The molecular and pharmacological properties of muscarinic cholinergic receptors expressed by rat sweat glands are unaltered by denervation.

Previous studies have indicated that denervation of adult rodent sweat glands results in the loss of secretory responsiveness to muscarinic agonists. To elucidate the molecular basis of this loss, we have characterized the muscarinic cholinergic receptor present in adult rat sweat glands and examined the effects of cholinergic denervation on its properties and expression. When homogenates of gland-rich tissue from adult animals were assayed with [N-methyl-3H]-scopolamine, a high-affinity muscarinic antagonist, the concentration of muscarinic receptors was 301 fmol/mg protein and the affinity was 131 pM. Autoradiographic analysis demonstrated that ligand binding sites were detectable only on glands. In competition studies with well-characterized muscarinic agents, the receptor exhibited typical muscarinic pharmacology. Further investigation with the selective muscarinic antagonists 4-diphenylacetoxy-N-methylpiperidine methiodide, pirenzepine, and AF DX-116 revealed that the sweat gland receptor belongs to the M2 glandular pharmacological subtype. In situ hybridization histochemistry with receptor subtype-specific oligonucleotide probes indicated that rat sweat glands express the m3 molecular receptor subtype. Seven days after sciatic nerve transection, when denervated glands were compared to those on the contralateral unoperated side, there was no significant difference either in the concentration or affinity of muscarinic binding sites or in receptor density or distribution. Furthermore, the molecular subtype and the level of its expression were unchanged. Thus, it appears that muscarinic binding sites and m3 receptor mRNA are present in denervated sweat glands that are unresponsive to muscarinic stimulation. These results suggest that the regulation of responsiveness occurs at a point distal to the expression of muscarinic receptors.     

Developmental expression of the high affinity choline transporter in cholinergic sympathetic neurons

Choline uptake by the high affinity choline transporter (CHT) is the rate-limiting step in acetylcholine synthesis. Induction of CHT is therefore a critical step in cholinergic differentiation, and we examined the developmental expression of CHT in cholinergic sympathetic neurons that innervate rodent sweat glands. During postnatal development the earliest sympathetic axons in the rear footpads are noradrenergic, containing intense tyrosine hydroxylase immunoreactivity and lacking CHT-immunoreactivity (CHT-IR). By postnatal day 7 (P7) in mouse, and P10 in rat, weak CHT-IR appeared in axons associated with the sweat gland anlagen. CHT staining intensity increased during the following weeks in conjunction with plexus arborization and gland maturation. The pattern of CHT-immunoreactivity (CHT-IR) in the sweat gland innervation was similar to staining for the vesicular acetylcholine transporter and vasoactive intestinal peptide. Immunoblots of tissue from sympathectomized rats confirmed that most of the CHT in footpad was contained in sympathetic neurons. Although CHT expression has been reported in noradrenergic sympathetic neurons of the superior cervical ganglion, these data indicate that in the sympathetic neurons projecting to sweat glands CHT is present at detectable levels only after association with the glands.     

Neonatal 6-hydroxydopamine treatment eliminates cholinergic sympathetic innervation and induces sensory sprouting in rat sweat glands

