Immunohistochemical, morphological and functional changes in the peripheral sudomotor neuro-effector system in elderly people

Normal values of sudomotor function assessed by electrochemical skin conductance in African population

BACKGROUND

Dysfunction of small nerve fibers remains a major public health concern. Subjects suspected of having small nerve fiber damage need to undergo reliable tests to confirm the diagnosis. Sudomotor function test is a reliable noninvasive exploration for detecting peripheral neuropathies. Nevertheless, the normal reference values derived from the sudomotor function test are not known in the African population. The objective of this study was therefore to describe the normal values of Electrochemical Skin Conductance (ESC) measured by the sudomotor function test in healthy African subjects.

MATERIALS AND METHODS

Between December 1st, 2021 and May 31st, 2022, ESC was measured in 475 healthy subjects (median age: 42 [31-53] years, 46% men) using a sudomotor function test, in the hands and feet. Investigators proposed the examination and received participants' consent; demographic, anthropometric, biological, and clinical data were obtained before the test. Data on 475 healthy study participants who underwent sudomotor function testing was collected and analyzed. The sociodemographic (age, sex), anthropometric (weight, height, waist circumference, body mass index), diastolic blood pressure, systolic blood pressure, heart rate, and electrochemical skin conductances of the hands and feet were assessed.

RESULTS

ESC values were statistically higher in men compared to women (right hand ESC: 70 [60-78] versus 63 [53-72], left hand ESC: 72 [61-80] versus 68 [57-75], right foot ESC: 77 [82-99] versus 72 [64-79], ESC left foot: 76 [68-82] versus 72 [62-78] respectively). ESC values were significantly inversely correlated with age (right hand ESC: r=-0.12, P=0.006; left hand ESC: r=-0.11, P=0.01; right foot ESC: r=-0.37, P<0.0001; ESC left foot: r=-0.38, P<0.0001). ESC values measured in feet were significantly inversely correlated with body mass index (right foot r=-0.22, P<0.0001; left foot r=-0.21, P<0.0001).

CONCLUSION

This study reports normal reference values for ESCs according to age and gender in the healthy African population. Progressive decrease in ESC with aging is confirmed by our data. The value of ESC seems lower in the African population than in other reported ethnicities. This finding needs to be further explored in additional studies.

Eccrine sweat glands' maximum ion reabsorption rates during passive heating in older adults (50-84 years)

PURPOSE

We examined whether eccrine sweat glands ion reabsorption rate declined with age in 35 adults aged 50-84 years. Aerobic fitness (VO_2max) and salivary aldosterone were measured to see if they modulated ion reabsorption rates.

METHODS

During a passive heating protocol (lower leg 42 °C water submersion) the maximum ion reabsorption rates from the chest, forearm and thigh were measured, alongside other thermophysiological responses. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate.

RESULTS

The maximum ion reabsorption rate at the forearm, chest and thigh (0.29 ± 0.16, 0.33 ± 0.15, 0.18 ± 0.16 mg/cm²/min, respectively) were weakly correlated with age (r ≤  - 0.232, P ≥ 0.05) and salivary aldosterone concentrations (r ≤  - 0.180, P ≥ 0.179). A moderate positive correlation was observed between maximum ion reabsorption rate at the thigh and VO_2max (r = 0.384, P = 0.015). Salivary aldosterone concentration moderately declined with age (r =  - 0.342, P = 0.021). Whole body sweat rate and pilocarpine-induced sudomotor responses to iontophoresis increased with VO_2max (r ≥ 0.323, P ≤ 0.027) but only moderate (r =  - 0.326, P = 0.032) or no relations (r ≤  - 0.113, P ≥ 0.256) were observed with age.

CONCLUSION

The eccrine sweat glands' maximum ion reabsorption rate is not affected by age, spanning 50-84 years. Aldosterone concentration in an aged cohort does not appear to modulate the ion reabsorption rate. We provide further support for maintaining cardiorespiratory fitness to attenuate any decline in sudomotor function.

The sweat glands' maximum ion reabsorption rates following heat acclimation in healthy older adults

NEW FINDINGS

What is the central question to this study? Do the sweat glands' maximum ion reabsorption rates increase following heat acclimation in healthy older individuals and is this associated with elevated aldosterone concentrations? What is the main finding and its importance? Sweat gland maximum ion reabsorption rates improved heterogeneously across body sites, which occurred without any changes in aldosterone concentration following a controlled hyperthermic heat acclimation protocol in healthy older individuals.

