The role of adenosine in up-regulation of p38 MAPK and ERK during limb ischemic preconditioning-induced brain ischemic tolerance.

Our previous studies have demonstrated that limb ischemic preconditioning (LIP) induced brain ischemic tolerance and up-regulated the expression of p38 MAPK and ERK in the hippocampal CA1 region in rats. The present study was undertaken to investigate the role of adenosine in brain protection and up-regulation of p38 MAPK and ERK induced by LIP. It was found that adenosine A1 receptor antagonist DPCPX dose-dependently inhibited the protective effect of LIP. The up-regulation of p38 MAPK and ERK induced by LIP could be blocked by DPCPX. Furthermore, we observed the effect of adenosine on the brain ischemia. The results showed that pre-administration of adenosine could partly mimic the neuroprotective effect on the brain, up-regulate the expression of p38 MAPK and ERK. Based on the above results, it can be concluded that adenosine participated in brain protection and up-regulation of the expression of p38 MAPK and ERK during the induction of brain ischemic tolerance after LIP.

GLT-1 Upregulation as a Potential Therapeutic Target for Ischemic Brain Injury.

Glutamate is the primary excitatory neurotransmitter in the mammalian central nervous system, which plays an important role in many aspects of normal brain function such as neural development, motor functions, learning and memory etc. However, excessive accumulation of glutamate in the extracellular fluid will induce excitotoxicity which is considered to be a major mechanism of cell death in brain ischemia. There is no enzyme to decompose the glutamate in extracellular fluid, so extracellular glutamate homeostasis within the central nervous system is mainly regulated by the uptake activity of excitatory amino acid transporters. Among the five excitatory amino acid transporters, glial glutamate transporter-1 (GLT-1) is responsible for 90% of total glutamate uptake. Thus, GLT-1 is essential for maintaining the appropriate level of extracellular glutamate, and then limiting excitotoxicity of glutamate in central nervous system. Therefore, the regulation of GLT-1 might be a potential therapeutic target for ischemic brain injury. This review summarizes recent advances including our findings in the methods or medicine that could protect neurons against brain ischemic injury via upregulation of GLT-1 and discuss the possible application of these strategies.

[Effect of limb ischemic preconditioning on the expression of p38 MAPK and HSP 70 in CA3 and DG regions of the hippocampus of rats].

OBJECTIVE: To observe the expression of p38 MAPK and HSP 70 in CA3 and dentate gyrus (DG) regions of the hippocampus of rats induced by limb ischemic preconditioning (LIP). METHODS: Ninety-six rats were randomly divided into sham and LIP groups. And the animals in the LIP group were further divided into LIP 6 h, LIP 12 h, LIP 1 d, LIP 2 d, LIP 3 d, LIP 4 d and LIP 5 d subgroups according to the time of reperfusion after LIP. Immunohistochemical staining and Western blot were used to observe the expression of p38 MAPK and HSP 70 in CA3 and DG regions of the hippocampus. RESULTS: The results of the immunohistochemical staining and Western blot were consistent, which indicated that there were fluctuation in the p-p38 MAPK and HSP 70 expression in CA3 and DG regions after LIP compared with those of the sham group. The expression of p-p38 MAPK began to be up-regulated 1d after LIP and reached its peak at 3 d and lasted for 4 d after LIP. However, the expression of HSP 70 was significantly up-regulated 2 d after LIP compared to the sham group, reached its peak at 3 d and lasted until the 4 d after LIP. CONCLUSION: LIP up-regulates the expression of p38 MAPK and HSP 70 in the CA3 and DG regions of the hippocampus of rats.

[Division of CA1, CA3 and DG regions of the hippocampus of Wistar rat].

