Treatment with dopamine ß-hydroxylase (DBH) inhibitors prevents morphine use and relapse-like behavior in rats.

BACKGROUND: Opioid use disorders are serious contributors to the harms associated with the drug use. Unfortunately, therapeutic interventions for opioid addicts after detoxification have been limited and not sufficiently effective. Recently, several studies have led to promising results with disulfiram (DSF), a dopamine ß-hydroxylase (DBH) inhibitor, showing that it is a potent agent against not only alcohol but also addiction to various drugs. MATERIALS AND METHODS: This study was designed to examine whether DSF and nepicastat (NEP; another DBH inhibitor) modify morphine intake and reinstatement of seeking-behavior using the rat model of intravenous morphine self-administration. Additionally, we intended to estimate the effects of both inhibitors on the locomotor activity as well as on extracellular dopamine and its metabolite levels in the nucleus accumbens using microdialysis in naive rats. RESULTS: We demonstrated that both DBH inhibitors reduced responding to morphine self-administration. Moreover, DSF and NEP administered acutely before reinstatement test sessions consistently attenuated the reinforcing effects of morphine and a morphine-associated conditioned cue. The observed effects for lower doses (6.25-25 mg/kg; ip) of both DBH inhibitors seem to be independent of locomotor activity reduction and dopamine level in the nucleus accumbens. Neither DSF nor NEP administered daily during morphine abstinence with extinction training sessions had any effect on active lever-responding and changed the reinstatement induced by morphine priming doses. Reinstatement of drug-seeking behavior induced by a conditioned cue previously associated with morphine delivery was attenuated following repeated administration of DSF or NEP during the abstinence period. CONCLUSION: These results seem to point to the significance  of DBH inhibition as a potential pharmacotherapy against morphine use disorders.

Modification of fentanyl analgesia by antidepressants.

Clinical practice often requires simultaneous administration of antidepressants with opioids (oncology, rheumatology). Coadministration may either attenuate or potentiate opioid analgesia. The purpose of this paper was to verify how the analgesic action of fentanyl (0.05 mg/kg) is affected by single administration as well as 4- or 21-day premedication with antidepressants characterized by various mechanisms of action. The effects of amitriptyline 3 mg/kg, moclobemide 5 mg/kg, fluoxetine 5 mg/kg and reboxetine 0.08 mg/kg were investigated. Experiments were conducted on normotensive Wistar Kyoto rats. The pain threshold was measured using an analgesimeter. It was concluded that the single administration of an antidepressant increases the analgesic action of fentanyl. Four-day premedication with fluoxetine and reboxetine significantly attenuated the antinociceptive action of fentanyl, whereas 21-day premedication with all antidepressants investigated (fluoxetine, amitriptyline, moclobemide, reboxetine) markedly decreased it. The potential clinical importance of this observation is discussed.

Bradykinin receptor antagonists and cyclooxygenase inhibitors in vincristine- and streptozotocin-induced hyperalgesia.

Pain that accompanies neuropathy is difficult to treat. Analgesics administered as monotherapies possess low activities in relieving this kind of pain. The effect of the simultaneous administration of indomethacin (a preferential inhibitor of cyclooxygenase-1; COX-1) or celecoxib (a relatively selective inhibitor of cyclooxygenase-2; COX-2), with selective antagonists of bradykinin(2) (B(2)) bradykinin(1) (B(1)) receptors (HOE 140 or des-Arg(10)-HOE 140) on the alleviation of diabetic and toxic neuropathic pain was investigated. Pretreatment with indomethacin (0.1 mg/kg, sc) increased the antihyperalgesic activity of low daily doses of HOE 140 or des-Arg(10)HOE 140 (70 nmol/kg, ip) in a diabetic (streptozotocin(STZ)-induced) neuropathy/hyperalgesia experimental model. Premedication with celecoxib before HOE 140 or des-Arg(10)HOE 140 administration resulted in a gradual reduction of STZ hyperalgesia. Furthermore, on days 23-24, almost complete abolishment of STZ hyperalgesia was observed. After cessation of drug administration, hyperalgesia quickly returned to the baseline threshold. The results of this study suggest that inhibitors of cyclooxygenases can increase the antihyperalgesic activity of selective antagonists of B(2) and B(1) receptors in diabetic and toxic neuropathic pain models. These observations may be clinically relevant.

