Effects of ageing on sensory nerve function in rat skin

Alpha-Lipoic Acid Supplementation Restores Early Age-Related Sensory and Endothelial Dysfunction in the Skin

Many changes characterize skin aging, and the resulting dysfunctions still constitute a real challenge for our society. The aim of this study was to compare the skin aging of two rat strains, Wistar and Brown Norway (BN), considered as "poorly aging" and "healthy aging" models, respectively, and to assess the effect of alpha-lipoic acid (LPA), especially on skin microcirculation. To this purpose, various skin characteristics were studied at 6, 12, and 24 months and compared to the results of LPA treatment performed at 12 or 24 months. Skin aging occurred in both strains, but we showed an early occurrence of different age-related disorders in the Wistar strain compared to BN strain, especially regarding weight gain, glycemia dysregulation, basal skin perfusion, endothelial function, and skin resistance to low pressure. LPA treatment tended to improve skin resistance to low pressure in BN but not in Wistar despite the improvement of basal skin perfusion, endothelial function, and skin sensory sensitivity. Overall, this study confirmed the healthier aging of BN compared to Wistar strain and the positive effect of LPA on both general state and skin microcirculation.

Neuropeptide Substance P Enhances Skin Wound Healing In Vitro and In Vivo under Hypoxia

Pressure ulcers (PUs) or sores are a secondary complication of diabetic neuropathy and traumatic spinal cord injury (SCI). PUs tend to occur in soft tissues located around bony prominences and may heal slowly or not at all. A common mechanism underlying impaired healing of PUs may be dysfunction of the local neurovascular system including deficiency of essential neuropeptides, such as substance P (SP). Previous studies indicate that disturbance in cutaneous sensory innervation leads to a defect in all stages of wound healing, as is the case after SCI. It is hypothesized that nerve fibers enhance wound healing by promoting initial inflammation via the releasing of neuropeptides such as SP. Therefore, we investigated whether exogenous SP improves skin wound healing using in vitro and in vivo models. For in vitro studies, the effects of SP on keratinocyte proliferation and wound closure after a scratch injury were studied under normoxia (pO₂ ~21%) or hypoxia (pO₂ ~1%) and in presence of normal serum (10% v/v) or low serum (1% v/v) concentrations. Hypoxia and low serum both significantly slowed cell proliferation and wound closure. Under combined low serum and hypoxia, used to mimic the nutrient- and oxygen-poor environment of chronic wounds, SP (10⁻⁷ M) significantly enhanced cell proliferation and wound closure rate. For in vivo studies, two full-thickness excisional wounds were created with a 5 mm biopsy punch on the dorsum on either side of the midline of 15-week-old C57BL/6J male and female mice. Immediately, wounds were treated topically with one dose of 0.5 μg SP or PBS vehicle. The data suggest a beneficial role in wound closure and reepithelization, and thus enhanced wound healing, in male and female mice. Taken together, exogenously applied neuropeptide SP enhanced wound healing via cell proliferation and migration in vitro and in vivo. Thus, exogenous SP may be a useful strategy to explore further for treating PUs in SCI and diabetic patients.

Density of nerve fibres and expression of substance P, NR2B-receptors and nerve growth factor in healthy human masseter muscle: An immunohistochemical study

Background

In skeletal muscle, free nerve endings are mostly located within the connective tissue. However, the distribution of sensory afferent fibres in healthy human masseter muscle tissues has not been studied.

Objectives

Primarily to investigate human masseter muscle nerve fibre densities as well as expression of NR2B receptors, substance P (SP) and nerve growth factor (NGF), and secondarily to compare this between a) nerve fibres associated with myocytes and within connective tissue; b) sexes; and c) ages.

Methods

Microbiopsies of the masseter muscle were obtained from 60 sex‐ and age‐matched healthy participants. Biopsy sections were analysed using immunohistochemistry and were visualised with a Leica TCS SPE confocal microscope. The Mann‐Whitney U test was used for statistical analyses.

Results

The density of nerve fibres within connective tissue was significantly greater than in nerve fibres associated with myocytes (P < .001). Nerve fibres within connective tissue expressed SP alone or together with NR2B significantly more often than those associated with myocytes (P < .001). The frequency of nerve fibres, which expressed SP alone or in combination with NR2B or NGF, was significantly greater in women than in men (P < .050). Moreover, the co‐expression of the three markers together was inversely correlated with age in women (P < .002).

Conclusions

There is a higher density and greater expression of sensory nerve fibres within the connective tissue than associated with myocytes in healthy human masseter muscle. This suggests that nerve fibres within connective tissue are more involved in nociception than nerve fibres associated with myocytes.

Nonlinear Inverted-U Shaped Relationship Between Aging and Epidermal Innervation in the Rat Plantar Hind Paw: A Laser Scanning Confocal Microscopy Study

The under-reporting of pain and atypical manifestations of painful syndromes within the elderly population have been well documented, however, the specific relationship between pain and aging remains ambiguous. Previous studies have reported degenerative changes in primary afferents with aging. In this study, we questioned whether there is any change in the density of primary afferent endings within the epidermis of aged animals. Rats were categorically assessed in 4 age groups, each representing a key developmental stage across their life span: juvenile (2 months), adult (7 months); aged (18 months), and senescent (24-26 months). The plantar hind paw skin was removed, post-fixed, cut, and immunostained for protein gene product 9.5 and type IV collagen. Rats in the adult aged groups had significantly increased epidermal nerve densities and total lengths of immunoreactive nerve fibers, compared with juvenile as well as senescent rats. However, the paw withdrawal thresholds to punctate mechanical stimulation progressively increased with age, and did not exhibit a clear relationship with epidermal innervation. We conclude a nonlinear, inverted-U shaped relationship between rat plantar epidermal nerve density with aging, which does not correlate with mechanically-induced paw withdrawal behaviors.

PERSPECTIVE

This article presents age-related decreased epidermal innervation in rat hind paw skin, which partly explains mechanisms underlying decreased pain sensitivity in aged subjects. The report may help clinicians to understand that any compromise of pain-sensing pathway can lead to under-reporting of pain, inadequate analgesia, and slower recovery from a painful condition.

Pain, Genes, and Function in the Post-Hip Fracture Period

Post-hip fracture generalized pain can lead to a progressive decline in function and greater disability. The purpose of this study was to explore the factors that influence pain among older adults post-hip fracture, including genetic variability, and evaluate whether pain directly or indirectly influenced upper and lower extremity function. This was a secondary data analysis using data from the first 200 participants in a Baltimore Hip Study (BHS), BHS-7. Assessments were done at 2 months post-hip fracture and included age, sex, marital status, education, cognitive status, comorbidities, body mass index (BMI), upper and lower extremity function, single nucleotide polymorphisms (SNPs) from 10 candidate genes, and total areas of pain and pain intensity. Model testing was done using the AMOS statistical program. The full sample included 172 participants with an average age of 81. Fifty percent were female and the majority was Caucasian (93%). Model testing was done on 144 individuals who completed 2 month surveys. Across all models, age, cognition, and BMI were significantly associated with total areas of pain. Thirty SNPs from five genes (BDNF, FKBP5, NTRK2, NTRK3, and OXTR) were associated with areas of pain and/or pain intensity. Together, age, cognition, BMI, and the SNP from one of the five genes explained 25% of total areas of pain and 15% of pain intensity. Only age and cognition were significantly associated with lower extremity function, and only cognition was significantly associated with upper extremity function. The full model was partially supported in this study. Our genetic findings related to pain expand prior reports related to BDNF and NTRK2.