OBJECTIVE: Division of the CA1, CA3 and dentate gyrus (DG) regions of the hippocampus of Wistar rat under the stereomicroscope. METHODS: Twenty-four Wistar rats were randomly assigned to three groups. (1) The brain was sectioned coronally (n = 6). The sections were stained with thionin and the morphology of cells in each region of the hippocampus was observed under microscopy. (2) The hippocampus was dissected out and observed on the whole. Then, the CA1, CA3 and DG regions of the hippocampus were divided. Every region divided was sectioned, and the morphology of cells was observed. (3) Rats with brain ischemia or not were also decapitated and the HSP 70 expressions were observed in CA1, CA3 + DG regions by Western blot and immunohistochemical staining (n = 12). RESULTS: (1) The CA1, CA3 and DG regions of the hippocampus could be clearly observed in coronal section of the brain stained by thionin. (2) Under the stereomicroscope, the CA1 and DG regions of the hippocampus could be separated along the hippocampal fissure between them in ventral surface of the hippocampus. The CA3 and DG regions of the hippocampus could be separated along a fissure between them. The appearance of cells in the sections of the divided CA1, CA3 and DG specimens is consistent with that in the brain coronal sections, respectively. (3) The results of Western blot indicated that the HSP 70 expression of the brain ischemia group was up-regulated significantly in CA3 + DG regions compared with the sham group. However, HSP 70 expression has no significant changes in CA1 region. The above results were consistent with those of the immunohistochemical staining. CONCLUSION: The CA1, CA3 and DG regions of the hippocampus of Wistar rat could be divided under stereomicroscope, and the divided each region was sensible for detection of protein using Western blot.

Intermittent hypobaric hypoxia preconditioning induced brain ischemic tolerance by up-regulating glial glutamate transporter-1 in rats.

Several studies showed that the up-regulation of glial glutamate transporter-1 (GLT-1) participates in the acquisition of brain ischemic tolerance induced by cerebral ischemic preconditioning or ceftriaxone pretreatment in rats. To explore whether GLT-1 plays a role in the acquisition of brain ischemic tolerance induced by intermittent hypobaric hypoxia (IH) preconditioning (mimicking 5,000 m high-altitude, 6 h per day, once daily for 28 days), immunohistochemistry and western blot were used to observe the changes in the expression of GLT-1 protein in hippocampal CA1 subfield during the induction of brain ischemic tolerance by IH preconditioning, and the effect of dihydrokainate (DHK), an inhibitor of GLT-1, on the acquisition of brain ischemic tolerance in rats. The basal expression of GLT-1 protein in hippocampal CA1 subfield was significantly up-regulated by IH preconditioning, and at the same time astrocytes were activated by IH preconditioning, which appeared normal soma and aplenty slender processes. The GLT-1 expression was decreased at 7 days after 8-min global brain ischemia. When the rats were pretreated with the IH preconditioning before the global brain ischemia, the down-regulation of GLT-1 protein was prevented clearly. Neuropathological evaluation by thionin staining showed that 200 nmol DHK blocked the protective role of IH preconditioning against delayed neuronal death induced normally by 8-min global brain ischemia. Taken together, the up-regulation of GLT-1 protein participates in the acquisition of brain ischemic tolerance induced by IH preconditioning in rats.

[P38 MAPK antisense oligodeoxynucleotide inhibited the brain ischemic tolerance induced by limb ischemic preconditioning].

OBJECTIVE: To better assess the role of p38 MAPK, this project was designed to investigate whether intraventricular injection of antisense oligodeoxynucleotide (As-ODN) directed against the p38 MAPK of pyramidal neurons in hippocampus could affect the brain ischemic tolerance induced by limb ischemic preconditioning (LIP). METHODS: The rat 4-vessel occlusion global cerebral ischemic model was used. Forty-eight male Wistar rats with permanently occlusion of the bilateral vertebral arteries were divided into 8 groups (n=6): sham, LIP, brain ischemic insult, LIP + brain ischemic insult, distilled water + LIP + brain ischemic insult, p38 MAPK As-ODN and p38 MAPK As-ODN + LIP + brain ischemic insult (two doses of 5 nmol/5 microl and 10 nmol/5 microl were used) groups. Thionin staining was used for observing histological changes of the hippocampus. RESULTS: No significant delayed neuronal death (DND) was detected in the CA1 hippocampus of the rats that underwent sham and LIP operation. Brain ischemic insult for 8 min induced obvious DND as represented with the increase in histological grade (HG) and decrease in neuronal density (ND) significantly compared with sham and LIP groups. LIP protected the CA1 hippocampal pyramidal neurons against DND induced by global brain ischemic insult, suggesting the occurrence of brain ischemic tolerance. However, pretreatment with p38 MAPK As-ODN effectively blocked the ischemic tolerance induced by LIP in a dose dependent manner. CONCLUSION: It could be concluded that p38 MAPK plays an important role in the brain ischemic tolerance induced by LIP.

Activation of p38 MAPK participates in brain ischemic tolerance induced by limb ischemic preconditioning by up-regulating HSP 70.