ABSTRACT

We examined whether the eccrine sweat glands' ion reabsorption rates improved following heat acclimation (HA) in older individuals. Ten healthy older adults (>65 years) completed a controlled hyperthermic (+0.9°C rectal temperature, T_re ) HA protocol for nine non-consecutive days. Participants completed a passive heat stress test (lower leg 42°C water submersion) pre-HA and post-HA to assess physiological regulation of sweat gland ion reabsorption at the chest, forearm and thigh. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate (SR). We explored the responses again after a 7-day decay. During passive heating, the T_b thresholds for sweat onset on the chest and forearm were lowered after HA (P < 0.05). However, sweat sensitivity (i.e. the slope), the SR at a given T_re and gross sweat loss did not improve after HA (P > 0.05). Any changes observed were lost during the decay. Pilocarpine-induced sudomotor responses to iontophoresis did not change after HA (P ≥ 0.801). Maximum ion reabsorption rate was only enhanced at the chest (P = 0.001) despite unaltered aldosterone concentration after HA. The data suggest that this adaptation is lost after 7 days' decay. The HA protocol employed in the present study induced partial adaptive sudomotor responses. Eccrine sweat gland ion reabsorption rates improved heterogeneously across the skin sites. It is likely that aldosterone secretion did not alter the chest sweat ion reabsorption rates observed in the older adults.

Sweating disorders in mice with and without nerve lesions

BACKGROUND

Hypersensitivity and altered sweating are often present in neuropathy patients. Nerve lesions are known to produce sudomotor dysfunctions but also patients suffering from complex regional pain syndrome, CRPS1-a condition without a nerve lesion-present with sweating disorders.

METHODS

Using proton nuclear magnetic resonance of sweat water, we quantified sweat output of mice suffering from a nerve lesion or a bone fracture without nerve lesion and correlated their sweating with behavioural paw hypersensitivity accessed in von Frey testings, water applications and weight-bearing measured with an incapacitance metre.

RESULTS

Lesioned animals sweat less and are hypersensitive compared to healthy controls, as expected. Fractured animals on the injured side sweat less acutely after the injury but more in the chronic phase. They are hypersensitive acutely as well as chronically after the fracture. These findings resemble human bone trauma patients in the acute phase and CRPS patients in the chronic phase.

CONCLUSIONS

Sweating disorders are present both in neuropathic animals and in those with a bone fracture without nerve lesions, and autonomic dysfunctions might be considered as an important component in the aetiology of neuropathies.

SIGNIFICANCE

Sweat output changes in mice after bone trauma, potentially indicative of posttraumatic processes leading to CRPS in humans.

Sudomotor function testing by electrochemical skin conductance: does it really measure sudomotor function?

OBJECTIVE

Electrochemical skin conductance (ESC) is a non-invasive test of sweat function developed as a potential marker of small fiber neuropathy. Here we systematically review the evolution of this device and the data obtained from studies of ESC across different diseases.

METHODS

Electronic databases, including MEDLINE, and Google Scholar were searched through to February 2018. The search strategy included the following terms: "electrochemical skin conductance," "EZSCAN," and "Sudoscan." The data values provided by each paper were extracted, where available, and input into tabular and figure data for direct comparison.

RESULTS

Thirty-seven studies were included this systematic review. ESC did not change by age or gender, and there was significant variability in ESC values between diseases, some of which exceeded control values. Longitudinal studies of disease demonstrated changes in ESC that were not biologically plausible. Of the 37 studies assessed, 25 received support from the device manufacturer. The extracted data did not agree with other published normative values. Prior studies do not support claims that ESC is a measure of small fiber sensory function or autonomic function.

CONCLUSIONS

Although many papers report significant differences in ESC values between disease and control subjects, the compiled data assessed in this review raises questions about the technique. Many of the published results violate biologic plausibility. A single funding source with a vested interest in the study outcomes has supported most of the studies. Normative values are inconsistent across publications, and large combined data sets do not support a high sensitivity and specificity. Finally, there is insufficient evidence supporting the claim that Sudoscan tests sudomotor or sensory nerve fiber function.

Career perspective: Kenneth J. Collins

A career interest in thermoregulation research has included wide contrasts in the subjects of enquiry, extending from heat stroke to hypothermia, special investigations in many different purpose-built climatic chambers, laboratory-based biomedical studies together with hospital practice, and field work in tropical climates to physiological surveys on urban populations in temperate environments. The scientific process and need to focus on careful planning of experiments, using the most appropriate methods, selecting the right controls and eventually applying correct statistical analysis do not always follow a smooth transition, as illustrated in this account. The result of endeavour to resolve a human environmental problem, however, is greatly satisfying, and sometimes becomes a unique experience when the solution reveals new fundamental facts.

Tool Chest

PURPOSE

The purpose of this study was to evaluate the new indicator test for sudomotor function (Neuropad) in the diagnosis of small-fiber impairment in patients with type 2 diabetes.

METHODS

This study included 123 patients with type 2 diabetes (59 men; mean age, 64.3 +/- 8.6 years; mean diabetes duration, 12 +/- 6.1 years). Sudomotor dysfunction was assessed by means of the new indicator test. Neuropathy was diagnosed by the Neuropathy Disability Score and small-fiber impairment by temperature perception (Tiptherm device) and pain perception (Neurotip).

