Cutaneous Vasoconstriction Research Articles

Cold Water Mediates Greater Reductions in Limb Blood Flow than Whole Body Cryotherapy.

Cold-water immersion (CWI) and whole body cryotherapy (WBC) are widely used recovery methods in an attempt to limit exercise-induced muscle damage, soreness, and functional deficits after strenuous exercise. The aim of this study was to compare the effects of ecologically valid CWI and WBC protocols on postexercise lower limb thermoregulatory, femoral artery, and cutaneous blood flow responses. Ten males completed a continuous cycle exercise protocol at 70% maximal oxygen uptake until a rectal temperature of 38°C was attained. Participants were then exposed to lower-body CWI (8°C) for 10 min, or WBC (-110°C) for 2 min, in a randomized crossover design. Rectal and thigh skin, deep, and superficial muscle temperatures, thigh, and calf skin blood flow (laser Doppler flowmetry), superficial femoral artery blood flow (duplex ultrasound), and arterial blood pressure were measured before, and for 40 min post, cooling interventions. Greater reductions in thigh skin (CWI, -5.9°C ± 1.8°C; WBC, 0.2°C ± 0.5°C; P < 0.001) and superficial (CWI, -4.4°C ± 1.3°C; WBC, -1.8°C ± 1.1°C; P < 0.001) and deep (CWI, -2.9°C ± 0.8°C; WBC, -1.3°C ± 0.6°C; P < 0.001) muscle temperatures occurred immediately after CWI. Decreases in femoral artery conductance were greater after CWI (CWI, -84% ± 11%; WBC, -59% ± 21%, P < 0.02) and thigh (CWI, -80% ± 5%; WBC, -59% ± 14%, P < 0.001), and calf (CWI, -73% ± 13%; WBC, -45% ± 17%, P < 0.001) cutaneous vasoconstriction was greater after CWI. Reductions in rectal temperature were similar between conditions after cooling (CWI, -0.6°C ± 0.4°C; WBC, -0.6°C ± 0.3°C; P = 0.98). Greater reductions in blood flow and tissue temperature were observed after CWI in comparison with WBC. These novel findings have practical and clinical implications for the use of cooling in the recovery from exercise and injury.

Influence of cold-water immersion on limb blood flow after resistance exercise

This study determined the influence of cold (8°C) and cool (22°C) water immersion on lower limb and cutaneous blood flow following resistance exercise. Twelve males completed 4 sets of 10-repetition maximum squat exercise and were then immersed, semi-reclined, into 8°C or 22°C water for 10-min, or rested in a seated position (control) in a randomized order on different days. Rectal and thigh skin temperature, muscle temperature, thigh and calf skin blood flow and superficial femoral artery blood flow were measured before and after immersion. Indices of vascular conductance were calculated (flux and blood flow/mean arterial pressure). The colder water reduced thigh skin temperature and deep muscle temperature to the greatest extent (P < .001). Reductions in rectal temperature were similar (0.2–0.4°C) in all three trials (P = .69). Femoral artery conductance was similar after immersion in both cooling conditions, with both conditions significantly lower (55%) than the control post-immersion (P < .01). Similarly, there was greater thigh and calf cutaneous vasoconstriction (40–50%) after immersion in both cooling conditions, relative to the control (P < .01), with no difference between cooling conditions. These findings suggest that cold and cool water similarly reduce femoral artery and cutaneous blood flow responses but not muscle temperature following resistance exercise.

Neurovascular mechanisms underlying augmented cold-induced reflex cutaneous vasoconstriction in human hypertension.

