Antinociceptive effects of trazodone and m-chlorophenylpiperazine (mCPP) in mice: interaction with morphine

Synthesis of N-substituted 4,6-dioxo-imidazo[3,4-c] thiazoles and their analgesic activity in mice

A new series of N-substituted dioxo-imidazo[3,4-c]thiazoles have been prepared and evaluated for their analgesic activity. The structures of these new derivatives were confirmed by lR, 1H NMR and 13C NMR spectra, and by elemental analysis. When administered intraperitoneally to mice all derivatives were devoid of any toxic effect, even at the high dose of 800 mg kg(-1). In the phenylbenzoquinone-induced abdominal constriction test in mice, eight of the nine synthesized compounds exhibited significant antinociceptive properties with ED50 values (50% effective dose) ranging from 46.7 to 104.7 mg kg(-1) intraperitoneally. Further investigation demonstrated that analgesic activity of the most effective derivatives 5e and 5f partly involved opioidergic and/or noradrenergic pathways.

Combined use of trazodone-naltrexone versus clonidine-naltrexone in rapid withdrawal from methadone treatment. A comparative inpatient study

Trazodone is a non-tricyclic antidepressant drug with specific antagonistic activities at 5-HT(2) and alpha-1 adrenoceptors. We test the efficacy of trazodone (T) compared with clonidine (C) in rapid opiate detoxification (ROD) from methadone after reduction to a daily maintenance dose </=20 mg. Forty five inpatients were consecutively assigned either to T (n=30) or to C (n=15) treatment in a 7-day ROD protocol with naltrexone administration starting at day 4. The maximum daily dosage was 800 mg for T and 1.2 mg for C. The retention rate was similar in both groups (93.3%). Overall, T was as effective as C in the ROD protocol. T was slightly superior in controlling some subjective and psychological symptoms, but not under naltexone challenge. No severe adverse effects were observed. We conclude that T is effective, safe and well-tolerated in acute withdrawal from methadone. Further investigation is needed to test the effectiveness and safety of T in ultra-rapid protocols and its usefulness in long-term administration to detoxified addicts.

Do alpha2-adrenoceptors play an integral role in the antinociceptive mechanism of action of antidepressant compounds?

Antidepressants are analgesic in the absence or presence of depression. The underlying mechanisms probably involve a complex interplay between several neurotransmitter systems and neuroreceptors. Alpha-adrenoceptors play an important role in pain processing and alpha2-adrenoceptor agonists have been used in clinical pain management so we have investigated whether alpha-adrenoceptor sub-types mediate the antinociceptive activity of antidepressants. Thus, the abdominal constriction assay in mice was used to examine the antinociceptive responses of a diverse range of antidepressants following alpha1- or alpha2-adrenoceptor antagonism. The antidepressants or monoamine reuptake inhibitors included the serotonin selective reuptake inhibitor paroxetine, the serotonin-noradrenaline reuptake inhibitor sibutramine, the resolved (+)- and (-)-enantiomers of the noradrenaline reuptake inhibitor oxaprotiline, plus the tricyclics amitriptyline and dothiepin. All these compounds have been previously shown to be antinociceptive in this paradigm. The respective alpha1- and alpha2-adrenoceptor antagonists prazosin and RX821002 ([2-(2-methoxy-1,-4-benzodioxan-2-yl)-2-imidazoline]) did not produce antinociception though at 1.0 mg kg(-1); s.c., RX821002 but not prazosin blocked clonidine antinociception. The antinociceptive activity produced by sub-maximal doses of amitriptyline, dothiepin, sibutramine, paroxetine, (+)- and (-)-oxaprotiline were all blocked by RX821002 but not by prazosin. Additionally, both morphine and aspirin antinociception was resistant to alpha1- and alpha2-adrenoceptor antagonism. Thus, alpha2- rather than alpha1-adrenoceptors may play an integral role in antidepressant antinociception irrespective of the propensity for inhibiting reuptake of not only noradrenaline but also serotonin. It is probable, however, that other differing pharmacological properties of some antidepressants, such as opioid-like activity, may complicate any empirical correlation between monoamine uptake and analgesia.