Effect of ageing on tactile transduction processes

With advancing age, a decline in the main sensory modalities including touch sensation and perception is well reported to occur. This review mainly outlines the peripheral components of touch perception highlighting ageing influences on morphological and functional features of cutaneous mechanical transducers and mechanosensitive ion channels, sensory innervation, neurotransmitters and even vascular system required to ensure efferent function of the afferent nerve fibres in the skin. This, in conjunction with effect of ageing on the skin per se and central nervous system, could explain the tactile deficit seen among the ageing population. We also discuss appropriate tools and experimental models available to study the age-related tactile decline.

The effect of sensory nerve stimulation on sensory nerve function in people with peripheral neuropathy associated with diabetes

OBJECTIVE

To assess the effect of sensory nerve stimulation in older people with peripheral neuropathy associated with diabetes (DPN).

MATERIALS AND METHODS

A randomized, placebo controlled, double blind trial was used to assess the effect of 12 weeks of low frequency sensory nerve stimulation (LF-SNS) in the lower limb [International Patent Application No. PCT/AU2004/001079: 'nerve function and tissue healing' (Z. Khalil)]. Response to capsaicin, basal microvascular blood flow, electric cutaneous threshold and oxygen tension were assessed pre- and post-treatment and between limbs.

PARTICIPANTS

People 55 years of age or older diagnosed with DPN: 35 active and 31 placebo participants.

RESULTS

Between groups comparisons: no significant differences occurred between stimulation groups. Within subject comparisons: in the active LF-SNS group, comparing stimulated to contralateral legs, there were significant increases in size of capsaicin flare [t(1,33)=3.65, p<0.05] and capillary blood flow [t(1,34)=-0.33, p<0.05]. There was a trend to improvement in time to initial flare response [t(1,34)=-1.86, p=0.07]. No changes were evident in the placebo group. RESPONDER ANALYSES: In a group of 'responders', the time to initial flare response (p<0.05, r=0.64), size of capsaicin flare (p<0.05 r=1.0) and microvascular blood flow (p<0.05, r=0.60) improved significantly after LF-SNS.

CONCLUSIONS

The observed data suggest that LF-SNS improves nerve function in a subset of people with DPN. Targeting toward probably 'responders' may deliver the greatest benefit from short-term therapy. Testing optimal application in others seems warranted.

Novel models for bacterial colonization and infection of full-thickness wounds in rats

An animal model is needed to study the pathophysiology of wound infections; however, an animal model that is reproducible and clinically relevant has not previously been available. In addition, an animal model of wound colonization generated in a manner similar to the wound infection model would be useful. Here, we describe new animal models of the wound infection continuum for the characterization of essential host-pathogen relationships. We determined the conditions needed to establish rat models of stable wound colonization and infection, without the use of disturbing factors (e.g., foreign bodies or induction of diabetes mellitus). We found that the age of the rats, bacterial inoculum size, and wound location were important elements in generating reproducible, obvious, spreading wound infections. We inoculated approximately 6-month-old rats with 2.06 × 10(9) or 4.12 × 10(9) colony-forming units of Pseudomonas aeruginosa to generate the wound colonization and wound infection models, respectively. Wounds were made 2 cm cranial to the greater trochanter. These clinically relevant and highly reproducible animal models can be used to investigate the mechanisms of wound infection and monitor the effect of therapeutic agents in vivo.

Pharmacological pain management in the elderly patient

With the increasing number of elderly patients the issue of pain management for older people is of increasing relevance. The alterations with aging of the neurobiology of pain have impacts of pain threshold, tolerance and treatment. In this review the available evidence from animal and human experimentation is discussed to highlight the differences between young and older subjects along with consideration of how these changes have practical effect on drug treatment of pain. Cognitive impairment, physical disability and social isolation can also impact on the accessibility of treatment and have to be considered along with the biological changes with ageing. Conventional pain therapies, while verified in younger adults cannot be automatically applied to the elderly without consideration of all these factors and in no other group of patients is a holistic approach to treatment more important.

Use of the sensory nerve stimulator to accelerate healing of a venous leg ulcer with sensory nerve dysfunction: a case study

A new therapy using sensory nerve stimulation [International Patent Application Number PCT/AU2004/001079: "nerve function and tissue healing" (Khalil, Z)] has been developed in our vascular physiology laboratory. This treatment has been found to improve the deficient sensory nerve function and associated deficient wound healing of older persons to levels seen in young people. An 82-year-old man with a small but persistent venous leg ulcer for 18 months, despite apparently appropriate wound dressings and compression therapy, was seen in a specialist wound management service. The patient's sensory and microvascular function was assessed in great detail using the vascular physiology laboratory techniques, and he was provided the sensory nerve stimulation therapy in addition to conventional therapy. His wound healed after 4 weeks. We report the case here. Prior to nerve stimulation therapy, cutaneous sensation, microvascular blood flow and oxygen tension were found to be reduced near the ulcer when compared with the opposite, non ulcerated leg. After therapy, oxygen tension and microvascular blood flow had improved. This case provides further evidence that sensory nerve stimulation therapy at the stipulated parameters improves wound healing. The observation that sensory nerve function improved provides support for the notion that improvement in healing is mediated by improved nerve function.

Age-related changes in microvascular blood flow and transcutaneous oxygen tension under Basal and stimulated conditions

BACKGROUND

Adequate cutaneous microvascular blood flow and tissue oxygen tension are important prerequisites for successful tissue repair. The efficacy of tissue repair decreases with age and is linked to the age-related functional decline of unmyelinated sensory neurons that are important for inflammation and tissue repair. However, available information on the effect of these neuronal changes on microvascular blood flow and tissue oxygen tension is limited, particularly under control and injury conditions. The authors had two aims in this study: (a) to assess age-related changes in the relationship between microvascular blood flow and tissue oxygen perfusion under basal and two different stimulated conditions (sensory dependent and sensory independent), and (b) to clarify the biological meaning of transcutaneous partial pressure of oxygen (tcPO2) measurements.

METHODS

The effects of a sensory-independent vasodilator (acetylcholine) and a sensory-dependent vasodilator (capsaicin) on microvascular blood flow and oxygen perfusion in persons of different ages were measured. Laser Doppler flowmetry and a commercially available transcutaneous oxygen monitor (with sensors set at 39 degrees C and 44 degrees C) were used. Healthy volunteers were recruited: 11 young, 14 middle aged, and 19 older.

RESULTS

Under basal conditions (skin temperature, 37 degrees C to 39 degrees C), both basal blood flow and tcPO2 increased with increasing age. However, with the sensor set at 44 degrees C, tcPO2 showed a significant decrease with age. Acetylcholine increased blood flow approximately equally in the three age groups. Capsaicin increased blood flow and tcPO2 in all age groups, with the young showing a greater increase compared with the older participants.

