Controlling Morphing Behavior in 4D Printing: A Review About Microstructure and Macrostructure Changes in Polylactic Acid.

Four-dimensional (4D) printing combines stimulus-responsive materials with additive manufacturing (AM) technologies. This new concept of printing three-dimensional (3D) objects opens the possibility for solving processing issues, through the production of complex geometries that can undergo programmed temporal changes in response to external stimuli. However, as 4D technology emerges from AM, various challenges still need to be explored, such as the controlled morphing effect. Understanding the aspects related to this behavior, both at the macroscopic level of the structure and at the microscopic level of the polymeric chain, is fundamental. Focused on thermoplastic poly(lactic acid) (PLA) printed by fused deposition modeling, this review addressed the influence of molecular weight, polymeric chain modifications, and 3D printing parameters on the shape change effect of a PLA-based material. The glass transition temperature proved to be a highly important parameter, which can be modified by molecular weight changes. Nozzle temperature, fill density, print patterns, and raster angle are 3D printing parameters that influence the material shape change. Shape recovery is highly dependent on the recovery temperature. Potential applications for shape memory structures are also addressed in this review.

Stimuli-Responsive Functional Micro-/Nanorobots: A Review.

Stimuli-responsive functional micro-/nanorobots (srFM/Ns) are a class of intelligent, efficient, and promising microrobots that can react to external stimuli (such as temperature, light, ultrasound, pH, ion, and magnetic field) and perform designated tasks. Through adaptive transformation into the corresponding functional forms, they can perfectly match the demands depending on different applications, which manifest extremely important roles in targeted therapy, biological detection, tissue engineering, and other fields. Promising as srFM/Ns can be, few reviews have focused on them. It is therefore necessary to provide an overview of the current development of these intelligent srFM/Ns to provide clear inspiration for further development of this field. Hence, this review summarizes the current advances of stimuli-responsive functional microrobots regarding their response mechanism, the achieved functions, and their applications to highlight the pros and cons of different stimuli. Finally, we emphasize the existing challenges of srFM/Ns and propose possible strategies to help accelerate the study of this field and promote srFM/Ns toward actual applications.

The Antinociceptive Effect of Magnesium Sulphate Administered in the Epidural Space in Standing Horses.

To study the antinociceptive properties of epidural magnesium sulphate (MgSO4) in standing horses Experimental, placebo-controlled, masked, cross-over A group of six healthy horses Through an epidural catheter, 1 mg kg -1 MgSO4 (treatment Mg) diluted to a volume of 15 mL or the same volume of saline (treatment S) was administered over 15 minutes. Electrical, thermal and mechanical nociceptive thresholds were determined on the pelvic limb before and 20, 40, 60, 80, 100, 120, 140, 160 and 180 minutes after the start of the injection. Heart rate (HR) and respiratory frequency (fR) were recorded every 10 minutes. Blood samples were collected before treatment and every 30 minutes throughout the study period. Data were assessed for normality using a Shapiro-Wilk test. A linear mixed model with horse as random effect and time, treatment and their interaction as fixed effects was used. Treatments were compared at 20, 60, 120 and 180 minutes using the Wilcoxon rank sum test stratified for horse (global α = 0.05, with Bonferroni correction α = 0.0125). Epidural MgSO4 caused a significant increase in the electrical threshold (mA) (P = .0001), but no significant differences in thermal and mechanical nociceptive thresholds. During the injection of MgSO4, two horses collapsed. One stood up within 20 minutes and was able to continue the study, the second one was excluded. A significant difference was found for HR at T180 (Mg 44 ± 23 beats minute-1; S 32 ± 9 beats minute-1) (P = .0090). Epidural administration of MgSO4 caused an increase in the electrical threshold of the pelvic limbs of horses. Caution is warranted however, as with the current dose, 2 horses collapsed.

Intravenous Magnesium Sulphate in Standing Horses: Effects on Physiological Parameters, Plasma Concentration of Magnesium and Nociceptive Threshold Tests☆.

