MK-801 changes the role of glutamic acid on modulation of algesia in nucleus accumbens.

Dizocilpine maleate (MK-801) causes the blockage of the glutamic acid (Glu) receptors in the central nervous system that are involved in pain transmission. However, the mechanism of action of MK-801 in pain-related neurons is not clear, and it is still unknown whether Glu is involved in the modulation of this processing. This study examines the effect of MK-801, Glu on the pain-evoked response of pain-excitation neurons (PENs) and pain-inhibition neurons (PINs) in the nucleus accumbens (NAc) of rats. The trains of electric impulses applied to the sciatic nerve were used as noxious stimulation. The electrical activities of PENs or PINs in NAc were recorded by a glass microelectrode. Our results revealed that the lateral ventricle injection of Glu increased the discharged frequency and shortened the discharged latency of PEN, and decreased the discharged frequency and prolonged the discharged inhibitory duration (ID) of PIN in NAc of rats evoked by the noxious stimulation, while intra-NAc administration of MK-801 produced the opposite response. On the basis of above findings we can deduce that Glu, MK-801 and N-methyl-D-aspartate (NMDA) receptor are involved in the modulation of nociceptive information transmission in NAc.

Cholecystokinin-8 antagonizes electroacupuncture analgesia through its B receptor in the caudate nucleus.

OBJECTIVES: The analgesic effect of electroacupuncture (EA) stimulation has been proved. However, its mechanism of action is not clear. It has been well-known that cholecystokinin-8 (CCK-8) is a neuropeptide which is mainly related to the mediation of pain. The caudate nucleus was selected to determine if the release of CCK and the neural activity in this nucleus were involved in producing EA analgesia. MATERIALS AND METHODS: Radiant heat focused on the rat-tail was used as the noxious stimulus. The pain threshold of rats was measured by tail-flick latency (TFL). EA stimulation at the bilateral Zusanli (ST 36) acupoints of rats was used to investigate the effects of EA analgesia. The electrical activities of pain-excited neurons (PEN) and pain-inhibited neurons (PIN) in the caudate nucleus were recorded with a glass microelectrode. The present study examined the antagonistic effects of the intracerebral ventricular injection of CCK-8 on EA analgesia and reversing effects of CCK-B receptor antagonist (L-365,260) injection into the caudate nucleus on CCK-8. RESULTS: The radiant heat focused on the tail of rats caused an increase in the evoked discharge of PEN and a reduction in the evoked discharge of PIN. EA stimulation at the bilateral ST 36 acupoints of rats resulted in the inhibition of PEN, the potentiation of PIN, and prolongation of TFL. The analgesic effect of EA was antagonized when CCK-8 was injected into the intracerebral ventricle of rats. The antagonistic effect of CCK-8 on EA analgesia was reversed by injection of CCK-B receptor antagonist (L-365,260) into the caudate nucleus of rats. CONCLUSIONS: Our results suggest that CCK-8 antagonize EA analgesia through its B receptor.

[Expression of heme oxygenase-1 and GFP gene mediated by recombinant adeno-associated-virus in transplanted liver in rats].

OBJECTIVE: To construct and purify heme oxygenase-1, GFP gene mediated by recombinant adeno-associated-virus and identify expression rate of GFP in transplanted liver in rats. METHODS: Heme oxygenase-1 gene of rat was cloned and subcloned to rAAV vector, the gene sequence was confirmed correct by restriction enzyme and DNA sequencing. The rAAV-HO-1 was then cotransfected into 293 cell line with accessory plasmid virus helper and AAV-cap-rep through CaCl2 coprecipitation. Virus particles were purified by heparin column chromatography and titre were detected by Real-time PCR. An orthotopic liver transplantation model by Wistar to Wistar was set up using Kamada's two cuff technique. Purified rAAV-GFP was injected into portal vein and incubated for 2 hours at the donor liver cold preserved stage, and then performed OLT. Recipients were killed and visceral organs were sampled at 1 and 3 months after operation respectively, frozen section (3-5 microm) were prepared and gene expression rate in different tissues was examined under fluorescence microscope. RESULTS: The inserted segment of HO-1 was identified through restriction enzyme cutting followed with electrophoresis, the result of DNA sequencing was in accordance with which found in Genbank. The GFP expression rate was over 80% in allograft at 1 and 3 month after transfection whereas there was no GFP expression in heart, lung, spleen, kidney and small bowel. CONCLUSIONS: High titre rAAV carried HO-1 and GFP were constructed successfully. Steady and effective expression of GFP mediated by rAAV was demonstrated in liver allograft in rats.

Modulatory role of glutamic acid on the electrical activities of pain-related neurons in the hippocampal CA3 region.

Glutamic acid (Glu) participates in pain modulation of the central nervous system. The CA3 region of the hippocampal formation has been suggested to be involved in nociceptive perception. However, it is unknown whether Glu could modulate the electrical activities of pain-related neurons in the hippocampal CA3 region. The present study aimed to determine the effects of Glu and its receptor antagonist MK-801 in the pain-evoked response of both pain-excited neurons (PENs) and pain-inhibited neurons (PINs) in the hippocampal CA3 region of normal rats. We used a train of electric impulses applied to the sciatic nerve as noxious stimulation. The electrical activities of either PENs or PINs in the hippocampal CA3 region were recorded by a glass microelectrode. The results revealed that intra-CA3 region microinjection of Glu (0.5 µg/1 µl) increased the evoked firing frequency and shortened the firing latency of PEN, while decreased the evoked firing frequency and prolonged the inhibitory duration of PIN in the hippocampal CA3 region of rat evoked by the noxious stimulation. Intra-CA3 region administration of MK-801 (0.25 µg/1 µl) produced the opposite response. These results suggest that Glu and its receptors in hippocampal CA3 region are involved in the modulation of nociceptive information transmission by affecting the electric activities of PENs and PINs.