CONCLUSIONS

The age-associated changes in basal and stimulated microvascular blood flow and tcPO2 could be attributed in part to altered neuronal function. Measuring tcPO2 at 39 degrees C showed a trend toward an increase with age. In contrast, a decrease with age was observed when tcPO2 was measured at 44 degrees C, a temperature sufficient to activate sensory nerve endings. The results may reflect a decline in sensory nerve function with age rather than a decrease in oxygen delivery for vascular reasons. This is supported by the complementary data showing a significant age-related decrease in stimulated blood flow in response to capsaicin, with no change in the response to the sensory-independent vasodilator acetylcholine. Thus, for clinical purposes, data obtained using the tcPO2 monitor should be interpreted with full knowledge of the conditions under which the measurements were made. Furthermore, for scientific purposes, the tcPO2 monitor could be used to assess sensory nerve function when sensors are heated to 44 degrees C.

Regulation of wheal and flare by tea tree oil: complementary human and rodent studies

When applied 20 min after injection of histamine into human forearm skin, tea tree oil (TTO) reduces the developing cutaneous vascular response. In this study, the effect of TTO on inflammatory microvascular changes was dissected at the base of an experimental blister on rat skin. 1,8-Cineole, representing 2% of TTO, reduced vascular changes induced by sensory neuropeptides released when the distal portion of a cut sciatic nerve was electrically stimulated. The pre-terminal modulatory effect of 1,8-Cineole was confirmed in tests in sensory-denervated rats. Terpinen-4-ol (approximately 40% TTO) reduced substance P-induced microvascular changes and protein extravasation by a direct nitric oxide-mediated effect on the microvasculature, without sensory nerve involvement. alpha-Terpineol (3% of TTO) regulated both pre- and post-sensory nerve terminals. In human skin, terpinen-4-ol applied 10 min after histamine injection, but not alpha-terpineol or 1,8-cineole, regulated the developing wheal and flare suggesting that the histamine-induced responses in humans (at the dose used in this study, 50 microL of 330 microM histamine) are in large part determined by histamine directly affecting the vasculature via post-terminal-mediated events. The underlying strength of these studies is the use of a well-established rat physiologic model to differentiate the mechanism of regulation of microvascular changes by modulatory agents.

Growth factors and chronic wound healing: past, present, and future

Growth substances (cytokines and growth factors) are soluble signaling proteins affecting the process of normal wound healing. Cytokines govern the inflammatory phase that clears cellular and extracellular matrix debris. Wound repair is controlled by growth factors (platelet-derived growth factor [PDGF], keratinocyte growth factor, and transforming growth factor beta). Endogenous growth factors communicate across the dermal-epidermal interface. PDGF is important for most phases of wound healing. Becaplermin (PDGF-BB), the only growth factor approved by the Food and Drug Administration, requires daily application for neuropathic wound healing. Gene therapy is under development for more efficient growth factor delivery; a single application will induce constitutive growth factor expression for weeks. Based on dramatic preclinical animal studies, a phase 1 clinical trial planned on a PDGF genetic construct appears promising.

A Review of Age Differences in the Neurophysiology of Nociception and the Perceptual Experience of Pain

OBJECTIVE

To better understand the nature of age differences in pain and nociception with the aging of the worlds' population.

METHODS

The evidence from numerous neurophysiologic and psychological studies suggest a small, but demonstrable age-related impairment in the early warning functions of pain. The increase in pain perception threshold and the widespread change in the structure and function of peripheral and CNS nociceptive pathways may place the older person at greater risk of injury. Moreover, the reduced efficacy of endogenous analgesic systems, a decreased tolerance of pain and the slower resolution of postinjury hyperalgesia may make it more difficult for the older adult to cope, once injury has occurred.

RESULTS

These age-related changes may be best conceptualized as a reduced capacity in the functional reserve of the pain system, at both ends of the intensity spectrum.

DISCUSSION

The clinical implications are obvious; older persons are likely to be especially vulnerable to the negative impacts of pain and pain associated events.

Electrotherapy Promotes Healing and Microcirculation of Infrapopliteal Ischemic Wounds: A Prospective Pilot Study

OBJECTIVE

To determine if high-voltage pulsed current (HVPC) electrotherapy augments ischemic wound healing and increases periwound microcirculation.

DESIGN

A prospective, randomized, single-blinded, sham-controlled clinical trial was conducted on a homogenous subset of quasi-stable ischemic wounds.

INTERVENTION

Active HVPC or sham HVPC was applied to wounds for a 14-week period.

MAIN OUTCOME MEASURE

Wounds were monitored every 4 weeks, except 2 weeks between weeks 12 and 14, for wound area, wound appearance, and microcirculation, which was measured by transcutaneous oxygen (TcPO2) levels and laser Doppler flow.

RESULTS

Ischemic wounds treated with active HVPC decreased in size, contrary to the expected increase in ischemic wound size that was observed in wounds in the control group (P <.05, Student t test; week 4). A trend toward smaller wound area occurred in wounds in the HVPC group compared with wounds in the control group (week 14). Among the HVPC group, an improvement in periwound microcirculation occurred at weeks 8 (P <.05, TcPO2; P <.01, laser Doppler) and 12 (P <.05, laser Doppler). These increases suggest that HVPC promotes arteriolar vasodilation and dermal capillary formation. HVPC was well tolerated.

CONCLUSION

The results of this study demonstrate that HVPC decreased the area of ischemic wounds, reversing the expected increase in wound size, and improved microcirculation. The promising results of this pilot study require a larger Phase II study to confirm and generalize these findings.

CLINICAL RELEVANCE

Electrotherapy may prove to be a relatively safe and effective complement to surgical revascularization to improve the odds of healing ischemic wounds and promoting limb salvage.

17Beta-estradiol enhances the production of nerve growth factor in THP-1-derived macrophages or peripheral blood monocyte-derived macrophages

We examined in vitro effects of 17beta-estradiol (E2) on nerve growth factor production by macrophages derived from monocytic cell line THP-1-or periphereal blood monocytes. E2 and membrane-impermeable bovine serum albumin-conjugated E2 (E2-BSA) enhanced nerve growth factor secretion and mRNA expression in both types of macrophages E2 enhanced nerve growth factor promotor activity in THP-1-derived macrophages and two activator protein-1 binding sites on the promoter were responsible for the enhancement. E2 and E2-BSA enhanced transcriptional activity and DNA binding of activator protein-1. E2 and E2-BSA shifted the activator protein-1 composition from c-Jun homodimers to c-Fos/c-Jun heterodimers. E2 and E2-BSA transiently induced c-Fos mRNA, which was constitutively undetectable in both types of macrophages. Adenylate cyclase inhibitor SQ22536 suppressed E2-induced nerve growth factor production and c-Fos expression. E2 and E2-BSA increased intracellular cyclic adenosine monophosphate level in both types of macrophages. Antisense oligonucleotide against guanine nucleotide-binding protein-coupled receptor, GPR30 suppressed the E2-induced cyclic adenosine monophosphate signal, c-Fos expression, and nerve growth factor secretion in both types of macrophages. These results suggest that E2 may enhance nerve growth factor production by inducing c-Fos expression via cyclic adenosine monophosphate signal in macrophages. These effects may be mediated via GPR30.

