Neuroscience letters
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Neuroscience letters · Dec 1996
Down-regulation of endogenous nitric oxide synthase in late-pregnancy and parturition in the rat hypothalamic magnocellular neurons and neurohypophysis.
Several recent lines of evidence suggest that nitric oxide (NO) may be an endogenous inhibitory regulator of the neurosecretory mechanism in magnocellular neurons of the paraventricular and the supraoptic nuclei in the hypothalamus. The NO synthase (NOS) system in the hypothalamo-neurohypophysial-axis is regulated in an activity-dependent manner. ⋯ The specific activity of NOS in the neurohypophysis also decreased in late-pregnancy through parturition, and increased shortly afterward. Together with the ability of a NO donor to significantly delay the progress of parturition when administered centrally in parturient rats, these observations suggest that this down-regulation of NOS activity in the hypothalamo-neurohypophysial axis in late-pregnancy and parturition may be of physiological importance in the onset and/or progress of parturition.
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Neuroscience letters · Nov 1996
Local application of anti-NGF blocks the collateral sprouting in rats following chronic constriction injury of the sciatic nerve.
Systemic administration of anti-nerve growth factor (NGF) antibodies can block nociceptive fiber sprouting into denervated adult rat skin. However, the effect of local application of anti-NGF on collateral sprouting in rats caused by chronic constriction injury (CCI) has not been well studied. We investigated the influence of local anti-NGF on collateral sprouting caused by CCI of the rat's sciatic nerve. ⋯ Our results showed that local application of anti-NGF either in a high or low dose significantly prevented the spread of collateral sprouting from the saphenous nerve into the sciatic innervation territory. In contrast, distilled water did not show a significant block of the saphenous nerve collateral sprouting. Our study suggests that collateral sprouting is dependent on the local availability of NGF by the nearby intact cutaneous nerve fibers.
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Neuroscience letters · Sep 1996
Effects of transcutaneous electrical nerve stimulation (TENS) on spontaneous and noxiously evoked dorsal horn cell activity in cats with transected spinal cords.
Effects of transcutaneous electrical nerve stimulation (TENS) on spontaneous and noxiously evoked dorsal horn neurons were studied in alpha-chloralose anesthetized cats after spinal cords had been transected at the T12 segment. Previous work in cats with intact cords showed that TENS applications to somatic receptive fields could significantly reduce and maintain decreased dorsal horn cell activity. ⋯ The results demonstrated that spontaneously and noxiously evoked cell activities were reduced significantly during TENS and no significant difference was found between pre-TENS control activity and post-TENS application cell activity. This information implies that initial gating (reduction cell activity), which occurs during TENS applications, is due to a segmental effect.
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Neuroscience letters · Sep 1996
Novel receptor mechanisms for heroin and morphine-6 beta-glucuronide analgesia.
The rapid metabolism of heroin to 6-acetylmorphine and its slower conversion to morphine has led many to believe that heroin and morphine act through the same receptors and that the differences between them are due to their pharmacokinetics. We now present evidence strongly implying that heroin and two potent mu drugs, fentanyl and etonitazine, act through a unique receptor mechanism similar to morphine-6 beta-glucuronide which is readily distinguished from morphine. Heroin, 6-acetylmorphine and morphine-6 beta-glucuronide show no analgesic cross tolerance to morphine in a daily administration paradigm, implying distinct receptors. ⋯ Antisense mapping of the mu opioid receptor MOR-1 reveals that oligodeoxynucleotide probes against exon 2, which are inactive against morphine analgesia, block morphine-6 beta-glucuronide, heroin, fentanyl and etonitazine analgesia. Finally, an antisense probe targeting Gi alpha 1 blocks both heroin and morphine-6 beta-glucuronide, but not morphine, analgesia. These results indicate that heroin, 6-acetylmorphine, fentanyl and etonitazine all can produce analgesia through a novel mu analgesic system which is similar to that activated by morphine-6 beta-glucuronide.
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Neuroscience letters · Aug 1996
Clinical TrialTopical acetylsalicylate attenuates capsaicin induced pain, flare and allodynia but not thermal hyperalgesia.
The effect of acetylsalicylic acid (ASA) on capsaicin-evoked activation of cutaneous nociceptors was tested in a double blind study in 10 volunteers. Capsaicin (2% in ethanol) was applied topically for 30 min. ⋯ In contrast, capsaicin-induced heat hyperalgesia was unaffected by ASA. It is concluded that ASA counteracts the excitatory effects of capsaicin on nociceptors and mechanical hyperalgesia but not its sensitizing action to heat.