Sympathetic innervation of fetal mouse thymus

This study was carried out to investigate the presence of sympathetic nerve fibers in the developing thymus. Thymic rudiments from 13 days of gestation up to birth and adult thymuses were examined by histofluorescence microscopy to detect the presence of these nerve fibers during ontogeny. Sympathetic nerve fibers were first visible around day 17 of gestation and increased in density and distribution by the time of birth and in the adult thymus. The appearance of immunoreactive cells about the same time as the presence of nerve fibers in the thymic rudiments has been discussed in light of a regulatory role for the sympathetic neuronal input on the maturation of thymocytes during ontogeny.     

Ontogeny of cholinergic innervation of thymus in mouse

In this study, identification of cholinergic nerves in the murine thymic rudiments during ontogenetic development, by immunonocytochemical localization of the enzyme cholin acetyltransferase (ChAT) was carried out. Fetal thymic rudiments from day 13 of gestation to the time of birth, and upto 8th post natal week were examined. Contrary to the earlier reports, the results indicate that the thymic rudiment is not innervated during early ontogenetic development and that the first ChAT positive nerve profiles were observed at around day 17/18 of gestation. Significance of cholinergic innervation in thymocyte maturation is suggested.     

The effects of chronic stress on thymus innervation in the adult rat

Various stressors induce changes in the immune system. However, it has not yet been analyzed how stressors affect thymus innervation. To examine whether chronic stress alters the morphology of the thymus by changing the nerve components of the thymus, adult male rats, 9-weeks old, were exposed to forced swimming during 21 successive days. The animals were sacrificed by decapitation after the last session and their thymuses were used for analysis of (i) the thymus compartments, (ii) distribution patterns of monoamine-containing nerve profiles and (iii) distribution patterns of acetylcholinesterase (AChE)-containing nerve profiles. Our results show that chronic stress in rats reduces the volume of both thymus cortex and medulla, numbers of thymocytes in the deep cortex and medulla and the density of fluorescent nerve profiles, whereas it increases density of fluorescent cells. The distribution patterns of nerve profiles containing monoamine and AChE were not affected. These changes indicate that chronic stress affects thymus development and T cell maturation by altering the sympathetic nerve component.     

Components of sympathetic innervation of the rat thymus during late fetal and postnatal development: histofluorescence and biochemical study. Sympathetic innervation of the rat thymus.

This study was performed in order to investigate development of sympathetic innervation in the rat thymus. To achieve this aim histofluorescence and biochemical methods were used. The histofluorescence method revealed the presence of sympathetic nervous profiles in this organ for the first time on day 18 of gestation. The density of these profiles and intensity of their fluorescence increased progressively during late embryonal and postnatal development of the organ. In the outer cortex of adult thymus the sympathetic nervous profiles were found mainly in apposition to thymocytes, while in deeper cortex and medulla they were revealed adjacent to thymic epithelial cells. These nervous profiles were also found in close association with thymic autofluorescent cells, which density increased during the thymic postnatal development. Using the fluorometric method the concentrations of neither noradrenaline (NA) and dopamine (DA) nor serotonin (5-HT) were measurable until day 19 of embryogenesis. Their content increased during the postnatal development. The patterns of NA and DA increase during the postnatal development were almost identical, while the pattern of 5-HT increase was quite different. The present results indicate that DA might also be one of the transmitters of the thymic sympathetic nerve supply, as well as that the transmitters of that system can be involved in the regulation of activity of thymic epithelial and autofluorescent cells, but also in the modulation of T cell maturation.     

Fine structural evidence for hormone secretion by the human thymus

The epithelial cells of the Hassall's corpuscles in 11 human thymus glands (nine cases of myasthenia gravis and two glands from patients undergoing surgical correction of congenital heart disease) have been examined by electron microscopy. In every instance the epithelial cells have the cytoplasmic organelle complex necessary for `export'-type secretory activity and in addition contain large numbers of membrane-limited small spheroidal secretion granules.     

