Cold water swim stress inhibits the nociceptive responses to intrathecally administered somatostatin,but not substance P

The effects of cold water swim stress (CWSS) on the nociceptive responses to i.t. administered substance P (SP) and somatostatin (SST) were examined. Male ICR mice, weighing about 30 g, were forced to swim in water at 20°C for 3 min. In unstressed mice, i.t. injection of SP (0.1 nmol) and SST (1 nmol), respectively, produced nociceptive-related behaviors. Although CWSS had no effect on the intensity of the SP-induced nociceptive responses, CWSS significantly reduced the intensity of the SST-induced nociceptive responses. The effect of CWSS on the SST-induced nociceptive responses was blocked by naloxone (5 mg/kg, s.c.) and naltrindole (1 mg/kg, s.c.), a selective δ-opioid receptor antagonist, but not by β-funaltrexamine (20 mg/kg, s.c.), a selective μ-opioid receptor antagonist. These results indicate that CWSS may selectively reduce the SST-induced nociceptive responses primarily through δ-opioid receptors.     

Clopheline-induced aggression in mice: role of genotype and the dopaminergic system

Clophelin (CLO) in a dose 10 mg/kg induced aggressive behaviour in mice significantly dependent of genotype. Pretreatment with flupentixol and haloperidol inhibited or blocked CLO-evoked aggression in high-aggressive mice. Apomorphine administered with CLO enhanced aggression in low-aggressive mice. Stimulation of D2 receptors by bromocriptine failed to change CLO-induced aggression. It was suggested that dopamine system was involved in CLO-aggression through D1 receptors.     

Effects of 5-HT3 receptor blockade on visceral nociceptive neurons in the ventrolateral reticular field of the rat medulla oblongata

The caudal ventrolateral reticular formation of the medulla oblongata is the first layer of visceral nociceptive processing. In experiments on rats, neuronal responses in this zone to nociceptive stimulation of the large intestine were examined and the effects of selective blockade of 5-HT3 receptors on these responses were assessed. By the character of responses to nociceptive colorectal stimulation (CRS), the recorded medullary neurons were divided into three groups—excited, inhibited and indifferent. Intravenous injection of 5-HT3 antagonist granisetron (1 and 2 mg/kg) as well as local application of this agent on the surface of the medulla oblongata (1.25 and 2.5 nmole) suppressed the background and evoked firing of CRS-excited reticular neurons in a dose-dependent manner but did not exert as pronounced influence on the cells inhibited by visceral nociceptive stimulation. Spike activity in the group of CRS-indifferent neurons under similar conditions was 5-HT3-independent. The results obtained provide evidence that 5-HT3 receptors mediate the facilitating effect of serotonin on supraspinal transmission of the abdominal nociceptive stimulus which, at least in part, is realized via selective activation of visceral medullary nociceptive neurons. A shutdown of this mechanism may underlie the analgesic effect of 5-HT3 antagonists in abdominal pain syndromes.     

Mechanical Conflict System: A Novel Operant Method for the Assessment of Nociceptive Behavior

A new operant test for preclinical pain research, termed the Mechanical Conflict System (MCS), is presented. Rats were given a choice either to remain in a brightly lit compartment or to escape to a dark compartment by crossing an array of height-adjustable nociceptive probes. Latency to escape the light compartment was evaluated with varying probe heights (0, .5, 1, 2, 3, and 4 mm above compartment floor) in rats with neuropathic pain induced by constriction nerve injury (CCI) and in naive control rats. Escape responses in CCI rats were assessed following intraperitoneal administration of pregabalin (10 and 30 mg/kg), morphine (2.5 and 5 mg/kg), and the tachykinin NK1 receptor antagonist, RP 67580 (1 and 10 mg/kg). Results indicate that escape latency increased as a function of probe height in both naive and CCI rats. Pregabalin (10 and 30 mg/kg) and morphine (5 mg/kg), but not RP 67580, decreased latency to escape in CCI rats suggesting an antinociceptive effect. In contrast, morphine (10 mg/kg) but not pregabalin (30 mg/kg) increased escape latency in naive rats suggesting a possible anxiolytic action of morphine in response to light-induced fear. No order effects following multiple test sessions were observed. We conclude that the MCS is a valid method to assess behavioral signs of affective pain in rodents.     

