大鼠皮肤的硫胺素单磷酸酶阳性神经支配

本实验用酶组织化学和辣根过氧化物酶(HRP)追踪技术证实:1.硫胺素单磷酸酶(TMPase)阳性神经未梢见于鼠爪掌皮肤,多位于真皮深部,成束地或单个游离地散在于汗腺之间的结缔组织。它们纤细、呈棕黑色,其表面串珠样膨体清晰可辩,与无髓C类纤维相似。另有部分纤维无TMPase活性。在表皮未见到阳性未梢。2.HRP肋间神经注射后,在后根节有散在的HRP标记细胞,以中小型细胞为主,大型细胞少见。仅有少数中小型标记细胞具有TMPase活性,有的小于20μ。结果表明:爪掌皮肤含TMPase阳性纤维,胸部皮肤具有TMPase阳性神经支配,提示TMPase可能是皮肤神经内一种新的化学成分,与皮肤的某一感觉形式有关。     

Studies on the nerve endings in the visceral pleura

The visceral pleura of 12 dogs, eight lambs, nine monkeys and four rabbits was studied by methylene blue immersion. Nerve terminations were found in the pleura of all specimens. The following types of nerve endings and patterns of innervation were observed. (1) Free fiber endings arose from small myelinated fibers and terminated in the caudo-ventral lips of the lobes. The parent fibers of these and all other endings arose, in the lamb, rabbit and dog, from nerve bundles radiating from the hilus onto the inter-lobar and diaphragmatic pleural surfaces. In the monkey, parent fibers arose from a complex hilar plexus of nerve bundles before spreading out within the pleural surfaces. (2) Complex unencapsulated endings were seen in all specimens distributed evenly over the inter-lobar and diaphragmatic pleural surfaces. These arose from myelinated fibers which terminated in two or more complex endings. In the monkey, parent fibers may form an anastomotic network before terminating. (3) In the dog, an “end-net” formation was found which appears to be a type of complex unencapsulated ending. This “end-net” is formed by the anastomosis of the terminal branches of several small myelinated fibers.     

Dual sensory innervation of pulmonary neuroepithelial bodies

The characteristics of the different populations of sensory nerve terminals that selectively contact pulmonary neuroepithelial bodies (NEBs) in rat lungs were investigated after chemical denervation with capsaicin and compared with control lungs. Vagal calbindin D28k and P2X(3) purinoceptor immunoreactive (IR) afferent nerve terminals contacting NEBs appeared to have their origin in the nodose ganglion. Thick CB/P2X(3)-IR nerve fibers were seen to be myelinated and to lose their myelin sheaths just before branching and protruding intraepithelially between the NEB cells. This vagal sensory component of the innervation of NEBs was not affected by capsaicin nor expressed capsaicin receptors (vanilloid receptor subtype 1). A second sensory nerve fiber population that selectively innervates pulmonary NEBs in the rat lung consists of thin unmyelinated nonvagal substance P/calcitonin gene-related peptide IR nerve fibers, contacting mainly the basal pole of pulmonary NEBs, and having their origin in dorsal root ganglia. In concordance with vanilloid receptor 1 expression on these nerve terminals, the spinal sensory substance P/calcitionin gene-related peptide-IR component of the innervation of NEBs was depleted by systemic capsaicin treatment. The complex sensory innervation pattern of pulmonary NEBs characterized in the present study strongly suggests that, physiologically, pulmonary NEBs represent a group of intraepithelial receptors that may be able to accommodate various local and central reflex actions, in relation to both chemo- and mechanosensory stimuli.     

Intraepithelial vagal sensory nerve terminals in rat pulmonary neuroepithelial bodies express P2X(3) receptors