A bolus of 50 mg kg -1 MgSO4 (treatment Mg) or the same volume of saline (treatment S) was infused over 15 minutes in 5 adult healthy horses. T0 was the end of the infusion. Physiological parameters were recorded throughout the study period. Measurements of electrical, thermal, and mechanical nociceptive thresholds were performed at the pelvic limbs at baseline (before T0), and at specific timepoints. Blood samples were taken at fixed timepoints before, during and until 12 hours after the infusion. For statistical analysis, the 95% confidence intervals (CI's) for the differences in nociceptive thresholds between treatments were calculated. Physiological parameters were compared using a linear mixed model (global α = 0.05, with Bonferroni correction α = 0.0125). The concentrations of ions were also compared with the baseline values at specific timepoints, using a linear mixed model. The Pearson's correlation coefficient was derived between the ion concentrations. The 95% CI's of thermal, mechanical and electrical thresholds were [-1; +2]°C, [0; +3] N and [-1; +1] mA (positive differences indicate higher thresholds for treatment Mg), respectively. Heart rate was significantly higher (P < .0001) and non-invasive systolic arterial pressure (P < .0001) and respiratory rate (P = .0002) significantly lower after treatment Mg compared to treatment S. Additionally, non-invasive systolic arterial pressure was significantly different at T45 (P < .001). Although mild changes in cardiovascular parameters and plasma concentrations were seen with intravenous administration of MgSO4, no changes in nociceptive thresholds were detected in standing non-sedated horses.

Insufficient ablation promotes the metastasis of residual non-small cell lung cancer (NSCLC) cells via upregulating carboxypeptidase A4.

BACKGROUND: Thermal ablation is a potentially curative therapy for early-stage non-small cell lung cancer (NSCLC). Early recurrence after thermal ablation necessitates our attention. METHODS: The invasion and migration abilities of NSCLC after sublethal heat stimulus were observed in vitro and in vivo. Sublethal thermal stimulus molecular changes were identified by RNA sequencing. A xenograft model of NSCLC with insufficient ablation was established to explore the epithelial-to-mesenchymal transition (EMT) and metastasis-related phenotypes alteration of residual tumors. RESULTS: In vitro, the invasion and migration abilities of NSCLC cells were enhanced 72 h after 44 °C and 46 °C thermal stimulus. Epithelial-mesenchymal transition (EMT) phenotypes were also upregulated under these conditions. RNA sequencing revealed that the expression of carboxypeptidase A4 (CPA4) was significantly upregulated after thermal stimulus. Significant upregulation of CPA4 and EMT phenotypes was also found in the xenograft model of insufficient NSCLC ablation. The EMT process and invasion and migration abilities can be reversed by silencing CPA4. CONCLUSIONS: This study demonstrates that sublethal heat stimulus caused by insufficient ablation can promote EMT and enhance the metastatic capacity of NSCLC. CPA4 plays an important role in these biological processes. Inhibition of CPA4 might be of great significance for improving early-stage NSCLC survival after ablation.

Effect of Photobiomodulation Therapy following Direct Pulp Capping on Postoperative Sensitivity by Thermal Stimulus: A Retrospective Study.

OBJECTIVE: The aim of this study was to investigate the effect of photobiomodulation therapy (PBMT) on postoperative pain provoked by thermal stimulation in direct pulp capping (DPC). SUBJECTS AND METHODS: A retrospective study was performed using the records of patients who received DPC using mineral trioxide aggregate. Teeth irradiated with a laser were assigned as the PBMT group, and nonirradiated teeth were considered as the control group. Before treatment and 6 h, 1 day, and 7 days after treatment, tooth sensitivity to a cold stimulus was recorded using a visual analog scale. RESULTS: From a total of 123 documented DPC procedures, only 72 directly capped permanent teeth met the inclusion criteria. Age, gender, and tooth location were comparable between the groups. A statistically significant difference was found in sensitivity to cold stimulus between groups on day 7 (p = 0.007), but no difference was found at the preoperative, 6 h, and day 1 time points (p = 0.055, p = 0.132, and p = 0.100, respectively). In the intragroup evaluation, a significantly greater decrease in sensitivity to cold stimulus was detected in the PBMT group than that in the control group, although both groups showed a reduction in discomfort throughout the follow-up period (p = 0.000). CONCLUSION: PBMT is an effective method for enhancing patient comfort by reducing thermal sensitivity following DPC procedures.

