament from this second structure. Anatomic and CT correlation proves that the line seen at the midportion of the inferior vena cava represents the right phrenic nerve and that the right pulmonary ligament is located posterior to it.

Spinal cord localization and characterization of the neurons which give rise to the accessory phrenic nerve in the adult rat

This study describes the spinal cord location and morphology of the neurons which give rise to the accessory phrenic nerve in the rat. The results indicate that the cell bodies of the accessory phrenic nerve are a caudal extension of the phrenic nucleus. These cell bodies are located from cervical spinal cord levels C5 to upper C6 and comprise approximately 11% of the total phrenic motoneuron pool. The substantial phrenic contribution indicates the importance of the accessory phrenic nerve in both experimental and clinical manipulations of diaphragm innervation.

Distribution of corticospinal motor fibres within the cervical spinal cord with special reference to the phrenic nucleus: a WGA-HRP anterograde transport study in the cat

The anterograde transport of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) was used to demonstrate the corticospinal fibres which originate in the motor cortex and project to the cervical spinal cord, specifically to the phrenic nucleus, in the cat. Following injections of WGA-HRP into the pericruciate cortex large numbers of fibres were labelled in the contralateral lateral and ventral funiculi and fewer fibres were labelled in the ipsilateral lateral and ventral funiculi. Labelled corticospinal motor fibres entered the gray matter laterally in laminae V and VI and terminated within these two laminae as well as throughout the entire extent of lamina VII. A few labelled fibres were present in medial lamina VIII and also in lamina IX where they were in close association with the phrenic motoneuron pool. Labelling was present in the gray matter at both sides, with a stronger labelling contralaterally. Labelled axons were also seen crossing from each side of the gray matter to the other side. The results suggest that in the cat the corticospinal motor fibres have a wider distribution in the spinal gray matter than has been previously shown, and that corticospinal motor axons may be in direct contact with phrenic motoneurons.

Anatomically selective peripheral nerve ablation using intraneural ricin injection

Anatomically selective destruction of sensory and motor neurons based upon which nerve contains the corresponding axons can be accomplished by intraneural pressure microinjection of the toxic lectin, ricin. Ricin is taken up by axons at the injection site and axonally transported to perikarya resulting in destruction of the neurons. In the present report, we describe a reliable procedure for making such lesions using pressure microinjection of ricin into nerve trunks. Consistent, complete lesions restricted to the appropriate sensory and motor neurons are documented after injection of the vagus, hypoglossal, phrenic and sciatic nerves and the superior cervical ganglion. Complete vagal ablations could be achieved with 100 ng or less of ricin; whereas, 1-3 micrograms was required to obtain similar results with hypoglossal and sciatic nerves. Although most neurons are dead within 24 h after the injection, survival times of 10-14 days may be necessary for complete disappearance of poisoned neurons. This technique can be valuable in making highly selective lesions for anatomical, neurochemical and neurophysiological experiments.

Origin and distribution of phrenic primary afferent nerve fibers in the spinal cord of the adult rat

Previous studies from this laboratory have localized and morphologically characterized phrenic motor neurons in the rat spinal cord at light and electron microscopic levels. The present investigation used a modification of the TMB method for the retrograde transport of horseradish peroxidase (HRP) to describe at light microscope levels the origin and distribution of phrenic primary afferent axons in the adult rat spinal cord. Dry HRP crystals were applied to the central stump of the transected phrenic nerve in the neck to label spinal ganglion cell bodies and thus determine the levels of origin of afferent axons in the phrenic nerve. Camera lucida drawings were then made from serial sections through the appropriate spinal cord levels to determine the specific distribution of transganglionically labeled phrenic central axonal processes within the spinal cord. HRP-labeled phrenic primary neurons were observed in the C3 to C7 spinal ganglia. The camera lucida studies indicated that the transganglionically labeled central processes of phrenic primary afferent axons distributed into the dorsal horn at the C4 and C5 levels of the spinal cord. Furthermore, central processes distributing to C5 were more numerous than those that distributed to C4. Afferent axons were never seen in the dorsal horn at C3, C6, or C7. As spinal ganglion cells were labeled at C3 above and C6 and C7 below, it follows that central processes of phrenic afferent fibers descend and ascend in the dorsal columns of the spinal cord before distributing into the dorsal horn. Specifically, the labeled primary afferent axons and their collateral branches were found in the fasciculus cuneatus, and in laminae I, II, III, and IV of the dorsomedial aspect of the dorsal horn. The function of these central axonal processes is unknown, but based on a comparison of our morphologic data with previous physiological and anatomical studies, we suggest that phrenic afferent fibers may arise from proprioceptors (muscle spindles and Golgi tendon organs), nociceptors, or rapidly adapting mechanoreceptors (Pacinian corpuscles) within the diaphragm.