This study investigates whether activation of p38 MAPK by the up-regulation of HSP 70 participates in the induction of brain ischemic tolerance by limb ischemic preconditioning (LIP). Western blot and immunohistochemical assays indicated that p38 MAPK activation occurred earlier than HSP 70 induction in the CA1 region of the hippocampus after LIP. P-p38 MAPK expression was up-regulated at 6h and reached its peak 12h after LIP, while HSP 70 expression was not significantly increased until 1 day and peaked 2 days after LIP. Neuropathological evaluation by thionin staining showed that quercetin (4 ml/kg, 50mg/kg, intraperitoneal injection), an inhibitor of HSP 70, blocked the protective effect of LIP against delayed neuronal death that is normally induced by lethal brain ischemic insult, indicating that HSP 70 participates in the induction of brain ischemic tolerance by LIP. Furthermore, SB 203580, an inhibitor of HSP 70, inhibited HSP 70 activation in the CA1 region of the hippocampus induced by LIP either with or without the presence of subsequent brain ischemic insult. Based on the above results, it can be concluded that activation of p38 MAPK participates in the brain ischemic tolerance induced by LIP at least partly by the up-regulation of HSP 70 expression.

Fluorocitrate, an inhibitor of glial metabolism, inhibits the up-regulation of NOS expression, activity and NO production in the spinal cord induced by formalin test in rats.

Previous experiments have suggested that nitric oxide plays an important role in nociceptive transmission in the spinal cord. In order to explore the involvement of glia in the NO-mediated nociceptive transmission, the present study was undertaken to investigate the effect of fluorocitrate (FC), an inhibitor of glial metabolism, on NOS expression and activity and NO production in the spinal cord during the process of peripheral inflammatory pain and hyperalgesia induced by formalin test in rats. Sixty adult male Sprague-Dawley rats were randomly assigned into sham, formalin, formalin + normal saline (NS), and formalin + FC groups. The NOS expression, NOS activity and NO production was detected by NADPH-d histochemistry staining, NOS and NO assay kit, respectively. It was found that formalin test significantly up-regulated NOS expression and activity and NO production in the laminae I-II of the dorsal horn and the grey matter around the central canal in the lumbar spinal cord at 1 h after the formalin test. Selective inhibition of glia metabolism with intrathecal administration of FC (1 nmol) significantly inhibited the up-regulation in NOS expression and activity and NO production normally induced by the formalin test, which was represented with decreases in the number and density of the NADPH-d positive cells in the dorsal horn and grey matter around the central canal, and decrease in density of NADPH-d positive neuropil in the dorsal horn in formalin + FC group compared with formalin group. The results suggested that glia may be involved in the NO-mediated nociceptive transmission in the spinal cord.

[Antisense oligodeoxynucleotides of glial glutamate transporter-1 inhibits the neuro-protection of cerebral ischemic preconditioning in rats].

The present study was undertaken to investigate the role of glial glutamate transporter-1 (GLT-1) in the brain ischemic tolerance induced by cerebral ischemic preconditioning (CIP) by observing the effect of GLT-1 antisense oligodeoxynucleotides (AS-ODNs) on the neuro-protection of CIP against brain ischemic insult in rats. Wistar rats with permanently occluded bilateral vertebral arteries were randomly assigned to 7 groups: (1) Sham group: the bilateral common carotid arteries (BCCA) were separated, but without occluding the blood flow; (2) CIP group: the BCCA were clamped for 3 min; (3) Brain ischemic insult group: the BCCA were clamped for 8 min; (4) CIP+brain ischemic insult group: 3 min CIP was preformed 2 d prior to 8 min ischemic insult; (5) Double distilled water group: 5 muL double distilled water was injected into the right lateral cerebral ventricle 12 h before, 12 h and 36 h after the BCCA was separated (but without occluding the blood flow), respectively; (6) AS-ODNs group: 5 microL AS-ODNs solution was injected into the right lateral cerebral ventricle 12 h before, 12 h and 36 h after the BCCA was separated (but without occluding the blood flow), respectively. This group was further divided into 9 nmol and 18 nmol subgroups according to the doses of AS-ODNs; (7) AS-ODNs+CIP+brain ischemic insult group: 5 microL AS-ODNs solution was injected into the right lateral cerebral ventricle 12 h before, 12 h and 36 h after CIP, respectively. This group was also further divided into 9 nmol and 18 nmol subgroups according to the doses of AS-ODNs. The other treatments were the same as those in CIP+brain ischemic insult group. The effect of the AS-ODNs on the expression of GLT-1 was assayed by using Western blot analysis. The profile of delayed neuronal death (DND) of pyramidal neurons in the CA1 hippocampus was evaluated by using thionin staining under light microscope by determining the neuronal density (ND) and histological grade (HG). Western blot analysis showed that AS-ODNs injected into the lateral cerebroventricle inhibited the expression of GLT-1 in the CA1 hippocampus in a dose-dependent manner. Neuropathological evaluation showed that there was no apparent DND in sham and CIP groups. Obvious DND of pyramidal neurons was found in brain ischemic insult group, which was represented by an increase in HG and a decrease in ND. CIP effectively protected the pyramidal neurons in the CA1 hippocampus against DND normally induced by ischemic insult, which indicating that CIP induced ischemic tolerance on the pyramidal neurons in the CA1 hippocampus. However, the injection of AS-ODNs into the lateral cerebroventricle blocked the neuro-protection of CIP against DND induced by brain ischemic insult. These results further proved the role of GLT-1 in the brain ischemic tolerance induced by CIP in rats.

