[Show abstract][Hide abstract] ABSTRACT: Ghrelin, an orexigenic (appetite stimulating) peptide activates binding sites in the ventral tegmental area (a structure linked with the neural reward system) allowing it to participate in reward-seeking behavior. An increasing number of studies over the past few years have demonstrated ghrelin's role in alcohol, cocaine, and nicotine abuse. However, the role of ghrelin, in opioid effects, has rarely been examined. The aim of the present study was to ascertain whether a ghrelin antagonist (JMV2959) was able to inhibit markers of morphine-induced activation of the neural reward system, namely morphine-induced increase of dopamine in the nucleus accumbens and behavioral changes in rats.
We used in vivo microdialysis to determine changes of dopamine and its metabolites in the nucleus accumbens shell in rats following morphine (MO, 5, 10 mg/kg s.c.) administration with and without ghrelin antagonist pretreatment (JMV2959, 3, 6 mg/kg i.p., 20 min before MO). Induced behavioral changes were simultaneously monitored.
JMV2959 significantly and dose dependently reduced MO-induced dopamine release in the nucleus accumbens shell and affected concentration of by-products associated with dopamine metabolism: 3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA). JMV2959 pretreatment also significantly reduced MO-induced behavioral stimulation, especially stereotyped behavior.
Ghrelin secretagogue receptors (GHS-R1A) appear to be involved in the opioid-induced changes in the mesolimbic dopaminergic system associated with the reward processing.
[Show abstract][Hide abstract] ABSTRACT: There is good evidence that opioids can potentiate analgesic activity of some older non-opioid analgesics (such as paracetamol or ibuprofen) but it is not known whether this also holds true for newer non-opioid analgesics that selectively inhibit cyclooxygenase 2 (coxibs). This study was undertaken to determine the nature of the interaction between codeine and celecoxib or etoricoxib in peritoneal irritation-induced visceral pain in mice. For comparison, interactions of codeine with paracetamol and ibuprofen were also tested using the same method.
A small volume of a weak acetic acid (0.6%) was injected into the peritoneal cavity and the number of writhes (contractions of abdominal muscles) was counted. All drugs were given orally. Their interaction was characterized using isobolographic analysis.
Codeine, etoricoxib, celecoxib, ibuprofen and paracetamol all independently produced dose-dependent suppression of writhing. The isobolographic analysis carried out using equipotent dose ratios showed that the interactions between codeine and etoricoxib or celecoxib were sub-additive or additive, respectively. This was in contrast to combinations of codeine with ibuprofen or paracetamol, which were supra-additive. Interaction indexes γ, determined as a ratio between experimental and theoretical ED50 values of the mixture, were as follows: 2.7 for codeine + etoricoxib, 0.62 for codeine + celecoxib, 0.43 for codeine + ibuprofen and 0.33 for codeine + paracetamol.
These and other results suggest that opioids do not seem to potentiate analgesic effects of selective COX-2 inhibitors, in contrast to nonselective COX inhibitors or paracetamol.
[Show abstract][Hide abstract] ABSTRACT: Paracetamol is converted to an active metabolite AM404 via fatty acid amide hydrolase (FAAH). The aim of the present study was to ascertain whether a FAAH inhibitor URB597 antagonizes paracetamol analgesic activity (and to asses by this way the role of FAAH in analgesic activity of paracetamol).
The interaction between a FAAH inhibitor URB597 and paracetamol was investigated in the writhing test in mice using an isobolographic analysis.
URB597 or paracetamol alone and in combinations produced dose-dependent antinociceptive effects. ED50 values were estimated for the individual drugs and an isobologram was constructed. The observed ED50 value for the URB57-paracetamol combination was 0.097 (0.062-0.247) mg/kg. This value did not differ significantly from the theoretical additive ED50 value for the URB597-paracetamol combination which was 0.108 (0.059-0.198) mg/kg. Thus, inhibition of FAAH by URB597 was not followed by the lack of analgesic activity in paracetamol.
The present results suggest that the analgesic activity of paracetamol is not dependent solely on FAAH metabolic conversion to AM404 and that paracetamol exerts analgesic activity also by additional mechanisms.
