Distribution of bombesin, somatostatin, substance-P and vasoactive intestinal polypeptide in feline and porcine skin

Innervation of cutaneous structures in the mouse hind paw: a confocal microscopy immunohistochemical study

The normal innervation of structures in mouse foot pads was investigated with immunohistochemistry and confocal microscopy. Nerves were visualized by incubating Zamboni fixed, thick, frozen sections with antibodies to protein gene product 9.5 (PGP 9.5), vasoactive intestinal peptide, substance P, calcitonin gene-related peptide, and protein zero. The antibodies were localized using cyanine 3.18 labeled anti-rabbit gamma globulin. PGP 9.5 immunolocalization showed dense nerve bundles at the base of the foot pad with branches to larger blood vessels, sweat glands and epidermis. Sweat gland tubules were surrounded by numerous sudomotor axons; single fibers accompanied the sweat duct toward the skin's surface. Nerve bundles containing myelinated and unmyelinated axons ran through and around the centrally located sweat gland cluster to end in free nerve endings and Meissner's-like corpuscles at the apex of the foot pad. Other bundles running parallel to the epidermis gave arcuate branches that supplied epidermis on the sides of the pads with a rich nerve network, principally with free nerve endings that often reached the most superficial cell layers of epidermis. Calcitonin gene-related peptide-immunoreactive (-ir) nerves were distributed to dermis and epidermis in lower density than PGP 9.5-ir fibers. Substance P-ir fibers were less numerous; most terminated as free endings in deeper layers of epidermis. Vasoactive intestinal peptide-ir nerves almost exclusively innervated sweat glands, ducts and blood vessels, but not epidermis. The mouse hind paw has potential to serve as a model system for investigations of functional and morphological changes that affect peripheral and autonomic nerves under diverse experimental conditions.

The regional distribution of neuropeptides in human skin as assessed by radioimmunoassay and high-performance liquid chromatography

In this study radioimmunoassay was used to determine neuropeptide levels in extracts from 17 differing anatomical regions of human skin. Marked regional variations of neuropeptide content for human skin were found and these variations are likely to reflect true physiological functions for the neuropeptides studied. In general the tachykinins, substance P (SP), neurokinin A (NKA) and calcitonin gene-related peptide (CGRP) were found in highest concentrations in regions of skin with the greatest tactile sensation. By contrast, highest concentrations of vasoactive intestinal peptide (VIP) and peptide histidine methionine (PHM) were found in axillary skin, where they probably play a part in axillary eccrine sweat production. Neurotensin was not found in any of the skin areas sampled, suggesting that it is relatively unimportant in human physiological skin control. Reverse-phase high-performance liquid chromatography (rpHPLC) was used to verify the results of radioimmunoassay. Both SP and NKA occurred in several regions in both their reduced and oxidized forms, as well as displaying molecular heterogeneity. CGRP occurred as one molecular species, this being alpha-CGRP, suggesting that this is the predominant molecular form in human skin. Likewise, both VIP and PHM displayed molecular homogeneity in the regions investigated by rpHPLC.

Morphological changes of neural and vascular peptides in human skin suction blister injury