[Intracerebroventricular administration of adenosine A1 receptor antisense oligodeoxynucleotide inhibites the neuroprotective effect of the cerebral ischemic preconditioning in rats].

AIM: To further explore the role of adenosine A1 receptor in the neuroprotective effect of cerebral ischemic preconditioning, the present study was undertaken to observe the effect of inhibiting expression of adenosine Al receptor with adenosine A1 receptor antisense oligodeoxynucleotide (ARA1 As-ODN) on the neuroprotective effect of cerebral ischemic preconditioning against delayed neuronal death (DND) normally induced by lethal brain ischemia. METHOD: The rat 4-vessel occlusion global cerebral ischemic model was used. Forty-eight male Wistar rats with permanent occlusion of the bilateral vertebral arteries were divided into 8 groups: Sham, CIP, brain ischemic insult, CIP + brain ischemic insult, Distilled water + CIP + brain ischemic insult, ARA1 As-ODN, ARA1 As-ODN +CIP, ARA1 As-ODN+ CIP + brain ischemic insult(two doses of 10 nmol/5 microl and 20 nmol/5 microl were used) groups. ARA1 As-ODN was dissolved in distilled water and injected into the right lateral cerebral ventricle. To illustrate the profile of DND, histological grade (HG) and neuronal density (ND) in the CA1 region of the hippocampus were examined 7 d after the sham operation or the last time of ischemia under thionin staining. RESULTS: The HG and ND in CIP group were similar to those in sham group. Brain ischemic insult induced obvious DND as represented with the increase in HG and decrease in ND significantly (P < 0.05 vs. sham and CIP groups). In CIP + ischemic insult group,no obvious DND was observed,which indicated that CIP protected pyramidal neurons against the ischemic insult.While the administration of ARA1 As-ODN in ARA1 As-ODN + CIP + brain ischemic insult group caused obvious increase in HG and decrease in ND compared with CIP + brain ischemic insult group (P < 0.05) in a dose dependent manner,which indicated that the neuroprotective effect of CIP against DND of hippocampal pyramidal neurons normally induced by ischemic insult was inhibited by the administration of ARA1 As-ODN. CONCLUSION: The results further demonstrate the association of up-regulation of adenosine A1 receptors with the induction of CIP-mediated BIT.

The role of nitric oxide in the neuroprotection of limb ischemic preconditioning in rats.

Brief limb ischemia was reported to protect neurons against injury induced by subsequent cerebral ischemia-reperfusion, and this phenomenon is known as limb ischemic preconditioning (LIP). To explore the role of nitric oxide (NO) in neuroprotection of LIP in rats, we observed changes in the content of nitric oxide (NO) and activity of NO synthase (NOS) in the serum and CA1 hippocampus of rats after transient limb ischemic preconditioning (LIP), and the influence of N(G)-nitro-L-arginine methylester (L-NAME), a NOS inhibitor, on the neuroprotection of LIP against cerebral ischemia-reperfusion injury. Results showed that NO content and NOS activity in serum increased significantly after LIP compared with the sham group. The increase showed a double peak pattern, in which the first one appeared at time 0 (immediate time point) and the second one appeared at 48 h after the LIP (P < 0.01). The NO content and NOS activity in the CA1 hippocampus in LIP group showed similar change pattern with the changes in the serum, except for the first peak of up-regulation of NO content and NOS activity appeared at 6 h after LIP. Pretreatment with L-NAME before LIP blocked the neuroprotection of LIP against subsequent cerebral ischemic insult. The blocking effect of L-NAME was abolished with pretreatment of L-Arg. These findings indicated that NO may be associated with the tolerance of pyramidal cells in the CA1 hippocampus to ischemia induced by LIP in rats.