In hypertensive adults (HTN), cardiovascular risk increases disproportionately during environmental cold exposure. Despite ample evidence of dysregulated sympathetic control of the peripheral vasculature in hypertension, no studies have examined integrated neurovascular function during cold stress in HTN. The findings of the present study show that whole-body cold stress elicits greater increases in sympathetic outflow directed to the cutaneous vasculature and, correspondingly, greater reductions in skin blood flow in HTN. We further demonstrate an important role for non-adrenergic sympathetic co-transmitters in mediating the vasoconstrictor response to cold stress in hypertension. In the context of thermoregulation and the maintenance of core temperature, sympathetically-mediated control of the cutaneous vasculature is not only preserved, but also exaggerated in hypertension. Given the increasing prevalence of hypertension, clarifying the mechanistic underpinnings of hypertension-induced alterations in neurovascular function during cold exposure is clinically relevant. Despite ample evidence of dysregulated sympathetic control of the peripheral vasculature in hypertension, no studies have examined integrated neurovascular function during cold stress in hypertensive adults (HTN). We hypothesized that (i) whole-body cooling would elicit greater cutaneous vasoconstriction and greater increases in skin sympathetic nervous system activity (SSNA) in HTN (n=14; 56±2years) compared to age-matched normotensive adults (NTN; n=14; 55±2years) and (ii) augmented reflex vasoconstriction in HTN would be mediated by an increase in cutaneous vascular adrenergic sensitivity and a greater contribution of non-adrenergic sympathetic co-transmitters. SSNA (peroneal microneurography) and red cell flux (laser Doppler flowmetry; dorsum of foot) were measured during whole-body cooling (water-perfused suit). Sympathetic adrenergic- and non-adrenergic-dependent contributions to reflex cutaneous vasoconstriction and vascular adrenergic sensitivity were assessed pharmacologically using intradermal microdialysis. Cooling elicited greater increases in SSNA (NTN: +64±13%baseline vs. HTN: +194±26%baseline ; P<0.01) and greater reductions in skin blood flow (NTN: -16±2%baseline vs. HTN: -28±3%baseline ; P<0.01) in HTN compared to NTN, reflecting an increased response range for sympathetic reflex control of cutaneous vasoconstriction in HTN. Norepinephrine dose-response curves showed no HTN-related difference in cutaneous adrenergic sensitivity (logEC50 ; NTN: -7.4±0.3log Mvs. HTN: -7.5±0.3log M; P=0.84); however, non-adrenergic sympathetic co-transmitters mediated a significant portion of the vasoconstrictor response to cold stress in HTN. Collectively, these findings indicate that hypertension increases the peripheral cutaneous vasoconstrictor response to cold via greater increases in skin sympathetic outflow coupled with an increased reliance on non-adrenergic neurotransmitters.

Cutaneous exposure to hypoxia does not affect skin perfusion in humans.

Experiments have indicated that skin perfusion in mice is sensitive to reductions in environmental O2 availability. Specifically, a reduction in skin-surface PO2 attenuates transcutaneous O2 diffusion, and hence epidermal O2 supply. In response, epidermal HIF-1α expression increases and facilitates initial cutaneous vasoconstriction and subsequent nitric oxide-dependent vasodilation. Here, we investigated whether the same mechanism exists in humans. In a first experiment, eight males rested twice for 8h in a hypobaric chamber. Once, barometric pressure was reduced by 50%, while systemic oxygenation was preserved by O2 -enriched (42%) breathing gas (HypoxiaSkin ), and once barometric pressure and inspired O2 fraction were normal (Control1 ). In a second experiment, nine males rested for 8h with both forearms wrapped in plastic bags. O2 was expelled from one bag by nitrogen flushing (AnoxiaSkin ), whereas the other bag was flushed with air (Control2 ). In both experiments, skin blood flux was assessed by laser Doppler on the dorsal forearm, and HIF-1α expression was determined by immunohistochemical staining in forearm skin biopsies. Skin blood flux during HypoxiaSkin and AnoxiaSkin remained similar to the corresponding Control trial (P=0.67 and P=0.81). Immunohistochemically stained epidermal HIF-1α was detected on 8.2±6.1 and 5.3±5.7% of the analysed area during HypoxiaSkin and Control1 (P=0.30) and on 2.3±1.8 and 2.4±1.8% during AnoxiaSkin and Control2 (P=0.90) respectively. Reductions in skin-surface PO2 do not affect skin perfusion in humans. The unchanged epidermal HIF-1α expression suggests that epidermal O2 homoeostasis was not disturbed by HypoxiaSkin /AnoxiaSkin , potentially due to compensatory increases in arterial O2 extraction.

Abstract 11874: Sympathetic Control of Reflex Cutaneous Vasoconstriction in Human Hypertension

