Motor innervation of striated oesophageal muscle. Part 2. Characteristics of the oesophagomotor fibres in the rat studied by implanting the vagus nerve into a skeletal muscle

In 12 rats the right vagus nerve distal to its recurrent laryngeal branch was implanted into the inferior segment of the denervated sternohyoid muscle. One month after implantation the first signs of neuromuscular transmission at the vagal motor endings could be recorded. Two months after implantation the reinnervated muscles showed vigorous contractions on electrical stimulation of the vagus nerve. During the performance of propulsive waves of the oesophagus the implanted vagus nerve caused clonic to tetanic contractions of the sternohyoid muscle, thus proving the oesophagomotor genesis of the reinnervating nerve fibres. In addition, the vagus-innervated motor end-plates were shown to exhibit the same ultrastructural peculiarities as the original neuromuscular junctions of the oesophagus. In sections stained for cholinesterase it could be demonstrated that the oesophagomotor fibres had preferentially reinnervated the denervated motor end-plates. In many instances the subneural apparatus was not completely covered by the vagal axon terminals. Newly formed, ectopic vagal motor endings were few in number and confined to muscle fibres immediately adjacent to the site of nerve-implantation. Six months after implantation some of the vagal motor endings showed signs of degeneration. As in the oesophagus, the reinnervating oesophagomotor fibres proved to be unmyelinated, sometimes forming a plexus-like intramuscular network before terminating at motor end-plates. Myelinated vagal nerve fibres were also observed running between the skeletal muscle fibres, but they did not establish any demonstrable form of neuromuscular contacts. It was concluded that, in the rat, the myelinated fibres of the oesophageal nerves are afferent, whereas the oesophagomotor fibres, although supplying striated muscle, are unmyelinated.     

Control of the heart rate by sympathetic nerves in cats

Pre- and postganglionic sympathetic nerves were electrically stimulated and heart rate was recorded in chloralose-anaesthetised cats. The vagal nerves and white rami were cut on both sides. Electrical stimulation was performed with a 15- or 30-s train of 0.2-ms pulses at a frequency of 30 Hz. The control heart rate was 150 beats/min. Heart rate was increased when the T3 white ramus on the left (52 beats/min above control) and T3, T4 white rami on the right side (100 beats/min above control) were stimulated electrically. The magnitude of the heart rate increase declined when the neighbouring thoracic white rami were stimulated. The increase of the heart rate was caused by group B preganglionic fibres. Electrical stimulation of the sympathetic fibres in the right vagus nerve and the right inferior cardiac nerve increased the heart rate by 92 beats/min and by 67 beats/min above the control level respectively. Electrical stimulation of the left inferior cardiac nerve, the left middle cardiac nerve and the sympathetic fibres in the left vagus nerve resulted in an increase of the heart rate of 43 beats/min, 30 beats/min and 49 beats/min from the control level respectively. This indicates that a majority of the preganglionic cardiac sympathetic fibres, whose activity influences the heart rate, originate from the T3 and T4 segments of the spinal cord. The majority of the postganglionic cardiac sympathetic fibres which affect the heart rate are located in the vagal nerves.     

Responses of cardiac vagus and sympathetic nerves to excitation of somatic and visceral nerves

