Reinnervation of sweat glands in the mouse: axonal regeneration versus collateral sprouting

A novel method to quantify cutaneous vascular innervation

INTRODUCTION

To develop a new method to quantify the density of nerves, vessels, and the neurovascular contacts, we studied skin biopsies in diabetes and control subjects.

METHODS

Skin biopsies with dual immunofluorescent staining were used to visualize nerves and blood vessels. The density of nerves, vessels, and their neurovascular contacts were quantified with unbiased stereology. Results were compared with examination findings, validated questionnaires, and autonomic function.

RESULTS

In tissue from 19 controls and 20 patients with diabetes, inter-rater and intra-rater intraclass correlation coefficients were high (>0.85; P < .001) for all quantitative methods. In diabetes, the nerve densities (P < .05), vessel densities (P < .01), and the neurovascular densities (P < .01) were lower compared with 20 controls. Results correlated with autonomic function, examination and symptom scores.

DISCUSSION

We report an unbiased, stereological method to quantify the cutaneous nerve, vessel and neurovascular density and offer new avenues of investigation into cutaneous neurovascular innervation in health and disease.

Technically successful ultrasound-guided percutaneous sural nerve needle biopsy in a patient with indeterminate peripheral neuropathy

OBJECTIVE

To determine whether ultrasound-guided percutaneous sural nerve needle biopsy yields sufficient tissue for analysis in a patient with suspected vasculitis-related peripheral neuropathy.

MATERIALS AND METHODS

With real-time ultrasound guidance, a hydrodissection of the sural nerve from the adjacent small saphenous vein was first performed. A 14-gauge biopsy needle was then manipulated under real-time ultrasound guidance to obtain two transverse samples of the sural nerve at the lateral distal calf.

RESULTS

The biopsy was technically successful and yielded adequate tissue for routine processing. The specimen showed mild epineurial perivascular chronic inflammation with marked loss of myelinated axons. These histologic findings are not diagnostically definitive for vasculitis-related peripheral neuropathy but were supportive of the diagnosis in combination with the patient's physical examination, laboratory, and electromyography findings. The patient suffered no immediate complications after the procedure.

CONCLUSIONS

This ultrasound-guided sural nerve needle biopsy, like many surgical biopsies, did not yield a definitive result in a patient with suspected vasculitis-related peripheral neuropathy; however, the procedure was technically successful. Given that percutaneous needle procedures offer many advantages over surgical procedures, we believe that this procedure warrants further investigation.

A device to measure secretion of individual sweat glands for diagnosis of peripheral neuropathy

There is a need for quantitative, precise assessment of small fiber peripheral nerve function. We tested a customized camera device and protocol designed to quantify secretions of individual sweat glands (SGs). Testing was performed on 178 healthy controls and 20 neuropathy subjects. Sweating was stimulated on a 2.25 cm² skin area by iontophoresis of pilocarpine. The camera imaged sweat from 50 to 400 sweat ducts. We calculated secretion rate of individual SGs, total sweat volume, and number of secreting SGs at four body sites. Neuropathy subjects were tested at the two distal sites to demonstrate the device's capability to detect abnormal sudomotor function. Normal ranges were calculated for each body site. Neuropathy subjects had lower sweat rates per SG, lower total sweat, and lower SG density. The normal values decreased with advancing age, were lower in females, and differed between body sites. There was good agreement with repeat testing. The device provides reliable, precise quantitative measures of sweat secretion from single SGs for characterization of sudomotor nerve function in healthy control subjects and in subjects with known peripheral neuropathy. The test combines the capabilities of existing tests of sudomotor function while providing additional capabilities.

Quantification of sweat gland volume and innervation in neuropathy: Correlation with thermoregulatory sweat testing

INTRODUCTION

No study has correlated thermoregulatory sweat testing (TST) with histopathologic study of sweat glands (SGs) and SG nerve fibers (SGNFs).

METHODS

We studied 10 neuropathy patients in whom anhidrosis was found by TST and 10 matched controls. Skin biopsies were taken from both anhidrotic and sweating skin and immunohistochemical staining was done for nerves and basement membrane. For each biopsy, total tissue volume, total SG volume, and total SGNF length were measured. SGNF length per biopsy volume, SG volume per biopsy volume (SG%), and SGNF length per SG volume were calculated.

