Thymic innervation in the rat: a light and electron microscopical study.

The innervation of the rat thymus was studied by light and electron microscopy in juvenile and aged rats. By light microscopy numerous fine nerves were found in the connective tissue septa penetrating between the thymic lobules. These septa were clearly delineated in the juvenile animals, but indistinct in the aged rats, thus creating the spurious impression that thymic parenchyma contains nerves. In the aged animals the nerves are thicker, tortuous, and more branched than in juvenile animals. Electron microscopy confirms the light microscopic observations: no nerves were found within the thymic parenchyma. The thymic capsule and larger connective tissue septa contain bundles of myelinated and unmyelinated axons, surrounded by a perineural sheath. Within the extraparenchymal compartment, which is greatly enlarged in aged animals, efferent and sensory nerves, devoid of perineurium, were found to contact mainly reticular cells, and in rare instances plasma cells and lymphocytes. The majority of axonal varicosities are not closely related to cellular elements, and, in general, vesicles are relatively infrequent. The possible functional significance of these observations is discussed.

Neuronally released (-)-noradrenaline relaxes smooth muscle of calf trachea mainly through beta 1-adrenoceptors: comparison with (-)-adrenaline and relation to adenylate cyclase stimulation.

The nature of the receptors that mediate the relaxation of smooth muscle by field stimulation, (-)-noradrenaline and (-)-adrenaline was investigated in calf tracheal smooth muscle. The relation between relaxation, stimulation of the adenylate cyclase and density of beta-adrenoceptor subtypes was studied with the help of antagonists of beta 1- and beta 2-adrenoceptors. The question of the existence of catecholamine-containing nerves was also investigated. (1) Nerves with varicosities exhibiting catecholaminergic fluorescence were observed between bundles of smooth muscle cells. (2) Consistent with the existence of adrenergic nerves (-)-noradrenaline was also found. The content of (-)-noradrenaline (1 microgram.g-1 w.w.) was the same in smooth muscle strips from the sublaryngeal region and from the region close to the bifurcation of the calf trachea. (-)-Adrenaline was not detected. (3) Smooth muscle relaxation by low (-)-noradrenaline concentration (0.6-2 nmol/l) was mediated through beta 1-adrenoceptors. Low concentrations of (-)-adrenaline (0.06-1 nmol/l) relaxed through beta 2-adrenoceptors. High concentrations of (-)-noradrenaline and (-)-adrenaline also caused relaxation through beta 2- and beta 1-adrenoceptors respectively. (4) Field stimulation caused relaxation which was half maximal at 0.2-0.8 Hz. Blockade of beta 1-adrenoceptors strongly attenuated the relaxant response to field stimulation and shifted the frequency-relaxation curves to 4 times higher frequencies. These results are consistent with a beta 1-adrenoceptor-mediated relaxation caused by (-)-noradrenaline released from sympathetic nerve endings at low stimulation frequencies. (5) Blockade of beta 2-adrenoceptors failed to reduce smooth muscle relaxation caused by field stimulation at low stimulation frequencies (0.1-1 Hz). However, after beta 1-adrenoceptor blockade, additional blockade of beta 2-adrenoceptors reduced the relaxant effects observed at high frequencies (2-400 Hz). The results suggest that high concentrations of endogenous (-)-noradrenaline cause relaxation through beta 2-adrenoceptors. (6) Binding experiments with 3H-(-)-bupranolol and 3H-ICI 118,551 revealed between 10,000 and 20,000 beta-adrenoceptors per smooth muscle cell of which 3/4 were beta 2 and 1/4 beta 1. The equilibrium dissociation constant of (-)-adrenaline for both beta 1- and beta 2-adrenoceptors and of (-)-noradrenaline for beta 1-adrenoceptors was 1 mumol/l. The affinity of (-)-noradrenaline for beta 2-adrenoceptors was 10 to 20 times lower than for beta 1-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 6-hydroxydopamine on pre- and post-junctional 5-HT1-like receptor-mediated responses in dog saphenous vein.

