Properties of transdermal histamine iontophoresis: differential effects of season, gender, and body region.

Histamine iontophoresis is demonstrated to be a reliable model for the study of inflammatory skin responses. It has the advantage of a non-invasive and uniform mode of application and is free of unwanted side effects. The wheal and flare responses to histamine are linearly related to dose over a wide range of stimulus strengths (r = 0.88). In summer, wheal responses were smaller, probably due to increased thickness of the epidermis. Female subjects generally expressed larger wheal responses than males, presumably due to differences in epidermal thickness and structure. There were significant regional differences in wheal, flare, and laser Doppler recorded flux responses. Ratings of itch sensations also showed clear, but less pronounced, differences of body regions. Significant regional differences of wheal and flare responses existed. Sensory discrimination of different stimulus levels was demonstrated with visual analogue scale ratings.

A novel, nongenomic action of estrogen on the cardiovascular system.

To examine the time course and mechanisms of action of single doses of estrogen on the skin microvasculature, two double-blind placebo-controlled cross-over studies were conducted in healthy young men using the noninvasive technique of laser Doppler velocimetry with iontophoretic application of vasodilator substances. Estradiol (2 mg sublingually) produced a significant increase in the response to the endothelial vasodilator acetylcholine (ACh) after 15 min, but not after 20 or 30 min. The mean plasma estradiol concentration increased from 89.4 +/- 9 pmol/L at baseline to 486.6 +/- 218 pmol/L at 15 min. An i.v. bolus of 25 mg conjugated equine estrogens produced significant increases in the responses to ACh at 15 and 20 min but not at 30 min. There was no change in responses to the nonendothelial vasodilators sodium nitroprusside or nicotine, and administration of placebo produced no change in ACh responses at any time point. These experiments show that, at plasma estradiol concentrations within the physiological range for premenopausal women, estrogens act directly on the cutaneous microvasculature through a rapid onset, rapid offset, nongenomic mechanism that is specific to the endothelium; in addition, it supports the view that estrogens can act on the male cardiovascular system in a manner that is potentially clinically beneficial.

Variations in endothelial function and arterial compliance during the menstrual cycle.

Female sex hormones have been implicated in the cardioprotection of premenopausal women. However, the cardiovascular actions of these hormones and the effects of their natural fluctuations during the menstrual cycle are not fully understood. We studied changes in vascular function during the menstrual cycle in 15 healthy premenopausal women. Four noninvasive procedures were performed during the early follicular (EF), late follicular (LF), early luteal (EL), and late luteal (LL) phases: flow-mediated dilatation (FMD) of the brachial artery during reactive hyperemia, laser Doppler velocimetry (LDV) with direct current iontophoresis of acetylcholine (ACh) and nitroprusside, whole body arterial compliance (WBAC), and pulse wave velocity. Hormone levels were consistent with predicted cycle phase and showed that all subjects ovulated during the cycle studied. FMD, LDV with ACh, and WBAC varied cyclically, with significant increases from the F to LF phase, sharp falls in the EL phase, and significant recoveries in the LL phase. These changes were most marked for FMD [EF, 8.8 +/- 0.6% (mean +/- SEM); LF, 10.0 +/- 0.7; EL, 4.2 +/- 0.6; LL, 8.6 +/- 0.9] and the LDV response to ACh (EF, 2.7 +/- 0.2 V/min; LF, 3.3 +/- 0.4; EL, 1.8 +/- 0.3; LL, 2.7 +/- 0.4). WBAC changed similarly (EF, 0.58 +/- 0.08 arbitrary units; LF, 0.84 +/- 0.06; EL, 0.65 +/- 0.05; LL, 0.68 +/- 0.06). Sodium nitroprusside-induced vasodilatation decreased significantly from EF to EL, with no other significant difference, and pulse wave velocity did not vary significantly over the four time points. Conductance and resistance artery endothelial reactivity and smooth muscle sensitivity to nitric oxide and arterial compliance are modulated significantly in response to the changing hormonal patterns of the menstrual cycle. These findings emphasize the importance of menstrual phase in the interpretation of data on endothelial function and may provide insights into the mechanisms underlying sex differences in cardiovascular risk and other disease processes in premenopausal women.

