Articles: pain.
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Centrifugal modulation from the midbrain, pons and medulla of the spinal nociceptive tail flick (TF) reflex evoked by graded noxious heating of the tail was studied in lightly pentobarbital-anaesthetized rats. In initial experiments, the relationship between the intensity of the noxious thermal stimulus and the TF latency was characterized. The thermal stimulus was provided by a lamp focused on the ventral surface of a rat's tail. ⋯ Type II modulations were produced by electrical stimulation in the dorsolateral pons, locus coeruleus-subcoeruleus and in the medial periaqueductal gray. This experimental approach has shown itself to be useful in the characterization of descending inhibition of nociception. Much simpler and less invasive than analogous spinal dorsal horn single cell electrophysiologic studies, it can be used to study the mechanisms of centrifugal modulation of nociceptive flexion reflexes and further establishes the utility of the lightly anaesthetized rat preparation for studies of nociception-antinociception.
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Nociceptive flexion reflexes, RIII reflex in particular, have been demonstrated to be a useful tool for pain research in humans, since the threshold of RIII reflex is that of pain. In this study a reduction of RIII reflex threshold, strictly related to the severity of the disease, is described in migraine with interval headache (MIH), that is considered a severe and evolutive form of common migraine (CM). ⋯ This fact supports the hypothesis that an impairment of serotoninergic antinociceptive system may exist in this type of headache. A significant correlation between percentage increase in RIII reflex threshold and reduction of PTI was also observed after amitriptyline treatment, indicating that pain reflex may be used for predicting treatment response in migraine.
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Recordings were made from convergent neurons in the lumbar dorsal horn of the spinal cord of the rat. These neurons were activated by both innocuous and noxious mechanical stimuli applied to their excitatory receptive fields located on the extremity of the hindpaw. Transcutaneous application of suprathreshold 2-ms square-wave electrical stimuli to the center of the excitatory field, resulted in responses to C-fiber activation being observed. ⋯ Again, a second lesion including the ipsilateral DLF induced a blockade of DNIC. It is concluded that the descending projections involved in the triggering of DNIC are mainly, if not entirely, confined to the DLF ipsilateral to the neuron under study. The contralateral DLF did not appear to play a role in these processes.