Introduction: Cardiovascular-related morbidity and mortality during environmental cold exposures increase disproportionally in hypertensive (HTN) adults. Although alterations in central control of sympathetic outflow and peripheral regulation of vascular function are evident in hypertension and contribute to increased cardiovascular risk, no studies have examined sympathetic control of reflex cutaneous vasoconstriction during cold stress in humans with hypertension. We hypothesized that 1) whole-body cold stress would elicit exaggerated increases in skin sympathetic nervous system activity (SSNA) and greater reductions in skin blood flow in HTN [n=10; 56±3 yrs; resting blood pressure (BP) 145±7/84±3 mmHg] compared to normotensive adults (NTN; n=12, 55±3 yrs; resting BP 126±4/79±3 mmHg) and 2) cutaneous adrenergic sensitivity would be increased in HTN adults. Methods: In Protocol 1, reflex vasoconstriction was induced by gradual whole-body cooling (to a mean skin temperature of 30.5°C) using a water-perfused suit. SSNA (peroneal microneurography) and red cell flux (laser Doppler flowmetry; dorsum of foot) were measured continuously. SSNA was expressed as a percent change from baseline. In Protocol 2, an intradermal microdialysis fiber was placed in the skin of the lateral calf to measure red cell flux in response to graded intradermal infusions of norepinephrine (NE; 10 -12 to 10 -2 M). In each study, cutaneous vascular conductance (CVC=flux/mean arterial pressure) was expressed as a change from baseline. Results: During cooling, HTN exhibited greater increases in SSNA compared to NTN adults (Δ = 194±26% HTN vs. 51±12% NTN; P&lt;0.01) but cutaneous vasoconstriction was not different between groups (ΔCVC base = -0.03±0.003 ητν vs. -0.02±0.01 flux units mmHg -1 NTN; P=0.97). The slope of the relation between ΔSSNA and ΔCVC base during cold stress was blunted in HTN adults (P&lt;0.01). There was no group difference in cutaneous adrenergic responsiveness to exogenous NE (dose-response logEC 50 ; -7.2±0.2 HTN vs. -7.5±0.4 NTN; P=0.75). Conclusion: Although cutaneous microvascular adrenergic responsiveness to NE is preserved, the sensitivity of the sympathetic reflex response to whole-body cold stress is diminished in human hypertension.

Hypoperfusion in response to epinephrine in local anaesthetics: Investigation of dependence on epinephrine concentration, spread of hypoperfusion and time to maximal cutaneous vasoconstriction

The present study aimed to examine hypoperfusion in response to epinephrine following the administration of a local anaesthetic. The concentration of epinephrine that causes maximal hypoperfusion, the spread of hypoperfusion in the tissue and the time to the stabilization of hypoperfusion were investigated. Blood perfusion was monitored using laser Doppler velocimetry and laser speckle contrast imaging of random-pattern advancement flaps (1×4cm) or intact skin on the pig flank. Epinephrine was either injected cumulatively (0.1, 1.0, 10 or 100μg/ml) after injecting 20mg/ml lidocaine, to determine the concentration response, or given as a single dose (12.5μg/ml epinephrine+20mg/ml lidocaine). Control experiments were performed with saline or lidocaine (without epinephrine). Increasing concentrations of epinephrine resulted in a gradual decrease in skin perfusion, approaching a minimum after injecting 10μg/ml. The area of hypoperfusion was 12mm in radius, and the time from the injection to the stabilization of hypoperfusion was approximately 120s. After the administration of 10μg/ml epinephrine in flaps with small pedicle, 25% blood perfusion still remained. Local anaesthetic with an epinephrine concentration of approximately 10μg/ml appears to be adequate for vasoconstriction before surgery. Incisions were required to be delayed only for 2min following local anaesthetic with epinephrine in pigs. The remaining 25% blood perfusion observed after the administration of epinephrine supports the use of epinephrine in flaps with a small pedicle. Obviously, these experimental findings must be clinically assessed before being considered for infiltration anaesthesia during plastic surgery procedures.

Desensitization of menthol-activated cold receptors in lower extremities during local cooling in young women with a cold constitution.

To test the hypothesis that topical menthol-induced reactivity of cold sensation and cutaneous vasoconstriction to local cooling is augmented in individuals with a cold constitution, we examined thermal sensation and cutaneous vasoconstrictor responses at menthol-treated and untreated sites in the legs during local skin cooling in young women complaining of chilliness (C group) and young women with no complaint as a normal control group (N group). During local skin cooling, the sensitivity to cold sensation was greater in the C group than in the N group. The application of menthol enhanced the cold sensation at a low temperature in the N group, but not in the C group. Cutaneous vasoconstrictor responses to local skin cooling were not altered by menthol treatment in either of the two groups. These findings suggest the desensitization of menthol-activated cold receptors in the legs of C group subjects, and a minor role of cold receptor activity in cutaneous vasoconstrictor response to local cooling.

Involvement of endocannabinoid neurotransmission in the bed nucleus of stria terminalis in cardiovascular responses to acute restraint stress in rats.