The neurotransmitters/modulators involved in the interaction between pulmonary neuroepithelial bodies (NEBs) and the vagal sensory component of their innervation have not yet been elucidated. Because P2X(3) purinoreceptors are known to be strongly expressed in peripheral sensory neurons, the aim of the present study was to examine the localization of nerve endings expressing P2X(3) purinoreceptors in the rat lung in general and those contacting pulmonary NEBs in particular. Most striking were intraepithelial arborizations of P2X(3) purinoceptor-immunoreactive (IR) nerve terminals, which in all cases appeared to ramify between calcitonin gene-related peptide (CGRP)- or calbindin D28k (CB)-labeled NEB cells. However, not all NEBs received nerve endings expressing P2X(3) receptors. Using CGRP and CB staining as markers for two different sensory components of the innervation of NEBs, it was revealed that P2X(3) receptor and CB immunoreactivity were colocalized, whereas CGRP-IR fibers clearly formed a different population. The disappearance of characteristic P2X(3) receptor-positive nerve fibers in contact with NEBs after infranodosal vagal crush and colocalization of tracer and P2X(3) receptor immunoreactivity in vagal nodose neuronal cell bodies in retrograde tracing experiments further supports our hypothesis that the P2X(3) receptor-IR nerve fibers contacting NEBs have their origin in the vagal sensory nodose ganglia. Combination of quinacrine accumulation in NEBs, suggestive of the presence of high concentrations of adenosine triphosphate (ATP) in their secretory vesicles, and P2X(3) receptor staining showed that the branching intraepithelial P2X(3) receptor-IR nerve terminals in rat lungs were exclusively associated with quinacrine-stained NEBs. We conclude that ATP might act as a neurotransmitter/neuromodulator in the vagal sensory innervation of NEBs via a P2X(3) receptor-mediated pathway. Further studies are necessary to determine whether the P2X(3) receptor-expressing neurons, specifically innervating NEBs in the rat lung, belong to a population of P2X(3) receptor-IR nociceptive vagal nodose neurons.     

Anatomy and function of sensory hepatic nerves

Vagal and spinal afferent innervation of the portal hepatic area has not been studied as thoroughly as the innervation of other important organs. It is generally agreed that unlike noradrenergic sympathetic efferent nerve fibers, sensory nerve fibers of either vagal or dorsal root/spinal origin do not directly innervate hepatocytes, but are restricted to the stroma surrounding triades of hepatic vasculature and bile ducts, and to extrahepatic portions of the portal vein and bile ducts. For vagal afferent innervation, retrograde and anterograde tracing studies in the rat have clearly shown that only a minor portion of the common hepatic branch innervates the liver area, while the major portion descends in the gastroduodenal branch toward duodenum, pancreas, and pylorus. Hepatic paraganglia, bile ducts, and portal vein receive the densest vagal afferent innervation. Calretinin may be a relatively specific marker for vagal afferent innervation of the portal-hepatic space. Calcitonin gene-related peptide (CGRP) is a specific marker for dorsal root afferents, and CGRP-immunoreactive fibers are mainly present near the intrahepatic vascular bundles and bile ducts, and in the same extrahepatic compartments that contain vagal afferents. Because of the specific anatomical organization of hepatic nerves, selective hepatic denervation, whether selective for the vagal or sympathetic division, or for efferents and afferents, is nearly impossible. Great caution is therefore necessary when interpreting functional outcomes of so-called specific hepatic denervation studies.     

Quantification of neuroepithelial bodies and their innervation in fawn-hooded and Wistar rat lungs

The Fawn-Hooded rat (FHR), a model for primary pulmonary hypertension, shows an unexplained hypersensitivity to airway hypoxia. Because pulmonary neuroepithelial bodies (NEBs) appear to express a functional oxygen-sensing mechanism and an extensive sensory innervation, possible changes in this system should be taken into consideration. In the present study a comparative analysis of NEBs and their selective innervation was performed in FHRs and Wistar control rats. In both rat strains, the number of NEBs was estimated to be around 3,500, approximately 40% of which were innervated by vagal sensory calbindin D28k-immunoreactive (IR) nerve endings and approximately 50% by spinal sensory calcitonin gene-related peptide (CGRP)-IR nerve terminals. The number of intrinsic pulmonary nitrergic neurons and the percentage of pulmonary NEBs revealing a nitrergic innervation were highly significantly lower in FHRs. In both FHRs and Wistar rats, a remarkable morphologic interaction was observed between the intrinsic nitrergic and the CGRP-IR sensory population contacting NEBs. Our findings suggest a possible link between the hypersensitivity to airway hypoxia observed in FHRs and a reduced intrinsic pulmonary nitrergic innervation, possibly via the interaction with pulmonary NEBs and their spinal sensory CGRP-IR innervation.     

