Functional sudomotor responses to cholinergic agonists and antagonists in the mouse

Proteomic quantitative study of dorsal root ganglia and sciatic nerve in type 2 diabetic mice

OBJECTIVE

Peripheral neuropathy is the most common and debilitating complication of type 2 diabetes, leading to sensory loss, dysautonomia, hyperalgesia, and spontaneous noxious sensations. Despite the clinical and economic burden of diabetic neuropathy, no effective treatment is available. More preclinical research must be conducted in order to gain further understanding of the aetiology of the disease and elucidate new therapeutic targets.

METHODS

The proteome of lumbar dorsal root ganglia and sciatic nerve of BKS-db/db mice, which contain a mutation of the leptin receptor and are an established type 2 diabetes model, was characterized for the first time by tandem mass tag labelling and mass spectrometry analysis.

RESULTS

Proteomic analysis showed differentially expressed proteins grouped into functional clusters in db/db peripheral nerves compared to control mice, underlining reduced glycolytic and TCA cycle metabolism, higher lipid catabolism, upregulation of muscle-like proteins in DRG and downregulation in SCN, increased cytoskeleton-related proteins, a mild dysregulation of folding chaperones, activation of acute-phase and inflammatory response, and alterations in glutathione metabolism and oxidative stress related proteins.

CONCLUSIONS

Our data validate previous transcriptomic and metabolomic results and uncover new pathways altered in diabetic neuropathy. Our results point out that energetic deficiency could represent the main mechanism of neurodegeneration observed in diabetic neuropathy. These findings may provide important information to select appropriate targets to develop new therapeutic strategies.

Multi-dry-electrode plate sensor for non-invasive electrocardiogram and heart rate monitoring for the assessment of drug responses in freely behaving mice

Monitoring of electrocardiogram (ECG) and heart rate (HR) is essential in a wide range of experiments. For conscious animal studies, telemetry is the preferred approach; however, it requires 1-3 weeks of recovery after surgical device-implantation. The present paper describes a novel multi-dry-electrode plate (MDEP) sensor system to monitor ECG/HR in freely behaving mice without the need for surgery for device/electrode implantation. The MDEP sensor is a rectangular plate with 15 gold-plated stripe pattern electrodes, on which a mouse can walk around freely, and detects ECG whenever ≥2 paws (footpads) come in contact with the electrodes. Here we show that the MDEP sensor detected distinct QRS complexes which, were fragmented due to locomotion and insufficient perspiration on the footpads. Nonetheless, the HR calculated from the QRS complexes were similar to the HR calculated from R-R intervals simultaneously recorded from lead-II ECG (difference = 0.0 ± 0.16 ms) as part of the validation exercise. Also, the archetypal responses to isoproterenol and metoprolol injections were successfully detected as a significantly elevation (+151 ± 15 bpm) and reduction (-77 ± 6 bpm) in HR, respectively, compared to vehicle at 20-60 min postdose. Conversely, the P wave was rarely identifiable unless signal averaging was undertaken. These results indicate a potential utility for the MDEP-sensor system for cardiac pharmacological studies. In addition, signal averaging appeared to be effective for detection of ECG intervals such as PR and QT, although the QT cannot be measured in the mouse heart as there is no T wave.

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.

Feasibility of monitoring stress using skin conduction measurements during intubation of newborns

The objective of this study was to assess the feasibility of monitoring stress responses in newborns during naso-tracheal intubation after two different premedication regimens, using skin conductance measurements (SCM). Twenty-two newborns were randomised and premedicated with morphine + vecuronium or propofol. SCM (peaks/s) were collected prior to, during and after the procedure. Threshold for interpreting responses as stressful was 0.21 peaks/s. Intubation conditions and physiological parameters were registered. Intubation conditions were good in all newborns. Administration of morphine (range 1.4-10.3 min) before administration of vecuronium did not affect SCM when a stressful stimulus was applied. Within 1.6 min (range 0.8-3 min) after administration of vecuronium, SCM disappeared in 10 of 11 newborns. Propofol reduced SCM in 10 of 11 newborns at the first attempt. Further attempts were associated with increasing SCM, mostly above a threshold of 0.21 peaks/s. There were no significant changes in physiological parameters during the procedure for either premedication regimen.