Bradykinin receptors antagonists and nitric oxide synthase inhibitors in vincristine and streptozotocin induced hyperalgesia in chemotherapy and diabetic neuropathy rat model.

PURPOSE: The influence of an irreversible inhibitor of constitutive NO synthase (L-NOArg; 1.0 mg/kg ip), a relatively selective inhibitor of inducible NO synthase (L-NIL; 1.0 mg/kg ip) and a relatively specific inhibitor of neuronal NO synthase (7-NI; 0.1 mg/kg ip), on antihyperalgesic action of selective antagonists of B2 and B1 receptors: D-Arg-[Hyp3,Thi5,D-Tic7,Oic8] bradykinin (HOE 140; 70 nmol/kg ip) or des Arg10 HOE 140 (70 nmol/kg ip) respectively, in model of diabetic (streptozotocin-induced) and toxic (vincristine-induced) neuropathy was investigated. METHODS: The changes in pain thresholds were determined using mechanical stimuli--the modification of the classic paw withdrawal test described by Randall-Selitto. RESULTS: The results of this paper confirm that inhibition of bradykinin receptors and inducible NO synthase but not neuronal NO synthase activity reduces diabetic hyperalgesia. Pretreatment with L-NOArg and L-NIL but not 7-NI, significantly increases antihyperalgesic activity both HOE 140 and des Arg10 HOE 140. It was also shown that both products of inducible NO synthase and neuronal NO synthase activation as well as bradykinin are involved in hyperalgesia produced by vincristine. Moreover, L-NOArg and 7-NI but not L-NIL intensify antihyperalgesic activity of HOE 140 or des-Arg10HOE 140 in toxic neuropathy. CONCLUSIONS: Results of these studies suggest that B1 and B2 receptors are engaged in transmission of nociceptive stimuli in both diabetic and toxic neuropathy. In streptozotocin-induced hyperalgesia, inducible NO synthase participates in pronociceptive activity of bradykinin, whereas in vincristine-induced hyperalgesia bradykinin seemed to activate neuronal NO synthase pathway. Therefore, concomitant administration of small doses of bradykinin receptor antagonists and NO synthase inhibitors can be effective in alleviation of neuropathic pain, even in hospital care.

Magnesium ions and opioid agonists in vincristine-induced neuropathy.

Neuropathic pain is difficult to treat. Classic analgesics (i.e., opioid receptor agonists) usually possess low activity. Therefore other agents such as antidepressants, anticonvulsants, and corticosteroids are used. It is commonly known that NMDA antagonists increase analgesic activity of opioids. Unfortunately, clinical use of NMDA antagonists is limited because of the relatively frequent occurrence of adverse effects e.g., memory impairment, psychomimetic effects, ataxia and motor in-coordination. Magnesium ions (Mg(2+)) are NMDA receptor blockers in physiological conditions. Therefore, in this study the effect of opioid receptor agonists and the influence of Mg(2+) on the action of opioid agonists in vincristine-induced hyperalgesia were examined. Opioid agonists such as morphine (5 mg/kg, ip), and fentanyl (0.0625 mg/kg, ip), as well as the partial agonist buprenorphine (0.075 mg/kg, ip) administered alone on 5 consecutives days did not modify the hyperalgesia in vincristine rats. In contrast, pretreatment with a low dose of magnesium sulfate (30 mg/kg, ip) resulted in a progressive increase of the analgesic action of all three investigated opioids. After discontinuation of drug administration, the effect persisted for several days.

Effect of cyclooxygenase and nitric oxide synthase inhibitors on vincristine induced hyperalgesia in rats.

The purpose of this study was to investigate the effect of cyclooxygenase (COX) inhibitors and nitric oxide synthase (NOS) inhibitors on the development of vincristine (VIN)-induced hyperalgesia. Indomethacin (IND) and celecoxib (CEX) were used as relatively selective inhibitors of COX-1 and COX-2, respectively. NOS inhibitors included the nonspecific inhibitor NG-nitro-Larginine (L-NOArg) and L-N6-(1-iminoethyl)lysine (L-NIL), which preferentially acts on inducible NOS, as well as 7-nitroindazole (7-NI), which is a relatively specific neuronal NO synthase inhibitor. Both IND and CEX markedly suppressed hyperalgesia, whereas all three NOS inhibitors prevented the development of hyperalgesia due to VIN administration. The results of this study suggest participation of COX-1 and COX-2 as well as iNOS and nNOS in the transmission of pain stimuli in VIN-induced hyperalgesia.

