British journal of anaesthesia
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Morphine stimulates angiogenesis and cancer progression in mice. We investigated whether morphine influences tumour onset, development, and animal model survival, and whether µ-opioid receptor (MOR), lymphangiogenesis, mast cell activation, and substance P (SP) are associated with the tumour-promoting effects of morphine. ⋯ Morphine does not affect the onset of tumour development, but it promotes growth of existing tumours, and reduces overall survival in mice. MOR may be associated with morphine-induced cancer progression, resulting in shorter survival. Mast cell activation by morphine may contribute to increased cytokine and SP levels, leading to cancer progression and refractory pain.
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Spinal serotonin (5-HT) receptors 3 (5-HT3R) and 7 (5-HT7R) are differentially involved in facilitatory or inhibitory descending modulation, respectively. Electrophysiological studies of the spinal cord have demonstrated that 5-HT3R is involved in nociception induced by intraplantar injection of formalin, but not carrageenan. In addition, depletion of spinal serotonin has been shown to attenuate pain behaviour in the formalin test, but there have been no such reports regarding the carrageenan model. This study compared the role of 5-HT7R and the influence of descending serotonergic modulation between formalin- and carrageenan-induced inflammatory pain. ⋯ Spinal 5-HT7R plays a significant inhibitory role in descending serotonergic modulation in pain induced by formalin but not carrageenan. Descending serotonergic modulation is differentially involved in inflammatory pain induced by formalin and carrageenan, with facilitatory and inhibitory effects, respectively.