A quantitative ultrastructural investigation of tyrosine hydroxylase-immunoreactive axons in the hairy skin of the guinea pig

Besides its thermoregulatory role, the sympathetic innervation of the skin is involved in a modulation of sensory processing and trophic functions that has not been fully characterized. To investigate possible sites at which such sympathosensory interactions might occur, a quantitative ultrastructural study of the sympathetic innervation of the skin was attempted. The hairy skin of the guinea pig was studied because the sympathetic and sensory nerve axons in this species can easily be discriminated by the presence of immunoreactivity to the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH). The thermoregulatory role of the sympathetic skin innervation was highlighted by the almost exclusive sympathetic innervation of piloarrector muscles which contained 62% (n = 195) of randomly selected TH-immunoreactive (TH-IR) axon profiles. Of TH-IR pilomotor axons, 53% were filled with vesicles. Vesicle-containing axonal profiles were equally frequent around dermal arterial blood vessels (partly associated with mast cells), hair follicles, and within nerve fibre bundles surrounded by a perineural sheath, in each case accounting for about 3% of all dermal TH-IR axonal profiles. In contrast to piloarrector muscles, at these locations TH-IR (sympathetic) and non-reactive (sensory) axons were found in close association. These findings are in line with the previously reported inhibitory influence of sympathetic stimulation upon hair follicle afferents and perivascular sensory nerve terminals. In addition, they point to a yet underestimated target of sympathetic axon terminals, i. e. preterminal nerve fibre bundles.     

Cerebellar monoamine nerve terminals,a new type of afferent fibers to the cortex cerebelli

Summary The monoamine innervation of the cerebellum of the rat has been studied by both in vivo and in vitro techniques using the histochernical fluorescence method for the demonstration of catecholamines (CA) and certain tryptamines. By way of a pharmacological approach using inter alia protriptyline, which acts mainly by blocking the membrane pump of the noradrenaline (NA) neurons, evidence was obtained that CA nerve terminals in the cerebellum mainly represent NA nerve terminals. These were found to innervate practically all parts of the cerebellar cortex with a patchy innervation pattern and with an innervation of especially the anterior and posterior lobes. The terminals mainly seem to make axodendritic contacts in the molecular and granular layers without any strict localization of the terminal plexus to any special plane of the cerebellar folia. The fibers enter the cerebellum via the inferior cerebellar peduncle and run in the white matter of the cortex cerebelli. Incubation studies with 6-hydroxytryptamine indicate that there exists also a 5-hydroxytryptamine (5-HT) innervation of the cortex cerebelli, although not as pronounced as the NA innervation. The 5-HT nerve terminals are very fine, varicose fibers and innervate mainly the molecular layer, especially of the anterior lobe. The terminals run mainly in the transverse plane of the folium parallel to the surface. Thus, the pattern of innervation of these 5-HT afferents is different from that of the NA nerve terminals. In the uvula, structures which may represent the rosettes of the mossy fibers or golgi axon terminals in the granular layer take up and accumulate monoamines after incubation with amine in vitro. The exact nature of these structures remains to be elucidated.The cerebellar nuclei receive a very low to low degree of innervation of NA and 5-HT nerve terminals.     

Immature and mature neurofilament-immunoreactive trigeminal fibers can innervate the iris as studied by intraocular grafting of iris and trigeminal ganglia