Cimetidine does not change the effect of Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) on the opiate form of footshock-induced analgesia.

It has been demonstrated that cimetidine blocks the effect of naloxone on footshock-induced analgesia. To study the effect of cimetidine on the antiopiate properties of an endogenous peptide Tyr-MIF-1, the opiate form of intermittent footshock-induced analgesia was elicited in the rat. The nociceptive responses were determined using the hot-plate test (52.5 degrees C). Intraperitoneal pretreatment with cimetidine (100 mg/kg) or chlorpheniramine maleate (20 mg/kg) did not affect the footshock-induced analgesia, and did not change the antagonizing effect of Tyr-MIF-1 (0.2 mg/kg) on this model of antinociception. It is concluded that cimetidine and chlorpheniramine maleate do not change the antagonizing effect of Tyr-MIF-1 on the opiate form of intermittent footshock-induced analgesia.     

Participation of the components of L-arginine/nitric oxide/cGMP cascade by chemically-induced abdominal constriction in the mouse

The purpose of this study was to investigate the role of the L-arginine/nitric oxide (NO)/cGMP pathway in p-benzoquinone-induced writhing model in mouse. L-arginine, a NO precursor, displayed antinociceptive effects at the doses of 0.125-1.0 mg/kg. When the doses of L-arginine were increased gradually to 10-100 mg/kg, a dose-dependent triphasic pattern of nociception-antinociception-nociception was obtained. The NO synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) (18.7515 mg/kg), possessed antinociceptive activity. Methylene blue (MB), a guanylyl cyclase and/or NOS inhibitor, (5-160 mg/kg) also produced a dose-dependent triphasic response. When L-arginine (50 mg/ kg) was combined with L-NAME (75 mg/kg). L-arginine-induced antinociception did not change significantly. Cotreatment of L-arginine with 5 mg/kg MB significantly decreased MB-induced antinociception and reversed the nociception induced by 40 mg/kg MB to antinociception. It is concluded that the components of L-arginine/nitric oxide/cGMP cascade may participate in nociceptive processes both peripherally and centrally by a direct effect on nociceptors or by the involvement of other related pathways of nociceptive processes induced by NO.     

Effects of melatonin, morphine and diazepam on formalin-induced nociception in mice

The possible analgesic effect of melatonin was investigated in young male ICR mice. The formalin test which elicits typically 2 phases of pain response, the acute (first) phase and tonic (second) phase, was used. The test was performed in the late light period when the mice have been reported to be more sensitive to pain. Compared to control mice, no significant difference in nociceptive response was observed when melatonin was injected intraperitoneally at doses of 0.1, 5, and 20, mg/kg body weight. The combined effects of melatonin with diazepam and/or morphine, were also investigated. Melatonin, injected at 20 mg/kg 15 min before formalin test, significantly increased the antinociceptive response of diazepam (1 mg/kg) or morphine (5 mg/kg) in the second phase. In addition, when melatonin was given at 20 mg/kg together with diazepam and morphine, antinociceptive responses in both the first and second phase were increased. These data indicate the synergistic analgesia effect of melatonin with morphine and diazepam and suggest the possible involvement of melatonin as an adjunct medicine for pain patients.     

Analysis of the mechanisms underlying the antinociceptive effect of epicatechin in diabetic rats

Aims

The purpose of this study was to investigate the antinociceptive effect of epicatechin as well as the possible mechanisms of action in diabetic rats.

Main methods

Rats were injected with streptozotocin to produce hyperglycemia. The formalin test was used to assess the nociceptive activity.