Chronic nicotine exposure enhances cutaneous axon reflexes in the rat.

The effect of chronic nicotine exposure on the cutaneous neurogenic flare response was investigated non-invasively in rats. Axon reflexes were evoked by transdermal iontophoresis of acetylcholine, and resultant changes in skin microvascular blood flux were measured by laser Doppler flowmetry. Rats given five injections of nicotinesulphate (1 mg kg-1 i.p.) daily for 14 days were compared to saline-injected littermates. Axon reflexes were enhanced by 143% after 7 days exposure to nicotine, and by 336% after 14 days exposure. Controls did not display these increases. Axon reflexes measured 7 days after nicotine cessation were similar to pre-nicotine levels. These results may suggest that nicotinic cholinoceptors on skin nociceptors and primary afferents upregulate in response to chronic nicotine exposure, and return to normal following nicotine cessation.

Maternal nicotine exposure enhances cutaneous axon reflexes in the neonatal rat.

Chronic nicotine exposure enhances axon reflexes in adult rats. Since smoking mothers expose their infants to nicotine, this study investigated whether late gestational and or lactational maternal nicotine exposure affects neonatal axon reflexes. Osmotic pumps, implanted subcutaneously in adult female rats, delivered either nicotine (5 mg kg-1 day-1) or saline. Axon reflex responses of infant progeny, evoked by iontophoresis of 2 mC acetylcholine, were measured by laser Doppler flowmetry. Nicotine-exposed infants showed significantly enhanced axon reflexes during both gestational and lactational nicotine exposure, which recovered after exposure ceased. Controls did not exhibit these changes. Maternal nicotine exposure reversibly sensitized nicotinic cholinoceptors on infant cutaneous sensory nerves, but not muscarinic cholinoceptors on vascular endothelium. This may result from upregulation of cutaneous nicotinic cholinoceptors.

Nicotinic acetylcholine receptors on capsaicin-sensitive nerves.

To study the density of nicotinic acetylcholine receptors on primary afferents and central nociceptive pathways, [3H](-)-nicotine binding was conducted in the cerebral cortex and spinal cord including dorsal roots and ganglia (DRG), of control rats and rats desensitized by neonatal capsaicin treatment. [3H](-)-nicotine binding in capsaicin-treated rats was reduced in cerebral cortex by 35% and spinal cord+DRG by 46% (p < 0.05). Functionally, both iontophoretically applied acetylcholine- and capsaicin-evoked flares (measured by laser Doppler flowmetry) were reduced in capsaicin-treated animals (p < 0.05); similarly, electrical stimulation-evoked flares were significantly lower in the same group, compared with controls (p < 0.05). These data provide direct evidence that many neuronal nicotinic acetylcholine receptors are associated with capsaicin-sensitive peptidergic neurones, including primary afferents, DRG and central nociceptive pathways.

Denervation impairs cutaneous microvascular function and blister healing in the rat hindlimb.

Skin sensory nerve nocifensor functions were investigated non-invasively in rats by measuring neurogenic inflammation and blister healing-rate after unilateral hindlimb denervation. Axon reflexes were evoked by transdermal iontophoresis of acetylcholine (ACh) or noxious electrical stimulation (TNS). Sodium nitroprusside (SNP) evoked direct dilator responses. Resultant changes in skin microvascular blood flux were measured by laser Doppler flowmetry. Compared with their sham-operated control limbs, denervation reduced inflammatory responses (ACh or TNS) by more than 85% and SNP responses by 28% (p < 0.05). Healing of dry-ice blisters raised on the hindpaw 14d post-denervation was significantly slower to complete healing (42d) than controls (26d) and initial inflammation was attenuated, confirming that innervation is important for inflammation and blister-healing.