Endocannabinoid signalling has been reported as an important neurochemical mechanism involved in responses to stress. Previous studies provided evidence of endocannabinoid release in the bed nucleus of the stria terminalis (BNST) during aversive stimuli. Nevertheless, a possible involvement of this neurochemical mechanism in stress responses has never been evaluated. Therefore, in the present study we investigated the involvement of BNST endocannabinoid neurotransmission, acting via local CB1 receptors, in the cardiovascular responses to acute restraint stress in rats. The selective CB1 receptor antagonist AM251 (1, 30 and 100 pmol 100 nL(-1) ) and/or the fatty acid amide hydrolase (FAAH) enzyme inhibitor URB597 (30 pmol 100 nL(-1) ) or the monoacylglycerol lipase (MAGL) enzyme inhibitor JZL184 (30 pmol 100 nL(-1) ) was microinjected into the BNST before the acute restraint stress. Microinjection of AM251 into the BNST enhanced the tachycardia caused by restraint stress, without affecting the increase in arterial pressure and the sympathetic-mediated cutaneous vasoconstrictor response. Conversely, the increased endogenous levels of AEA in the BNST evoked by local treatment with the FAAH enzyme inhibitor URB597 decreased restraint-evoked tachycardia. Inhibition of the hydrolysis of 2-arachidonoylglycerol (2-AG) in the BNST by local microinjection of the MAGL enzyme inhibitor JZL184 also decreased the HR response. These effects of URB597 and JZL184 were abolished by BNST pretreatment with AM251. These findings indicate an involvement of BNST endocannabinoid neurotransmission, acting via CB1 receptors, in cardiovascular adjustments during emotional stress, which may be mediated by the local release of either AEA or 2-AG.

Central control of body temperature.

Central neural circuits orchestrate the behavioral and autonomic repertoire that maintains body temperature during environmental temperature challenges and alters body temperature during the inflammatory response and behavioral states and in response to declining energy homeostasis. This review summarizes the central nervous system circuit mechanisms controlling the principal thermoeffectors for body temperature regulation: cutaneous vasoconstriction regulating heat loss and shivering and brown adipose tissue for thermogenesis. The activation of these thermoeffectors is regulated by parallel but distinct efferent pathways within the central nervous system that share a common peripheral thermal sensory input. The model for the neural circuit mechanism underlying central thermoregulatory control provides a useful platform for further understanding of the functional organization of central thermoregulation, for elucidating the hypothalamic circuitry and neurotransmitters involved in body temperature regulation, and for the discovery of novel therapeutic approaches to modulating body temperature and energy homeostasis.

Mechanisms of Pronounced and Sustained Cutaneous Vasoconstriction during Cryotherapy

Cryotherapy is a common therapeutic technique using ice or cold water to reduce local blood flow. While beneficial, it can be associated with some negative physiological side effects such as pronounced tissue ischemia sustained for hours during a post-treatment rewarming period. Previous findings in our laboratory have indicated that this cutaneous vasoconstriction during cryotherapy is abolished following blockade of Rho Kinase. The Rho Kinase enhances vasoconstriction in part via down regulation of nitric oxide synthase (NOS). PURPOSE: To test the hypothesis that a reduction in nitric oxide (NO) bioavailability is involved in the pronounced and sustained cutaneous vasoconstriction that occurs during a typical cyrotherapy protocol. METHODS: 8 healthy individuals (6 male) participated in this protocol. A cryotherapy unit with a water perfused bladder was used. The bladder was placed on the lateral portion of the calf. Four microdialysis membranes were placed in the skin underneath the bladder. One site was perfused with lactated ringers (CON); neuronal NOS (nNOS) was blocked in another site (NPLA); endothelial NOS (eNOS) was blocked in another site (NLIO); and the last site received non-selective NOS blockade (LNAME). All solutions were dissolved in sterile lactated Ringers. Skin temperature (SkT) and skin vascular conductance (SkVC) was measured at each site. 0 °C water perfused through the cryotherapy bladder for 30 min, followed by passive rewarming (i.e. water shut off) for 1 hr, followed by direct heating with 46 °C water for 10 min. RESULTS: SkT fell from 34°C to 19°C during 30 min of cooling in all sites. SkVC at CON was reduced ~75% after 30 min of cooling and was similar to LNAME, NPLA, and LNIO (78, 75, 77%, reduction respectively; P>0.05). During passive rewarming SkVC remained blunted to a similar degree at all sites (Con: 87±1, LNAME: 85±2, NPLA: 87±2, LNIO: 85±1 % reduction; P>0.05). SkVC during 10 min of active warming was also similar between sites (CON: 62%, LNAME: 65%, NPLA: 67%, and LNIO: 68% reduction; P<0.05) CONCLUSION: The current data suggest that reductions in NO bioavailability do not contribute to pronounced and sustained vasoconstriction during cryotherapy. Supported by the National Institute of Biomedical Imaging and Bioengineering; R01EB015522 (Multi PI: K.R. Diller & R.M. Brothers).

