Spinal N-Methyl-D-Aspartate Receptors May Mediate the Analgesic Effects of Emulsified Halogenated Anesthetics

5-HT1A Receptors Mediate Analgesia Induced by Emulsified Sevoflurane in Thermal Nociception but Have Little Effect on Chemical Nociception

OBJECTIVE

The study aimed to investigate the relationship between the analgesic effect of sevoflurane and 5-serotonin receptor 1A (5-HT1A R) in the spinal cords of mice.

METHODS

Analgesic mouse models were established by intraperitoneal injection of emulsified sevoflurane, and the influence of p-MPPF (a specific antagonist of 5-HT1A Rs) intrathecal injection on the changes in tail-flick latency in tail-withdrawal test, pain threshold in hot-plate test (HPPT), and writhing times in acetic acid-induced writhing test were recorded.

RESULTS

Intraperitoneal injection of emulsified sevoflurane alone produced an analgesic effect (p < 0.05). p-MPPF (2, 4, and 8 μg) alone had no impact on tail-flick latency, HPPT, and writhing times in mice (p > 0.05). The 3 doses of p-MPPF reduced the tail-flick latency or HPPT. p-MPPF 8 μg can increase the writhing times (p < 0.05) in analgesic mice with sevoflurane, while p-MPPF 2 and 4 μg did not affect the writhing times.

CONCLUSION

5-HT1A Rs in the spinal cord may be an important target for the analgesic effect of sevoflurane on the thermal nociception, but it has little relation to the anti-chemical chemical nociceptive effect of sevoflurane.

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors participate in the analgesic but not hypnotic effects of emulsified halogenated anaesthetics

The present study was designed to investigate the role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in hypnosis and analgesia induced by emulsified inhalation anaesthetics. After having established the mice model of hypnosis and analgesia by intraperitoneally injecting appropriate doses of emulsified enflurane, isoflurane or sevoflurane, we intracerebroventricularly or intrathecally injected different doses of AMPA and then observed the effects on the sleep time using hypnosis test and the tail-withdrawal latency using the tail-withdrawal test. In hypnosis test, AMPA (50, 75 and 100 ng, intracerebroventricularly) had no distinctive effects on the sleep time of the mice treated with emulsified inhalation anaesthetics (P > 0.05). In tail-withdrawal test, AMPA (0.25, 0.5 and 1.0 ng, intrathecally) significantly and dose-dependently decreased the tail-withdrawal latency (P < 0.05 or P < 0.01) in the mice treated with emulsified anaesthetics. These results suggest that AMPA receptors may participate in the analgesic but not in the hypnotic effects induced by emulsified enflurane, isoflurane or sevoflurane.

SPINAL ?-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLEPROPIONIC ACID RECEPTORS MAY MEDIATE THE ANALGESIC EFFECTS OF EMULSIFIED HALOGENATED ANAESTHETICS

1. The present study was designed to investigate the relationship between spinal cord alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and the analgesic effects of emulsified halogenated anaesthetics. 2. After having established the mouse model of analgesia by intraperitoneal or subcutaneous injections of appropriate doses of emulsified enflurane, isoflurane or sevoflurane, we injected different doses of AMPA intrathecally and observed effects on the pain threshold using the hot-plate and acetic acid-induced writhing tests. 3. The results showed that intrathecal injection of AMPA (0.25, 0.5 and 1.0 ng) did not affect the pain threshold on the hot-plate test or the writhing times in conscious mice. In contrast, AMPA (0.25, 0.5 and 1.0 ng intrathecally) significantly and dose-dependently decreased the pain threshold on the hot-plate test and increased the writhing times in mice treated with emulsified anaesthetics. 4. These results suggest that spinal AMPA receptors may be important targets for the analgesic effects of emulsified enflurane, isoflurane and sevoflurane.