Age-specific modification of local cutaneous vasodilation by capsaicin-sensitive primary afferents

Age-related changes in neurogenic vasodilation mediated by sensory nerves may alter local skin blood flow (SkBF) responses in older individuals. The purpose of this study was to determine the age-specific modification of cutaneous vasodilation by capsaicin-sensitive primary afferent (CSPA) nerves during local heating. Nine young (18-30 yr), eight middle-aged (40-55 yr), and eight older (65-80 yr) healthy men participated in the experiments. Two local-heating protocols (rapid and slow) were performed before and after 1 wk of capsaicin pretreatment (CP), used to desensitize CSPAs. All temperatures were below those that elicit pain. SkBF was measured with a laser-Doppler imager and indexed to percentage of maximal cutaneous vascular conductance (%CVCmax). CP caused a significant reduction in %CVCmax in the middle-aged and older groups during slow heating (P < 0.05), without affecting %CVCmax in the young group. During rapid heating, CP significantly reduced (53.9 +/- 4.4 vs. 74.4 +/- 7.4% CVCmax, P < 0.05), but did not abolish, the initial sensory nerve-mediated rise in SkBF in the young group. No significant effects of CP on SkBF were observed during rapid heating in the middle-aged or older groups. These results indicate that, with advanced age, CSPA activity is more important to the maximal SkBF response during prolonged local heating, whereas it has a reduced role in the initial SkBF peak elicited by rapid local heating. In summary, CSPA activity contributes modestly to the overall SkBF response to local heating in an age-specific manner.

Effect of short-term and long-term antioxidant therapy on primary and secondary ageing neurovascular processes

Previous studies from our laboratory demonstrated an age-related functional decline in sensory neurones and their modulation of microvascular blood flow (primary ageing processes) that correlated with a deficiency in tissue repair (a secondary ageing process). We also raised the notion of a possible role for free radicals in these age-related changes. The aim of this study was to investigate the impact of antioxidant therapy on modulating sensory neurovascular function and tissue repair with age. Twenty-four-month-old Sprague-Dawley rats were treated with vitamin E for short-term (40 mg/kg, i.p., every other day for 2 weeks) or long-term (for 12 months in advance, 10 g/kg, incorporated in food). These treated rats were assessed for the effectiveness of treatment and tested for their sensory neurovascular function, repair of full-thickness burn, and recovery from hyperalgesia following nerve injury. The results indicate that both short- and long-term vitamin E treatments are effective in improving sensory neurovascular function and in reducing the time required for complete wound closure of full-thickness burn injury. Short-term vitamin E treatment was more effective in protecting against the development of hyperalgesia following nerve injury. An initial increase in wound size and in hyperalgesia was observed in the treated animals, and could reflect possible side effects of the antioxidant therapy and support the importance of free radicals in early stages of the repair process. The data, overall, support the notion that oxidative damage contributes to both primary and secondary ageing processes.

Age-specific skin blood flow responses to acute capsaicin

Local skin blood flow (SkBF) responses can be modified by vasoactive neurotransmitters released from sensory nerves, notably, capsaicin-sensitive primary afferents (CSPAs). Age-specific CSPA function was examined in this study by assessing the SkBF response to acute capsaicin (CPZ). Eight young (18-30 years), 8 middle-aged (40-55 years), and 9 older (65-80 years) healthy men participated in the study. Treatment patches of varying CPZ concentration (ethanol and 0.001%-10.0% CPZ) were applied to sites on the ventral forearm. SkBF was measured with a laser Doppler imager. There were significant (p <.001) age-specific differences in the SkBF response to CPZ. In the older group, SkBF was reduced at least 2-fold at all concentrations of CPZ compared with the younger group. The middle-aged group showed an intermediate response. SkBF was significantly elevated above that obtained with a vehicle solution when sites were treated with CPZ concentrations > or = 0.1% in middle-aged and younger skin, whereas a significant elevation in SkBF was only achieved with 10% CPZ in older skin. The elevated SkBF in the young and middle-aged groups at higher concentrations of CPZ was the result of both an increased area of vasodilation and an increased magnitude of vasodilation within the vasodilated areas. In the older group, the increase in cutaneous vascular conductance at the highest concentration of CPZ was entirely the result of an increased area of vasodilation. These results suggest impaired CSPA function in aged skin and age-specific differences in the ability of sensory nerves to modify local inflammatory SkBF responses.

Electrotherapy reverses inframalleolar ischemia: a retrospective, observational study

OBJECTIVE

To determine if high-voltage pulsed current (HVPC) augments ischemic wound healing and increases periwound perfusion.

DESIGN

A 5-year, retrospective, observational study was conducted on successive patients with ischemic wounds who were poor candidates for revascularization.

INTERVENTION

HVPC was applied directly to wounds at greater than 100 volts, 100 pulses per second, 1 hour per day. In addition to HVPC, patients received standard care for ischemic wounds at the study facility. Ischemic wounds for which HVPC was not clinically indicated or not available received standard care alone.

MAIN OUTCOME MEASURES

Wound area measured by planimetry, wound appearance observed by digital imaging techniques, and microcirculation monitored by transcutaneous oxygen (TcPo(2)) levels.

RESULTS

The group that received HVPC plus standard care showed smaller wound areas from weeks 20 though 52 after the start of treatment compared with the group that received standard care alone (P <.05; Mann-Whitney test). One year after the start of treatment, 90% of HVPC-treated wounds were healed, compared with 29% of the wounds that received only standard care (P <.05; Fisher exact test). For the HVPC group, maximum periwound TcPo(2) improved during electrotherapy (6 +/- 8 mm Hg [standard deviation; SD] at baseline improved to 26 +/- 20 SD, during HVPC, P <.05; Wilcoxon signed rank test).

CONCLUSION

The results of this retrospective trial demonstrate that HVPC plus standard care improved the healing rate of high-risk ischemic wounds. A direct relationship was shown between improved healing rates and increased periwound perfusion. A prospective randomized controlled trial is needed to further support these observational, preliminary findings.