The upregulation of glial glutamate transporter-1 participates in the induction of brain ischemic tolerance in rats.

Glial glutamate transporter-1 (GLT-1) plays an essential role in removing glutamate from the extracellular space and maintaining the glutamate below neurotoxic level in the brain. To explore whether GLT-1 plays a role in the acquisition of brain ischemic tolerance (BIT) induced by cerebral ischemic preconditioning (CIP), the present study was undertaken to observe in vivo changes in the expression of GLT-1 and glial fibrillary acidic protein (GFAP) in the CA1 hippocampus during the induction of BIT, and the effect of dihydrokainate (DHK), an inhibitor of GLT-1, on the acquisition of BIT in rats. Immunohistochemistry for GFAP showed that the processes of astrocytes were prolonged after a CIP 2 days before the lethal ischemic insult, which could protect pyramidal neurons in the CA1 hippocampus against delayed neuronal death induced normally by lethal ischemic insult. The prolonged processes extended into the area between the pyramidal neurons and tightly surrounded them. These changes made the pyramidal layer look like a 'shape grid'. Simultaneously, the prolonged and extended processes showed a great deal of GLT-1. Western blotting analysis showed significant upregulation of GLT-1 expression after the CIP, especially when it was administered 2 days before the subsequent lethal ischemic insult. Neuropathological evaluation by thionin staining showed that DHK dose-dependently blocked the protective role of CIP against delayed neuronal death induced normally by lethal brain ischemia. It might be concluded that the surrounding of pyramidal neurons by astrocytes and upregulation of GLT-1 induced by CIP played an important role in the acquisition of the BIT induced by CIP.

[Neural pathway participates in protection of limb ischemic preconditioning against brain injuries induced by ischemia/reperfusion in rats].

AIM: To explore the role of femoral nerves section (FNS) on the protection of limb ischemic preconditioning (LIP) against cerebral ischemia/reperfusion injuries. METHODS: Model of brain ischemia induced by Four-vessel occlusion was used. LIP was performed by clamping the bilateral femoral arteries for 10 min 3 times in a interval of 10 min. Rats with vertebral arteries permanently occluded were divided into sham group, cerebral ischemic group, FNS + cerebral ischemic group, LIP + cerebral ischemic group, FNS + LIP + cerebral ischemic group. The changes of neural density (ND) in the CA1 hippocampus were observed 7d after the sham operation or brain ischemia under thionin staining. The expression of c-Fos in the CA1 hippocampus was measured 6 h after the sham operation or brain ischemia under immunohistochemistry method. RESULTS: Thionin staining revealed that serious neuronal damage was visualized in the CA1 hippocampus in both cerebral ischemic group and FNS + cerebral ischemic group as compared with sham group. LIP attenuated the neuronal damage of the CA1 subfield induced normally by cerebral ischemia/reperfusion, and ND in LIP + cerebral ischemic group was significantly higher than that in cerebral ischemic group (P < 0.01). But obvious neuronal damage of the CA1 subfield was found in FNS+ LIP + cerebral ischemic group, and ND was significantly decreased as compared with LIP + cerebral ischemic group (P < 0.01). These results suggested that the protection of LIP against cerebral ischemia/reperfusion injuries might be cancelled by preceding section of femoral nerve. It was found that there was almost no c-Fos expression in the CA1 hippocampus in sham group. Changes of c-Fos expression in the CA1 subfield in cerebral ischemic group were similar to that in sham group. But in LIP + cerebral ischemic group, c-Fos expression in the CA1 subfield was markedly increased and the number of positive cells and optical density of c-Fos expression were significantly higher than those in sham and cerebral ischemic group. c-Fos expression in the CA1 subfield was again decreased in FNS + LIP + cerebral ischemic group, and the number of positive cells and optical density of c-Fos expression were significantly lower than those in LIP + cerebral ischemic group. CONCLUSION: Neural pathway participated in the protective effect of LIP on brain, and increased c-Fos expression in the CA1 hippocampus by LIP after cerebral ischemia/reperfusion, might be a part of neural pathway by which LIP induced brain ischemic tolerance.