RESULTS

SGNF length per biopsy volume was reduced in anhidrotic site biopsies of patients compared with controls. SG% was decreased and SGNF length per SG volume increased in patients compared with controls.

CONCLUSIONS

The results suggest a concomitant loss of SG volume and SGNF length in neuropathy, with greater loss of SGNFs in anhidrotic skin, possibly exceeding collateral reinnervation.

Patterns of target tissue reinnervation and trophic factor expression after nerve grafting

BACKGROUND

Reinnervation of target tissues determines functional outcomes after nerve grafting, which is important in traumatic injury caused by accidents or consequences resulting from surgical removal of tumors. Previous studies documented the influences of nerve repair mainly based on nerve morphometry but rarely compared the final outcomes according to target reinnervation patterns by nerve fibers of different categories.

METHODS

In a mouse model of nerve grafting, the authors analyzed the innervation indexes of different target tissues after transection-reimplantation on the sciatic nerve, which were defined as a parameter on the operated side normalized to that on the control side.

RESULTS

Muscle reinnervation appeared to be the best compared with skin reinnervation (p < 0.0001) and sweat gland reinnervation (p < 0.0001) at postoperative month 3. The sudomotor reinnervation was relatively higher than the cutaneous reinnervation (p = 0.014). The abundance of trophin transcripts for brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and neurotrophin 3 (NT3) was higher in plantar muscles on the operated side than those on the control side. In contrast, transcripts of BDNF, GDNF, nerve growth factor, and NT3 were all similar in the footpad skin between the operated and control sides.

CONCLUSIONS

The results suggested that, compared with the skin, muscles achieved the best reinnervation after nerve grafting, which was related to higher expression of BDNF, GDNF, and NT3 in muscles than in the skin.

Thoracoscopic and anatomic landmarks of Kuntz's nerve: implications for sympathetic surgery

BACKGROUND

Kuntz's nerves (KN) have been blamed for surgical failures of endothoracic sympathectomy. The prevalence of these fibers, however, varies between the surgical (about 10%) and anatomic literature (about 80%). This clinically orientated cadaveric study was conducted to explain this discrepancy, to reveal possible reasons for the low thoracoscopic detection rate, and to define anatomic structures as possible landmarks of KNs.

METHODS

Video-assisted thoracoscopy was performed in 33 thoracic cavities of fresh human cadavers within 48 hours postmortem, followed by anatomic dissection of the first intercostal space. Kuntz's nerves and concomitant blood vessels were of special interest. Statistical analysis included frequencies and chi(2) tests.

RESULTS

Kuntz's nerves were identified in 12.1% by thoracoscopy, whereas anatomic dissection revealed KNs in 66.7% (p = 0.003). Subpleural veins (mean diameter, 2.2 +/- 0.9 mm) parallel to KNs were found in 81.8%. No collateral arteries were identified. Diameters of KNs were 1.4 +/- 0.7 mm; distances between the first thoracic ganglion and the middle of KNs were 9.7 +/- 3.0 mm. Thoracoscopic recognition of these Kuntz veins was higher than that of KNs (62.5% vs 18.2%, p < 0.005).

CONCLUSIONS

The low thoracoscopic detection rate of KNs may be due to the low color contrast of these small fibers. They have, however, most frequently concomitant subpleural veins that are easier to detect. These veins may serve as orientation landmarks of KNs and thus contribute to a more complete denervation improving the outcome of thoracoscopic sympathectomies.

Sex-related differences in recovery of cutaneous nociception after end-to-side nerve repair in the rat

Sex-related differences in the recovery of cutaneous nociception after end-to-side nerve repair were examined in rats. Recovery of nociception in the dorsal foot was determined by skin pinch test 19 weeks after the proximal end of the distal stump of the transected peroneal nerve was sutured to the side of the adjacent intact sural nerve (end-to-side nerve coaptation). Axon sprouts in the recipient peroneal nerve were counted by light and electron microscopy. Recovery of nociception due to axon sprouting through the end-to-side coaptation was found in 87% of females and in 60% of males. The area of nociception was not significantly different (P=0.59) between females and males (13+/-8% and 11+/-9%, respectively). The number of myelinated axons in the recipient peroneal nerve (but not of unmyelinated axons) was significantly larger (P=0.028) in females (median=512, 25th and 75th percentiles: 467 and 594) than in males (median=322, 25th and 75th percentiles: 239 and 468). The majority of these axons in females and males were thin fibres, and recipient nerves in both groups were responsive to nerve pinch test. In conclusion, collateral sprouting of thin myelinated nociceptive axons into the end-to-side coapted nerve is more abundant in female than in male rats. However, recovery of cutaneous mechano-nociception due to sprouting of these axons was not different between the two sexes. Possible reasons are discussed.

