Search results for "Noxious stimulus"

Inactivation and tachyphylaxis of heat-evoked inward currents in nociceptive primary sensory neurones of rats.

2000

In contrast to other sensory modalities, pain does not decrease when a noxious stimulus is applied at constant intensity (Greene & Hardy, 1962). From this lack of adaptation on the perceptive level it has traditionally been implied that primary nociceptive afferents also do not adapt upon constant stimulation. This is in contrast to the results of recordings from these afferents, which exhibit pronounced adaptation for physical as well as chemical stimuli (Meyer et al. 1994). Peripheral adaptation of nociceptive nerve endings is compensated by central summation (Mendell & Wall, 1965; Price et al. 1977); this slow summation process of small fibre input to the dorsal horn of the spinal cord i…

The effects of morphine on the temporal structure of Wistar rat behavioral response to pain in hot-plate

2016

Rationale: The largest amount of researches on the hot-plate test was carried out using quantitative assessments. However, the evaluation of the relationships among the different elements that compose the behavioral response to pain requires different approaches. Although previous studies have provided clear information on the behavioral structure of the response, no data are available on its temporal structure. Objectives: The objective of this study was to investigate the temporal structure of the behavioral response to pain in Wistar rat tested in hot-plate and how this structure was influenced by morphine-induced analgesia. Methods: The behavior of four groups of subjects tested in hot-…

Spontaneous Cingulate High-Current Spikes Signal Normal and Pathological Pain States

2019

Prominent 7–12 Hz oscillations in frontal cortical networks in rats have been reported. However, the mechanism of generation and the physiological function of this brain rhythm have not yet been clarified. Multichannel extracellular field potentials of the ACC were recorded and analyzed using the current source density method in halothane-anesthetized rats. Spontaneous high-current spikes (HCSs) were localized in the deep part of layer II/III and upper part of layer V of the ACC. The frequency of HCSs in the ACC was 7–12 Hz, with an amplitude of 6.5 ± 0.76 mV/mm(2) and duration of 55.24 ± 2.43 ms. The power density significantly decreased (84.56 ± 6.93%, p < 0.05, t test) after pinching the…

Newborn Infant Parasympathetic Evaluation Index for the Assessment of Procedural Pain in Nonanesthetized Infants: A Multicenter Pilot Study

2020

Abstract Objective The aim of this study is to evaluate the ability of the Newborn Infant Parasympathetic Evaluation (NIPE) index to detect the response to nociceptive stimuli in nonanesthetized infants and to compare these results to simultaneous scoring by behavioral scales. Study Design Thirty-six nonanesthetized infants admitted to neonatal/pediatric intensive care unit (N/PICUs) were enrolled to the study. Due to faulty records of the data, three patients had to be excluded. To detect pain caused by noxious stimuli, the heart-rate-variability-derived NIPE index and behavioral pain scales designed for measuring procedural pain in nonverbal children were used. Results Forty-one painful e…

Naloxone inhibits not only stress-induced analgesia but also sympathetic activation and baroreceptor-reflex sensitivity

2012

Interactions between the sympathetic nervous system and pain are manifold and still have not been sufficiently characterized. Accordingly, several possible neuronal pathways have been described as being involved in mental stress-induced analgesia. We studied the role of the endogenous opioidergic system in stress-induced analgesia in 14 healthy participants in a double-blind cross-over trial. Naloxone or placebo was applied while electrical pain stimulation was started and electrical current increased. After reaching a constant stimulation at 30 mA, a color word interference test (Stroop task) was performed in a stressful and a non-stressful version. Blood pressure, heart rate and barorefle…

Pain elicited by blunt pressure: neurobiological basis and clinical relevance.

2002

Is lack of habituation a biomarker of migraine? A critical perspective

2015

Processing of sensory stimuli has been supposed to be dysfunctioning in migraine. A basis for such abnormality has been identified in a defective ability to habituate to repetitive sensorial stimulation. Habituation, i.e. the way the nervous system attenuates response to repeated non noxious stimuli is a fundamental function of sensory systems, that allows appropriate adaptation of neural responses to the relevance of incoming stimuli. In humans, habituation can be studied by evoked potentials where it is indexed by a reduction of amplitude of the evoked response to repeated stimulation. After the first evidence by Schoenen et al in 1995[1] of reduced habituation to visual evoked potentials…

Secondary hyperalgesia to punctate mechanical stimuli

1999

Tissue injury induces enhanced pain sensation to light touch and punctate stimuli in adjacent, uninjured skin (secondary hyperalgesia). Whereas hyperalgesia to light touch (allodynia) is mediated by A-fibre low-threshold mechanoreceptors, hyperalgesia to punctate stimuli may be mediated by A- or C-fibre nociceptors. To disclose the relative contributions of A- and C-fibres to the hyperalgesia to punctate stimuli, the superficial radial nerve was blocked by pressure at the wrist in nine healthy subjects. Secondary hyperalgesia was induced by intradermal injection of 40 microg capsaicin, and pain sensitivity in adjacent skin was tested with 200 micron diameter probes (35-407 mN). The progress…