Influence of Thermal and Mechanical Stimuli on the Behavior of Al-CAU-13 Metal-Organic Framework.

The response of the metal-organic framework aluminum-1,4-cyclohexanedicarboxylate or Al-CAU-13 (CAU: Christian Albrecht University) to the application of thermal and mechanical stimuli was investigated using synchrotron powder X-ray diffraction (SPXRD). Variable temperature in situ SPXRD data, over the range 80-500 K, revealed a complex evolution of the structure of the water guest containing Al-CAU-13H2O, the dehydration process from ca. 310 to 370 K, and also the evolution of the guest free Al-CAU-13 structure between ca. 370 and 500 K. Rietveld refinement allowed this complexity to be rationalized in the different regions of heating. The Berman thermal Equation of State was determined for the two structures (Al-CAU-13H2O and Al-CAU-13). Diamond anvil cell studies at elevated pressure (from ambient to up to ca. 11 GPa) revealed similarities in the structural responses on application of pressure and temperature. The ability of the pressure medium to penetrate the framework was also found to be important: non-penetrating silicone oil caused pressure induced amorphization, whereas penetrating helium showed no plastic deformation of the structure. Third-order Vinet equations of state were calculated and show Al-CAU-13H2O is a hard compound for a metal-organic framework material. The mechanical response of Al-CAU-13, with tetramethylpyrazine guests replacing water, was also investigated. Although the connectivity of the structure is the same, all the linkers have a linear e,e-conformation and the structure adopts a more open, wine-rack-like arrangement, which demonstrates negative linear compressibility (NLC) similar to Al-MIL-53 and a significantly softer mechanical response. The origin of this variation in behavior is attributed to the different linker conformation, demonstrating the influence of the S-shaped a,a-conformation on the response of the framework to external stimuli.

N-isopropyl chitosan. A pH- and thermo-responsive polysaccharide for gel formation.

The present contribution deals with the synthesis and characterization of N-isopropyl chitosan in which the introduction of hydrophobic groups leads to an increased flexibility of the polysaccharide backbone. The isopropyl groups extend the solubility of the modified-chitosan samples and render the modified chitosan a pH- and thermo-sensitive system for hydrogel formation. Indeed, upon varying the pH of the system and/or its temperature within a range compatible with biological applications, a non-reversible sol-gel transition occurs, as determined through extended rheological analyses. The modified chitosan samples show a very good biocompatibility as determined through preliminary viability and cell growth experiments.

Effect of Sex and Menstrual Cycle on Skin Sensory Nerve Contribution to Local Heating.

The purpose of this study was to determine sex differences in the contribution of sensory nerves to rapid cutaneous thermal hyperemia. Healthy young females (n = 15, tested during both the early follicular (EF) and the mid-luteal (ML) phase of the menstrual cycle) and males (n = 15) had a 4 cm2 area of skin on one forearm and one leg treated with a eutectic mixture of local anesthetic (EMLA). EMLA sites, along with corresponding control sites, were instrumented with laser Doppler flowmetry probes and local skin heaters. Baseline (33 °C), rapid and sustained vasodilation (42 °C), and maximal vasodilation (44 °C) skin blood flow data were obtained and expressed as a percentage of maximal cutaneous vascular conductance (%CVCmax). Contribution of sensory nerve involvement was determined by comparing the EMLA site to its matched control site utilizing the formula [(% CVCmax control - % CVCmax treatment) / % CVCmax control] × 100. The contribution of sensory nerves to rapid cutaneous thermal hyperemia in the forearm was 24 ± 18 %CVCmax in males, 41 ± 17 %CVCmax in ML females (p = 0.02 vs. males), and 35 ± 17 %CVCmax in EF females (p > 0.05 vs. males). In the leg, the contribution of sensory nerves was 16 ± 15 %CVCmax in males, 34 ± 17 %CVCmax for ML females (p = 0.02 vs. males), and 28 ± 21 %CVCmax in EF females (p > 0.05 vs. males). ML females exhibited a greater contribution of sensory nerves to rapid cutaneous thermal hyperemia in the forearm and leg, possibly attributed to elevated reproductive hormones during the ML phase.

Reversible Thermal Gradient Device to Control Biased Thermotactic Response of C. elegans.

