Reinnervation of free skin autografts in the rat

Substance P axons and sensory threshold increase in burn-graft human skin

BACKGROUND

Our knowledge of afferent nerve fiber reinnervation of grafted skin following third-degree burn is limited by a lack of quantitative histological and psychophysical assessment from the same cutaneous area. The current study compares fiber profile and functional recovery measurements in injured and control skin from the same subject.

MATERIALS AND METHODS

Nerve regeneration and modality-specific sensory thresholds were compared using immunocytochemical labeling with protein gene product 9.5 antibody to stain all axons and anti-substance P to label substance P axons (which are predominantly unmyelinated), as well as computerized instrumentation to obtain psychophysical estimates.

RESULTS

Compared to control skin, threshold measures of pinprick (P < 0.001), warming (P < 0.001), touch (P < 0.001), and vibration (P < 0.01) were significantly elevated in burn-graft skin and correlated with histological analysis of skin biopsies obtained from the same site. Immunohistochemical staining of all axons innervating the dermis and epidermis revealed a significant reduction in burn-graft relative to control skin (54% decrease, P < 0.0001). In contrast, the incidence of substance P nerve fibers was significantly elevated in burn-graft (177% increase, P < 0.05) and appeared to correlate with patient reports of pruritus and pain.

CONCLUSIONS

Observations support the hypothesis that sensory regeneration is fiber-size-dependent in burn-graft skin. The findings that substance P fiber growth increased while total fiber count decreased and that thermal threshold showed the greatest degree of functional recovery suggest that unmyelinated neurons have the greater ability to transverse scar tissue and reinnervate grafted skin following third-degree burn injury.

The pattern of neurovascular development in the forelimb of the quail embryo

Peripheral nerve and vascular patterns are congruent in the adult vertebrate, but this has been disputed in vertebrate embryos. The most detailed of these studies have used the avian forelimb as a model system, yet neurovascular anatomical relationships and critical vascular remodeling events remain inadequately characterized in this model. To address this, we have used a combination of intravascular marker injection, multilabel fluorescent stereomicroscopy, and confocal microscopy to analyze the spatiotemporal relationships between peripheral nerves and blood vessels in the forelimb of 818 quail embryos from E2 (HH13) to E15 (HH41). We find that the neurovascular anatomical relationships established during development are highly stereotypic and congruent. Blood vessels typically arise before their corresponding nerves, but there are several critical exceptions to this rule. The vascular pattern is extensively remodeled from the earliest stage examined (E2; HH13), whereas the peripheral nerves, the first of which enter the forelimb at E3.5-E4 (HH21-HH24), have a progressively unfolding pattern that, once formed, remains essentially unchanged. The adult neurovascular pattern is not established until E8 (HH34). Peripheral nerves are always found to track close and parallel to the vasculature. As they track distally, peripheral nerves always lie on the side of the vasculature away from the center of the forelimb. Neurovascular patterns have a hierarchy of congruence that is highest in the dorsoventral plane, followed by the anteroposterior, and lastly the proximodistal planes.

Sensory restoration of the skin graft on a free muscle flap: experimental rabbit study

Transplantation of a muscle flap with free skin graft for wound coverage is a common procedure in reconstructive microsurgery. However, the grafted skin has little or no sensation. Restoration of the sensibility of the grafted skin on the transferred muscle is critically important, especially in palmar hand, plantar foot, heel, and oral cavity reconstruction. The purpose of this study was to investigate the possibility of sensory restoration of the grafted skin on a trimmed muscle surface that has been sensory neurotized after sensory nerve-to-motor nerve transfer, using the rabbit gracilis muscle as an animal model. The ipsilateral saphenous nerve (sensory) was transferred to the motor nerve of the gracilis muscle for sensory neurotization. A 4 x 4-cm2 area of skin island over the midportion of the gracilis muscle was harvested as a full-thickness skin graft. The upper half of the gracilis muscle was then excised, becoming a rough surface. The harvested skin was reapplied on the trimmed rough surface of the muscle. After 6 months, retrograde and antegrade horseradish peroxidase labeling studies were performed through skin and muscle injection. The group with a free skin graft was compared with the group with an intact surface of the gracilis muscle. This study clearly shows that sensory nerves can regenerate and penetrate into the trimmed muscle surface and grow into the overlying grafted skin. However, if the muscle surface is intact as with the compared group, sensory reinnervation of the grafted skin is not possible.

