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

Abstract

The present study was designed to investigate the relationship between spinal cord N-methyl-D-aspartate (NMDA) receptors and the analgesic effects of emulsified halogenated anesthetics. After having established the mouse model of analgesia by intraperitoneally or subcutaneously injecting appropriate doses of emulsified enflurane, isoflurane or sevoflurane, we intrathecally injected different doses of NMDA and then observed the effects on the pain threshold using the hot-plate test and the acetic acid-induced writhing test. The results showed that intrathecal injection of NMDA (2.5, 5 and 10 ng) did not affect the pain threshold on the hot-plate test or the writhing times in conscious mice (p > 0.05); in contrast, NMDA (2.5, 5 and 10 ng intrathecally) can significantly and dose dependently decrease the pain threshold on the hot-plate test (p < 0.05 or p < 0.01) and increase the writhing times (p < 0.05 or p < 0.01) in the mice treated with emulsified anesthetics. These results suggest that spinal NMDA receptors may be important targets for the analgesic effects of emulsified enflurane, isoflurane and sevoflurane.

Spinal Α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic Acid Receptors May Mediate the Analgesic Effects of Emulsified Halogenated Anaesthetics

“…So, our animal model ultimately excludes sedative effects on analgesia. According to pharmacokinetics and the results of pilot experiments, 26 we confirmed that i.p. or s.c. injection of emulsified inhalation anaesthetics can achieve the same analgesic effect as the inhalation route.…”

5-HT_1A Receptors Mediate Analgesia Induced by Emulsified Sevoflurane in Thermal Nociception but Have Little Effect on Chemical Nociception

“…In the case of inhalation, some experiments such as HPPT and tail-withdrawal test cannot be implemented. General pharmacokinetics and pilot experiments confirmed that intraperitoneal and subcutaneous injection of emulsified sevoflurane can offer the same analgesic effect as inhalation [29]. Sub-anesthetic doses were selected for intraperitoneal or subcutaneous injection to establish the analgesic model.…”

Effects of Intrathecal Injection of Nicotine on the Analgesic Effects of Isoflurane in a Model of Inflammatory Pain

“…As an important aspect of anaesthesia, analgesia means the loss of pain sensation without loss of consciousness or immobility [33]. According to general pharmacokinetics and our pilot experiments, we have confirmed that intraperitoneal injection of inhalation anaesthetics can offer the same analgesic effect as inhalation [34]. We chose the doses of isoflurane (0.4 ml/kg) intraperitoneal injection to establish the analgesic model.…”