Neuroscience letters
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Neuroscience letters · May 1991
In vivo distribution of opioid receptors in man in relation to the cortical projections of the medial and lateral pain systems measured with positron emission tomography.
In vivo opioid receptor binding in the cortical projections of the medial (cingulate and prefrontal cortex) and lateral pain system (primary somatosensory cortex) in male volunteers has been quantitated using [11C]diprenorphine and positron emission tomography. High levels of opioid receptor binding were seen in the cortical projections of the medial pain system in the cingulate and prefrontal cortex as has previously been observed in post-mortem studies. However, a focal reduction of opioid receptor binding was observed and quantitated in the primary motor/sensory strip when compared to surrounding parietal cortex. This new finding suggests that the medial pain system is likely to be more susceptible to exogenous and endogenous opioid neuromodulation than the so-called lateral pain system.
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Neuroscience letters · Feb 1991
Controlled noxious chemical stimulation: responses of rat trigeminal brainstem neurones to CO2 pulses applied to the nasal mucosa.
The nasal mucosa of halothane-anesthetized rats was stimulated with defined CO2 pulses. Recordings were performed from single trigeminal brainstem neurons to characterize their responses to this controlled chemical irritation. ⋯ The application of chemical irritants, notably mustard oil or acetic acid induced vigorous ongoing discharges in all cells tested. The CO2 stimulation method described here thus provides an ideal model for the quantitative physiological and pharmacological examination of chemically induced nociception.
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Neuroscience letters · Jul 1990
A-fibers mediate mechanical hyperesthesia and allodynia and C-fibers mediate thermal hyperalgesia in a new model of causalgiform pain disorders in rats.
Unilateral tight ligation of about half of the sciatic nerve in rats rapidly produces sympathetically dependent neuropathic pain which lasts many months and resembles causalgia in humans. The sensory abnormalities detected at the plantar side of the hindpaws include: (1) nocifensive responses to repetitive light touch (allodynia); (2) bilateral reduction in withdrawal thresholds to repetitive von-Frey hair stimulation (mechanical hyperesthesia); (3) bilateral reduction in withdrawal thresholds to CO2 laser heat pulses; and (4) unilateral increase in response duration to an intense laser heat pulse (thermal hyperalgesia). Using neonatal capsaicin treatment, we determined the type of afferent fiber remaining in the partially injured nerve, which mediates these disorders. ⋯ These disorders were, therefore, mediated by myelinated fibers. In contrast, thermal hyperalgesia failed to develop in capsaicin-treated rats following partial nerve injury. Thus, thermal hyperalgesia produced by partial nerve injury appears to be mediated by heat-nociceptive C-fibers.
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Neuroscience letters · Mar 1990
Differential effects of serotonin on respiratory activity of hypoglossal and cervical motoneurons: an in vitro study on the newborn rat.
Newborn rat respiratory activity was recorded on hypoglossal nerve and ventral cervical roots during in vitro experiments performed on superfused brainstem spinal cord preparations. The addition of serotonin (5-HT) to the bathing medium increased the respiratory frequency and selectively depressed the hypoglossal activity. ⋯ When 5-HT was applied on isolated hemispinal cord, a tonic activity could still be elicited. These results indicate that serotonin (i) modulates the activity of neurons involved in the generation of respiratory rhythm, (ii) depresses the activity of hypoglossal motoneurons, and (iii) evokes tonic activity in cervical motoneurons, probably as the result of direct spinal effects.