[Show abstract][Hide abstract] ABSTRACT: The aim of the present study was to evaluate and compare the analgesic activity and serum levels of meloxicam (CAS 71125-38-7) after administration of meloxicam associated with beta-cyclodextrin (BCD, CAS 7585-39-9) and unmodified meloxicam. The analgesic activity was measured using the plantar test (rats) and the writhing test (mice). In the plantar test, BCD-meloxicam (3 mg/kg and 10 mg/kg orally) showed higher analgesic activity than corresponding doses of meloxicam alone; in the writhing test BCD-meloxicam (7 mg/kg and 15 mg/kg orally) showed stronger analgesic activity than unmodified meloxicam. Serum levels of meloxicam were significantly higher, at 0.5 h and 1 h after administration of BCD-meloxicam orally than those of unmodified meloxicam (both dosed at 10 mg/kg). The present results suggest that association with beta-cyclodextrin increases the analgesic activity of meloxicam. This may be due to an icreased systemic bioavailability of meloxicam after oral administration of its complex with beta-cyclodextrin.
[Show abstract][Hide abstract] ABSTRACT: Previously, we found that guaifenesin enhances analgesia induced by paracetamol. The aim of the present study was to determine whether guaifenesin is able to also increase analgesic activity in the non-steroid anti-inflammatory drugs ibuprofen, nimesulide and celecoxib. In addition we investigated the influence of guaifenesin on plasma levels of nimesulide.
A model of visceral pain consisting of intraperitoneal injection of acetic acid (writhing test) was used. Levels of nimesulide in plasma were measured by HPLC. All drugs were given orally and tested in mice.
Guaifenesin alone did not produce any antinociceptive effect. Simultaneous administration of guaifenesin (200 mg/kg) and subanalgesic doses of ibuprofen (10 and 30 mg/kg), nimesulide (10 and 20 mg/kg) or celecoxib (1 and 5 mg/kg) resulted in a significant antinociceptive effects. The plasma levels of nimesulide were significantly higher in combination with guaifenesin at 30, 60 and 90 min after oral administration in comparison to nimesulide monotherapy.
The present results suggest that guaifenesin might enhance the analgesic activity of various non-steroidal anti-inflammatory drugs.
[Show abstract][Hide abstract] ABSTRACT: The aim of the study was to ascertain whether rilmenidine, a second generation imidazoline-alpha-2-adrenoreceptor agonist, is able to increase analgesic effects of ibuprofen in the writhing test in mice. Experimental studies combining these agents have not yet been published.
An acetic acid (0.7%) solution was injected into the peritoneal cavity and the number of writhes was counted. The influence on locomotor performance was tested using the rotarod test.
Rilmenidine, ibuprofen, and rilmenidine-ibuprofen fixed-ratio combinations produced dose-dependent antinociceptive effects. ED50 values were estimated for the individual drugs and an isobologram was constructed. The derived theoretical additive ED50 value for the rilmenidine-ibuprofen combination was 34.00 +/- 9.39 mg/kg. This value was significantly greater than the observed ED50 value which was 18.07 +/- 5.41 mg/kg, indicating a synergistic interaction. Rilmenidine did not impair motor coordination, as measured by the rotarod test, at antinociceptive and higher doses.
The present results suggest that rilmenidine enhances the analgesic activity of ibuprofen. If rilmenidine produces antinociception in humans, then the synergistic antinociception of rilmenidine with ibuprofen could offer therapeutic advantage for clinical treatment of pain.
[Show abstract][Hide abstract] ABSTRACT: Some individually-housed male mice behave aggressively during encounters with strange males, while others are timid or sociable in the same situation. The objective of the present study was to examine concentrations of glutamate, aspartate, and GABA in the brain of aggressive, timid, and sociable mice.
Random-bred albino mice were housed individually for three weeks and then classified in three groups (aggressive, timid, and sociable mice) according to their behavior during social interaction with non-aggressive group-housed male mice in a neutral cage. One week after categorization, by means of the social conflict test, levels of glutamate, aspartate, and GABA were measured by in vivo microdialysis of the medial prefrontal cortex (mPFC) of the isolated and group-housed mice.