Suction blister injury is an experimental model for the investigation of the possible derangement of dermal/epidermal interaction in injury. An extensive fibre network can be stained in skin using antisera to the pan-neuronal marker protein gene product 9.5 (PGP) and the sensory neuropeptide calcitonin gene-related peptide (CGRP), while microvessels are identifiable with antisera to the endothelial marker von Willebrand's factor (vWf) and the peptide endothelin (ET). To investigate the possible involvement of superficial cutaneous innervation and microcirculation during the repair process in injury, human skin biopsies taken at different times after suction blister injury were investigated by quantitative immunohistochemistry. Neural and endothelial changes were seen in both edge and blister areas. PGP- and CGRP-immunoreactive nerves showed an increase in both areas compared with control skin up to 6 h after injury, followed by a decrease which lasted until 72 h. This was followed by a gradual increase of both nerve types starting from the blister edge and lasting up to 8 days after injury when the values were similar to controls. Similarly, in the blister area of the skin, vWF-immunoreactive capillaries showed statistically significant increases between 0 and 6 h after injury, followed by a decrease at 12 and 18 h which was maintained up to 72 h. ET-1 immunoreactivity showed a similar, although more variable, pattern of changes. At the blister edge from 23 h onwards, both vWf and ET-1 immunoreactivities showed a second increase from the edge of the blister spreading towards the centre of the blister ahead of the nerve increase. This lasted up to 8 days, when vWf immunoreactivity showed a statistically significant increase compared with control skin. Generally the numerical increase observed at early time points was accompanied by a strong staining intensity, which reverted to a normal staining intensity at later time points. These results suggest that there is a reactive process for all immunoreactive elements in the early stages of injury, followed by changes indicative of neuronal and endothelial damage (depletion phase) and the subsequent repair process. The repair started with re-epidermalization from the blister edge, followed by revascularization and, lastly, by reinnervation of the tissue. These results indicate a close relationship between epidermis, blood vessels, and nerve fibres during the healing process which follows suction blister injury.

Methodological aspects on immunohistochemistry in dermatology with special reference to neuronal markers

In an attempt to optimize the immunohistochemical procedure for visualizing neuronal markers, such as neuropeptides, in the human skin, different alternatives in all steps of the process were compared. We have studied the influence of type of immunohistochemical method, the biopsy technique, including the size of the punch biopsy, anaesthesia, the choice of fixative and the time of fixation, the storage process, the sectioning parameters, incubation procedure, the type of fluorophore-conjugated antibody and its dilution, mounting and storage, and, finally, microscopical examination. The following procedure was found to give the best result: punch biopsies of 3 mm, taken under local anaesthesia using lidocaine injected into the dermis-subcutis at the place of biopsy; fixation by a buffered 10% formalin solution containing 14% of saturated picric acid for 2 h at 4 degrees C; storage in 10% sucrose buffer for at least 24 h up to 1 month at 4 degrees C or deep-frozen to -70 degrees C for 2 months (with only a minor structural deterioration); cryostat sectioning of the biopsies with a section thickness of 14 microns and with the cutting edge perpendicular to the skin surface; rhodamine (TRITC)-conjugated, instead of fluorescein-isothiocyanate (FITC)-conjugated, secondary antiserum, since it gives a lower background fluorescence; and for the incubation and mounting procedures, our standard laboratory routines were applied. The result is an optimal indirect immunofluorescence technique, to be applied in dermatology. We also found that biopsies taken under local anaesthesia with chloroethyl spray lost almost all immunofluorescence for several neuronal markers in the epidermis-upper dermis.

Physiology of endocrine skin interrelations

Hormones influence the skin and play a role in normal biologic processes. Keratinocytes can convert and synthesize endocrine hormones. Endocrine dysregulation of the skin and abnormalities of endocrine functions of keratinocytes may produce abnormal changes in the skin. Knowledge of the cutaneous metabolism of thyroid hormones, steroids, peptide hormones, and vitamin A derivatives is being rapidly updated. Skin manifestations of endocrine disorders result from imbalance in feedback loops maintaining endocrine homeostasis. Define molecular mechanisms of hormonal action on target cells underlie functional agonism and antagonism of hormonal signals aimed at governing epidermal turnover. The molecular synergism between vitamin A and other hormones may explain the therapeutic efficiency of combining retinoids with other therapies.

Symptoms of notalgia paresthetica may be explained by increased dermal innervation