Previous studies of the development of cholinergic sympathetic innervation of sweat glands in rat footpads suggested that these terminals initially exhibit noradrenergic properties which are lost as the glands and their innervation mature. We have treated neonatal and adult rats with 6-hydroxydopamine (6-OHDA), a toxic congener of norepinephrine, and compared its effects on the cholinergic sympathetic innervation of sweat glands and the noradrenergic sympathetic innervation of the iris, salivary gland, and blood vessels. As reported by others, 6-OHDA treatment of neonates caused the destruction of noradrenergic fibers in the iris and salivary gland but did not affect other fibers projecting to these targets that stain for acetylcholinesterase (AChE). We found that 6-OHDA treatment of neonatal animals also caused the destruction of the sympathetic axons in immature sweat glands that possess catecholamine histofluorescence and tyrosine-hydroxylase-like immunoreactivity. Furthermore, when such animals were examined as adults, we found no AChE staining, vasoactive intestinal peptide (VIP)-like immunoreactivity, or characteristic sympathetic axonal varicosities. However, the denervated glands were invested by a plexus of sensory axons, some of which exhibited substance P-like immunoreactivity (SP-IR). An increase in the number of SP-IR fibers also occurred in the sympathetically denervated irides of these animals. Chronic treatment of neonates with guanethidine, another adrenergic sympathetic neurotoxin, resulted in similar loss of cholinergic sweat gland innervation. Treatment of adults rats with doses of 6-OHDA identical to those used to treat neonates caused the loss of noradrenergic fibers from the iris, salivary gland, and many blood vessels but did not noticeably affect AChE and VIP staining or axonal ultrastructure in the sweat glands. However, treatment with higher doses of 6-OHDA did cause significant axonal degeneration. The response of the sympathetic innervation of developing but not mature sweat glands to 6-OHDA provides evidence for a transition from noradrenergic to cholinergic phenotype during the development of sympathetic neurons in vivo similar to the transition observed in cell culture. The sprouting of sensory axons may be caused by NGF-like trophic influences present in some sympathetically denervated tissues.     

Sympathetic cholinergic target innervation requires GDNF family receptor GFR alpha 2

Many cholinergic parasympathetic and enteric neurons require neurturin signaling through GDNF family receptor GFRalpha2 for target innervation. Since a distinct minority of sympathetic neurons are cholinergic, we examined whether GFRalpha2 is important for their development. We detected GFRalpha2 in neonatal sympathetic cholinergic neurons and neurturin mRNA in their target tissues, sweat glands in footpads, and periosteum. Lack of GFRalpha2 in mice did not affect the number of sympathetic cholinergic neurons, but their soma size was decreased in comparison to wild types. In adult and in 3-week-old GFRalpha2 knockout mice, the density of sympathetic cholinergic innervation was reduced by 50-70% in the sweat glands, and was completely absent in the periosteum. Sympathetic noradrenergic innervation of blood vessels in the footpads was unchanged. The density of sympathetic axons in sweat glands was unaffected at postnatal day P4 reflecting successful growth into the target area. Our results indicate that the cholinergic subpopulation of sympathetic neurons requires GFRalpha2 signaling for soma size and for growth or maintenance of target innervation. Thus, neurturin may be a general target-derived innervation factor for postganglionic cholinergic neurons in all parts of the autonomic nervous system.     

Development of choline acetyltransferase (CAT) in the sympathetic innervation of rat sweat glands

It has been postulated that the developing sympathetic innervation of rat eccrine sweat glands changes from adrenergic to cholinergic under the influence of its target. In agreement with previous evidence that the sympathetic innervation of adult rat sweat glands is cholinergic, we found that choline acetyltransferase (CAT)-immunoreactive nerve fibers are present in adult glands, and that gland-rich chunks of adult footpads contain CAT enzyme activity. We were therefore interested in determining when CAT activity is first expressed in the developing gland innervation. Low levels of acetylating activity were observed in rat footpads as early as postnatal day 4, when sympathetic fibers first contact the glands. A greater than fourfold increase in CAT specific activity occurred between postnatal days 11 and 21. Neonatal treatment of rats with the adrenergic neurotoxin 6-hydroxydopamine (6-OHDA) eliminated most of the CAT activity in 14 and 19 d footpads. In contrast, the acetylating activity observed prior to day 11 was unaffected by neonatal 6-OHDA treatment, and only slightly reduced by the selective CAT inhibitor, naphthylvinylpyridine. These results indicate that the sympathetic fibers that innervate rat sweat glands do not acquire detectable levels of CAT activity until a full week after they contact the glands.     

