Involvement of brain serotonergic system in the antinociceptive action of acetylsalicylic acid in the rat

The pain-threshold in the hot-plate test and serotonin (5-HT) receptor binding capacity in the cortex and pontine areas of rat brain were studied after intraperitoneal (ip) administration of acetyl salicylate of lysine equivalent to 400 mg/kg of acetylsalicylic acid (ASA). The antinociceptive activity of ASA was prevented by ip pre-treatment with Parachlorophenylalanine (PCPA) at the rate of 100 mg/kg/day for 4 days. PCPA pre-treatment increased the number of 5-HT receptors and abolished the ASA-induced reduction in 5-HT receptor binding capacity in the cortex but did not affect serum salicylate levels. These results provide support for the hypothesis that the antinociceptive action of ASA, at least in the hot-plate test, involves the central serotonergic system.     

Effect of rofecoxib on nociception and the serotonin system in the rat brain

OBJECTIVE AND DESIGN: The purpose of the present study was to determine whether the antinociceptive activity of rofecoxib is mediated, at least in part, through changes in the brain serotonergic system. MATERIALS AND SUBJECTS: Male Wistar rats weighing 180-200 g (groups of eight) were subjected to the hot-plate and formalin tests after rofecoxib treatment. Cortical areas were removed for serotonin (5-HT) level, 5-HT2 and mu-receptor evaluation. TREATMENT: Rofecoxib was administered orally at doses of 5, 10, 20 and 50 mg/kg for the time course evaluation in the hot-plate test (30, 60 and 120 min), and at the dose of 10 mg/kg for the formalin test and biochemical determinations. METHODS: The tests performed were the hot-plate and the formalin assays. HPLC was used to determine 5-HT levels and radioligand-binding assays were utilized to evaluate the characteristics of 5-HT2 and mu-receptors. The data were analysed by ANOVA or Student's t test. RESULTS: The lowest active dose of rofecoxib in the hot-plate test was 10 mg/kg. The percentage of the maximum possible effect (%MPE) values were: control = 1.7+/-3.4; treated 23.4+/-6.5 (p<0.05). The same dose had a significant effect on both phases of the formalin test. Pretreatment with p-chlorophenylalanine (PCPA) significantly decreased the activity of rofecoxib in the hot-plate test. Rofecoxib treatment increased serotonin levels and decreased the maximum number of 5-HT2 receptors. 5-HT levels (ng/g) were: control = 240.1 +/- 28.5, rofecoxib = 326.1 +/- 19.9 in the frontal cortex. The characteristics of mu-receptors did not change. CONCLUSIONS: These results suggest that rofecoxib may exert its therapeutic effect, at least in part, through the central serotonergic system. The opioidergic system, on the other hand, seems to be unaffected.     

Differential involvement of central 5-HT<Subscript>1B</Subscript> and 5-HT<Subscript>3</Subscript> receptor subtypes in the antinociceptive effect of paracetamol

Objective: We investigated the effect of pre-treatment with ondansetron or CP 93129 (a 5-HAT_1B agonist) on the antinociceptive activity of paracetamol and the changes in central 5-HT₃ receptors induced by paracetamol alone or co-administered with ondansetron.Materials and Subjects: Male Wistar rats (eight per group) were injected with ondansetron (2 and 4 mg/kg s.c.) or CP 93129 (0.5, 1 and 2 mg/kg s.c.) 15 min before paracetamol (400 mg/kg, i.p.).Methods: Pain threshold was evaluated in the hot-plate or in the paw pressure test 30 min after the last treatment. 5-HT₃ receptor binding capacity was measured in the frontal cortex, temporal-parietal cortex and midbrain by means of radioligand binding technique. Statistical analysis was done using ANOVA followed by Student-Newman-Keuls test and 2 X 2 factorial analysis when appropriate.Results: Pre-treatment with ondansetron, at doses of 2 and 4 mg/kg, did not affect the antinociceptive activity of paracetamol in the hot-plate test and in the paw pressure test. Paracetamol did not change the characteristics of 5-HT₃ receptors in all the areas investigated. Ondansetron (4 mg/kg s.c) per se significantly increased the 5-HT₃ receptor number in the areas used, the effect not being modified by co-administration with paracetamol. On the other hand, CP 93129 (2 mg/kg s.c.) significantly prevented the effect of paracetamol in both algesimetric tests used.Conclusions: Our data indicate that 5-HT_1B but not 5-HT₃ receptors are involved in the antinociceptive effect of paracetamol in our experimental conditions.Received 25 November 2002; returned 10 April 2003; accepted by G. Geisslinger 22 April 2003     

