Choong Hyun Lee

Ischemia-induced changes in glucagon-like peptide-1 receptor and neuroprotective effect of its agonist, exendin-4, in experimental transient cerebral ischemia

Glucagon‐like peptide‐1 receptor (GLP‐1R) protects against neuronal damages in the brain. In the present study, ischemia‐induced changes in GLP‐1R immunoreactivity in the gerbil hippocampal CA1 region were evaluated after transient cerebral ischemia; in addition, the neuroprotective effect of the GLP‐1R agonist exendin‐4 (EX‐4) against ischemic damage was studied. GLP‐1R immunoreactivity and its protein levels in the ischemic CA1 region were highest at 1 day after ischemia/reperfusion (I/R). At 4 days after I/R, GLP‐1R immunoreactivity was hardly detected in CA1 pyramidal neurons, and its protein level was lowest. GLP‐1R protein level was increased again at 10 days after I/R, and GLP‐1R immunoreactivity was found in astrocytes and GABAergic interneurons. In addition, EX‐4 treatment attenuated ischemia‐induced hyperactivity, neuronal damage, and microglial activation in the ischemic CA1 region in a dose‐dependent manner. EX‐4 treatment also induced the elevation of GLP‐1R immunoreactivity and protein levels in the ischemic CA1 region. These results indicate that GLP‐1R is altered in the ischemic region after an ischemic insult and that EX‐4 protects against ischemia‐induced neuronal death possibly by increasing GLP‐1R expression and attenuating microglial activation against transient cerebral ischemic damage.

Pre- and post-treatments with escitalopram protect against experimental ischemic neuronal damage via regulation of BDNF expression and oxidative stress

Selective serotonin re-uptake inhibitors (SSRI) have been widely used in treatment of major depression because of their efficacy, safety, and tolerability. Escitalopram, an SSRI, is known to decrease oxidative stress in chronic stress animal models. In the present study, we examined the neuroprotective effects of pre- and post-treatments with 20 mg/kg and 30 mg/kg escitalopram in the gerbil hippocampal CA1 region (CA1) after transient cerebral ischemia. Pre-treatment with escitalopram protected against ischemia-induced neuronal death in the CA1 after ischemia/reperfusion (I/R). Post-treatment with 30 mg/kg, not 20 mg/kg, escitalopram had a neuroprotective effect against ischemic damage. In addition, 20 mg/kg pre- and 30 mg/kg post-treatments with escitalopram increased brain-derived neurotrophic factor (BDNF) protein levels in the ischemic CA1 compared to vehicle-treated ischemia animals. In addition, 20 mg/kg pre- and 30 mg/kg post-treatments with escitalopram reduced microglia activation and decreased 4-hydroxy-2-nonenal and Cu,Zn-superoxide dismutase immunoreactivity and their levels in the ischemic CA1 compared to vehicle-treated ischemia animals after transient cerebral ischemia. In conclusion, these results indicated that pre- and post-treatments with escitalopram can protect against ischemia-induced neuronal death in the CA1 induced by transient cerebral ischemic damage by increase of BDNF as well as decrease of microglia activation and oxidative stress.

Late expression of Na+/H+ exchanger 1 (NHE1) and neuroprotective effects of NHE inhibitor in the gerbil hippocampal CA1 region induced by transient ischemia.

Although acidosis may be involved in neuronal death, the participation of Na(+)/H(+) exchanger (NHE) in delayed neuronal death in the hippocampal CA1 region induced by transient forebrain ischemia has not been well established. In the present study, we investigated the chronological alterations of NHE1 in the hippocampal CA1 region using a gerbil model after ischemia/reperfusion. In the sham-operated group, NHE1 immunoreactivity was weakly detected in the CA1 region. Two and 3 days after ischemia/reperfusion, NHE1 immunoreactivity was observed in glial components, not in neurons, in the CA1 region. Four days after ischemia/reperfusion, NHE1 immunoreactivity was markedly increased in CA1 pyramidal neurons as well as glial cells. These glial cells were identified as astrocytes based on double immunofluorescence staining. Western blot analysis also showed that NHE protein level in the CA1 region began to increase 2 days after ischemia/reperfusion. The treatment of 10 mg/kg 5-(N-ethyl-N-isopropyl) amiloride, a NHE inhibitor, significantly reduced the ischemia-induced hyperactivity 1 day after ischemia/reperfusion. In addition, NHE inhibitor potently protected CA1 pyramidal neurons from ischemic damage, and NHE inhibitor attenuated the activation of astrocytes and microglia in the ischemic CA1 region. In addition, NHE inhibitor treatment blocked Na(+)/Ca(2+) exchanger 1 immunoreactivity in the CA1 region after transient forebrain ischemia. These results suggest that NHE1 may play a role in the delayed death, and the treatment with NHE inhibitor protects neurons from ischemic damage.