Sociable mice had almost triple the levels of GABA in their mPFC than aggressive or timid mice. No significant differences in aspartate and glutamate levels were found in these three types of individually-housed mice. Forebrain chemistry of group-housed mice did not differ from that of individually-housed mice with the exception of levels of glutamate and GABA which were significantly lower in group-housed mice than in sociable individually-housed mice.
The present results suggest that GABA might play a role in sociable behavior. Results also corroborate other findings indicating that the GABAergic system represents an important molecular and neuronal substrate for the selective attenuation of anxiety and aggression.
[Show abstract][Hide abstract] ABSTRACT: The aim of the study was to ascertain antinociceptive effects of rilmenidine, a second-generation imidazoline-alpha-2-adrenoreceptor agonist, and to see whether rilmenidine was able to increase the analgesic effects of paracetamol in the writhing test in mice. An acetic acid (0.7%) solution was injected into the peritoneal cavity and the number of writhes was counted. The influence on locomotor performance was tested using the rotarod test. Rilmenidine, paracetamol, and rilmenidine-paracetamol fixed-ratio combinations produced dose-dependent antinociceptive effects. ED(50) values were estimated for the individual drugs and an isobologram was constructed. The derived theoretical additive ED(50) value for the rilmenidine-paracetamol combination was 109.23 +/- 35.05 mg/kg. This value was significantly greater than the observed ED(50) value which was 56.35 +/- 20.86 mg/kg, indicating a synergistic interaction. Rilmenidine did not impair motor coordination, as measured by the rotarod test, at antinociceptive and higher doses.
Archiv für Experimentelle Pathologie und Pharmakologie 03/2009; 379(6):575-80. · 2.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Preemptive versus therapeutic effects of levetiracetam were investigated in a model of postoperative incisional pain in rats.
Levetiracetam (250, 500, and 1000 mg/kg intraperitoneal (i.p.) or morphine (5 mg/kg i.p.) was administered either 1 h before (preemptive administration) or 1 h after (therapeutic administration) incisional surgery to the hind paw of rats. The effects of levetiracetam were evaluated based on thermal hyperalgesia measured by the plantar test.
All preoperatively treated levetiracetam groups showed a significant, dose dependent, increase in paw withdrawal latency. However, post-incisional administration of levetiracetam produced no antihyperalgesic effect at any dose or at any time. In contrast, post-incisional administration of morphine reduced thermal hyperalgesia, while preemptive administration of morphine did not produce any significant antihyperalgesic effects.
The present results suggest that levetiracetam might possess preemptive analgesic activity.
[Show abstract][Hide abstract] ABSTRACT: Knowledge on the involvement of spinal COX-1 and COX-2 in pain due to osteoarthritis could be useful for better understanding of its pathogenesis and therapy. In this study we have investigated a long-term pattern of expression and production of spinal COX-1 and COX-2 in the model of osteoarthritis induced in rats by injection of monoiodoacetate (MIA) into the knee joint. MIA injection produced thermal hyperalgesia (assessed by the plantar test) and tactile allodynia (measured with von Frey hairs). The pain measures reached maximum on the fifht day, then remained relatively stable. The expression of spinal COX-2 mRNA reached maximum on day 5 (5.2 times; P<0.001) and remained increased until day 31 (4.9 times; P<0.001). Expression of spinal COX-1 mRNA increased gradually reaching maximum on the day 31 (4.5 times; P<0.001) when the relative expression of both genes was almost equal. The production of both proteins was almost similar at the beginning of the experiment. The highest production of COX-2 protein was observed on day 5 after the induction of osteoarthritis (increased 3.9 times). The levels of COX-1 protein increased gradually with maximum on day 31 (3.4 times). The present findings indicate that not only expression of COX-2 mRNA but also that of COX-1 mRNA is significantly increased in the spine during osteoarthritis pain. Thus, in contrast to inflammatory pain, the upregulation of spinal COX-1 may be important in osteoarthritis pain.
