Neuroscience letters
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The effects of capsaicin were investigated on different populations of dorsal root ganglion cells in the in vitro mouse spinal cord-dorsal root ganglion preparation using intracellular electrodes. Dorsal root ganglion cells were characterised by the conduction velocity of their propagated action potential evoked by electrical stimulation of the dorsal root, and by the shape of their action potential. All cells with C-fiber characteristics (conduction velocity < 0.6 m/s; broad action potential with shoulder on the descending slope) were depolarised and generated action potentials when capsaicin (100-700 nM) was added to the bathing solution for 30 s. ⋯ Passive depolarization of the membrane by intrasomal current injection mimicked the conduction block in neurons with large myelinated fibers. These observations confirm that capsaicin applied directly to the dorsal root ganglion affects, in a dose-dependent manner, both myelinated and unmyelinated primary afferents with a higher potency for C-neurons. Capsaicin evoked action potentials in C-neurons but not in neurons with myelinated fibers.(ABSTRACT TRUNCATED AT 250 WORDS)
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Neuroscience letters · Jun 1993
Distribution of NADPH-diaphorase in the cerebral blood vessels of rats: a histochemical study.
NADPH-diaphorase (neuronal nitric oxide synthase) activity in the cerebral blood vessels was investigated by light and electron microscopic histochemistry to elucidate the sites of nitric oxide production. Networks of adventitial nerves containing NADPH-diaphorase were distributed in all parts of the circle of Willis. ⋯ Endothelial cells were intensely stained in arteries and arterioles. These results support the hypothesis that vascular tone is regulated by nitric oxide, which is derived from endothelial cells and adventitial nerves.
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Neuroscience letters · May 1993
Sustained graded pain and hyperalgesia from harmless experimental tissue acidosis in human skin.
The present study was performed to decide whether tissue acidosis can induce sustained pain and, by that, possibly contribute to the pain in inflammation or ischaemia. A motorized syringe pump was used to infuse an isotonic phosphate buffer solution (pH 5.2) via sterile filter and cannula into the palmar forearm skin of human subjects (n = 6). This resulted in a localized burning pain sensation (edema and flare response) that was sustained as long as a constant flow was maintained. ⋯ Prolonged infusion at flow rates producing pain ratings around 20% VAS led to localized changes in mechanical sensitivity: The touch threshold increased--as it did with control infusion of phosphate buffer at pH 7.4. However, the punctate force producing a threshold sensation of pain dropped from 64 to 5.7 mN (median values); the final level was usually reached within 15 min. In conclusion, experimental tissue acidosis provides a controllable and harmless method to produce sustained, graded and spatially restricted pain and hyperalgesia to mechanical stimulation.
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Neuroscience letters · Apr 1993
Appearance of new receptive fields in rat dorsal horn neurons following noxious stimulation of skeletal muscle: a model for referral of muscle pain?
To test the hypothesis that painful stimuli to skeletal muscle lead to a widespread unmasking of synaptic connections in dorsal horn neurons, intramuscular injections of bradykinin (BKN) were made outside the receptive fields (RFs) of these cells in the rat. Following BKN injections, new RFs all of which were located in the deep tissues and had high mechanical thresholds appeared in 9 out of 21 (42.8%) nociceptive dorsal horn neurons which originally had a single RF in deep tissues or in the skin. The appearance of new RFs may lead to a mislocation of the source of pain if in fact the impulse activity of a nociceptive dorsal horn neuron contains information on the site of the stimulus.
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Neuroscience letters · Feb 1993
Electrical stimulation of the ventroposterolateral thalamic nucleus (VPL) reduces mechanical allodynia in a rat model of neuropathic pain.
The effect of electrical stimulation of the ventroposterolateral (VPL) thalamic nucleus on mechanical allodynia in the unrestrained awake rat was investigated. In 7 rats, a monopolar stimulation and recording electrode was implanted in the VPL thalamic representation area of the hindpaw. Exact target localisation was performed by means of thalamic evoked potentials induced by stimulating the contralateral tibial nerve. ⋯ The effect of VPL stimulation outlasted the stimulation period by 15 min. No effect on the withdrawal thresholds at the control (sham operated) side was observed. These animals data support the clinical reports that stimulation of the sensory thalamus may alleviate pain of neuropathic origin.