Mast cells, neuropeptides, histamine, and prostaglandins in UV-induced systemic immunosuppression

There is a direct correlation between dermal mast cell prevalence in dorsal skin of different mouse strains and susceptibility to UVB-induced systemic immunosuppression; highly UV-susceptible C57BL/6 mice have a high dermal mast cell prevalence while BALB/c mice, which require considerable UV radiation for 50% immunosuppression, have a low mast cell prevalence. There is also a functional link between the prevalence of dermal mast cells and susceptibility to UVB- and cis-urocanic acid (UCA)-induced systemic immunosuppression. Mast cell-depleted mice are unresponsive to UVB or cis-UCA for systemic immunosuppression unless they are previously reconstituted at the irradiated or cis-UCA-administered site with bone marrow-derived mast cell precursors. cis-UCA does not stimulate mast cell degranulation directly. Instead, in support of studies showing that neither UVB nor cis-UCA was immunosuppressive in capsaicin-treated, neuropeptide-depleted mice, cis-UCA-stimulated neuropeptide release from sensory c-fibers which, in turn, could efficiently degranulate mast cells. Studies in mice suggested that histamine, and not tumor necrosis factor alpha (TNF-alpha), was the product from mast cells that stimulated downstream immunosuppression. Histamine receptor antagonists reduced by approximately 60% UVB and cis-UCA-induced systemic immunosuppression. Indomethacin administration to mice had a similar effect which was not cumulative with the histamine receptor antagonists. Histamine can stimulate keratinocyte prostanoid production. We propose that both histamine and prostaglandin E(2) are important in downstream immunosuppression; both are regulatory molecules supporting the development of T helper 2 cells and reduced expression of type 1 immune responses such as a contact hypersensitivity reaction.

Electrotherapy reoxygenates inframalleolar ischemic wounds on diabetic patients: a case series

OBJECTIVE

To retrospectively evaluate the ability of high voltage pulsed current (HVPC) to increase microcirculation in critically ischemic wounds (transcutaneous oxygen [TcPO(2)] less than 10 mm Hg) and, as a result, to improve wound healing.

DESIGN AND METHODS

Clinical case series with successive adult diabetic subjects (3 men and 3 women) with nonsurgical ischemic malleolar or inframalleolar skin lesions, each subject serving as his or her own control. Wound area and TcPO(2) were measured periodically. Presence of distal arteriosclerosis was assessed on 5 patients by 2-dimensional, time-of-flight magnetic resonance angiography. End point was either complete wound closure or leg amputation.

RESULTS

Maximum mean TcPO(2) was 2 +/- 2 mm Hg at the wound edge before the start of electrotherapy. After electrotherapy began, maximum TcPO(2) was 33 +/- 18 mm Hg (N=6; P<.05, Wilcoxon signed rank test). After treatment with HVPC, 4 patients' wounds healed and 2 patients underwent amputation. As expected, healed patients initially deteriorated after the start of treatment, but their wounds began healing when the perilesion TcPO(2) measurement exceeded 20 mm Hg. Thereafter, the wounds closed at a predictable rate. Complete closure occurred for patients who had a relatively low atherosclerotic burden.

CONCLUSION

The results of this clinical case series suggest that electrotherapy can improve periwound microcirculation of ischemic inframalleolar skin lesions.

cis-Urocanic acid stimulates neuropeptide release from peripheral sensory nerves

Previous studies using an antibody to cis-urocanic acid and mast-cell-depleted mice implicated both cis-urocanic acid and mast cells in the mechanisms by which ultraviolet B light suppresses systemic contact hypersensitivity responses in mice. In the absence of a direct stimulatory effect of cis-urocanic acid on connective tissue mast cells, an indirect association was investigated. A blister induced in the rat hind footpad was used to examine the effects of slowly perfused cis-urocanic acid on cutaneous blood flow. cis-Urocanic acid but not trans-urocanic acid increased microvascular flow by a mechanism largely dependent on the combined activity of the neuropeptides, substance P and calcitonin gene-related peptide. Perfusion of cis-urocanic acid over the base of blisters induced in sensory-neuropeptide-depleted rats did not have any stimulatory effect above that seen with perfusion of cis-urocanic acid together with neuropeptide receptor antagonists in control rats. There was a small direct effect of cis-urocanic acid on microvascular blood flow. As both substance P and calcitonin gene-related peptide could directly degranulate connective tissue mast cells, this study suggests that cis-urocanic acid indirectly activates mast cells via its effects on peripheral terminals of unmyelinated primary afferent sensory nerves. cis-Urocanic-acid-induced neuropeptides may also contribute to ultraviolet-B-induced cutaneous inflammation and alterations to Langerhans cell activity.

Differential involvement of conotoxin-sensitive mechanisms in neurogenic vasodilatation responses: effects of age

During aging there is a decline in sensory nerve function that is associated with reduced neurogenic inflammation and poor wound repair. The cellular mechanism(s) responsible for this decline in function with age is not well understood. We previously reported that sensory nerves in aged rats release sensory neuropeptides preferentially in response to low-frequency (5 Hz) as compared with higher-frequency (15 Hz) antidromic electrical stimulation, and that low-frequency transcutaneous electrical nerve stimulation accelerates wound healing. The present study investigates possible mechanisms for this preferential response. Using laser Doppler techniques, we have measured changes in blood flow in the base of vacuum-induced blisters induced in the rat hind footpad of young and old animals in response to low-frequency (5 Hz) or high-frequency (15 Hz) electrical stimulation (20 V, 2 ms for 1 minute) of the sciatic nerve. The relative contributions of the sensory neuropeptides, substance P and calcitonin gene-related peptide (CGRP), and of N-type voltage-gated calcium channels to the vascular responses were assessed by using the specific receptor antagonists RP67580, which is 2-(1-imino-2-(2 methoxy phyenyl) ethyl)-7,7 diphenyl-4 perhydroisoindolone-(3aR, 7aR); CGRP(8-37); and omega-conotoxin GVIA (Conus geographus), respectively. The results showed a greater involvement of substance P at high-frequency electrical stimulation and of CGRP at low-frequency stimulation. Our finding that omega-conotoxin-sensitive N-type calcium channel function was preserved with age and was only involved in the vascular response to low-frequency electrical stimulation could explain our previous report demonstrating beneficial effects of low-frequency transcutaneous electrical nerve stimulation to wound repair in aged animals. The current results have important practical implications for improving tissue repair in the aged.

Mitochondrial DNA deletions parallel age-linked decline in rat sensory nerve function

In rats, the function of sensory nerves in the hind limb declines significantly with age. Normally aging rats and rats treated neonatally with capsaicin were studied here. Quantification of vascular response and substance P in young (3 months) and old (24 months) rats showed additive effects of age and capsaicin treatment. The levels in dorsal root ganglion of a particular deletion in mitochondrial DNA (mtDNA(4834)) were about 300-fold higher in old compared to young rats. Capsaicin treatment had no significant effect on mtDNA(4834) abundance. Dorsal root ganglia of old (but not young) rats were found to contain a spectrum of multiple deletions. The abundance of mtDNA(4834) in dorsal root ganglia from individual rats correlated strongly with their decline in vascular function, even where vascular responses were systematically depressed due to prior capsaicin treatment. One possibility is that mitochondrial DNA mutations directly lead to functional decline at mitochondrial and tissue levels. Alternatively, loss of mitochondrial DNA integrity and physiological decline may be consequences of the same factor, such as oxidative stress.