Key findings

Acute pre-treatment with epicatechin (0.03–30 mg/kg, i.p.) prevented formalin-induced nociception in diabetic rats. Furthermore, daily or every other day treatment for 2 weeks with epicatechin (0.03–30 mg/kg, i.p.) also prevented formalin-induced nociception in diabetic rats. Acute epicatechin-induced antinociception was prevented by l-NAME (N^ω-nitro-l-arginine methyl ester hydrochloride, 1–10 mg/kg, non-selective nitric oxide synthesis inhibitor), 7-nitroindazole (0.1–1 mg/kg, selective neuronal nitric oxide synthesis inhibitor), ODQ (1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one, 0.2–2 mg/kg, guanylyl cyclase inhibitor) or glibenclamide (1–10 mg/kg, ATP-sensitive K⁺ channel blocker). Moreover, epicatechin (3 mg/kg)-induced antinociception was fully prevented by methiothepin (0.1–1 mg/kg, serotonergic receptor antagonist), WAY-100635 (0.03–0.3 mg/kg, selective 5-HT_1A receptor antagonist) or SB-224289 (0.03–0.3 mg/kg, selective 5-HT_1B receptor antagonist). In contrast, BRL-15572 (0.03–0.3 mg/kg, selective 5-HT_1D receptor antagonist) only slightly prevented the antinociceptive effect of epicatechin. Naloxone (0.1–1 mg/kg, opioid antagonist) did not modify epicatechin's effect.

Significance

Data suggest the involvement of the nitric oxide–cyclic GMP–K⁺ channel pathway as well as activation of 5-HT_1A and 5HT_1B, and at a lesser extent, 5-HT_1D, but not opioid, receptors in the antinociceptive effect of epicatechin in diabetic rats. Our data suggest that acute or chronic treatment with epicatechin may prove to be effective to treat nociceptive hypersensitivity in diabetic patients.     

Morphine induces aggression but not analgesia in the naked mole-rat (Heterocephalus glaber)

1. The antinociceptive effect in the mole-rat of morphine (1, 10, 20 or 30 mg/kg) and nefopam (10 or 20 mg/kg) was studied. 2. In the hotplate test, morphine had no analgesic effect. A reduced response latency after morphine (10 and 20 mg/kg) could possibly be explained by hyperactivity and excited behaviour. 3. After morphine (10, 20 and 30 mg/kg) most of the animals died after fighting when kept in colony cages. Aggressive behaviour and death was prevented by naloxone, or by keeping the animals in single cages. 4. Nefopam (20 mg/kg) significantly increased the latency for the nociceptive response. 5. It was concluded that in the mole-rat, opioid systems in the CNS may not be involved in the regulation of nociception, but in the regulation of agonistic and motor behaviour.     

Antinociceptive effect induced by intraperitoneal administration of vitamin K2 (menatetrenone) in ICR mice

The antinociceptive effect of vitamin K2 (menatetrenone) in mice was examined using tail-flick and formalin test. Menatetrenone at doses of 10, 50 and 100 mg/kg, i.p. produced a dose-dependent and significant inhibition of the tail-flick response in mice. Menatetrenone (50 and 100 mg/kg, i.p.) had no significant effect on the duration of the first phase of the formalin-induced flinching. However, menatetrenone (100 mg/kg, i.p.) significantly inhibited the second phase of the formalin-induced flinching. I.p. administration of menatetrenone (100 mg/kg) significantly reduced the duration of nociceptive responses induced by i.t. injection of bradykinin, but not of substance P, prostaglandin E2 or N-methyl-D-aspartate (NMDA). These present data suggest that i.p. pretreatment with menatetrenone produced dose-dependent antinociceptive effect in mice. This effect may be, at least in part, mediated by the inhibition of bradykinin dependent nociceptive transmission in the spinal cord.     

Experimental study of the effect of captopril on pain reactions

The experiments on the electrical stimulation of the isolated guinea-pig ileum have shown that captopril (10(-6)-10(-4) g/ml) caused dose-dependent inhibition of the organ contractions, abrogated by naloxone. In mice, the drug in the doses of 0.1 to 0.5 mg/kg administered subcutaneously had hyperalgesic effect and, with the dose increase (1-25 mg/kg), progressively attenuated the degree of nociceptive reactions caused by thermal and chemical stimulation. When kininogen accumulations were depleted due to the injection of kininogenase activator-cellulose sulfate, captopril in all the doses studied had an analgetic effect, with it reduced by naloxone. The data obtained show that dipeptidyl-carboxypeptidase inhibition by captopril can affect the degree of nociceptive reactions caused by various nociceptive stimuli.     