C. elegans exhibits a directional migration toward a remembered temperature setpoint (Ts) by activating thermo-sensorimotor neurons. While cryophilic thermotaxis is well reproduced, thermophilic thermotaxis requires very stringent temperature regulations - otherwise, worms exhibit random migration in colder side of Ts. Here, we introduce a thermal stimulus device developed to control worms with different thermotactic behaviors on both colder and warmer sides of the Ts. On a linear gradient, the worm population displayed a Gaussian distribution near Ts but in a skewed shape with a peak shifted to the colder side due to their atactic motion in colder temperature than Ts. By repetitive application of thermal gradient-reversals, we found that their population density became higher near Ts because the speed at which the worms accumulate toward Ts was much faster than that of the dispersion by diffusion to the cold side, resulting in forced aggregation of worms at the desired temperature.

Sedative and antinociceptive effects of different detomidine constant rate infusions, with or without methadone in standing horses.

BACKGROUND: Standing surgery avoids the risks of general anaesthesia in horses. OBJECTIVES: To assess sedation, antinociception and gastrointestinal motility in standing horses after a detomidine loading dose and 2-h constant rate intravenous (i.v.) infusion, with or without methadone. STUDY DESIGN: Blinded, randomised, crossover with seven healthy adult cross-bred horses, three geldings and four females (404 ± 22 kg). METHODS: Five i.v. treatments were administered to all horses with 1-week washout period: saline (SAL), detomidine low (2.5 µg/kg bwt + 6.25 µg/kg bwt/h) (DL) and high doses (5 µg/kg bwt + 12.5 µg/kg bwt/h) (DH) alone or combined with methadone (0.2 mg/kg bwt + 0.05 mg/kg bwt/h), (DLM) and (DHM), respectively. Height of head above the ground (HHAG), electrical (ET), thermal (TT) and mechanical (MT) nociceptive thresholds and gastrointestinal motility were evaluated at predetermined times between 5 and 240 min. A mixed effect model and Kruskal-Wallis test were used to analyse normally and non-normally distributed data, respectively. RESULTS: Sedation (<50% basal HHAG) was achieved for the duration of the infusion, and for an additional 15 min in DH and DHM groups. Nociceptive thresholds were higher than baseline, to the greatest degree and the longest duration, with DHM (ET and TT for 135 min and MT for 150 min). After DH, TT was significantly higher than baseline from 30 to 120 min and MT from 15 to 135 min. After DLM, ET was increased at 90 min, TT at 30 min and MT for 120 min. Gastrointestinal motility was reduced for up to 135 min after DL, 150 min after DLM and 210 min after DH and DHM. MAIN LIMITATIONS: Nociceptive thresholds are not equivalent to surgical stimuli. CONCLUSION: Methadone with the highest detomidine dose (DHM) may provide sufficient sedation and analgesia for standing surgical procedures and warrants further investigation.

Development of a Fully Flexible Sheet-Type Tactile Display Based on Electrovibration Stimulus.

Tactile displays have been extensively studied for several decades. However, owing to their bulkiness and stiffness, it has been difficult to integrate these displays with information devices to enable tactile communication between the devices and their users. This paper proposes a novel sheet-type electrovibration tactile display that consists of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate conductive layers and an insulation layer of polydimethylsiloxane. The tactile display is sufficiently thin and flexible for attaching onto various surfaces. In this study, the tactile display was micro-fabricated and characterized through experiments. The experimental results indicated that the tactile display exhibited good durability under bending and that it could present various tactile sensations depending on the type of voltage waveform. In addition, the effect of using a combination of electrovibration and thermal stimuli was also demonstrated. The sheet-type display was attached onto a Peltier element; the thinness of the structure enabled the display to conform to the element and ensure good heat transfer. In the experiment, subjects were asked to scan the display with their fingertips. The results showed that multiple tactile stimuli were also successfully perceived by the subjects.

A novel method to assess the potential role of sweating abnormalities in the pathogenesis of atopic dermatitis.