Immunological and in-vivo neurological studies on a benzoic acid-specific T cell-derived antigen-binding molecule from the serum of a toluene-sensitive patient

T-cell-derived antigen-binding molecules (TABMs) specific for benzoic acid were isolated from the serum of a toluene-sensitive patient. The resulting purified TABMs (BA-TABMs) did not contain immunoglobulin G and were associated with the cytokine transforming growth factor-beta (TGF-beta). BA-TABMs bound to benzoic acid conjugated to human serum albumin (BA-HSA), as well as to other chemicals conjugated to human serum albumin-including dinitrophenol and oxazolone. The binding of BA-TABMs to the conjugated chemicals increased the level of detectable TGF-beta, and a similar effect was observed with the unconjugated chemicals, benzoic acid and 2,4-dinitrophenol glycine. The increase in TGF-beta was critically dependent on the ratio between BA-TABMs and the conjugated or unconjugated chemicals; the increase was optimum at intermediate concentrations and absent at low and high concentrations. The authors used an established animal model in vivo and demonstrated that TGF-beta enhanced the inflammatory response induced by the release of neuropeptides from sensory nerves; this enhancement occurred in a dose-dependent manner. The BA-TABMs also enhanced this neurogenic inflammatory response in a dose-dependent manner, and this effect was blocked by anti-TGF-beta antibody. When the authors added either BA-HSA or benzoic acid, the effect of BA-TABMs on neurogenic inflammation was further enhanced at intermediate concentrations of antigen and was unaltered or reduced at higher concentrations. TABMs specific to particular chemicals, as a result of their association with cytokines (e.g., TGF-beta), may be implicated in symptom production in chemically sensitive patients.

Effects of aging on neurogenic vasodilator responses evoked by transcutaneous electrical nerve stimulation: relevance to wound healing

We have previously shown an age-related decline in the modulation of skin vascular reactivity by sensory nerves that correlates with a decline in wound repair efficacy. This study was designed to examine the possibility that improving the functional ability of aged sensory nerves using noninvasive transcutaneous electrical nerve stimulation (TENS) could also accelerate tissue repair. TENS of the sciatic nerve, combined with measuring blood flow responses in the rat hind-footpad using laser Doppler flowmetry, was used to establish the vascular effects. Following TENS (using parameters 20V, 5 Hz for 1 min), similar increases in vascular responses were obtained in both young (13.2+/-0.9 cm2) and old rats (11.6+/-2.3 cm2). In contrast, capsaicin-pretreated rats showed markedly diminished responses. Sympathetic fibers did not appear to modulate these sensory nerve responses. In the second part, a thermal wound was induced (using a CO2 laser) in the interscapular region of old rats (under anesthesia). In the active treatment group, TENS was applied twice daily for the initial 5 days, and the sham group received inactive TENS. Using the healing endpoint as the time when full wound contraction occurred, the active group required 14.7+/-0.2 days for complete healing, a significant improvement over the sham group (21.8+/-0.3 days). We contend that low-frequency TENS can improve the vascular response of old rats. In addition, wound healing in aged rats can be accelerated by peripheral activation of sensory nerves at low-frequency electrical stimulation parameters.

Regulation of neurotrophin signaling in aging sensory and motoneurons: dissipation of target support?

A hallmark of senescence is sensorimotor impairment, involving locomotion and postural control as well as fine-tuned movements. Sensory and motoneurons are not lost to any significant degree with advancing age, but do show characteristic changes in gene-expression pattern, morphology, and connectivity. This review covers recent experimental findings corroborating that alterations in trophic signaling may induce several of the phenotypic changes seen in primary sensory and motoneurons during aging. Furthermore, the data suggests that target failure, and/or breakdown of neuron-target interaction, is a critical event in the aging process of sensory and motoneurons.

Comparison of [125I]-bolton-hunter substance P binding in young and aged rat spinal cord

Binding of [125I]-labeled Bolton-Hunter substance P ([125I]-BHSP) to NK1 receptors was investigated in the spinal cord of young (3-4 month) and aged (14-16 month) rats. In homogenates of whole spinal cord, the affinity (equilibrium dissociation constant, approximately 210 pM) and maximum density of [125I]-BHSP binding sites ( approximately 0.25 fmol/mg wet weight) were similar for young and aged rats. Autoradiographic studies revealed a similar distribution of [125I]-BHSP sites in both young and old rats at all spinal levels. Intense binding was observed in the superficial dorsal horn (laminae I-III), grey commissure (lamina X) and thoracic intermediolateral cell column (IML) with lower levels of binding in the deeper dorsal horn (laminae IV-VI) and ventral horn (laminae VII-IX). However, the density of [125I]-BHSP sites was significantly (P<0.05) lower in lamina X of lumbar sections of aged rats compared with young controls. These studies suggest that ageing is associated with a selective loss of NK1 receptors in lamina X of the lumbar spinal cord, although the affinity of NK1 receptors in aged rats is unchanged.

CGRP and nitric oxide of neuronal origin and their involvement in neurogenic vasodilatation in rat skin microvasculature

1. Sensory nerves are important for the initiation of neurogenic inflammation and tissue repair. Both calcitonin gene-related peptide (CGRP) and nitric oxide (NO) have been implicated in neurogenic vasodilatation and inflammatory responses. 2. A blister model in the rat hind footpad was used as a site to induce neurogenic vasodilatation in response to antidromic electrical stimulation of the sciatic nerve. Blood flux was monitored with a laser Doppler flow monitor. 3. The quantitative contributions of CGRP and NO to vasodilatation were examined by use of the CGRP receptor antagonist CGRP8-37 and NO synthase inhibitors 7-nitroindazole (7-NI), 3-bromo 7-NI and N(G)-nitro L-arginine methyl ester (L-NAME). The potential modulatory role of endothelin was examined by use of the ET(A) receptor antagonist BQ-123. 4. CGRP8-37 (10 microM) was perfused over the blister base before nerve stimulation and continuously throughout the post-stimulation period, resulting in a significant reduction (41%) in the blood flux vascular response. 5. Pretreatment with the specific neuronal NO synthase inhibitors, 7-NI and 3-bromo 7-NI (10 mg kg(-1), i.v.), and of the non-specific L-NAME (100 microM), resulted in significant inhibition of the blood flux response (36%, 72% and 57% decrease, respectively). In contrast, 7-NI treatment in young rats pretreated with capsaicin had no further effect on the vascular response, suggesting that the source of NO is the sensory nerves. 6. BQ-123 (10 microM) significantly enhanced the stimulation-induced blood flux response (61% increase). When 7-NI was co-administered with either CGRP8-37 or BQ-123, the drug actions were additive, suggesting that there was no interaction between NO and CGRP or endothelin. 7. These data suggest that both NO and CGRP participate in neurogenic vasodilatation in rat skin microvasculature and that this response is modulated by endogenous endothelin.

Selective restoration of sensation by peripheral nerve grafts directly implanted into the contralateral C7 dorsal root ganglion: an experimental study in rat brachial plexus

OBJECTIVE

In brachial plexus injuries, when the dorsal root ganglion (DRG) is avulsed from the spinal cord there is no possibility of direct repair. Therefore, in the present report the median nerve was connected directly to the contralateral C7 DRG, to restore forepaw sensation.

METHODS

The ulnar nerve was sectioned, and a 15-mm segment of nerve was removed. The median nerve was sectioned, transposed dorsally, and repaired using a sural nerve graft directly implanted into the C7 contralateral DRG. Rats were then assessed 6 and 12 months later by behavioral, histological, and plasma extravasion techniques.