Test-dependent antinociceptive effect of spinal serotonin release induced by intrathecal p-chloroamphetamine in mice

The effect of direct intrathecal injection of p-chloroamphetamine (PCA) into the lumbar subarachnoid space was investigated in mice. PCA (0.6 - 20 micrograms) induced a dose-related prolongation of response latencies in the tail-flick test, but failed to affect the hind-paw lick response in a hot-plate test employing slowly rising temperature. PCA (5 micrograms) given intracerebroventricularly did, however, significantly elevate the response temperature in the hot-plate test. The antinociceptive effect of PCA in the tail-flick test was prevented by spinalization, by pretreatment with the selective serotonergic re-uptake blocker zimelidine (20 mg X kg-1 i.p.) and by the serotonin synthesis inhibitor p-chlorophenylalanine (300 + 300 + 150 mg X kg-1 i.p. 72, 48 and 24 h before test). It is concluded that PCA given intrathecally releases serotonin from spinal terminals, which may under certain conditions induce antinociception.     

Caffeine and a selective adenosine A(2B) receptor antagonist but not imidazoline receptor antagonists modulate antinociception induced by diphenyl diselenide in mice

The present study examined the antinociceptive effect of diphenyl diselenide (PhSe)2, given orally (p.o.), in the hot-plate test in mice. The administration of diphenyl diselenide (10-100 mg/kg, p.o.) caused a significant inhibition of thermal nociception induced by hot-plate test in mice. Pretreatment of animals by intraperitoneal route (i.p.) with caffeine (10 mg/kg; a non-specific adenosine receptor antagonist) and PSB1115 (1 mg/kg; an adenosine A(2B) receptor antagonist), but not DPCPX (2 mg/kg; an adenosine A(1) receptor antagonist) and SCH5826 (3 mg/kg; an adenosine A(2A) receptor antagonist) significantly blockaded the antinociceptive effect caused by diphenyl diselenide (10 mg/kg, p.o.) in the hot-plate test. Moreover, the pretreatment of animals with efaroxan (1 mg/kg, i.p.; a mixed I(1) imidazoline/alpha(2)-adrenoceptor antagonist) and idazoxan (3 mg/kg, i.p.; a mixed I(2) imidazoline/alpha(2)-adrenoceptor antagonist) did not significantly reverse the antinociception caused by oral administration of diphenyl diselenide (10 mg/kg, p.o.) in the hot-plate test. These results indicate that diphenyl diselenide produced antinociception in a thermal model of pain in mice and its effect was prevented by caffeine and by a selective adenosine A(2B) receptor, but not by imidazoline receptor antagonists in mice.     

Differential sensitivity of selected rat brain areas to excitatory neurotransmitters released by K+ depolarization

When injected intrathecally in mice in a volume of 5 microliter, adenosine had no effect on tail-flick or hot-plate reaction latencies at dosages up to 1 mM concentration. There were no other behavioral effects observed either. Injecting 1 mM of the adenosine receptor agonist, 5'-N-ethylcarboxamide adenosine (NECA) caused both motor paralysis of the hind-legs with a duration of approximately 4 h and simultaneous antinociception. A slight weakness of the hindlegs, but a profound antinociceptive effect, was observed after the 100 microM dose only. After 10 microM, there was no effect on motor behavior but still a prolongation of the tail-flick and hot-plate reaction latencies. Pretreatment with the adenosine receptor antagonist theophylline attenuated the antinociceptive effect of NECA. Activation of spinal adenosine receptors thus appears to selectively elicit analgesia.     