RESULTS

The frequency of sudomotor dysfunction was significantly (P = .001) higher in patients with neuropathy (95%) than in those without neuropathy (30.2%). Sensitivity of the indicator test for neuropathy was 95%, and specificity was 69.8%. Frequency of neuropathy was significantly (P = .018) higher with the indicator test (74.8%) than with conventional clinical examination (65.4%). Sudomotor dysfunction was significantly (P = .001) more frequent in patients with small-fiber impairment (99%) than in those without small-fiber impairment (21.7%). Sensitivity for small-fiber impairment was 99%, and specificity was 78.3%. There was no difference (P = .999) in the frequency of small-fiberimpairment as diagnosed with the indicator test (80.5%) and with clinical examination (81.3%).

CONCLUSIONS

The indicator test has a very high sensitivity and specificity for small-fiber impairment in patients with type 2 diabetes.

Normative Values for Electrochemical Skin Conductances and Impact of Ethnicity on Quantitative Assessment of Sudomotor Function

BACKGROUND

Sudomotor dysfunction is one of the earliest pathophysiologic abnormalities in diabetes. Sudoscan™ (Impeto Medical, Paris, France) was developed as a noninvasive, rapid, and quantitative assessment of sudomotor function and has been shown to be sensitive in the detection of neuropathy. This global collaborative analysis aimed to establish reference values in healthy subjects of different ethnic groups, age, and gender, to define factors potentially affecting results, and to provide standardization of the methodology.

MATERIALS AND METHODS

Data from 1,350 generally healthy study participants who underwent sudomotor function testing were collected and analyzed. The relationship between age, height, weight, gender, glycemic and lipid profiles, ethnicity, and hand and foot electrochemical skin conductance (ESC) was assessed among subgroups of participants.

RESULTS

Lower mean hands and feet ESC values were observed in African American, Indian, and Chinese subjects (P < 0.0001). No participant discomfort or safety concern was reported in 1,376 tests. No significant difference in ESC was observed between women and men at the hands (75 [57-87] vs. 76 [56-89] μS; P = 0.35) or feet (83.5 [71-90] vs. 82.5 [70-91] μS; P = 0.12). The coefficient of correlation between right and left side ESC was r = 0.96, P < 0.0001 for hands and r = 0.97, P < 0.0001 for feet. A significant but weak correlation was observed between ESC and age: for hands, r = -0.17, P < 0.0001; for feet, r = -0.19, P < 0.0001.

CONCLUSIONS

A normative reference range was established in whites showing that there was no effect of sex or body mass index and a slight decrease in ESC with age. Ethnicity influenced ESC scores, but additional studies are necessary to validate this effect and determine its mechanism and impact on nerve function.

Skin biopsies in the assessment of the autonomic nervous system

Cutaneous punch biopsies are widely used to evaluate nociceptive C fibers in patients with suspected small-fiber neuropathy. Recent advances in immunohistochemical techniques and interest in cutaneous autonomic innervation has expanded the role of skin biopsy in the evaluation of the peripheral nervous system. The dermal layers of the skin provide a unique window into the structural evaluation of the autonomic nervous system. Peripheral adrenergic and cholinergic fibers innervate a number of cutaneous structures, such as sweat glands and arrector pili muscles, and can easily be seen with punch skin biopsies. Skin biopsies allow for both regional sampling, in diseases with patchy distribution, and the opportunity for repeated sampling in progressive disorders. The structural evaluation of cutaneous autonomic innervation is still in its scientific infancy, with a number of different methodologies and techniques that will require standardization and widespread acceptance before becoming a standard of care. Future studies of autonomic innervation in acquired, hereditary, neurodegenerative, or autoimmune disorders will be necessary to determine the clinical utility of skin biopsy in these disease states.

Orthostatic hypotension before and after meal intake in diabetic patients and healthy elderly people

Objectives:

The symptoms of orthostatic hypotension may be ignored or go unnoticed and may predispose some diabetic or elderly people to repeated falls and trauma, leading to immobility and prolongation of rehabilitation. The present investigation is concerned mainly with testing the reaction of the cardiovascular system in response to physiological stimuli, such as, standing upright from a supine position before and after meal intake in diabetic patients and the healthy Saudi population.

Materials and Methods:

Seventy-five healthy and 49 diabetic patients were selected for this study. Parameters of heart rate, systolic and diastolic blood pressures, and electrocardiograms (ECG) were obtained for each subject by Dinamap (an automatic recorder), after 10 minutes of rest in the supine position and then after one and two minutes of standing. All parameters were taken before and after an intake of a standard meal. The results were compared between the diabetic and non-diabetic groups, and between the elderly diabetic and the healthy elderly ≥ 65 year olds, and between the young adults ≤ 40 year olds and the elderly ≥ 65 year olds.

Results:

The postural changes of blood pressure and heart rate between the diabetic and non-diabetic groups, and between the elderly diabetic and the healthy elderly groups, were not significant. However, a highly significant postural drop in blood pressure, and an increase in the resting heart rate were recorded before and after a meal intake in the elderly compared to the young adults.

