Serotonin receptor subtypes involved in the spinal antinociceptive effect of 5-HT in rats.

The present study was designed to investigate which subtypes of spinal 5-HT receptors are involved in 5-HT-induced antinociception using the mechanical pain test. Serotonin and various selective antagonists or agonists for 5-HT receptor subtypes (5-HT(1A), 5-HT(1B), 5-HT(2A), 5-HT(2C), 5-HT(3) and 5-HT(4)) were administered intrathecally (i.t.) in rats. The i.t. injection of 5-HT (1 microg) produced significant antinociceptive effects using the paw pressure test. Pretreatment with the 5-HT(2C) receptor antagonist mesulergine (1 and 10 microg) and the 5-HT(3) receptor antagonist tropisetron (1 and 10 microg) reversed totally the antinociception induced by 5-HT. Furthermore, at a dose of 10 microg, both the 5-HT(2A) receptor antagonist ketanserin and the 5-HT(1B) receptor antagonist penbutolol, but neither the 5-HT(1A) receptor antagonist WAY 100635 nor the 5-HT(4) receptor antagonist GR113808, attenuated the antinociceptive effect induced by 5-HT. In addition, an i.t. injection of the 5-HT(3) agonist mCPBG induced significant antinociceptive effects whereas the 5-HT(2) agonist DOI did not produce analgesia. These results suggest that although the precise degree of the involvement of spinal serotonergic 5-HT(3) receptors remains to be elucidated due to some differences in the effect of agonists or antagonists, these receptors seem to play a role in the antinociceptive effect of 5-HT against a mechanical acute noxious stimulus. The involvement of 5-HT(2C) is more questionable due to the observed discrepancies between the effects of the used agonist and antagonist. 5-HT(1A) and 5-HT(4) receptors do not seem to be involved. In addition, a possible functional interaction between spinal serotonergic receptors may exist.

Evidence for a role for bulbospinal pathways in the spinal antinociceptive effect of systemically administered vapreotide in normal rats.

Numerous neurotransmitters are involved in nociceptive transmission or regulation. Several reports have shown the analgesic effects of somatostatin and its analogues. Somatostatin, when given intrathecally, markedly reduced pain in cancer patients. Somatostatin analogues that possess a longer half-life time are more convenient for therapeutic use. Vapreotide, a somatostatin analogue, was shown to induce a long-lasting antinociceptive effect in rats. We studied the site and the mechanism of action of vapreotide in rats using the paw pressure test. Intrathecal administration of vapreotide induced no antinociception. Systemically administered vapreotide-induced antinociception was inhibited by several intrathecal (i.t.) administered antagonists (yohimbine, naloxone and to a lesser degree tropisetron). These results show a lack of spinal effect and suggest a supraspinal site of action with an involvement of noradrenergic and to a lesser degree serotonergic bulbospinal pathways. In addition, spinal opioid receptors also seen to be involved.

Educational interest of systematic collection of adverse drug reactions (with regard to an experience of nearly 20 years).

In 1978, a systematic collection of adverse drug reactions (ADRs) was set up in a hospital including several departments and continued for more than 18 years. Quarterly meetings were organized gathering clinicians, students, nurses and pharmacologists to discuss the clinical cases collected each quarter. Approximately 100 cases were analysed each year (1823 over the 18-year period). Educational interest resulted from (1) discussion about some ADRs frequently leading to hospitalization or consultation; (2) information about recent drugs and new and/or not well known ADRs; (3) education of physicians for a good prescription of drugs and increasing awareness of pharmacovigilance.

Differential influence of two serotonin 5-HT3 receptor antagonists on spinal serotonin-induced analgesia in rats.