Notalgia paresthetica is a sensory neuropathy characterized by infrascapular pruritus, burning pain, hyperalgesia, or tenderness. To assess whether the symptoms may be caused by alterations in the cutaneous innervation, skin from the affected area of patients (n = 5) was compared with controls (n = 10) comprising the contralateral unaffected area from the same patients and site-matched biopsies of normals, using immunohistochemistry. Frozen sections were immunostained with antisera to the neuropeptides substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide, and neuropeptide with tyrosine, and to the general neural marker PGP 9.5 and the glial marker S-100 to show the overall innervation and glial cells, respectively. No discernible change in the distribution of neuropeptide-immunoreactive axons was found, but all of the specimens from the affected areas had a significant increase in the number of intradermal PGP 9.5-immunoreactive nerve fibers compared with unaffected areas from the same patients and normal controls. Epidermal dendritic cells immunoreactive for S-100, possibly Langerhans cells, were substantially increased. It is concluded that there is an increase in the sensory epidermal innervation in the affected skin areas in notalgia paresthetica, which could contribute to the symptoms, and that neural immunohistochemistry of skin biopsies could be helpful in the diagnosis of the disease.

An immunocytochemical study of cutaneous innervation and the distribution of neuropeptides and protein gene product 9.5 in man and commonly employed laboratory animals

The cutaneous nerves of rat, cat, guinea pig, pig, and man were studied by immunocytochemistry to compare the staining potency of general neural markers and to investigate the density of nerves containing peptides. Antiserum to protein gene product 9.5 (PGP 9.5) stained more nerves than antisera to neurofilaments, neuron-specific enolase (NSE), and synaptophysin or histochemistry for acetylcholinesterase (AChE). Peptidergic axons showed species variation in density of distribution and were most abundant in pig and fewest in man. However, the specific peptides in nerves innervating the various structures were consistent between species. Nerve fibers immunoreactive for calcitonin gene-related peptide (CGRP) and/or vasoactive intestinal polypeptide (VIP) predominated in all the species; those immunoreactive to tachykinins (substance P and neurokinin A [NKA]) and neuropeptide tyrosine (NPY) were less abundant. Neonatal capsaicin, at the doses employed in this study, destroyed approximately 70% of CGRP- and tachykinin-immunoreactive sensory axons; whereas 6-hydroxydopamine (6-OHDA) at the doses employed resulted in a complete loss of NPY and tyrosine hydroxylase (TH) immunoreactivity without affecting VIP, CGRP, and tachykinins. Thus, this study confirms that antiserum to PGP 9.5 is the most suitable and practical marker for the demonstration of cutaneous nerves. Species differences exist in the density of peptidergic innervation, but apparently not for specific peptides. Not all sensory axons immunoreactive for CGRP and substance P/NKA are capsaicin-sensitive. However, all sympathetic TH- and NPY-immunoreactive axons are totally responsive to 6-OHDA; but no change was seen in VIP-immunoreactive axons, suggesting some demarcation of cutaneous adrenergic and cholinergic sympathetic fibers.

Neuropeptides in skin disease: increased VIP in eczema and psoriasis but not axillary hyperhidrosis

The neuropeptides vasoactive intestinal polypeptide (VIP), substance P and somatostatin were studied in skin biopsies from patients with eczema, psoriasis and axillary hyperhidrosis. VIP concentrations were elevated in skin affected by eczema and psoriasis, whereas substance P and somatostatin levels did not differ from controls. There was a higher concentration of VIP, but not of substance P or somatostatin, in normal axillary skin when compared to adjacent trunk skin, with abundant VIP-containing fibres surrounding eccrine sweat glands. The VIP concentration was unchanged in skin affected by axillary hyperhidrosis. VIP may increase local blood flow in eczema and psoriasis, but does not appear to play a role in axillary hyperhidrosis.

Neuropeptides of the primary sensory neurones in rat skin: an ontogenic study

Cutaneous primary sensory neurones contain a number of biologically-active peptides, including substance P (SP), neurokinin A (NKA) and calcitonin gene-related peptide (CGRP). However, little information is available on ontogenic changes in the tissue concentrations of these neuropeptides. In this study, the concentrations of these neuropeptides have been assessed in dorsal and ventral abdominal rat skin at various stages of development from foetal, early neonatal, late neonatal, weaner to adult, using sensitive and specific radioimmunoassays. In addition, the levels of peptide histidine isoleucine (PHI), a peptide found in non-sensory cutaneous nerves, were assessed to control the study. The levels of PHI and NKA immunoreactivity did not change significantly at any stage of development. However, the levels of SP and CGRP immunoreactivity were significantly elevated in the early neonate with CGRP remaining elevated in the late neonate. The levels of both SP and CGRP were not significantly different between other developmental groups. Significant elevations in cutaneous SP and CGRP concentrations in early neonatal life in the rat, at a time when the pups are blind and naked, may be related to control of cutaneous sensitivity, which during this period of development, has positive survival value for the pups.

