8-OH-DPAT prevents morphine-induced apoptosis in rat dorsal raphe nucleus: a possible mechanism for attenuating morphine tolerance.

Background: Previously, we found that activation of serotonin 1A (5-HT1A) receptors in the dorsal raphe nucleus (DRN) decreased the development of tolerance to the analgesic effect of morphine. It has been indicated that tolerance to the analgesic effect of morphine is associated with apoptosis in the central nervous system. In this investigation we attempted to evaluate the effect of 8-OH-DPAT (8-hydroxy-2-[di-n-propylamino]tetralin), a specific 5-HT1A receptor agonist, on morphine-induced tolerance and apoptosis in rat DRN.

Effect of testosterone on morphine withdrawal syndrome in rats.

Aim: To determine whether testosterone is involved in morphine withdrawal syndrome (WS).

Methods: In order to induce dependency, rats were treated with subcutaneous injection of morphine (days 1-2, 5 mg/kg; days 3-5, 7.5 mg/kg; days 6-8, 10 mg/kg), and after the last dose of morphine (day 8) WS was induced by intraperitoneal injection of naloxone (1 mg/kg).

Role of 5-HT(1A) and 5-HT(2) receptors of dorsal and median raphe nucleus in tolerance to morphine analgesia in rats.

Several studies indicate that central serotonergic neurons have important role in morphine analgesia and tolerance. The aim of this study was to investigate possible role of 5-HT(1A) and 5-HT(2) receptors in dorsal and median raphe nucleus on development of tolerance to analgesic effect of morphine using hot plate test. Chronic injection of 5-HT(1A) receptor agonist 8-OH-DPAT (8-hydroxy-2-[di-n-propylamino]tetralin) (2, 4 and 8 mug/rat/day) to dorsal raphe nucleus (DRN) delayed tolerance to morphine analgesia, whereas injection of the same doses of 8-OH-DPAT to the median raphe nucleus (MRN) did not alter tolerance to morphine.

Involvement of serotoninergic mechanism in analgesia by castration and flutamide, a testosterone antagonist, in the rat formalin test.

Several studies have suggested that testosterone has a role in nociception. Recently, we have shown that castration and flutamide, a testosterone antagonist, induce analgesia in the late phase of formalin test, which is related to increase of 5-HT levels in the dorsal horn of the lumbar spinal cord. The aim of the present study was to investigate the effect of fluoxetine, a selective serotonin reuptake inhibitor, on castration and flutamide-induced analgesia in order to further explore the role of 5-HT systems in such analgesia.