CONCLUSION

The variation in SCM between individual newborns limits the usefulness of SCM as stress monitor during intubation. The use of neuromuscular blockers for premedication precludes monitoring of SCM completely in newborns.

WHAT IS KNOWN

Skin conductance measurements have been used successfully to monitor pain in awake newborn infants.

WHAT IS NEW

Premedicated newborns display significant interindividual variation in skin conductance measurements during an intubation procedure. Neuromuscular blockade causes skin conductance measurements to disappear completely.

Therapeutic applications of botulinum neurotoxins in head and neck disorders

Objective

The aim of this article is to review the mechanism of action, physiological effects, and therapeutic applications of botulinum neurotoxins in the head and neck area.

Study design

An extensive literature search was performed using keywords. The resulting articles were analyzed for relevance in four areas: overview on botulinum neurotoxins, the role of botulinum neurotoxins in the management of salivary secretory disorders, the role of botulinum neurotoxins in the management of facial pain, and the role of botulinum neurotoxins in head and neck movement disorders. Institutional review board approval was not needed due the nature of the study.

Results

Botulinum neurotoxin therapy was demonstrated to be a valuable alternative to conventional medical therapy for many conditions affecting the head and neck area in terms of morbidly, mortality, and patient satisfaction with treatment outcomes.

Conclusion

Botulinum neurotoxin therapy provides viable alternatives to traditional treatment modalities for some conditions affecting the head and neck region that have neurological components. This therapy can overcome some of the morbidities associated with conventional therapy. More research is needed to determine the ideal doses of botulinum neurotoxin to treat different diseases affecting the head and neck regions.

Dynamic analysis of histamine-mediated attenuation of acetylcholine-induced sweating via GSK3β activation

Sweating has been associated with the exacerbation of atopic dermatitis (AD) in diverse ways. Acetylcholine (ACh)-mediated sweating is known to be attenuated in AD, but its cause remains obscure. To address this issue, the impact of histamine on ACh-induced sweating was evaluated. Sweating was measured by counting the number of active sweat pores by the starch-iodine reaction and dynamic optical coherence tomography; sweat was visualized using two-photon excitation fluorescence microscopy in mice and the quantitative sudomotor axon reflex test in humans. Both histamine receptor antagonists and H1 receptor (H1R)-knockout (KO) mice were used to determine methodological specificity. Histamine demonstrably inhibited ACh-induced sweating in both mice and humans via H1R-mediated signaling. In sweat glands, ACh inactivated glycogen synthase kinase 3β (GSK3β), a kinase involved in endocytosis and secretion, whereas simultaneous stimulation with histamine activated GSK3β. Results of two-photon excitation fluorescence microscopy confirmed the dynamic motion of sweat and sweat glands after ACh treatment, showing that simultaneous stimulation with histamine altered their dynamic properties. These results indicate that histamine inhibits sweat gland secretions by blocking ACh-induced inactivation of GSK3β. Histamine-mediated hypohidrosis might be involved in the mechanism of abnormal skin dryness in patients with AD.

Peripheral choline acetyltransferase in rat skin demonstrated by immunohistochemistry

Conventional choline acetyltransferase immunohistochemistry has been used widely for visualizing central cholinergic neurons and fibers but not often for labeling peripheral structures, probably because of their poor staining. The recent identification of the peripheral type of choline acetyltransferase (pChAT) has enabled the clear immunohistochemical detection of many known peripheral cholinergic elements. Here, we report the presence of pChAT-immunoreactive nerve fibers in rat skin. Intensely stained nerve fibers were distributed in association with eccrine sweat glands, blood vessels, hair follicles and portions just beneath the epidermis. These results suggest that pChAT-positive nerves participate in the sympathetic cholinergic innervation of eccrine sweat glands. Moreover, pChAT also appears to play a role in cutaneous sensory nerve endings. These findings are supported by the presence of many pChAT-positive neuronal cells in the sympathetic ganglion and dorsal root ganglion. Thus, pChAT immunohistochemistry should provide a novel and unique tool for studying cholinergic nerves in the skin.

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.