Somato-vagal and somato-sympathetic reflex responses were studied by recording simultaneously the activity of cardiac vagal and sympathetic efferents following excitation of various somatic (and 1 visceral) nerves in chloralose-anesthetized dogs.Stimulation of pure cutaneous (infraorbital, superficial radial, sural nerves), muscle (gastrocnemius, hamstring nerves) and mixed nerves (sciatic, brachial, intercostal, spinal) with short trains of pulses inhibited the activity of cardiac vagus nerve and excited that of cardiac sympathetic nerve after a latency of approximately 40–60 ms, depending on the nerve stimulated. These responses were followed by the opposite response, i.e. excitation of vagus and long-lasting inhibition (`silent period') of sympathetic nerve activity. These biphasic reflex responses recorded from both autonomic nerves had similar latencies so that a clear reciprocal relationship was observed. In addition to the above reflex responses which were observed in most instances, two peaks of excitation of short duration were recorded from the vagus nerve, in some instances, and an ‘early (spinal) reflex’ in sympathetic nerve was also observed. Both excitatory and inhibitory responses described above in either nerve were readily evoked by excitation of Group II (Aβ), but not Group I (Aα), afferent fibers and increased in magnitude when Group III (Aδ) afferents were also excited. Group IV (C) afferent contributed insignificantly to the somato-vagal reflex. The vagus nerve discharge evoked by sinus nerve stimulation was inhibited during reflex inhibition produced by somatic nerve stimulation. The latency of such inhibition was less than 20 ms and lasted for 100 ms after sural nerve stimulation. We conclude that, as in case of the baroreceptor reflex and autonomic component of the ‘defense reaction’, the somato-vagal and somato-sympathetic reflex responses are reciprocal in nature.     

Spinal segmental sympathetic outflow to cervical sympathetic trunk, vertebral nerve, inferior cardiac nerve and sympathetic fibres in the thoracic vagus

The spinal segmental localization of preganglionic neurons which convey activity to the sympathetic nerves, i.e. vertebral nerve, right inferior cardiac nerve, sympathetic fibres in the thoracic vagus and cervical sympathetic trunk, was determined on the right side in chloralose anaesthetized cats. For that purpose the upper thoracic white rami were electrically stimulated with a single pulse, suprathreshold for B and C fibres, and the evoked responses were recorded in the sympathetic nerves. The relative preganglionic input from each segment of the spinal cord to the four sympathetic nerves was determined from the size of the evoked responses. It was found that each sympathetic nerve receives a maximum preganglionic input from one segment of the spinal cord (dominant segment) and that the preganglionic input gradually decreased from neighbouring segments. The spinal segmental preganglionic outflow to the cervical sympathetic trunk, thoracic vagus, right inferior cardiac nerve and vertebral nerve gradually shifted from the most rostral to the most caudal spinal cord segments. In some cases, a marked postganglionic component was found in the cervical sympathetic trunk. It was evoked by preganglionic input from the same spinal cord segments which transmitted activity to the vertebral nerve. These results indicate that there is a fixed relation between the spinal segmental localization of preganglionic neurons and the branch of the stellate ganglion receiving the input from these neurons.     

The excitation of the fibers of the funiculus dorsalis medullae spinalis during the stimulation of different groups of cutaneous and muscle nerve fibers in the cat]

Electric stimulation of various groups of fibres of cutaneous and muscle nerve of cat has been studied for its effect on action potentials in the gray dorsal column fibres, Registration was performed at the level L2--L3 from ipsi- and contralateral dorsal columns, using needle electrodes. Action potentials of dorsal columns, arisen by stimulation of cutaneous nerves, had a more complex form than those of stimulated muscle nerves. Nonmyelinated fibres of a cutaneous nerve are shown to relate to those of dorsal columns. Excitation of high-threshold A- and C-fibres activates the most fast-conducting fibres of dorsal columns. When a stimulus was applied to all fibres of the cutaneous nerve, the action potentials with conduction velocities of 146-0.24 m/s were recorded in dorsal columns. It was shown that such conduction velocities remained in dorsal columns to level C7. Stimulation of muscle nerves excited only myelinic fibres of dorsal columns, the conduction velocities ranging from 90 to 2.3 m/s. By alternating stimulation of either nerve with a 30-300 ms interval we decreased the action potential amplitude of the nerve that was the second to be stimulated. It is likely be related to convergence of the cutaneous and muscle nerve inputs in the spinal cord on the same neurons. A suggestion is made that faster transfer of high-threshold cutaneous signals in dorsal column are associated with the necessity of rapid information about damaging stimulation.     