Effect of selenium compound (selol) on the opioid activity in vincristine induced hyperalgesia.

PURPOSE: Effect of organoselenium compound (selol), on antinociceptive action of opioid agonists in vincristine neuropathic pain model was investigated. METHODS: The changes in pain thresholds were determined using mechanical stimuli--the modification of the classic paw withdrawal test described by Randall-Selitto. RESULTS: Daily administration of VIN (70 microg/kg, iv) resulted in progressive decrease of pain threshold. Neither morphine, fentanyl nor buprenorphine administered alone in 5 consecutive days modified the vincristine-induced hyperalgesia, whereas selol slightly increased the nociceptive threshold. Co-administration of selol with opioids markedly enhanced the analgesic activity of all three investigated compounds. CONCLUSIONS: Therefore, concomitant administration of selenium and opioids may be beneficial in terminal neoplastic states.

Effect of cannabinoid receptor agonists on streptozotocin-induced hyperalgesia in diabetic neuropathy.

The effect of CB-1 and CB-2 receptor agonists, as well as an influence of a non-selective inhibitor of nitric oxide synthase (NOS), L-NOArg, and an inhibitor acting preferentially on cyclooxygenase-1 (COX-1), indomethacin, on the action of cannabinoid receptor agonists in a streptozotocin (STZ)-induced neuropathic model was investigated. When administered alone, a non-selective cannabinoid receptor agonist, WIN 55,212-2, a potentially selective CB-1 cannabinoid receptor agonist, Met-F-AEA, and a selective CB-2 cannabinoid receptor agonist, AM1241, dose-dependently reduced STZ-induced hyperalgesia. The results of the present study also demonstrated that inhibitors of COX and NOS increase antihyperalgesic activity of low doses of CB-1 and CB-2 receptor agonists. Hypothetical consequences of this phenomenon are discussed.

Alpha(1) and alpha(2)-adrenoreceptor antagonists in streptozotocin- and vincristine-induced hyperalgesia.

The effect of alpha(1)- and alpha(2)-adrenoreceptor antagonists (prazosin and yohimbine, respectively) on streptozotocin (STZ)- and vincristine (VIN)-induced hyperalgesia in rats was studied. In two experimental models, yohimbine (1.0 mg/kg ip) completely abolished STZ and VIN-induced hyperalgesia. This effect was markedly prolonged in diabetic rats. Prazosin (0.3 mg/kg ip) attenuated and delayed development of STZ-induced hyperalgesia. In VIN-elicited neuropathy, the administration of prazosin not only delayed hyperalgesia but also produced antinociception. After cessation of drug administration, a significant decrease in nociceptive threshold was observed. The obtained results seem to indicate that both alpha(1)- and alpha(2)-adrenoreceptors are engaged in diabetic (STZ) and toxic (VIN) neuropathy.

Magnesium ions and opioid agonist activity in streptozotocin-induced hyperalgesia.

Streptozotocin-induced hyperglycemia accompanied by a chronic decrease in the nociceptive threshold is considered a useful model of experimental hyperalgesia. We examined (1) the effect of the opioid receptor agonists and (2) the effect of the magnesium ions (Mg(2+)) on the antinociceptive action of opioid agonists in a diabetic neuropathic pain model. When administered alone, opioid agonists like morphine (5 mg/kg i.p.) and fentanyl (0.0625 mg/kg i.p.), as well as the partial agonist buprenorphine (0.075 mg/kg) had only little effect on streptozotocin-induced hyperalgesia. However, pretreatment with Mg(2+) at a dose of 40 mg magnesium sulfate/kg i.p. markedly enhanced the analgesic activity of all three investigated opioids. Practical aspects of co-administration of magnesium and opioids in diabetic neuropathy are discussed.

Effect of bradykinin receptor antagonists on vincristine- and streptozotocin-induced hyperalgesia in a rat model of chemotherapy-induced and diabetic neuropathy.

