Brain research
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Participation of the hippocampal theta rhythm in memory formation was studied using an eight-arm radial maze task in rats. The numbers of reference memory and working memory errors were decreased gradually by daily training from session 10 and 6, respectively. ⋯ Theta power in the hippocampal CA1 area was gradually decreased from session 9, and there is a close relationship between the changes in theta power in the hippocampus and the number of reference memory errors. Based on those observations, it can be concluded that the hippocampal theta wave is intimately associated with the reference memory of the eight-arm radial maze in rats.
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Comparative Study
Activation and sensitization of C and Adelta afferent fibers mediated by P2X receptors in rat dorsal skin.
The present study investigated the activation and sensitization effects of local injection of P2X receptor agonist alpha,beta-methylene ATP (alphabeta-meATP) into the receptive fields of afferent fibers innervating dorsal hairy skin in anesthetized rats. Single unit activities of afferent fibers were recorded by means of isolation of the fiber filaments from the dorsal cutaneous nerve branch. A total of 237 fibers were obtained. ⋯ Furthermore, injection of alphabeta-meATP (10 microl) at a concentration of 100 microM resulted in a significant decrease of mechanical thresholds in C and Adelta fibers compared with pre-injection baseline (P < 0.05). In control experiments, injection of the vehicle phosphate-buffered saline (PBS, 10 microl) had no effect on all units tested. alphabeta-meATP (100 microM, 10 microl) followed by pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a P2X receptor antagonist, successfully blocked the activation and sensitization effects of alphabeta-meATP on C and Adelta fibers tested. These results suggest that peripheral P2X receptors are involved in mediating peripheral excitation of C and Adelta fibers.
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Comparative Study
The selective mu opioid receptor antagonist, alvimopan, improves delayed GI transit of postoperative ileus in rats.
Postoperative ileus (POI) is often exacerbated by opioid analgesic use during and following surgery, since mu opioid receptor activation results in a further delay of gastrointestinal (GI) transit. The effects of alvimopan, a novel, selective, and peripherally acting mu opioid receptor antagonist, and the reference compound methylnaltrexone, upon POI were investigated in rats. Under isoflurane anesthesia, POI was induced by laparotomy with intestinal manipulation. ⋯ Under these conditions, alvimopan (1 and 3 mg/kg) also significantly improved delayed GI transit when administered before surgery. Methylnaltrexone was inactive under all experimental conditions. These data suggest that mu opioid receptors play a role in the pathogenesis of POI, and that the clinical benefit reported to be afforded by alvimopan may be in part mediated via inhibition of an endogenous opioid release as well as blockade of the unwanted GI actions of analgesic agents.