AMPA receptors bring on the pain

Involvement of glutamate receptors of the paragigantocellularis lateralis nucleus in the pain modulatory effect of 17β-estradiol in male rats

The pain modulatory role of the paragigantocellularis lateralis nucleus (LPGi) and the 17β-estradiol has thoroughly been probed. This study investigates the contribution of ionotropic glutamate receptors in pain modulatory effect of intra-LPGi injection of 17β-estradiol. For this purpose, the LPGi nucleus cannulation was performed and drugs were injected into this nucleus, 15 min prior to the formalin test. The duration of formalin-induced flexing and licking behaviors was recorded for 60 min immediately after formalin injection. The results showed that the flexing behavior is significantly decreased by intra-LPGi injection of 0.8 µmol 17β-estradiol duringboth phases of formalin test (P < 0.001). However, 17β-estradiol attenuated the licking duration only in the second phase (P < 0.001). Interestingly, NMDA and AMPA/kainate receptor antagonists (AP5 and CNQX, respectively) significantly counteracted the analgesic effect of intra-LPGi injection of 17β-estradiol in both phases of the formalin test (P < 0.001). Consequently, the revealing results showed that the analgesic effect of intra-LPGi injection of 17β-estradiol on acute inflammatory pain might be mediated via the activation of ionotropic glutamate receptors.

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.

Regulation of Ca2+-permeable AMPA receptors: synaptic plasticity and beyond

AMPA-type glutamate receptors (AMPARs) mediate most fast excitatory synaptic transmission in the brain. Diversity in excitatory signalling arises, in part, from functional differences among AMPAR subtypes. Although the rapid insertion or deletion of AMPARs is recognised as important for the expression of conventional forms of long-term synaptic plasticity--triggered, for example, by Ca2+ entry through NMDA-type glutamate receptors--only recently has attention focused on novel forms of plasticity that are regulated by, or alter the expression of, Ca2+-permeable AMPARs. The dynamic regulation of these receptors is important for normal synaptic function and in disease states.