Rapid actions of insulin on sensory nerve function.

The acute action of insulin on neurogenic flare was investigated using iontophoresis. Twenty-five patients with insulin-dependent diabetes mellitus (IDDM) and 25 age- and gender-matched controls were studied. Axon reflex vasodilatation was evoked by transdermal iontophoresis of acetylcholine (ACh) before and after skin treatment by the iontophoresis of insulin and measured using laser Doppler velocimetry. Axon reflex responses were reduced in IDDM patients compared with controls (p< 0.001) but were restored after the iontophoresis of insulin. Insulin iontophoresis had no effect on the size of the axon reflex response in control subjects (p > 0.05). This study confirms the reduction of the ACh-induced flare in human patients with IDDM and has demonstrated relatively rapid effects of insulin on this cutaneous neurogenic response.

Insulin sensitivity and sensory nerve function in non-diabetic human subjects.

The direct effect of reduced insulin sensitivity (measured by insulin tolerance test and fasting plasma insulin) on sensory nerve function was examined in non-diabetic human subjects. Thermal sensation (measured by warm and cold perception thresholds) deteriorated with fasting hyperinsulinaemia in the presence of normoglycaemia and normal glucose tolerance. The results suggest a possible role for insulin in sensory nerve function, also that deficits in insulin action per se may adversely affect the function of small sensory nerves independent of glycaemic levels, and may thus be implicated in the aetiology of diabetic neuropathy.

Non-invasive tests of neurovascular function: reduced responses in diabetes mellitus.

Painful transcutaneous electrical nerve stimulation (TENS) of the foot dorsum evoked axon reflex vasodilatation, measured by laser Doppler flowmetry. In addition, acetylcholine (ACh) and sodium nitrite (NaNO2) were iontophoresed to cause vasodilatation by endothelium dependent and independent mechanisms, respectively. Compared with healthy volunteers, diabetic patients with clinically diagnosed neuropathy showed reduced electrical axon reflex flare and ACh responses, but not NaNO2 responses. Such reduced cutaneous nocifensor functions may contribute to some symptoms and complications of diabetes mellitus.

Laser Doppler measurements of skin vasodilation elicited by percutaneous electrical stimulation of nociceptors in humans.

This study was designed to assess the quantitative features of the skin protecting mechanism of axon reflexes by monitoring stimulus related changes in skin blood flow using laser Doppler flowmetry. Skin vasodilatation induced by trains of brief transcutaneous electrical pulses (0.5 ms, 150 V) was strictly related in magnitude to the number of pulses (trains of 1-32). This vascular response was reduced by 95% when the skin had been pretreated by painting it for two days with a 1% alcoholic solution of capsaicin. The sensitivity of vascular responses to activation of afferent C-fibers indicates a role of this mechanism in the protection of the skin against noxious events.

Neurogenic vasodilation in the rat hairy skin measured using a laser Doppler flowmeter.

Intradermal stimulation of the saphenous nerve of anesthetized rats at C-fiber strength elicited stimulus-dependent vasodilator responses in saphenous-innervated hairy skin. A laser Doppler flowmeter (Periflux, Pf1d) was used to measure these neurovascular responses non-invasively. Capsaicin pretreatment significantly attenuated the vasodilator response. Furthermore, intraperitoneal administration of atropine or mepyramine significantly reduced the skin vascular responses. The responses of halothane-anesthetized rats were significantly attenuated when compared with rats anesthetized with pentobarbitone. Results of this study suggest the presence of endothelium-dependent vasodilator peptidergic, cholinergic and histaminergic contributions to electrically-evoked axon reflex vasodilation in the rat hairy skin.

Factors associated with impaired vibration perception in Mauritians with normal and abnormal glucose tolerance. Mauritius NCD Study Group.