Although atopic dry skin is believed to be caused by defects in skin genes important for maintaining skin barrier function, the role of sweat in atopic dermatitis (AD) has been apparently underestimated. Given the great capacity of sweat to maintain and increase skin hydration, defective sweating responses may be a logical place to look for changes that predispose individuals to the disease. We investigated how disease process and sweating defects progress from early asymptomatic stages to the onset of clinically apparent disease by employing the impression mould technique, which allows an accurate quantification of individual sweat gland/duct activity in relation to skin surface topography. Insensible and sensible sweating responses under baseline conditions and after thermal stimulus, respectively, were measured in various stages of AD patients and healthy controls. In controls, under baseline conditions, sweat ducts/glands at the dermal folds secreted basal levels of sweat (insensible sweating), thereby maintaining skin hydration. Not only such insensible sweating but also sensible sweating markedly decreased even in the earliest asymptomatic stage and the decrease was followed by compensatory hyperhidrosis at the ridge: leakage of sweat into the dermis could represent the initial event resulting in the decreased sweating and inflammation. The defects eventually progressed involving all of the ducts/glands to develop systemic dry skin. AD skin is characterized by varying degrees of functional impairment of sweat ducts/glands depending on the stage, and this defect would be among the reasons for the inability of AD patients to maintain skin hydration.

Sedative and antinociceptive effects of different combinations of detomidine and methadone in standing horses.

OBJECTIVE: To evaluate intravenous (IV) detomidine with methadone in horses to identify a combination which provides sedation and antinociception without adverse effects. STUDY DESIGN: Randomized, placebo-controlled, blinded, crossover. ANIMALS: A group of eight adult healthy horses aged (mean ± standard deviation) 7 ± 2 years and 372 ± 27 kg. METHODS: A total of six treatments were administered IV: saline (SAL); detomidine (5 µg kg-1; DET); methadone (0.2 mg kg-1; MET) alone or combined with detomidine [2.5 (MLD), 5 (MMD) or 10 (MHD) µg kg-1]. Thermal, mechanical and electrical nociceptive thresholds were measured, and sedation, head height above ground (HHAG), cardiopulmonary variables and intestinal motility were evaluated at 5, 15, 30, 45, 60, 75, 90, 120 and 180 minutes. Normal data were analyzed by mixed-model analysis of variance and non-normal by Kruskal-Wallis (p < 0.05). RESULTS: Nociceptive thresholds in horses administered methadone with the higher doses of detomidine (MMD, MHD) were increased above baseline to a greater degree and for longer duration (MMD: 15-30 minutes, MHD: 30-60 minutes) than in horses administered low dose with methadone or detomidine alone (MLD, DET: 5-15 minutes). No increases in nociceptive thresholds were recorded in SAL or MET. Compared with baseline, HHAG was lower for 30 minutes in MMD and DET, and for 45 minutes in MHD. No significant sedation was observed in SAL, MET or MLD. Intestinal motility was reduced for 75 minutes in MHD and for 30 minutes in all other treatments. CONCLUSIONS: Methadone (0.2 mg kg-1) potentiated the antinociception produced by detomidine (5 µg kg-1), with minimal sedative effects. CLINICAL RELEVANCE: Detomidine (5 µg kg-1) with methadone (0.2 mg kg-1) produced antinociception without the adverse effects of higher doses of detomidine.

Duration of Venodilation for Peripheral Intravenous Cannulation, as Induced by a Thermal Stimulus on the Forearm.

BACKGROUND: Application of a thermal stimulus is a common procedure used to promote venodilation for peripheral intravenous cannulation (PIVC); however, the effects of thermal stimulation on the duration of venodilation and skin temperature of the forearm are unclear. AIM: To investigate the duration of venodilation induced by a thermal stimulus on the forearm. METHOD: Healthy female adults ( N = 40) from Japan participated in this study from November to December 2013. A heat pack was warmed to 40°C ± 2°C and placed over the forearm for 15 min. Vein diameter was measured via ultrasound and skin temperature via temperature sensor at six time points: before application of the thermal stimulus and at 1-min intervals for 5 min upon removal of the thermal stimulus. The main outcomes were vein diameter, proportional change in vein diameter, and skin temperature. We calculated proportional change in vein diameter after application of the thermal stimulus using vein diameter before the thermal stimulus to represent 100%. RESULTS: Compared with vein diameter before thermal stimulus, the diameter at each time point after thermal stimulus was significantly increased ( p < .05) as were proportional change in vein diameter ( p < .05) and skin temperature. CONCLUSION: A thermal stimulus of 40°C ± 2°C on the forearm dilated veins significantly for PIVC, and the effect persisted for at least 5 min.