Acute Activation of the Peripheral Chemoreceptors Briefly Induces Cutaneous Vasoconstriction

Recent evidence indicates that five minutes of breathing hypoxic gas elicits cutaneous vasodilation. However, it is unclear if skin blood flow is influenced by a brief hypoxic exposure. PURPOSE: We tested the hypothesis that cutaneous vasodilation is increased following a brief hypoxic exposure. METHODS: Seven healthy participants (2 women, 25 ± 2 years, BMI 26 ± 3 kg/m2) breathed 4–6 breaths of 100% nitrogen. We continuously measured skin blood flow on the ventral side of the forearm (laser Doppler), arterial oxygen saturation (finger pulse oximeter), mean arterial pressure (Finometer), and heart rate (ECG) at baseline and following the hypoxic exposure for one minute, during which data were analyzed in 15 s time bins. Skin blood flow was also normalized to mean arterial pressure (MAP) and expressed as a percentage of the local heating induced maximal cutaneous vascular conductance (%CVCmax). RESULTS: Arterial oxygen saturation was lower at 45 s (89 ± 7%; P < 0.05) and 60 s (90 ± 5%; P < 0.05) vs. baseline (97 ± 1%). Skin blood flow was lower 15 s after the hypoxic exposure when compared to baseline (4.2 ± 0.9 vs. 5.1 ± 0.9 PU, P = 0.001). MAP was greater at 15 s vs. baseline (94 ± 7 vs. 88 ± 7 mmHg; P < 0.05) and returned to baseline values at 30 s. %CVCmax was reduced within the first 15 s following the hypoxic exposure compared to baseline (4.3 ± 1.0 vs. 5.6 ± 1.2%; P < 0.05). Skin blood flow and %CVCmax returned to baseline values 30 s following the hypoxic exposure. Heart rate was significantly greater than baseline (64 ± 9 bpm) at 15 s (76 ± 13 bpm; P < 0.01), 30 s (76 ± 14 bpm; P < 0.01), 45 s (69 ± 11 bpm; P < 0.01), and 60 s (67 ± 11 bpm; P < 0.05). CONCLUSIONS: Contrary to our hypothesis, a brief hypoxic exposure induces cutaneous vasoconstriction and attenuates skin blood flow. This suggests that activation of the peripheral chemoreceptors acutely lowers skin blood flow.

Attenuated cold defense responses in orexin neuron-ablated rats

ABSTRACTRecent reports of the use of transgenic mice targeting orexin neurons show that the ablation of orexin neurons in the hypothalamus causes hypothermia during cold exposure. This suggests the importance of orexin neurons for cold-induced autonomic and physiological defense responses, including brown adipose tissue (BAT) thermogenesis and vasoconstriction in thermoregulatory cutaneous vascular bed. The present study investigated whether the ablation of orexin neurons attenuated cold-elicited BAT thermogenesis and cutaneous vasoconstriction. The study took advantage of our established conscious rat experimental model of direct measurement of BAT and body temperature and tail cutaneous blood flow. The study used transgenic orexin neurons-ablated (ORX-AB) rats and wild type (WT) rats. BAT temperature and tail artery blood flow with pre-implanted probes were measured, as well as behavioral locomotor activity under conscious free-moving condition. Gradually, the ambient temperature was decreased to below 5°C. ORX-AB rats showed an attenuated cold-induced BAT thermogenesis and behavioral activity, and delayed tail vasoconstriction. An ambient temperature that initiated BAT thermogenesis and established full cutaneous vasoconstriction was 14.1 ± 1.9 °C, which was significantly lower than 20.5 ± 1.9 °C, the corresponding value in WT rats (n = 10, P < 0.01). The results from this study suggest that the integrity of orexin-synthesising neurons in thermoregulatory networks is important for full expression of the cold defense responses.