Pro-Leu-Gly-NH2 serves as a conditioned stimulus in the acquisition of conditioned tolerance

The effect of Pro-Leu-Gly-NH2 (MIF) on the acquisition of tolerance to morphine-induced antinociception and its efficacy as a cue predictive of morphine administration was examined. Daily administration of MIF prior to morphine injection did not attenuate the acquisition of tolerance to the antinociceptive properties of morphine, as measured by the latency to hindpaw lick in a hot-plate test of analgesia. When the animals were tested 72 hr later without MIF pretreatment, they appeared to lose tolerance, as indicated by longer latencies to paw lick. These data suggest that in some situations MIF may interfere with the acquisition of tolerance by acting as a cue that reliably predicts the antinociceptive properties of morphine.     

The effect of formalin pretreatment on nicotine-induced antinociceptive effect: the role of mu-opioid receptor in the hippocampus

Nicotine is attractive as an analgesic component despite that its antinociceptive mechanism is not well known until now. In the present study, we examined the antinociceptive effect of nicotine administered supra-spinally on acetic acid-induced visceral pain induction (writhing test), and found that the antinociceptive effect of nicotine was abolished by mu-, delta-, and kappa-opioid receptor antagonist administered i.c.v. In addition, s.c. 5% formalin pretreatment at 5 h, 20 h, 40 h, and 1 week prior to i.c.v. nicotine injection abolished the antinociceptive effect of nicotine in the writhing test, suggesting that s.c. formalin pretreatment induced tolerance to the antinociceptive effect of nicotine in the supra-spinal region. Furthermore, neuronal loss of the hippocampal cornus ammonis (CA) 3 region reduced nicotine-induced an antinociceptive effect in the writhing test. In Western blot assay, we examined s.c. formalin injection down-regulated mu-opioid receptor in the hippocampus after 40 h, and its effect was maintained for 1 week. However, various acetylcholine receptor subunits and delta-, and kappa-opioid receptors were not altered. These results suggest that s.c. formalin pretreatment can contribute to induce tolerance on nicotine-induced antinociception as down-regulating mu-opioid receptor in the hippocampus, especially 40 h after s.c. formalin injection.     

Effect of compound GB-115 on morphine-induced analgesia

Experiments on outbred mice showed that compound GB-115, a retropeptide analogue of the tetrapeptide cholecystokinin, produced a naloxone-dependent potentiating effect on morphine-induced analgesia in the hot-plate test, but did not modulate animal behavior in the tail-flick test in outbred mice. This potentiation of antinociceptive activity of morphine was probably related to the interaction of GB-115 with supraspinal opioidergic mechanisms. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 6, pp. 645–647, June, 2007     

Antinociceptive and neurotoxic actions of substance P analogues in the rat's spinal cord after intrathecal administration

Intrathecal administration of both (D-Pro2,D-Trp7,9)-substance P (DPDT) and (D-Arg1,D-Trp7,9,Leu11)-substance P (DADTL) elicited antinociception in hot-plate and tail-flick test, with DADTL as the most potent. The animals injected with 2.0 micrograms DADTL, and several animals administered with DPDT at the same dose, developed bilateral motor blockade of the hind-legs, persisting for up to 3 days after DADTL. The effect of DPDT appeared to be reversible at this dose. On histopathological examination it was found that these animals with persistent paralysis had widespread neuronal necrosis in the lumbar region of the spinal cord. It is concluded that the peptides have antinociceptive effects after the intrathecal administration in rats, but that there is a small margin between the dose producing this effect and that causing irreversible toxic reactions in the spinal cord.     