Comparison of the Efficacy of Two Different Desensitizing Agents: A Randomized Controlled Trial.

AIM: To evaluate and compare the efficacy of oxalate-containing desensitizer BisBlock™ and glutaraldehyde-containing desensitizer Gluma©. MATERIALS AND METHODS: A subject-blind randomized controlled trial was conducted among 50 adult patients of age ranging from 18 - 65 years who self-reported dentine hypersensitivity. Each participant with at least one tooth with hypersensitivity in two different quadrants and showing a response of ≥ 3 on a visual analogue scale (VAS) to an evaporative stimulus was included in the study. The teeth were evaluated immediately after treatment, and after 24 hrs, one week, one month and 3 months from the baseline after application of BisBlock™, an oxalate-containing desensitizer, and Gluma©, a glutaraldehyde-containing desensitizer. RESULTS: Fifty participants were enrolled in the study. Means and standard deviations of VAS scores were calculated. The level of significance was set to p < 0.05. Statistically significant reduction in mean scores was found after application of Gluma© and BisBlock™ desensitizer (p < 0.001) at all time intervals. BisBlock™ yielded a statistically significant greater reduction in dentine hypersensitivity at 1 week (p < 0.05) and 1 month (p < 0.01) with evaporative stimulus. CONCLUSION: Compared with Gluma©, BisBlock™ gave statistically significantly greater reduction in hypersensitivity.

Value of Quantitative Sensory Testing in the Evaluation of Genital Sensation: Its Application to Female Sexual Dysfunction.

INTRODUCTION: Female sexual dysfunction (FSD) is multifactorial, with psychological and organic elements. Genital sensation, an important component of sexual response, has until recently not been subjected to adequate clinical appraisal. During the past 15 years we have performed Quantitative Sensory Testing (QST) to assess genital sensation in healthy women and women with FSD. AIM: To review available evidence of QST in the investigation of genital sensation in women with FSD. METHODS: We examined data obtained from assessment of genital sensation in normal women and those with different conditions, including multiple sclerosis, pelvic floor disorders, effect of hysterectomy, and vulvar vestibulitis. MAIN OUTCOME MEASURE: Use of QST for assessment of FSD. RESULTS: Normograms for healthy women were used to measure parameters during arousal, orgasm, and the refractory phase. Using QST, genital sensation was found to be impaired in women with multiple sclerosis. Clitoral vibratory sensation most significantly correlated with FSD parameters. Women with greater deficit in vibratory sensation encountered more sexual dysfunction. Women with urinary incontinence had a significant decrease in sensitivity to warm, cold, and vibratory thresholds in the anterior vaginal wall and clitoral area. A study comparing women with and without pelvic organ prolapse showed mean thresholds for vibratory and warm stimuli to be significantly higher and mean thresholds for cold stimuli to be significantly lower in the group with prolapse. QST of women undergoing hysterectomy showed a significant decrease in sensation to cold, warm, and vibratory stimuli at the anterior and posterior vaginal wall; clitoral thermal and vibratory sensation thresholds remained unchanged after surgery. In a study of vulvar vestibulitis, patients reported significantly lower heat pain thresholds compared with controls. CONCLUSION: QST appears useful for evaluating various gynecologic disorders associated with disturbed sexual function and with multiple sclerosis, which might be accompanied by disturbed genital sensation.

Thermal Sensitivity and Dimethyl Sulfoxide (DMSO).

Dimethyl sulfoxide (DMSO) is commonly used as a solvent for hydrophobic substances, but the compound's innate bioactivity is an area of limited understanding. In this investigation we seek to determine the analgesic potential of DMSO. We addressed the issue by assessing the perception of thermal pain stimulus, using a 55 °C hotplate design, in conscious mice. The latency of withdrawal behaviors over a range of incremental accumulative intraperitoneal DMSO doses (0.5-15.5 g/kg) in the same mouse was taken as a measure of thermal endurance. The findings were that the latency, on average, amounted to 15-30 s and it differed inappreciably between the sequential DMSO conditions. Nor was it different from the pre-DMSO control conditions. Thus, DMSO did not influence the cutaneous thermal pain perception. The findings do not lend support to those literature reports that point to the plausible antinociceptive potential of DMSO as one of a plethora of its innate bioactivities. However, the findings concern the mouse's footpad nociceptors which have specific morphology and stimulus transduction pathways, which cannot exclude DMSO's antinociceptive influence on other types of pain or in other types of skin. Complex and as yet unresolved neural mechanisms of perception of cutaneous noxious heat stimulus should be further explored with alternative experimental designs.