Immunocytochemical evidence for the presence of somatostatin-like immunoreactive nerves in human dental pulp

Specific antiserum to somatostatin was used for the immunocytochemical detection of this neuropeptide in human dental pulp. Immunoreactive axon varicosities were observed in the radicular as well as coronal pulp. Fibers displaying somatostatin-like immunoreactivity were detectable within radicular nerve trunks and were found to be associated mainly with blood vessels. Nevertheless, positive fibers with no apparent relation to blood vessels were also observed. No pulp cell was found to be immunoreactive. Previous physiological studies demonstrated that somatostatin may function as a regulatory peptide in feline dental pulp via a pre-synaptic inhibition of substance P release from sensory nerve terminals. It is tempting to speculate that such a mechanism may also be effective in human teeth and may be of value in the regulation of pulpal blood flow and in situations when sensory nerve fibers are activated, e.g., during pulpal inflammation.

Calcitonin gene-related peptide (CGRP) immunoreactivity in the neuroendocrine Merkel cells and nerve fibres of pig and human skin

The presence of calcitonin gene-related peptide (CGRP) in the skin of pig snout and human fingertip was investigated using immunohistochemical techniques. CGRP immunoreactivity was found in Merkel cells and nerve fibres of both species. In pig snout skin, Merkel cells containing CGRP were seen forming clusters at the tips of rete ridge epidermis and in the external root sheath of sinus hair follicles (vibrissae). Human Merkel cells immunostained for CGRP were found isolated or forming small groups in the basal layer of glandular epidermal ridges. In all cases, immunoreactivity was more intense on the side of the Merkel cell facing the associated nerve terminal (which was never positive for CGRP). This part of the Merkel cell has the greatest density of dense-cored granules, suggesting that CGRP must be stored in these granules. Nerve bundles containing CGRP-immunoreactive fibres were found at dermal and hypodermal level, and blood vessels were often surrounded by CGRP nerve fibres. In pig snout skin some nerve fibres containing CGRP penetrated the epidermis and terminated as free endings, and in the human fingertip a small number of CGRP-immunoreactive nerve fibres were seen in Meissner's corpuscles.

Peripheral patterns of calcitonin-gene-related peptide general somatic sensory innervation: cutaneous and deep terminations

The distribution of calcitonin-gene-related peptide (CGRP) immunoreactivity (IR) was studied in peripheral tissues of rats. The ganglionic origin, somatosensory nature, and anatomic relations of this thin-axon population were evaluated with particular emphasis on possible nociceptive roles. In animals untreated with colchicine, CGRP-IR is found in a vast proportion of small- and medium-diameter sensory ganglion cells that give rise to numerous thinly myelinated and unmyelinated axons that display CGRP-IR throughout the body. The integumentary innervation consists, in part, of an extensive subpapillary network largely traced to dermal blood vessels, sweat glands, and "free" nerve endings, some of which are found within regions containing only mast cells, fibroblasts, and collagen. Dermal papillae contain CGRP-IR axons surrounding each vascular loop; other papillary axons end freely or occasionally surround Meissner corpuscles. Intraepithelial axons enter glabrous epidermal pegs, branching and exhibiting terminals throughout the stratum spinosum. A similar pattern is found in hairy skin with additional innervation entering the base and surrounding the lower third of each hair follicle, but apparently not supplying sebaceous glands and arrector pili muscle. Axons innervating nonkeratinized oral epithelium are similar or greater in number and distribution compared to epidermis, often with more extensive branching. The high density of intraepithelial CGRP-IR innervation does not appear to correlate with the sensitive mechanoreceptor-based increase in spatial sensory discriminative capacities in the distal portions of the limb. In deep somatic tissues, CGRP-IR is principally related to vasculature and motor end plates of striated muscle, but there is an extensive network of thin axons within bone, principally in the periosteum, and focally in joint capsules, but not in relation to muscle spindles or tendon organs. These findings, together with the distribution in cranial tissues described in an accompanying paper (Silverman and Kruger: J. Comp. Neurol. 280:303-330, '89), are considered in the context of a "noceffector" concept incorporating the efferent role of these sensory axons in various tissues. It is suggested that involvement in tissue maintenance and renewal during normal function, as well as following injury, may predominate over the relatively infrequent nociceptive role of this peptidergic sensory system.