Oligopeptidases B from Trypanossoma cruzi and Trypanossoma brucei Inhibit Inflammatory Pain in Mice by Targeting Serotoninergic Receptors

In the present study, the antinociceptive profile of oligopeptidases B from Trypanosoma cruzi (OPTc) and Trypanosoma brucei (OPTb) were examined in mice evaluated by the acetic acid-induced writhing test. Both OPTc and OPTb injected intraperitoneally attenuated the writhing numbers in the acetic acid-induced writhing test. This effect was not dependent on the enzymatic activity, but the enzyme structure was important for this purpose. Intraperitoneal pretreatment with methysergide (5-HT serotonergic receptor antagonist) attenuated antinociceptive effect induced by both OPTc and OPTb in the writhing test. However, naloxone (opioid receptor antagonist) or yohimbine (α2-adrenergic receptor antagonist) did not affect antinociception induced by both oligopeptidases. Our results suggest that OPTc and OPTb show antinociceptive property in the writhing test. Furthermore, this antinociceptive effect may be mediated by serotonergic receptor but not opioidergic or α2-adrenergic receptors.     

Involvement of protein kinase C in the galanin-induced antinociception in the brain of rats

Previous study in our laboratory demonstrates that microinjection of galanin into the arcuate nucleus of hypothalamus produced antinociceptive effects in rats. In the present study we investigated the involvement of protein kinase C (PKC) and PKC signaling pathways in the galanin-induced antinociception in the brain of rats. Intracerebroventricular injection of galanin produced antinociceptive effects in rats tested by hot-plate and Randall Selitto test. Interestingly, the galanin-induced antinociception was significantly attenuated by intracerebroventricular injection of the PKC inhibitor chelerythrine, indicating an involvement of PKC in the galanin-induced antinociception in rats. Taken together, the results demonstrate that galanin induces antinociceptive effects in the rat brain, and PKC is involved in the galanin-induced antinociception in the brain of rats.     

Modulation of morphine-induced antinociception in mice by histamine H3-receptor ligands

The effects of compounds active at histamine H₃-receptors on morphine-induced antinociception have been investigated in thermal and chemical tests in mice; tail-immersion (50°C) and hot-plate (49° and 55°C) tests and acetic acid-induced writhing. Neither (R)α-methylhistamine, a specific agonist, (S)α-methylhistamine, a chemical control, nor thioperamide, an antagonist, had any antinociceptive action alone but thioperamide (3 mg kg⁻¹) attenuated the effects of morphine in the tailimmersion test wile (R)α-methylhistamine (1 mg kg⁻¹), but not the (S) isomer, potentiated its effects in the hot-plate test at 55°C. These results are consistent with the morphine potentiation seen with H₁-antagonists and suggest that central histaminergic mechanisms can modulate opioid actions.

     

Sensory thresholds and the antinociceptive effects of GABA receptor agonists in mice lacking the beta3 subunit of the GABA(A) receptor

A line of mice was recently created in which the gabrb3 gene, which encodes the beta3 subunit of the GABA(A) receptor, was inactivated by gene-targeting. The existence of mice with a significantly reduced population of GABA(A) receptors in the CNS enabled an investigation of the role of GABA and GABA(A) receptors in nociception. The present study examined the sensory thresholds of these mice, as well as the antinociceptive effects of subcutaneously or intrathecally administered GABA(A) and GABA(B) receptor agonists. Homozygous null (beta3-/-) mice displayed enhanced responsiveness to low-intensity thermal stimuli in the tail-flick and hot-plate test compared to C57BL/6J and 129/SvJ progenitor strain mice, and their wild-type (beta3+/+) and heterozygous (beta3+/-) littermates. The beta3-/- mice also exhibited enhanced responsiveness to innocuous tactile stimuli compared to C57BL/6J, 129/SvJ and to their beta3+/+ littermates as assessed by von Frey filaments. The presence of thermal hyperalgesia and tactile allodynia in beta3-/- mice is consistent with a loss of inhibition mediated by presynaptic and postsynaptic GABA(A) receptors in the spinal cord. As expected, subcutaneous administration of the GABA(A) receptor agonist 4,5,6,7-tetrahydroisoxazolo-(5,4-c)pyridin-3-ol did not produce antinociception in beta3-/- mice, whereas it produced a dose-dependent increase in hot-plate latency in C57BL/6J, 129/SvJ, beta3+/+ and beta3+/- mice. However, the antinociceptive effect of the GABA(B) receptor agonist baclofen in the tail-flick and hot-plate tests was also reduced in beta3-/- mice compared to the progenitor strains, beta3+/+ or beta3+/- mice after either subcutaneous or intrathecal administration. This finding was unexpected and suggests that a reduction in GABA(A) receptors can affect the production of antinociception by other analgesic drugs as well.     