Conclusion:

The highly significant postural drop in blood pressure and increase in the resting heart rate in the elderly diabetic and healthy elderly people can be attributed to a defect in the arterial baroreceptors control of blood pressure and parasympathetic control of heart rate in this population.

Sensitivity and specificity of a new indicator test (Neuropad) for the diagnosis of peripheral neuropathy in type 2 diabetes patients: a comparison with clinical examination and nerve conduction study

OBJECTIVE

The objective of this study was to evaluate the sensitivity and specificity of a new indicator test (Neuropad) for the diagnosis of peripheral neuropathy in type 2 diabetes patients as compared with clinical examination and nerve conduction study (NCS).

PATIENTS AND METHODS

This study included 120 type 2 diabetes patients (58 men) with a mean age of 67.3 +/- 5.9 years and a mean diabetes duration of 13.1 +/- 3.2 years. Diabetic neuropathy was diagnosed through the Neuropathy Disability Score. An NCS was performed on radial, ulnar, sural, and common and deep peroneal nerves. Patients were also examined with the new indicator test. The "time to complete color change of the test" from blue to pink was recorded. The test was considered abnormal in patients who exhibited a time to complete color change of the test exceeding 600 s in at least one foot.

RESULTS

Neuropathy was diagnosed by clinical examination in 83 (69.2%) patients. The sensitivity of the indicator test for clinical neuropathy was 95.2%, and its specificity was 67.6%. The sensitivity of NCS for clinical neuropathy was 94%, and its specificity was 62.1%. The sensitivity of the indicator test for abnormal NCS was 97.8%, and its specificity was 96.4%.

CONCLUSIONS

The new indicator test has a very high sensitivity not only for the diagnosis of clinical neuropathy but also for the diagnosis of neurophysiological neuropathy. Specificity is moderately high for the diagnosis of clinical neuropathy, while it is particularly high for the diagnosis of neurophysiological neuropathy. The indicator test has a validity comparable to that of NCS for the diagnosis of diabetic neuropathy. Finally, the time to complete color change of the test is associated with the severity of nerve conduction impairment.

Determinants of epidermal nerve fiber density in normal individuals

We studied the relationship between epidermal innervation and age, gender, height, and weight. Intraepidermal nerve fiber density (IENFD) of skin biopsies obtained from the proximal thigh and ankle of 84 normal individuals was quantified. A linear regression model was performed using IENFD at the thigh, IENFD at the ankle, and the thigh IENFD/ankle IENFD ratio, with age, gender, and height-weight interaction as predictors. An independent, negative correlation was found between age and IENFD at the ankle. No correlation was found between age and IENFD at the thigh. With increasing age the thigh IENFD/ankle IENFD ratio, a measure of the length-dependent distal-to-proximal gradient of epidermal nerve density, increased significantly. Gender, height, and body weight did not independently influence IENFD at either site. In normal individuals, distal epidermal innervation decreases in a length-dependent manner with advancing age. This must be considered when interpreting IENFD in disease states.

Chemically and electrically induced sweating and flare reaction

Both thin afferent (nociceptors) and efferent (sympathetic sudomotor) nerve fibers can be activated electrically and chemically, resulting in neurogenic erythema and sweating. These reactions have been used before to assess the impairment of sympathetic and nociceptor fibers in humans. In this study, electrically induced sweating and erythema were assessed simultaneously in the foot dorsum and thigh, and were compared to chemically induced activation. Reproducible intensity-response relations (stimulation intensities 0-30 mA, 1 Hz) were obtained from 32 subjects. The steepest increase of the sweat response was induced at lower intensities as compared to that of the erythema (18.3 mA vs. 25.7 mA, p<0.01) and reached a plateau for intensities above 25 mA, suggesting lower electrical thresholds for sudomotor fibers. Maximum flare areas induced electrically with 30 mA were smaller than those evoked chemically (flare size: 4.5 cm2 vs. 10.6 cm2). In contrast, the electrically evoked sweating rate was higher than that evoked chemically (acetylcholine, or ACh; sweating rate 0.31 vs. 0.21 microl/cm2/min, p<0.01), which might be attributed to an increased effectiveness of synchronized discharge in sympathetic fibers upon electrical stimulation.

Age-associated synapse elimination in mouse parasympathetic ganglia

Little is known about the effects of aging on synapses in the mammalian nervous system. We examined the innervation of individual mouse submandibular ganglion (SMG) neurons for evidence of age-related changes in synapse efficacy and number. For approximately 85% of adult life expectancy (30 months) the efficacy of synaptic transmission, as determined by excitatory postsynaptic potential (EPSP) amplitudes, remains constant. Similarly, the number of synapses contacting individual SMG neurons is also unchanged. After 30 months of age, however, some neurons (23%) dramatically lose synaptic input exhibiting both smaller EPSP amplitude and fewer synaptic boutons. Attenuation of both the amplitude and frequency of miniature EPSPs was also observed in neurons from aged animals. Electron micrographs revealed that, although there were many vesicle-laden preganglionic axonal processes in the vicinity of the postsynaptic membrane, the number of synaptic contacts was significantly lower in old animals. These results demonstrate primary, age-associated synapse elimination with functional consequences that cannot be explained by pre- or postsynaptic cell death.

