Changes in mouse sudomotor function and sweat gland innervation with ageing

Identification of Meibomian gland stem cell populations and mechanisms of aging

Meibomian glands secrete lipid-rich meibum, which prevents tear evaporation. Aging-related Meibomian gland shrinkage may result in part from stem cell exhaustion and is associated with evaporative dry eye disease, a common condition lacking effective treatment. The identities and niche of Meibomian gland stem cells and the signals controlling their activity are poorly defined. Using snRNA-seq, in vivo lineage tracing, ex vivo live imaging, and genetic studies in mice, we identified markers for stem cell populations that maintain distinct regions of the gland and uncovered Hh signaling as a key regulator of stem cell proliferation. Consistent with this, human Meibomian gland carcinoma exhibited increased Hh signaling. Aged glands displayed decreased Hh and EGF signaling, deficient innervation, and loss of collagen I in niche fibroblasts, indicating that alterations in both glandular epithelial cells and their surrounding microenvironment contribute to age-related degeneration. These findings suggest new approaches to treat aging-associated Meibomian gland loss.

Characterization of age-associated gene expression changes in mouse sweat glands

Evaporation of sweat on the skin surface is the major mechanism for dissipating heat in humans. The secretory capacity of sweat glands (SWGs) declines during aging, leading to heat intolerance in the elderly, but the mechanisms responsible for this decline are poorly understood. We investigated the molecular changes accompanying SWG aging in mice, where sweat tests confirmed a significant reduction of active SWGs in old mice relative to young mice. We first identified SWG-enriched mRNAs by comparing the skin transcriptome of Eda mutant Tabby male mice, which lack SWGs, with that of wild-type control mice by RNA-sequencing analysis. This comparison revealed 171 mRNAs enriched in SWGs, including 47 mRNAs encoding 'core secretory' proteins such as transcription factors, ion channels, ion transporters, and trans-synaptic signaling proteins. Among these, 28 SWG-enriched mRNAs showed significantly altered abundance in the aged male footpad skin, and 11 of them, including Foxa1, Best2, Chrm3, and Foxc1 mRNAs, were found in the 'core secretory' category. Consistent with the changes in mRNA expression levels, immunohistology revealed that higher numbers of secretory cells from old SWGs express the transcription factor FOXC1, the protein product of Foxc1 mRNA. In sum, our study identified mRNAs enriched in SWGs, including those that encode core secretory proteins, and altered abundance of these mRNAs and proteins with aging in mouse SWGs.

Role of basal sweating in maintaining skin hydration in the finger: A long-standing paradox in dry skin resolved

A long-standing paradox in dermatology is why skin dehydration in the fingers can be triggered by repeated water exposure despite the action of water to hydrate skin tissue. Potential clues might be provided by identifying a mechanism through which water is held in the skin of the fingers. We speculated that this mechanism would be impaired after repeated water exposure. Here, we investigated whether there might be glabrous skin-specific water-holding machinery and whether this machinery might be impaired in dry skin/hand eczema. We examined this by using an impression-mould technique, allowing for an accurate quantification of sweat gland/duct activity and optical coherence tomography. Unlike in hairy skin, sweat pores were rarely detected at the folds of the finger at baseline. Surprisingly, after water exposure, sweat pores at the folds opened and those at the ridges closed in healthy controls (HCs). Sweating in the dermal folds of the hands correlated with skin hydration, and decreased in dry skin/hand eczema, suggesting that its impairment may be one of the causes of dry skin. After repeated water exposure, basal sweating response at the folds was exhausted in patients with dry skin/hand eczema as well as HCs. This exhaustion was rescued by exposing individuals to high humidity. Basal sweating defects would be a target for dry skin/hand eczema. Maintaining basal sweating responses in the finger is the best preventive measures in achieving prevention of dry skin/hand eczema.

Protein profiles from used nesting material, saliva, and urine correspond with social behavior in group housed male mice, Mus musculus

Current understanding of how odors impact intra-sex social behavior is based on those that increase intermale aggression. Yet, odors are often promoted to reduce fighting among male laboratory mice. It has been shown that a cage of male mice contains many proteins used for identification purposes. However, it is unknown if these proteins relate to social behavior or if they are uniformly produced across strains. This study aimed to compare proteomes from used nesting material and three sources (sweat, saliva, and urine) from three strains and compare levels of known protein odors with rates of social behavior. Used nesting material samples from each cage were analyzed using LC-MS/MS. Sweat, saliva, and urine samples from each cage's dominant and subordinate mouse were also analyzed. Proteomes were assessed using principal component analyses and compared to behavior by calculating correlation coefficients between PC scores and behavior proportions. Twenty-one proteins from nesting material either correlated with affiliative behavior or negatively correlated with aggression. Notably, proteins from the major urinary protein family, odorant binding protein family, and secretoglobin family displayed at least one of these patterns, making them candidates for future work. These findings provide preliminary information about how proteins can influence male mouse behavior. SIGNIFICANCE: Research on how olfactory signals influence same sex social behavior is primarily limited to those that promote intermale aggression. However, exploring how olfaction modulates a more diverse behavioral repertoire will improve our foundational understanding of this sensory modality. In this proteome analysis we identified a short list of protein signals that correspond to lower rates of aggression and higher rates of socio-positive behavior. While this study is only correlational, it sets a foundation for future work that can identify protein signals that directly influence social behavior and potentially identify new murine pheromones.