Data on the innervation of the mucous membrane of the stomach in mammals and man

Summary The author stained the nerves with methylene blue and revealed nerve plexuses both in its mucous membrane (where ganglia were also found, especially in man), and in the t. propria. In man such plexuses are located at the floor of the glands. There are additional plexuses in cats and dogs — on the level of transition of the gastric fossae into glands. These plexuses have fibers with ramifications with form numerous nerve endings in the connective tissue and at the bases of the epithelial cells.Presented by Academician L. A. Orbeli     

Sympathetic innervation of murine thymus and spleen: a comparative histofluorescence study

Fluorescence microscopy of thymus and spleen from four strains of mice (C3H and ICR controls, AKR spontaneously leukemic and NZB autoimmune) revealed varicose noradrenergic (NE) fibers in perivascular and parenchymal regions of both organs. Thymic innervation was largely perivascular, but isolated islands and strings of free NE fibers were noted among thymic parenchymal cells. A morphological proximity between NE fibers in the thymus and mast cells was noted in all strains studied, but was exceptionally prominent in the NZB thymus. Perivascular plexuses within the splenic white pulp sent single NE fibers between the surrounding lymphocytes. Catecholamines and histamine have been shown to modulate lymphocyte development and activity in vitro. The present study provides morphological evidence that both NE and histamine are available to lymphocytes in thymus and spleen, and thus provides morphological evidence for neural modulation of immune activity in vivo.     

Premotor cortex in man: Evidence for innervation of proximal limb muscles

Summary Fourteen patients with frontal CT-lesions involving premotor cortex showed moderate weakness of contralateral shoulder and hip muscles. This premotor syndrome in man resembles that described for lesions of brainstem pathways in monkeys, except that axial musculature was not disturbed when these lesions were unilateral. Medial extent of the lesion involving the SMA was accompanied by additional slight limb-kinetic apraxia.     

Evidence for bilateral innervation of certain homologous motoneurone pools in man.

1. Surface EMG recordings were made from left and right homologous muscle pairs in healthy adults. During each recording session subjects were requested to maintain a weak isometric contraction of both the left and right muscle. 2. Cross-correlation analysis of the two multiunit EMG recordings from each pair of muscles was performed. Central peaks of short duration (mean durations, 11.3-13.0 ms) were seen in correlograms constructed from multiunit EMG recordings obtained from left and right diaphragm, rectus abdominis and masseter muscles. No central peaks were seen in correlograms constructed from the multiunit EMG recordings from left and right upper limb muscles. 3. To investigate descending pathways to the homologous muscle pairs, the dominant motor cortex was stimulated using a focal magnetic brain stimulator whilst recording from homologous muscle pairs. 4. Following magnetic stimulation of the dominant motor cortex, a response was recorded from both right and left diaphragm, rectus abdominis and masseter muscles. In contrast, when recording from homologous upper limb muscles, a response was only seen contralateral to the side of stimulation. 5. The finding of short duration central peaks in the cross-correlograms constructed from multiunit recordings from left and right diaphragm, rectus abdominis and masseter, suggests that muscles such as these, that are normally co-activated, share a common drive. The mechanism is discussed and it is argued that the time course of the central correlogram peaks is consistent with the hypothesis that they could be produced by a common drive that arises from activity in last-order branched presynaptic fibres although presynaptic synchronization of last-order inputs is also likely to be involved. 6. The results of the magnetic stimulation experiments suggest that this common drive may involve the corticospinal tract. 7. We saw no evidence for a common drive to left and right homologous muscle pairs that may be voluntarily co-activated but often act independently.     

Parasympathetic innervation of the rat thymus during first life period: histochemical and biochemical study.

