Enhancement of the analgesic effect of morphine by sodium diethyldithiocarbamate in rats

Effects of clonidine and yohimbine, alone and in combination with morphine, on supraspinal analgesia

Morphine raised the threshold for escape from aversive electrical stimulation, delivered to the mesencephalic reticular formation. Clonidine, given alone, had no effect; however, when administered with morphine it blocked the analgesic effect of morphine. Conversely, clonidine, but not morphine, increased the latency to respond to the aversive stimulation, suggesting that clonidine may not have analgesic properties but may merely impair the ability of the animal to respond to the nociceptive stimulation. Yohimbine produced hyperalgesia and also blocked the effect of morphine. These findings are similar to those seen with dopamine agonists and may be related to the effects of yohimbine on the release of dopamine.

Copper complexes of non-steroidal antiinflammatory agents: analgesic activity and possible opioid receptor activation

Cu(II)2(acetylsalicylate)4, Cu(II)(anthranilate)2, Cu(II)2[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolylacetate]4, Cu(II)(3,5-diisopropylsalicylate)2, Cu(II)(salicylate)2, Cu(II)2(2-[3-(trifluoromethyl)-phenyl]aminonicotinate)4, Cu(II)(L-alaninate)2, Cu(II)(L-cystinate)2, and Cu(II)(glycinate)2 were generally found to be more effective analgesics than their parent ligands, Cu(II)(chloride)2, and Cu(II)2(acetate)4 in the Writhing Mouse and Adjuvant Arthritic Rat pain models following subcutaneous and oral administration. Comparison of the time course of analgesia for salicylic acid and Cu(II)(salicylate)2 in the adjuvant arthritis pain model revealed that this complex had more sustained activity in addition to being more potent than salicylic acid. Cu(II)2(indomethacin)4 was also found to be as effective as morphine in both pain models. These data and pertinent literature are discussed in support of the hypothesis that copper complexes activate copper-dependent opioid receptors.

The effects of divalent ions on morphine analgesia and abstinence syndrome in morphine-tolerant and -dependent mice

Intracerebral administration of copper sulfate potentiated morphine analgesia in morphine-tolerant and -dependent mice, but copper failed to affect other abstinence signs. When abstinence was precipitated with a partial antagonist, nalorphine, stereotyped jumping was not inhibited by either calcium or copper. These modifications of narcotic effects by copper were produced without alterations in the brain disposition of morphine. Total radioactivity in the brain following radioactive naloxone administration was also not altered.

Effect of apomorphine on the antinociceptive activity of morphine

Apomorphine pretreatment potentiated the analgesic effect of morphine in a dose-dependent manner both in rats and in mice measured by five different tests (writhing, hot plate, inflamed foot, tail-pinch and tail-flick procedures). Furthermore, apomorphine augmented the antinociceptive activity of morphine in tolerant animals as well. In morphine dependent mice the nalorphine precipitated jumping--a withdrawal symptom--was found inhibited by apomorphine treatment. The results are discussed in the light of the numerous but contradictory data available in the literature.

Selective depleting effect of syrosingopine on brain catecholamine levels with relation to morphine analgesia in the rat

Reserpine was the most potent, rescinnamine the next and syrosingopine the weakest in the depleting effects on brain amines of rauwolfia alkaloids. After syrosingopine, brain dopamine (DA) was decreased to a smaller degree and with a shorter duration as compared with norepinephrine (NE) and serotonin (5-HT), whereas reserpine elicited a marked and long lasting reduction in these amines. Accordingly, syrosingopine induced a depletion of brain NE and 5-HT without alteration in brain DA content 2-4 days after administration. Repeated administrations of syrosingopine, 2 mg/kg daily for 2 or 4 days, resulted in similar alterations in brain amine levels. This selective depleting effect of syrosingopine on brain amines was potentiated by combined treatment with disulfiram or fusaric acid, a dopamine beta-hydroxylase inhibitor. Under the condition of selective depletion of brain amines induced by repeated administrations of syrosingopine, 2 mg/kg daily for 2 days, the analgesic action of morphine was not affected, whereas reserpine and tetrabenazine antagonized morphine analgesia, concomitant with inducing a depletion of all brain amines. The results suggest that brain DA may be more important than brain NE or 5-HT with regard to the mechanisms by which morpine produces analgesia.

Pharmacological properties of centrally-administered agents which interfere with neurotransmitter function: a comparison with the central depressant effects of ouabain

1. Centrally administered sodium diethyldithiocarbamate (DDC) produced hypothermia, central nervous depression and potentiation of the antinociceptive effect of morphine. These effects resemble those seen with centrally administered ouabain. Furthermore, the interactions of (+)-amphetamine, desmethylimipramine and nialamide with DDC and ouabain were similar.2. 6-Hydroxydopamine by the same route also produced central nervous depressant effects including hypothermia, decreased locomotor activity and catalepsy but not ptosis.3. Both ouabain and chlorpromazine produced similar effects on behaviour and body temperature including selective abolition of a conditioned avoidance response.4. Although centrally administered tetrabenazine produced ptosis, decreased locomotor activity and catalepsy, it had no significant effect on body temperature. However, the hypothermia produced by peripherally administered reserpine was reversed by centrally administered dibutyryl cyclic 3',5'-adenosine monophosphate.5. Centrally administered cocaine and desmethylimipramine produced no depressant effects but an increased excitability and responsiveness were apparent in both cases.6. Although the observed behavioural depression and hypothermia can occur independently both seem to involve an interference with dopaminergic systems.

Comparison of the dose-response effects of morphine on brain amines, analgesia and activity in mice

1. Noradrenaline, dopamine, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid concentrations in the mouse brain were measured 30 min after subcutaneous injection of doses of morphine ranging from 0.1 to 100 mg/kg: motor activity was also measured.2. The noradrenaline concentration in the mouse brain was reduced by moderate (2 to 20 mg/kg) but not by high (above 20 mg/kg) and low (below 2 mg/kg) doses of morphine.3. The dopamine concentration in the mouse brain was reduced by moderate (1 to 20 mg/kg) doses but was raised by high doses (above 20 mg/kg) of morphine.4. The 5-hydroxytryptamine concentration in the mouse brain was reduced by moderate (1 to 20 mg/kg) doses of morphine but not by high (above 20 mg/kg) and low (below 1 mg/kg) doses of morphine.5. The 5-hydroxyindoleacetic acid concentration was not affected by low doses (0.1 to 2 mg/kg), raised by a dose of 5 mg/kg, lowered by doses of 10-50 mg/kg and not affected by 100 mg/kg of morphine.6. These results are discussed with reference to the possible implication of changes in monoamines for the analgesic and behavioural effects of morphine.