Differential impairment of the sudomotor and nociceptor axon-reflex in diabetic peripheral neuropathy

It is not known whether C-fiber functional subclasses are differentially affected by diabetes mellitus or whether the patterns of C-fiber dysfunction are different between type 1 and type 2 diabetes. We therefore examined efferent sympathetic sudomotor and primary afferent nociceptor C-fiber function in diabetic patients. Acetylcholine (10%) was used to evoke C-fiber (axon-reflex)-mediated responses. The nociceptor (flare) response was measured using a laser Doppler device. The sudomotor response was quantified with silastic imprints. The nociceptor C-fiber-mediated flare response was reduced in type 2 diabetic patients (P < 0.008) but was similar to controls in type 1 diabetic patients. The sympathetic C-fiber-mediated responses, including sweat volume (P < 0.05) and the number of activated sweat glands (P = 0.003), were increased in patients with type 1 diabetes. There also was a trend toward a larger axon-reflex sweat area in patients with type 1 diabetes (P = 0.09). No differences in these sweat responses were found in patients with type 2 diabetes compared to controls. These findings suggest that the functional abnormalities in diabetic peripheral neuropathy are not homogeneous and that C-fiber subclasses are differentially affected in type 1 and 2 diabetes mellitus.

FK506 enhances reinnervation by regeneration and by collateral sprouting of peripheral nerve fibers

We examined the effects of FK506 administration on the degree of target reinnervation by regenerating axons (following sciatic nerve crush) and by collateral sprouts of the intact saphenous nerve (after sciatic nerve resection) in the mouse. FK506-treated animals received either 0.2 or 5 mg/kg/day, dosages previously found to maximally increase the rate of axonal regeneration in the mouse. Functional reinnervation of motor, sensory, and sweating activities was assessed by noninvasive methods in the hind paw over a 1-month period following lesion. Morphometric analysis of the regenerated nerves and immunohistochemical labeling of the paw pads were performed at the end of follow-up. In the sciatic nerve crush model, FK506 administration shortened the time until target reinnervation and increased the degree of functional and morphological reinnervation achieved. The recovery achieved by regeneration was greater overall with the 5 mg/kg dose than with the dose of 0.2 mg/kg of FK506. In the collateral sprouting model, reinnervation by nociceptive and sudomotor axons was enhanced by FK506. Here, the field expansion followed a faster course between 4 and 14 days in FK506-treated animals. In regard to dose, while collateral sprouting of nociceptive axons was similarly increased at both dosages (0.2 and 5 mg/kg), sprouting of sympathetic axons was more extensive at the high dose. This suggests that the efficacy of FK506 varies between subtypes of neurons. Taken together, our findings indicate that, in addition to an effect on rate of axonal elongation, FK506 improves functional recovery of denervated targets by increasing both regenerative and collateral reinnervation.

Interneuronal signalling is involved in induction of collateral sprouting of nociceptive axons

Collateral sprouting of cutaneous nociceptive axons into the adjacent denervated skin critically depends on the nerve growth factor, presumably originating from the degenerated neural pathways and denervated skin. We hypothesised that the degenerated neural pathways are necessary, but not sufficient, to induce collateral sprouting of nociceptive axons, and, in addition, that the interaction between the injured and non-injured neurones within a dorsal root ganglion can trigger sprouting of nociceptive axons also in the absence of the denervated skin. End-to-side nerve anastomosis, made in female Wistar rats by suturing the end of an excised peroneal nerve segment to the side of the intact sural nerve, was used as a model for sprouting which allowed us to study the putative induction mechanisms separately. If the nerves adjacent to the sural nerve were transected concomitantly with the coaptation of the end-to-side anastomosis, robust nociceptive axon sprouting into the anastomosed nerve segment was observed by the nerve pinch test and counting of myelinated axons. Collateral sprouting did not occur, however, either if the cells in the anastomosed nerve segment were killed by freezing and thawing, or if the adjacent nerves had not been injured. However, if the ipsilateral dorsal cutaneous nerves, having their neurones in the same dorsal root ganglia as the sural nerve, were transected, but no other nerves were injured, then the sural nerve axons sprouted in abundance through the anastomosis even in the absence of denervated skin around the sural nerve terminals. From these results we suggest that cells (probably proliferating Schwann cells) in the degenerated neural pathways are necessary but not sufficient to induce collateral sprouting of nociceptive axons, and that interactions between the injured and non-injured neurones within the dorsal root ganglion (i.e. direct or indirect interneuronal signalling) are important in this regard.