Changes in nerves and neuropeptides in skin from 100 leprosy patients investigated by immunocytochemistry

The cutaneous innervation is now known to contain neuropeptides including substance P (SP) and calcitonin gene-related peptide (CGRP) in sensory nerves, and vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY), principally in autonomic nerves. Skin biopsies from 100 leprosy patients and equivalent areas from 50 non-leprosy controls were fixed in p-benzoquinone solution for immunofluorescence staining and in Bouin's fluid for classification of leprosy type. Antisera to the neural markers, neurofilaments, and protein gene product 9.5 (PGP 9.5), and to neuropeptides were used. Cutaneous nerves and nerve endings immunoreactive for neuropeptides, neurofilaments, and PGP 9.5 were seen in all non-leprous control cases. In leprosy, PGP 9.5- and neurofilament-immunoreactive nerve fibres were seen in all 14 cases of the indeterminate (early) type and in the majority (33/43) of lepromatous cases, but in a smaller proportion (15/43) of tuberculoid cases. Neuropeptide immunoreactivity was seen in only 2/14 of the indeterminate leprosy specimens and was completely absent in other types. This early disappearance may be of diagnostic significance. Thus, cutaneous sensory and autonomic dysfunctions in leprosy are well reflected by changes in nerve fibres and neuropeptides.

Characterization of neuropeptide-induced histamine release from human dispersed skin mast cells

1. Human skin mast cells, unlike other human mast cells so far studied, released histamine in a concentration-related manner in response to substance P, vasoactive intestinal peptide (VIP) and somatostatin (1 microM to 30 microM). In contrast, eledoisin, physalaemin, neurokinin A, neurokinin B, calcitonin gene-related peptide (CGRP), neurotensin, bradykinin and Lys-bradykinin induced negligible histamine release. 2. The low histamine releasing activity of physalaemin, eledoisin, neurokinin A and neurokinin B relative to substance P suggests that the human skin mast cell activation site is distinct from the tachykinin NK-1, NK-2 or NK-3 receptors described in smooth muscle. 3. The relative potencies of substance P and its fragments SP2-11, SP3-11, SP4-11 and SP1-4 in releasing histamine from human skin mast cells suggests that both the basic N-terminal amino acids and the lipophilic C-terminal portion of substance P are essential for activity. 4. Peptide-induced histamine release, like that induced by compound 48/80, morphine and poly-L-lysine, is rapid, reaching completion in 10-20 s, is largely independent of extracellular calcium but requires intact glycolysis and oxidative phosphorylation. 5. The substance P analogue, [D-Pro4,D-Trp7,9,10] SP4-11 (SPA), not only reduced substance P-induced histamine release in a concentration-related manner but also inhibited that induced by VIP, somatostatin, compound 48/80, poly-L-lysine and morphine but not anti-IgE. 6. The similar characteristics of histamine release induced by substance P, VIP, somatostatin, compound 48/80, poly-L-lysine and morphine suggest that they share a common pathway of activation-secretion coupling distinct from that of IgE-dependent activation. Furthermore, the ability of human skin mast cells to respond to basic non-immunological stimuli including neuropeptides may reflect a specialised function for these cells.