Disappearance of catecholamine fluorescence from the adrenergic nerves in arterial grafts in rats: an experimental fluorescence histochemical study

The disappearance of catecholamine fluorescence from the noradrenaline-containing sympathetic nerve fibres after arterial transplantation was studied using a femoral artery graft sutured to rat carotid artery. Glyoxylic acid-induced fluorescence was used to demonstrate adrenergic nerves histochemically. At six hours the network of fibres had started to degenerate, and catecholamine fluorescence from the adrenergic nerves had almost completely disappeared within 24 hours of grafting. Control specimens from normal femoral arteries showed a dense network of fluorescent adrenergic nerves. Based on observations of the relatively rapid liberation of catecholamines from the degenerating adrenergic nerves, we suggest that catecholamines liberated from degenerating adrenergic nerves may have an important role in early vasospasm in microvascular and coronary bypass surgery.

Innervation of skin grafts over free muscle flaps

Skin grafts regain their sensory innervation from the graft bed by the regeneration of nerve endings. Although some clinical studies report sensory recovery in skin grafts implanted on free muscle flaps, the mechanism of recovery is obscure. The purpose of this study was to investigate nerve regeneration in experimental skin grafts on free muscle flaps to elucidate this phenomenon. Thirty-eight male Sprague-Dawley rats, weighing 450-550 g were used in the study. The rat gracilis muscle flap was the free flap model transferred from one groin to the other using microvascular anastomoses. Full-thickness skin grafts harvested from the abdomen were used to cover the free muscle flaps after transfer. Four study groups were formed: Group I (n = 10): Free muscle flaps were transferred without any nerve anastomosis; Group II (n = 10): Free flaps transferred with the anastomosis of the muscle's motor nerve to a sensory nerve at the recipient site; Group III (n = 10): Free flaps transferred with the anastomosis of the muscle's motor nerve to a motor nerve at the recipient site; Group IV (n = 8): Skin grafts were placed directly on the fascia layer over the medial hindlimb muscles and served as controls. The specimens were harvested for histologic examination after 12 weeks. Histologic examination was performed to visualise regenerating nerve endings using H&E, S100, Luxol Fast Blue and tyrosine hydroxylase staining. The specimens were categorically scored according to the staining pattern of neural structures around pilosebaceous units and statistical comparisons were performed by using paired t-test. Skin grafts in both Group II and Group III markedly received tyrosine hydroxylase at the base of their pilosebaceous units in many of the specimens and functional nerve twigs could also be traced from the muscle layer to the overlying skin graft. In contrast, the skin grafts in Group I did not show any nerve function in the central parts. The overall staining scores of Groups II, III and IV were significantly higher than Group I (P < 0.05; P < 0.001; P < 0.05, respectively). There was no statistically significant difference between other groups. No myelinated nerve fibres could be detected in any of the skin grafts with Luxol Fast Blue technique. It was concluded in the present study that skin grafts over reinnervated free muscle flaps can develop significantly better innervation than skin grafts over non-innervated muscle flaps. However, the activity in skin appendages indicating nerve regeneration may only imply a gross sensation and in the absence of any myelinated nerve fibres transmission of finer sensation cannot be expected in any of the study groups.

Neuropeptide-containing C-fibres and wound healing in rat skin. Neither capsaicin nor peripheral neurotomy affect the rate of healing

Wound healing in rat skin was studied in standardized wounds inflicted on both hind legs after unilateral sciatic nerve sectioning and/or capsaicin-induced depletion of sensory nerve (C-fibre) neuropeptide content. Daily visual inspection, histological examination and immunohistochemistry with antibodies against substance P, calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide, neuropeptide Y and a pan-neuronal marker, protein gene product 9.5 (PGP 9.5) were used to assess wound healing and determine the distribution of dermal nerve fibres. In controls, nerve fibre density in the wound tissue was low during the first few days after wound infliction, but started to increase on day 4, reaching a peak on day 7 when 25% of medial wounds and 70% of lateral wounds were healed. All wounds were healed on day 11, a scar appearing on day 14 followed by a decrease in nerve fibre density. Capsaicin treatment and/or sciatic nerve sectioning reduced the density of CGRP-immunoreactive nerve fibres by 70% and that of PGP 9.5-immunoreactive fibres by 50%. The capsaicin-induced reduction in PGP 9.5-immunoreactive nerve fibre density is attributable to partial destruction of peripheral nerve fibres. CGRP-immunoreactive and PGP 9.5-immunoreactive nerve fibre density was restored both in capsaicin-treated and denervated groups, reaching a maximum, corresponding to the original level, by days 4-10. Neither the reduction in nerve fibre density following sciatic nerve sectioning nor the impairment of sensory nerve functional capacity following capsaicin treatment affected the rate of wound healing, all wounds being closed on day 11. The study shows that it is difficult to knock out all cutaneous sensory innervation. Thirty per cent of C-fibre innervation seems enough to ensure a normal wound healing.

