The efficacy of opioids is limited in chronic pain treatment, as a result of development of opioid tolerance. Based on previous demonstration of the effect of anticonvulsant drugs on morphine antinociception, the present study investigated the effects of vigabatrin (VGB) on the development and expression of morphine tolerance in mice. 101 male NMRI mice weighing 20-25 g were used in these experiments. To evaluate the VGB effects on the development or expression of morphine tolerance, animals received VGB (5, 10 or 20 mg/kg; i.p.), 30 min before morphine (50 mg/kg; s.c.) during induction period once daily for 3 days; or 30 min before challenge dose of morphine (5 mg/kg) before and after morphine-induced tolerance, respectively. The analgesic effect of VGB was evaluated at 30-time intervals (30, 60, 90 and 120 min) by tail-flick analgesiometer. The results showed that VGB at the dose of 20 mg/kg significantly attenuated the development and expression of morphine tolerance. Additionally, VGB alone did not affect the tail-flick latency times. Therefore, while VGB alone has no antinociceptive effect, it can prevent the development of morphine tolerance in mice.
"Co-administration of a second drug with an opioid enhances the latter's antinociceptive effect and attenuates the development of tolerance (12). Lamotrigine was originally designed as an anticonvulsant but was subsequently shown to have analgesic activity as well, such that it is now used to treat different types of neuropathic pain. "
[Show abstract][Hide abstract] ABSTRACT: Glial cells play a critical role in morphine tolerance, resulting from repeated administration of morphine. Both the development and the expression of tolerance are suppressed by the analgesic lamotrigine. This study investigated the relationship between the ability of lamotrigine to maintain the antinociceptive effect of morphine during tolerance development and glial cell activation in the spinal cord. In a rat model, morphine (15 µg) was intrathecally injected once daily for 7 days to induce morphine tolerance. Lamotrigine (200 µg) was co-administered with morphine either for 7 days or the first or last 3 days of this 7 day period. Thermal nociception was measured. OX-42 and GFAP immunoreactivity, indicating spinal microglial and astrocytic activation were evaluated on day 8. Tolerance developed after 7 days of intrathecal morphine administration; however, this was completely blocked and reversed by co-administration of lamotrigine. When lamotrigine was coinjected with morphine on days 5-7, the morphine effect was partially restored. Glial cell activation increased with the development of morphine tolerance but was clearly inhibited in the presence of lamotrigine. These results suggest that, in association with the suppression of spinal glial cell activity, intrathecally coadministered lamotrigine attenuates antinociceptive tolerance to morphine.
Journal of Korean medical science 02/2013; 28(2):300-7. DOI:10.3346/jkms.2013.28.2.300 · 1.27 Impact Factor
"One specific possibility is that reduced mGluR5 receptor activity decreased the internalization and desensitization of mu opioid receptors produced by chronic morphine exposure, thus preserving the analgesic efficacy of morphine (Schröder et al., 2009). Considering the evidence that morphine tolerance is inhibited by directly acting GABA agonists and GABA-transaminase inhibitors, it is equally possible that GLT-1 transporter activation prevented tolerance by enhancing GABA transmission, perhaps by increasing GABA synthesis via the glial glutamate-GABA shunt (McKenna, 2007; Sivam and Ho, 1985; Chavooshi et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: Glutamate transporter subtype 1 (GLT-1) activation is a promising - and understudied - approach for managing aspects of morphine tolerance caused by increased glutamatergic transmission. Identification of beta-lactam antibiotics as pharmaceuticals which activate GLT-1 transporters prompted us to hypothesize that repeated beta-lactam antibiotic (ceftriaxone) administration blocks development of tolerance to morphine antinociception through GLT-1 activation. Here, we injected rats with morphine (10mg/kg, s.c.) twice daily for 7 days to induce tolerance and used the hot-plate assay to determine antinociception on days 1, 4 and 7 of repeated morphine administration. Ceftriaxone and a selective GLT-1 transporter inhibitor dihydrokainate (DHK) were co-administered with morphine to determine if GLT-1 activation mediated the ceftriaxone effect. Tolerance was present on days 4 and 7 of repeated morphine administration. Ceftriaxone (50, 100 or 200mg/kg, i.p.) administration dose-dependently blocked development of morphine tolerance. DHK (10mg/kg, s.c.), administered 15 min before each morphine injection, prevented inhibition of morphine tolerance by ceftriaxone (200mg/kg, i.p.). These results identify an interaction between ceftriaxone and morphine in opioid-tolerant rats and suggest beta-lactam antibiotics preserve analgesic efficacy during chronic morphine exposure.
Drug and alcohol dependence 12/2009; 107(2-3):261-3. DOI:10.1016/j.drugalcdep.2009.10.010 · 3.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Previous studies have demonstrated that some anticonvulsant drugs can modulate tolerance to the opioid analgesia. In the present study, the effects of lamotrigine (LTG) on the development and expression of tolerance to the morphine-induced antinociception were evaluated using tail-flick test. To assess the LTG effects on tolerance development, the animals received LTG (3, 10 or 30 mg/kg; i.p.), 30-min prior to morphine (50 mg/kg; s.c.) administration during tolerance induction period once daily for 3 days. Also, to evaluate the effects of LTG on tolerance expression, different doses of LTG were administered 30-min before challenge dose of morphine (4 mg/kg; s.c.) following morphine-induced tolerance. In each experiment the antinociceptive response to the challenge dose of morphine was evaluated before (on day 1) and after tolerance induction (on day 4) every 30-min till 2 h by tail-flick test. Furthermore, the analgesic effect of various doses of LTG alone or with the challenge dose of morphine was evaluated as well. The results showed that LTG at the doses of 10 and 30 mg/kg could inhibit the development of tolerance. Also, LTG at the dose of 30 mg/kg attenuated the expression of morphine-induced tolerance. LTG alone injection was associated significantly with higher latency period when compared to the control group. Moreover, LTG (10 and 30 mg/kg) significantly enhanced antinociceptive effect of morphine challenge dose in non-tolerant animals. These data indicated that, while LTG can attenuate both development and expression of morphine-induced tolerance, it can enhance morphine-induced antinociception. These effects may have important clinical implications.
Brain research 08/2009; 1291:32-9. DOI:10.1016/j.brainres.2009.07.014 · 2.84 Impact Factor
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