Behavioural brain research
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The cortical system underlying perceptual ability to localize tactile and noxious cutaneous stimuli in humans is still incompletely understood. We used transcranial magnetic stimulation (TMS) to transiently interfere with the function of the parietal cortex, at different times after the beginning of noxious or non-noxious mechanical stimulation of the hairy skin overlying the dorsal surface of the first metacarpal of the contralateral hand. Peripheral stimuli consisted of rounded (1mm diameter) or sharp (0.2 mm) metal tips; skin contact lasted on average 242 ms (noxious) and 228 ms (non-noxious). ⋯ No impairment in stimulus detection was found in comparison with control sham TMS. The timing of parietal TMS interference with the ability to localize tactile and painful stimuli is compatible with known time differences in the arrival of non-noxious and noxious information in the postcentral gyrus. On these grounds, our findings support the existence of overlapping cortical populations in the contralateral parietal lobe, exerting a role in spatial discriminative aspects of touch and mechanically induced pain.
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Previous studies have established a relationship between sleep disruption and pain, and it has been suggested that hyperalgesia induced by paradoxical sleep deprivation (PSD) could be due to a reduction of opioidergic neurotransmission in the brain. In the present study rats deprived of sleep for 96 h as well as rats allowed to recover for 24h after PSD and normal controls received vehicle or morphine (2.5, 5 and 10 mg/kg, i.p.) and were tested on a hot plate 1h later. Quantitative receptor autoradiography was used to map alterations in binding to brain mu-opioid receptors in separate groups. ⋯ Binding of [3H]DAMGO to mu sites did not differ significantly among the three groups in any of the 33 brain regions examined. These results do not exclude the participation of the opioid system in PSD-induced pain hypersensitivity since sleep-deprived rats were clearly resistant to morphine. However, the fact no changes were seen in [3H]DAMGO binding indicates that mechanisms other than altered mu-opioid binding must be sought to explain the phenomenon.
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Comparative Study
Gender difference in hemodynamic responses of prefrontal area to emotional stress by near-infrared spectroscopy.
Presentation of negative pictures was used as emotional stress to assess gender differences in prefrontal area activation in a functional near-infrared spectroscopy (NIRS) study. Compared with neutral condition, the response of oxy-HB for men yielded no significant difference during stress period, but the response induced by stress pictures for women showed significant enhancement. It was indicated that it is crucial to take gender difference into account when negative stimuli are used in functional brain imaging.
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Acute treatment with the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) or chronic environmental enrichment (EE) hasten behavioral recovery after experimental traumatic brain injury (TBI). The aim of this study was to determine if combining these interventions would confer additional benefit. Anesthetized adult male rats received either a cortical impact or sham injury followed 15min later by a single intraperitoneal injection of 8-OH-DPAT (0.5mg/kg) or saline vehicle (1.0mL/kg) and then randomly assigned to either enriched or standard (STD) housing. ⋯ However, there was no difference between the TBI+8-OH-DPAT+EE and TBI+VEHICLE+EE groups. These data replicate previous results from our laboratory showing that both a single systemic administration of 8-OH-DPAT and EE improve recovery after TBI and extend those findings by elucidating that the combination of treatments in this particular paradigm did not confer additional benefit. One explanation for the lack of an additive effect is that EE is a very effective treatment and thus there is very little room for 8-OH-DPAT to confer additional statistically significant improvement.
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It was recently found that cooling the skin to temperatures as mild as 25-30 degrees C can induce nociceptive sensations (burning, stinging or pricking) that are strongly suppressed by dynamic contact between the thermode and skin (contact suppression). Here we investigated whether nociceptive sensations produced by menthol can be similarly suppressed. In the first experiment subjects rated the intensity of cold and burning/stinging/pricking sensations before and after application of 10% l-menthol to the forearm. ⋯ A second experiment tested whether contact suppression of menthol's cold and nociceptive sensations at resting skin temperature was caused by slight deviations of thermode temperature above skin temperature. The results showed that suppression occurred even when the thermode was slightly cooler (-0.5 degrees C) than the skin. These findings support other evidence that the menthol-sensitive channel, TRPM8, plays a role in cold nociception, and raise new questions about how dynamic tactile stimulation may modify perception of nonpainful cold stimulation.