Coexpression of cholinergic and noradrenergic phenotypes in human and nonhuman autonomic nervous system

It has long been known that the sympathetic innervation of the sweat glands is cholinergic in most mammalian species and that, during development, rodent sympathetic cholinergic sweat gland innervation transiently expresses noradrenergic traits. We show here that some noradrenergic traits persist in cholinergic sympathetic innervation of the sweat glands in rodents but that lack of expression of the vesicular monoamine transporter renders these cells functionally nonnoradrenergic. Adult human sweat gland innervation, however, is not only cholinergic but coexpresses all of the proteins required for full noradrenergic function as well, including tyrosine hydroxylase, aromatic amino acid decarboxylase, dopamine beta-hydroxylase, and the vesicular monoamine transporter VMAT2. Thus, cholinergic/noradrenergic cotransmission is apparently a unique feature of the primate autonomic sympathetic nervous system. Furthermore, sympathetic neurons innervating specifically the cutaneous arteriovenous anastomoses (Hoyer-Grosser organs) in humans also possess a full cholinergic/noradrenergic cophenotype. Cholinergic/noradrenergic coexpression is absent from other portions of the human sympathetic nervous system but is extended in the parasympathetic nervous system to intrinsic neurons innervating the heart. These observations suggest a mode of autonomic regulation, based on corelease of norepinephrine and acetylcholine at parasympathocardiac, sudomotor, and selected vasomotor neuroeffector junctions, that is unique to the primate peripheral nervous system.     

Developmental changes in the transmitter properties of sympathetic neurons that innervate the periosteum.

During the development of sweat gland innervation, interactions with the target tissue induce a change from noradrenergic to cholinergic and peptidergic properties. To determine whether the change in neurotransmitter properties that occurs in the sweat gland innervation occurs more generally in sympathetic neurons, we identified a new target of cholinergic sympathetic neurons in rat, the periosteum, which is the connective tissue covering of bone, and characterized the development of periosteal innervation of the sternum. During development, sympathetic axons grow from thoracic sympathetic ganglia along rib periosteum to reach the sternum. All sympathetic axons displayed catecholaminergic properties when they reached the sternum, but these properties subsequently disappeared. Many axons lacked detectable immunoreactivities for vesicular acetylcholine transporter and vasoactive intestinal peptide when they reached the sternum and acquired them after arrival. To determine whether periosteum could direct changes in the neurotransmitter properties of sympathetic neurons that innervate it, we transplanted periosteum to the hairy skin, a noradrenergic sympathetic target. We found that the sympathetic innervation of the transplant underwent a noradrenergic to cholinergic and peptidergic change. These results suggest that periosteum, in addition to sweat glands, regulates the neurotransmitter properties of the sympathetic neurons that innervate it.     

Innervation of footpads of normal and mutant mice lacking sweat glands

Footpads of normal adult mice are innervated by sympathetic and sensory fibers. The sympathetic fibers associated with sweat glands contain acetylcholinesterase and immunoreactivity for vasoactive intestinal peptide. Although catecholamine histofluorescence is absent, the gland innervation exhibits immunoreactivity for tyrosine hydroxylase. A distinct population of sympathetic fibers, which possess catecholamines and neuropeptide Y as well as tyrosinehydroxylase immunoreactivity, innervates blood vessels. Sensory fibers containing immunoreactivity for substance P and calcitonin gene-related peptide course beneath the epidermis and some form endings in it. Treatment of neonatal mice with the adrenergic neurotoxin, 6-hydroxydopamine, results in loss of sympathetic innervation of sweat glands and blood vessels, permits growth of sensory axons into sweat glands, but does not alter the peptidergic sensory innervation of the dermis and epidermis. Three mouse mutations, Tabby (Ta), crinkled (cr), and downless (dl), disrupt the interactions between the mesenchyme and epidermis that are required for normal development of specific epidermal derivatives, including sweat glands. The sympathetic innervation of blood vessels and sensory innervation of footpad skin of the three mutant mice that lack sweat glands is indistinguishable from normal. The sympathetic fibers that normally innervate sweat glands, however, are not present. These results indicate that in the absence of their normal target, the sympathetic fibers that innervate sweat glands are lacking. Furthermore, they suggest that, although sensory fibers may sprout into sympathetic targets in the footpad, the domains occupied by sensory fibers are not normally accessible to sympathetic axons. © 1994 Wiley-Liss, Inc.     

