Embryonic origin of substance P containing neurons in cranial and spinal sensory ganglia of the avian embryo

The ontogeny of the neurons exhibiting substance P-like immunoreactivity (SPLI) was examined in the spinal and cranial sensory ganglia of chick and quail embryos. It was shown that in dorsal root ganglia (DRG) virtually all neuronal somas occupying the mediodorsal (MD) region of the ganglia are SPLI-positive while the larger neurons of the lateroventral (LV) area are SPLI-negative. In the cranial nerve ganglia, both types of neurons coexist in the trigeminal ganglion but with a different distribution: small neurons with SPLI are proximal while large neurons without SPLI occupy the maxillomandibular and ophthalmic lobes. The distal ganglia of nerves VII and IX (i.e., geniculate, petrosal) do not show cell bodies with SPLI in the two species considered. A few of them only (about 12%) are found in the nodose (distal ganglion of nerve X). The proximal ganglia of nerves IX and X (i.e., superior-jugular complex) are composed of small neurons which virtually all exhibit SPLI. Chimaeric cranial sensory ganglia were constructed by grafting the quail hind-brain primordium into chick embryos. Revelation of SPLI was combined with acridine orange staining on the same sections in order to ascertain the placodal (chick host) or neural crest (quail donor) origin of the SP-positive neurons in each type of ganglion. We found that all the neurons showing SPLI are derived from the neural crest in the trigeminal and in the superior and jugular ganglia. In the geniculate, petrosal, and nodose all the neurons are derived from the placodal ectoderm. The small number of SPLI-positive cells of the nodose ganglia are not an exception to this rule. Therefore, generally speaking, the sensory neurons of the cranial ganglia that express the SP phenotype are derived from the crest, with the exception of some neurons present in the nodose of both quail and chick embryos and which are of placodal origin. The vast majority of placode-derived neurons do not have amounts of SP that can be detected under the conditions of the present study.     

Transduction mechanisms in airway sensory nerves.

The induction of action potentials in airway sensory nerves relies on events leading to the opening of cation channels in the nerve terminal membrane and subsequent membrane depolarization. If the membrane depolarization is of sufficient rate and amplitude, action potential initiation will occur. The action potentials are then conducted to the central nervous system, leading to the initiation of various sensations and cardiorespiratory reflexes. Triggering events in airway sensory nerves include mechanical perturbation, inflammatory mediators, pH, temperature, and osmolarity acting through a variety of ionotropic and metabotropic receptors. Action potential initiation can be modulated (positively or negatively) through independent mechanisms caused mainly by autacoids and other metabotropic receptor ligands. Finally, gene expression of sensory nerves can be altered in adult mammals. This neuroplasticity can change the function of sensory nerves and likely involve both neurotrophin and use-dependent mechanisms. Here we provide a brief overview of some of the transduction mechanisms underlying these events.     

Peripheral development of avian trigeminal nerves

Development of the trigeminal nerve branches was studied in stage -17 to -27 chick embryos stained with an antibody to neurofilament protein. The following findings were obtained. 1) Ectopic ganglia transiently appeared in the ectoderm of the supraorbital region and were considered as remnant ophthalmic-placode-derived ganglia. 2) Most of the cutaneous sensory branches of the maxillomandibular nerve arose from a loosely arborized mass of neurites, provisionally termed the maxillomandibular reticulum, in which the fibers intermingled in a seemingly random fashion. 3) The growth of the trigeminal branches was mainly correlated with the development of the facial processes; however, irregular communications between different groups of branches were observed, suggesting that topographical organization of the peripheral branches is not rigid in early stages. 4) From the ophthalmic nerve around stage 23, transient dorsal rami developed and were distributed in the mesenchymal space, the cavum epiptericum, and passed near the ectoderm. Their homology with the rr. tentorii in human anatomy is suggested.     