Redistribution of sudomotor responses is an early sign of sympathetic dysfunction in type 1 diabetes

Patients with diabetic neuropathy typically have decreased sweating in the feet but excessive sweating in the upper body. Previous studies of sudomotor function in diabetes have included patients with longstanding disease. The present study was designed to test for the early presence of sudomotor dysfunction and to characterize its relation to glycemic control and other aspects of peripheral nerve function. A total of 37 patients (10 males, 27 females) enrolled in a longitudinal study, in which autonomic function was evaluated annually for 3 years. Patients enrolled 2-22 months after the diagnosis of type 1 diabetes. Forty-one age- and sex-matched healthy control subjects were also studied. Sweat production in response to acetylcholine stimulation was dramatically increased in the forearm at the time of the first evaluation (1.67 +/- 0.24 micro/cm2 in the diabetic patients vs. 1.04 +/- 0.14 microl/cm2 in the control subjects, P < 0.05). Likewise, the ratio of sweating in the forearm to sweating below the waist was higher in the diabetic patients (0.553 +/- 0.07 microl/cm2) than in the control subjects (0.385 +/- 0.04 microl/cm2, P < 0.05). Forearm sweat was negatively associated with the renin-toprorenin ratio and vanillylmandelic acid (VMA) excretion (P < 0.025), tests of sympathetic nerve function. The ratio of sweating in the forearm to sweating in the foot was likewise increased in diabetic patients with poor glycemic control. We interpret this redistribution of sudomotor responses to be indicative of sympathetic nerve injury and conclude 1) that the sympathetic nervous system is especially vulnerable to the adverse effects of chronic hyperglycemia and 2) that sympathetic dysfunction can be detected very early in type 1 diabetes.

Functional reinnervation of sweat glands in the adult cat paw by inappropriate postganglionic axons

Sympathetic postganglionic neurons were allowed to reinnervate the hairless skin of the cat paw pad, normally supplied by the tibial nerve, after suturing the central stump of the superficial peroneal nerve (supplying both hairy and hairless skin, eight animals) or of the sural nerve (supplying only hairy skin, seven animals) to the distal stump of the tibial nerve. Neural activation of sweat glands was studied by the starch iodine method and by recording the skin potential from the skin surface. Postganglionic neurons were activated by electrical stimulation of peripheral nerves or reflexly. There was good functional reinnervation of sweat glands by sudomotor neurons in all animals. The superficial peroneal nerve contains a few fibers that normally supply < 20% of the sweat glands on the foot pads. When this nerve regenerated into the innervation territory of the tibial nerve, sudomotor fibers consistently made functional contacts with sweat glands on the pads in all animals. These functional contacts were always weaker than those in the controls. Electrical stimulation of the sural nerve does not activate sweat glands in the paw pads of normal animals, indicating that this nerve does not contain postganglionic sudomotor axons. When the sural nerve regenerated into the foot pads, electrical stimulation activated some sweat glands in five of seven animals. We conclude that sudomotor neurons have a high capacity to functionally reinnervate sweat glands in the adult cat. There was also evidence that some noradrenergic vasoconstrictor neurons might take on "cholinergic features' in the adult animal when they reinnervate sweat glands suggesting that the peripheral target can specify the phenotypic properties of postganglionic neurons in the adult animal.