We tested the antinociceptive effect of intrathecal (i.t.) administration of 5-HT3 and the 5-HT3 receptor agonist, 1-(m-chlorophenyl)-biguanide (mCPBG), in rats submitted to a mechanical noxious stimulus and the influence of the 5-HT3 receptor selective antagonists, tropisetron and granisetron. Both 5-HT and mCPBG (0.01, 0.1, 1, 10, 20 micrograms/rat) produced a significant dose-dependent antinociception. The lowest active doses were 0.1 and 1 microgram for 5-HT and mCPBG, respectively. The effect, observed with 20 micrograms, was significantly lower with mCPBG (+33 +/- 6%) than with 5-HT (+63 +/- 7%). For 5-HT-induced antinociception, the minimal inhibitory doses were 0.001 micrograms/rat for tropisetron and 10 micrograms/rat for granisetron. In contrast, the same doses of the two antagonists (from 0.1 microgram/rat) similarly inhibited the effect of mCPBG. This study provides evidence that contrary to tropisetron, doses of granisetron able to inhibit the effect of a 5-HT3 receptor agonist failed to reduce that of 5-HT. This demonstrates a heterogeneity between 5-HT3 receptor antagonists and questions the true involvement of these receptors in spinal 5-HT-induced antinociception.

Psychiatric and sexual disorders induced by apomorphine in Parkinson's disease.

A similar pattern of psychosexual disorders has been observed after long-term treatment with levodopa therapy in four male parkinsonian patients treated with apomorphine for severe on-off motor fluctuations. An acute episode in each case had led them to the hospital in the context of a psychiatric emergency (after punishable sexual acts in two cases). In each case, this episode had been preceded by an increase of self-administered apomorphine, whereas other antiparkinsonian drugs remained unchanged. Questioning had revealed psychosexual disturbances as early as the onset of apomorphine treatment, which tended to progressively worsen with the number of apomorphine daily doses. A decrease in the dosage of apomorphine had been followed by the improvement of the psychiatric condition without worsening of the motor status. Recurrence of psychiatric disorders with similar features had been observed when two patients again increased the number of apomorphine daily injections. The absence of somatic manifestations when apomorphine treatment was withdrawn or reduced, with persistence of psychosexual disturbances, could suggest a psychological dependence from the drug.

Magnesium deficiency induces an hyperalgesia reversed by the NMDA receptor antagonist MK801.

The aim of this study was to determine the changes of the nociceptive thresholds in response to an acute mechanical stimulus (paw pressure) in magnesium (Mg)-deficient rats, and the involvement of the NMDA receptor in these changes. Changes in vocalization thresholds was determined after 7 days of feeding with a Mg-depleted diet. Compared with the control group, Mg-deficient rats showed a significant decrease in the vocalization thresholds (-35.8 +/- 2.5%, p < 0.001) reflecting hyperalgesia. In Mg-deprived rats, three doses (0.06, 0.12 and 0.24 mg/kg s.c.) of dizocilpine (MK801), a non-competitive NMDA receptor antagonist, significantly reversed the hyperalgesia in a dose-dependent manner for at least 48 h. No effect of MK801 was observed in the control group. These data provide evidence that Mg deficiency could constitute a new model of hyperalgesia involving NMDA receptors.

Comparison of amitriptyline metabolism in hepatocytes from streptozocin-induced diabetic rats and from non-diabetic rats.

Biotransformation of amitriptyline (AMI) was studied at different intervals in freshly isolated hepatocytes from healthy or streptozocin-induced diabetic rats in order to investigate the influence of the diabetic state. Levels of free and conjugated AMI, demethylated and hydroxylated metabolites, were assessed by HPLC analysis. In hepatocytes isolated from diabetic rats, AMI was less completely metabolized and the demethylation reaction became more important than in non-diabetic rat hepatocytes. Although the proportions of hydroxylated metabolites decreased in diabetic rats, it always remained predominant. Furthermore, glucuronidation of metabolites was greater, especially for (Z)-10-hydroxynortriptyline in diabetic animals.

Effect of intrathecal serotonin on nociception in rats: influence of the pain test used.