Characterization of somatosensory neuron involvement in the SOD1G93A mouse model

SOD1^G93A mice show loss of cutaneous small fibers, as in ALS patients. Our objective is to characterize the involvement of different somatosensory neuron populations and its temporal progression in the SOD1^G93A mice. We aim to further define peripheral sensory involvement, analyzing at the same time points the neuronal bodies located in the dorsal root ganglia (DRG) and the distal part of their axons in the skin, in order to shed light in the mechanisms of sensory involvement in ALS. We performed immunohistochemical analysis of peptidergic (CGRP), non-peptidergic (IB4) fibers in epidermis, as well as sympathetic sudomotor fibers (VIP) in the footpads of SOD1^G93A mice and wild type littermates at 4, 8, 12 and 16 weeks of age. We also immunolabeled and quantified neuronal bodies of IB4, CGRP and parvalbumin (PV) positive sensory neurons in lumbar DRG. We detected a reduction of intraepidermal nerve fiber density in the SOD1^G93A mice of both peptidergic and non-peptidergic axons, compared with the WT, being the non-peptidergic the fewest. Sweat gland innervation was similarly affected in the SOD1^G93A mouse at 12 weeks. Nonetheless, the number of DRG neurons from different sensory populations remained unchanged during all stages. Cutaneous sensory axons are affected in the SOD1^G93A mouse, with non-peptidergic being slightly more vulnerable than peptidergic axons. Loss or lack of growth of the distal portion of sensory axons with preservation of the corresponding neuronal bodies suggest a distal axonopathy.

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.

Compounds from plantar foot sweat, nesting material, and urine show strain patterns associated with agonistic and affiliative behaviors in group housed male mice, Mus musculus

Excessive home cage aggression often results in severe injury and subsequent premature euthanasia of male laboratory mice. Aggression can be reduced by transferring used nesting material during cage cleaning, which is thought to contain aggression appeasing odors from the plantar sweat glands. However, neither the composition of plantar sweat nor the deposits on used nesting material have been evaluated. The aims of this study were to (1) identify and quantify volatile compounds deposited in the nest site and (2) determine if nest and sweat compounds correlate with social behavior. Home cage aggression and affiliative behavior were evaluated in 3 strains: SJL, C57BL/6N, and A/J. Individual social rank was assessed via the tube test, because ranking may influence compound levels. Sweat and urine from the dominant and subordinate mouse in each cage, plus cage level nest samples were analyzed for volatile compound content using gas chromatography-mass spectrometry. Behavior data and odors from the nest, sweat, and urine were statistically analyzed with separate principal component analyses (PCA). Significant components, from each sample analysis, and strain were run in mixed models to test if odors were associated with behavior. Aggressive and affiliative behaviors were primarily impacted by strain. However, compound PCs were also impacted by strain, showing that strain accounts for any relationship between odors and behavior. C57BL/6N cages displayed the most allo-grooming behavior and had high scores on sweat PC1. SJL cages displayed the most aggression, with high scores on urine PC2 and low scores on nest PC1. These data show that certain compounds in nesting material, urine, and sweat display strain specific patterns which match strain specific behavior patterns. These results provide preliminary information about the connection between home cage compounds and behavior. Salient compounds will be candidates for future controlled studies to determine their direct effect on mouse social behavior.

Methods for in vivo studies in rodents of chemotherapy induced peripheral neuropathy

Peripheral neuropathy is one of the most common, dose limiting, and long-lasting disabling adverse events of chemotherapy treatment. Unfortunately, no treatment has proven efficacy to prevent this adverse effect in patients or improve the nerve regeneration, once it is established. Experimental models, particularly using rats and mice, are useful to investigate the mechanisms related to axonal or neuronal degeneration and target loss of function induced by neurotoxic drugs, as well as to test new strategies to prevent the development of neuropathy and to improve functional restitution. Therefore, objective and reliable methods should be applied for the assessment of function and innervation in adequately designed in vivo studies of CIPN, taking into account the impact of age, sex and species/strains features. This review gives an overview of the most useful methods to assess sensory, motor and autonomic functions, electrophysiological and morphological tests in rodent models of peripheral neuropathy, focused on CIPN. We include as well a proposal of protocols that may improve the quality and comparability of studies undertaken in different laboratories. It is recommended to apply more than one functional method for each type of function, and to perform parallel morphological studies in the same targets and models.