Assessment of sympathetic nerve activity in the practice of lumbar sympatholysis: interest of sympathetic skin responses

The place of lumbar sympathectomy in the treatment of occlusive arterial disease of the lower limbs remains controversial. An adequate assessment of sympathetic nerve function in the practice of sympathectomy may reduce unsatisfactory results of this procedure. We report a series of 25 lumbar sympatholyses indicated for claudication, rest pain or distal arterial ulcer, and attempted by means of phenol injection in sympathetic ganglia under tomographic guidance. Sympathetic skin response (SSR) recording, an electrophysiological test of sympathetic activity, was performed before and after phenol injection, and its results were compared to the clinical outcome. SSR was abolished in the treated limb after phenol injection in only 64% of the cases. The post-injection abolition of SSR was correlated with the clinical improvement rate: 11% when SSR was still present, but 75% when SSR was abolished. In this latter case, the pre-injection values of SSR amplitudes could predict the clinical benefit of sympatholysis. It is necessary to assess the sympathetic activity in a limb before and after doing sympatholysis. Preoperatively, this activity may be diminished or already abolished in patients suffering from neuropathy involving the autonomic nervous system, limiting the indication of sympathectomy. Postoperatively, if sympathetic activity is still present in the treated limb, it implies that the sympathectomy is not completed, and it supports the indication of a new sympatholysis attempt. These observations show the usefulness of SSR recording in the practice of phenol sympatholysis, this test being simple and specific of sympathetic nerve function.

Abolition of sympathetic skin responses following endoscopic thoracic sympathectomy

The recording of sympathetic skin responses (SSRs) is a simple, electrophysiological method to assess sympathetic nerve function. Within the last 10 years, SSRs have mainly been applied to delineate peripheral and central nervous system diseases, although the sympathetic nature of these responses was not fully documented, e.g., by a study of sympathectomy. We therefore recorded SSRs before and after 30 cases of endoscopic thoracic sympathectomy. The main indication was palmar hyperhidrosis, in which we found two types of SSR abnormalities. Most patients exhibited normal SSR waveforms but with increased amplitudes. The other patients exhibited abnormal SSRs which did not occur as single responses but as several consecutive waves. Thoracic sympathectomy always led to significant clinical improvement and to the abolition of ipsilateral palmar SSRs, demonstrating the sympathetic origin of these responses. We suggest that the assessment of sympathetic nerve activity by SSR recordings may be useful in sympathectomy.

Functional changes of the peripheral nervous system with aging in the mouse

The influence of aging on peripheral nerve and target organ function was investigated in six groups of mice aged 2, 6, 9, 12, 18, and 24 months. Sudomotor, motor, and sensory functions mediated by the sciatic nerve were evaluated by silicone imprints, electrophysiological recordings and pinprick test from the distal hindpaw. Nerve conduction was also studied in the caudal nerves. The results showed that the number of sweat glands reactive to pilocarpine does not change significantly with aging, but the size of the sweat droplets is smaller in aged mice than in young mice. The amplitude of muscle and nerve action potentials evoked by stimulation of sciatic and caudal nerves decreased progressively from 2 to 24 months, while the latencies decreased from 2 to 6 months, remained unchanged until 12 months and increased thereafter. All the animals of the six groups studied showed positive, indistinguishable responses to pinprick. These results indicate that neurophysiological responses mediated by large diameter nerve fibers deteriorated with age, while those dependent of small fibers were preserved.

Functional sudomotor responses to cholinergic agonists and antagonists in the mouse

This study evaluates the functional activity of the mouse sweat glands in response to cholinergic agonists and antagonists using the silicone imprint technique. In intact mice the response to acetylcholine, methacholine and pilocarpine did not differ significantly from control saline injection, indicating that immobilization induces high levels of sweating, masking the effects of cholinergic stimulation. Plantar emotional sweating was completely abolished by local anesthesia at the ankle. Under these conditions, administration of acetylcholine only provoked detectable sweating when injected locally into the sole skin. Methacholine activated an increasing number of sweat glands in a dose-dependent manner between 0.5 and 10 mg/kg; the response was maximal after 5-10 min of administration and decreased subsequently. With pilocarpine the maximum number of reactive sweat glands was observed at a dose of 2.5 mg/kg. The response was stable for 45 min with doses 2.5 and 5 mg/kg, but decreased exponentially with higher doses. The subtype of sweat gland muscarinic receptor was characterized by determining the inhibitory effect of different cholinergic antagonists on pilocarpine response. Atropine and 4-DAMP were equally potent inhibitors, showing a dose-related effect from 0.05 mg/kg. Pirenzepine only showed inhibitory effects with doses 10-times higher, whereas gallamine and hexamethonium did not induce inhibition at any of the doses tested. These findings suggest that the mouse eccrine sweat gland muscarinic receptors are predominantly M3.