Tropical Malaysians and temperate Koreans exhibit significant differences in sweating sensitivity in response to iontophoretically administered acetylcholine

Natives of the tropics are able to tolerate high ambient temperatures. This results from their long-term residence in hot and often humid tropical climates. This study was designed to compare the peripheral mechanisms of thermal sweating in tropical natives with that of their temperate counterparts. Fifty-five healthy male subjects including 20 native Koreans who live in the temperate Korean climate (Temperate-N) and 35 native tropical Malaysian men that have lived all of their lives in Malaysia (Tropical-N) were enrolled in this study after providing written informed consent to participate. Quantitative sudomotor axon reflex testing after iontophoresis (2 mA for 5 min) with 10% acetylcholine (ACh) was used to determine directly activated (DIR) and axon reflex-mediated (AXR) sweating during ACh iontophoresis. The sweat rate, activated sweat gland density, sweat gland output per single gland activated, and oral and skin temperature changes were measured. The sweat onset time of AXR (nicotinic-receptor-mediated) was 56 s shorter in the Temperate-N than in the Tropical-N subjects (P < 0.0001). The nicotinic-receptor-mediated sweating activity AXR (1), and the muscarinic-receptor-mediated sweating activity DIR, in terms of sweat volume, were 103% and 59% higher in the Temperate-N compared to the Tropical-N subjects (P < 0.0001). The Temperate-N group also had a 17.8% (P < 0.0001) higher active sweat gland density, 35.4% higher sweat output per gland, 0.24 degrees C higher resting oral temperature, and 0.62 degrees C higher resting forearm skin temperature compared to the Tropical-N subjects (P < 0.01). ACh iontophoresis did not influence oral temperature, but increased skin temperature near where the ACh was administered, in both groups. These results suggest that suppressed thermal sweating in the Tropical-N subjects was, at least in part, due to suppressed sweat gland sensitivity to ACh through both recruitment of active sweat glands and the sweat gland output per each gland. This physiological trait guarantees a more economical use of body fluids, thus ensuring more efficient protection against heat stress.

Heat Acclimatization in Hot Summer for Ten Weeks Suppress the Sensitivity of Sweating in Response to Iontophoretically-administered Acetylcholine

To determine the peripheral mechanisms involved in thermal sweating during the hot summers in July before acclimatization and after acclimatization in September, we evaluated the sweating response of healthy subjects (n=10) to acetylcholine (ACh), a primary neurotransmitter involved in peripheral sudomotor sensitivity. The quantitative sudomotor axon reflex test (QSART) measures sympathetic C fiber function after iontophoresed ACh evokes a measurable reliable sweat response. The QSART, at 2 mA for 5 min with 10% ACh, was applied to determine the directly activated (DIR) and axon reflex-mediated (AXR) sweating responses during ACh iontophoresis. The AXR sweat onset-time by the axon reflex was 1.50+/-0.32 min and 1.84+/-0.46 min before acclimatization in July and after acclimatization in September, respectively (p<0.01). The sweat volume of the AXR(1) [during 5 min 10% iontophoresis] by the axon reflex was 1.45+/-0.53 mg/cm(2) and 0.98+/-0.24 mg/cm(2) before acclimatization in July and after acclimatization in September, respectively (p<0.001). The sweat volume of the AXR(2) [during 5 min post-iontophoresis] by the axon reflex was 2.06+/-0.24 mg/cm(2) and 1.39+/-0.32 mg/cm(2) before and after acclimatization in July and September, respectively (p<0.001). The sweat volume of the DIR was 5.88+/-1.33 mg/cm(2) and 4.98+/-0.94 mg/cm(2) before and after acclimatization in July and September, respectively (p<0.01). These findings suggest that lower peripheral sudomotor responses of the ACh receptors are indicative of a blunted sympathetic nerve response to ACh during exposure to hot summer weather conditions.