Involvement of NMDA Receptors in Thiopental-Induced Loss of Righting Reflex, Antinociception and Anticonvulsion Effects in Mice

Potentiation of GABA(A) receptor-mediated inhibitory neurotransmission contributes to the anesthetic action of thiopental. However, the inhibiting action of general anesthetic on excitatory neurotransmission also purportedly underlies its effects. The aim of the study was to elucidate the role of glutamate receptors (NMDA and AMPA receptors) in thiopental-induced anesthesia. Intracerebroventricular (i.c.v.) NMDA (50 ng) significantly increased the induction time of loss of righting reflex and decreased sleep time induced by intraperitoneal injection (i.p.) of thiopental (50 mg/kg). Furthermore, NMDA at 50 ng i.c.v. increased the 50% effective dose values for thiopental to produce loss of righting reflex and immobility in response to noxious tail clamp by 25% and 21% (p < 0.05), respectively. However, intrathecal (IT) administration of NMDA or both of i.c.v. or IT administration of AMPA did not show such antagonizing effects on thiopental action at subconvulsive dose. Finally, thiopental (25 mg/kg i.p.) inhibited convulsions induced by NMDA (0.4 microg i.c.v.) or bicuculline (0.6 microg i.c.v.). However, i.p. muscimol (1 mg/kg) blocked the convulsions induced by bicuculline, but not those induced by NMDA at 3 mg/kg. Similarly, i.p. MK-801 (0.1 mg/kg) antagonized NMDA-induced convulsions, but not bicuculline-induced convulsions at 0.3 mg/kg. Therefore, we suggest that the effects of the selective GABA(A) and NMDA receptors on convulsive behavior are special to their sites of action, and that the inhibitory action of thiopental on NMDA receptors is possibly not mediated by secondary effects of its GABA(A) receptors agonism. These results above indicate the involvement of NMDA receptors in thiopental-induced anesthesia in mice.

Strychnine-sensitive glycine receptors mediate the analgesic but not hypnotic effects of emulsified volatile anesthetics

The present study was designed to investigate the role of strychnine-sensitive glycine receptors in hypnosis and analgesia induced by emulsified volatile anesthetics. After having established the mice model of hypnosis and analgesia by intraperitoneally injecting (i.p.) appropriate doses of ether, enflurane, isoflurane or sevoflurane, we intracerebroventricularly (i.c.v.) or intrathecally (i.t.) injected different doses of strychnine and then observed the effects on the sleeping time using the awaken test and the pain index in hot-plate test (HPPI) using the hot-plate test. In the awaken test, strychnine 1, 2, 4 microg (i.c.v.) had no distinctive effect on the sleeping time of the mice treated with the four emulsified inhalation anesthetics mentioned above (p > 0.05); in the hot-plate test, strychnine 0.1, 0.2, 0.4 microg (i.t.) can significantly and dose-dependently decrease the HPPI of the mice treated with emulsified ether, enflurane and sevoflurane (p < 0.05, p < 0.01); strychnine 0.1 microg (i.t.) did not affect the HPPI of the mice treated with emulsified isoflurane (p > 0.05), but 0.2 and 0.4 microg (i.t.) can significantly decrease the HPPI of the mice treatedwith emulsified isoflurane (p < 0.05, p < 0.01). These results suggest that strychnine-sensitive glycine receptors may contribute to the analgesic but not to the hypnotic effects induced by ether, enflurane, isoflurane and sevoflurane.

Strychnine-sensitive glycine receptors mediate analgesia induced by emulsified inhalation anaesthetics in thermal nociception but not in chemical nociception

The present study was designed to investigate the role of strychnine-sensitive glycine receptors in analgesia induced by emulsified inhalation anaesthetics. After having established the mice model of analgesia by intraperitoneal or subcutaneous injections of appropriate doses of ether, enflurane, isoflurane or sevoflurane, we injected different doses of strychnine intrathecally and then observed the effects on the tail-flick latency using the tail-withdrawal test and the writhing times and acetic acid-induced writhing test. In the tail-withdrawal test, all four emulsified inhalation anaesthetics (intraperitoneally) significantly increased the tail-flick latency (P < 0.01) compared with baseline, and the increase of tail-flick latency induced by four emulsified inhalation anaesthetics can be abolished by intrathecally injected strychnine. In the acetic acid-induced writhing test, writhing times inhibition induced by subcutaneous administration of four emulsified inhalation anaesthetics was not effected by intrathecal strychnine (0.1, 0.2 and 0.4 microg). The data presented in this study suggest that glycine receptors are specifically involved in mediating the analgesic effect of ether, enflurane, isoflurane and sevoflurane on thermal-induced nociception but not chemically induced nociception.