Innervation of the guinea pig trachea: a quantitative morphological study of intrinsic neurons and extrinsic nerves

The innervation of the guinea pig trachea was studied in wholemount preparations stained for acetylcholinesterase, catecholamines, and substance P immunoreactivity and by electron microscopy. The majority of parasympathetic and afferent nerve fibres arrive from the vagus via branches of the recurrent laryngeal nerves. The recurrent laryngeal nerves are composed of several fascicles comprising 600-700 small myelinated fibres (2-5 microns diameter) and about 1,000-2,000 unmyelinated fibres; both components exit from the nerve and project in fine branches to the trachea. A separate component of 200-250 large myelinated fibres (more than 5 microns diameter) runs the full length of the nerve and innervates the striated muscles of the larynx. The recurrent laryngeal nerves are slightly asymmetric in their origin, length, number, and composition of fibres, with the right nerve being shorter but with more numerous and thinner myelinated fibres. At the distal end of the recurrent nerve, a fine branch called the ramus anastomoticus connects it to the superior laryngeal nerve. In the tracheal plexus, there are on average 222 ganglion cells (range 166-327), distributed mostly in small ganglia of 12 or fewer neurons. The ganglionated plexus is situated entirely outside the tracheal wall, overlying the smooth muscle. Ligation experiments show that sympathetic nerve fibres reach the trachea with the recurrent nerves via anastomoses between the sympathetic chain and vagus nerves, or occasionally with recurrent nerves directly, the largest being at the level of the ansa subclavia. There are also perivascular sympathetic nerve plexuses. Substance P immunoreactive fibres enter the trachea from the vagus nerves and by pathways similar to those of sympathetic nerves. There are also paraganglion cells within the recurrent laryngeal nerve that contain catecholamines and are surrounded by substance P immunoreactive fibres. After cervical vagotomy, all the large myelinated fibres of the ipsilateral recurrent laryngeal nerve degenerate and so do all but 10 or 20 small myelinated fibres and all but a few unmyelinated fibres. Degenerating fibres are found within the entire tracheal plexus, indicating bilateral innervation. The small myelinated fibres that survive cervical vagotomy probably represent sympathetic or afferent nerves with their cell bodies located in sympathetic or dorsal root ganglia.     

Reinnervation of a striated muscle by vagal sensory axons

Fibres of the sterno-cleido-mastoid (s.c.m.) muscle normally innervated by effects of the accessory nerve have been reinnervated by afferent fibres of the vagus nerve after supranodose vagal-accessory nerve anastomoses or direct implantation of the vagus nerve into the s.c.m. in 58% of the rabbits, 60% of the cats and 75% of sheep in which experiments were performed. Afferents of the vagus growing from cell bodies of the nodose ganglion after severance of central connections can replace the efferent of motor supply to the muscle. Evidence that there was reinnervation of the s.c.m. muscle by vagal afferent fibres was provided from the observations that: (i) electrical stimulations of the anastomosed cervical vagus nerve elicited potentials in the s.c.m. muscle which were abolished by local anaesthesia or final section of the nerve proximal to the site of stimulation; (ii) discharges recorded as bursts of electromyographic potentials occurred during spontaneous movements of larynx, respiratory tract, oesophagus and stomach and on their mechanical or evoked stimulation; and (iii) horseradish peroxidase injected into the reinnervated s.c.m. muscle was detected in somata of ipsilateral nodose ganglia cells. The afferent fibres contributing to the reinnervation were confirmed to be cholinergic as transmission was blocked by gallamine and histochemical evidence obtained of cholinergic motor end-plates. Factors which may have limited the small extent of reinnervation--only one vagal sensory axon out of 600 is able to form functional connections--are discussed.     

Adrenergic innervation of vasa and nervi nervorum of optic, sciatic, vagus and sympathetic nerve trunks in normal and streptozotocin-diabetic rats

Adrenergic nerves were studied in nervi nervorum and perivascular nerve plexus of vasa nervorum in whole-mount nerve sheath preparations of optic, sciatic and vagus nerves and in the paravertebral sympathetic chain in normal and streptozotocin-treated diabetic rats. A substantial or complete loss of fluorescent adrenergic fibres around blood vessels in the optic nerves was observed 8 weeks after induction of diabetes. This was in marked contrast to the increase in perivascular adrenergic fibres in the sciatic, vagus and sympathetic chain nerve trunks of the same animals at the same time. Assays of noradrenaline levels in whole nerve segments also showed that they were not biochemically detectable in the optic nerves but were significantly higher in the vagus of diabetic animals (P less than 0.05). There was also an increase in numbers of mast cells in the vicinity of vasa nervorum of diabetic nerves.     