Nitric oxide participates in the induction of brain ischemic tolerance via activating ERK1/2 signaling pathways.

The present study was undertaken to observe in vivo changes of expression and phosphorylation of ERK1/2 proteins during brain ischemic preconditioning and effects of inhibiting generation of nitric oxide (NO) on the changes to determine the role of ERKs in the involvement of NO participating in the acquired tolerance. Fifty-five Wistar rats were used. Brain ischemic preconditioning was performed with four-vessel occlusion for 3 min. Total ERK1/2 proteins and phospho-ERK1/2 in the CA1 hippocampus were assayed with Western immunoblot. Total ERK1/2 proteins did not change in period from 5 min to 5 days of reperfusion after preconditioning stimulus. While the level of phospho-ERK1/2 increased obviously to 223, 237, 300, 385 and 254% of sham level at times of 5 min, 2 h, 1, 3 and 5 days after preconditioning stimulus, respectively (P < 0.01). Administration of L-NAME, an inhibitor of NO synthase, 30 min prior to preconditioning stimulus failed to induce change in total ERK1/2 proteins (P > 0.05). However, phospho-ERK1/2 increased only to 138 and 176% of sham level at 2 h and 3 days after preconditioning stimulus, respectively, when animals were pretreated with L-NAME. The magnitudes of the increase were obviously low compared with those (237 and 385%) in animals untreated with L-NAME at corresponding time points (P < 0.01), which indicated that phosphorylation of ERK1/2 normally induced by preconditioning stimulus was blocked apparently by administration of L-NAME. The results suggested that phosphorylation of ERK1/2, rather than synthesis of ERK1/2 proteins, was promoted in brain ischemic preconditioning, and that the promotion was partly mediated by NO signal pathway.

Limb ischemic preconditioning induces brain ischemic tolerance via p38 MAPK.

It has been reported that limb ischemic preconditioning (LIP) could induce brain ischemic tolerance. In the present study, we investigated the role of p38 MAPK in the induction of brain ischemic tolerance by observing expression of phosphorylated p38 (p-p38) MAPK in the hippocampus after LIP and the effect of p38 MAPK inhibitor SB 203580 on the protection of LIP against delayed neuronal death (DND) in the CA1 hippocampus induced normally by brain ischemic insult. The results of Flow cytometry and Western blotting showed that expression of p-p38 MAPK initially increased at 6 h after LIP compared with sham group in the CA1 hippocampus. The increases reached peak at 12 h and lasted to 24 h after LIP. Expression of p-p38 MAPK was also increased in the CA3/dentate gyrus (DG) regions after LIP, but the beginning and peaking times were 1 and 3 days after LIP, which were relatively later than those in the CA1. Histological evaluation showed that LIP protected the CA1 hippocampal pyramidal neurons against DND induced by global brain ischemic insult for 8 min, suggesting the occurrence of brain ischemic tolerance. Pretreatment with SB 203580 at 30 min before LIP effectively blocked the ischemic tolerance induced by LIP. Together, it could be concluded that activation of p38 MAPK played an important role in the brain ischemic tolerance induced by LIP, and that components of the p38 MAPK cascade might be targets to modify neuronal survival in ischemic tolerance.

The role of extracellular signal-regulated kinases in the neuroprotection of limb ischemic preconditioning.

To clarify the role of phosphorylated extracellular signal-regulated kinases (pERK1/2) in the neuroprotection of limb ischemic preconditioning (LIP) in rats, we investigated the expression of pERK1/2 using Western blot and flow cytometry in the hippocampus after LIP and the effect of pERK1/2 inhibitor PD 98059 on the neuroprotection of LIP against delayed neuronal death (DND) in the CA1 hippocampus normally induced by severe ischemic insult. It demonstrated that pERK1/2 in the hippocampus increased after LIP. In the CA1 hippocampus, ERK1/2 activation began to increase at 6h and reached peak at 12h after LIP, and decreased to sham level at 5d after LIP. On the other hand, in the CA3/DG, pERK1/2 enhanced at 1d, reached peak at 3d, and lasted to 5d after LIP. Pretreatment with PD 98059 before LIP blocked the neuroprotection of LIP in a dose-dependent manner. These findings supported that the upregulation of pERK1/2 in the CA1 hippocampus contributed to the neuroprotection of LIP against DND normally caused by the brain ischemic insult.