RESULTS

All animals recovered sensation in the forepaw. Retrogradely labeled sensory neurons were demonstrated in the C7 DRG, and the whole forepaw was labeled after plasma extravasion induction by median nerve antidromic stimulation. Several myelinated and positively neurofilament-stained fibers were demonstrated in the grafted median nerve.

CONCLUSION

The surgical strategy proposed might be a useful alternative to selective sensory repair in the emerging field of brachial plexus reconstruction by direct spinal cord surgery.

Sympathetic modulation of sensory nerve activity with age: human and rodent skin models

1. Sensory nerves serve an afferent role and mediate neurogenic components of inflammation and tissue repair via an axon reflex release of sensory peptides at sites of injury. Dysfunction of these nerves with age could contribute to delayed tissue healing. 2. Complementary animal and human skin models were used in the present studies to investigate changes in the modulation of sensory nerve function by sympathetic efferents during ageing. Laser Doppler flowmetry was used to monitor neurogenic skin vascular responses. 3. The animal model used skin of the hind footpad of anaesthetized rats combined with electrical stimulation of the sciatic nerve, while the human model comprised capsaicin electrophoresis to the volar surface of the forearm. Sympathetic modulation was effected by systemic phentolamine pretreatment in animals and local application in the human model. 4. The results obtained from the human model confirmed the reported decline in sensory nerve function and showed no change in sympathetic modulation with age. The results from the animal model confirm and expand results obtained from the human model. 5. The use of low (5 Hz) and high (15 Hz) frequency electrical stimulation (20 V, 2 ms for 1 min) revealed a preferential response of aged sensory nerves to low-frequency electrical stimulation parameters with differential sympathetic modulation that is dependent on the frequency of stimulation.

Mechanisms underlying the vascular activity of beta-amyloid protein fragment (beta A(4)25-35) at the level of skin microvasculature

Deposition of beta-amyloid protein (beta A4) in extracellular senile plaques is a pathologic hallmark of Alzheimer's disease (AD). The neurotoxic effect of beta A4 has been ascribed to a discrete 11-amino acid internal sequence (beta A(4)25-35). Substance P (SP) has been found to be depleted in the brain of AD patients while its presence was found to protect against the neurodegenerative effect of beta A(4)25-35. Our previous studies, in vivo, in aged rats showed that beta A(4)25-35 exhibits a potent vasoconstrictor (VC) effect in rat skin microvasculature and can prevent SP but not calcitonin gene-related peptide (CGRP) from inducing a vasodilator (VD) response. It was postulated that beta A(4)25-35 might be interacting with SP at the level of the second messenger system via the phosphoinositide pathway. Using a blister model of inflammation in the rat hind footpad, we examined the ability of beta A(4)25-35 to modulate the vascular activity of bradykinin (BK) and serotonin (5-HT) which also activate the phosphoinositide pathway. In addition, the role of nitric oxide (NO), endothelin (ET, an endothelium-derived constrictor factor) and protein kinase C (PKC) in the vascular effects of beta A(4)25-35 were examined using the NO synthase inhibitor, NG-nitro-L-arginine (L-NOARG), the ET-receptor antagonist, BQ-123, and the PKC inhibitor, bisindolylmaleimide (BIM) respectively. Changes in microvascular blood flow were monitored using laser Doppler flowmetry and the area within the response curve measured. The results showed that beta A(4)25-35 (10 microM) induced a VC effect and inhibited the subsequent VD response to BK (10 microM) and 5-HT (1 microM) in a similar fashion to its effect on SP (1 microM). In the presence of L-NOARG (100 microM), the VD effect of SP was reduced and further attenuated after perfusion of beta A(4)25-35. Superfusion of the blister base with BQ-123 (10 microM) or BIM (1 microM) prior to and during perfusion with beta A(4)25-35 abolished its VC effect and allowed SP to induce a normal VD response in both young and old rats. Based on these results, we suggest that the vascular activity of the active fragment, beta A(4)25-35, is mediated by ET via activation of PKC. This study provides new findings which may help to elucidate the signal transduction mechanisms involved in the vascular activity of beta A(4)25-35. The relevance of these mechanisms to those underlying the pathological effects of beta A4 and their significance in AD remains to be determined.

Functional characterization of cutaneous mechanoreceptor properties in aged rats

We investigated the effects of aging on rapidly (RA) and slowly adapting (SA) cutaneous mechanoreceptors by means of single fiber recordings and evoked sensory nerve action potentials (EAPs) of the hindpaw of the N. plantaris in adult and old Wistar rats. EAPs revealed comparable shapes and amplitudes in all animals of all age groups. In old rats, conduction velocities were slightly (15%) lengthened. The mechanoreceptor composition was different from adults, resulting in a lower number of SA units. We were not able to detect significant differences in the sizes of receptive fields and in the thresholds between old and adult animals. The absence of significant age-related changes in the cutaneous periphery of the hindpaw is discussed in respect to the previously reported alterations of cortical receptive field properties in old rats.

Effect of chronic sciatic nerve lesion on the neurogenic inflammatory response in intact and acutely injured denervated rat skin

A supersensitivity to the neuropeptide substance P (SP) has been shown to develop in post-terminal membranes of many denervated tissues. This study examined changes in the sensitivity of post-terminal vascular receptors to SP and calcitonin gene-related peptide (CGRP) in rat skin microvasculature following sciatic nerve section. In anaesthetised rats, 0.5 cm of sciatic nerve in the right mid-thigh region was removed. Two weeks later, SP (100 microM) and sodium nitroprusside (SNP, 1 mM), a direct smooth muscle vasodilator, were introduced into denervated intact footpad skin, via the electrophoresis technique. Laser doppler flowmeter was used to record changes in relative blood flow in the rat hind footpad. The results showed a significant increase in SP response over controls and slight increase in smooth muscle reactivity as determined by an increase in the vascular response to SNP. In another set of experiments, the sensitivity of post-terminal receptors was examined over a 4 weeks period in an acutely injured footpad skin of sciatic nerve lesioned rats. A vacuum-induced blister was raised on the hind footpad and SP, CGRP (each at 1 microM) or SNP (100 microM) were superfused over the blister base. In nerve lesioned rats, using the acutely injured footpad skin model, the results showed a reduction in the vascular responses to SP, CGRP and SNP. The response to SP continued to decrease over time reaching 22% of control values by 4 weeks. Responses to SNP and CGRP were reduced to 53% and 45% respectively by 2 weeks and then improved to 75% of control values by 4 weeks. Possible contributions of sympathetic efferents and the saphenous nerve to these reduced responses in acutely injured skin of nerve lesioned rats were examined using guanethidine (50 mg/kg i.p.) or sectioned saphenous nerve respectively. These procedures did not significantly modify the reduced vascular responses in the blister base of lesioned rats. Possible activation of endogenous opioids and/or the release of endothelin due to blister induction in nerve lesioned rats was examined using naloxone and the endothelin receptor antagonist, BQ-123, respectively. Treatment with naloxone increased SP response in lesioned rats to 41% of control value with no change in smooth muscle reactivity. BQ-123 significantly increased the responses to SP and SNP to 51% and 100% of their own control values respectively. It is concluded that supersensitivity of post-terminal vascular receptors develops in intact skin following chronic nerve lesion. On the other hand, acute injury of the denervated skin area induces activation of endogenous inhibitory modulatory mechanisms that masks this supersensitivity.

