Life sciences
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The development of tolerance and cross tolerance to morphine at spinal cord levels on the tall flick inhibition was studied in rats tolerant to D-Ala2-D-Leu5-enkephalin (DADL). The long term intrathecal infusion of DADL was accomplished by means of osmotic minipumps. ⋯ Concomitant intrathecal infusion of naloxone which was more sensitive in blocking mu-opioid receptor than delta-opioid receptor blocked the development of cross tolerance to morphine while the development of tolerance to DADL was left unaffected. The studies present the evidence that two types of opioid receptors, delta- and mu-opioid in the spinal cord of rats are involved in the development of tolerance by chronic DADL exposure.
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The effects of gamma-hydroxybutyrate (GHB) upon sleep wakefulness patterns and quantified nuchal muscle activity were examined in the rabbit in a dose-response paradigm (25-1,000 mg/kg). Relative to control (saline) values, there was no facilitation of sleep onset or epileptogenic activity at any of the dosages studied. ⋯ An enhancement of paradoxical sleep observed at lower GHB levels in other species occurred in attenuated form in the rabbit. The results indicate dose-related effects on both sleep and motor activation in the rabbit, but the absence of seizure activity for the concentrations of GHB studied.
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Recent evidence suggests that the vascular sodium-potassium pump suppression previously observed in animals with various models of low renin hypertension results from a circulating heat stable ouabain-like agent. It appears to come from or be influenced by the anteroventral third ventricle area of the brain and its action on blood vessels results in depolarization of the smooth muscle cell. Suppression of the vascular sodium-potassium pump, with ouabain for example, increases contractile activity and the contractile responses to vasoactive agents. Thus the humoral pump inhibitor may be involved in the genesis and maintenance of experimental low renin hypertension.