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Physical dependence is a widely known consequence of morphine intake. Although commonly associated with prolonged or repeated morphine administration, withdrawal symptoms can be elicited even after a single prior morphine exposure. What remains contentious is the extent to which physical dependence following acute and chronic morphine treatment is mediated(More)
The present study assessed the analgesic potency of morphine in 11 inbred mouse strains before and after chronic morphine treatment. Using the 49 degrees C tail-withdrawal test, significant strain differences in morphine AD(50) estimates derived from cumulative dose-response curves were noted prior to tolerance induction on Day 1. AD(50) estimates were(More)
The present study compared male and female mice for frequency of naloxone-precipitated jumping and naloxone ED(50) values, two common indices of physical dependence, following acute and chronic morphine administration. Both sexes displayed a positive dose-response relationship between acute morphine and naloxone doses and jumping frequency. There was a(More)
It has been hypothesized that morphine tolerance and dependence in mice following chronic exposure may reflect increased compensatory activity of antiopioid systems. The endogenous peptide nociceptin/orphanin FQ has been shown to have anti-opioid effects, for example antagonizing morphine analgesia. Moreover, chronic morphine administration increases(More)
Studies comparing morphine tolerance in males and females are rare, and all studies to date have utilized the rat. To generalize from findings with rats morphine tolerance was investigated in male and female mice using the tail-withdrawal test. Three and 7 days of systemic morphine injections produced significant but unequal rightward shifts in the morphine(More)
Morphine analgesic potency following systemic administration was assessed in male and female mice undergoing prior and repeated intrathecal morphine injections. Although morphine ED50 values were significantly increased in both sexes relative to their respective saline-injected controls, the magnitude of tolerance was greater in females. Intrathecal(More)
We compared morphine analgesia ED(50) values of male and female mice prior to (Day 1) and after (Day 4) 3 days of intracerebroventricular morphine injections. Increases in ED(50) values from Day 1 to Day 4, indicating tolerance, were of similar magnitude in both sexes. The data suggest that spinal opioid analgesic mechanisms, acting alone or in synergy with(More)
Serotonergic, NMDA, or opioid antagonists in the rostral ventromedial medulla (RVM) reduce morphine analgesia elicited from the periaqueductal gray (PAG). Continuous (CCWS) and intermittent (ICWS) cold-water swims elicit respective naltrexone-insensitive and naltrexone-sensitive analgesic responses. CCWS analgesia is reduced by systemic NMDA receptor(More)
Sex differences in thermoregulation have been reported following acute morphine administration in rats only. This study assessed whether male and female mice also differ in thermoregulatory responses following acute and chronic morphine administration. Females displayed significantly higher baseline colorectal temperature and greater morphine (24mg/kg,(More)
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