To investigate whether 5-HT1-like receptor-mediated inhibition of adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation occurs in nerves or smooth muscle of saphenous vein, infusions of 6-hydroxydopamine (6-OHDA) were administered to dogs with the aim of inducing sympathetic nerve damage. The effects of 6-OHDA on other 5-HT1-like receptor-mediated responses at the pre- and post-junctional level were investigated for comparison by studying 5-hydroxytryptamine (5-HT)-induced inhibition of 3H-noradrenaline release and contraction of smooth muscle respectively. Disruption of nerve function by 6-OHDA was revealed by the lack of catecholaminergic fluorescence and neurogenic contractile responses in saphenous veins from dogs treated with 6-OHDA. In addition, severe impairment of neuronal uptake mechanisms were apparent since basal efflux of 3H-noradrenaline, electrically-evoked release of 3H-noradrenaline and remaining 3H-noradrenaline content were considerably reduced. Some 3H-noradrenaline was taken up and released in 6-OHDA-treated tissues which is consistent with the existence of nerve varicosities resistant to the present dosing regime of 6-OHDA, an observation substantiated by electron microscopy studies showing inconsistent lesions of nerve terminals. 6-OHDA pre-treatment potentiated the smooth muscle contractile responses mediated by 5-HT1-like receptors as well as potentiating 5-HT-evoked inhibition of prostaglandin E2-stimulated cyclic AMP accumulation. It did not, however, affect 5-HT-induced inhibition of 3H-noradrenaline release. The present results suggest that inhibition of cyclic AMP accumulation by 5-HT occurs predominantly in smooth muscle.

Incontinentia pigmenti with ultrastructurally disordered leucocytes.

Incontinentia pigmenti (IP) is a rare X-linked genodermatosis in which skin changes are combined with anomalies of other tissues, mainly of ectodermal origin. Mutations of the IKBKG gene are responsible for IP. Haematological disorders among IP patients are rare. Four female patients from a single family, with typical clinical characteristics of IP, are reported. In addition, all affected family members show a distinct haematological phenotype: hypogranular granulocytes, leucocytes with pseudoplatelets, and different anomalies of nuclei. Pseudoplatelets are a typical finding in patients with leukaemia. As there is dysfunction of the IKBKG gene in leukaemia, it is hypothesised that mis-regulation of the NEMO pathway may cause the appearance of pseudoplatelets in acute leukaemias as well as in IP. These observations suggest that IP may not be only linked to skin and organs of the ectodermal origin.

Ultrastructural analysis of lymph node innervation in the rat.

The morphological analysis of nerves in axillary lymph nodes of the rat revealed the presence of two types of axon possessing either a more or a less electron-lucent matrix. The more electron-lucent axons enter the node finely myelinated, do not contain synaptic vesicles and quickly divide to form branches approaching the basement membranes of blood vessels, as well as cellular elements. They may be interpreted as sensory axons. The less electron-lucent axons are unmyelinated, and contain three distinct populations of synaptic vesicles. These may all be present in one axonal varicosity, so that the existence of cotransmitters is highly probable.

A relative volumetric analysis of the lateral geniculate nucleus after enucleation.

The relative volumes occupied by nerve cell somata, axons, myelin, the remaining neuropil, glial cell nuclei, blood vessels and degenerating terminals have been determined in the foveal and parafoveal portions of laminae 5 and 6 of the monkey (Macaca fascicularis) lateral geniculate nucleus, in control animals and at varying times after unilateral enucleation. The proportions occupied by these tissue components are very similar within the same lamina of all control animals, but differ significantly between lamina 5 and 6. After enucleation there are alterations, not only in the denervated lamina 6, but also in lamina 5.

Observations on the lateral geniculate nucleus of the monkey (Macaca fascicularis) after eye removal: a light and electron microscopic study. I. Classification and degeneration of optic fibre terminals.

The morphological signs of terminal degeneration are compared at the light and electron microscopic levels in the lateral geniculate nucleus of Macaca fascicularis, from 29 hours to 10 days after eye removal. A close correlation can be found between the appearance of degenerating RLP-terminals (i.e. large terminals containing round vesicles and pale mitochondria), which display marked, unorganized neurofilamentous hyperplasia, and the club-shaped structures revealed by neurofibrillary staning. The ring-shaped entities present in silver-impregnated material closely resemble annular bundles of neurofilaments located in smaller retinal terminals within the neuropil. Various non-filamentous degenerative forms of particularly small terminals are also described. It is concluded that the clubs and rings visualized by neurofibrillary stains in the lateral geniculate nucleus of the monkey do, indeed, represent synaptic structures. The implications of this conclusion are discussed, as are possible reasons that contrary conclusions have been drawn by other investigators. It is further suggested that club and ring formation of degenerating retinal afferents may be related to Y and X axons in the optic tract, respectively.

