Pain
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Pain responsiveness was investigated experimentally as a function of age and childbirth pain experience. Sensitivity to cold pressor-induced pain was assessed through threshold, tolerance, and visual analog pain ratings. It was hypothesized that childbirth pain experience would mostly modify experimental pain judgment, in accordance with the adaptation-levels model. ⋯ Thus, painful childbirth experience is sufficient to raise cold pressor pain threshold. This finding has never before been reported in the pain literature. It is consistent with anecdotal reports from parous women who, when providing cold pressor pain judgments, say that "nothing compares to labor pain."
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The effects of the major morphine metabolites, morphine-3-glucuronide and morphine-6-glucuronide, on nociception were assessed by the tail-flick, hot-plate and writhing tests in the rat. Morphine-3-glucuronide (M3G) 1.1 x 10(-9) mol (0.5 micrograms) or saline was injected intracerebroventricularly (i.c.v.) or intrathecally (i.t.) followed by a second injection of 2.0 x 10(-10) mol (0.1 microgram) or 2.0 x 10(-11) mol (0.01 microgram) morphine-6-glucuronide (M6G) 10 min later. Administration of M3G (i.c.v.) significantly attenuated the antinociceptive effects of M6G in the hot-plate test. ⋯ In animals receiving M3G there was a prevention or attenuation of the M6G induced depression of respiratory frequency, tidal volume and minute ventilation compared to control groups receiving M6G in combination with saline. These results show that M3G may functionally antagonize the central antinociceptive effects as well as the ventilatory depression induced by M6G. Interestingly, M3G was more potent in antagonizing the M6G-induced analgesia after i.t. administration than that after i.c.v. administration, which may suggest that the spinal cord is more sensitive to the non-opioid excitatory effects of M3G than supraspinal structures.