Dual origin of avian lymphatics

The earliest signs of the lymphatic vascular system are the lymph sacs, which develop adjacent to specific embryonic veins. It has been suggested that sprouts from the lymph sacs form the complete lymphatic vascular system. We have studied the origin of the jugular lymph sacs (JLS), the dermal lymphatics and the lymph hearts of avian embryos. In day 6.5 embryos, the JLS is an endothelial-lined sinusoidal structure. The lymphatic endothelial cells (LECs) stain (in the quail) positive for QH1 antibody and soybean agglutinin. As early as day 4, the anlagen of the JLS can be recognized by their Prox1 expression. Prox1 is found in the jugular section of the cardinal veins, and in scattered cells located in the dermatomes along the cranio-caudal axis and in the splanchnopleura. In the quail, such cells are positive for Prox1 and QH1. In the jugular region, the veins co-express the angiopoietin receptor Tie2. Quail-chick-chimera studies show that the peripheral parts of the JLS form by integration of cells from the paraxial mesoderm. Intra-venous application of DiI-conjugated acetylated low-density lipoprotein into day 4 embryos suggests a venous origin of the deep parts of the JLS. Superficial lymphatics are directly derived from the dermatomes, as shown by dermatome grafting. The lymph hearts in the lumbo-sacral region develop from a plexus of Prox1-positive lymphatic capillaries. Both LECs and muscle cells of the lymph hearts are of somitic origin. In sum, avian lymphatics are of dual origin. The deep parts of the lymph sacs are derived from adjacent veins, the superficial parts of the JLS and the dermal lymphatics from local lymphangioblasts.     

Patterns of slow transport in sensory nerves

An examination of the pattern of outflow of radioactivity in sciatic nerves was made at times from 1 to 82 days in the rat and up to 132 days in the cat after injecting the L5 and L7 dorsal root ganglia, respectively, with 3H-leucine. Slow waves moving at a rate of 1-2 mm/day were looked for on the basis of their reported presence in the motor fibers of the rat. A consistent pattern of slow waves was not seen in the cat or rat sensory fibers of the sciatic nerves nor was evidence of a slow wave found in the cat dorsal columns. Irregularities in the pattern of outflow which at times appeared as "waves" did so in an irregular fashion, a pattern inconsistent with a steady progression of slow waves in the fibers. The decrease of radioactivity appearing first near the ganglia helps create the impression of a wave along with irregular decreases in the overall levels of radio-activity with time. The results were explained on the basis of the unitary hypothesis. The labeled components are considered to be moved down the fiber by the fast transport mechanism, those components dropping off locally in the fibers early on, constituting the slow wave. As those components turn over locally in the various organelles of fiber and are further redistributed, they may at times give rise to what appears as waves.     

Ablation of sensory nerves favours melanoma progression

The tumour mass is composed not only of heterogeneous neoplastic cells, but also a variety of other components that may affect cancer cells behaviour. The lack of detailed knowledge about all the constituents of the tumour microenvironment restricts the design of effective treatments. Nerves have been reported to contribute to the growth and maintenance of numerous tissues. The effects of sensory innervations on tumour growth remain unclear. Here, by using state‐of‐the‐art techniques, including Cre/loxP technologies, confocal microscopy, in vivo‐tracing and chemical denervation, we revealed the presence of sensory nerves infiltrating within the melanoma microenvironment, and affecting cancer progression. Strikingly, melanoma growth in vivo was accelerated following genetic ablation or chemical denervation of sensory nerves. In humans, a retrospective analysis of melanoma patients revealed that increased expression of genes related to sensory nerves in tumours was associated with better clinical outcomes. These findings suggest that sensory innervations counteract melanoma progression. The emerging knowledge from this research provides a novel target in the tumour microenvironment for therapeutic benefit in cancer patients.     