Heat shock protein 90 and its cochaperone, p23, are markedly increased in the aged gerbil hippocampus.

In the present study, we compared HSP90 and its co-chaperone, p23, immunoreactivity and their protein levels in the hippocampus between adult (postnatal month 6) and aged (postnatal month 24) gerbils using immunohistochemistry and western blot analysis. HSP90 immunoreactivity was markedly increased in pyramidal cells in the hippocampus proper and in polymorphic cells in the dentate gyrus of the aged group compared to the adult group. p23 immunoreactivity was slightly increased in pyramidal cells of the hippocampus proper and in granule cells of the dentate gyrus in the aged group. In addition, HSP90 and p23 protein levels in the aged hippocampus were much higher than the adult hippocampus. These results indicate that HSP90 and p23 immunoreactivity and protein levels in the hippocampus are distinctively increased in the aged gerbils compared to the adult gerbils.

Increase in Trx2/Prx3 redox system immunoreactivity in the spinal cord and hippocampus of aged dogs

We previously reported that no distinct neuronal loss occurred in the aged dog spinal cord, although oxidative stress was increased in the aged dog spinal cord. Thioredoxin 2 (Trx2)/peroxiredoxin 3 (Prx3) redox system is a major route for removing H(2)O(2) in the central nervous system. In the present study, we compared the distribution and immunoreactivity of thioredoxin reductase 2 (TrxR2), Trx2 and Prx3 and their protein levels in the spinal cord and hippocampus between the adult (2-3 years) and aged (10-12 years) dogs. The number of TrxR2-immunoreactive neurons was slightly increased; however, its immunoreactivity was significantly increased in the aged spinal cord compared to that in the adult spinal cord. On the other hand, the number and immunoreactivity of both Trx2- and Prx3-immunoreactive neurons were significantly increased in the spinal cord of the aged dog. Similarly, in the hippocampus of the aged dog, TrxR2, Trx2 and Prx3 immunoreactivity and protein levels were markedly increased compared to those in the adult dog. These results indicate that the increases of TrxR2, Trx2 and Prx3 immunoreactivity and their protein levels in the aged spinal cord and hippocampus may contribute to reducing neuronal damage against oxidative stresses during normal aging.

The role of peroxisome proliferator-activated receptor γ, and effects of its agonist, rosiglitazone, on transient cerebral ischemic damage

Peroxisome proliferator-activated receptor γ (PPARγ) is expressed in neurons and glia, and its synthetic agonist, rosiglitazone (RSG), regulates inflammatory process and has neuroprotective effects against neurological disorders. In the present study, we examined the role of PPARγ in the hippocampal CA1 region (CA1) after transient cerebral ischemia and the neuroprotective effects of RSG on ischemic damage. RSG attenuated neuronal damage in the ischemic CA1, not showing perfect neuroprotection: the RSG appeared to delay neuronal death after ischemia/reperfusion (I/R). PPARγ immunoreactivity and protein levels were increased after I/R, and most of PPARγ-immunoreactive cells colocalized with microglia, not astrocytes. In addition, RSG attenuated glial activation and increased IL-4 and IL-13 levels in the ischemic CA1. These results indicate that PPARγ increases and expresses in microglia after I/R, and that RSG delays neuronal damage by interfering with glial activations and increases anti-inflammatory cytokines in response to ischemic damage.

Comparison of immunoreactivities in 4-HNE and superoxide dismutases in the cervical and the lumbar spinal cord between adult and aged dogs.

Aging shows slowly progressive changes and is associated with many functional and morphological changes in the central nervous system. The accumulation of reactive oxygen species causes age-related deterioration in neuronal function and contributes to the increase of disease susceptibility during normal aging. In the present study, we compared the neuronal distribution and immunoreactivities of 4-hydroxy-2E-nonenal (4-HNE, end product of lipid peroxidation), and superoxide dismutase 1 (SOD1) and SOD2 in the cervical and lumbar spinal cord between adult (2-3 years) and aged (10-12 years) dogs. No significant change in neuronal morphology was observed after cresyl violet staining. The number of NeuN (a marker for neurons)-immunoreactive neurons was not significantly changed in the aged group compare to the adult group. In addition, we could not find Fluoro-Jade B (a marker for degenerating neurons) positive cells in both the adult and aged dogs. However, numbers of 4-HNE-, SOD1- and SOD2-immunoreactive cells were significantly increased in both the cervical and lumbar spinal cord of the aged dog: The increase rates of these cells in the aged spinal cord were higher in the lumbar level than the cervical level. In brief, 4-HNE, SOD1 and SOD2 levels are much increased in the aged spinal cord compared to the adult spinal cord.