Reinnervation of split skin grafts in humans: comparison of two different methods of operation

Studies on the reinnervation of split skin grafts have produced contradictory results. As the difference in sensitivity may be caused by the method of grafting, sensory reinnervation was studied in split skin grafted by two different methods. Thirty-nine patients given split skin grafts after the excision of malignant melanoma took part in the study. In 17 patients, split skin was grafted on to the intact muscle fascia. In another 22 patients the skin was grafted directly on to the muscle after the fascia had been removed. In all patients, sensitivity (to touch, heat/cold, and pain) was tested on the grafts and the skin from the opposite side. Sensory functions on grafted skin were generally reduced. Patients with split skin grafted on to the intact muscle fascia had better reinnervation than the ones in whom the fascia had been removed. However, individual patients from both groups showed surprisingly good reinnervation of transplanted skin. The reasons for this finding are not clear, but it is quite possible that the characteristics of the grafted skin have some influence on the reinnervation.

Nerve and blood vessel growth in response to grafted dermis and cultured keratinocytes

The aim of this study was to study innervation and angiogenesis in response to grafts of dermis and cultured keratinocytes using immunohistochemical techniques. In a porcine model, fresh autologous de-epidermalized dermis and cultured autologous keratinocytes were combined using a two-stage technique, to produce keratodermal grafts. Wounds were encased within skin graft chambers that prevented the influence of the surrounding skin. As grafts contracted, a peripheral rim of granulation tissue became exposed, allowing us to compare the wound bed beneath grafts with that beneath the raw granulating surface. Grafts were studied for 6 weeks. Angiogenesis was studied using antisera to von Willebrand factor to detect endothelial cells. Nerve growth was studied using antisera to S-100, a Schwann cell marker, and to four axonal markers: protein gene product 9.5, C-flanking peptide of neuropeptide Y, calcitonin gene-related peptide, and vasoactive intestinal peptide. In kerato-dermal grafts (n = 28), organization of blood vessels and nerve growth occurred only beneath areas with epidermal cover as compared with the surrounding granulation tissue. Initially, the immunoreactivity to von Willebrand factor was high, but in areas with epidermal cover it assumed a more orderly pattern with fewer blood vessels. Innervation was first detected by S-100 immunoreactivity seen at 1 to 2 weeks, closely followed by that to protein gene product 9.5 and much later to calcitonin gene-related peptide. C-flanking peptide of neuropeptide Y and vasoactive intestinal peptide immunoreactivity were detected in the wound depth surrounding large blood vessels at 4 to 6 weeks. In control wounds that had been either grafted with de-epidermalized dermis alone (n = 10) or allowed to granulate (n = 10), persistently there was high immunoreactivity to von Willebrand factor but minimal immunoreactivity to the neural markers. In conclusion, kerato-dermal grafts become innervated, and beneath their surface there is also vascular organization to resemble normal skin. Keratinocytes themselves may influence angiogenesis and innervation, as both processes failed to occur beneath granulating areas.