Changes in mouse sudomotor function and sweat gland innervation with ageing

Age-related changes in sudomotor neuroeffector function have been evaluated in mice aged 2 (young), 6, 12 (adult) and 18 (old) months. We evaluated sudomotor function by determining the number of sweat glands reactive to pilocarpine and the sweat output per gland on the plantar surface of the hindpaws with the impression mould technique. Protein gene product 9.5 (PGP) and vasoactive intestinal polypeptide (VIP) were immunohistochemically localised in footpads. A marked decrease (44%) in sweat output per gland was observed in old mice as well as a slight (17%), not significant decline in the number of secreting sweat glands. The sudomotor innervation, expressed as the area of sweat gland occupied by VIP and PGP immunoreactive nerve profiles, showed an initial increase from 2 to 6 months and a significant decline (35%) in 18- vs. 6-month-old mice. These results indicate that, in contrast to the number of secreting sweat glands, sweat output per gland does not reach the maximum in adult mouse until 6 months old and that sweating decreases in aged mice mainly due to a decline of sweat output per gland and to a lesser extent to a decrease in number of secreting glands. A reduction of sweat glands size in aged mice was also found, suggesting that the diminished sweat gland responsiveness with ageing may be attributed to sweat gland atrophy as well as to loss of innervation.

Vasoactive intestinal polypeptide (VIP) innervation of the human eyelid glands

This study was conducted to obtain morphological proof of innervating nerve fibres in the glands of the human eyelid (accessory lacrimal glands of Wolfring, meibomian glands, goblet cells, glands of Zeis, glands of Moll, sweat glands, glands of lanugo hair follicles) and identification of the secretomotorically active neuropeptide vasoactive intestinal polypeptide (VIP) as a common transmitter. Epoxy-embedded ultrathin sections of tissue samples from human eyelids were studied using electron microscopy. Paraffin sections fixed in Bouin-Hollande solution were immunostained with rabbit antiserum against VIP. With the electron microscope we were able to identify nerves in the glandular stroma of all the glands examined with the exception of goblet cells. Intraepithelial single axons were only seen in the parenchyma of Wolfring glands. The morphological findings corresponded with the immunological finding of VIP-positive, nerve-like structures in the same locations, with the exception of lanugo hair follicle glands, and goblet cells. Our findings indicate that the glands of the eyelids and main lacrimal gland represent a functional unit with VIP as a possible common stimulating factor.

Immunohistochemical evidence suggests intrinsic regulatory activity of human eccrine sweat glands

Immunohistochemistry of normal eccrine sweat glands was performed on paraffin sections of human skin. Immunoreactivity (ir) for neuron specific enolase, S100 protein (S100), regulatory peptides, nitric oxide synthase type I (NOS-I) and choline-acetyltransferase (ChAT) was found in small nerve bundles close to sweat glands. In the glands, secretory cells were labelled with anticytokeratin antibody. Using antibodies to S100, calcitonin gene-related peptide (CGRP) and substance P (SP) a specific distribution pattern was found in secretory cells. Granulated (dark) and parietal (clear) cells were immunopositive for CGRP, and S100 and SP, respectively. Immunoreactivity was diffuse in the cytoplasm for CGRP and S100, and peripheral for SP. Myoepithelial cells were not labelled. Electron microscopy revealed electron dense granules, probably containing peptide, in granulated cells. Using antibodies to NOS-I and ChAT, ir was exclusively found in myoepithelial cells. Immunoreactivity for the atrial natriuretic peptide was absent in sweat glands. These results provide evidence for the presence of both regulatory peptides involved in vasodilation and key enzymes for the synthesis of nitric oxide and acetylcholine in the secretory coil of human sweat glands. It is suggested that human sweat glands are capable of some intrinsic regulation in addition to that carried out by their nerve supply.

Epidermal innervation: changes with aging, topographic location, and in sensory neuropathy

In previous work we demonstrated little effect of aging on the density and spatial pattern of epidermal innervation, however, this was restricted to two sites proximal and distal in the leg. To expand on these observations, we used punch skin biopsy in ten healthy controls to examine the variation in intra-epidermal nerve fiber (IENF) density at multiple specific sites in the leg. There was a consistent gradient in IENF from proximal to distal sites in all subjects, but minimal effect of age was noted. In the older age group (> or =70 years), the IENF densities ranged from 28.6+/-1.9 IENF/mm at the trunk to 15.5+/-1.5 at the distal leg. In a group of six patients with painful sensory neuropathy, we confirmed a length-dependent reduction in IENF. We observed what may be a predegenerative change, namely increased branching of epidermal nerve fibers at clinically unaffected sites. These data suggest little age-related change in IENF, at least up to age 75 years, in healthy normals. The increased branching complexity noted in unaffected sites in patients with sensory neuropathies implies that this may be a predegenerative change, preceding the actual loss of nerve fibers. Skin biopsy may be a useful tool for assessing the topographic extent and degree of nerve fiber damage in sensory neuropathies and its quantitative interpretation should be little affected by aging changes.