Effects of Nelumbo nucifera Rhizome Extract on Cell Proliferation and Neuroblast Differentiation in the Hippocampal Dentate Gyrus in a Scopolamine‐induced Amnesia Animal Model

A large aquatic herb, Nelumbo nucifera Gaertn, has psychopharmacological effects similar to minor tranquillizers and antistress agents. This study examined the effects of Nelumbo nucifera rhizome extracts (NRE) on cell proliferation and neuroblast differentiation in the hippocampal dentate gyrus (DG) of a rat model of scopolamine‐induced amnesia. Immunohistochemical markers included Ki67, an endogenous marker for active cell cycle, and doublecortin (DCX), a marker for immature neurons and migratory neuroblasts. Scopolamine was administered for 28 days via an ALzet minipump (44 mg/mL delivered at 2.5 µL/h). NRE was administered by gavage, 1 g/kg per day for 28 days. The administration of scopolamine significantly reduced the number of Ki67‐ and DCX‐immunoreactive cells in the DG, whereas scopolamine did not induce any significant changes in mature neurons in the DG. The administration of NRE significantly ameliorated the scopolamine‐induced reduction of Ki67‐ and DCX‐immunoreactive cells in the DG. In addition, the administration of NRE significantly restored the scopolamine‐induced reduction of brain‐derived neurotrophic factor in DG homogenates. These results suggest that NRE can ameliorate the scopolamine‐induced reductions of cell proliferation, neuroblast differentiation and BDNF levels. Copyright

Grape seed extract enhances neurogenesis in the hippocampal dentate gyrus in C57BL/6 mice.

The effects of grape seed extract (GSE), a major source of phenolic compounds, were examined on cell proliferation, neuroblast differentiation and integration into granule cells in the hippocampal dentate gyrus (DG) of middle‐aged (12 month‐old) mice using Ki67, doublecortin (DCX) immunohistochemistry and 5′‐bromo‐2‐deoxyguanosine (BrdU)/calbindin D‐28k (CB) double immunofluorescence study, respectively. GSE (25, 50 and 100 mg/kg) was administered orally for 28 days, and the animals were treated with 50 mg/kg BrdU intraperitoneally on the day of first GSE treatment. In the vehicle‐treated group, Ki67 and DCX immunoreactivity was detected in the subgranular zone of the DG (SZDG). GSE treatment dose‐dependently increased the number of Ki67 and DCX immunoreactive cells, particularly the number of DCX immunoreactive neuroblasts with well‐developed (tertiary) dendrites. GSE also dose‐dependently increased DCX protein levels. In addition, GSE treatment increased significantly the number of BrdU/CB double labeled granule cells. These results suggest that GSE significantly increases cell proliferation, neuroblast differentiation and integration into granule cells in the DG, and the consumption of GSE enhances the plasticity of hippocampus in middle‐aged mice. Copyright

Comparison of glucocorticoid receptor and ionized calcium-binding adapter molecule 1 immunoreactivity in the adult and aged gerbil hippocampus following repeated restraint stress

Stress leads to changes in homeostasis and internal balance of the body and is known to be one of important factors in the development of several diseases. In the present study, we investigated changes in glucocorticoid receptor (GR) and ionized calcium-binding adapter molecule 1 (Iba-1) immunoreactivity in the adult and aged gerbil hippocampus after chronic restraint stress. Serum corticosterone level was much higher in both the stress-groups than the control groups. No neuronal death was found in all hippocampal subregions of the adult and aged gerbil after chronic restraint stress. GR immunoreactivity was decreased in both the adult and aged groups after repeated restraint stress; however, GR immunoreactivity in the adult-stress-group was decreased much more than that in the aged-stress-group. Iba-1 immunoreactive microglia were hypertrophied and activated in the adult group after repeated restraint stress; in the aged-stress-group, there was no any significant change in Iba-1 immunoreactive microglia. In brief, level of GR, not Iba-1, in the hippocampus was much decreased in the adult gerbil compared to the aged gerbil following chronic restraint stress.