Neuropeptide-containing nerves in painful hypertrophic human scar tissue

Specimens of hypertrophic scar tissue (n = 9), non-hypertrophic, flat scar tissue (n = 5) and control skin (n = 3) were obtained from eight adult females (aged 22-56) and three adult males (aged 22-59). The specimens were studied histologically and immunohistochemically for vasoactive intestinal polypeptide, neuropeptide Y, calcitonin gene-related peptide, substance P, somatostatin, [Met]enkephalin, [Leu]enkephalin, and the enzyme dopamine beta-hydroxylase. The non-hypertrophic scar tissues were not dissimilar to the control tissue, but contained connective tissue in bundles with a greater number of collagen fibres. In the hypertrophic scar tissue of some patients, the dermis contained adipose tissue displaced upwards from the hypodermis. The connective tissue contained densely packed collagen fibres and fibroblasts; this region was devoid of hair follicles, sweat glands and blood vessels, although they were observed in the region of loosely packed connective tissue. The normal skin contained all the neuropeptides studied, except somatostatin-, and dopamine beta-hydroxylase-immunoreactive nerves, which were seen as single fibres or in nerve bundles, and were associated with blood vessels in the dermis. Neuropeptide Y-immunoreactive nerves were found in the arrector pili muscle, and neuropeptide Y-, vasoactive intestinal polypeptide-, calcitonin gene-related peptide-, [Met]enkephalin- and dopamine beta-hydroxylase-containing nerves were found within sweat glands. In patients with flat, non-hypertrophic scar tissue, neuropeptides and dopamine beta-hydroxylase-containing nerves were absent. In patients with hypertrophic scars, the density of neuropeptide Y-, vasoactive intestinal polypeptide-, substance P-, calcitonin gene-related peptide- and dopamine beta-hydroxylase-immunoreactive nerves was greater in the dermis when compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Human glabrous skin autografts partially reinnervated without sensory corpuscles. An immunohistochemical study

The reinnervation of human glabrous skin autografts was investigated in biopsy specimens obtained four weeks to 15 months after transplantation. The grafted skin was taken from the volar aspect of the wrist and transplanted to the fingers. Immunohistochemical methods were used to detect the presence of nerve fibres and sensory corpuscles, using monoclonal antibodies against neurofilament proteins and S-100 protein. In normal skin, immunoreactivity of neurofilament proteins was localised in the axons of nerves and sensory corpuscles, while S-100 protein immunoreactivity was found in Schwann cells, lamelar cells and inner core cells of sensory corpuscles. In the transplanted skin, there was no positive immunoreactivity in the youngest grafts (four weeks), but in eight week old grafts immunoreactivity to both proteins, identified as axons or Schwann cells, respectively, were seen in the deep nerve plexus, and these reached subepithelial dermis in the 15 month old grafts. In no case, however, were immunoreactive structures found that resembled reinnervated or regenerated sensory nerve corpuscles. Clinical assessment of sensibility was consistent with morphological findings. These results suggest that reinnervation of human skin autografts is far from normal, and that sensory corpuscles are not able to regenerate in grafted human glabrous skin, at least during the times studied.

An increase in the growth of hair associated with hyperinnervation of the underlying vessels in rabbit skin

The localization of sympathetic nerves was studied histochemically in specimens of abdominal free flaps or revascularized graft and anastomosed epigastric arteries (i.e. the cut epigastric artery was resutured) from the operated and contralateral sides of rabbits, compared to controls. In the abdominal skin from control animals, noradrenaline-containing nerves were seen around blood vessels, hair follicles, sweat glands and dermis. In the free flaps, no noradrenaline-containing nerves were present after day 7. However, on the contralateral side, there was an increase in the density of these nerves by day 30, compared with controls. In the epigastric artery, noradrenaline-containing nerves were confined to the adventitial-medial border in control animals and were absent from the anastomosed epigastric arteries, but on the contralateral side they penetrated a third of the medial wall by day 15. Concomitantly, there was excessive growth of hair on the contralateral side. Understanding of the mechanism involved may be of importance in solving the problems associated with hair loss.

Neovascularisation precedes neural changes in the rat groin skin flap following denervation: an immunohistochemical study

We have employed immunohistochemical techniques to study neural and vascular changes in rat skin flaps. Following partial or total denervation, flaps were studied at 4, 7 or 12 days using antisera to PGP 9.5 (panneural marker), the neuropeptides CGRP (sensory nerves) and CPON (adrenergic nerves) and an endothelial marker VWF. In partially denervated flaps, moderate increases in PGP-immunoreactive (PGP-IR) and CGRP-IR nerves and a mild increase in CPON-IR nerves in immediate surrounding skin preceded smaller increases in similar nerves around the pedicle. Following total denervation, mild increases in all nerve types at these locations were accompanied by a marked increase of these nerves in distant surrounding skin, 1-2 cm from the suture line. A gradual increase in endothelial cell staining (VWF) of blood vessels was seen in surrounding skin, flap beds and pedicles. Angiogenesis preceded flap reinnervation which occurred initially from surrounding skin, and later from the base, with sensory fibres appearing first.