Enteric co-innervation of striated muscle fibres in human oesophagus

Abstract  Oesophageal striated muscle of several mammalian species receives dual innervation from both vagal motor fibres originating in the brain stem and enteric nerve fibres originating in myenteric ganglia. The aim of this study was to investigate this so-called enteric co-innervation in the human oesophagus. Histochemical and immunohistochemical methods combined with confocal laser scanning microscopy were utilized to study innervation of 14 oesophagi obtained from body donors (age range 47–95 years). In addition, the distribution of striated and smooth muscle in longitudinal and circular layers of the tunica muscularis was studied semiquantitatively. The upper half of the oesophagus was built up of both muscle types with a predominance (>50–60%) of striated muscle, whereas the lower half consisted of smooth muscle only. The majority of motor endplates was compact and ovoid. Enteric nerve fibres on ∼17% of motor endplates stained for neuronal nitric oxide synthase, vasoactive intestinal polypeptide, galanin and neuropeptide Y and were completely separated from vagal cholinergic nerve terminals. There was remarkable variability of co-innervation rates between striated muscle bundles with some reaching almost 50%. Myenteric neurons representing the putative source of enteric co-innervating nerve fibres, stained for all these markers, which were almost completely colocalized with NADPH-diaphorase. Our study provides evidence for enteric co-innervation of striated muscle in human oesophagus. From these and recent functional results in various rodent species, we suggest that this innervation component represents an integral part of an intramural reflex mechanism for local most likely inhibitory modulation of oesophageal motility.     

Extrinsic pathways of the adrenergic innervation of the guinea-pig trachealis muscle

Origins and extrinsic pathways of the adrenergic innervation of the guinea-pig trachealis muscle were studied using fluorescence histochemical techniques. Bilateral superior cervical ganglionectomy caused a marked reduction in the adrenergic innervation of the extra-thoracic region, which suggests that these ganglia are a major source of adrenergic innervation to this muscle. Combined anterior and posterior transection of the recurrent laryngeal nerves also caused a marked reduction in the density of adrenergic fibres in the extra-thoracic trachealis muscle. Crushing of these nerves revealed adrenergic fibres running both anteriorly and posteriorly. The majority of these adrenergic nerves were lost after superior cervical ganglionectomy and thus the fibres running in both directions originate in the superior cervical ganglion. Antero-posteriorly directed fibres entered the recurrent laryngeal nerve from the superior cervical ganglion via an anastomosis at the level of the cricoid cartilage, while those running postero-anteriorly entered the recurrent laryngeal nerve posteriorly from the vagus nerve and these adrenergic fibres were lost after cervical vagotomy.     

Reactions of cardiac postganglionic sympathetic neurons to movements of normal and inflamed knee joints

The effects of passive movements of normal and inflamed knee joints on unitary activity in filaments of the inferior cardiac nerve (ICN) were studied in cats anesthetized with chloralose and urethane. The effects were compared with those obtained by electrical stimulation of afferent A- and C-fibers in the medial articular nerve, in muscle and in cutaneous hind limb nerves. The vagus nerves were cut and the right carotid artery was tied off. The left carotid sinus was intact. All ICN units used in this study displayed spontaneous activity which was usually related to the cardiac and respiratory rhythms. The ICN units were regularly excited by electrically evoked single or short repetitive A-volleys in articular, cutaneous and muscle nerves. The excitation was followed by a silent period. Inclusion of C-fibers in the afferent volleys gave a second, long-latency burst of impulses which was seen only with short repetitive stimulation. Passive movements in the normal working range of the joint did not influence the activity of ICN units. However, noxious joint movements, particularly of inflamed joints, led to pronounced excitation of ICN units accompanied by rises in blood pressure. Most of these effects could still be seen after all nerves to the hind limbs, except the medial articular nerve, were cut. It is proposed (a) that ICN units form a homogeneous population of sympathetic postganglionic units whose reaction pattern to somatovisceral input is distinctly different from that of other sympathetic subsystems, and (b) that articular receptors make a substantial contribution to the ICN input particularly when many fine afferent units are sensitized to mechanical stimulation by an acute joint inflammation.     