Infrared thermography based studies on the effect of age on localized cold stress induced thermoregulation in human

Thermoregulatory control of blood flow plays an important role in maintaining the human body temperature and it provides physiological resistance against extreme environmental thermal stresses. To understand the role of age on thermal signals from veins and the thermoregulatory mechanism, the dynamic variation of the vein temperature on the hands of 17 human subjects, under a localized cold stress, was studied using infrared thermography. It was observed that the vein temperature of the stimulated hand initially decreased with time up to a time interval (called ‘inversion time’), which was attributed to the localized cutaneous vasoconstriction. Beyond inversion time, a rise in the vein temperature of the stimulated hand was observed. A shift in the inversion time to higher values was observed for the older subjects, which was attributed to the reduced efficiency and responsiveness of the cutaneous vasoconstriction mechanism in these subjects. Our studies indicated that the inversion time increased linearly with subject age with strong positive Pearson’s correlation coefficient of 0.94. It was also observed that the contralateral symmetry in vasoconstriction was much lower in older subjects than the younger subjects. The absolute difference between the left and right inversion time varied between 11–118s and 5–28s for the older and younger subjects, respectively. Our study clearly demonstrated that infrared thermography is one of the most effective experimental tool for studying dynamic variation in vein pixel temperature under localized thermal stresses.

Sustained cutaneous vasoconstriction during and following cyrotherapy treatment: Role of oxidative stress and Rho kinase

Cryotherapy is a therapeutic technique using ice or cold water applied to the skin to reduce bleeding, inflammation, pain, and swelling following soft tissue trauma and injury. While beneficial, there are some side effects such as pronounced vasoconstriction and tissue ischemia that are sustained for hours post-treatment. This study tested the hypothesis that this vasoconstriction is mediated by 1) the Rho-kinase pathway and/or 2) elevated oxidative stress. 9 subjects were fitted with a commercially available cryotherapy unit with a water perfused bladder on the lateral portion of the right calf. Participants were instrumented with three microdialysis probes underneath the bladder. One site received lactated ringers (control site), one received the Rho-Kinase inhibitor Fasudil, and one received Ascorbic Acid. Skin temperature (Tskin) and cutaneous vascular conductance (CVC) was measured at each site. Subjects had 1°C water perfused through the bladder for 30min, followed by passive rewarming for 90min. Tskin fell from ~34°C to ~18.0°C during active cooling across all sites and this response was similar for all sites (P>0.05 for all comparisons). During passive rewarming Tskin rose to a similar degree in all sites (P>0.05 relative to the end of cooling). %CVC was reduced during active cooling in all sites; however, the magnitude of this response was blunted in the Fasudil site relative to control (P<0.001 for all comparisons) and min 25 and 30 of cooling in the Ascorbic Acid site (P<0.05). During passive rewarming %CVC at the control and Ascorbic Acid sites did not change such that values were similar to the end of cooling (P>0.05 for each comparison). %CVC at the Fasudil site remained elevated during passive rewarming such that values were higher compared to the control and Ascorbic Acid sites throughout the 90min of passive rewarming (P<0.001 main effect of Fasudil). These findings indicate that the Rho-kinase pathway contributes to pronounced vasoconstriction during cryotherapy as well as the sustained vasoconstriction during the subsequent rewarming period post treatment.

An Optogenetic Test for the Functional Specificity of Bulbospinal Sympathoexcitatory Neurons

Sympathetic preganglionic neurons are functionally specialised, each belonging to one of a limited number of functional classes (e.g. muscle vasoconstrictor, cutaneous vasoconstrictor, sudomotor). How far this functional specificity applies to the premotor neurons that drive them is uncertain. We devised an optogenetic test for the existence of premotor neurons that are collateralised to drive more than one functional class of sympathetic neuron.Bulbospinal neurons were transduced by a retrogradely transported viral vector (canine adenovirus) encoding Cre recombinase (CAV‐CMV‐Cre; provided by Eric Kremer, Montpellier). This was injected around sympathetic preganglionic neurons at the T12‐L1 spinal levels. At the same time, a Cre‐activated adeno‐associated virus (AAV) encoding Channelrhodopsin‐2 (ChR2) and the fluorescent label mCherry (AAV1.EF1.dflox.hChR2(H134R)‐mCherry.WPRE.hGH; provided by Deisseroth, Stanford via UPenn) was injected into the left RVLM. Only neurons transduced by both viral vectors should then express the ChR2 and mCherry. Spinal injections were made at T12‐L1 because they were considered unlikely to overlap with the preganglionic supply to the heart. The bulbospinal presynaptic terminals infected with CAV‐Cre were thus presumably on preganglionic neurons that supplied end organs such as hindlimb muscle, but not the heart.Terminal functional experiments under urethane anaesthesia were performed 2–8 weeks after the viral injections. Activity was simultaneously recorded from the left cardiac and lumbar sympathetic nerves, whilst pulses of blue laser light (473 nm, 10–12 mW, 20 ms) were flashed onto the left RVLM through a 100 μm diameter fibre‐optic probe.In about one‐third of experiments, we were able to show functional activation of sympathetic nerves that was time‐locked to the flashed laser light. In all successful experiments, we found cardiac sympathetic activation as well as lumbar sympathetic activation (peak response latencies 135–150 ms and 215–230 ms, respectively). Subsequent fluorescence microscopy on brainstem sections confirmed the presence of small numbers of mCherry expressing bulbospinal neurons in those rats.This study demonstrates that at least some bulbospinal neurons send excitatory synaptic inputs to preganglionic neurons of more than one functional type. It also demonstrates the feasibility of using anatomically‐based optogenetic transduction as a test for functional collateralisation in central pathways.Support or Funding InformationAustralian Research Council DP13014661