Effect of perivascular sympathectomy on distal adrenergic innervation in the hands of monkeys

Perivascular sympathectomy has been thought to cause distal adrenergic denervation. We performed perivascular sympathectomy for a distance of 1 cm. on two common digital arteries in the right hands of two anaesthetised Macaca arctoides monkeys. Four days later, samples were taken for glyoxylic acid-induced fluorescence examination of the operated and opposite control hand. The distal adrenergic nerves were morphologically normal in appearance after the perivascular sympathectomy. The operation should perhaps be called adventitectomy rather than perivascular sympathectomy and its positive effects may be due to the loss of adventitial support for the vasospastic arteries rather than adrenergic denervation.

Perivascular sympathectomy does not remove adrenergic nerves from distal vessels. The effect of various denervations on the rat saphenous bundle: a histochemical study

It has been claimed earlier that perivascular sympathectomy removes distal adrenergic innervation of the vessels. Based on preliminary results suggesting the contrary, the purpose of this work was to reconsider the denervation effect of perivascular sympathectomy. We operated on 40 rats using different denervation methods mainly to test the effects of perivascular sympathectomy on the distal saphenous vessels of the leg. The operations were performed on the right leg, while the left leg was used as a control. Samples were taken 2 days after the operations for glyoxylic acid-induced fluorescence examination for the histochemical demonstration of adrenergic nerves. Perivascular sympathectomy seemed to remove the adrenergic innervation only from the operated segment of the vessel. There was a short segment of diminished innervation a few millimeters in length just distal to the perivascular sympathectomy while the more distal adrenergic nerves around the vessels appeared to be normal. When the saphenous nerve was cut the adrenergic innervation seemed to disappear for 1 cm and to continue to be diminished at the medial malleolus site. Lumbar sympathectomy did not seem to remove the distal adrenergic nerves around the vessels, but caused only a slight decrease in innervation. It can be concluded that the peripheral adrenergic innervation is apparently normal after perivascular sympathectomy and that the operation does not have the previously assumed denervation effects.

The return of sensitivity to cold, warmth and pain from excessive heat in free microvascular flaps

Recovery of sensitivity to cold, warmth and pain caused by excessive heat in various types of free microvascular flaps was studied psychophysically in 27 patients who had undergone such operations four months to four years earlier. A thermal stimulator based on the Peltier principle and controlled by a microprocessor was used to measure the sensitivity to temperature in the transplants. The results were compared with the measured thresholds in the opposite sites in corresponding normal body areas. The present study showed that sensitivity to cold, warmth, and pain caused by excessive heat did return to some free microvascular flaps. According to the measurements the sensation started to return after 6 months in some flaps, and all types of thermal stimuli were felt by one patient as early as 10 months after operation. The return was more pronounced in younger people and in smaller flaps. If the hands, feet, or head defects were reconstructed with a thin skin flap (posterior aspect of thigh, dorsum of foot, or subscapular) the recovery of sensitivity was verified. Sensation returned to the musculocutaneous and osteomusculocutaneous transfers if they were on the hands or the head, or if they were sutured to healthy tissue with normal sensation. The main advantage of the psychophysical sensory testing method that we used is that it gave exact numerical data that made it possible to compare results among the different patient groups and even those obtained at different clinics and laboratories.

Reinnervation and neuropeptides in mouse skin flaps

Degeneration and regeneration of nerves in skin flaps has so far been studied mainly by classical staining methods and there is little information on neuropeptide involvement. Therefore, we have investigated immunocytochemically the temporal course of reinnervation of neuropeptide appearance in skin flaps of mice. Fibres immunoreactive for a general neural marker protein gene product 9.5 (PGP 9.5), and for the neuropeptides substance P, calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) disappeared by 24 h in the flap and surrounding skin. By the 7th day, PGP 9.5-immunoreactive nerves were seen close to the pedicle. By 15 days, they were seen within the body of the flap, clustered focally without specific organisation in greater density than in control skin. Many were also immunoreactive for CGRP and substance P. Neural immunoreactivity for VIP and NPY appeared later (day 30). Thus, regrowing nerves appear initially to be denser than normal innervation. The early appearance of apparently hypertrophic sensory neuropeptide-containing (CGRP and substance P) fibres may have a role in trophic, regulatory and reparative processes.