Immunohistochemical localization of voltage-activated calcium channels in the rat oesophagus

Voltage-activated calcium channels play an important role in the physiology of the enteric nervous system. To determine which types of voltage-activated calcium channels are present in the rat oesophagus, an immunohistochemical study was performed using specific antibodies for the alpha1 subunits of Cav2.1 (P/Q-type), Cav2.2 (N-type), Cav1.2 and Cav1.3 (L-type) calcium channels. All myenteric cell bodies showed Cav2.2 immunoreactivity, whereas labelling for this N-type channel was absent in nerve fibres. Cav1.2 immunoreactivity was found on nerve fibres in the myenteric plexus and on fibres innervating the striated muscle of the rat oesophagus, whereas no labelling was detected on neuronal somata. Immunoreactivity against Cav1.3 was not detected in the myenteric plexus or at the level of the striated muscle. Labelling for Cav2.1 was absent at the level of the myenteric plexus, but present in the striated muscle layer at the level of the motor endplates. Comparison with recent literature data from rat small intestine reveals region-specific distribution patterns of the various subtypes of voltage-activated calcium channels within the enteric nervous system. In addition, the present immunohistochemical data corroborate our physiological data (see accompanying paper), which indicate that the Cav2.2 (N-type) channel is the predominant channel involved in the generation of the calcium-dependent action potential evoked by intrasomatic depolarizing current pulses in all rat oesophageal myenteric neurones.     

Effect of truncal vagotomy and capsaicin on mast cells and IgA-positive plasma cells in rat jejunal mucosa

Immunocompetent cells, including mast cells and plasma cells (PC), in the intestinal mucosa are closely apposed to nerve fibres. Recent work has shown that vagal afferent nerves penetrate the jejunal mucosa and contact intestinal mucosal mast cells (IMMC); and that electrical stimulation of the vagus results in increased IMMC histamine content. To determine if the vagus nerve exerts a trophic effect on immunocompetent cells in the gut mucosa, the effects of truncal vagotomy and neonatal capsaicin treatment on IMMC and IgA containing PC in the lamina propria of rat jejunum were investigated. Three weeks after vagotomy, microdensitometric assessment of Alcian blue stained sections revealed 25% fewer IMMC in vagotomized animals than in controls (P < 0.05). Three months after neonatal capsaicin administration 28% fewer IMMC were found in treated rat jejunum, compared with littermate controls (P < 0.05). Three weeks post-surgery, IgA-PC densities were increased in both vagotomized animals (that also underwent pyloroplasty) and pyloroplasty controls, compared to animals subjected to laparotomy only. The proportion of lamina propria areas remained stable, indicating that the observations reflected real reductions in the numbers of IMMC. We also determined the densities of B-50 (a nerve growth-associated protein, also called GAP-43) immunoreactive nerve fibres in the lamina propria, as well as nerve profile areas, three weeks after vagotomy, and these parameters were unchanged. Taken together, these findings support the hypothesis that the vagus exerts a trophic effect on IMMC; and that capsaicin-sensitive nerves also affect the IMMC population. These data add to the growing body of evidence for a functional connection between IMMC and the nervous system.     

Responses in sympathetic nerves of the dog evoked by stimulation of somatic nerves

Responses in thoracic and renal sympathetic nerves evoked by electrical stimulation of cutaneous and muscle nerves in anaesthetized mongrel dogs were observed. Supramaximal stimulation of cutaneous nerves evoked two responses in both thoracic and renal nerves with latencies in the ranges 58--184 msec and 349--733 msec which are referred to as the early and late responses. It was shown that the early and late responses were evoked by group III and group IV afferent fibres respectively. Stimulation of muscle nerves of the forelimb and the hypoglossal nerve evoked smaller early responses which were considered to be due to activation of group III fibres and which had latencies in the range 92--157 msec. Supramaximal stimulation of muscle nerves in the hind limb failed to evoke any responses in approximately two-thirds of preparations and in the remainder only low level inconsistent early responses were observed. No matter how intense the stimuli applied to muscle nerves there were never any responses which could be related to the activation of group IV fibres.     