Analgesic effect of tianeptine in mice

The effects of tianeptine, a novel and unusual tricyclic antidepressant drug, on tail-flick and hot-plate tests, which are two thermal analgesia evaluating methods, have been investigated in mice. Tianeptine (5 and 10 mg/kg), para-chlorophenylalanine (pCPA) (100 mg/kg) and a combination of pCPA and tianeptine (10 mg/kg) or saline were injected to mice intraperitoneally. pCPA (100 mg/kg) was injected 24 h before tianeptine or saline treatment when it was combined with tinaeptine (10 mg/kg) or tested alone. The tail-flick latencies and hot-plate reaction times of the mice were measured between 15th and 180th minutes following injections. Tianeptine (10 mg/kg) exhibited a significant antinociceptive activity that could be measured by both tests as compared to groups which were treated with saline or pCPA alone between 15th and 180th min of the observation period. The lower dose of tianeptine (5 mg/kg) or pCPA (100 mg/kg) did not produce any significant changes on tail-flick latency or hot-plate reaction time of the mice. However, pretreatment with pCPA completely blocked the antinociceptive effect induced by tianeptine (10 mg/kg) in both tests used in the present study. Furthermore, tianeptine (10 mg/kg) did not cause any significant impairment effects on rotarod performance of the mice. Our results suggested that tianeptine has a prominent thermal antinociceptive activity in mice and that increased serotonergic activity may be responsible for the analgesic effect of tianeptine.

Synthesis of thiazolotriazine derivatives and their antinociceptive effects in mice

Ans raci A series of 2-(4-arylpiperazin-1-yl-methyl)-4-methyl-1-oxo-5,6,8,8a-tetrahydro -thiazolo[3,4-d] [1,2,4]triazines was prepared and tested for antinociceptive activity. The compounds were prepared by the Mannich reaction from the corresponding 2-unsubstituted thiazolotriazines. When administered intraperitoneally most were found to have potent analgesic activity in the mouse during tests of phenylbenzoquinone-induced abdominal constriction; ED50 values (doses resulting in half the maximum effect) ranged from 10 to 87 mg kg(-1). Derivatives with a 3-chloro- or 4-fluorophenylpiperazinylmethyl side-chain in the 2-position of the bicyclic system were, when administered intraperitoneally at doses greater than 25 mg kg(-1), also effective in the hot-plate test without associated sedative effects. The compounds have a large therapeutic index; intraperitoneal LD50 values (doses which result in the death of half the animals) were > 700 mg kg(-1). Naloxone attenuated the analgesic activity of the 3-chloro derivative, suggesting the participation of micro-receptors in the antinociceptive effects of this drug. In addition, a nonopioid mechanism, probably related to enhancement of the release of 5-hydroxytryptamine and noradrenaline, or inhibition of the neuronal re-uptake of these compounds, has been evinced to explain the analgesic properties of the 3-chloro or 4-fluoro derivatives. These results provide evidence for the involvement of noradrenergic and 5-hydroxytryptaminergic pathways in the analgesic activity of 3 and 4. Because of their potential effectiveness, the 3-chloro- or 4-fluorophenylpiperazinylmethyl derivatives might be suitable for treatment of a wide variety of painful conditions and could be attractive reserve agents for patients dissatisfied with opioids.

Effects of two N-arylpiperazinylmethylpyrazolo [1,5-d][1,2,4]triazine derivatives in pain and antidepressant tests in mice

The antinociceptive and antidepressant effects of two pyrazolotriazine derivatives, 2-phenyl-3,3a-dihydro-4-oxo-5-(4-phenylpiperazin-1-yl) methyl-pyrazolo[1,5-d][1,2,4]-triazine (SM1) and 2-phenyl-3,3a-dihydro-4-oxo-5-[4-(4-fluorophenyl)piperazin-1-yl] methylpyrazolo[1,5-d][1,2,4] triazine (SM3) have been investigated in mice using classical pharmacological tests. The intraperitoneal LD50 values of SM1 and SM3 were 253.4 and 218.8 mg kg-1 respectively. SM1 and SM3 showed analgesic properties in the phenylbenzoquinone-induced abdominal constriction test (ED50 approximately 10-15 mg kg-1, i.p.) and in the hot-plate test. The antinociceptive effects of the triazines were significantly reduced by administration of naloxone (1 and 3.2 mg kg-1, s.c.) and yohimbine (1 mg kg-1, p.o.). Acute intraperitoneal administration of both compounds (1 mg kg-1 SM1 or 1.5 mg kg-1 SM3) potentiated morphine (0.15 mg kg-1, s.c.) analgesia in the phenylbenzoquinone test. Although this synergistic activity was not reversed by methysergide (0.5 mg kg-1, i.p.), the analgesic activity of both compounds was enhanced by administration of 5-hydroxytryptophan (50 mg kg-1, i.p.) in conjunction with carbidopa (25 mg kg-1, i.p.). Furthermore, neither compound (at 100 mg kg-1, i.p.) significantly reduced the duration of immobility of mice in the forced swimming test, and both (at 75 mg kg-1, i.p.) were ineffective at enhancing the toxic effects of yohimbine (30 mg kg-1, s.c.). Only SM3 (ED50 = 74.5 mg kg-1, i.p.) significantly antagonized reserpine (2.5 mg kg-1, i.p.)-induced ptosis. Thus, the results suggest that SM1 and SM3 have antinociceptive properties related to co-involvement of opioidergic and alpha 2-adrenoceptor mechanism without associated antidepressant properties.