VIP modulates substance P-induced plasma extravasation in vivo

Substance P (SP), a putative mediator of neurogenic inflammation, has previously been shown to induce plasma extravasation when exogenously perfused over a blister base induced on the rat hind foot pad. Using the same animal model, we have studied the role of vasoactive intestinal polypeptide (VIP), one of the neuromodulators in primary afferent neurons, on SP-induced plasma extravasation. At all concentrations tested (2.5, 5 and 10 microM), VIP did not cause plasma extravasation by itself, however, it increased that due to 1 microM SP, in a dose-related manner. We have also studied the effect of VIP on the local blood flow in the blister base using a laser doppler-flowmeter. VIP was also found to increase the local blood flow in a dose-dependent manner. The present results provide evidence for the first time in vivo of a role for VIP in modulating a neurogenic inflammatory response induced by SP. The mechanism underlying this action is probably related to the vasodilator activity of VIP.

Presence of calcitonin gene-related peptide (CGRP) and substance P (SP) immunoreactivity in intraepidermal free nerve endings of cat skin

Immunocytochemistry against neuropeptides contained within primary afferent neurons was used to study the morphology and distribution of intraepidermal free nerve endings in cat facial skin. Calcitonin gene-related peptide (CGRP) and substance P (SP) immunoreactivity was found in similar intraepidermal nerve endings of cat glabrous and hairy skin epithelia. The greatest density of immunoreactive intraepidermal nerve endings was located in the nose epidermis. Small limited areas with immunoreactive intraepidermal nerve endings were also found in facial hairy skin.

Immunohistochemical studies of the neurochemical markers, CGRP, enkephalin, galanin, gamma-MSH, NPY, PHI, proctolin, PTH, somatostatin, SP, VIP, tyrosine hydroxylase and neurofilament in nerves and cells of the human attached gingiva

Punch biopsies were obtained from the buccal gingiva of the lower third molars. Thin nerve fibres, immunoreactive for calcitonin gene-related peptide (CGRP) or substance P (SP), with possible sensory function, were found in the propria often close to the epithelium, sometimes even penetrating into the basal layers. gamma-Melanocyte stimulating hormone (gamma-MSH)-like immunoreactivity was found in sparsely distributed single cells (except in one specimen containing a dense infiltration), resembling neutrophilic granulocytes of the propria. gamma-MSH was present in several single smooth axons and in thick axon bundles of the propria. Surrounding the blood vessels, neuropeptide Y (NPY), tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine amide (PHI) immunoreactive nerve fibres were observed. NPY and TH-positive fibres probably represent sympathetic nerve terminals and VIP/PHI-immunoreactive ones may have a parasympathetic function. Papillae of the propria contained VIP-positive fibres not obviously related to blood vessels. The distribution in papillae of PHI-like immunoreactivity was similar but the PHI-positive reaction was also present in a few cells of the propria, especially near blood vessels. Somatostatin (SOM)-positive reaction occurred in a few dendritic-type cells near or in the epithelium and single nerve fibres close to the epithelium. Several thick axon bundles of the propria contained neurofilament (NF)-immunoreactive material. Some thin NF-fibres were found in the papillae and some seemed to penetrate into the epithelium. No galanin, methionine-enkephalin, parathyroid hormone or proctolin immunoreactive material was found. The rather rich content of several neuropeptides in human attached gingiva, as well as other neurochemical markers, is probably associated with sensory and autonomic functions.

Innervation of facial skin but not masticatory muscles or the tongue by trigeminal primary afferents containing somatostatin in the rat

Using retrograde transport of a fluorescent dye, True blue, the peripheral tissues innervated by trigeminal ganglion neurones containing somatostatin have been investigated. Of ganglion neurones retrogradely labelled from injections of dye into the facial skin, 3.45% were found to be immunoreactive for somatostatin. In contrast, none of the neurones labelled from injections of dye into the tongue or masseter muscle were found to contain this peptide. This demonstration of a restricted distribution of somatostatin-containing primary afferents raises the possibility that somatostatin may be involved in functions which are specific to skin and not to the other tissues examined.