Neurophysiological effects of recurrent laryngeal and thoracic vagus nerves on mediating the neurogenic inflammation of the trachea, bronchi, and esophagus of rats

The present study aims to investigate the neurophysiological effects of recurrent laryngeal nerve and thoracic vagus nerve on the non-cholinergic regulation of neurogenic plasma extravasation of the rat trachea, bronchi, and esophagus. Through thoracotomy, three nerve components, the right thoracic vagal trunk, thoracic vagus nerve, and recurrent laryngeal nerve, were identified. The experiment was sequentially conducted in four steps. First, the individual nerve component was electrically stimulated and the induced inflammatory responses, as quantified by the area density of India ink-labelled blood vessels in the trachea, bronchial trees and esophagus, were compared. Second, we assessed the relative importance of medial and lateral side of the right thoracic vagus nerve in inducing the inflammatory responses by alternative stimulation of one side with simultaneous severance of the other side of this nerve. Third, we examined the effects of transection of the lateral half of the right thoracic vagus nerve on the degeneration of axon fibers located at the following three sites: the nerve segment proximal to cutting site, bronchial and esophageal nerve branches. Finally, we directly observed the inflammatory histopathology of the right lower trachea after stimulation of the medial half of the right thoracic vagus nerve with transection of its lateral half. In this study, we found that the right recurrent laryngeal nerve was predominant in mediating the neurogenic inflammatory responses of upper and dorsal portions of trachea, whereas the right thoracic vagus nerve was predominant in mediating those of the right lower ventral wall of trachea, right main bronchus, and right lobar bronchial trees. The axon fibers of the right thoracic vagus nerve responsible for mediating the neurogenic inflammatory responses of the right lower ventral trachea were mainly accumulated in the medial half, whereas those innervating the right main bronchus, right lobar bronchial trees, and lower esophagus were largely in the lateral half of this nerve. Transection of the lateral half of the right thoracic vagus nerve resulted in significant degeneration of myelinated fibers in its bronchial and esophageal nerve branches. Histopathological examination of the right lower trachea after electrical stimulation of the medial half of thoracic vagus nerve demonstrated the silver-stained leaky venules with accumulations of inflammatory cells. We thus concluded that afferent C-fibers to upper and dorsal portions of trachea were mainly from recurrent laryngeal nerve. In contrast, the neurogenic inflammatory responses of the right lower trachea were predominantly mediated by the medial half of the right thoracic vagus nerve, and those of the right main bronchus, bronchial trees and lower esophagus were largely by the lateral half of this nerve.     

5-Hydroxytryptamine selectively activates the vagal nodose C-fibre subtype in the guinea-pig oesophagus

Abstract  The afferent neurons innervating the oesophagus originate from two embryonic sources: neurons located in vagal nodose ganglia originate from embryonic placodes and neurons located in vagal jugular and spinal dorsal root ganglia (DRG) originate from the neural crest. Here, we address the hypothesis that 5-hydroxytryptamine (5-HT) differentially stimulates afferent nerve subtypes in the oesophagus. Extracellular recordings of single unit activity originating from nerve terminals were made in the isolated innervated guinea-pig oesophagus. Whole cell patch clamp recordings (35 °C) were made from the primary afferent neurons retrogradely labelled from the oesophagus. 5-Hydroxytryptamine (10  μ mol L⁻¹) activated vagal nodose C-fibres (70%) in the oesophagus but failed to activate overtly vagal jugular nerve fibres and oesophagus-specific spinal DRG neurons. The response to 5-HT in nodose C-fibre nerve terminals was mimicked by the selective 5-HT₃ receptor agonist 2-methyl-5-HT (10  μ mol L⁻¹) and nearly abolished by the 5-HT₃ receptor antagonists ondansetron (10  μ mol L⁻¹) and Y-25130 (10  μ mol L⁻¹). In patch clamp studies, 2-methyl-5-HT (10  μ mol L⁻¹) activated a proportion of isolated oesophagus-specific nodose capsaicin-sensitive neurons (putative cell bodies of nodose C-fibres). We conclude that the responsiveness to 5-HT discriminates placode-derived (vagal nodose) C-fibres from the neural crest-derived (vagal jugular and spinal DRG) afferent nerves in the oesophagus. The response to 5-HT in nodose C-fibres is mediated by the 5-HT₃ receptor in their neuronal membrane.     

