Donepezil attenuates the development of morphine tolerance in rats with cancer-induced bone pain: The role of cortical N-methyl-D-aspartate receptors

Aspirin attenuates morphine antinociceptive tolerance in rats with diabetic neuropathy by inhibiting apoptosis in the dorsal root ganglia

Morphine is a drug used in chronic pain such as diabetic neuropathy, but the development of tolerance to its antinociceptive effect is an important clinical problem. Aspirin is an analgesic and antiapoptotic drug used in combination with morphine as an adjuvant in diabetic neuropathy. Our aim in this study was to investigate the effects of aspirin on morphine-induced neuronal apoptosis and analgesic tolerance in rats with diabetic neuropathy. The antinociceptive effects of aspirin (50 mg/kg) and morphine (5 mg/kg) were evaluated by thermal pain tests. Streptozotocin (65 mg/kg) was injected intraperitoneally to induce diabetic neuropathy. To evaluate apoptosis, ELISA kits were used to measure caspase-3, Bax and Bcl-2 levels. Apoptotic cells were detected histologically by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method. Study results indicate that prior administration of aspirin to diabetic rats significantly increased the antinociceptive efficacy of morphine compared to morphine alone. Thermal pain tests showed that aspirin significantly reduced morphine tolerance in rats with diabetic neuropathy. Biochemical analysis revealed that aspirin significantly decreased the levels of pro-apoptotic proteins, caspase-3 and Bax, while increasing the anti-apoptotic Bcl-2 in DRG neurons. Semiquantitative scoring demonstrated that aspirin provided a significant reduction in apoptotic cell counts in diabetic rats. In conclusion, these data suggested that aspirin attenuated morphine antinociceptive tolerance through anti-apoptotic activity in diabetic rat DRG neurons.

Comparative investigation of analgesic tolerance to taurine, sodium salicylate and morphine: Involvement of peripheral muscarinic receptors

Nowadays various analgesic medications are used for the management of acute and chronic pain. Among these opioid and non-steroidal anti-inflammatory drugs stand in the first line of therapy, however, prolonged administration of these substance is generally challenged by development of analgesic tolerance in patients. Therefore, it is highly valuable to find new pharmacological strategies for prolonged therapeutic procedures. In this respect, Taurine, a free amino acid, has been shown to induce significant analgesia at both spinal and peripheral levels through cholinergic mechanisms. In the present study, we used hot-plate analgesic test to investigate how taurine either as a single medication or in combination with sodium salicylate and morphine may affect both acute response to pain and development of analgesic tolerance. The effect of taurine was also tested on morphine withdrawal syndrome. Hyoscine butyl bromide was used to assess the role of muscarinic receptors in taurine-mediated effects. Finally, biochemical assay was done to reveal how the activity of brain acetylcholinesterase may change in relation with muscarinic receptor activity. Results indicated that acute administration of taurine-sodium salicylate combination causes more potent analgesia compared to the use of tau (but not SS alone) and this seems to be mediated via activity of muscarinic receptors in peripheral nervous system. Furthermore, the effect of this combination undergoes less analgesic tolerance during time. Combination of taurine and morphine is an effective strategy to attenuate both morphine analgesic tolerance and dependence and this also seems to depend on activity of muscarinic receptors, however through differential cellular mechanisms.