Proteome characterization of used nesting material and potential protein sources from group housed male mice, Mus musculus

Laboratory mice (Mus musculus) communicate a variety of social messages through olfactory cues and it is often speculated that these cues are preserved in nesting material. Based on these speculations, a growing number of husbandry recommendations support preserving used nests at cage cleaning to maintain familiar odors in the new cage. However, the content of used nesting material has never been chemically analyzed. Here we present the first comprehensive proteome profile of used nesting material. Nests from cages of group housed male mice contain a variety of proteins that primarily originate from saliva, plantar sweat, and urine sources. Most notably, a large proportion of proteins found in used nesting material belong to major urinary protein (“MUP”) and odorant binding protein (“OBP”) families. Both protein families send messages about individual identity and bind volatile compounds that further contribute to identity cues. Overall, this data supports current recommendations to preserve used nesting material at cage cleaning to maintain odor familiarity.

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.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

How does a newly born mouse get to the nipple? Odor substrates eliciting first nipple grasping and sucking responses

It is a mammalian female strategy to emit odor cues and signals that direct their inexperienced newborns to the nipple, and optimize their initial sucking success and, hence, viability. Here, natural odorous substrates that contribute to nipple grasping were investigated in mice, a species that has not been much scrutinized on this topic. The response of pups toward the nipples of lactating females (LF) versus nonlactating females (NLF) were first assessed right after watched birth, before and after the first suckling experience, and at 1 day old, after more extended suckling experience. It appeared that only nipples of LF induced grasping at these early ages, leading to take NLF as the baseline setting to present various odor substrates sampled from LF, viz. amniotic fluid, murine milk, LF saliva, pup saliva, LF urine, and an odorless control stimulus (water). Results indicate that: (1) only amniotic fluid and fresh milk induced nipple grasping before the first suckling experience; (2) LF saliva started inducing grasping after the first suckling experience; (3) pup saliva released grasping after 24-36 hr of suckling experience; finally (4) neither LF urine, nor water induced any nipple grasping. In conclusion, the activity of amniotic fluid and murine milk on neonatal pup behavior before any postnatal suckling experience suggests that either prenatal learning and/or predisposed olfactory mechanisms do operate, while the behavioral activation due to maternal and infantile salivas clearly depends on postnatal exposure.

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.

Quantitation of sudomotor innervation in skin biopsies of patients with diabetic neuropathy

Previous assessments of the sudomotor system have depended on functional tests, and only a few studies document the pathologic findings of postganglionic nerve degeneration quantitatively and at the ultrastructural level. We developed a quantitative system of sudomotor innervation in skin biopsies of the distal leg by immunostaining of nerve fibers with anti-protein gene product 9.5 (PGP9.5) and by counterstaining with Congo red. A computerized area-based morphometric analysis was used to quantify the sweat gland innervation index (SGII), defined as the area of nerve fibers normalized to the area of sweat glands. This approach reduced the variations in measurements of sweat gland areas compared to the commonly used method by ∼5.6-fold (2.47% ± 2.54% vs 13.97% ± 14.24%, p < 0.001); hence, variations in SGII were also reduced. We examined 35 Type 2 diabetic patients (24 men and 11 women; mean age, 56.5 ± 12.8 years), with symmetrical length-dependent neuropathy and reduced intraepidermal nerve fiber density (0.76 ± 0.95 fibers/mm). By light and electron microscopy, PGP9.5-positive nerve terminals surrounded Congo red-positive sweat gland secretory coils in controls; these periglandular nerve terminals were either absent or markedly reduced in diabetic patients. Diabetic patients had lower SGII values than age- and sex-matched controls (2.60% ± 1.96% vs 4.84% ± 1.51%, p < 0.0001). The SGII values were lower in patients with anhidrosis of the feet versus those with normal sweating of the feet (0.89% ± 0.71% vs 3.10% ± 1.94%, p < 0.01). Thus, skin biopsy offers combined assessment of sudomotor innervation.

Enhanced water and salt intake in transgenic mice with brain-restricted overexpression of angiotensin (AT1) receptors

To address the relative contribution of central and peripheral angiotensin II (ANG II) type 1A receptors (AT(1A)) to blood pressure and volume homeostasis, we generated a transgenic mouse model [neuron-specific enolase (NSE)-AT(1A)] with brain-restricted overexpression of AT(1A) receptors. These mice are normotensive at baseline but have dramatically enhanced pressor and bradycardic responses to intracerebroventricular ANG II or activation of endogenous ANG II production. Here our goal was to examine the water and sodium intake in this model under basal conditions and in response to increased ANG II levels. Baseline water and NaCl (0.3 M) intakes were significantly elevated in NSE-AT(1A) compared with nontransgenic littermates, and bolus intracerebroventricular injections of ANG II (200 ng in 200 nl) caused further enhanced water intake in NSE-AT(1A). Activation of endogenous ANG II production by sodium depletion (10 days low-sodium diet followed by furosemide, 1 mg sc) enhanced NaCl intake in NSE-AT(1A) mice compared with wild types. Fos immunohistochemistry, used to assess neuronal activation, demonstrated sodium depletion-enhanced activity in the anteroventral third ventricle region of the brain in NSE-AT(1A) mice compared with control animals. The results show that brain-selective overexpression of AT(1A) receptors results in enhanced salt appetite and altered water intake. This model provides a new tool for studying the mechanisms of brain AT(1A)-dependent water and salt consumption.

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.

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

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