Roles of adenosine and serotonin receptors on the antinociception of sildenafil in the spinal cord of rats

Purpose

The phosphodiesterase 5 inhibitor sildenafil has antinociceptive effects, mediated by an increase in cGMP. This study examined the role of spinal adenosine and serotonin receptors played in the antinociceptive effects of intrathecal sildenafil.

Materials and Methods

Intrathecal catheters were inserted into the subarachnoid space of Sprague-Dawley male rats as a drug delivery device. Pain was induced by injecting formalin into the plantar surface of rats and observing nociceptive behavior (flinching response) for 60 mininutes. Then, the effects of intrathecal adenosine and serotonin receptor antagonists on the antinociceptive activity of intrathecal sildenafil were examined.

Results

Intrathecal sildenafil suppressed the flinching response in a dose-dependent manner during phases 1 and 2 in the formalin test. Both CGS 15943 and dihydroergocristine decreased the antinociceptive effects of sildenafil during phases 1 and 2 in the formalin test.

Conclusion

Intrathecal sildenafil effectively attenuated the pain evoked by formalin injection. Both adenosine and serotonin receptors may be involved in the antinociceptive action of sildenafil at the spinal level.     

Ovariotomy and persistent pain affect long-term Fos expression in spinal cord

Sex differences in pain have been confirmed both in clinical and experimental studies. Estrogen has a great role in this process and can affect response to noxious stimuli. In this study, we used Fos as a marker to investigate the mechanism underlying the phenomenon. Sprague-Dawley rats were randomly assigned to ovariotomy (OVX) or sham surgery (OVX-sham) group (n=20 rats/condition). All the rats received CCI surgery three weeks after ovariotomy. We used hot-plate test as a sign of neuropathic pain. On PO days 3, 7, 14, and 21, paw withdrawal latency was determined and 2 h later, the L4-L5 segments of the spinal cord were removed and immunostained for Fos protein. Number of Fos-like immunoreactive (Fos-LI) neurons of each section was counted bilaterally. We find that ovariotomy can regulate the sensitivity to thermal stimuli and Fos protein level will change in the spinal dorsal horn. However, the alternation of Fos expression does not extremely account for the behavior.     

Effect of acute and repeated administration of paracetamol on opioidergic and serotonergic systems in rats

Objective and design: We investigated the antinociceptive effect of paracetamol or morphine after repeated administration and the changes in the characteristics of central μ-, κ- and 5-HT₂ receptors. Treatment: Male rats were injected twice a day for seven days with paracetamol (400 mg/kg, i. p.) or morphine (5 mg/kg, s. c.). Methods: The antinociceptive effect was evaluated 30 min after single and multiple doses of paracetamol and morphine through the hot-plate test. Binding techniques were used to evaluate the receptor characteristics in the frontal cortex. Results: Both paracetamol and morphine induced an antinociceptive effect on day 1 but only paracetamol maintained this effect for seven days while morphine did not. The number of μ-opioid receptors decreased on days 1, 3, and 7 by a similar percentage after paracetamol administration (by 29, 31 and 34 %, respectively), while morphine produced a progressive decrease in comparison with controls (by 37, 49 and 60 %, respectively) and κ-opioid receptors were unaffected. Both drugs similarly decreased the 5-HT₂ receptor number on all days of treatment (by about 30 %). Conclusions: The opioidergic and serotonergic systems are involved in different ways in the induction and maintenance of antinociception after paracetamol or morphine treatment. Received 10 May 2006; returned for revision 14 September 2006; accepted by G. Geisslinger 30 October 2006     