The involvement of serotonin (5-HT) in the modulation of nociceptive impulse in the spinal cord has been widely studied. However, its activity, considering the nature of noxious stimuli and the type of 5-HT receptors involved, merits to be further elucidated. The present behavioural study was performed to compare the dose-antinociceptive effect relationship of 5-HT in rats, after intrathecal (i.t.) injection (10 microliters/rat), using mechanical (paw pressure), thermal (tail immersion and tail-flick) and chemical (formalin) pain tests. In rats submitted to the paw pressure test, 5-HT was found to possess a dose-dependent antinociceptive activity (0.01, 0.1, 1, 10 and 20 micrograms/rat) when vocalization threshold was assessed as a pain parameter. A peak effect occurred 5 min after the injection and the effect was maintained for 45 min. The lowest active dose was 0.1 microgram (maximum increase in vocalization thresholds, 23 +/- 3%) and a plateau was observed for 10 micrograms and 20 micrograms (maximum increase in vocalization thresholds, 72 +/- 7% and 71 +/- 6%, respectively). When paw withdrawal was assessed, 5-HT induced a weak hyperalgesic effect for the highest dose (60 micrograms), while other doses were ineffective. In the tail-immersion (warmth and cold) and tail-flick tests, different doses (0.01, 0.1, 1, 10, 30, 60 and 100 micrograms/rat) were studied. In the two immersion tests, only the highest doses (60 micrograms and 100 micrograms) significantly increased the withdrawal thresholds from 5 to 45 min after the injection. The maximum effect was observed at 5 min (23 +/- 4% and 21 +/- 6% for 60 micrograms; 27 +/- 3% and 30 +/- 6% for 100 micrograms in the warmth and cold immersion test, respectively). In the tail-flick test, the doses of 30, 60 and 100 micrograms/rat dose-dependently and significantly increased the withdrawal thresholds from 5 to 45 min after the injection, with a maximum effect at 5 min (30 +/- 5% for 30 micrograms; 37 +/- 6% for 60 micrograms; and 45 +/- 4% for 100 micrograms). In the formalin test, 5-HT (10, 25, 50, 75 and 100 micrograms/rat) produced dose-related antinociception. The nociceptive response (licking of the injected paw) was significantly reduced from 25 micrograms (-59 +/- 11%) in the early phase, whereas the lowest active dose in the late phase was 50 micrograms (-46 +/- 17%). For both phases, a total inhibition was obtained with 100 micrograms. It is concluded that the effect of 5-HT on pain tests may differ according to the applied stimulus and the parameter assessed; unspecific effects of 5-HT may modify motor reactions to noxious stimuli. Mechanical test (assessment of vocalization) was the most sensitive to 5-HT. These observations are of importance in order to further study the pharmacological mechanisms involved in 5-HT spinally induced antinociception.

Daily insulin treatment relieves long-term hyperalgesia in streptozocin diabetic rats.

Painful neuropathy is common in human diabetes. In rats, experimental diabetes results in altered pain sensitivity. We examined the effect of chronic insulin treatment on diabetes-induced hyperalgesia in streptozocin diabetic rats. A 20-week period of diabetes resulted in a 62% decrease in paw withdrawal thresholds compared with age-matched normal rats. Daily injections of insulin progressively reversed mechanical hyperalgesia to normal values parallel to the correction of hyperglycaemia. When the treatment was stopped, mechanical hyperalgesia reappeared, but never reached the degree of hyperalgesia observed before insulin treatment, suggesting that indirect mechanisms underlie the effect of normoglycaemia on nociception. The present data suggest that appropriate blood glucose control can help relieve pain in long-term diabetes through indirect mechanisms.

Paracetamol exerts a spinal antinociceptive effect involving an indirect interaction with 5-hydroxytryptamine3 receptors: in vivo and in vitro evidence.

Rats (Sprague-Dawley), submitted to a mechanical noxious stimulus (paw pressure), were tested to determine 1) the antinociceptive effects of p.o. (200, 400 and 800 mg/kg), i.v. (50, 100, 200 and 300 mg/kg) and intrathecal (i.t.) (100 and 200 micrograms/rat) administrations of paracetamol; 2) the influence of i.t. administered tropisetron, a 5-hydroxytryptamine3 (5-HT3) receptor antagonist (0.5, 1 or 10 micrograms/rat) on paracetamol-induced antinociception; 3) the influence of indomethacin (25 mg/kg s.c.), naloxone (10 micrograms/rat i.t.) and yohimbine (1 mg/kg i.v.) on the effect of paracetamol (200 mg/kg i.v.) to determine the involvement of prostaglandins, opioids and alpha-2 adrenoceptors. The displacement by paracetamol of radioligand binding to various receptors was also investigated. Paracetamol induced a significant antinociceptive effect after p.o., i.v. and i.t. administration. A total inhibition of the effect of paracetamol, administered p.o. or i.t., occurred at the dose of 0.5 microgram/rat of tropisetron, whereas 10 micrograms/rat of this antagonist was needed to totally inhibit the action of i.v. administered paracetamol. Indomethacin, naloxone and yohimbine failed to modify paracetamol antinociceptive action. In vitro studies failed to show any binding of paracetamol to 5-HT3 and several other receptors and to 5-HT uptake sites. It is concluded that paracetamol has a central antinociceptive effect, based on an indirect involvement of spinal 5-HT3 receptors.