Immunohistochemical evidence for the presence of somatostatin-containing sensory nerve fibres in the human skin

Somatostatin-like immunoreactivity has been found to occur in nerve terminals and fibres of the normal human skin using immunohistochemistry. The immunoreactivity seemed predominantly to be associated with sensory nerves. Thus, nerve fibres displaying weak or moderately strong somatostatin immunofluorescence were observed as free nerve endings of the epidermis and as nerve fibres in the dermis. The immunoreactive nerves were found in low numbers in skin from arm, back and chest, however, only single fibres were seen in sensory specialized areas, such as fingertips. Very few fibres were found close to e.g. blood vessels and sweat glands. Somatostatin, generally believed to be a strongly inhibitory substance, should also be considered when examining the role of different sensory chemical messenger candidates in the human skin.

Depletion of neuropeptides during wound healing in rat skin

The peptides substance P, calcitonin gene-related peptide and somatostatin are present in nerve fibres in mammalian, including human, skin. There is evidence that in addition to having a putative neurotransmitter role, they may be trophic agents: a study was therefore undertaken of peptide changes during wound healing in rat skin. A significant depletion of the neuropeptides was found in the region of the wound within two days, and this persisted for two weeks. A smaller and delayed depletion also occurred in intact skin of the same dermatome, but not in an adjacent dermatome.

A detailed account of NPY-immunoreactive nerves and cells of the human skin. Comparison with VIP-, substance P- and PHI-containing structures

Neuropeptide Y (NPY)-like immunoreactivity has been found in autonomic nerve terminals and fibres of the normal human dermis by the use of indirect immunohistochemistry. Also a granular immunoreactivity was observed in the basal cells of the epidermis as well as in the cells of the outer root sheath of hair follicles. Thus, NPY should be considered when examining the role of different autonomic neurotransmitter candidates. Furthermore, NPY and norepinephrine may, at this level, serve together as co-transmitters or co-modulators of autonomic function. Finally, the immunoreactivity found in cells of the epidermis and the outer root sheath of hair follicles points to other functional effects so far not understood.

Somatostatin localization in tissues

The development of specific antibodies to somatostatin has enabled investigations on the distribution (radioimmunoassay) and precise tissue localization (immunocytochemistry) of somatostatin-immunoreactive (IR) material. Somatostatin immunoreactivity is broadly distributed both in the central nervous system and in many peripheral organs, including the gastrointestinal tract, pancreas, genitourinary system, heart, eye, thyroid, thymus, and skin. Somatostatin-IR cells display characteristic morphological features, including cytoplasmic elongations, which lend support to the postulated local or paracrine role for somatostatin. The intracytoplasmic electron-dense secretory granules in somatostatin-IR endocrine cells are characterized by their round shape, flocculent matrix, and closely apposed limiting membrane. Somatostatin-IR nerves are abundant in the gut and contain large, dense, P-type neurosecretory granules, which are distinct from those storing other peptidergic neurotransmitters. Somatostatin immunoreactivity is found frequently in neuroendocrine tumours, but the existence of the 'somatostatinoma syndrome' has recently been questioned.

On the actions of substance P, somatostatin, and vasoactive intestinal polypeptide on rat peritoneal mast cells and in human skin

Substance P (SP), somatostatin (Som), and vasoactive intestinal polypeptide (VIP) induced a concentration-dependent release of histamine from isolated rat peritoneal mast cells. The release of histamine induced by these neuropeptides was inhibited by preincubation of the cells with the SP analogue [D-Pro4,D-Trp7,9,10]-SP4-11 (SP-A) (10 microM), and also by benzalkonium chloride (10 microM). In addition, SP-A inhibited histamine release induced by compound 48/80, whilst that induced by goat anti-(rat-IgE) was unaffected. In human skin, intradermal injection of SP, Som, or VIP produced flare and wheal responses. The flares to all three peptides were inhibited by preinjection of the skin with SP-A (25 pmol), whilst the wheal responses were unaffected. It is concluded that the receptors mediating histamine release and the flare response are similar, and that SP, Som, and VIP are acting at a similar receptor to produce these effects. It is probable that this receptor is also the site of action of compound 48/80.