Nitric oxide in coronary artery disease: roles in atherosclerosis, myocardial reperfusion and heart failure

Nitric oxide (NO), derived from the vascular endothelium or other cells of the cardiovascular system, has an important role in physiological regulation of blood flow and has pathophysiological functions in cardiovascular disease. The mechanisms and enzymes involved in the biosynthesis of NO and biological actions of NO, including vasodilatation, cytotoxicity and inflammation, are briefly reviewed. These reactions involving NO cause pathological disturbances of arterial function, coronary blood flow regulation, and may contribute to cardiac myocyte dysfunction. NO and prostacyclin (PGI2), which is also released from the endothelium, act synergistically to inhibit platelet aggregation and adhesion, and in some arteries these mediators also synergise in terms of vasodilatation. In addition, NO is capable of hyperpolarizing vascular smooth muscle, but activation of the endothelium may cause hyperpolarization and may thus promote vasodilatation by an additional mechanism. After myocardial ischemia and reperfusion, production of NO and superoxide radicals represent important mechanisms of cytotoxicity, causing injury to the coronary endothelium and myocytes and compromising ventricular contractile function. Moreover, upon reperfusion endothelium-dependent vasodilatation is impaired and the coronary arteries constrict, leading to irregular myocardial perfusion. This is a consequence of the accumulation of activated leucocytes that we found to generate endogenous inhibitors of NO. These factors have yet to be fully characterised, but clearly they may have a role in irregularities of myocardial reperfusion and cellular injury. Chronic heart failure is associated both with impairment of endothelium-dependent vasodilatation and with excess production of NO via the inducible NO synthase (iNOS), although it is unclear whether the latter assists or compromises ventricular contractile performance under these conditions. Disturbances in the activity of isoforms of NO synthase in the artery wall also accompany the development of atherosclerosis, providing conditions propitious for vasospasm and thrombosis, and perhaps contributing to cell proliferation. Reversing these NO defects with therapeutic agents including angiotensin converting enzyme (ACE) inhibitors offers promise in protecting against some manifestations of vascular disease.

Endogenous nitric oxide in cardiovascular disease and transplantation

Nitric oxide (NO), derived from the vascular endothelium and other cells of the cardiovascular system, has important roles in physiological regulation of blood flow and may have pathophysiological functions in cardiovascular disease. The mechanisms involved in NO-induced vasodilatation and cytotoxicity are briefly reviewed in the context of inflammatory reactions and cardiovascular function. Although NO can hyperpolarize vascular smooth muscle, activation of the endothelium can induce hyperpolarization and vasodilatation by other means. Endogenous inhibitors of NO generated by leucocytes may compromise blood flow distribution after ischaemia and reperfusion injury. Chronic heart failure is associated simultaneously with impairment of endothelium-dependent vasodilatation and with excess production of NO via the inducible NO synthase (iNOS), although it is unclear whether the latter ameliorates or exacerbates ventricular dysfunction. Excess NO production is also one of the earliest signs of transplant rejection, and suppression of iNOS expression by immunosuppressant drugs such as cyclosporin A might be one means by which these drugs protect allografts. Disturbances in the activity of NOS isoforms in the artery wall also accompany the development of atherosclerosis, providing conditions propitious for vasospasm and thrombosis. Reversing the NO defects with therapeutic agents, including angiotensin converting enzyme (ACE) inhibitors, offers promise in protecting against some manifestations of vascular disease.

Fos induction in the medullary dorsal horn and C1 segment of the spinal cord by acute inflammation in aged rats

In order to elucidate the effect of aging on nociceptive neurons in the central nervous system, c-fos was used as a marker of excitability of neurons in the medullary dorsal horn (MDH) and the first spinal segment (C1) following noxious stimulation of the lateral face of young and aged rats. The distribution of c-fos-positive cells was dense in the superficial laminae and sparse in the deep laminae of the MDH and C1 in both young and aged animals following subcutaneous injection of formalin into the lateral face, whereas few c-fos-positive cells were labeled after saline injection. The distribution of c-fos-positive cells in the superficial laminae of the aged rats was found to be denser and more rostro-caudally expanded compared to that in the young rats. C-fos-positive cells were distributed more rostro-caudally in aged than in young rats. There was no difference between young and aged rats in the distribution of c-fos-positive cells in the deep laminae. Substance P (SP), 5-HT and calcitonin gene-related peptide-like immunoreactive (CGRP-LI) fibers and varicosities showed similar distribution density in the MDH and C1. Furthermore, many 5-HT-LI aberrant fibers and varicosities were observed in the MDH and C1 of the aged rats. The SP-LI and CGRP-LI cells in the trigeminal ganglion of aged rats were larger than those of young rats. These findings suggest that a deficit of the descending 5-HT inhibitory system produces the increment of c-fos-positive cells in the MDH and C1 of aged rats, resulting in the recruitment of a larger number of neurons in the superficial laminae of the MDH and C1 for conveying nociceptive sensory information to the central nervous system.

Beta A4(25-35) modulates substance P effect on rat skin microvasculature in aged rats: pharmacological manipulation using SEC-receptor ligands

The primary constituent of the senile plaque core in Alzheimer's disease (AD) is the beta-amyloid protein (beta A4). A discrete 11 amino acid fragment of the beta A4, beta A4(25-35), has been implicated in mediating in vitro neurotoxicity and an inflammatory response surrounding senile plaques in AD via interaction with the Serpin Enzyme Complex (SEC) receptor. Substance P (SP), a neuropeptide of the tachykinin family and a major mediator of neurogenic inflammation, shows sequence homology to beta A4(25-35) and has been shown to protect against the neurotoxicity of beta-amyloid. SP also competes with beta A4(25-35) for binding to the SEC-receptor. SP neurons have also been found to be depleted in AD. Using a blister model of inflammation in the rat hind footpad, we have examined the effect of beta A4(25-35) and its interaction with SP in rat skin microvasculature and determined age-related changes to these phenomena. In addition, pharmacological manipulation of these responses using SEC-receptor ligands (peptide 105Y and 105C) was also undertaken. Because of the evidence for co-existence and co-release of SP and calcitonin gene-related peptide (CGRP) from the peripheral terminals of sensory nerves, it was of interest to examine the interaction of CGRP with beta A4(25-35) on rat skin microvasculature. beta A4(25-35) (10 microM) was perfused over the base of a blister raised on the hind footpad of anaesthetised young and old rats. This was followed by perfusion of SP (1 microM) or CGRP (1 microM) after Ringer's solution. Relative blood flow was monitored using a Laser-Doppler Flowmeter.(ABSTRACT TRUNCATED AT 250 WORDS)