Ultrastructure of the corneal nerves in the Rat

Summary The ultrastructure of the corneal nerves of the rat was studied in tissue fixed by immersion in and by perfusion with glutaraldehyde-containing fixatives. Of the four types of axonal terminal identified in the nerves, those with the features of adrenergic and cholinergic terminals were confined to the nerves at the limbus and were concentrated in the perivascular plexuses. The remaining two types of terminal were found on axons located in all parts of the cornea and on both intraepithelial axons and axons in the stromal nerves. Of these, one contained the numerous mitochondria which occur in the terminals of axons associated with known mechanoreceptors and the second contained variable and often small numbers of both clear and large dense-cored vesicles. While most of the mitochondria-containing terminals were seen in nerves located near the periphery, vesicle-containing terminals were numerous in all of the nerves, and especially in those in the avascular cornea. In material fixed by immersion in glutaraldehyde-paraformaldehyde, the vesicle-containing terminals appeared to be dilated, but in material fixed by perfusion there was little evidence of any increase in the diameter of the axons in the terminal regions. The structure of the terminals was compared with that of the terminals of axons identified in the nerves of the skin and the urinary tract and the differences in the vesicle content of the terminals to those reported in other studies of the corneal nerves was related to the use of different fixation procedures. The possibility that axons possessing such terminals are identical with the beaded axons and both the cholinesterase-positive and fluorescent axons demonstrated in light microscopical studies of the corneal nerves is discussed, and the widespread distribution of the axons in the cornea is equated with the hypothesis that they are afferent in nature and represent the peripheral receptors for pain impulses.     

Galanin in porcine vagal sensory nerves: immunohistochemical and immunochemical study.

In this work, the presence of galanin was examined by immunohistochemistry, radioimmunoassay and high performance liquid chromatography (HPLC) in porcine nodose ganglia, mainly constituted of cell bodies from the vagal sensory neurons. Galanin-like immunoreactivity (Gal-LI) was revealed in 10 to 15% of the total cell bodies by the indirect immunofluorescent technique of Coons. For comparison, a positive staining was revealed in a few cell bodies of the submucous plexus and in fibers located in the different layers of the ileum. The extractable Gal-LI content in nodose ganglia was 7.2 +/- 0.8 pmol/g wet tissue, which represents a concentration about nine times lower than that found in the ileum. HPLC of extractable material revealed a predominant peak which coeluted with the synthetic peptide. We propose that, in pigs, galanin may play a role in the transmission of visceral information through the vagal afferences.     

Embryonic origin and differentiation of the Drosophila heart

We have followed the normal development of the different cell types associated with the Drosophila dorsal vessel, i.e. cardioblasts, pericardial cells, alary muscles, lymph gland and ring gland, by using several tissue-specific markers and transmission electron microscopy. Precursors of pericardial cells and cardioblasts split as two longitudinal rows of cells from the lateral mesoderm of segments T2-A7 (cardiogenic region) during stage 12. The lymph gland and dorsal part of the ring gland (corpus allatum) originate from clusters of lateral mesodermal cells located in T3 and T1/dorsal ridge, respectively. Cardioblast precursors are strictly segmentally organized; each of T2-A6 gives rise to six cardioblasts. While moving dorsally during the stages leading up to dorsal closure, cardioblast precursors become flattened, polarized cells aligned in a regular longitudinal row. At dorsal closure, the leading edges of the cardioblast precursors meet their contralateral counterparts. The lumen of the dorsal vessel is formed when the trailing edges of the cardioblast precursors of either side bend around and contact each other. The amnioserosa invaginates during dorsal closure and is transiently attached to the cardioblasts; however, it does not contribute to the cells associated with the dorsal vessel and degenerates during late embryogenesis. We describe ultrastructural characteristics of cardioblast differentiation and discuss similarities between cardioblast development and capillary differentiation in vertebrates. Correspondence to: V. Hartenstein     

Trophic interactions between sensory nerves and their targets

Neurotrophins are target-derived trophic factors essential for the survival and maintenance of neurons. Among these, nerve growth factor (NGF) and neurotrophin-3 (NT-3) are particularly important for sensory neurons. The actions of neurotrophins are through the p75 low-affinity receptor and the high-affinity receptor tyrosine kinase(trk). Each neurotrophin has its preferred receptor, i.e.trkA for NGF, andtrkC for NT-3. The primary sensory neurons in the dorsal root ganglion are classified into two categories, namely, the large and small sensory neurons based on their size. The large sensory neurons with the expression oftrkC depend on NT-3 for development and subserve the function of position sensations. Some of the small sensory neurons expresstrkA and are NGF-dependent. They are responsible for nociceptive sensation, the detection of painful and thermal stimuli. A more intriguing observation is the bidirectional interactions between nociceptive nerves and their target, the skin. The peripheral processes of small sensory neurons innervate the epidermis of the skin as free nerve endings. In denervated skin, there is a drastic reduction in the epidermal thickness, a finding corroborated by the phenomenon of trophic change, the shining and thinning of the skin, in the disorders of peripheral nerves. The performance of animals with peripheral nerve disorders improved after administration of neurotrophic factors. Based on these results, the therapeutic potentials of neurotrophic factors in human are under investigation.     

