Glutamate has a key role in pain perception and also development of tolerance and dependence to morphine. It has been reported that clavulanic acid affects glutamatergic transmission via activation of glutamate transporter. Therefore the present study was aimed to evaluate the possible antinociceptive effect of clavulanic acid and its preventive activity against development of morphine toleranc...

Glycyl-glutamine (Gly-Gln; beta-endorphin(30-31)) is an endogenous dipeptide synthesized from beta-endorphin(1-31). Previous investigations have shown that Gly-Gln inhibits the cardiovascular and respiratory depression caused by morphine and beta-endorphin(1-31), but it does not interfere with opioid analgesia. In this study, we tested whether Gly-Gln administration would influence morphine-ind...

We investigated the effect of chronic administration of morphine on noxious stimulus-induced antinociception (NSIA) produced by intraplantar capsaicin injection. In the untreated (naive) rat, we previously found that NSIA depends on activation of dopamine, nicotinic acetylcholine, and mu- and delta-opioid receptors in nucleus accumbens. Rats chronically implanted with subcutaneous morphine pell...

Pruritus (itch sensation) is the most common side effect associated with spinal administration of morphine given to humans for analgesia. A variety of agents have been proposed as antipruritics with poorly understood mechanisms and they are effective with variable success. kappa-Opioid agonists possess several actions that are opposite to micro -opioid agonists. We proposed to investigate the r...

We have shown in past isobolographic studies that a small amount of Δ-tetrahydrocannabinol (Δ-THC) can enhance morphine antinociception in mice. However, previous studies of the Δ-THC/morphine interaction were performed using normal mice or rats and evaluated acute thermal antinociception. Less is known about cannabinoid and opioid interactions involved in mechanical nociception and in chronic ...

In the present study the effects of both CCK receptor agonists and antago­ nists on antinociception induced by morphine in the tail-flick test have been evalu­ ated. M orphine induced dose-dependent antinoci�eption in mice. The response of morphine was potentiated by sulfated cholecystokinin-8 (CCK-8S) but not by unsulfated cholecystokinin-8 (CCK-8U). The CCK receptor antagonists MK-329 and L-3...

The present study focused on the role of peripheral ionotropic N-methyl-D-aspartate (NMDA) receptors in the development of tolerance to morphine-induced antinociception. An initial experiment revealed that NMDA channel blocker memantine, and NMDA receptor/glycine(B) site antagonist MRZ 2/576 inhibited maximal electroshock-induced convulsions (MES) in female NMR mice with respective potency of 5...

The effect of the &selective agonist [D-Pen2,D-PenS]enkephalin (DPDPE) on the antinociception produced by intracerebroventricular (i.c.v.) administration of the # agonists morphine, [D-Ala2,NMePhe4,Gly-olS]enkephalin (DAGO), [NMePhe3,D-Proa]morphiceptin (PLO17), fl-endorphin, phenazocine, etorphine and sufentanil was studied in mice. Only the antinociceptive effects of morphine and normorphine ...

Two separate lines of evidence suggested the present study. First, intracerebroventricularly (i.c.v.) administered morphine (a μ-opioid receptor agonist) and β-endorphin (an ε-opioid receptor agonist) produce antinociception by activating different descending pain inhibitory systems. Second, γ-irradiation attenuates the acute antinociceptive action of i.c.v. injected morphine, but not DPLPE (a ...