Using immunohistochemistry on stretch-prepared whole mounts of adult rat irides, a dense, well-organized plexus of neurofilament-positive nerves originating in the trigeminal ganglion can be visualized. Such a two-dimensional tissue preparation is well-suited for studies on sensory and autonomic nerve fiber growth. In the present study the growth capacity of such neurofilament-positive nerves has been studied immunohistochemically. In irides homologously transplanted to the anterior eye chamber of adult albino rats, the intrinsic neurofilament-positive network had almost completely disappeared 4 days postoperatively. In whole mounts of iris grafts after 15 days and 4 weeks in oculo a gradually increasing plexus of nerves was observed. After 3.5 months in oculo a dense, regular network of fluorescent fibers had formed in the iris grafts to the same magnitude as in situ. However, whereas large axon bundles constituted a prominent feature of the distribution of neurofilament-positive nerves in situ, only a few and relatively thin axon bundles were seen in the grafts. The growth capacity of the neurofilament-positive trigeminal nerves was also studied by grafting fetal trigeminal ganglia to the anterior eye chamber. As visualized in cryostat sections, trigeminal grafts contained a large number of strongly fluorescent perikarya and a high density of positive fibers after intraocular maturation. Such grafts readily innervated the host iris. In the area immediately adjacent to the grafts, thin, parallel, rather weakly fluorescent fibers radiated out from the ganglia. When mature trigeminal grafts with attached host iris were regrafted to the anterior eye chamber of adult animals for a few days, in order to remove the intrinsic host iris innervation, such irides showed outgrowing fibers, often organized in small axon bundles, at long distances from the ganglion graft. The present report shows that both mature and immature neurofilament-immunoreactive neurons are capable of innervating the iris. Furthermore, this ingrowth can occur both in the presence and absence of normal intrinsic neurofilament-positive nerve fibers.     

Cholinesterase-positive and catecholamine-containing nerves in the guinea-pig pericardium

The functions of the pericardium are traditionally defined in terms of lubrication and support. However, its complement of autonomic nerve fibers, shown by physiologc experimnts to be sensory, suggests that the pericardium may also serve as a mechanoreceptor site. In this study acetycholinesterase-positive, and catecholamine-containing elements of the pericardial plexus of the guinea-pig were visualized, using thiocholine and fluorescence techniques, respectively. A cholinesterase-positive nerve net, containing the preterminal segments of unmyelinated fibers and simple nerve endings, extended over the entire parietal pericardium. Some of the cholinesterase-positive endings, apparently separate from effector structures were assumed to be sensory. A few heavily myelinated fibers were contributed by the phrenic nerve. The parietal pericardium covering the atria contained many adrenergic nerves and endings. Not all pericardial adrenergic endings were linked to effector structures, such as blood vessels. Some fibers ended freely. It is suggested that liberation of catecholamines from “unattached terminals” may serve to lower the threshold, and prolong the adaptation of adjacent cholinesterase-positive mechanoreceptor terminals.     

Motor and sensory innervation of muscle spindles in the neonatal rat

Summary Neural and muscular elements of three muscle spindles from the soleus muscles of 4-day-old rats were reconstructed by electron microscopy of skip-serial transverse ultrathin sections. Each spindle contained four encapsulated intrafusal fibers, including a minimum of one bag₁, one bag₂ and one chain fiber. The fibers were innervated by unmyelinated motor and sensory axons. The primary and secondary afferents approached the spindles as single axons and terminated on the central region of the intrafusal fibers. Single profiles of terminal axons occupied the sites of sensory neuromuscular junctions, similar to adult sensory endings. No morphological features suggested retraction of afferents from 4-day postnatal spindles. Motor axons approached spindles tightly packed in bundles of 5–20 axons and terminated in the juxtaequatorial and polar regions of both bag and chain fibers. Multiple profiles of terminal axons were visible for each intrafusal motor ending. More motor axons innervated 4-day postnatal spindles and a greater number of axon terminals were visible in immature intrafusal motor endings than in adult spindles. The data suggest that postnatal maturation of motor innervation to intrafusal fibers involves the elimination of supernumerary motor nerve inputs. Synapse elimination in the development of the fusimotor system might represent a mechanism whereby individual axons adjust the number of spindles they innervate.     

Distribution and origin of extrinsic nerve fibers containing calcitonin gene-related peptide, substance P and galanin in the rat upper rectum.