Quantitative sweat testing using acetylcholine for direct and axon reflex mediated stimulation with silicone mold recording; controls versus neuropathic diabetics

Sweat glands were stimulated by iontophoresed acetylcholine (ACh). Using a two-chamber capsule, one group of sweat glands was stimulated directly by ACh, and another stimulated indirectly via axon reflexes. Sweat droplets were recorded with a silicone mold and counted by a dissecting microscope and a computerized scanner. Responses from 32 diabetics with generalized somatic peripheral neuropathy were compared with 32 controls. Counting sweat droplets by computerized scanning was more accurate than by microscope. The numbers of droplets, their total areas, and mean areas were all larger in the direct response. Counts of droplet numbers was more diagnostically useful than measuring the total area and the mean areas of the droplets. There was a high correlation between droplet numbers of the direct and the indirect sweat responses. Droplet number counts of the direct response had a slightly higher diagnostic yield than those of the technically more complicated indirect response: for a specificity of 95%, the direct response had a sensitivity of 55%, the indirect being 50%.

Comparison of directly stimulated with axon-reflex-mediated sudomotor responses in human subjects and in patients with diabetes

The muscarinic receptors of human eccrine sweat gland may be directly stimulated by iontophoresis of acetylcholine (direct response; DIR) and indirectly via nicotinic receptors and an axon "reflex" (AXR). Using a specially designed multicompartmental sweat cell and dual sudorometers, we were able to simultaneously record the evoked DIR and AXR responses. On a second day, we repeated the experiment under identical ambient and stimulus conditions but instead obtained silastic imprints of DIR and AXR for morphometry. Studies were done on 24 controls (mean +/- SD = 47.6 +/- 15.1 years) and 23 diabetic subjects (mean +/- SD = 49.6 +/- 16.3 years). In control subjects, sudorometric DIR recordings were consistently larger than AXR. There was no difference in sweat droplet density by sex, but the size of droplets was larger in males. In diabetic patients 3 of 23 had absent AXR but preserved DIR, suggesting that failure of AXR preceded DIR in patients with neuropathy. Patients with mild neuropathy had an overrepresentation of large diameter droplets in the silastic imprints of both DIR and AXR, while patients with severe neuropathy had a markedly reduced density and small diameter droplets.

Abnormalities of sympathetic sudomotor function in experimental acrylamide neuropathy

The possible involvement of sympathetic sudomotor function by acrylamide intoxication was investigated in the mouse, and compared with nerve conduction studies and global motor tests. Acrylamide (40 mg/kg, 3 days per week, 8 weeks) was given per os to a group of mice (A1). Their motor ability to stand on the rotarod was impaired from day 11, reaching a minimum between 46 and 60 days. The number of pilocarpine reactive sweat glands (SG), evaluated by the silicone mold technique, was similar to controls at 40 days and slightly decreased at 54 days. Another group of mice (A2), given acrylamide at a higher dose (50 mg/kg, 5 days per week, 5 weeks), showed abnormalities on the rotarod by 11 days, a progressive decrease of muscle action potential (CMAP) amplitude, and significantly decreased number of reactive SG from 15 days, with respect to controls. Comparatively, sudomotor dysfunction was milder and appeared later in time than alphamotor involvement, being noticeable only after severe poisoning. The decrease in SG response is attributable to damage by acrylamide intoxication of postganglionic sudomotor nerve fibers, which are unmyelinated sympathetic efferents.

Electrophysiological responses in the rat tail artery during reinnervation following lesions of the sympathetic supply