Effects of topiramate on mouse eccrine sweat gland responsiveness to heat exposure

Young mice (2 weeks old) were given topiramate daily for 1 month, and sudomotor function was evaluated utilizing impression mould techniques to determine the number of sweat glands reactive to heat exposure and sweat output per gland on the plantar surface of mice hind-paws. Immunohistochemical quantitation of protein gene product 9.5, choline acetyltransferase and tyrosine hydroxylase in footpads was determined after topiramate treatment. While a 25% decrease in the number of secreting sweat glands and a 42% decline in sweat output per gland were observed following topiramate treatment, no significant differences were noted in sudomotor innervation, expressed as length of choline acetyltransferase, tyrosine hydroxylase and protein gene product 9.5 immunoreactive nerve profiles in single secretory coils or in sweat gland sizes within the secretory coil area. Long-term topiramate stimulation resulted in a reduction in the number of reactive sweat glands, without changes in sweat gland innervation, suggesting that the diminished responsiveness of the glands to heat exposure induced by topiramate might have resulted from a decrease in the intrinsic regulatory activity of sweat glands, as opposed to the loss of periglandular neurotransmitters or the impairment of the structure of the glands.

Topiramate reduced sweat secretion and aquaporin-5 expression in sweat glands of mice

Decreased sweat secretion is a primary side effect of topiramate in pediatric patients, but the mechanism underlying this effect remains unclear. This study aimed to better understand how topiramate decreases sweat secretion by examining its effect on the expression of carbonic anhydrase (CA) II and aquaporin-5 (AQP5), total CA activity, as well as on tissue morphology of sweat glands in mice. Both developing and mature mice were treated with a low (20 mg/kg/day) and high dose (80 mg/kg/day) of topiramate for 4 weeks. Sweat secretion was investigated by an established technique of examining mold impressions of hind paws. CA II and AQP5 expression levels were determined by immunofluorescence and immunoblotting and CA activity by a colorimetric assay. In mature mice, topiramate treatment decreased the number of pilocarpine reactive sweat glands from baseline in both the low and high dose groups by 83% and 75%, respectively. A similar decrease was seen in developing mice. Mature mice with reactive sweat glands that declined more than 25% compared to baseline were defined as anhidrotic mice. These mice did not differ from controls in average secretory coil diameter, CA II expression and CA activity. In contrast, anhidrotic mice did show a reduction in membrane AQP5 expression in sweat glands after topiramate delivery. Thus, sweat secretion and membrane AQP5 expression in mouse sweat glands decreased following topiramate administration. These results suggest dysregulation of AQP5 may be involved in topiramate-induced hypohidrosis and topiramate may serve as a novel therapy for hyperhidrosis.

Postnatal expression and denervation induced up-regulation of aquaporin-5 protein in rat sweat gland

The evolution of aquaporin-5 (AQP5) expression during postnatal development has not been defined in the sweat gland. Previous studies have suggested that AQP isoforms in several peripheral targets are regulated by a neural mechanism. We have examined, in rat sweat glands, the expression of AQP5 during postnatal development and the effects of denervation on AQP5 expression. Both AQP5 mRNA and protein begin to be expressed at postnatal day 10, before sweat-secretory responsiveness first appears; this expression coincides with the occurrence of vasoactive intestinal peptide (VIP) immunoreactivity. Early noradrenergic and later cholinergic interaction between sweat glands and their innervation are disrupted by neonatal chemical sympathectomy or postnatal severance of the sciatic nerve. Examination of such denervated developing rats has shown that secretory responsiveness fails to arise later in the adults, and AQP5 immunostaining increases in the denervated glands, whereas gland morphogenesis and the occurrence of AQP5 expression proceed normally. Immunobloting has revealed an increase of AQP5 abundance after the denervated mature glands lose their secretory ability. These findings suggest that AQP5 protein is necessary for sweat secretion, and that the expression of AQP5 in rat sweat glands is independent of sympathetic innervation. Our data also indicate that factor(s) regulating the normal morphological development of sweat gland might be responsible for controlling AQP5 expression.