Observations on the lateral geniculate nucleus of the monkey (Macaca fasicularis) after eye removal: a light and electron microscopic study. II. Axonal and dendritic degeneration.

Morphological parameters of the axons and dendrites in the lateral geniculate nucleus have been studied in the normal monkey and after varying periods of enucleation, at the light and electron microscopic levels. Gross aspects of the alterations evident at the ultrastructural level can be correlated with changes visible in the light microscope. Signs of axonal fragmentation were never observed following enucleation; retinal afferent fibres seem to gradually thin out and disappear, taking on an osmiophilic appearance in the electron microscope during this process. Changes in the surface structure of axons are considered to be due to an altered reaction of myelin in the degenerating nucleus. Myelin is not removed to any great extent. The dendritic responses to enucleation (including those of synaptic profiles containing flat vesicles) are believed to result from an unspecific compensatory reaction to increased hydration and are not considered to be primarily degenerative. Since pale terminal degeneration seems to be of the same nature it is concluded that such early signs of presumed terminal death are unreliable. Dark degeneration of dendrites was not observed in the lateral geniculate nucleus of the enucleated monkey.

A ventral tract from the bed nucleus of the stria terminalis to the amygdaloid complex in the monkey (Macaca fascicularis): possible pathway in the regulation of ovulation [proceedings].

PIP: Characteristics of a ventral tract from the bed nucleus of the stria terminalis (BST) to the amygdaloid complex in the monkey (Macaca fascicularis) are described. A system of approximately 200 fiber bundles lying between the BST and baso-lateral part of the amygdaloid complex was identified and postulated to be monosynaptic. The bundles consist of unmyelinated fibers with a median diameter of .16-.20 mcm. No axons could be found with a diameter greater than .55 mcm, and 8% of the fibers had a diameter of less than .10 mcm. The total number of axons in the tract was calculated to be 500,000. It is concluded that the direction of conduction in this pathway is from BST to the amygdala, and, since the neurones of BST contain estradiol, that this tract may be involved in the regulation of ovulation.^ieng

Synaptic ring images after silver impregnation.

In view of the contradictory results obtained from a number of studies on the nature of ring images found after neurofibrillar silver impregnation, this question was reinvestigated at the ultrastructural level in the lateral geniculate nucleus of the monkey. The ring images found here are produced by silver deposits on ring-shaped accumulations of neurofilaments in the afferent synapses of retinal origin. Tubular impregnation of axons was not found to be a factor in the genesis of ring images.

Formation of cytoplasm-containing vesicles from double-walled coated invaginations containing oligodendrocytic cytoplasm at the axon-myelin sheath interface in adult mammalian central nervous system.

Double-walled coated invaginations ( DWCIs ) of the axolemma, containing oligodendroglial cytoplasm and presumably giving rise to double-walled coated vesicles ( DWCVs ), are observed in the central nervous system (CNS) of adult monkey and mouse. By means of serial sections, DWCIs are clearly distinguishable from the also observable adaxonal invaginations of oligodendroglial cytoplasm. DWCIs range in diameter from 60 to 190 nm with a circular or oval cross section. Their incidence in different regions of the CNS has been determined and evidence is adduced that DWCIs occur randomly along the axolemma.

On the distribution of retinal afferents to the primate lateral geniculate nucleus.

A quantitative study has been carried out on the number of synaptic ring images, visible after neurofibrillar silver impregnation, in laminae 5 and 6 of the primate lateral geniculate nucleus in normal animals and after enucleation of the contralateral eye. In a statistical experiment the number of rings was found to be significantly increased between 6 and 11 d after unilateral enucleation in both lamina 6 and lamina 5 of the contralateral geniculate nucleus. Analysis of the time course of ring proliferation suggests the presence of 2 separate generative processes in lamina 6 at different times after enucleation. Only the second of these processes appears to exist in lamina 5. It is proposed that these observations are compatible with the hypothesis that there is a diffuse, sparse projection of collaterals of retinal Y axons from one eye to more than one lamina of the lateral geniculate nucleus.

Observations on the lateral geniculate nucleus of the monkey (Macaca fascicularis) after eye removal: a light and electron microscopic study. III. Glial reactions.