Oral L‐Tyrosine Supplementation Augments Cutaneous Vasoconstriction to Whole Body Cooling

Healthy older adults exhibit a blunted cutaneous vasoconstriction (VC) response to cold exposure, which increases their susceptibility to rapid heat loss and hypothermia. We hypothesized that oral supplementation of L‐tyrosine, the primary substrate for catecholamine biosynthesis, would augment the VC response to gradual whole‐body cooling (Tsk = 30.5 °C) in older adults. Eleven young (Y = 24±1 years) and eleven older (O = 68±4‐‐‐‐‐‐ years) participants completed a randomized, double‐blinded, placebo‐controlled, cross‐over study consisting of two visits separated by &gt;3 days. At the beginning of each visit, participants ingested either 150 mg/kg L‐tyrosine or placebo. An hour after consumption, whole‐body cooling commenced, causing a gradual decline in skin temperature from 34 to 30.5 °C over a 30 minute period. Laser Doppler flux (LDF) was measured at the ventral forearm and cutaneous vascular conductance (CVC) was calculated as CVC = LDF/mean arterial pressure and expressed as a percent change from baseline (%ΔCVC). Two minutes of static handgrip exercise (35% MVC) followed by 3 minutes of post‐exercise ischemia was implemented before and toward the end of the cooling bout. No changes in blood pressure or heart rate were identified with tyrosine supplementation. However, the VC response to whole‐body cooling was blunted in older adults (Placebo: Y = 29±3; O = 21±5 %ΔCVC) and this was augmented with tyrosine supplementation (Tyrosine: Y = 37±5; O = 31±4 %ΔCVC; p&lt;0.05). These results indicate that oral L‐tyrosine supplementation restores the VC response to whole‐body cooling in older adults. This suggests that L‐tyrosine may be a limiting factor in the full expression of the cutaneous VC response and supplementation may help maintain body core temperature during cold exposure particularly in an older population.Support or Funding InformationDMU IOER Grant 03‐14‐01

The role of metaboreceptor on exercise in hyperthermic environment with college basketball players.

The objective of this study is to review physiological differences of college basketball players cardiovascular responses and group IV metaboreceptor interactions appearing post muscular ischemia exercise (PEMI) caused by a static handgrip exercise (SHE). The subjects were placed in a temperature and moisture stabilized indoor environment for 2 h in order to measure blood pressure. For the SHE, maximal voluntary contraction of arms with a relative strength of 50 % of the maximum muscular strength was put into isometric training for 2 min. After completing the exercises, cuffs worn on the arms of the subjects were pressurized up to 200 mmHg by applying PEMI to block the artery and vein. In this way, the cardiovascular responses created by SHE and PEMI were measured. Blood samples of subjects were collected from the vein of each upper arm before SHE and after PEMI to measure the metabolite hormone and catecholamine in the blood. Results from the measurements showed a significant decrease of blood pressure under high temperature environments compared to normal temperature environments. With respect to PEMI, increases in blood pressure under the high temperature environment were significantly lower compared to the normal temperature environment. In conclusion, this study revealed that college basketball players with good physical strength had higher sensitivities of arterial baroreceptor. However, blood pressure was not increased accordingly because the increase of cutaneous vasoconstriction due to stimuli of the metaboreceptor under a high temperature environment could not be compensated by arterial baroreflex due to the increase of total vascular conductance.

Central neural control of thermoregulation and brown adipose tissue.