Recovery of sensation in free flaps

A clinical study of touch, pain, warm and cold stimuli and two-point discrimination was performed in 27 free flaps four months to four years after the microsurgical procedure. There were 5 free skin flaps (2 with nerve suture), 15 musculocutaneous, 4 muscle-covered with split skin grafts and 3 osteomusculocutaneous flaps transplanted to various sites on the body. The results show full or nearly full recovery of touch and pain sensation in all free skin flaps. The musculocutaneous and osteomusculocutaneous free flaps developed good sensation if firmly grown onto the healthy recipient skin with normal sensation. Muscle flaps covered with split skin grafts and all flaps surrounded by scar tissue had a clinical absence of sensation. This study and our earlier findings of the regeneration of nerves in free skin grafts, in skin flaps and in experimental free flaps, lead us to suggest that the healthy denervated skin of the free flap provides a strong neurotrophic stimulus to the cut cutaneous nerves in the edges of the recipient skin. Cutaneous nerves freely regenerate in the loose subcutaneous tissue of the flap. We therefore conclude that all free flaps with skin islands have a potential for developing sufficient protective touch and pain sensation and even some superficial sensitivity.

Adrenergic innervation of aortic patch-grafts in rats

The regeneration of vascular adrenergic nerves was studied using the glyoxylic acid-induced fluorescence method for the specific demonstration of adrenergic nerves in syngeneic patch-grafts of the right atrium of the heart, vena cava and glutaraldehyde-treated vena cava transplanted into the abdominal aorta of the rat. Glutaraldehyde-treated segments of the supradiaphragmatic inferior vena cava were transplanted into the abdominal aorta of rats as well. At the end of the observation period of 24 weeks limited, patchy and defective innervation was observed in the syngeneic vena cava and atrial patches. No adrenergic nerves were found in the glutaraldehyde-treated vein patch-grafts or vein grafts. Owing to the very poor innervation of atrial and venous patch-grafts the results are not entirely in agreement with the target organ concept of adrenergic nerve regeneration. In this study the suture line around the patch graft probably hampers regeneration of vascular adrenergic nerves in the patches.

Degeneration and regrowth of adrenergic nerves after microvascular anastomosis. A fluorescence histochemical study on end-to-end anastomoses of femoral vessels in the rat

The normal femoral artery and its branches were found to be innervated with a dense network of adrenergic nerves. The nerve plexus around the vein was sparse. Adventitial stripping of the femoral vessels, with or without division and reanastomosis, caused local disappearance of catecholamine fluorescence in the stripped area. The distal adrenergic innervation remained normal if the femoral nerve was left intact. Division of the femoral nerve, alone or in combination with blood vessel division and reanastomosis, caused total disappearance of catecholamine fluorescence from the adrenergic nerves of the entire distal neurovascular tree examined. At the end of the observation period of 36 weeks from the time of division of the nerve, artery and vein with subsequent microvascular anastomosis, numerous adrenergic nerves were observed to have crossed the suture line. The vascular nerve plexus around the femoral vessels was dense in places, but in other places sparse or absent. It seems that the reinnervation occurs not only over the suture line, but also together with other regenerating nerves from the adjacent tissues and by collateral sprouting from adjacent adrenergically normally innervated areas.

Trophic interactions between rat nerves and blood vessels in denervated peripheral arteries and in anterior eye chamber transplants

This investigation was undertaken to examine trophic interrelationships between nerves and arteries in male Wistar rats. Two approaches were used. (1) Surgical denervation of two peripheral muscular arteries in the thigh (the superficial epigastric and saphenous) was carried out on young animals (5-20 days old). (2) Arteries from young adults, either with a high density of innervation in situ (the tail artery), or virtually uninnervated (the femoral artery), were transplanted into intact or sympathectomized anterior eye chambers of adult rat hosts. In the denervation experiments, the maximum length of time before reinnervation occurred was 15 days postoperatively. The only evidence of morphological change in the vessel wall was in the external elastic lamina that became irregular and laminated. Reinnervation followed the typical developmental sequence, and was accelerated in the younger animals and by a double lesion. Translocating the proximal part of the nerve carrying the vasomotor innervation indicated that sprouting was directional toward the muscular arteries, bypassing an artery with very sparse innervation. The transplant experiments into the anterior eye chamber showed that only an artery densely innervated in situ (the tail artery) could induce reinnervation by iridean nerve sprouting. The tail artery, in the chamber lacking adrenergic innervation of the iris, became reinnervated by terminals with small agranular vesicles. These vesicles were part of Schwann cell complexes, at a similar relative density, occupying the same position in the vessel wall, as the ingrowing nerves in the fully innervated iris. The latter also had a proportion of terminals with the small clear vesicles. A small population of large granular vesicles could also be found in both types of terminals. Therefore, tissue normally having only sympathetic innervation cannot be assumed to be completely noninnervated when transplanted into a sympathectomized anterior eye chamber. The denervation and transplant experiments described here demonstrated the presence of trophic interactions between nerves and arteries, but also revealed a heterogeneity of response between vessels with very high and extremely low levels of innervation in situ.