Identification of phrenic afferents to the external cuneate nucleus: a fluorescent double-labeling study in the cat

In the cat, C5-C6 dorsal root ganglion cells related to phrenic afferents projecting directly to the ipsilateral external cuneate nucleus (ECN) were submitted to a double-labeling procedure using anterogradely transported Fast Blue and retrogradely transported Nuclear yellow. These afferents, certainly related to muscle spindles and/or Golgi tendon organs, are very few and terminate preferentially in the intermediate and rostral parts of the ECN. Our results confirm previous electrophysiological and histological studies on the participation of phrenic afferents to the spino-cuneo-cerebellar pathway ascending through the dorsal columns.

Localization of the spinal accessory motoneurons in the cervical cord in connection with the phrenic nucleus: an HRP study in cats

The localization of the spinal accessory motoneurons (SAMNs) that innervate the accessory respiratory muscles, the sternocleidomastoid (SCM) and trapezius (TP) muscles, was identified in the cat using the horseradish peroxidase (HRP) method. In the cases of HRP bathing of the transected spinal accessory nerve (SAN), HRP-labeled motoneurons were observed ipsilaterally from the C1 to the rostral C6 segments of the spinal cord. Labeled neurons were located principally in the medial and central regions of the dorsomedial cell column of the ventral horn in the C1 segment, in the lateral region of the ventrolateral cell column in the C2-C4 segments, between the ventrolateral and ventromedial cell columns in the C5 segment and in the lateral region of the ventromedial cell column in the C6 segment. In the cases of HRP injection into either SCM or TP muscles, labeled SCM motoneurons were found in the C1-C3 segments of the spinal cord and labeled TP motoneurons were chiefly localized more caudally within the spinal accessory nucleus. The present study revealed that, in the C5 and C6 segments, the SAMNs have a very similar topographic localization to the phrenic nucleus in the ventral horn. This finding implicated the functional linkage of the SAMNs with the phrenic motoneurons in particular types of respiration.

A retrograde tracer strategy using True Blue to label the preganglionic parasympathetic innervation of the abdominal viscera

A simple and reliable method for labeling the preganglionic neurons which innervate the abdominal viscera is described. Infusion of a True Blue (TB) suspension in several different concentrations directly into the peritoneal cavity consistently labeled the medullary vagal nuclei including the dorsal motor nucleus (DMN), nucleus ambiguus (NA), and retrofacial nucleus (RFN). Quantitative analysis of cell labeling after 30 microliters infusions of a large range of concentrations of TB (0.001-20.0%) showed that: (1) as little as 0.0075 mg of TB was sufficient to label DMN cells distinctly while only 0.075 mg (or larger) doses of TB were adequate for labeling cells of the NA and the RFN, and (2) doses of 3.0 mg (or greater) labeled the maximum number of cells in the DMN, NA, and RFN. Qualitative analysis suggested that medium range doses (0.075-0.75 mg) were optimal for discerning cell size and type throughout each of these nuclei.

Projections from the ventral respiratory group to phrenic and intercostal motoneurons in cat: an autoradiographic study

Anterograde transport of tritiated amino acids (leucine, lysine, and proline) was used to examine the spinal projections of respiratory premotor neurons in the ventral respiratory group (VRG) of cats. This population of neurons corresponds anatomically with the nucleus ambiguus-retroambigualis. Small volumes (20 to 50 nl) of tritiated amino acids were pressure ejected into the middle of the VRG through a micropipette which permitted simultaneous recording of respiratory modulated activity. In two cats injections were made caudal to the obex in regions which contained expiratory modulated neurons. In five cats injections were made rostral to the obex in regions containing inspiratory neurons. After a 2-week survival period, cats were anesthetized and perfused. The entire neuraxis was removed and processed using standard autoradiographic techniques. Transport of tritiated amino acids revealed a marked bilateral projection to lamina IX of the spinal cord at the C4 to C6 level and a primarily contralateral projection to laminae VIII and IX in the thoracic spinal cord. Distinct descending pathways to the phrenic motor neurons were observed in the lateral funiculus and in the ventral funiculus; descending fibers to the intercostal motoneurons in the thoracic cord appeared to be restricted to the ventral funiculus. Labeling of axon terminals in both the cervical and thoracic cords was confined to ventral horn regions which contain motoneurons. These results suggest that monosynaptic projections from brainstem bulbo-spinal neurons to spinal motoneurons are important in controlling respiratory movements of the diaphragm and intercostal muscles.