Central neural circuits orchestrate the homeostatic repertoire that maintains body temperature during environmental temperature challenges and alters body temperature during the inflammatory response. This review summarizes the experimental underpinnings of our current model of the CNS pathways controlling the principal thermoeffectors for body temperature regulation: cutaneous vasoconstriction controlling heat loss, and shivering and brown adipose tissue for thermogenesis. The activation of these effectors is regulated by parallel but distinct, effector-specific, core efferent pathways within the CNS that share a common peripheral thermal sensory input. Via the lateral parabrachial nucleus, skin thermal afferent input reaches the hypothalamic preoptic area to inhibit warm-sensitive, inhibitory output neurons which control heat production by inhibiting thermogenesis-promoting neurons in the dorsomedial hypothalamus that project to thermogenesis-controlling premotor neurons in the rostral ventromedial medulla, including the raphe pallidus, that descend to provide the excitation of spinal circuits necessary to drive thermogenic thermal effectors. A distinct population of warm-sensitive preoptic neurons controls heat loss through an inhibitory input to raphe pallidus sympathetic premotor neurons controlling cutaneous vasoconstriction. The model proposed for central thermoregulatory control provides a useful platform for further understanding of the functional organization of central thermoregulation and elucidating the hypothalamic circuitry and neurotransmitters involved in body temperature regulation.

Human physiological responses to cold exposure: Acute responses and acclimatization to prolonged exposure.

Cold exposure in humans causes specific acute and chronic physiological responses. This paper will review both the acute and long-term physiological responses and external factors that impact these physiological responses. Acute physiological responses to cold exposure include cutaneous vasoconstriction and shivering thermogenesis which, respectively, decrease heat loss and increase metabolic heat production. Vasoconstriction is elicited through reflex and local cooling. In combination, vasoconstriction and shivering operate to maintain thermal balance when the body is losing heat. Factors (anthropometry, sex, race, fitness, thermoregulatory fatigue) that influence the acute physiological responses to cold exposure are also reviewed. The physiological responses to chronic cold exposure, also known as cold acclimation/acclimatization, are also presented. Three primary patterns of cold acclimatization have been observed, a) habituation, b) metabolic adjustment, and c) insulative adjustment. Habituation is characterized by physiological adjustments in which the response is attenuated compared to an unacclimatized state. Metabolic acclimatization is characterized by an increased thermogenesis, whereas insulative acclimatization is characterized by enhancing the mechanisms that conserve body heat. The pattern of acclimatization is dependent on changes in skin and core temperature and the exposure duration.

Abstract OT3-02-08: Scalp cooling alopecia prevention trial (SCALP) for patients with early stage breast cancer

Abstract Background Adjuvant chemotherapy treats micro-metastatic disease and decreases the risk of breast cancer recurrence. However, it may be associated with distressing side effects, including alopecia. Women with breast cancer rate chemotherapy-induced alopecia as one of the most severe, troublesome, and distressing side effects of chemotherapy. In many countries, scalp cooling has been introduced to prevent or reduce chemotherapy-induced alopecia. The theory is that scalp cooling causes cutaneous vasoconstriction, which reduces blood flow to the hair follicles during peak plasma concentrations of the chemotherapeutic agents and therefore reduces cellular uptake of these agents. It also results in reduced biochemical activity, which makes hair follicles less susceptible to the damage of the chemotherapy agents. Historically success rates are have been variable, but based on non-randomized studies, scalp cooling appears to be effective in preventing chemotherapy-induced alopecia especially in more recent studies. Methods We are conducting a prospective multi-center randomized controlled non-blinded trial to evaluate the safety and efficacy of the Orbis Paxman Hair Loss Prevention System in reducing the incidence of chemotherapy-induced alopecia. Women with stage I-II breast cancer who will receive neoadjuvant or adjuvant anthracycline- or taxane-based chemotherapy, for at least four cycles are eligible. Participants are randomized in a 2:1 ratio to scalp-cooling or no cooling. Scalp-cooling is done using the Orbis Paxman Hair Loss Prevention System prior to, during and after each chemotherapy administration. The primary efficacy endpoints are hair preservation, defined as CTCAE v4 alopecia &amp;lt;2, and device safety. Two hundred and thirty five (235) patients are planned to be enrolled which will provide 85% power to detect a 20% difference in hair preservation, 15% in control group and 35% in scalp-cooling group . Secondary endpoints include: wig/scarf use and quality of life assessed by the EORTC QLQ-30, HADS and BIS. Study participants will be followed for 5 years post-study for time to first recurrence, overall survival, site of first recurrence, and incidence of isolated scalp metastasis. Citation Format: Nangia JR, Wang T, Rude M, Osborne C, Papish S, Abraham J, Holmes F, Savin M, Paxman R, Hilsenbeck SG, Osborne CK, Rimawi M. Scalp cooling alopecia prevention trial (SCALP) for patients with early stage breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT3-02-08.