Coexistence of calcitonin gene-related peptide and vasoactive intestinal peptide in cholinergic sympathetic innervation of rat sweat glands

Immunoreactivity for calcitonin gene-related peptide (CGRP) has been localized with indirect immunofluorescence techniques in the cholinergic sympathetic fibers that innervate eccrine sweat glands in the rat. This innervation also contains vasoactive intestinal peptide-like immunoreactivity (VIP-IR). A small proportion of principal neurons in stellate and lumbar sympathetic ganglia which provide innervation to the sweat glands contain detectable CGRP-immunoreactivity. The CGRP-IR neurons are immunoreactive for VIP; however, many VIP-IR neurons in these ganglia do not contain detectable levels of CGRP-IR.     

Sudomotor function and sweat gland innervation in galanin knockout mice

The presence of galanin and galanin binding sites in sweat gland has been demonstrated previously. In order to investigate whether galanin can influence sweat gland function, we compared sweating induced in footpads of wild type and galanin knockout mice by cholinergic and thermal stimulation using the silicone impression technique. Pilocarpine injections resulted in a similar number of reactive sweat glands and non-significant difference in the amount of sweat secretion in wild type and galanin knockout mice. However, thermal stimulation led to a significant increase in the number of secreting sweat glands in galanin knockout mice. To further evaluate possible differences in the innervation of sweat glands that could explain differences in their secretory activity, immunohistochemical labeling of cutaneous and sudomotor innervations against protein gene product 9.5, vasoactive intestinal polypeptide and choline acetyltransferase in plantar pads was performed. Immunohistochemical analysis revealed no significant differences in the distribution and intensity of the innervations between wild type mice and galanin knockout mice. Although our results indicate normal cholinergic responses and innervation of the sweat glands in galanin knockout mice, they also demonstrate that galanin plays a role in regulating the sudomotor activity in response to thermal stimulation.     

Visualization of muscarinic receptor-mediated phosphoinositide turnover in the hippocampus of young and aged, learning-impaired Long Evans rats.

Hippocampal receptor-mediated phosphoinositide (PI) turnover is severely blunted in aged rats that demonstrate cognitive deficits in the Morris water maze. To further examine the anatomical localization of this deficit, we examined the topography of muscarinic receptor-mediated PI turnover in young and aged-learning impaired rats by taking advantage of an autoradiographic method that visualizes PI turnover by measuring the diacylglycerol (DAG) branch of the PI turnover signal transduction system. Using this method, muscarinic cholinergic receptors were stimulated in hippocampal slices with agonist, and the receptor-mediated incorporation of [3H] cytidine into [3H]CDP-DAG was subsequently quantified in subregions of the hippocampus using film autoradiography. Our results show a significant decrease in basal incorporation of [ 3H]CDP-DAG in the subiculum and in the dentate gyrus in the aged rats. The muscarinic receptor-mediated [3H]CDP-DAG response was significantly blunted in the aged rats in subiculum, CA3, and CA1. In contrast, the receptor-mediated response was maintained in the dentate gyrus and hilus. These results indicate that the age-associated impairment in receptor-mediated PI turnover differs regionally, with a reduction in the subiculum and hippocampus proper that is pronounced relative to the hilus and dentate gyrus.     

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.     

Multiple types of neurotransmitter binding sites in the rat neuroblastoma B 50 cell line. II. Response of second messenger systems to physiological stimuli in proliferating and differentiated cells

The functionality of the alpha 1-, beta-adrenergic and muscarinic cholinergic binding sites of neuroblastoma B 50 is investigated under proliferating and differentiating conditions. In proliferating cells, the stimulation of the alpha 1-adrenergic and muscarinic cholinergic binding sites by their respective agonists causes an increase in both extracellular calcium association with the cells and phosphatidylinositol (PI) turnover; effects usually associated with functional receptors. When the cells are induced to differentiate morphologically with dibutyryl cyclic AMP (db-cAMP), extracellular calcium or a combination of both, the activity of the muscarinic receptor-coupled PI turnover is strictly correlated with the binding affinity of the receptor. This is not the case for the alpha 1-adrenergic receptor stimulation of PI turnover. The latter result, however, may be explained in terms of the intrinsic properties of the inducing agents used to cause neurite extension. The stimulation of the beta-adrenergic binding site with isoproterenol in proliferating cells, both with and without a phosphodiesterase inhibitor present, does not result in cellular cAMP accumulation. In morphologically differentiated cells, only the db-cAMP-induced state exhibits an increase in [3H]adenosine incorporation into cellular cAMP upon isoproterenol stimulation. This happens only in the presence of a phosphodiesterase inhibitor. The data presented in this study are discussed in terms of the affinity of the receptors for their respective ligands and in terms of the intrinsic properties of the inducing agents.     

