Tolerance induced by morphine remains a major unresolved problem and significantly limits its clinical use. Recent evidences have indicated that dopamine D2 receptor (D2DR) is likely to be involved in morphine-induced antinociceptive tolerance. However, its exact effect and molecular mechanism remain unknown. In this study we examined the effect of D2DR on morphine antinociceptive tolerance in ...

Previous work has shown that glucocorticoid hormones facilitate the behavioral and dopaminergic effects of morphine. In this study we examined the possible role in these effects of the two central corticosteroid receptor types: mineralocorticoid receptor (MR), and glucocorticoid receptor (GR). To accomplish this, specific antagonists of these receptors were infused intracerebroventricularly and...

1 The nerve-induced secretion produced by the rat parotid gland is proportional to the frequency of stimulation. Morphine decreased the flow rate during stimulation at 2.5 and 5 Hz, but not at 20 Hz. This frequency-dependent action of morphine and was partially reversed by naloxone. 2 The secretion produced by the rat parotid gland during an intravenous infusion of acetylcholine was not diminis...

BAKGROUND : Morphine exerts immunomodulatory effects dependent on several factors including species and parameter examined. The aim of this study was to assess the influence of morphine on experimental peritonitis and leukocyte activity in young chickens of both sexes. METHODS: Peritonitis was elicited by intraperitoneal injection of thioglycollate (TG) alone or supplemented with morphine; addi...

Parallel to the "poppy-seed defense" strategy commonly reported in the United States, donors of urine samples tested positive for opiates in Taiwan often claimed the consumption of Brown Mixture (BM) as the source of the observed morphine and codeine. Because BM contains opium powder (10.0-10.5% morphine), opium tincture (0.9-1.1% morphine), or camphorated opium tincture (0.045-0.055% morphine)...

When coadministered spinally, morphine and clonidine interact synergistically to produce antinociception. The mechanism for the synergism is unknown, but may depend on intracellular messenger systems. Agents that alter the activities of protein kinases alter antinociception produced by opioids, but their effects on clonidine-induced antinociception or the morphine/clonidine interaction are not ...

BACKGROUND Moxonidine, a novel imidazoline-alpha2-adrenergic receptor-selective analgesic, was recently identified as antinociceptive but has yet to be evaluated in neuropathic pain models. alpha2-adrenergic receptor-selective analgesics, and high-efficacy opioids, effectively inhibit neuropathic pain behaviors in rodents. In contrast, morphine potency and efficacy decreases in states of neurop...

Acute administration of morphine stimulates the secretion of hypothalamic-pituitary-adrenal (HPA) hormones, ACTH, beta-endorphin and corticosterone in the rat. In this study we investigated the effects of repeated multiple-dose morphine on HPA activity under two different conditions: without or with water restriction stress. Rats received six intermittent injections of morphine (6.25 mg/kg per ...

Consumption of ethanol is a considerable risk factor for death in heroin overdose. We sought to determine whether a mildly intoxicating concentration of ethanol could alter morphine tolerance at the cellular level. In rat locus coeruleus (LC) neurons, tolerance to morphine was reversed by acute exposure of the brain slice to ethanol (20 mM). Tolerance to the opioid peptide [d-Ala(2),N-MePhe(4),...

Regulating main brain-uptake transporter of morphine may restrict its tolerance generation, then modify its antinociception. In this study, more than 2 fold higher intracellular uptake concentrations for morphine and morphine-6-glucuronide (M6G) were observed in stable expression cells, HEK293-hOATP2B1 than HEK293-MOCK. Specifically, the Km value of morphine to OATP2B1 (57.58 ± 8.90 μM) is 1.4-...