The distributions of nerve fibers containing calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) were examined in the rat rectum of mutants rats, aganglionic rats (AGRs), which completely lack the intramural nerve cells in the large intestine, and of their normal littermates. The origin of extrinsic peptide-containing nerve fibers was examined using retrograde tracing combined with immunohistochemistry in normal rats. In the rectum of normal rats, CGRP-, SP- and GAL-immunoreactive varicose fibers were observed throughout all layers of the rectal wall, and immunoreactive nerve cells were present in the enteric ganglia of colchicine-treated rats. In the aganglionic rectum of AGR, a rich supply of CGRP-immunoreactive fibers was observed in the mucosa, around the blood vessels, and in the submucous and intermuscular spaces. SP- and GAL-immunoreactive fibers in the aganglionic rectum showed a similar distribution to CGRP-immunoreactive fibers but were less dense. These results suggest that most of CGRP-positive fibers in the rectum are extrinsic whereas a large part of SP- or GAL-positive fibers are intrinsic. Fluoro-gold injected into the upper rectum of normal rat labelled nerve cells (less than 10% of total ganglion cells) in the lumbar (L1 and L2) and lumbosacral (L6 and S1) dorsal root ganglia. More than half of nerve cells in the dorsal root ganglia (L6 and S1) projecting to the rectum were immunoreactive for CGRP, and less than 10% were immunoreactive for SP or GAL. Comparison of serial sections of the dorsal root ganglion revealed that about half of the CGRP-immunoreactive cells were also positive for SP or GAL. These results indicate that SP- or GAL-positive neurons projecting to the rectum are scarce in the dorsal root ganglia. The present investigation suggests that CGRP-containing nerves are visceral afferents forming a major component of the sensory innervation of the rat rectum, and SP- and GAL-containing nerves which share their extrinsic origins appear to form a lesser proportion of the sensory innervation.     

Stretch receptor-associated expression of alpha 3 isoform of the Na+, K+-ATPase in rat peripheral nervous system

Expression of the neuronal alpha(3) isoform of the Na(+),K(+)-ATPase (alpha(3) Na(+),K(+)-ATPase) was studied in the rat peripheral nervous system using histological and immunohistochemical techniques. Non-uniform expression of the alpha(3) Na(+),K(+)-ATPase was observed in L5 ventral and dorsal roots, dorsal root ganglion, sciatic nerve and its branches into skeletal muscle. The alpha(3) Na(+),K(+)-ATPase was not detected in nerve fibers in skin, saphenous and sural nerves. In dorsal root ganglion 12+/-2% of neurons were immunopositive for alpha(3) Na(+),K(+)-ATPase and all these neurons were large primary afferents that were not labeled by Griffonia simplicifolia isolectin B4 (marker of small primary sensory neurons). In dorsal and ventral roots 27+/-3% and 40+/-3%, respectively, of myelinated axons displayed immunoreactivity for alpha(3) Na(+),K(+)-ATPase. In contrast to the dorsal roots, strong immunoreactivity in ventral roots was observed only in myelinated axons of small caliber, presumably gamma-efferents. In the mixed sciatic nerve alpha(3) Na(+),K(+)-ATPase was detected in 26+/-5% of myelinated axons (both small and large caliber). In extensor hallicus proprius and lumbricales hind limb muscles alpha(3) Na(+),K(+)-ATPase was detected in some intramuscular axons and axonal terminals on intrafusal muscle fibers in the spindle equatorial and polar regions (regions of afferent and efferent innervation of the muscle stretch receptor, respectively). No alpha(3) Na(+),K(+)-ATPase was found in association with innervation of extrafusal muscle fibers or in tendon-muscle fusion regions. These data demonstrate non-uniform expression of the alpha(3) isoform of the Na(+),K(+)-ATPase in rat peripheral nervous system and suggest that alpha(3) Na(+),K(+)-ATPase is specifically expressed in afferent and efferent axons innervating skeletal muscle stretch receptors.     

Distribution of the growth associated protein GAP-43 in the central processes of axotomized primary afferents in the adult rat spinal cord; presence of growth cone-like structures.

GAP-43-immunolabelled structures were visualized by electron microscopy in the adult rat L4-L5 superficial dorsal horn 2 weeks after sciatic nerve transection. The majority of immunolabelled elements were unmyelinated axons, but some synaptic terminals and myelinated axons also labelled. The labelled unmyelinated axons were commonly located in prominent bundles which on serial section analysis could be followed into larger single trunks. These enlargements contain many organelles and give rise to smaller processes, which is compatible with their being growth cones. Sciatic nerve transection may result, therefore, in central regenerative processes which reorganize the neuropil and contribute to the decreased sensibility and pain that follows peripheral nerve section.     