Differentiation of multiple analgesic opiate receptors

In order to analyse opiate receptors mediating anti-nociception, the activity pattern of different opiates was determined by using hot-plate (45 degrees C and 56 degrees C), tail-flick and algolytic tests on rats, and the acetic acid stretching test on mice, for evaluation of analgesic activity. Potentiation of barbiturate anaesthesia, measurement of pupillary diameter, and a modification of pentetrazol convulsion, were used for evaluation of non-analgesic activity. The efficacy and affinity constant (pA2) of the proposed opiate A receptor agonist and B receptor antagonist drug N-cyclopropylmethyl-norazido-dihydroisomorphine (CAM) were determined. CAM produced several opiate agonist (morphine-like) effects, often stronger than morphine, in three of the analgesic tests and two of the non-analgesic tests. On the other hand CAM proved to be a very strong narcotic antagonist, as potent as naloxone as evidenced by identical pA2 values, in the algolytic, 45 degrees C hot-plate and pentetrazol tests, but not in the 56 degrees C hot-plate, tail-flick and acetic acid tests. The potency differences for the actions of morphine and CAM in a heat test (56 degrees C hot-plate) compared with a non-heat test (acetic acid stretching) were found to be 8.6 and 540 respectively. It is concluded that opiate analgesia might be mediated by at least two receptors classified in terms of the antagonistic or agonistic activity of CAM.     

Evaluation of Anti-Inflammatory and Antinociceptive Activity of Triphala Recipe

The anti-inflammatory and antinociceptive activities of Triphala recipe were studied in animal models. Triphala recipe (4 mg/ear) significantly exhibited an inhibitory effect on the ear edema formation induced by ethyl phenylpropiolate-induced, but not on the arachidonic acid-induced ear edema in rats. Furthermore, Triphala recipe at the doses of 300, 600 and 1,200 mg/kg significantly reduced carrageenan-induced hind paw edema. Next, the anti-inflammatory action in chronic inflammation was measured using the cotton pellet-induced granuloma formation assay in rats. Triphala recipe (1,200 mg/kg) reduced neither transudative weight nor granuloma formation. It also did not affect on body weight gain and thymus weight indicating that Triphala recipe does not have a steroid-like effect. In antinociceptive study, Triphala recipe (300, 600, 1,200 mg/kg), elicited significant inhibitory effect on both phases, especially in late phase, of the formalin test in mice suggesting that the antinociceptive action of Triphala recipe may be via both peripheral and at least partly centrally acting.     

皖南地区眼镜蛇毒活性组分镇痛效应的初步研究

 目的：从皖南地区眼镜蛇毒粗毒中分离纯化出活性组分眼镜蛇毒镇痛因子（cobra venom analgesic factor, CVAF),并研究其镇痛效应。方法：采用阳离子交换色谱（cation-exchange chromatography, CEC）和分子排阻层析（size-exclusion chromatography, SEC）从眼镜蛇粗毒中分离纯化出镇痛活性组分CVAF,SDS-聚丙烯酰胺凝胶电泳法和毛细管区带电泳法进行纯度及相对分子量的鉴定;将小鼠随机分为生理盐水正常对照组和盐酸吗啡阳性对照组、CVAF实验组,采用小鼠热板法和醋酸扭体法评估活性组分CVAF的镇痛效应。结果：纯化后得到活性产物为单一组分,相对分子量为6 500 D;热板法显示吗啡组在给药0.5 h后达高峰,6 h镇痛作用消失;活性组分CVAF的镇痛作用自用药后0.5 h开始,且持续8 h仍存在。扭体法中0.03 mg/kg、0.1 mg/kg和0.3 mg/kg的活性组分在给药后小鼠扭体抑制率分别为27%、50%和70%;0.3 mg/kg实验组与吗啡组相比无明显差异（P> 0.05）。结论：从皖南地区眼镜蛇粗毒中分离纯化出的活性组分CVAF具有剂量依赖性镇痛效应。