Buspirone-induced antinociception is mediated by L-type calcium channels and calcium/caffeine-sensitive pools in mice

Pre-treatment with Tandospirone attenuates fentanyl-induced respiratory depression without affecting the analgesic effects of fentanyl in rodents

Opioid analgesics are widely used to treat acute, postoperative, and chronic pain. However, opioid receptor activation can result in severe respiratory depression. In this study, we demonstrated that Tandospirone (TS), a selective serotonin-1A receptor partial agonist, is effective against opioid-induced respiratory depression. Fentanyl was used to establish a respiratory depression model in rodents. We observed the effects of TS on respiratory depression in rats by using plethysmographic recordings and arterial oxygen saturation. In addition, we evaluated the effects of TS on fentanyl-induced sedation and analgesia by using the loss of righting reflex (LORR) and hot-plate tests, respectively. Rats (n = 5) were treated with TS or saline 5 min prior to fentanyl administration. TS [2 mg/kg, intravenous (i.v.)] dose-dependently attenuated fentanyl-induced respiratory depression versus saline + fentanyl group. Furthermore, pre-treatment with TS (2 mg/kg, i.v.) increased arterial oxygen saturation to 76.5 ± 2.0% at 5 min after fentanyl injection, compared with 35.9 ± 2.5% in saline pre-treated rats (P < 0.001), whereas the time to induction of LORR (P > 0.99) and duration of LORR (P = 0.95) did not differ between the "TS + fentanyl" and "saline + fentanyl" group. The antinociceptive effect of fentanyl was not affected by the administration of TS (P = 0.99) in mice (n = 10). In conclusion, we found that TS, a novel non-benzodiazepine anxiolytic/antidepressant drug, could attenuate severe fentanyl-induced respiratory depression and did not affect the analgesic/sedative effect of fentanyl. The clinical application of TS could significantly improve pain management.

Fluoxetine increases analgesic effects of morphine, prevents development of morphine tolerance and dependence through the modulation of L-type calcium channels expression in mice

Here, we aimed to investigate the effects of fluoxetine on morphine-induced analgesia, as well as preventive effects of it on morphine induced tolerance and dependence in mice. We also elucidate the involvement of L-type Ca²⁺ channels in these phenomena. To induce morphine tolerance, mice were treated with morphine (50 mg/kg) for 3 consecutive days. To evaluate the involvement of the calcium channel in the effects of fluoxetine (5, 20 mg/kg), combination ineffective doses of the two L-type calcium channel blockers, nimodipine (5 mg/kg) or diltiazem (20 mg/kg) with flouxetine were used with each morphine dose. Nociceptive behavior was evaluated using hot-plate test, while physical dependence assessed by naloxone-precipitated withdrawal on the fourth day of experiment. The expression of Cav1.2 and Cav1.3 subunits of the L-type calcium channels in cortex and mesolimbic tissues were measured using western immunoassay. Results showed that co-administration of fluoxetine (20 mg/kg) with morphine increased its acute analgesia effect and prevented the induction of morphine antinociceptive tolerance and physical dependence in mice. Moreover, these effects was potentiated by pre-treatment with diltiazem or nimodipine. Results also showed up-regulation of the Cav1.3 and Cav1.2 expression in the cerebral cortex and mesolimbic regions through the development of morphine dependence. Moreover, chronic administration of fluoxetine with morphine reduced the observed up-regulation of Cav1.3 and Cav1.2 expression in cortex and mesolimbic tissues. Our data indicated that co-administering of fluoxetine with morphine could potentiate the antinociceptive effect of morphine, prevent morphine analgesia tolerance and attenuated the morphine withdrawal signs during induction phases. Moreover, we also pointed out for the first time the role of L-type Ca²⁺ channel channels in the modulatory effects of fluoxetine on the morphine-related effects.