Sensory innervation of the Achilles tendon by group III and IV afferent fibers

Summary In sympathectomized cats the innervation of the Achilles tendon by fine afferent nerve fibers was studied with semithin and ultrathin sections. Several different types of sensory endings of group III and group IV nerve fibers were identified.Of the five different types of endings in the group III range (T III endings), two are located within vessel walls. One of them ends in the circumference of the venous vessels (T III/VV). Its lanceolate terminals have characteristic receptor areas at their edges. The second type ends in the adventitia of lymphatic vessels (T III/LV). Its receptive areas are scattered along their terminal course. Two further group III endings ramify within the connective tissue compartments of the vessel-nerve-fascicles of the peritenonium externum and internum. One type is tightly surrounded by collagen fibrils (T III/PTic); the other terminates between the collagen fiber bundles (T III/PTgc). The latter arrangement recalls the ultrastructural relation between nerve terminals and collagen tissue in Golgi tendon organs.The fifth type innervates the endoneural connective tissue of small nerve fiber bundles (T III/EN). At least some of them come into close contact with bundles of collagen fibers which penetrate the perineural sheath to terminate within the endoneurium.The endings of group IV afferents (T IV endings) show a striking topographic relationship to the blood and lymphatic vessels of all connective tissue compartments of the Achilles tendon. They form penicillate endings which may contain granulated vesicles. In any event, they can easily be discriminated from the T III endings in the vessel walls.In close neighborhood to Remak bundles, a cell has been regularly found which fulfilled all ultrastructural criteria for mast cells. But this cell is not a mast cell proper because it is surrounded by a basal lamina (pseudo mast cell).     

Nitrergic and peptidergic innervation in the developing rat heart

The phenotypic expression and anatomic distribution of nitrergic and peptidergic innervation in the developing rat heart was localized by reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and immunohistochemistry using antibodies against neuronal isoform of nitric oxide synthase (nNOS), neuropeptide Y (NPY) and calcitonin-gene-related peptide (CGRP). NPY-immunoreactive nerve fibers showed the earliest expression by 16 days of gestation, with preferential innervation of the nodal and perinodal areas, followed by the innervation of the valves and ventricles by postnatal day 7. NPY immunoreactivity was also localized to a large proportion of the intrinsic cardiac ganglia from 16 days of gestation onwards with a progressive increase in the number of neuronal cell bodies per ganglia with age. CGRP-positive nerve fibers appeared by 19 days of gestation and were less dense during the gestational and early postnatal periods, and showed a quantitative increase in density by 7 days, followed by a decrease by 3 weeks postnatal. None of the intrinsic ganglia were stained positive for CGRP, indicating the extrinsic sensory origin of these stained fibers. Nitrergic innervation paralleled the sensory innervation, with the cardiac ganglia and nerve fibers showing a positive labeling from 19 days of gestation onwards. NADPH-d and nNOS were partially co-localized. Double-label immunohistochemistry showed that a considerable proportion of sensory CGRP-immunopositive fibers were also immunoreactive for NOS. The results of the present study show that neuropeptides and nitric oxide are expressed by the late gestational period and that autonomic efferent innervation precedes sensory and nitrergic innervation in the developing heart. Accepted: 4 January 2000     

Catecholamine-containing, dopamine-beta-hydroxylase-immunoreactive perivascular nerve specializations in the rat kidney

Fluorescence histochemical visualization of catecholamines and immunolabeling of dopamine beta hydroxylase (DBH) were employed to study noradrenergic nerve terminals and perivascular nerve specializations in the rat kidney. Plexuses of catecholamine-containing and dopamine-beta-hydroxylase-immunoreactive nerves innervate the intrarenal arterial tree and larger intrarenal veins. Some perivascular nerve bundles have specialized segments composed of clusters of axonal enlargements that are immunoreactive for DBH and fluoresce intensely in ultraviolet light after fixation in a solution of formaldehyde and glutaraldehyde or treatment with glyoxylic acid. No fluorescent neural structures were found in denervated rat kidney sections treated with glyoxylic acid. Many such structures are associated with arteriolar branches of interlobar, arcuate, and interlobular arteries and are composed, in part, of axonal enlargements that contain mitochondria, microtubules, and one or more clusters of synaptic vesicles. These perivascular nerve specializations may be sites of axoaxonal interactions between noradrenergic axons or between these axons and other types of autonomic or sensory axons. The synaptic vesicles evidently store large amounts of catecholamine, but there is no evidence whether it is released into the surrounding tissue. These structures may be involved in changes in intrarenal innervation patterns which may occur as the rat ages. Regardless of the autonomic or sensory nature of intrarenal neural structures, close association of most such structures with arterioles suggests some neurovascular interaction.     