The regeneration of adrenergic nerves in a free microvascular groin flap in the rat

The regeneration of adrenergic nerves in free microvascular groin flaps in the rat was investigated. The adrenergic nerves were revealed with glyoxylic acid-induced fluorescence and with formaldehyde-induced fluorescence methods. In the control specimens taken from the contralateral groin, adrenergic nerves were seen in the erector pili muscles and as networks around arteries and arterioles. In the free flap four weeks postoperatively, a few regenerating adrenergic nerves were observed at the margins under the flap and following the pedicle. Eight weeks postoperatively many tiny regenerating nerves were observed to invade the flap at the margins and under it. Many regenerating nerves were observed to reinnervate the artery and vein, forming a nerve plexus in the pedicle. The number of single nerve fibres invading the flap at the margins decreased sixteen weeks postoperatively, but more nerves were observed along arterioles in the flap and pedicle. Twenty-four weeks postoperatively some regenerating adrenergic nerves were observed around arteries and arterioles in different areas in the flap and in erector pili muscles. A rich network of nerves remained around the pedicle. However, the reinnervation of the vasculature of the flap remained patchy and inadequate, and many arteries and arterioles remained without innervation.

Innervation of syngeneic vein grafts in the rat. The regeneration of adrenergic nerves

Regeneration of adrenergic nerves was studied sequentially in segments of the supradiaphragmatic inferior vena cava transplanted from one rat into the abdominal aorta of another of the same inbred strain. Nontransplanted vein segments were examined as controls. The adrenergic nerves were demonstrated by using the glyoxylic acid-induced fluorescence method and the formaldehyde-induced fluorescence method for the demonstration of cathecholamines. A total of 16 syngeneic grafts were examined 3, 5, 8, 16, 27, and 32 weeks after transplantation. Three additional grafts were wrapped inside a silicone tube during the operation to prevent regeneration of nerves from the surroundings. These rats were then killed 8 weeks after the operation. In the control specimens the supradiaphragmatic inferior vena cava was innervated with a rather dense plexus of adrenergic nerves showing varicosities. No nerves were seen in the 3-week-old grafts. In the 5-week-old grafts some sparsely distributed solitary nerve fibres were seen. In the 8-week-old grafts sparsely distributed regenerated nerves reinnervating the vasa vasorum and nerve plexa were observed. The 16-, 27-, and 32-week-old grafts showed rather poorly innervated areas and areas where the nerve plexus was dense. One graft showed very dense reinnervation with morphologically abnormal adrenergic nerves forming "droplet fibers" and showing dense accumulations of catecholamines. The grafts surrounded with silicone tubes had no adrenergic nerves and showed only some regenerated nerves crossing the suture line. The results of the present study indicated that syngeneic inferior vena cava transplanted into the abdominal aorta will be reinnervated with adrenergic nerves. The pattern of the nerve regeneration remains incomplete and patchy.

The regeneration of substance P-containing nerve fibers in the process of burn wound healing in the guinea pig skin

The regeneration of substance P (SP)-containing nerve fibers in the process of burn wound healing in the guinea pig skin has been studied by immunohistochemistry. SP-like immunoreactivity, which was specifically localized in neural elements of intact skin, was found to disappear in the burn wound including its margin on day 2 post burn. The SP-containing nerve fibers were first detected in periods later than day 2 post burn, and the regeneration seemed to occur in association with regeneration of blood vessels at the wound margins. These nerve fibers gradually increased in number and acquired maximum density on day 14 post burn. In addition, such renewed fibers showed sprouting to form a dense network, which has never been observed in intact skin, in the upper granulation tissue just beneath the regrowing epidermis. Following that peak period, the density of the fibers gradually decreased to less than that of controls. The characteristic process of regeneration of SP-containing nerve fibers, having a peak period of fiber density at least in burn wound healing, appeared similar to that of the regeneration of sympathetic catecholaminergic nerve fibers reported previously.

