Ischemic pain nonsegmentally produces a predominant reduction of pain and thermal sensitivity in man: A selective role for endogenous opioids

Ischemic pain was produced by a blood pressure cuff placed to the arm of healthy human subjects for 15 min which produced a mean pain score of 59% (visual analogue scale). Ischemia induced a significant dental pain threshold elevation (mean 67%) and 2 mg of naloxone did not reduce it. Thermal sensitivity of the upper lip had a tendency to reduction during ischemia and 2 mg of naloxone reduced this effect. Tactile thresholds in the forehead or in the contralateral arm were not markedly elevated. Neither ACTH nor prolactin level in the plasma was related to the dental pain threshold elevation during ischemia. The findings of the present study suggest that ischemic pain nonsegmentally produces a predominant inhibition of responses to thin afferents. Endogenous opioids may markedly contribute to the reduction of thermal sensitivity induced by ischemia, but their contribution to dental pain threshold elevations seems to be less important. Stress or other adenohypophyseal mechanisms involving the release of ACTH or prolactin do not explain the effects of ischemia found in the present study.     

THE LOCALIZATION OF NON TACTILE THERMAL SENSATIONS

An experiment by Nathan and Rice (1966) on the localization of thermal sensations was replicated. The present, somewhat more detailed, results essentially confirm the findings of the earlier authors. Thermal sensations evoked by non-tactile thermal stimuli can be localized; their localization is less accurate than that of tactile stimuli; and the accuracy of localization increases with increasing intensity of stimulation and sensation. To account for these findings several alternative hypotheses concerning the interaction between thermal and tactile modalities and large and small fiber sensory systems have been suggested.     

Mechanoreceptive afferents in the human sural nerve

Microneurography was used to characterize 104 low-threshold mechanoreceptive afferents in the human sural nerve. The afferents were readily classified into four types using criteria developed for the glabrous skin of the hand: SA I (31%), SA II (11%), FA I (49%), and FA II (9%). The distribution of fascicle fields and receptive fields of individual afferents on the lateral side of the foot indicates that the glabrous skin portion of the innervation territory of the sural nerve is more densely innervated than the non-glabrous skin portion. The different populations in the glabrous and non-glabrous skin regions were similar regarding proportion of unit types, receptive field sizes, and force thresholds. The receptive field sizes of the type I units of the present sample were about twice the size compared to those of the glabrous hand units, and the force threshold were at least three times higher for three of the unit types (SA I, FA I, and FA II). Given their receptive properties, it is likely that mechanoreceptive afferents in the sural nerve provide rich information about contact patterns between the foot and environment during stance and locomotion.     

The effects of digital anaesthesia on predictive grip force adjustments during vertical movements of a grasped object

Grip force adjustments to fluctuations of inertial loads induced by vertical arm movements with a grasped object were analysed during normal and impaired finger sensibility. Normally grip force is modulated in a highly economical way in parallel with fluctuations of load force. Two subjects performed vertical up and down movements of a grasped object, both with normal finger sensibility and then cutaneously anaesthetized finger sensibility. Short breaks were taken in between single movements, during which the object was held stationary. After digital anaesthesia was applied to the grasping fingers, both subjects substantially increased the grip force. The grip force amplitude and timing still anticipated changes in load force, although the established grip force had already overcome movement-induced load force peaks. This implies that the increase of grip force and consequently the elevated force ratio between maximum grip and maximum load force are not processed to alter the feedforward system of grip force control. Cutaneous afferent information from the grasping digits appears to be necessary for economic scaling of the grip force level, but it plays a subordinate role in the precise anticipatory temporal coupling of grip and load forces during voluntary object manipulation.     

von Frey hairs: new materials for a new design.

von Frey filaments are widely used in pain research. Conventionally, they are made of synthetic fibres. This plastic material is susceptible to changes in humidity and temperature, and such filaments do not keep their calibration. Filaments made of optical glass fibres are highly elastic and do not suffer these problems. Their optical properties can be used to make thin fibres more visible.     

湿性年龄相关性黄斑变性患者抗血管内皮生长因子治疗敏感性的影响因素:基于房水细胞因子分析

目的 通过分析湿性年龄相关性黄斑变性(wAMD)患者抗血管内皮生长因子(VEGF)治疗后房水细胞因子浓度的改变及房水细胞因子与相关指标之间的相关性,探讨影响wAMD患者抗VEGF治疗敏感性的因素.方法 选取2019年8月至2020年1月于广州中医药大学第一附属医院就诊的wAMD患者(观察组)和白内障患者(对照组)各30...     