Vibration perception threshold (VPT) was measured in 1185 Indian, Creole, and Chinese men and women in Mauritius, where the current prevalence of diabetes mellitus in adults aged 25-74 years is estimated to be 13%. Vibration perception threshold was measured using a biothesiometer, at seven sites in the hand, wrist, foot, and ankle, during a population survey in 76% of 574 known diabetic patients (KDM), 79% of 525 newly diagnosed diabetic patients (NDM), 18% of 1121 subjects with impaired glucose tolerance (IGT), and in 127 normal subjects. The association of VPT with glucose tolerance and other risk factors was assessed in order to identify individuals most at risk of foot ulceration and to determine whether risk factors and normal levels for VPT in these ethnic groups were consistent with those reported for Caucasians. After adjusting for age and height, geometric mean VPT at six of seven sites increased significantly with worsening glucose tolerance and increasing duration of diabetes in both men and women, VPT also increased significantly with level of fasting plasma glucose in men, but not women. Smoking and alcohol consumption had no effect on VPT, and body-mass index (BMI) was positively associated only at some sites. Chinese subjects had lower VPTs than Indians or Creoles. In multiple linear regression models, age, male gender, duration of diabetes, ethnic group, and height (lower extremity sites) were significantly associated with VPT among diabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Forehead and forearm skin blood flows in newborn infants measured by laser Doppler flowmetry: short-term variability and relationship to sleep states.

Laser doppler flowmeters were used to measure blood flow in the skin of the forehead and volar surface of the forearm of infants at 2-9 days of age, and at 8-12 weeks of age. At both ages mean skin blood flow was higher during active sleep compared to quiet sleep. In infants up to 9 days of age, mean skin blood flow was higher in forehead skin compared to forearm skin. Skin blood flow was highly variable at both recording sites, and was significantly higher and more variable during active compared to quiet sleep in the forehead, but not in the forearm. The results indicate that recordings of skin blood flow over at least two cycles of active and quiet sleep are needed to describe the normal variation with sleep state. The factors which regulate forehead and forearm skin blood flows may differ in importance between the two sites, perhaps reflecting the different thermoregulatory importance of cutaneous blood flow in the forehead and forearm.

Palmar cold threshold test and median nerve electrophysiology in carpal tunnel compression neuropathy.

The diagnosis of median nerve compression neuropathy at the carpal tunnel is usually confirmed by clinical electrophysiology. The classical findings of a significantly slowed median nerve conduction velocity for both sensory and motor fibres, with a prolonged distal motor latency and a reduced amplitude compared to age-related norms are unambiguous, but these criteria are often present only in part. In such cases another quantitative indicator of compression neuropathy would be extremely helpful. The present study aimed to test whether measurement of warm and cold sensory acuity in cases of putative median nerve carpal tunnel compression would aid diagnostic certainty. Warm sensation is mediated by unmyelinated C-afferents, while cold sensation is conveyed by thinly myelinated A delta afferents. Because compression usually blocks larger diameter fibres first, cold perception on the skin of the palm distal to the compression should be more impaired than is warm perception. Standard electrophysiological measurements (median and ulnar motor and sensory nerve conduction velocities) were made, then perceptual thresholds for both warm and cold stimuli were measured on the skin of the wrist above the carpal tunnel and on the palm of the affected hand in 59 subjects. There was a significantly reduced median motor nerve conduction velocity and prolonged distal motor latency compared to normals. Further, although both thermal thresholds at the wrist were normal, those on the palm were elevated, cold being significantly raised (P less than 0.02) compared both to warm and to age-matched controls. Correlation of the nerve conduction velocity findings and thermal sensory acuity did not yield significant covariance of the positive and negative findings. Overall the results suggest that detection of preferentially elevated cold perceptual threshold (ie reduced cold sensory acuity) on the skin of the palm may aid in the diagnosis of putative carpal tunnel compression in patients with minimal or ambiguous electrophysiological data and provide a functional index of recovery after decompression.