Electrophysiological Studies of Cervical Vagus Nerve Stimulation in Humans: I. EEG Effects

Evidence from studies of experimental animals indicates that electrical stimulation of the vagus nerve alters EEGs under certain stimulus parameters. We report EEG effects of electrical stimulation of the vagus nerve in 9 patients with medically intractable seizures as part of a clinical trial of chronic vagal stimulation for control of epilepsy. The mechanism of action of the vagal antiepileptic effect is unknown, and we believed that analysis of electrophysiologic effects of vagal nerve stimulation would help elucidate the brain areas affected. The left vagus nerve in the neck was stimulated with a programmable implanted stimulator. Stimulation at various stimulus frequencies and amplitudes had no noticeable effect on EEG activity whether the patient was under general anesthesia, awake, or asleep, but vagus nerve stimulation may interrupt ongoing ictal EEG activity.     

Spinal segmental preganglionic outflow to cervical sympathetic trunk and postganglionic cardiac sympathetic nerves

The aim of this study was to verify in which spinal cord segments the preganglionic neurones projecting to the cervical sympathetic trunk or converging onto the somata of the postganglionic cardiac sympathetic neurones are located in cats. The thoracic white rami T1 to T5 were electrically stimulated and the evoked responses were recorded in the cervical sympathetic trunks and postganglionic cardiac nerves. The responses were mostly evoked by electrical stimulation of group B preganglionic fibres. The maximum amplitude of evoked responses in the cervical sympathetic trunk was obtained when the T2 white ramus was stimulated and decreased gradually when followed by the stimulation of T1, T3, T4 and T5 white rami. In most cases the maximum amplitude of evoked responses in the left inferior cardiac nerve, right inferior cardiac nerve and left middle cardiac nerve was obtained when the T3 white ramus was stimulated. The size of the responses decreased when more cranial and caudal white rami were stimulated. It was found that the somata of the postganglionic neurones of the right and left inferior cardiac nerves were placed in the right and left stellate ganglion, respectively. Somata of the postganglionic neurones with axons in the left middle cardiac nerve were mainly located in the left middle cervical ganglion and some in the left stellate ganglion.     

Neuropathology of the oesophagus in diabetes mellitus

Abnormalities of the innervation of the oesophagus have been shown in 18 out of 20 unselected diabetics without clinical dysphagia or neuropathy. The changes appear to be in the axons of the extrinsic and intrinsic parasympathetic fibres. It is probable that, as in the peripheral nerves, the major changes are in the Schwann cells, although here the affected fibres are unmyelinated.     

The effect of selective, chronic stimulation on motor unit size in developing rat muscle

One of the two peripheral nerves which innervate rat lumbrical muscle was stimulated chronically in vivo during the postnatal period of synapse elimination to determine whether the differential stimulation would affect the outcome of the elimination process. Rats were anesthetized for about 4 hr a day for 5 to 6 consecutive days, during which time the sural nerve (or, in other animals, the lateral plantar nerve) was electrically stimulated. Each animal received about 10(6) stimuli. After the last stimulation period, the sizes of motor units in both nerves were estimated from motor unit tension recorded in vitro. We found that, on average, sural motor units were larger than others in animals which had received sural nerve stimulation and smaller than others in animals which had received lateral planter nerve stimulation. These results are consistent with the hypothesis that more active nerve terminals possess a relative advantage in competing for occupancy of the endplate.