Antinociceptive effects of methadone combined with detomidine or acepromazine in horses.

REASONS FOR PERFORMING STUDY: To investigate two protocols to provide antinociception in horses. OBJECTIVES: To evaluate the antinociceptive effects of intravenous methadone combined with detomidine or acepromazine in adult horses. STUDY DESIGN: Randomised, blinded, crossover study. METHODS: Mechanical, thermal and electrical stimuli were applied to the dorsal left and right metacarpus and coronary band of the left thoracic limb, respectively. A thermal stimulus was applied caudal to the withers. The horses were treated with saline (C), a combination of methadone (0.2 mg/kg bwt) and detomidine (10 µg/kg bwt) (MD) or methadone (0.2 mg/kg bwt) and acepromazine (0.05 mg/kg bwt) (MA) at 1 week intervals. Nociceptive thresholds were measured before and at 15 min intervals until 150 min after treatment. Wilcoxon rank-sum and Wilcoxon signed rank tests were used to compare data between groups at each time point and over time within each group, followed by the Bonferroni method to adjust the P value. RESULTS: The mechanical stimulus was the most sensitive test to differentiate the antinociceptive effects of the treatments. Mechanical thresholds were greater after MD than MA between 15 and 30 min and with both MD and MA these thresholds were greater than C from 15 to 60 min. Electrical and thermal limb thresholds were greater after MD than C at 15 and 45 min and at 15, 30, 45, 75 and 105 min, respectively. Thermal limb thresholds were greater with MA than C at 30 min. Thoracic thermal threshold in MD and MA were higher than C at 45, 75, 90 and 120 min and from 30 to 75 min, respectively. CONCLUSIONS: Methadone and acepromazine produced less pronounced mechanical antinociception than MD.

Validation of mechanical, electrical and thermal nociceptive stimulation methods in horses.

REASONS FOR PERFORMING STUDY: To validate a model for investigating the effects of analgesic drugs on mechanical, thermal and electrical stimulation testing. OBJECTIVES: To investigate repeatability, sensitivity and specificity of nociceptive tests. STUDY DESIGN: Randomised experiment with 2 observers in 2 phases. METHODS: Mechanical (M), thermal (TL) and electrical (E) stimuli were applied to the dorsal metacarpus (M-left and TL-right) and coronary band of the left thoracic limb (E) and a thoracic thermal stimulus (TT) was applied caudal to the withers in 8 horses (405 ± 43 kg). Stimuli intensities were increased until a clear avoidance response was detected without exceeding 20 N (M), 60°C (TL and TT) and 15 V (E). For each set of tests, 3 real stimuli and one sham stimulus were applied (32 per animal) using a blinded, randomised, crossover design repeated after 6 months. A distribution frequency and, for each stimulus, Chi-square and McNemar tests compared both the proportion of positive responses detected by 2 observers and the 2 study phases. The κ coefficients estimated interobserver agreement in determining endpoints. Sensitivity (384 tests) and specificity (128 tests) were evaluated for each nociceptive stimulus to assess the evaluators' accuracy in detecting real and sham stimuli. RESULTS: Nociceptive thresholds were 3.1 ± 2 N (M), 8.1 ± 3.8 V (E), 51.4 ± 5.5°C (TL) and 55.2 ± 5.3°C (TT). The level of agreement after all tests, M, E, TL and TT, was 90, 100, 84, 98 and 75%, respectively. Sensitivity was 89, 100, 89, 98 and 70% and specificity 92, 97, 88, 91 and 94%, respectively. CONCLUSIONS: The high interobserver agreement, sensitivity and specificity suggest that M, E and TL tests are valid for pain studies in horses and are suitable tools for investigating antinociceptive effects of analgesics in horses.