Catecholaminergic properties of cholinergic neurons and synapses in adult rat ciliary ganglion

Parasympathetic neurons of the ciliary ganglion are innervated by preganglionic cholinergic neurons whose cell bodies lie in the brain stem; the ganglion cells in turn provide cholinergic innervation to the intrinsic muscles of the eye. Noradrenergic innervation of the iris is supplied by sympathetic neurons of the superior cervical ganglion. Using immunocytochemical and histochemical techniques, we have examined the ciliary ganglion of adult rats for the expression of cholinergic and noradrenergic properties. As expected, the postganglionic ciliary neurons possessed detectable levels of choline acetyltransferase immunoreactivity (ChAT-IR). Unexpectedly, many ciliary neurons also exhibited immunoreactivity for tyrosine hydroxylase (TH-IR). Some had dopamine beta-hydroxylase-like (DBH-IR) immunoreactivity, but none contained detectable catecholamines, even after treatment with nialamide and L-DOPA. A sparse plexus of fibers exhibiting faint TH-IR was present in the irises of acutely sympathectomized rats. The terminals of preganglionic axons in the ciliary ganglion exhibited not only immunoreactivity for ChAT, but also for TH and contained stores of endogenous catecholamine. Neither ciliary neurons nor their preganglionic innervation accumulated detectable stores of exogenous catecholamines. Rats sympathectomized as neonates by treatment with 6-hydroxydopamine subsequently had a greater proportion of neurons possessing detectable TH-IR in the ciliary ganglion; both the TH-IR perikarya and their axons in the iris were more intensely immunofluorescent. TH-IR was present in the ciliary neuron cell bodies of mouse, guinea pig, and ferret. These species, however, lacked detectable TH-IR or catecholamine stores in preganglionic terminals. These observations indicate that mature, functionally cholinergic neurons from 2 different embryonic origins, postganglionic ciliary neurons derived from the neural crest and preganglionic neurons derived from the neural tube, display several catecholaminergic properties.     

Distribution of muscarinic receptors and acetylcholinesterase in the rat heart

Experiments were performed to determine the degree of overlap in the distribution of muscarinic receptors and cholinergic innervation of the rat heart. Localization of muscarinic receptors was determined by autoradiography with [3H]quinuclidinyl benzilate. Adjacent sections were stained for acetylcholinesterase to determine innervation. The distribution of muscarinic receptors and cholinergic innervation overlapped in cardiac parasympathetic ganglia, nodal tissue, His bundle-Purkinje system, vena cava and pulmonary veins. Cholinergic innervation to the right atrium was greater than to the left atrium while muscarinic receptor density was equal in the two atria. Innervation of the ventricles was confined primarily to the base of the right ventricle. A low density of muscarinic receptors was observed throughout the ventricles. Neither cholinergic innervation nor muscarinic receptors were detected in the pulmonary trunk, ascending aorta or cardiac valves. Muscarinic receptors and cholinergic innervation in the nodal regions, ventricular conduction system and myocardium probably mediate negative chronotropic, dromotropic and inotropic effects of vagal nerve stimulation. Muscarinic receptors at sites not containing cholinergic innervation may be associated with noradrenergic nerves of the myocardium.     

Effect of sympathetic input on ontogeny of β-adrenergic receptors in rat pineal gland

The ontogeny of beta-adrenergic receptors was investigated in the pineal glands of rats 1–64 days of age. The density of beta-receptors increased about 3-fold between 1 and 16 days of age and decreased slightly by 64 days, correlating temporally with the development of the sensitivity of adenylate cyclase to norepinephrine in pineal gland. Preventing adrenergic innervation of the pineal gland by neonatal ganglionectomy or decentralization failed to prevent the development of beta-adrenergic receptors in pineal gland. Bilateral adrenal demedullation alone or in combination with ganglionectomy also failed to prevent the normal developmental increase of betareceptors in the gland. These results, showing that the ontogeny of pineal beta-receptors correlates temporally with that of the responsiveness of adenylate cyclase to adrenergic neurohormones, support the hypothesis that the responsiveness of tissues to beta-agonists is dependent on the development of the beta-receptor. In addition, these experiments show that the beta-adrenergic receptor can develop even in the absence of sympathetic innervation or circulating catecholamines produced by the adrenal medullae.     