Innervation of syngeneic vein grafts in the rat. The regeneration of cholinesterase positive nerves

The regeneration of cholinesterase positive nerves into segments of the supradiaphragmatic inferior vena cava transplanted from one rat into the abdominal aorta of another rat of the same inbred strain and sex were studied, using a histochemical thiocholine method for the demonstration of cholinesterase. Iso-OMPA and BW-284 C 51 were used as inhibitors for nonspecific cholinesterase (nsChE) and acetylcholinesterase (AChE), respectively. A total of 12 grafts were examined 3, 5, 8, 16, 27 and 32 weeks after transplantation. One single regenerating nsChE reactive nerve was seen near the suture line in a 3-week-old graft. Some solitary regenerating nerves were regularly seen in the grafts at 5 weeks. Eight weeks after grafting some solitary sparsely distributed nerves were found in the outer layers of the graft. In the 16-, 27-, and 32-week-old grafts, nsChE reactive nerves and small nerve bundles were running either solitary or forming nerve plexa in addition to nerves in the vicinity of vasa vasorum. These regenerated nsChE reactive nerves are probably vasomotor in nature. The AChE reaction showed a clear activity in the intimal layer of the grafted veins. No AChE reactive nerves were seen in the 3-, 5-, and 8-week-old grafts. Only occasional AChE positive nerves were observed 16, 28 and 32 weeks after transplantation. These nerves are probably sympathetic cholinergic nerves.

The regeneration of cholinesterase-positive structures in the process of burn wound healing in the skin of the guinea-pig

The regeneration of acetylcholinesterase-positive structures was studied during the process of third-degree burn wound healing in the skin of guinea-pigs. The procedure in this study generally followed the histochemical thiocholine technique of Karnovsky and Roots (1964) with slight modification. Acetylcholinesterase activity in the skin was found to disappear from the burn wound including its margin within 14 days post burn. True regeneration of acetylcholinesterase activity became visible after 21 days post burn. The cholinergic fibres reinnervating arterioles became visible on the twenty-first day, and thereafter gradually increased in number and staining intensity at the deep region of scar margins. The cholinergic fibres detected at the upper region of the scar centre on the twenty-first day disappeared on the twenty-eighth day. Such denervation of the cholinergic fibres may be elicited by the absence of the target organs or by a dense collagenous scar which induces degenerative changes in regenerated nerves. The denervation of cholinergic nerve fibres occurred in association with degeneration of the target organs. On the other hand, the regeneration of the cholinergic nerve fibres was not always associated with the regeneration of the target organs, but occurred later than that of the target organs.

The regeneration of the sympathetic catecholaminergic nerve fibers in the process of burn wound healing in guinea pigs

In the present study, morphological alterations of cutaneous catecholaminergic nerve fibers in the process of burn wound healing have been investigated by using glyoxylic acid induced fluorescence histochemistry. The sympathetic denervation is detected within 48 hr after burns as well as in various excisions. The regenerating sympathetic fibers are observed on the 7th day after burns. These regenerating fluorescent fibers seem to develop in accordance with the regeneration of blood vessels in the wound margins at various stages of healing. Regenerating sympathetic fibers gradually increase in number and the maximum density of these fibers is found approximately at 2 weeks after burns. Thereafter, the density of the fibers gradually decreases to less than that of sympathetic innervation of intact skin. On the 14th day after burns, dense regenerating fibers are observed around the regenerated arterial vessels in the deep granulation tissue of the wound margins. These fibers may correlate with the degeneration of regenerated blood vessels in the center of the wound because of contracting the blood vessel of the wound margins. Moreover, dense collateral sprouting of regenerating fibers is observed around the degenerative blood vessel in the center of the wound on the 16 day after burns. This sprouting occurs not because of searching after a new target organ following the degeneration of the target organ but because of playing important roles in certain functions during wound healing.

Innervation of scar tissue in the skin of the rat

In this study the reinnervation of scar tissue was investigated histochemically to demonstrate catecholamine fluorescence and nonspecific cholinesterase activity. The scarring was produced by healing and contraction of a defect in the dorsal skin of the rat. The first regenerating nerves showing nonspecific cholinesterase activity were observed in the scar four weeks postoperatively. Throughout the investigation period, that is up to twenty weeks after the operation, only free regenerated nerves were found in the scar; no encapsulated nerve endings were observed. No fluorescent adrenergic nerves were found in the dense collagenous part of the scar tissue. Regenerated fluorescent nerves were, however, observed in the loose regenerated connective tissue under the scar. Most of these nerves followed the course of blood vessels. In the present work a vigorous contraction of the scar tissue was noted and a poor innervation of the scar tissue with free nerves was observed. The role of these regenerated nerve endings in sensory discrimination, and the importance of different transmitters acting in the sensory system are discussed.