大鼠效力试验模型对肾综合征出血热灭活疫苗的敏感性

目的　研究实验大鼠效力试验模型对肾综合征出血热灭活疫苗的敏感性。方法　用不同剂量、不同浓度肾综合征出血热灭活疫苗免疫大鼠 ,然后采用直接免疫酶斑减少中和试验检测血清汉坦病毒中和抗体 (NA)。结果与讨论　采用每剂 0 12 5ml的疫苗免疫大鼠可产生有效的免疫应答 ;疫苗应采用原液免疫 ,不宜做稀释 ;大鼠可作为疫苗效力评价的实验动物。     

Validation of a questionnaire for the detection of cluster headache

BACKGROUND: In the absence of biological markers, the diagnosis of cluster headache (CH) rests on clinical evidence as reported through ad-hoc interviews. OBJECTIVE: The aim of this study was to validate a 16-item self-administered questionnaire designed to screen CH cases. METHODS: The questions were based on the second edition of the International Headache Society classification (ICHD-II) criteria for CH (n = 12) and on specific disease features (n = 3). Answers to each question were either "Yes,"No," or "Don't know." The validity of this screening tool was assessed using a two-step procedure. In Step 1, the 16 questions were submitted to 30 healthy subjects with different cultural backgrounds to verify content clarity. In Step 2, the questionnaire was given to 71 patients (32 women and 39 men) aged 15 to 78 years (mean 37.5 years), who were seen at the University of Parma Headache Center with a diagnosis of CH (episodic, 17; chronic, 13), migraine (without aura, 18; with aura, 3), and tension-type headache (episodic, 16; chronic, 4) according to the ICHD-II criteria. Sensitivity, specificity, and the positive and negative predictive values were calculated for each question as measures of validity. RESULTS: Severity, unilaterality, and location of pain had the highest sensitivity (100%), but low (34.1%) or fairly low specificity (61.0% and 58.5%, respectively). In contrast, a positive response to lithium or verapamil had a 66.7% sensitivity and a 97.6% specificity. Sensitivity and specificity were 100% and 90.2% for duration of attacks (<180 to 240 minutes), and 90.0% and 92.7% for compulsory movements, respectively. The best discriminatory pattern for symptom detection was unilaterality of pain and the presence of at least five of the following seven features: pain severity and location, duration, frequency and daily recurrence of attacks, rhinorrhea and restlessness as accompanying symptoms. CONCLUSIONS: Our findings confirm that this questionnaire is a useful method for CH screening in epidemiological studies.     

Classification of muscle spindle receptors

The conduction velocities of muscle spindle afferent fibers have a bimodal distribution, and classifications of spindle receptors based on afferent fiber diameter have therefore divided these receptors into two groups, the well known primary and secondary endings. However, measures of spindle function that are likely to be important for kinesthetic sensibility such as dynamic response, adaptation and linear directionality (hysteresis) are distributed rather uniformly. Therefore, from this functional perspective it might be argued that muscle spindle receptors should not be subdivided at all. On the other hand, different receptors demonstrate these properties to varying degrees, and there are simple, linear correlations among log (dynamic response), log (adaptation), linear directionality and conduction velocity. Thus, the receptors can be divided into as many as 5–10 different subpopulations that differ significantly in one or more of these properties.     

Nondigital afferent input in reactive control of fingertip forces during precision grip

Sensory inputs from the digits are important in initiating and scaling automatic reactive grip responses that help prevent frictional slips when grasped objects are subjected to destabilizing load forces. In the present study we analyzed the contribution to grip-force control from mechanoreceptors located proximal to the digits when subjects held a small manipulandum between the tips of the thumb and index finger. Loads of various controlled amplitudes and rates were delivered tangential to the grip surfaces at unpredictable times. Grip forces (normal to the grip surfaces) and the position of the manipulandum were recorded. In addition, movements of hand and arm segments were assessed by recording the position of markers placed at critical points. Subjects performed test series during normal digital sensibility and during local anesthesia of the index finger and thumb. To grade the size of movements of tissues proximal to the digits caused by the loadings, three different conditions of arm and hand support were used; (1) in the hand-support condition the subjects used the three ulnar fingers to grasp a vertical dowel support and the forearm was supported in a vacuum cast; (2) in the forearm-support condition only the forearm was supported; finally, (3) in the no-support condition the arm was free. With normal digital sensibility the size of the movements proximal to the digits had small effects on the grip-force control. In contrast, the grip control was markedly influenced by the extent of such movements during digital anesthesia. The poorest control was observed in the hand-support condition, allowing essentially only digital movements. The grip responses were either absent or attenuated, with greatly prolonged onset latencies. In the forearm and no-support conditions, when marked wrist movements took place, both the frequency and the strength of grip-force responses were higher, and the grip response latencies were shorter. However, the performance never approached normal. It is concluded that sensory inputs from the digits are dominant in reactive grip control. However, nondigital sensory input may be used for some grip control during impaired digital sensibility. Furthermore, the quality of the control during impaired sensibility depends on the extent of movements evoked by the load in the distal, unanesthetized parts of the arm. The origin of these useful sensory signals is discussed.