The role of bradykinin receptor blockade in the development of neuropathies caused by diabetes mellitus and vincristine was examined. The effects of a potent and selective B(1) receptor antagonist (des-Arg(10)-HOE 140) as well as a specific antagonist of B(2) receptors (HOE 140) were investigated. Both agents significantly decreased hyperalgesia caused otherwise by vincristine. In a diabetic neuropathy model, both agents almost completely suppressed hyperalgesia in the first 10 days of the study. However, from day 11 after administration of streptozotocin, the action of des-Arg(10)-HOE 140 was significantly weaker than that of HOE 140. The results of the study suggest involvement of both B(1) and B(2) receptors in transmission of nociceptive stimuli in the vincristine-induced as well as diabetic neuropathy model.

Effect of cyclooxygenase and nitric oxide synthase inhibitors on streptozotocin-induced hyperalgesia in rats.

We examined a possible involvement of cyclooxygenase (COX) and nitric oxide synthase (NOS) products in hyperalgesia occurring during streptozotocin (STZ)-induced diabetes. Indomethacin and celecoxib were used as relatively selective inhibitors of COX-1 and COX-2, respectively. NOS inhibitors included: non-specific inhibitor N(G)-nitro-L-arginine and L-N(6)-(1-iminoethyl)lysine preferentially acting on inducible NOS (iNOS) as well as 7-nitroindazole relatively specific inhibitor neuronal NOS (nNOS). The above-mentioned agents, except 7-nitroindazole, suppressed hyperalgesia occurring after administration of STZ. The results of the study suggest participation of COX-1, COX-2 and iNOS, but not nNOS, in transmission of pain stimuli in STZ-induced diabetic hyperalgesia.

Effect of selol on the opioids activity in streptozotocin induced hyperalgesia.

We examined the effect of the opioid receptor agonists and the effect of an antioxidant selol, which is an organoselenium compound on antinociceptive action of opioid agonists in diabetic neuropathic pain model. Streptozotocin (STZ) induced hyperglycemia accompanied by a prolonged decrease in nociceptive threshold is considered a useful model of experimental hyperalgesia. The changes in pain thresholds were determined using mechanical stimuli--the modification of the classic paw withdrawal Randall-Selitto test. Neither morphine, fentanyl nor buprenorphine administered alone in 7 consecutives days modified the STZ induced hyperalgesia, whereas selol slightly increased the nociceptive threshold. Pretreatment with selol markedly enhanced the analgesic activity of all three investigated opioids. Concomitant administration of selol and opioids in alleviation of neoplastic pains seems to be justified.

Effect of cyclooxygenase and NO synthase inhibitors administered centrally on antinociceptive action of acetaminophen (Part II).

As it has been demonstrated in a previous study, both cyclooxygenases (COXs) and nitric oxide synthases (NOSs) participate in the mechanism of acetaminophen (ACETA) action. Results obtained in this study indicate that intrathecal (it) or intracerebroventricular (icv) pretreatment with LG-nitro-L-arginine (L-NO-Arg), a non-selective inhibitor of NOS activity, as well as with 7-nitroindazole (7-NI), a selective nNOS inhibitor, potentiated the antinociceptive activity of subceiling doses of ACETA, but were without effect on the action of supramaximal doses in Randall-Selitto test. Similar effect of L-NO-Arg and 7-NI it was observed in writhing test, whereas L-NO-Arg icv or L-NIL it did not influence the action of ACETA in this model. Indomethacin (IND), an inhibitor preferentially acting on COX-1, as well as nimesulide (NIM) and celecoxib (CECOX), i.e. preferential and selective inhibitor of COX-2, respectively, administered icv almost completely blocked the antinociceptive effect of ACETA in Randall-Selitto method. On the other hand, pretreatment with NSAIDs it initially increased and then attenuated the ACETA antinociception. Yohimbine (YOH), an alpha2-adrenergic receptor antagonist, did not modify the antinociceptive action of ACETA administered alone. However, YOH decreased the nociceptive threshold increased by simultaneously administered IND and ACETA, NIM and ACETA, as well as CECOX and ACETA in Randall-Selitto model. In contrast to the peripheral (sc) application, IND administered centrally (icv or it) did not modify the ACETA antinociception in writhing test. Neither NIM nor CECOX administered sc, it or icv changed the ACETA antinociception in this model. Possible mechanisms and sites of antinociceptive effects of ACETA are discussed.