Synthesis and analgesic effects of 3-substituted 4,6-diarylpyridazine derivatives of the arylpiperazine class

A new series of 4,6-diaryl pyridazines substituted in the 3-position by arylpiperazinyl moieties was synthesized and evaluated for analgesic activity. Five out of the nine tested compounds possessed significant antinociceptive effects in the phenylbenzoquinone-induced writhing test (PBQ test) with ED50 values ranging from 26.0 to 37.7 mg/kg ip. The most active derivatives 2a, 2d and 2h had a low toxicity (LD50 > 800 mg/kg ip) but showed some sedative and neurotoxic effects from the dose of 50 mg/kg ip. The three selected pyridazines were devoid of activity in the hot-plate test. However, analgesic activity of 2d and 2h was significantly reversed by naloxone in the PBQ test. Administered at the low dose of 5 mg/kg ip, 2h greatly potentiated the antinociceptive response induced by morphine (0.15 mg/kg sc). In addition, analgesic effects of 2h (2.5 mg/kg ip) were also potentiated by 5-hydroxytryptophan combined with carbidopa. These results suggest that pyridazine 2h induces analgesia, which is mediated via both opioid and serotonergic mechanisms.

Interaction of opioids with antidepressant-induced antinociception

The antinociceptive activity of antidepressant drugs is poorly understood. In this study, using the acetic acid writhing test in mice, the antinociception produced by clomipramine (CLO), maprotiline (MAP), imipramine (IMI), and zimelidine (ZIM) was tested and correlated with opioid drugs. All the compounds displayed a significant dose-dependent antinociception, which was not antagonized by naloxone (NX) or naltrexone (NTX). The administration of morphine (M) plus CLO, MAP, IMI or ZIM resulted in a significant additive effect that was antagonized by 1 or 10 mg/kg NX or NTX, except in the case of IMI. This finding suggests that the additive effect seems to be partially due to activation of opioid receptors, except for the case of imipramine. However, aminophylline, a non-selective blocker of A1/A2 adenosine receptors, significantly antagonized the antinociceptive activity of CLO, IMI, MAP and ZIM, demonstrating an interaction at the level of adenosine receptors. This work suggests that the antinociceptive activity of antidepressants could be dependent on critical levels of free 5-HT and NE at receptor(s) site(s) in CNS and on their interaction with opioid and adenosine receptors.

Effect of p-chlorophenylalanine and alpha-methyltyrosine on the antinociceptive effect of antidepressant drugs

The role of para-chlorophenylalanine and alpha-methyl-DL-p-tyrosine in the antinociceptive effects of the intracerebroventricular administration of the antidepressant drugs clomipramine, zimelidine, imipramine and maprotiline was studied using the acetic acid writhing test in mice. The results demonstrated an antinociceptive effect for all these antidepressants. Pretreatment with para-chlorophenylalanine significantly reduced the antinociception induced by the ED50's of imipramine and maprotiline, and did not modify the effects of zimelidine and clomipramine, pretreatment with alpha-methyl-tyrosine did not modify the antinociception induced by these drugs except maprotiline. Pretreatment with para-chlorophenylalanine plus alpha-methyltyrosine significantly reduced the antinociceptive effect of all the antidepressants tested. The main finding of the present study is that the association of para-chlorophenylalanine plus alpha-methyltyrosine reduced the antinociceptive action of all the antidepressants. This means that critical levels of both 5-HT and NA are responsible for mediating the antinociceptive effects of antidepressants on the writhing test in mice.

Effects of trazodone and m-chlorophenylpiperazine (m-CPP) on acute dependence in mice

The antidepressant trazodone and its main metabolite, m-CPP, having an antiserotoninergic and serotoninergic activity respectively, were studied in an acute dependence model in mice, to establish whether 5-hydroxytryptaminergic systems are involved in the manifestations of acute opiate dependence and in its development. When drugs were administered 15 min before naloxone, all signs of abstinence decreased, with the exception of teeth chattering that was increased by m-CPP and unaffected by trazodone. When injected 15 min before morphine, jump episodes were decreased by the highest doses of both drugs, while teeth chattering was decreased by m-CPP only. When administered 1 h before morphine, trazodone increased paw and head shakes and mCPP decreased teeth chattering and both left the other signs unaffected. Serotoninergic systems seem to have a significant role in events involved in the withdrawal syndrome and a minor one in those leading to the development of dependence.