Cells of origin of corticospinal projections to phrenic and thoracic respiratory motoneurones in the cat as shown by retrograde transport of HRP

A combined electrophysiological and histological approach was employed to identify neurones within the motor cortex which project to the vicinity of spinal respiratory motoneurones, and which may be involved in the alteration of the pattern of breathing under certain conditions. Recording of respiratory phased activity from phrenic, or from thoracic motoneurones within either the upper (T3-4) or lower (T8-9) segments, was followed by the iontophoretic injection of HRP at these recording sites. After injections within the cervical or thoracic ventral horn, 219 cells were retrogradely labelled in 14 experiments. The majority of these cells (88%) were labelled contralateral to the injection site. Following the injection of HRP into the phrenic nucleus, labelling was observed at two major sites within the anterior sigmoid gyrus (ASG), one along the anterolateral edge of the cruciate sulcus, and the other along the ventrolateral border of the ASG. In contrast, cells labelled after injections into the thoracic ventral grey matter were located more medially within the ASG and the posterior sigmoid gyrus (PSG). The populations of cells labelled following phrenic and thoracic injections overlapped, primarily at the lateral edge of the cruciate sulcus. The somas of labelled cells were pyramidal, round or oval. The mean diameters of cortical cells labelled after injections into the lower or upper thoracic segments were 30.5 +/- 6.2 and 31.5 +/- 5.6 respectively, which were not significantly different in size. However, they were significantly larger than the mean diameter of the cells labelled from injections into the phrenic nucleus (22.7 +/- 4.2 micron).(ABSTRACT TRUNCATED AT 250 WORDS)

The identification of brainstem neurones projecting to thoracic respiratory motoneurones in the cat as demonstrated by retrograde transport of HRP

Brainstem neurones which project to the immediate vicinity of the spinal motoneurones which supply the intercostal and abdominal respiratory muscles were identified by means of the retrograde transport of horseradish peroxidase (HRP). A combined electrophysiological and histological technique was used in which recording of phasic inspiratory or expiratory motoneurone activity within upper (T3-T4) or lower (T8-T9) thoracic segments was followed by the ion-tophoretic injection of HRP at these recording sites. HRP labelled cells were concentrated in those brainstem regions known to contain phasic respiratory neurones, namely the ventrolateral nucleus of the solitary tract (vl-NTS) or dorsal respiratory group (DRG), the ambiguus complex or ventral respiratory group (VRG) and the parabrachial pontine (PB) nuclei. In 18 cats, 248 cells were labelled in these three respiratory regions of the brainstem while 668 were much more diffusely distributed in other regions of the medulla and pons. The ipsilateral and contralateral contributions within the respiratory regions were respectively; 23%:77% (DRG), 33%:67% (VRG), 95%:5% (PB). These results are considered in the general context of previous electrophysiological and histological findings, but also with particular reference to a related study of the projections from brainstem neurones to the phrenic nucleus [32].

Catecholamine innervation of cervical dendrite bundles: possible phrenic nucleus innervation

The catecholaminergic innervation of three recently described dendrite bundles (midline, central and lateral) in the cervical spinal cord of the adult Long-Evans hooded rat [41] was examined using Golgi impregnation, fluorescence histochemistry for catecholamines, and cholinesterase histochemistry. The midline and lateral bundles were similar in appearance to those described by the Scheibel and Scheibel [50,51], while the central bundle, present in the region of the phrenic nucleus, has not been described previously. Analysis of Golgi-Cox impregnated horizontal sections demonstrated the presence of fine varicose fibers within all three bundles. These profiles entered the bundles at right angles, either singly or within small transverse dendritic subunits, then turned in a rostral or caudal direction, and coursed adjacent to dendrites of motoneurons in the bundles. Catecholamine histofluorescence in horizontal sections revealed abundant varicosities within all three bundles, similar in size and appearance to the varicose fibers seen in Golgi-Cox impregnated sections. Catecholamine fibers entered the dendrite bundles at right angles then turned rostrally or caudally and coursed horizontally within the bundles. Varicose fluorescent profiles formed pericellular rings around the motoneurons and linear profiles adjacent to the dendrites, sometimes outlining the entire proximal portion of primary dendrites. Catecholamine fibers entered the dendrite bundles at right angles then turned rostrally or caudally to course adjacent to the dendrites within the bundles. Cholinesterase histochemistry in alternate sections revealed staining of motoneurons and their dendrites, and confirmed the location of the catecholamine varicosities within the motoneuron dendrite bundles.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of phrenic afferents in the dorsal columns: a fluorescent double-labeling study in the cat

In this study in the cat, the tracer combination of the anterogradely transported Fast Blue and the retrogradely transported Nuclear Yellow was used to label dorsal root ganglion cells related to phrenic afferents running up through the ipsilateral dorsal column. These afferents are few; some of them leave the dorsal column near their segment of entry. Their localization in the dorsal column suggests that they are related to tendon and muscle receptors, which confirms previous electrophysiological studies.