Pharmacokinetics of amitriptyline and its demethylated and hydroxylated metabolites in streptozocin-induced diabetic rats.

Plasma and brain levels of amitriptyline (AMI), its demethylated and hydroxylated metabolites were determined after acute IP administration of AMI (20 mg/kg) in streptozocin-induced diabetic Sprague-Dawley rats. Results showed 1. in plasma: rapid AMI absorption, but slow elimination; the proportion of AMI similar to those of the rest of compounds; the proportion of its demethylated metabolite, nortriptyline, 1.8-fold higher than that of 10-hydroxy-nortriptyline. 2. in brain: the proportions of AMI and nortriptyline were 9.5- and 2.6-fold higher respectively, than those of whole hydroxylated metabolites, which represented 7.4% of the total amount.

Application of HPLC with silica-phase and reversed-phase eluents for the determination of clomipramine and demethylated and 8-hydroxylated metabolites.

A rapid and efficient high-performance liquid chromatographic method using a reversed-phase eluent of methanol-water with butylamine on a silica column was developed for the separation and quantitation of clomipramine (CMI), its demethylated metabolites (desmethyl-clomipramine and didesmethyl-clomipramine [DDCMI]), and its hydroxylated metabolites (8-hydroxy-clomipramine and 8-hydroxy-desmethylclomipramine). A liquid-liquid extraction procedure, which involved an alkaline extraction with heptane-isoamyl alcohol, first from a 1-mL serum sample and then from the acidic back extract, was used. The chromatographic separation was rapid (20 min), and the ultraviolet detection (at 254 nm) was sufficiently sensitive (limit of detection, 5-10 ng/mL). Except for DDCMI, the calibration was linear (r > 0.99, n = 5), and within-day and day-to-day coefficients of variation remained less than 11%. The method was used to analyze CMI and its metabolites in the serum of depressive patients and to determine their hydroxylation and demethylation capacities.

Plasma and brain pharmacokinetics of amitriptyline and its demethylated and hydroxylated metabolites after one and six half-life repeated administrations to rats.

The purposes of the present study were as follows: 1. After an acute intraperitoneal (IP) administration of amitriptyline (AMI) to male Sprague-Dawley rats we found that: (i) its absorption rate is rapid; (ii) its elimination half-life is much shorter than in humans; and (iii) its levels largely exceeded those of its metabolites. The most important metabolites being 10-hydroxynortriptyline and nortriptyline in plasma and brain, respectively. 2. After six (every half-life) repeated IP administrations: (i) AMI kinetic parameters were unchanged; and (ii) amounts of metabolites were significantly increased and the levels of AMI were lowered both in plasma and brain.

In vitro and in vivo evidence for a tachykinin NK1 receptor antagonist effect of vapreotide, an analgesic cyclic analog of somatostatin.

Vapreotide, a long-acting somatostatin analog, possesses an analgesic effect. The purpose of this work was to determine a tachykinergic involvement. Vapreotide reduced substance P-induced biting and scratching in mice. This inhibitory effect of substance P action was confirmed by experiments performed on the bronchial apparatus of guinea-pigs known to possess tachykinin NK1 and NK2 receptors. (i) Vapreotide reduced the substance P-induced plasmatic exudation. (ii) It inhibited selectively the tachykinin-dependent second contractile phase induced by electrical field stimulation of isolated bronchi. (iii) It shifted to the right the concentration-effect curve of substance P-induced contraction of isolated main bronchi. The peptide displaced [3H]substance P (IC50 = 3.3 +/- 1.8 x 10(-7) M) from guinea-pig bronchial tachykinin NK1 sites. The displacement of [125I]neurokinin A, a specific tachykinin NK2 receptor ligand, needed higher concentrations (IC50 = 4.5 +/- 0.6 x 10(-6) M). It is concluded that vapreotide possesses an antagonist activity on guinea-pig tachykinin NK1 receptors; the involvement in its analgesic action is discussed.