Analgesic and anti-inflammatory effects of phosphodiesterase inhibitors

The aim of the present study was to investigate the role of phosphodiesterase (PDE) enzyme inhibitors namely rolipram and theophylline in pain and inflammation in experimental animals. Rolipram, a selective PDE IV inhibitor and theophylline a nonspecific PDE inhibitor exerted dose dependent analgesic and anti-inflammatory effect against acetic acid-induced writhing in mice and carrageenan-induced paw edema in rats, respectively. Nimesulide (1, 2 mg/kg) produced significant anti-inflammatory effect. Further, nimesulide (0.5 mg/kg) potentiated analgesic effect of rolipram but it failed to modulate the anti-inflammatory effect of PDE inhibitors. Present study suggests that PDE enzymes might be playing a role in nociceptive and inflammatory responses in animals.     

Characteristics of the neuronal reaction of the substantia nigra to nociceptive stimulation

The nature of neurone response of substance nigra (SN) to nociceptive stimulation of the cat's peroneal nerve has been studied. The recording of neurone SN firing rate revealed that the majority (71.0%) of the SN neurones responded to the nociceptive repetitive stimulation of the peroneal nerve. But the thresholds of nociceptive activation in SN neurones turned to be very high. As a result of it the number of SN neurones responding to repetitive peroneal stimulation was twice as many as the number of cells responding to single stimulation of the nerve. The intravenous injection of naloxone in dose 1.0 mg/kg changed both excitatory and inhibitory responses in majority (71.4%) of SN neurones responding to repetitive peroneal stimulation. Naloxone did not modify the firing rate of neurones nonresponsive to nociception.     

Further characterization of nociception-related and arterial pressure-related neuronal responses in the nucleus reticularis gigantocellularis of the rat

The present study was undertaken to further characterize the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata in the central processing of nociceptive and cardiovascular signals, and its modulation by metenkephalin. In Sprague-Dawley rats anesthetized with pentobarbital sodium, we found that all 125 spontaneously active NRGC neurons that responded to noxious stimuli (tail clamp) also exhibited arterial pressure-relatedness. Forty neurons additionally manifested cardiac periodicity that persisted even during nociceptive responses. While maintaining their cardiovascular responsive characteristics, the nociception-related NRGC neuronal activity was blocked, naloxone-reversibly (0.5 mg/kg, i.v.), by morphine (5 mg/kg, i.v.). Microiontophoretically applied met-enkephalin suppressed the responsiveness of NRGC neurons to individually delivered tail clamp or transient hypertension induced by phenylephrine (5 µg/kg, i.v.). Interestingly, in NRGC neurons that manifested both nociception and arterial pressure relatedness, the preferential reduction in the response to noxious stimuli upon simultaneous elevation in systemic arterial pressure was reversed to one that favored nociception in the presence of met-enkephalin. All actions of met-enkephalin were discernibly blocked by the opioid receptor antagonist, naloxone. Our results suggest that individual NRGC neurons may participate in the processing of both nociceptive and cardiovascular information, or in the coordination of the necessary circulatory supports during nociception. In addition, neuropeptides such as met-enkephalin may exert differential modulation on neuronal responsiveness according to the prevailing physiologic status of the animal. They also showed that NRGC may be a central integrator for pain and cardiovascular-related functions.     