In the present study we analyzed development of the rat thymus parasympathetic innervation using histochemical determination of distribution and density of acetylcholinesterase (AChE) positive nerve profiles, as well as biochemical measuring of the activity of this enzyme. Rat thymuses from late embryonal to adult periods of life were analyzed. The AChE-positive nerve profiles were found, for the first time, on day 18 of fetal life in capsule and interlobulary septae, but also in the subcapsulary and cortico-medullary areas. The density of these profiles increased during the thymic development. The AChE positive nerve profiles in subcapsulary region were observed mainly in close proximity to the thymic epithelial cells, while in the cortico-medullary region they were found in apposition to the thymocytes. The biochemical analysis showed that the specific AChE activity in rat thymus was high on day 19 of gestation. A significant increase in the activity of this enzyme was measured by the third day of postnatal development, and its activity remained approximately at the same level up to the day 90. The present results suggest that thymus receives parasympathetic innervation relatively early in ontogeny; in addition, these nerve fibers could be involved in the regulation of the organ activity, at least, through action upon the thymocytes and/or by modulation of the thymic epithelial cell activity.     

Fine structure of the taste bud in guinea pigs. I. Cell characterization and innervation patterns

Guinea pig taste buds were observed by transmission electron microscopy with special reference to cell types and innervation. The taste bud comprised four distinct cell types: basal, type I, type II, and type III cells. Basal cells, residing at the baso-lateral region of the taste bud without extending to the taste pore, were considered precursors of the other types of cells. The rest were all spindle-shaped cells reaching apically to the taste pit. Type I cells were characterized by the darkest appearance of the cytoplasm, apically possessing large, electron-dense granules and basally enveloping intragemmal nerves. This cell type, intervening between the other types of cells, was postulated to be sustentacular in nature. Type II cells, the largest and lightest cells in the taste bud, possessed a conspicuous stack of smooth endoplasmic reticulum above the nucleus. Due to their intimate and specialized relationships with nerves, the type II cells were presumed to receive an efferent innervation. Type III cells made synaptic contacts with nerves and contained dense-cored vesicles, which accumulated in the synaptic areas. This finding strongly suggests a gustatory function for the cells. The occurrence of such numerous peptidergic-type granules gathering to gustatory synapses as demonstrated in this report has not been recorded in previous papers on mammalian taste buds. The nerve terminals on the type III cell also contained synaptic vesicles, thus suggesting a reciprocal synapse here. The taste bud often included degenerating cells which were demonstrated to be phagocytosed by extrinsic cells identified as macrophages.     

Development of innervation of skeletal muscle fibers in man: Relation to acetylcholine receptors

The aim of this study was to establish the time scale of developmental changes in innervation of skeletal muscle fibers in man. Specimens of thigh and intercostal muscle from 19 embryos and 18 infants were examined with histological methods which enabled the discrimination between fetal (gamma) and adult (epsilon) types of acetylcholine receptors (AChRs). At 8 weeks of development, AChRs were distributed diffusely in the myotube membranes. Following onset of innervation in approximately the ninth week the length of the AChR positive area diminished and reached its shortest size at the sixteenth developmental week. At the sixteenth and eighteenth week some nerve terminals opposed the muscle membrane outside the AChR positive area. Decrease in the number of nerve terminals, strongly suggesting elimination of polyneuronal innervation, started in the sixteenth week and was completed in the twenty-fifth week. This fetal (gamma) type of AChR could no longer be demonstrated after the thirty-first week. The length of the end-plates as determined by the presence of AChRs increased again in the last week before birth and reached a plateau size by the end of the first year after birth. It is concluded that in man the transition from poly- to mononeuronal innervation takes place between the sixteenth and twenty-fifth weeks of development. The evidence available suggests that the retraction of nerve terminals is preceded by loss of AChRs from the muscle membrane facing the terminals. There is no relationship between retraction of nerve terminals and the switch from fetal to adult type of AChR. The size of the presynaptic apparatus changes little after the first year of life. © 1993 Wiley-Liss, Inc.