[MK-801 inhibits formalin-induced cyclooxygenase-2 expression in the dorsal horn of the spinal cord in rats].

To investigate the effect of N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 on the formalin-induced cyclooxygenase-2 (COX-2) expression in the dorsal horn of the rat spinal cord. Forty-eight male Sprague-Dawley rats were divided into 4 groups: control, formalin, formalin+normal saline (NS) and formalin+MK-801 groups. Rats in formalin, formalin+NS and formalin+MK-801 groups were subcutaneously injected with 0.2 ml 5% formalin into the plantar surface of the right hind paw. NS or MK-801 solution (10 microl) was intrathecally injected under transient ether anesthesia 15 min prior to the formalin injection in the formalin+NS and formalin+MK-801 groups, respectively. Flinch reflex was measured within 1 h after the formalin injection and expression of COX-2 in the dorsal horn of the L(5) segment of the spinal cord was assayed 24 h after the formalin injection using immunohistochemistry. Formalin evoked a biphasic flinch reflex. MK-801 produced a limited effect on the flinch reflex of phase 1, but produced significant and dose-dependent suppression on the flinch reflex of phase 2. The number and immunostaining density, shown by grey degree which was inversely proportional to the immunostaining density, of immunoreactive soma in the superficial (mainly I-II) and deep (IV-VI) laminae of the L(5) spinal cord in formalin and formalin+NS groups increased significantly, in contrast to those in the control group (p<0.01). The number and immunostaining density of immunoreactive soma decreased significantly in formalin+MK-801 group, in comparison with the formalin+NS group (p<0.05). The degree of the decrease was proportional to the dosage of MK-801 used. In addition, there were some immunoreactive processes especially in the superficial laminae, which extended as a continuous band across the dorsal horn after the formalin injection. Change in immunostaining density of the processes after administration of MK-801 was similar to that in the immunoreactive soma. The results showed that intrathecal injection of MK-801 significantly inhibited the increase of COX-2 expression in the spinal dorsal horn induced by the formalin injection in a dose-dependent manner, suggesting that the activation of NMDA receptor is one of the mechanisms for the formalin-induced increase of COX-2 expression in the spinal dorsal horn.

[Effect of CGRP receptor antagonist CGRP8-37 on nociceptive response, NOS expression and NO content in the dorsal horn of spinal cord during formalin-induced inflammatory pain in rats].

AIM: To study the effect of CGRP receptor antagonist CGRP8-37 on nociceptive response and expression of nitric oxide synthase (NOS) and content of nitric oxide (NO) in the dorsal horn of the spinal cord of rats during formalin-induced inflammatory pain. METHODS: Using formalin injection into right hind paw induced inflammatory pain. Counting the times of flinching reflex was used to observe the degree of spontaneous pain. NADPH-d histochemistry was used to observe the changes of NOS expression. The content of NO was observed by measuring the contents of nitrate/nitrite (NO3- / NO2-). RESULTS: spontaneous pain behavioral was elicited by formalin injection. The NOS expression and NO content significantly increased in the spinal cord at 24 h after formalin injection. Intrathecal injection of CGRP8-37 could significantly inhibit the response of spontaneous pain and the increases of NOS expression and NO content induced by formalin injection. CONCLUSION: The activation of CGRP receptors enhances NOS expression and NO production in the dorsal horn of the spinal cord during formalin-induced inflammatory pain.

[Changes of COX-2 expression in the dorsal horn of the spinal cord during formalin-induced inflammatory pain and hyperalgesia in rats].

AIM: To observe the changes of cyclooxygenase-2 (COX-2) expression and especially the time course of the changes in dorsal horn of the spinal cord during formalin-induced inflammatory pain and hyperalgesia in rats. METHODS: COX-2 immunohistochemistry staining was used in rat formalin pain model. RESULTS: Compared with control group the number and immunostaining density of COX-2 immunoreactive cells in the laminae I-VI of the dorsal horn of the spinal cord increased significantly 4 h, 1 d and 3 d after formalin injection (P < 0.05). The most obvious increase was observed 1 d after the injection. CONCLUSION: COX-2 in the dorsal horn of the spinal cord is involved in the formalin-induced inflammatory pain and hyperalgesia.