The light and electron microscopic morphology of non-neuronal elements within the lateral geniculate nucleus has been studied in normal monkeys and after enucleation. In the normal lateral geniculate nucleus it is possible to find light and dark astrocytes; light, medium and dark oligodendrocytes; microglia, and the so-called "third" glial element of VAUGHN and PETERS (1968). Two types of perivascular elements are also present. After enucleation, the first overt response is an oedematous reaction in the denervated regions, without concomitant disruption of the capillary endothelium. The oedema seems to be connected with swelling and disruption of astroglia. After the first days of enucleation, the microglia disappear and are replaced by phagocytic glia (WONG-RILEY, 1972). From the presence of intermediate stages at characteristic sites within the nucleus, it is concluded that phagocytic glia develop from the same precursor as the "third" glial elements and that they are both immature forms of microglial cells.

A direct ventral connection between the bed nucleus of the stria terminalis and the amygdaloid complex in the monkey (Macaca fascicularis).

A direct ventral connection, between the bed nucleus of the stria terminalis and the amygdaloid complex in the monkey is described. It consists of bundles of extremely fine unmyelinated axons of a median diameter between 0.16 and 0.2 micrometer. The total number of axons is estimated at over 500,000. Using observations gained by other authors it is deduced, that the direction of conduction is probably from the bed nucleus of the stria terminalis to the amygdala. Other observations in the literature indicate, that the pathway may be concerned with the regulation of ovulation.

The effect of immunostimulation on thymic innervation in the rat.

In order to test whether the thymic innervation shows morphological plasticity in response to thymic functional changes, the density of thymic innervation was determined in sterile control animals and three groups of antigenically stimulated sterile rats. Thymic function was defined from the numbers of mitotic cells present in the thymic cortex, and these were reduced by antigenic stimulation. The innervation was determined separately for the various compartments of the thymus. Nerves were present in the capsule and the septa, but could not be found in either cortex or medulla of the thymic parenchyma. A statistically significant increase in the density of innervation after antigenic stimulation was found for the vessel and the non-vessel innervation of the septa. No significant changes were found in the innervation of the capsule.

Intraepidermal nerves in human digital skin.

Intraepidermal nerve fibers of human glabrous digital skin were investigated using a new silver impregnation method. Nerves were observed to enter the epidermis without regional preference, and to extend into the stratum granulosum. They are non-varicose (smooth) or varicose and range from less than 0.2 micron to approximately 2 micron in diameter, with varicosities up to 3 micron in diameter. Some axons branch profusely within the epithelium, giving off fine branches of differing diameters, while others appear to remain unbranched. At least some intraepidermal axons are fine branches of larger axons taking a horizontal course below the epithelial layer. Others are, at least topically, closely associated with Meissner's corpuscles. At 57 nerves per mm2 surface area, the density of intraepidermal nerves found in this investigation is much greater than that reported in recent publications, and agrees closely with values given in several older studies.

Innervation of lymph nodes: a combined silver impregnation and electron-microscopic study.

Using silver impregnation and electron-microscopic techniques, nerves have been demonstrated in rat axillary, cervical and inguinal lymph nodes, and their distribution was investigated. With the electron microscope, vesicle-containing varicosities or terminals are demonstrated in close proximity to reticulum cells, lymphocytes, plasmablasts and mature plasma cells. Nerves supplying the blood vessels possibly differ from those supplying stromal or lymphocytic elements.

Quantification of thymic innervation in juvenile and aged rats.

Thymic innervation has been quantified using silver impregnation and light microscopy on 5 juvenile and 5 aged rats. There is an increase in innervation density of the thymus with age, exceeding the reduction of thymic volume due to involution. The density of innervation correlates inversely with thymic volume. From previous studies, we conclude that thymic innervation is confined to the extraparenchymal compartment. Ultrastructural morphometry shows this compartment to maintain its volume during involution of the remaining thymic tissue. Related only to the extraparenchymal compartment, the innervation increases by a factor two with age.

Silver impregnation of peripheral and central axons.

A silver impregnation method suitable for peripheral and central nervous system axons is described. Essential features are the use of reagent grade chemicals only, a pretreatment solution to ensure optimal impregnation of different organs from different animals and species, and an unvarying procedure. The results are compared to those obtainable with a number of current impregnation methods and with modern immunocytochemical reactions.