Resveratrol-induced antinociception is involved in calcium channels and calcium/caffeine-sensitive pools

Resveratrol has been widely investigated for its potential health properties, although little is known about its mechanism in vivo. Previous studies have indicated that resveratrol produces antinociceptive effects in mice. Calcium channels and calcium/caffeine-sensitive pools are reported to be associated with analgesic effect. The present study was to explore the involvement of Ca²⁺ channel and calcium/caffeine-sensitive pools in the antinociceptive response of resveratrol. Tail-flick test was used to assess antinociception in mice treated with resveratrol or the combinations of resveratrol with MK 801, nimodipine, CaCl₂, ryanodine and ethylene glycol tetraacetic acid (EGTA), respectively. The Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and brain-derived neurotrophic factor (BDNF) levels in the spinal cord were also investigated when treated with the above drugs. The results showed that resveratrol increased the tail flick latency in the tail-flick test, in dose-dependent manner. N-methyl-D-aspartate (NMDA) glutamate receptor antagonist MK 801 potentiated the antinociceptive effects of sub-threshold dose of resveratrol at 10 mg/kg. Ca²⁺ channel blocker, however, abolished the antinociceptive effects of resveratrol. In contrast to these results, EGTA or ryanodine treatment (i.c.v.) potentiated resveratrol-induced antinociception. There was a significant decrease in p-CaMKII and an increase in BDNF expression in the spinal cord when combined with MK 801, nimodipine, ryanodine and EGTA. While an increase in p-CaMKII level and a decrease in BDNF expression were observed when high dose of resveratrol combined with CaCl₂. These findings suggest that resveratrol exhibits the antinociceptive effects by inhibition of calcium channels and calcium/caffeine-sensitive pools.

Involvement of 5-HT1A/1B receptors in the antinociceptive effect of paracetamol in the rat formalin test

The mechanism of analgesic action of paracetamol (acetominophen) remains still unknown. However, a relationship between serotonergic system and the effect of paracetamol has been previously demonstrated. The serotonin activity in the brainstem is primarily under the control of 5-HT_1A somatodendritic receptors, although some data also suggest the involvement of 5-HT_1B receptors. To determine whether the 5-HT_1A and 5-HT_1B receptors are involved in the antinociceptive effect of paracetamol, we evaluated the effect of paracetamol (0.125-1 g/kg i.p.) followed by different antagonists [WAY 100,635 (0.8 mg/kg s.c.) and SB 216,641 (0.8 mg/kg s.c.)] or agonists [8-OH-DPAT (0.125 mg/kg s.c.) and CP 93,129 (0.125 mg/kg s.c.)] of 5-HT_1A and 5-HT_1B receptors, respectively, in the rat model of formalin-induced pain. We demonstrated that paracetamol administration showed a dose-dependent antinociceptive effect in the formalin test. WAY 100,635 (5-HT_1A antagonist) induced an increase in the antinociceptive effect of paracetamol at 250 mg/kg doses. Conversely, 8-OH-DPAT (5-HT_1A agonist) decreased the antinociceptive effect of paracetamol at 500-1000 mg/kg doses. However, SB216641 (5-HT_1B antagonist) modified weakly the antinociceptive effect of paracetamol at 250 mg/kg doses and CP 93,129 (5-HT_1B agonist) not produce a clear effect in the antinociceptive effect of paracetamol. These results suggest that the antinociceptive effect of paracetamol can be enhanced mainly by compounds having 5-HT_1A antagonist properties in the formalin test and maybe by 5-HT_1B receptors antagonists.

The analgesic effect of trans-resveratrol is regulated by calcium channels in the hippocampus of mice