Cholinergic-NO-cGMP mediation of sildenafil-induced antinociception

Acetylcholine and cholinomimetic agents with predominant muscarinic action are known to increase the concentration of cGMP by activation of nitric oxide signaling pathway in the nociceptive conditions. The present study was aimed to investigate the NO-cGMP-PDE5 pathway in nociceptive conditions in the experimental animals. Nociceptive threshold was assessed by acetic acid-induced writhing assay (chemonociception) or carrageenan-induced hyperalgesia. Sildenafil [1-5 mg/kg, ip, 50-200 microg/paw, intraplantar (ipl)] produced dose dependent antinociception in both the tested models. Coadministration of acetylcholine (50 mcg/paw, ipl) or cholinomimetic agent, neostigmine (0.1 mcg/kg, ip and 25 ng/paw, ipl) augmented the peripheral antinociceptive effect of sildenafil. This effect was sensitive to blockade by L-NAME (20 mg/kg, ip, 100 microg/paw, ipl), a non-selective NOS inhibitor and methylene blue (1 mg/kg, ip), a guanylate cyclase inhibitor, which per se had little or no effect in both the models of nociception. Further, the per se analgesic effect of acetylcholine and neostigmine was blocked by both L-NAME and methylene blue in the models of nociception, suggesting the activation of NO-cGMP pathway. Also, both L-NAME and methylene blue blocked the per se analgesic effect of sildenafil. These results indicate the peripheral accumulation of cGMP may be responsible for antinociceptive effect, and a possible interaction between cholinergic agents and PDE5 system in models of nociception.     

Twenty-four-hour variation of L-arginine/nitric oxide/cyclic guanosine monophosphate pathway demonstrated by the mouse visceral pain model

The L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway is known to be involved in central and peripheral nociceptive processes. This study evaluated the rhythmic pattern of the L-arginine/NO/cGMP pathway using the mouse visceral pain model. Experiments were performed at six different times (1, 5, 9, 13, 17, and 21 h after light on) per day in male mice synchronized to a 12 h:12 h light-dark cycle. Animals were injected s.c. with saline, 2 mg/kg L-arginine (a NO precursor), 75 mg/kg L-N(G)-nitroarginine methyl ester (L-NAME, a NOS inhibitor), 40 mg/kg methylene blue (a soluble guanylyl cyclase and/or NOS inhibitor), or 0.1 mg/kg sodium nitroprusside (a nonenzymatic NO donor) 15 min before counting 2.5 mg/kg (i.p.) p-benzoquinone (PBQ)-induced abdominal constrictions for 15 min. Blood samples were collected after the test, and the nitrite concentration was determined in serum samples. L-arginine or L-NAME caused both antinociception and nociception, depending on the circadian time of their injection. The analgesic effect of methylene blue or sodium nitroprusside exhibited significant biological time-dependent differences in PBQ-induced abdominal constrictions. Serum nitrite levels also displayed a significant 24 h variation in mice injected with PBQ, L-NAME, methylene blue, or sodium nitroprusside, but not saline or L-arginine. These results suggest that components of L-arginine/NO/cGMP pathway exhibit biological time-dependent effects on visceral nociceptive process.     

Non-opioid nociceptive activity of human dynorphin mutants that cause neurodegenerative disorder spinocerebellar ataxia type 23

We previously identified four missense mutations in the prodynorphin gene that cause human neurodegenerative disorder spinocerebellar ataxia type 23 (SCA23). Three mutations substitute Leu(5), Arg(6), and Arg(9) to Ser (L5S), Trp (R6W) and Cys (R9C) in dynorphin A(1-17) (Dyn A), a peptide with both opioid activities and non-opioid neurodegenerative actions. It has been reported that Dyn A administered intrathecally (i.t.) in femtomolar doses into mice produces nociceptive behaviors consisting of hindlimb scratching along with biting and licking of the hindpaw and tail (SBL responses) through a non-opioid mechanism. We here evaluated the potential of the three mutant peptides to produce similar behaviors. Compared to the wild type (WT)-peptide, the relative potency of Dyn A R6W, L5S and R9C peptides for SBL responses was 50-, 33- and 2-fold higher, and Dyn A R6W and L5S induced the SBL responses at a 10-30-fold lower doses. Dyn A R6W was the most potent peptide. The SBL responses induced by Dyn A R6W were dose dependently inhibited by morphine (i.p.; 0.1-1 mg/kg) or MK-801, an NMDA ion channel blocker (i.t. co-administration; 5-7.5 nmol). CP-99,994, a tachykinin NK1 receptor antagonist (i.t. co-administration; 2 nmol) and naloxone (i.p.; 5 mg/kg) failed to block effects of Dyn A R6W. Thus, similarly to Dyn A WT, the SBL responses induced by Dyn A R6W may involve the NMDA receptor but are not mediated through the opioid and tachykinin NK1 receptors. Enhanced non-opioid excitatory activities of Dyn A mutants may underlie in part development of SCA23.     

