The composition of the vagus nerve of the cat

Summary The number and caliber of myelinated and non-myelinated fibers of entire and sensory vagal nerves of cats were studied by means of light and electron microscopy. The results obtained with electron microscopy show that the non-myelinated component is particularly rich (about 40,000 elements at the cervical level), with clearly higher numbers of fibers than demonstrated thus far with light microscopy. The ratio of myelinated to non-myelinated fibers is on the average 1 4 for the total vagi and only 1 8 for the sensory vagal component. The comparison of the nerve above and below the level of the nodose ganglion shows that (1) mean fiber diameter is usually greater at the infranodose than at the supranodose level, and (2) some myelinated fibers of small diameter occurring below the nodose ganglion become non-myelinated above it. Additionally, the number of non-myelinated fibers per Schwann cell is greater at the supranodose than at the infranodose level; this speaks in favor of a reorganization of the C-fiber population from one level to the other.     

Origin and the functional role of adrenergic fibers of the vagus nerve in cats

Origin of adrenergic fibres of vagus is studied. They are shown to appear in the thoracic vagus through caudal anastomosis introduction. The observations indicated that axons of spinal neurons and neurons of the ganglion stellate passed through caudal anastomosis and entered a thoracic vagus nerve. Stimulation of the thoracic vagus in cats after atropine sulphate injection increases the heart rate.     

Capsaicin-sensitive afferents in the vagus nerve

Vanilloids were shown to interact with over 70% of vagal C-afferents first causing an excitation followed by desensitisation and a lasting destruction of nerve fibres. Capsaicin induces a secretion of some neuropeptides from 10-30% of vagal sensory terminals and therefore serves as a pharmacological tool for testing local "effector function" of primary afferents. Vagal afferents seem to have their own subtype of vanilloid receptors (VR), not completely identical with the VR receptors in the dorsal root ganglia. Considering potentiation of the capsaicin receptors sensitivity by some factors such as local heating, pH, free oxygen radicals, a possible role of the VRs as integrators of chemical and physical components of nociceptive stimuli, is discussed.     

Myeloarchitectonics of the vagus nerve in man

In serial electively stained transversal sections of the vagus nerve trunk taken at the levels beginning from its exit out of the brain, up to terminal branches in the abdominal cavity (10 corpses of mature persons) myelin fibers of three classes have been counted. Along the course of the nerve trunk in the craniocaudal direction the total number of the myelin fibers decreases. Only about 10% of the initial amount of the myelin conductors revealed at the level of the intracranial part of the vagus nerve get into the abdominal cavity. Simultaneously, the ratio of the myelin fibers belonging to different classes changes: the part of the fine conductors increases, and that of the fibers having middle and large diameters decreases. The most important in the dynamics of the whole amount of myelin fibers and in the number of the conductors belonging to different classes at all the levels of the nerve trunk is the getting off the organs' branches with various functional specialization.     

Improved mood and remission of symptoms in long-term major depression using vagus nerve stimulation

This is a case study of a 68-year-old woman with previously unremitting depression. The patient came to our care in 1994 following a series of treatment interventions that did not alter the course of chronic depression. We report our treatment approach and results seen with this patient, including her tepid response to traditional antidepressants and the positive results seen in the past year using vagus nerve stimulation (VNS) therapy. The patient experienced broad gains in measures of depression severity and well-being under her current treatment regimen. She has had no serious adverse events associated with the regimen, which includes VNS therapy and decreased doses of common antidepressant medications.     

PAF and the role of the vagus nerve in the breathing pattern of the pig.

In 14 anesthetized, spontaneously breathing pigs we examined the changes in breathing pattern, in respiratory mechanics and in systemic and pulmonary vascular parameters after i.v. PAF administration. In another 3 pigs, the effects of PAF were also examined after bilateral vagotomy. In intact pigs, PAF induces apnea, bronchoconstriction, pulmonary hypertension and systemic hypotension. Our results also show that administration of PAF alters the phasic vagal activity, modifying the slope of VT vs TI and TE vs TI relationships and the TI0/TI ratio. These effects and apnea are vagus-dependent. The central excitatory timing effect of PAF on inspiratory duration (TI0) was correlated with a decrease in passive compliance but not with active compliance. We postulate that the activation by vagal input strengthens the mechanisms that counteract the bronchoconstrictor effect of PAF.     