Resveratrol has been widely studied in terms of it's potential to slow the progression of many diseases. But little is known about the mechanism of action in neuropathic pain. Neuropathic pain is the main type of chronic pain associated with tissue injury. Calcium channels and calcium/caffeine-sensitive pools are associated with analgesic pathway involving neuropathic pain. Our previous study suggested that the antinociceptive effect of resveratrol was involved in Ca²⁺/calmodulin-dependent signaling in the spinal cord of mice. The aim of this study was to explore the involvement of Ca²⁺ in analgesic effects of trans-resveratrol in neuropathic pain and signal pathway in hippocampus. Hot plate test was used to assess antinociceptive response when mice were treated with trans-resveratrol alone or in combination with Mk 801, nimodipine, CaCl₂, ryanodine or EGTA. The effects of trans-resveratrol and the combination on Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and BDNF (brain-derived neurotrophic factor) expression in hippocampus were also investigated. The results showed that trans-resveratrol increased paw withdraw latency in the hot plate test. The effect of resveratrol was enhanced by Mk 801 and nimodipine. Central administration of Ca²⁺, however, abolished the antinociceptive effects of resveratrol. In contrast, centrally administered EGTA or ryanodine improved trans-resveratrol induced antinociception. There was a significant increase in p-CaMKII and BDNF expression in the hippocampus when resveratrol were combined with Mk 801, nimodipine, ryanodine and EGTA. Administration of CaCl₂ blocked changes in p-CaMKII and BDNF levels in the hippocampus. These findings suggest that trans-resveratrol exerts the effects of antinociception through regulation of calcium channels and calcium/caffeine-sensitive pools.

Maternal buspirone protects against the adverse effects of in utero stress on emotional and pain-related behaviors in offspring

Previous investigations from our laboratory demonstrated that prenatal stress exacerbates inflammatory pain-related behavior in adult rats and that fetal serotonin (5-HT) is involved in this phenomenon. In the present study we test the hypothesis that injections of buspirone, a 5-HT1A agonist, to rat dams before restraint stress during the last week of pregnancy (between pregnant days 15 and 20) can improve the characteristics of emotional and inflammatory pain-related behaviors in the adult offspring. Buspirone was injected to dams between the 9 and 20 days of pregnancy, during restraint stress, five min before it. The depression-like behavior in the forced swim test, formalininduced pain and body weight were investigated in the adult offspring. Prenatal stress exacerbated the licking behavior, the index of formalin-induced pain, and increased the time of immobility, the index of depression-like behavior. Buspirone normalized the licking behavior and profoundly reduced the time of immobility, which indicates differences in the mechanisms of antinociceptive and antidepressant effects of buspirone. The present new findings demonstrate that adverse influences of prenatal stress on emotional and inflammatory pain-related behaviors can be prevented by using prenatal buspirone, which shows long-term anxiolytic, antidepressant and antinociceptive effects. The new fact of body weight decrease in buspirone+stress males is worth noting in the context of the important problem of body weight gain as a common side effect of treatment with antidepressant drugs.

Antinociceptive action of myricitrin: Involvement of the K+ and Ca2+ channels

The present study was designed to investigate the mechanisms involved in the antinociception afforded by myricitrin in chemical models of nociception in mice. Myricitrin given by intrathecal (i.t.) or intracerebroventricular (i.c.v.) route produced dose-related antinociception when evaluated against acetic acid-induced visceral pain in mice. In addition, the intraperitoneal administration of myricitrin caused significant inhibition of biting behaviour induced by i.t. injection of glutamate, substance P, capsaicin, interleukin 1 beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). The antinociception caused by myricitrin in the acetic acid test was fully prevented by i.t. pre-treatment with pertussis toxin, a Gi/o protein inactivator, and by i.c.v. injection of calcium chloride (CaCl(2)). In addition, the i.t. pre-treatment of mice with apamin, a blocker of small (or low)-conductance calcium-gated K(+) channels and tetraethylammonium, a blocker of voltage-gated K(+) channels significantly reversed the antinociception induced by myricitrin. The charybdotoxin, a blocker of large (or fast)-conductance calcium-gated K(+) channels and glibenclamide, a blocker of the ATP-gated K(+) channels had no effect on myricitrin-induced antinociception. Calcium uptake analysis revealed that myricitrin inhibited (45)Ca(2+) influx under a K(+)-induced depolarization condition. However, calcium movement was modified in a non-depolarizing condition only when the highest concentration of myricitrin was used. In summary, our findings indicate that myricitrin produces consistent antinociception in chemical models of nociception in mice. These results clearly demonstrate an involvement of the Gi/o protein dependent mechanism on antinociception caused by myricitrin. The opening of voltage- and small-conductance calcium-gated K(+) channels and the reduction of calcium influx led to the antinociceptive of myricitrin.