A comparison of the self-stimulation reaction and of conditioned place preference with fenamine administration in rats]

The reinforcing properties of different doses of amphetamine (1 and 5 mg/kg) were examined using two variants of self-stimulation reaction (in the Skinner box and locomotor self-stimulation in a shuttle box) and place preference test. Amphetamine in dose of 1 mg/kg increased the frequency of self-stimulation in the Skinner box and prolonged the time of rat staying in active zone of a shuttle box to a greater degree than 5 mg/kg of the drug. On the contrary, the aversive phase of self-stimulation, determined by a coefficient of "disagreement", grew higher after 5 mg/kg amphetamine than following 1 mg/kg. The study of effects by place preference test revealed the other regularity: the most positive reinforcing properties possessed the drug in a dose of 5 mg/kg. Thus, there are dissociation between the two doses of amphetamine (1 and 5 mg/kg) in their action on different physiological conditioned responses. The mechanisms of this dissociation are discussed.     

Effect of diphenylhydramine on the Tyr-MIF-1 antinociception in rats.

Tyr-MIF-1 is a representative of the MIF's family of endogenous peptides. It has been isolated from bovine hypothalamus and human parietal cortex that suggests its involvement in nociception. Tyr-MIF-1 can bind to the mu-receptors as well as to its specific non-opiate receptors in the brain. Data in the literature rise the idea that histamine (HA), a well known nociceptive agent, and Tyr-MIF-1 might have a common pathway in their effects on nociception. We tested that possibility by investigation of the combined action of diphenhydramine (DPH, an H (1) -antagonist) and Tyr-MIF-1 on nociception. The changes in the nociceptive effects were examined in the male Wistar rats by the Randall-Sellito paw-pressure (PP) and the tail-flick (TF) tests. Tyr-MIF-1 in a dose of 1 mg/kg exerted strong naloxone-reversible analgesic effects. DPH (100 microg/kg, i.p.) had an antinociceptive action, too. The co-administration of Tyr-MIF-1 and DPH enhanced the antinociceptive effect, as compared to DPH (PP) and to TYR-MIF-1 alone (TF). These effects were reversed when methylene blue (MB, 500 microg/rat) was applied 1h before the combination. However, naloxone (1 mg/kg, i.p.) only slightly affected the antinociceptive effect of DPH and TYR-MIF-1, compared to that of MB. The results obtained confirmed the hypothesis that cyclic nucleotides are involved in the realization of nociceptive effects of both HA and Tyr-MIF-1.     

The antinociceptive effect of tramadol on a model of neuropathic pain in rats

The antinociceptive activity of tramadol was investigated on the vocalization threshold to paw pressure in a rat model of unilateral mononeuropathy produced by loose ligatures around the common sciatic nerve. Despite the analgesic activity of tramadol was clearly established in motor and sensory responses of the nociceptive system in rats, the effect of this atypical opioid on experimental neuropathic pain models is not investigated. The intraperitoneally injected tramadol (2.5, 5 and 10 mg/kg) produced a potent and dose-dependent antinociceptive effect on both lesioned and non-lesioned hind paws. However, the analgesic effect on the lesioned paw was significantly more potent than the non-lesioned paw. This effect was partially antagonized by intraperitoneally administered naloxone (0.1 mg/kg) suggesting an additional non-opioid mechanism. Our results suggest that tramadol may be useful for the alleviation of some symptoms in peripheral neuropathic conditions