Depletion of cutaneous peptidergic innervation in HIV-associated xerosis

Severe xerosis occurs in approximately 20% of human immunodeficiency virus seropositive patients. Changes in cutaneous innervation have been found in various inflammatory skin diseases and in xerotic skin in familial amyloid. We have therefore carried out a quantitative examination of the cutaneous peptidergic innervation in human immunodeficiency virus-associated xerosis. Immunohistochemistry and image analysis quantitation were used to compare total cutaneous innervation (protein gene product 9.5), calcitonin gene-related peptide, substance P, and vasoactive intestinal peptide peptidergic fibers, at two sites in the skin of human immunodeficiency virus-associated xerosis patients (upper arm, n = 12; upper leg, n = 11) and site-matched seronegative controls (upper arm, n = 10; upper leg, n = 10). Measurement of lengths of fibers of each type was carried out for each subject in the epidermis and papillary dermis, and around the sweat glands. Immunostained mast cells in these areas were counted. Epidermal integrity and maturation were assessed by immunostaining for involucrin. There were significant (Mann-Whitney U test; p < 0.02) decreases in total lengths of protein gene product 9.5 fibers in both epidermis/papillary dermis and sweat gland fields; of calcitonin gene-related peptide innervation in the epidermis/papillary dermis; and of substance P innervation of the sweat glands. There were no differences in the distribution of mast cells, or in the epidermal expression of involucrin. Depletion of the calcitonin gene-related peptide innervation may affect the nutrient blood supply of the upper dermis, and the integrity and function of basal epidermis and Langerhans cells. Diminished substance P innervation of the sweat glands may affect their secretory activity. Both of these changes may be implicated in the development of xerosis.

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Transplanted sweat glands from mature and aged donors determine cholinergic phenotype and altered density of host sympathetic nerves

Contact with sweat gland acini causes sympathetic neurons to switch from a catecholaminergic to a cholinergic phenotype during development and following experimental manipulations. Substantial reductions of cholinergic innervation have been shown in the sweat glands of ageing rats and humans. Using in oculo transplantation, we have now studied whether sweat gland target tissues retain the capacity to regulate changes in the phenotype of sympathetic neurons observed in maturity and old age, including a switch from catecholaminergic to cholinergic characters. Markers have been used which indicate changes in nerve fibre morphology (the pan-neuronal marker, PGP9.5) as well as neurotransmitter expression (acetylcholinesterase (AChE), vasocative intestinal polypeptide (VIP) and tyrosine hydroxylase (TH). Sweat glands from young and old donor rats became reinnervated by an organotypic pattern of cholinergic host nerves. Surgical sympathectomy demonstrated that these cholinergic nerve fibres originate from sympathetic neurons of the host superior cervical ganglion (SCG). Retrograde tracing combined with staining for VIP (a marker associated with cholinergic phenotype in neurons supplying sweat glands) showed that SCG neurons projecting to irises with sweat gland implants may be induced to express VIP. We hypothesise that these neurons have been switched from their normal catecholaminergic phenotype to a cholinergic one by contact with the sweat gland implants. Transplants from old donors attracted a density of reinnervation by young host nerves which was appropriate to the age of the donor, thus old sweat glands received a significantly reduced density of innervation compared to young glands. Despite the reduced density of innervation, there was no obvious difference in the ability of young and old implants to induce the switch to a cholinergic phenotype, suggesting that different mechanisms regulate nerve growth and neurotransmitter phenotype.

Autonomic nervous system as a model of neuronal aging: the role of target tissues and neurotrophic factors

The aim of this study was to determine the role of target tissues and neurotrophic factors in the growth and atrophy of autonomic neurons during development and aging. Using quantitative neuroanatomical techniques, it is shown that, although axonal and dendritic growth is apparent throughout postnatal development, different patterns of growth are found in autonomic neurons innervating different target tissues. For example, sympathetic neurons innervating the submandibular gland continue to grow well into maturity, but those innervating the iris cease net growth early in postnatal development. Similarly, although neuronal atrophy was observed in aged autonomic ganglia, this was not a general phenomenon but was specific to neurons innervating particular target tissues. Sympathetic neurons innervating the middle cerebral artery showed significant axonal and dendritic atrophy in old age, whereas neurons innervating the iris were morphologically unchanged. The trophic influence of peripheral target tissues on their innervating neurons has been shown to decline in old age possibly as a result of decreased availability of target-derived neurotrophic factors such as nerve growth factor (NGF) [Gavazzi et al. (1992) Neuroreport, 3:717-720]. Therefore, in an attempt to reverse neuronal atrophy where it occurred, NGF was infused via miniosmotic pumps over the peripheral axons of aged neurons. NGF induced increases in soma size, dendritic length and axonal arborization. However, in contrast to young adult neurons, no increase in the number of dendritic branch points or primary dendrites was observed, suggesting that some aspects of neuronal plasticity are impaired in old age. In sum, these results show a range of age- and target-specific differences in the axonal and dendritic morphology of autonomic neurons that may result from differing trophic interactions with their target tissues.