Target finding of pain nerve fibers: neural growth mechanisms in the tooth pulp

The tooth pulp has a dense sensory innervation which, upon stimulation, conveys sensory signals perceived as pain. This innervation, which originates from the trigeminal ganglion, is established through a series of regulated steps during development, and represents an interesting example of tissue targeting by pain-specific nerves. We have investigated various potentially neurotrophic and neurorepulsive influences during this process. The dental papilla/pulp appears to secrete neurite growth inhibitory molecular factors at early stages, which prevent nerve fibers from entering the tissue at what appears to be inappropriate timepoints. Later, a shift from repulsive to attractive factors apparently takes place, and nerve fibers then enter the tooth. When nerve fibers have invaded the dental mesenchyme, a complicated interplay of secreted and membrane-bound factors probably directs the nerve terminals to appropriate sites. Laminin-8 (alpha4beta1gamma1, Lm-411), which is produced by pulpal cells, emerges as an important candidate molecule in this context. Insights into the interactions between the dental pulp nerve fibers and their environment may become important in the search for novel ways to ameliorate pain in the tooth, as well as at other sites.     

Innervation of developing intrafusal muscle fibers in the rat

The chronology of development of spindle neural elements was examined by electron microscopy in fetal and neonatal rats. The three types of intrafusal muscle fiber of spindles from the soleus muscle acquired sensory and motor innervation in the same sequence as they formed—bag₂, bag₁, and chain. Both the primary and secondary afferents contacted developing spindles before day 20 of gestation. Sensory endings were present on myoblasts, myotubes, and myofibers in all intrafusal bundles regardless of age. The basic features of the sensory innervation—first-order branching of the parent axon, separation of the primary and secondary sensory regions, and location of both primary and secondary endings beneath the basal lamina of the intrafusal fibers—were all established by the fourth postnatal day. Cross-terminals, sensory terminals shared by more than one intrafusal fiber, were more numerous at all developmental stages than in mature spindles. No afferents to immature spindles were supernumerary, and no sensory axons appeared to retract from terminations on intrafusal fibers. The earliest motor axons contacted spindles on the 20th day of gestation or shortly afterward. More motor axons supplied the immature spindles, and a greater number of axon terminals were visible at immature intrafusal motor endings than in adult spindles; hence, retraction of supernumerary motor axons accompanies maturation of the fusimotor system analogous to that observed during the maturation of the skeletomotor system. Motor endings were observed only on the relatively mature myofibers; intrafusal myoblasts and myotubes lacked motor innervation in all age groups. This independence of the early stages of intrafusal fiber assembly from motor innervation may reflect a special inherent myogenic potential of intrafusal myotubes or may stem from the innervation of spindles by sensory axons.     

Histochemical and ultrastructural study on the innervation of human and porcine atrio-ventricular valves

Summary The presence of nerve fibers was investigated in porcine and human atrio-ventricular valves by AChE technique, formaldehyde-induced fluorescence, en bloc silver and gold chloride impregnation and electron microscopy.Elaborate nerve plexuses were observed in every leaflet and in some chordae tendineae of all the samples examined, without significant species differences in the pattern of innervation.The presence of a sensory innervation was inferred from the demonstration, in whole mount samples processed for acetylcholinesterase, of thick myelinated nerve fibers and of endings with dot-like or brush-like appearance. Moreover the results of the combined histochemical and ultrastructural methods showed the existence of both cholinergic and adrenergic efferent nerve fibers. Nerve varicosities with clear or dense-cored vesicles were frequently observed in proximity to blood vessels and to cardiac and smooth muscle bundles, which therefore can be considered as the targets of the efferent nerve supply.The complex pattern of the innervation herein demonstrated suggests the existence of a nervous control of valvular function through the regulation of contractile elements.