1. Responses to perivascular stimuli have been recorded with intracellular microelectrodes from the smooth muscle of isolated segments of the main caudal artery of rats at various times between 7 and 128 days after all four collector nerve trunks had been lesioned near the base of the tail at 21 days of age. 2. In proximal segments (< 40 mm distal to the lesions), excitatory junction potentials (EJPs) and neurogenic alpha-depolarizations (NADs) evoked by stimuli presented via a proximally located suction electrode were similar to those in the same segments of unoperated control animals of the same age. Supramaximal EJPs in these segments decreased in amplitude with age. 3. Stimuli just supramaximal for EJPs in innervated preparations failed to evoke responses in segments farther than 30-40 mm distal to the lesions at any time after the nerves had been cut and 1 cm excised. Higher voltages evoked slow depolarizing potentials (SDPs) which were of longer time course than EJPs. Similar responses occurred in segments over 60 mm distal to the lesions at 20-50 days after the nerves had been frozen, and in all segments sampled over 100 mm distal to nerve lesions. 4. Spontaneous transient depolarizations (STDs) were recorded at all depths of the media in denervated segments. These occurred at frequencies similar to those of spontaneous events (including attenuated spontaneous EJPs) in innervated segments. 5. The earliest signs of reinnervation (24-42 days after freeze lesions) consisted of very small amplitude EJPs of normal time course which facilitated markedly during a short train of stimuli (5-10 Hz); these were followed by NADs which were large relative to the amplitudes of the EJPs. Less commonly, small focal EJPs of brief time course (resembling spontaneous EJPs in superficial cells of innervated arteries) were evoked in very restricted regions of the vessel wall. 6. At later times (57-128 days postoperative), six of eight segments located 40-70 mm distal to freeze lesions showed EJPs of nearly control amplitude, but NADs that were larger than in equivalent segments from control animals. In the remaining two cases, reinnervation at this level was similar to that seen at the earliest postoperative times. High stimulus voltages prolonged the decay of EJPs in both control and reinnervated arteries. 7. Sensitivity to exogenous noradrenaline, assessed in terms of membrane depolarization, was increased in both denervated and reinnervated segments. 8. Catecholamine fluorescence disappeared from the arteries at a distance greater than 30-40 mm distal to the site of the nerve lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of autologous nerve transplants on motor and sudomotor reinnervation by regenerative axons

The functional reinnervation rate of sweat glands (SGs) and muscle in the mouse paw were compared following resection of a 4 mm segment of sciatic nerve. Repair was by graft of the same segment with epineural sutures or by suturing the proximal and distal stumps to a teflon tube that contained saline alone or saline plus the unattached nerve segment. Pilocarpine activated SGs first reappeared at 23 days postoperation in mice with a direct graft, at 29 days in mice with a nerve transplant in the tube, and at 32 days in mice with an empty tube. The number of reinnervated SGs increased progressively in number to a maximum of about 65% of the control counts by 60, 60 and 67 days, respectively. Compound muscle action potentials evoked by sciatic nerve stimulation were first recorded from the interossei muscles at 24, 27 and 31 days postoperation in the same groups of mice. The action potential amplitude increased to average values of about 2 mV by 58, 62 and 69 days. These results indicate that a direct nerve graft allows faster and higher functional recovery than tubulation repair, and that a nerve transplant slightly accelerates the reinnervation rate, probably due to the presence of nerve trophic products inside the tube. Unmyelinated and myelinated axons regenerated at equal rates.

Changes in cholinergic sweat gland activation in diabetic neuropathy identified by computerised sweatspot analysis

Peripheral small-fibre denervation has been reported to result in decreased activation of eccrine sweat glands to muscarinic cholinergic agents. Using computerised image-analysis of pilocarpine-activated sweatspot prints of a 4 cm2 area of the dorsum of the foot in 79 randomly selected diabetic patients we have identified a group of neuropathic patients (18%) with decreased sweatspot activation (less than 20/cm2), and a smaller group (6%) of younger patients with less marked neuropathy who had increased activation (greater than 132/cm2), probably resulting from denervation supersensitivity. The associations between sweatspot density and other conventional tests of peripheral nerve function were weak. The prevalence of abnormal sweatspot density, 24%, was similar to that of other tests, except thermal thresholds at the feet (35-37%), which were not correlated with sweatspot activation, suggesting that diabetic neuropathy has differing effects on afferent and efferent small fibres. The method is rapid and reproducible (median coefficient of variation 14%) and its ability to identify patients with increased, as well as decreased, peripheral nerve function may be of value in the characterisation and longitudinal follow-up of small-fibre abnormalities in diabetes.