Physiological research / Academia Scientiarum Bohemoslovaca 01/2009; 58(3):419-25. · 1.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Alpha-2 adrenoceptors (alpha(2)-ARs) are critically involved in regulating neurotransmitter release from sympathetic nerves and neurons and play an important role in the regulation of awareness, arousal and vigilance. In our recent study, dexmedetomidine, a full alpha(2)-AR agonist, produced antiaggressive effects in the social conflict test in mice at doses that were twice smaller than those producing sedation. The aim of this study was to ascertain antiaggressive effect of a novel drug naphthylmedetomidine, with a more selective alpha(2)-AR activity. Behavioral effects of naphthylmedetomidine (150-1200 microg/kg i.p.) were studied in the activity cage and in the social conflict tests in mice. Naphthylmedetomidine dose dependently decreased aggressive behavior during social conflict in aggressive mice with significant reduction already at the lowest doses tested (150 microg/kg), whereas locomotion and social investigation were significantly decreased only after four times bigger dose of naphthylmedetomidine (600 microg/kg) in aggressive mice. Naphthylmedetomidine had no effect on aggression in nonaggressive mice. Naphthylmedetomidine reduced locomotion in the activity cage significantly only at the highest doses tested (600 and 1200 microg/kg), and this effect was only partially reversed by administration of high doses of an alpha-2 antagonist atipamezole (3 and 10 mg/kg). In nonaggressive mice, the difference between the dose reducing dominant social behavior (social investigation) and locomotion (150 and 300 microg/kg, respectively) was smaller than in aggressive mice. In conclusion, naphthylmedetomidine showed a very strong and selective antiaggressive effect in aggressive mice, which was devoid of locomotion-inhibiting/sedative effect. This study suggests that naphthylmedetomidine may have clinical potential as antiaggressive drug.
[Show abstract][Hide abstract] ABSTRACT: Cultural evolution has predominated over biological evolution in modern man (Homo sapiens sapiens). Cultural evolution differs from biological evolution not only by inheritance of acquired characteristics but also, as is proposed in the present essay, by another kind of selection mechanism. Whereas selection in biological evolution is executed according to a criterion of reproductive success (the natural selection), selection in cultural evolution appears to be carried out according to human and humanistic criteria (success or fitness in meeting human needs, interests and humanistic values--"humanistic selection"). Many humanistic needs or values do not seem to be prerequisite for reproductive success, yet some of them (e.g. a need for freedom) seem to be inborn. Innateness, humanistic selection (decisive at a community level) and hierarchy of some human needs, interests and values appear to give cultural evolution a generally upward trend although long periods of stagnation or even regression may occur. Modern humans appear to be still at the early stage of their cultural evolution. A further cultural evolution of man appears to be, in contrast to biological evolution, predictable (with an optimistic outlook) and testable. The problem is that the hopeful result of this test will probably be known only in the fairly remote future provided that this species will not become extinct before that.
[Show abstract][Hide abstract] ABSTRACT: Levels of cyclooxygenase-2 (COX-2) mRNA, but not those of COX-1, were reported to be raised significantly after peripheral inflammation in the rat spinal cord. The aim of the present study was to ascertain whether this pattern of COX-2 and COX-1 expression applies also to other pain conditions induced by surgical procedure. Experiments were performed on two types of pain models. In a model of postoperative pain, 1 cm longitudinal incision was made through skin, fascia and muscle of the plantar aspect of the right hind paw in anaesthetized rats. In the second model, peripheral inflammation was induced by unilateral, intraplantar injection of carrageenan in the right hind paw. Carrageenan injection or skin incision produced marked and significant reduction of paw withdrawal latencies to noxious radiant heat stimuli after 2 and 6 hr. Under the acute inflammation 2 and 6 hr after carrageenan injection levels of COX-2 mRNA were markedly raised (7.8 and 15.5 times; P<0.001, respectively) while spinal levels of COX-1 mRNA were not significantly altered (n.s.). In contrast, spinal levels of COX-2 mRNA were raised less markedly in a model of postoperative pain (4.9 times at 2 hr; P<0.001 and 2.9 times (n.s.) at 6 hr after surgery) whilst levels of COX-1 mRNA in the lumbar spine were increased significantly (2.3 times; P<0.001) 6 hr after surgery. The present findings indicate that expression of COX-2 mRNA in the spine is less dominant in postoperative pain than in inflammatory pain and that spinal COX-1 mRNA is upregulated in postoperative pain.