Transplanted sweat glands from mature and aged donors determine cholinergic phenotype and altered density of host sympathetic nerves

Contact with sweat gland acini causes sympathetic neurons to switch from a catecholaminergic to a cholinergic phenotype during development and following experimental manipulations. Substantial reductions of cholinergic innervation have been shown in the sweat glands of ageing rats and humans. Using in oculo transplantation, we have now studied whether sweat gland target tissues retain the capacity to regulate changes in the phenotype of sympathetic neurons observed in maturity and old age, including a switch from catecholaminergic to cholinergic characters. Markers have been used which indicate changes in nerve fibre morphology (the pan-neuronal marker, PGP9.5) as well as neurotransmitter expression (acetylcholinesterase (AChE), vasocative intestinal polypeptide (VIP) and tyrosine hydroxylase (TH)). Sweat glands from young and old donor rats became reinnervated by an organotypic pattern of cholinergic host nerves. Surgical sympathectomy demonstrated that these cholinergic nerve fibres originate from sympathetic neurons of the host superior cervical ganglion (SCG). Retrograde tracing combined with staining for VIP (a marker associated with cholinergic phenotype in neurons supplying sweat glands) showed that SCG neurons projecting to irises with sweat gland implants may be induced to express VIP. We hypothesise that these neurons have been switched from their normal catecholaminergic phenotype to a cholinergic one by contact with the sweat gland implants. Transplants from old donors attracted a density of reinnervation by young host nerves which was appropriate to the age of the donor, thus old sweat glands received a significantly reduced density of innervation compared to young glands. Despite the reduced density of innervation, there was no obvious difference in the ability of young and old implants to induce the switch to a cholinergic phenotype, suggesting that different mechanisms regulate nerve growth and neurotransmitter phenotype.

Neuropeptides in the skin of patients with atopic dermatitis

There is increasing evidence that neuropeptides may be involved in the pathogenesis of atopic dermatitis (AD). This study examines whether neuropeptide distribution in the skin of patients with AD differs from normal controls. The distribution and density of several neuropeptides were examined in lesional and non-lesional skin of AD patients (n = 5) and in normal controls (n = 4) using indirect immunofluorescence and image analysis. Cholinergic innervation was studied using cholinesterase histochemistry. Staining with the general neuronal marker protein gene product 9 x 5 showed a subepidermal network of nerves with fibres penetrating the epidermis, and nerves around blood vessels, sweat glands and hair follicles. Image analysis of nerves around sweat glands showed a significantly higher nerve density in non-lesional compared with both normal controls and lesional skin (P < 0.05); lesional compared with control skin showed no significant difference. In the epidermis the density of nerves was not significantly greater in non-lesional compared with lesional skin and controls. Calcitonin gene-related peptide immunoreactivity was similar in all subjects except in three of the AD patients, where more nerves appeared to penetrate the epidermis. Substance P immunoreactivity in the papillary dermis was seen in all AD patients but no controls. Vasoactive intestinal polypeptide and neuropeptide Y staining were similar in all groups. Acetylcholinesterase-positive nerves were found around sweat glands in all subjects, the staining being greatest in non-lesional and least in lesional skin. Occasional nerves were seen in the papillary dermis in lesional skin of two out of the four patients. We have demonstrated quantitative differences in nerve growth in clinically normal skin of AD patients, and altered cutaneous neuropeptide expression in these patients which may contribute to the pathogenesis of AD. The cause of atopic dermatitis (AD) has not been fully established but it is believed that there is a complex interaction between genetic susceptibility, precipitating environmental factors and disordered immune responsiveness. There is increasing evidence that neuropeptides may be involved in the pathogenesis of AD. Exacerbations of the disease can be provoked by stress, scratching and sweating which may be the result of neurogenic inflammation. One of the first features of an exacerbation is flushing of the affected skin and pruritus. Several neuropeptides that have been identified in human skin are potent inducers of vasodilation and may induce pruritus. Substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) all cause vasodilation when injected intradermally, and SP and CGRP have been shown to be mediators of the weal and flare reaction. Spantide, a competitive antagonist of SP, has been shown to inhibit immediate and delayed-type hypersensitivity reactions. Part of these responses may be due to release of histamine and indeed elevated concentrations of histamine have been found in vivo in the skin and plasma of patients with AD. In this study the distribution and density of several neuropeptides were examined in lesional and nonlesional skin of AD patients and in normal controls using indirect immunofluorescence and image analysis. Cholinergic innervation was studied using cholinesterase histochemistry. Because many afferent fibres do not express CGRP or SP, the general neuronal marker protein gene product (PGP 9 x 5) was used to assess the overall nerve supply to the skin.