Assessment of basal and stimulated sweating in diabetes using a direct-reading computerized sudorometer

Abnormalities of eccrine sweating are thought to be common in diabetes. We describe a ventilated-capsule sudorometer for the continuous measurement of basal and stimulated sweat secretion. It is sensitive (detecting as little as 200 ng water vapour), precise, and stable. Since it measures dewpoint rather than relative humidity, it can be calibrated to read sweat volumes directly and independently of ambient temperature and humidity. Preliminary studies using this technique show that basal skin water loss is significantly diminished in patients with established diabetic neuropathy (0.91 +/- 0.18 g (+/- SD) cm-2 h-1) compared with normal subjects (1.21 +/- 0.39 g cm-2 h-1; p = 0.04) and non-neuropathic diabetic subjects (1.32 +/- 0.48 g cm-2 h-1; p = 0.04), and that local sweating induced by iontophoresis of 10 g l-1 acetylcholine is significantly reduced in diabetic subjects up to 5 min of recording (0.95 +/- 0.43 vs 1.26 +/- 0.40 mg; p = 0.02). In neuropathic subjects both low- and high-amplitude responses are seen, the latter probably representing denervation supersensitivity. Further studies with sensitive sudorometry should enable the mechanisms of these abnormal responses to be established.

The effect of a conditioning lesion on sudomotor axon regeneration

The effects of a conditioning lesion on the rate of sudomotor axon regeneration were judged by the recovery of sweat gland (SG) secretion after cholinergic stimulation. Three groups of mice were given a conditioning lesion by crushing the sciatic nerve at mid-thigh 4, 7, and 14 days before a test lesion. A 4th group received a conditioning crush of the tibial nerve at the ankle 7 days before the test lesion. Control mice had a single test lesion. SG reinnervation in control mice began 19 days after the test lesion, and was functionally complete by 41 days. In groups with the conditioning lesion 4, 7, and 14 days before the test operation, the first reactive SGs reappeared at 16, 15, and 16 days respectively after the test lesion, and maximal recovery occurred by 33, 32, and 39 days. In mice with the distal conditioning lesion, reinnervation began at 19 days and was maximal by 36 days. In summary, a nerve conditioning lesion placed from 4 to 14 days prior to and at the same site as a test lesion significantly accelerated the growth rate of the fastest regenerating unmyelinated sudomotor axons and reduced the time until most SGs were reinnervated. A more distally placed test lesion reduced the interval for recovery.

Effect of age on collateral reinnervation of sweat glands in the mouse

This study demonstrates that the number of sweat glands (SGs) innervated by individual peripheral nerves in the mouse hind paw decreases with aging but the ability for reinnervation by collateral sprouting is maintained throughout life. In one experiment, the saphenous, peroneal and tibial nerves were cut and tied, denervating all SGs of the hind paw except those receiving axons from the intact sural nerve. In another, the saphenous was the only nerve left intact. The initial number of SGs supplied only by the single intact nerve was significantly higher in young adult than older mice. The capacity of the sural and saphenous nerves to collaterally reinnervate the denervated SGs was followed by serial testing for the return of sensitivity to pilocarpine stimulation. Collaterally reinnervated SGs appeared during the second and third weeks postoperation adjacent to already active SGs, thereby increasing the total sweat area of the intact nerve, and its SG number about 3, 2 and 5 times for the sural, and 8, 2 and 2 times for saphenous nerve, in young, adult and old animals respectively. Reinnervation was slightly faster and the degree of extension greater in young than adult mice, and the degree of extension was decreased in older mice. These observations suggest that the number of sudomotor axons in the peripheral nerve, as well as their capacity for collateral reinnervation, is reduced with aging.

Effect of age and maturation on sudomotor nerve regeneration in mice

This study demonstrates that regeneration of unmyelinated sudomotor axons in mice becomes progressively slower during aging. Identical lesions were made in mice aged 0, 2, 4, 6, 7, 24 and 60 weeks. The peroneal, sural and saphenous nerves were cut and tied to prevent regeneration. The sciatic nerve was then frozen at the thigh, leaving the hind paw completely denervated. By 7 days, sweat glands (SGs) of the paw had ceased sweating after pilocarpine injection. Subsequent regeneration of sudomotor axons was judged by the rate of return of pilocarpine sensitivity. SGs in the hind paws of normal newborn mice did not sweat at birth. Cholinergic stimulation first activated sweating at 13 days of life. The number of responsive SGs increased progressively to reach the adult level by 30 days. In one-week-old mice, whose sciatic nerve had been sectioned, the SG response to cholinergic stimulation was very delayed in time and reduced in number. Sweat glands of young mice, between 2 and 4 weeks of age, regained cholinergic sensitivity at a faster rate than mature animals and attained normal SG counts. Throughout a broad intermediate range of age in adulthood (7-24 weeks), the rate of sudomotor nerve regeneration was the same, but in older mice (60 weeks) it was slower and less complete.