Distribution and localization of regulatory peptides

A new group of modulatory substances present in both endocrine cells and central and peripheral nerves has been described in the past few years. These substances are biochemically recognized as peptides and their actions affect many bodily functions. They are now widely known as regulatory peptides. The development of new immunocytochemical techniques, closely allied to radioimmunoassay, has disclosed that the regulatory peptides are present either in cells or in nerves, in almost every tissue of the body. The presence of peptides (the classical hormones) in endocrine cells was already known at the beginning of the century, but the presence of similar substances in nerve fibers, where they probably act as neurotransmitters, is a recent and revolutionary discovery. More than 30 peptides (neuropeptides) have been found to be present in nerves, to which the term "peptidergic" has been applied, although it is now known that in certain cases a neuropeptide can be present in the same nerves as a classical neurotransmitter, for example acetylcholine with VIP, or noradrenaline with NPY. Little is known about the physiological role of these neuropeptides. It is not yet fully accepted that they act as neurotransmitters although there is strong evidence for this, particularly in the case of substance P and VIP. The investigation of the regulatory peptides is now in an initial phase. The involvement of new disciplines, such as molecular biology, in this field is producing new and very exciting discoveries, including the isolation of novel peptides and precursors, the study of which will further contribute to the understanding of the basic control mechanisms.

Preputial skin as a model for the demonstration of substance P-like immunoreactive human peripheral nerve endings

Preputial skin from circumcisions has been used to demonstrate the localization of substance P-like immunoreactivity. It is observed mainly in the dermis, as isolated fibers beneath the basal layer of the epidermis and near the blood vessel walls, and in nerve bundles in the deeper layers. Some fibers even penetrate the epidermis very deeply, until the stratum corneum.

VIP-immunoreactivity in the skin of various mammals: immunohistochemical, radioimmunological and experimental evidence for a dual localization in cutaneous nerves and merkel cells

In the present study VIP-immunoreactive (IR) nerve fibers were found in the skin of several mammalian species (cat, dog, pig and man). They supplied predominantly the arteries and arterial portions of arteriovenous anastomoses. Far fewer VIP-IR nerve fibers innervated veins and arterioles. Capillaries were supplied by VIP-IR fibers only in sweat and Meibomian glands. Some non-vascular VIP-IR nerve fibers were seen in contact with dermal smooth muscle strands. In eccrine sweat glands and in Meibomian glands VIP-IR fibers were targeting glandular cells. In addition, VIP-IR nerve fibers innervated the upper parts of facial hair follicles. In non-neuronal localization VIP-IR occurred in Merkel cells in all species and sites, while the intraepidermal axons consistently were not VIP-IR. Radioimmunoassay of different skin regions of cats also suggested both a neuronal and a Merkel cell origin of VIP-IR. Under physiological conditions VIP which is released from its neuronal and non-neuronal cutaneous pools may have an impact on thermoregulation by influencing blood flow and sweat production. It may also modulate axon-endings in Merkel cell-axon complexes and hair follicle receptors. Under pathological conditions an enhanced release of cutaneous VIP may lead to local inflammatory processes partly mediated via release of histamine from cutaneous mast cells.

Vasoactive intestinal polypeptide (VIP): current status

Research on VIP continues at a rapid pace. Recent progress includes: insights into its biosynthesis (and that of a closely related PHI-like peptide) and its neuronal localization, discovery of novel biological actions, new data on its release and binding to specific receptors, and additional evidence for its roles in physiological regulation and in the pathogenesis of disease.

Topical capsaicin pretreatment inhibits axon reflex vasodilatation caused by somatostatin and vasoactive intestinal polypeptide in human skin

1 Wheal and flare reactions are described following intradermal injections of somatostatin, vasoactive intestinal polypeptide, substance P and histamine in normal human forearm skin. Bombesin failed to produce a significant wheal and flare.2 Pretreatment of skin with capsaicin in all cases dramatically inhibited the flare but not the wheal. This result is in accord with the hypothesis that capsaicin blocks the effector side of the axon reflex, perhaps by depleting nerve terminals of vasodilatory peptide(s).