Cutaneous Microdialysis as a Novel Means of Continuously Stimulating Eccrine Sweat Glands In Vivo

Previous studies of the pharmacological regulation of sweat gland function in humans have administered agonists or antagonists systemically, by local intradermal injection or by iontophoresis. This has not allowed prolonged or steady-state activation of sweat glands to be examined. In this study, we used the technique of dermal microdialysis to administer pharmacological agents singly and in combination for up to 5 hours. Muscarinic stimulation with pilocarpine nitrate (50 mug ml(-1) to 1.66 mg ml(-1)) produced a sigmoid dose response curve, with maximal sweating (measured as transepidermal water loss) (mean 70 g m(-2) hour(-1)) after 15 minutes. This was sustained at steady-state levels (55 g m(-2) hour(-1)) until perfusion stopped. Perfusion with atropine (0.003 mg ml(-1)) reduced sweating below baseline and blocked pilocarpine-induced sweating completely. Noradrenaline (0.005 mg ml(-1)) induced much lower sweat rates than pilocarpine (56.8+/-1.62 g m(-2) hour(-1) vs 8.2+/-1.2 g m(-2) hour(-1), respectively, P<0.001) and this was unaffected by co-administration of atropine. This method has made it possible to show that sweat glands are capable of sustaining near maximal activity for at least 5 hours. The method has future application in investigation of conditions with disordered sweat gland activity.

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.

Catecholamines are required for the acquisition of secretory responsiveness by sweat glands

The sympathetic innervation of sweat glands undergoes a developmental change in transmitter phenotype from catecholaminergic to cholinergic. Acetylcholine elicits sweating and is necessary for development and maintenance of secretory responsiveness, the ability of glands to produce sweat after nerve stimulation or agonist administration. To determine whether catecholamines play a role in the development or function of this system, we examined the onset of secretory responsiveness in two transgenic mouse lines, one albino and the other pigmented, that lack tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. Although both lines lack TH, their catecholamine levels differ because tyrosinase in pigmented mice serves as an alternative source for catecholamine synthesis (Rios et al., 1999). At postnatal day 21 (P21), 28 glands on average are active in interdigital hind footpads of albino TH wild-type mice. In contrast, fewer than one gland is active in albino TH null mice, which lack catecholamines in gland innervation. Treatment of albino TH null mice with DOPA, a catecholamine precursor, from P11 to P21 increases the number of active glands to 14. Pigmented TH null mice, which have faint catecholamine fluorescence in the developing gland innervation, possess 12 active glands at P21, indicating that catecholamines made via tyrosinase, albeit reduced from wild-type levels, support development of responsiveness. Gland formation and the appearance of cholinergic markers occur normally in albino TH null mice, suggesting that catecholamines act directly on gland cells to trigger their final differentiation and to induce responsiveness. Thus, catecholamines, like acetylcholine, are essential for the development of secretory responsiveness.

Inhibitory effects of muscarinic receptor autoantibodies on parasympathetic neurotransmission in Sjögren's syndrome

OBJECTIVE

Sjögren's syndrome (SS) is an autoimmune disorder characterized by dry eyes and mouth (sicca syndrome) and lymphocytic infiltration of the lacrimal and salivary glands. Abnormalities of parasympathetic neurotransmission may contribute to the glandular dysfunction. In this study, we used a functional assay to investigate autoantibody-mediated effects on parasympathetic neurotransmission and smooth muscle contraction.

METHODS

Serum and purified IgG were obtained from patients with primary and secondary SS and from control subjects. Contraction of isolated bladder strips in response to stimulation of M3-muscarinic receptors by a muscarinic receptor agonist, carbachol, or by endogenous acetylcholine released from postganglionic parasympathetic nerves was measured before and after the addition of patient serum or IgG.

RESULTS

Sera from 5 of 9 patients with primary SS and from 6 of 6 patients with secondary SS inhibited carbachol-evoked bladder contraction by approximately 50%. Sera from these patients also inhibited the action of neuronally released acetylcholine at M3-muscarinic receptors. Sera from 7 of 8 healthy individuals, from patients with rheumatoid arthritis without sicca symptoms, and from patients with systemic lupus erythematosus had no effect. The anti-muscarinic receptor activity was localized in the IgG fraction, since purified IgG from patients with SS also inhibited agonist- and nerve-evoked contractions. In this preliminary study, the autoantibodies seemed to be associated with the presence of bladder symptoms and other autonomic features.

CONCLUSION

Autoantibodies that act as antagonists at M3-muscarinic receptors on smooth muscle occur in a subset of patients with primary and secondary SS. Their presence in secondary SS was unexpected and provides new evidence for a common pathogenetic link between primary and secondary SS. These autoantibodies appear to contribute to sicca symptoms and may explain associated features of autonomic dysfunction in some patients.