Muscarinic receptors of rat parotid gland enlarged by gland ablation and bulk diet. Effects of denervation

The density of muscarinic binding sites was increased 10% in the rat parotid gland enlarged (2 times control) as a result of ablation of the submandibular-sublingual glands and maintenance of rats on bulk diet (50% inert cellulose plus 50% solid chow) for 4 weeks. When either the parasympathetic or sympathetic innervation to the gland was unilaterally removed at the time of submandibular-sublingual ablation and introduction of the bulk diet, the density of muscarinic receptors showed an even greater increase from levels of innervated glands of chow-fed controls (29%); with removal of both nerves, the increase was 39%. A 36% increase in cyclic guanosine monophosphate levels accompanied the increase in receptors of the enlarged gland, but when the parotid was denervated, there was no change in cyclic GMP. Absence of either or both nerves led to a maximal decrease of 24-29% in density of muscarinic receptors of parotid gland of chow-fed controls, but to no change in cyclic GMP levels. While autonomic influences mediate the changes in density of muscarinic receptors of parotid gland of chow-fed rats, some additional factor is apparently involved in their increase in the enlarged gland.     

Overexpression of nerve growth factor in epidermis disrupts the distribution and properties of sympathetic innervation in footpads

Sympathetic and sensory neurons form distinct axonal arborizations in several peripheral targets. The developmental mechanisms responsible for partitioning sympathetic and sensory axons between potential target tissues are poorly understood. We have used rodent footpads to study this process because three populations of peripheral axons innervate topographically segregated targets in the footpad; cholinergic sympathetic axons innervate sweat glands, noradrenergic sympathetic axons innervate blood vessels, and sensory axons form a plexus at the epidermal/dermal junction. To examine how nerve growth factor (NGF), a trophic and survival factor for sympathetic and some sensory neurons, may contribute to the generation of the patterned distribution of axons among targets, we studied transgenic mice (K14-NGF mice) in which NGF expression was significantly increased in the epidermis. Whereas the temporal sequence in which sensory and sympathetic fibers arrived in the footpad was not affected, the normal partitioning of axons between target tissues was disrupted. The two sympathetic targets in footpads, sweat glands, and blood vessels lacked substantial innervation and instead a dense plexus of catecholaminergic sympathetic fibers was found commingled with sensory fibers in the dermis. Those sympathetic fibers present in sweat glands expressed an abnormal dual catecholaminergic/cholinergic phenotype. Our findings indicate that overexpression of NGF in skin interferes with the segregation of sensory and sympathetic axonal arbors and suggests a role for target-derived NGF in the establishment of distinct axonal territories. Our data also suggest that by determining where axon arbors form, NGF can indirectly influence the phenotypic properties of sympathetic neurons. J. Comp. Neurol. 393:231–243, 1998. © 1998 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.     

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.     

Generalised anhidrosis: different lesion sites demonstrated by microneurography and skin biopsy

Generalised anhidrosis (GA) shows a uniform clinical picture whether the pathogenesis involves intrinsic abnormalities of sweat glands or postganglionic sympathetic cholinergic nerve dysfunction. We describe two patients who presented intolerance to heat and anhidrosis. In the first patient, symptoms started at 33 years of age, and were associated with absent tendon reflexes and a mydriatic right pupil unreactive to light. The other patient had been unable to sweat since birth. GA was diagnosed on the basis of clinical findings and thermoregulatory tests. Microneurography and morphological analysis of the skin and its innervation disclosed a different lesion site underlying GA in the two patients, and distinguished between a postganglionic autonomic nerve fibre lesion and sweat gland dysfunction.