Image analysis in dermatopathology

BACKGROUND/AIMS

Image analysis in dermatopathology has been used for DNA ploidy analysis, morphometry, stereology, and quantitative immunohistochemistry. The object is to review image analysis in dermatopathology and evaluate these modalities and their application in pigmented lesion pathology, for elucidation of tumor behaviour and architecture and as an aid in tumor identification and prognostication.

CONCLUSION

Image analysis in dermapathology has a huge potential. The techniques are difficult and at present mainly used in specialized centres.

Changes in the sweatspot test with ageing and relation to cardiovascular autonomic function

The sweatspot test assesses the local sweat response to an intradermal injection of acetylcholine. It has been reported as a more sensitive indicator of autonomic dysfunction in important diabetic men than either pupillary or cardiovascular tests, and has been used to establish the presence of autonomic dysfunction in patients with idiopathic chronic constipation. However, the usefulness of this test as a simple and quick method of diagnosing autonomic dysfunction in an elderly population has not been established. This is important given the high prevalence of reduced autonomic function with ageing and hypertension. We compared the age-associated responses in the sweatspot test and its relation to cardiovascular autonomic function in elderly normotensive and hypertensive subjects. We studied eleven normotensive and 24 untreated hypertensive elderly subjects (mean age 75.7 years, range 63-85) and compared the results of the sweatspot test to a young control group (n = 11, mean age 32.0 years, range 25-41), and to a standard battery of cardiovascular autonomic function tests. The median sweatspot score was significantly lower in the elderly compared with young subjects (1.9 vs. 12.0, p < 0.0001) although there was no difference between elderly normotensive and hypertensive subjects (1.6 vs. 2.4, p = 0.8). No correlation was demonstrated between the median sweatspot score and the number of abnormal cardiovascular tests. The sweatspot test was grossly abnormal in all elderly subjects and was not correlated to changes in cardiovascular autonomic function. Its diagnostic use in the elderly is therefore of very limited value.

Sympathetic sudomotor function and aging

Many studies have reported the influence of aging on different portions of the autonomic nervous system components but only partially for the sympathetic cholinergic system. We evaluated postganglionic sudomotor function in 196 healthy subjects, 104 women and 92 men, by determining sweat gland density (SGD) per square centimeter of skin, on the dorsum of the hand and foot, with the impression mold technique. The age range was from 5 to 84 years. A significant decrease of SGD was observed in both hand and foot in relation to age (P < 0.001). The ANOVA analysis of foot data shows that age is the only significant factor for SGD reduction. In the hand, both sex and body surface area are significant covariates with age. The dorsum of the foot is the most appropriate place to examine sweating in studies of aging. The lower normal limits for SGD in the foot are 213/cm2 for subjects younger than 30 years, 199/cm2 for those from 30 to 59 years, and 123/cm2 for subjects over 59 years old.

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.

Neurodegeneration in sweat glands and skin of aged rats

In order to compare age-associated neurodegenerative changes in peripheral nerves of laboratory mammals and humans, we have investigated the density and pattern of different nerve populations innervating sweat glands of ageing rats and compared our results with a previous study of the innervation of human sweat glands. We have also studied age-changes in subepidermal afferent nerves that may be involved in reflex activation of sweat glands. Total nerve density, measured by immunohistochemical staining for the general neuronal marker, protein gene product (PGP9.5) and image analysis, showed a significant decline around secretory coils of sweat glands of old compared to young rats. Marked reductions of acetylcholinesterase (AChE) histochemical staining and of vasoactive intestinal polypeptide (VIP)- and calcitonin gene-related peptide (CGRP)-like immunoreactivity were observed in nerves around sweat glands. In the sub-epidermis, PGP- and CGRP-like immunoreactive nerves were significantly reduced in old rats. The age-related changes in sweat gland innervation of old rats were comparable to those reported in elderly human subjects suggesting that these tissues may provide a suitable model for experimental studies of neuronal ageing.

Differential regulation of tyrosine hydroxylase protein and activity in rabbit sympathetic neurones after long-term cold exposure: altered responses in ageing

The aim of this study was to investigate the response of sympathetic neurones to prolonged neural stimulation, using cold exposure as a non-invasive experimental paradigm. We examined the effects of prolonged (8 days and 4 wk) cold exposure on tyrosine hydroxylase (TH) protein and activity and neuropeptide Y (NPY) levels in sympathetic neurones of the superior cervical ganglion (SCG), together with NPY levels in the ear artery from young and aged rabbits. The main findings were as follows. In young rabbits, TH levels and TH activity were differentially regulated in response to prolonged cold exposure. TH levels rose whilst TH activity tended to decline. Decentralization of SCG from young animals before cold exposure abolished the rise in TH levels. TH activity in SCG from young rabbits was reduced by decentralization whilst cold exposure resulted in an increase in TH activity. Thus, TH activity was induced in the SCG in the absence of pre-ganglionic input, demonstrating a non-synaptic regulatory mechanism. In old rabbits, cold-induced changes were either delayed or failed to occur, indicating that the responses of sympathetic neurones to cold stress are impaired in old age.