Evaluation of direct and axon reflex sweating in the mouse

The nicotinic axon reflex-mediated sudomotor response was studied in mice and rats by recording the impressions of sweat droplets made in silicone molds after local injection of nicotine, and compared with sweating induced by acetylcholine and pilocarpine. Nicotine failed to activate mouse plantar sweat glands at any of the concentrations used (from 3 x 10(-6) to 3 x 10(-1) M). On the contrary, both acetylcholine and pilocarpine produced a dose-dependent increase in the number of secreting sweat glands. The location of sweat glands reactive to pilocarpine and acetylcholine was similar and restricted to the pads near the site of injection. We conclude that the sudomotor axon reflex response mediated by nicotinic receptors is not present in the mouse and the rat.

Development of muscarinic receptors and regulation of secretory responsiveness in rodent sweat glands

Sweat glands are innervated by sympathetic neurons which undergo a change in transmitter phenotype from noradrenergic to cholinergic during development. As soon as the glands begin to differentiate, M3 muscarinic receptor mRNA and binding sites are detectable. Receptor expression appears in the absence of innervation and is maintained after denervation. While receptor expression is not regulated by innervation, secretory responsiveness is. Muscarinic blockade during development or in adult animals results in the loss of responsiveness and its reappearance requires several days. Cholinergic muscarinic activation is most likely to regulate one or more steps in the signalling cascade that are downstream of calcium mobilization. The anterograde regulation of sweat gland responsiveness is one facet of the reciprocal interactions are required to establish a functional synapse in this system.

Physiological and immunohistochemical characterization of cisplatin-induced neuropathy in mice

We investigated the neuropathic effects of cisplatin in two groups of mice treated with 5 or 10 mg/kg/week of cisplatin for 7 or 8 weeks. Peripheral nerve functions were evaluated by sweat imprints, and electrophysiological, rotarod, and nociceptive tests. Protein gene product 9.5 (PGP), calcitonin gene-related peptide (CGRP), and vasoactive intestinal peptide (VIP) were immunohistochemically localized in footpads. Tibial nerves were analyzed morphometrically. Functional deficits developed progressively with higher cumulative doses, more markedly in mice treated with high than in those with low doses. From cumulative doses of 10 mg/kg, significant declines in sensory nerve conduction velocity and sudomotor responses were found, whereas motor and nociceptive functions were involved later. There were no morphometrical changes in tibial nerves. A marked decrease of CGRP- and VIP-immunoreactive nerves occurred in samples from treated mice, whereas PGP-labeled profiles decreased mildly at late stages. Impairment of the content of neuropeptides with neurosecretor role was detectable earlier than functional abnormalities. Immunohistochemical analysis of skin biopsies offers a useful diagnostic tool for peripheral neuropathies.

Changes in cholinergic responses of sweat glands during denervation and reinnervation

Functional sudomotor responses have been studied in sweat glands reinnervated after sciatic nerve crush and partially denervated by cisplatin intoxication in the mouse. The sudomotor function mediated by the sciatic nerve was evaluated by silicone imprints on the plantar surface of the hindpaws. Five days after nerve crush, completely denervated sweat glands became unresponsive to cholinergic stimulation with pilocarpine. During the following weeks, the number of reinnervated, reactive sweat glands increased progressively to reach a maximum of 89% of preoperative control counts by 40 days after nerve crush. At this time, the mean volume of sweat secreted per gland was normal, but reinnervated glands showed a secretory activity abnormally sustained over time after pilocarpine stimulation and, on the other hand, had an increased resistance to the inhibition of secretion induced by atropine. The effects of cisplatin administration on sudomotor function were investigated in two groups of mice, one treated with high doses of cisplatin (10 mg/kg/week for 4 weeks) and another treated with low doses of cisplatin (5 mg/kg/week for 8 weeks). Cisplatin intoxication produced abnormal sudomotor responses indicative of denervation from cumulative doses of 10 mg/kg. The first abnormality found was a partial resistance of sweat glands to atropine, followed by a decrease in the sweat output per gland and finally a decline in the number of sweat glands activated by pilocarpine. These abnormalities in the sudomotor responses were more pronounced in mice treated with a high dose than in those with a lower dose regime.