The vagus nerve, food intake and obesity

Food interacts with sensors all along the alimentary canal to provide the brain with information regarding its composition, energy content, and beneficial effect. Vagal afferents innervating the gastrointestinal tract, pancreas, and liver provide a rapid and discrete account of digestible food in the alimentary canal, as well as circulating and stored fuels, while vagal efferents, together with the sympathetic nervous system and hormonal mechanisms, codetermine the rate of nutrient absorption, partitioning, storage, and mobilization. Although vagal sensory mechanisms play a crucial role in the neural mechanism of satiation, there is little evidence suggesting a significant role in long-term energy homeostasis. However, increasing recognition of vagal involvement in the putative mechanisms making bariatric surgeries the most effective treatment for obesity should greatly stimulate future research to uncover the many details regarding the specific transduction mechanisms in the periphery and the inter- and intra-neuronal signaling cascades disseminating vagal information across the neuraxis.     

Ultrastructure of nodose ganglia of the vagus nerve in burns

Ultrastructural changes of neurons of vagus nodal ganglia on section material of 30 dead persons in different periods of burn disease aged from 14 to 75 have been studied. Examination of the state of the nodal ganglia in different periods of burn disease showed ultrastructural changes in neurons, glial cells, blood capillary endotheliocytes, mitochondria, endoplasmatic net nuclei and cell membranes. The most marked destructive changes were seen in patients who died in late term of burn disease.     

Occurrence of methionine-enkephalin-like immunoreactive cells in the feline vagus nerve

The occurrence of peptidergic cellular elements in the feline vagus nerve was examined by an immunohistochemical method. Some methionine-enkephalin-like immunoreactive cells were present around a few capillaries within the vagus nerve, whereas substance-P- and vasoactive-intestinal-polypeptide-like immunoreactive cells were not observed. The methionine-enkephalin-like immunoreactive cells had an oval shape and their diameter was 7-10 micron. These cells appeared to be in contact with the pericyte of the capillaries. Though the physiological function of these enkephalin-positive cells is unclear, our findings suggest that they can act as endocrine cells and release methionine-enkephalin into the capillaries.     

The spectrogram of heart rate in cats following burst stimulation of the vagus nerve

Denervation of the heart (bilateral vagotomy and propranolol) in artificially ventilated cats didn't remove respiratory peaks on the spectrogram of heart rate, while burst stimulation of vagus nerve increased or decreased them several times by synchronization of the heart and vagus rhythms, which in its turn was observed under the bradycardia only. At the same time, the desynchronization of rhythms provoked severe sinus arrhythmia which had a distinct periodic character. Under these conditions, there were high non-respiratory peaks appearing at the spectrogram of the heart rate that indicated existence of two vagus chronotropic effects: a well known tonic one and special intracycle synchronizing effect correcting duration of every cardiac cycle.     

迷走神经刺激对记忆的影响

迷走神经刺激(vagus nerve stimulation, VNS)用于终止癫痫发作已经有二十年的历史.期间VNS也用于难治性抑郁的治疗.在治疗过程中研究者发现VNS 对癫痫、抑郁患者的学习和记忆能力有改善作用,这种改善作用在一些动物和人体实验中也得到证实.但VNS在记忆形成的哪个阶段起作用以及如何起作用的具体机制尚不十分清楚.因此,进一步了解VNS对记忆的影响及作用机制有利于探讨记忆形成的生理机制,也为临床治疗特异性记忆障碍和相关神经精神疾病提供新的思路和有益补充.本文综述了近十几年来VNS对记忆的影响及相关机制.