Insulin sensitivity and sensory nerve function.

The central and peripheral nervous systems do not require insulin for glucose uptake. However, insulin receptors have been detected in these regions. The aim of this study was to examine peripheral sensory nerve function and its dependence on insulin using healthy non-diabetic control subjects, obese individuals, and diabetic (insulin dependent and non-insulin dependent diabetes mellitus) subjects. The results revealed that the warm and cold perception thresholds, reflecting the functional states of unmyelinated C-fibres and A-delta fibres respectively, increased with reduced insulin sensitivity and with increased fasting insulin concentrations. From such data in non-diabetic subjects with measured insulin sensitivity, it appeared that sensory nerve function was disturbed in normoglycemic but insulin resistant states, suggesting that insulin has an action on nervous tissue in addition to its effects on glucose metabolism. The mechanisms of this action remain to be elucidated.

Induced changes in the thresholds for voluntary activation of human spindle endings.

1. Recordings were made from forty-two muscle spindle afferents from the pre-tibial muscles of human subjects. For each afferent, the contraction level at which its discharge accelerated (its 'threshold for activation') was defined using isometric voluntary contractions of the receptor-bearing muscle. The effects on these thresholds of various manoeuvres designed to activate descending pathways or segmental sensory inputs were studied to determine whether the balance between the skeletomotor and fusimotor drives to the contracting muscle could be altered. 2. The Jendrassik reinforcement manoeuvre raised the threshold for voluntary activation of one spindle ending slightly but had no significant effect with seven other endings. It is concluded that the Jendrassik manoeuvre does not excite fusimotor neurons selectively or even preferentially. 3. Caloric vestibular stimulation altered the thresholds for voluntary activation of eight of eleven spindle endings, the most common effect being lowering of the threshold during the irrigation and for 1--1 . 5 min after its cessation. 4. Cutaneous stimulation by vibration lowered the thresholds for voluntary activation of some spindle endings when applied to the dorsum of the foot, and raised thresholds when applied to the lateral plantar surface. 5. Passive stretch of the receptor-bearing muscle by plantar flexion of the ankle and passive stretch of synergistic muscles in isolation raised thresholds for spindle activation; passive stretch or vibration of triceps surae lowered thresholds. 6. These studies suggest that the relationship between the skeletomotor and fusimotor drives to a muscle during a voluntary contraction is not rigidly fixed, but can be varied appropriately with the changing motor role demanded of the muscle by supraspinal drives and with the changes in sensory feed-back generated by the movement itself. 7. It is concluded that, provided the skeletomotor effects of a stimulus are known, changes in the threshold for spindle activation in a voluntary contraction can provide a means of determining the effects of that stimulus on fusimotor neurons even when the stimulus alone is not adequate to alter fusimotor drive.

The properties of motor units in a fast and a slow twitch muscle during post-natal development in the kitten.

1. Motor units were functionally isolated from a fast and a slow twitch muscle of kittens: flexor digitorum longus (FDL) and soleus. Both muscles were examined in two groups: one aged about 2 weeks and the other 6 weeks.2. A clear division into alpha and gamma axons could be made. The mean conduction velocity of alpha axons from FDL was higher than that of soleus axons at both ages.3. Tetanic tensions were expressed as a percentage of whole muscle tension. The distributions of motor unit tensions were symmetrical in soleus muscles but were skewed towards large values in FDL. In both types of muscle the scatter of motor unit tensions was greater at 2 weeks than at 6, the mean percentage tension also fell with age.4. The motor unit twitch times to peak were symmetrically distributed in soleus but skewed towards large values in FDL. The variance was less than in adults.5. Motor unit axonal conduction velocity was related to tetanic tension and twitch speed. The relationship between twitch time to peak and the ratio of twitch to tetanic tension varied with age but was not seen so clearly.