Capsaicin-sensitive afferent sensory nerves in modulating gastric mucosal defense against noxious agents.

In the rat stomach, evidence has been provided that capsaicin-sensitive sensory nerves (CSSN) are involved in a local defense mechanism against gastric ulcer. In the present study capsaicin or resiniferatoxin (RTX), a more potent capsaicin analogue, was used to elucidate the role of these sensory nerves in gastric mucosal protection, mucosal permeability, gastric acid secretion and gastrointestinal blood flow in the rat. In the rat stomach and jejunum, intravenous RTX or topical capsaicin or RTX effected a pronounced and long-lasting enhancement of the microcirculation at these sites, measured by laser Doppler flowmetry technique. Introduction of capsaicin into the rat stomach in very low concentrations of ng-microg x mL(-1) range protected the gastric mucosa against damage produced by topical acidified aspirin, indomethacin, ethanol or 0.6 N HCl. Resiniferatoxin exhibited acute gastroprotective effect similar to that of capsaicin and exerted marked protective action on the exogenous HCl, or the secretagogue-induced enhancement of the indomethacin injury. The ulcer preventive effect of both agents was not prevented by atropine or cimetidine treatment. Capsaicin given into the stomach in higher desensitizing concentrations of 6.5 mM markedly enhanced the susceptibility of the gastric mucosa and invariably aggravated gastric mucosal damage evoked by later noxious challenge. Such high desensitizing concentrations of capsaicin, however, did not reduce the cytoprotective effect of prostacyclin (PGI2) or beta-carotene. Capsaicin or RTX had an additive protective effect to that of atropine or cimetidine. In rats pretreated with cysteamine to deplete tissue somatostatin, capsaicin protected against the indomethacin-induced mucosal injury. Gastric acid secretion of the pylorus-ligated rats was inhibited with capsaicin or RTX given in low non-desensitizing concentrations, with the inhibition being most marked in the first hour following pylorus-ligation. Low intragastric concentrations of RTX reduced gastric hydrogen ion back-diffusion evoked by topical acidified salicylates. It is concluded that the gastropotective effect of capsaicin-type agents involves primarily an enhancement of the microcirculation effected through local release of mediator peptides from the sensory nerve terminals. A reduction in gastric acidity may contribute to some degree in the gastric protective action of capsaicin-type agents. The vasodilator and gastroprotective effects of capsaicin-type agents do not depend on vagal efferents or sympathetic neurons, involve prostanoids, histaminergic or cholinergic pathways.     

Embryonic infection with the endogenous avian leukosis virus Rous-associated virus-0 alters responses to exogenous avian leukosis virus infection.

We inoculated susceptible chicken embryos with the endogenous avian leukosis virus Rous-associated virus-0 (RAV-0) on day 6 of incubation. At 1 week after hatching, RAV-0-infected and control chickens were inoculated with either RAV-1 or RAV-2, exogenous viruses belonging to subgroups A and B, respectively. The chickens injected with RAV-0 as embryos remained viremic with exogenous virus longer and either failed to develop type-specific humoral immunity to exogenous virus or developed it later than the control chickens not inoculated with RAV-0. The RAV-0-injected chickens also developed neoplasms at a much higher frequency than did the control chickens. We suggest that the lower immune responses of the RAV-0-injected chickens were due to an immunological tolerance to envelope group-specific glycoproteins shared among endogenous and exogenous viruses.     

Distribution of motor and sensory fibers in the intercostal nerves. Significance in reconstructive surgery.

If the distribution of the types of nerve fibers in the various intercostal nerves is taken into consideration, an intercostal nerve segment can be an acceptable donor nerve graft for sensory and/or motor nerve replacements. We describe the distribution of motor and sensory axons in various segments of the upper and lower intercostal nerves.