Seung-Mook Jo

Astroglial loss and edema formation in the rat piriform cortex and hippocampus following pilocarpine‐induced status epilepticus

In the present study we analyzed aquaporin‐4 (AQP4) immunoreactivity in the piriform cortex (PC) and the hippocampus of pilocarpine‐induced rat epilepsy model to elucidate the roles of AQP4 in brain edema following status epilepticus (SE). In non‐SE‐induced animals, AQP4 immunoreactivity was diffusely detected in the PC and the hippocampus. AQP4 immunoreactivity was mainly observed in the endfeet of astrocytes. Following SE the AQP4‐deleted area was clearly detected in the PC, not in the hippocampus. Decreases in dystrophin and α‐syntrophin immunoreactivities were followed by reduction in AQP4 immunoreactivity. These alterations were accompanied by the development of vasogenic edema and the astroglial loss in the PC. In addition, acetazolamide (an AQP4 inhibitor) treatment exacerbated vasogenic edema and astroglial loss both in the PC and in the hippocampus. These findings suggest that SE may induce impairments of astroglial AQP4 functions via disruption of the dystrophin/α‐syntrophin complex that worsen vasogenic edema. Subsequently, vasogenic edema results in extensive astroglial loss that may aggravate vasogenic edema. J. Comp. Neurol. 518:4612–4628, 2010.

Blockade of P2X receptor prevents astroglial death in the dentate gyrus following pilocarpine-induced status epilepticus

Abstract Objective: The P2 receptor is involved in diverse signal cascades, including the initiation of the rapid release and processing of proinflammatory cytokines, the induction of cytoskeletal rearrangements and transcription factor activation. Therefore, we investigated whether blocking the P2 receptor would prevent the astroglial death induced by status epilepticus (SE). Methods: We performed seizure induction and drug treatments. After tissue processing, we executed immunoreactivities: mouse anti-glial fibrillary acidic protein (GFAP) IgG (diluted 1 : 200; Chemicon, Billerica, MA, USA rabbit anti-P2X7 receptor IgG (diluted 1 : 200; Chemicon). Results: In control animals, P2X7 receptor-immunoreactive (P2X7+) microglia had small cell bodies with thin ramified processes. Seven days after SE, P2X7 receptor immunoreactivity in microglia was significantly elevated in the dentate gyrus, and the microglia appeared amoeboid or phagocytic. At this point, loss of GFAP immunoreactivity in the dentate gyrus was even more pronounced, indicating that the network of astrocytes was disrupted and a large empty zone was observed. Treatment with pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid and suramin (2, 20 and 200 mg/kg, i.p., respectively) markedly, but not completely, inhibited microglial activation following SE. The morphology of microglia was similar to that of the astrocytes in that they appeared hyper-ramified. In addition, P2X7 receptor antagonist treatments effectively prevented astroglial degeneration. Discussion: These findings suggest that astroglial death induced by ATP-mediated microglia activation may be an important pathophysiological pathway in epileptogenesis.

Distribution and characteristics of cholecystokinin-like immunoreactivity in the olfactory bulb of the cat

The distribution and characteristics of cholecystokinin (CCK)-like immunoreactive (LIR) nerve fibers was examined in the cat olfactory bulb using immunohistochemistry. CCK-LIR cell bodies were not found; fine varicose CCK-LIR fibers were observed in the most layers. In the main olfactory bulb, no staining was seen in the olfactory nerve layer and white matter. The directions of CCK-LIR fibers in the glomerular, external plexiform and mitral cell layers were generally perpendicular to the bulbar surface; those in the deep granule cell layer were parallel; and those in the internal plexiform and superficial granule cell layers were mixed. In the accessory olfactory bulb, CCK-LIR fibers were localized only in the granule cell layer. The presence of CCK-LIR fibers of the cat olfactory bulb may be involved in the modulation of olfactory transmission.

The expression of somatostatin receptors in the hippocampus of pilocarpine-induced rat epilepsy model

During the course of this study, we sought examine whether the expression of somatostatin receptors (SSTRs) is altered in the hippocampus following pilocarpine-induced status epilepticus (SE) in order to understand the role/function of SSTRs in the hippocampus after epileptogenic insults. SSTR1 and SSTR4 immunoreactivities were increased in the hippocampus at 1 week after SE. At 4 weeks after SE, SRIF1-family (SSTR 2A, SSTR2B, and SSTR5) immunoreactivity was increased only in neuropil. Both SSTR2A and 2B immunoreactivities were increased in CA2-3 pyramidal cells. However, SSTR3 and SSTR4 immunoreactivities were reduced in the CA1 pyramidal cells of epileptic rat due to neuronal loss. In addition, SSTR5 immunoreactivity was reduced in CA2 pyramidal cells and various interneurons. Both SSTR2B and SSTR4 immunoreactivities were increased within microglia following SE. Our findings suggest that increases in neuron-glial SSTR expressions may be closely related to the enhanced inhibition of the dentate gyrus and regulation of reactive microgliosis in the hippocampus of a pilocarpine model of temporal lobe epilepsy.

Distribution of Serotonin Immunoreactivitiy in the Main Olfactory Bulb of the Mongolian Gerbil

The distribution of serotonin immunoreactivity in the main olfactory bulb (MOB) of the Mongolian gerbil (Meriones unguiculatus) was examined by immunohistochemistry. Seven distinct layers of the Mongolian gerbil MOB‐stained with cresyl violet were identified. Serotonin‐immunoreactive (IR) cell bodies were not found in the MOB. The serotonin‐IR nerve fibres had a specific laminar distribution and morphology in the gerbil MOB. Serotonin‐IR nerve fibres were observed in the glomerular, external plexiform and granule cell layers of the MOB. These serotonin‐IR nerve fibres showed varicosities that were larger than the thickness of the axon. The highest density of serotonin‐IR nerve fibres was in glomeruli of the glomerular layer. The average fibre density in the glomerular layer was more than three to four times the density in the infraglomerular layers. Glomerular serotonin‐IR fibres were much more intensively stained than infraglomerular serotonin‐IR fibres. This result suggests that serotonin‐IR nerve fibres of Mongolian gerbil MOB are extrinsic and may act to modulate the olfactory transmission.

Microglial AGE-albumin is critical for neuronal death in Parkinson’s disease: a possible implication for theranostics

Advanced glycation end products (AGEs) are known to play an important role in the pathogenesis of neurodegenerative diseases, including Parkinson’s disease (PD), by inducing protein aggregation and cross-link, formation of Lewy body, and neuronal death. In this study, we observed that AGE-albumin, the most abundant AGE product in the human PD brain, is synthesized in activated microglial cells and accumulates in the extracellular space. AGE-albumin synthesis in human-activated microglial cells is distinctly inhibited by ascorbic acid and cytochalasin treatment. Accumulated AGE-albumin upregulates the receptor to AGE, leading to apoptosis of human primary dopamine (DA) neurons. In animal experiments, we observed reduced DA neuronal cell death by treatment with soluble receptor to AGE. Our study provides evidence that activated microglial cells are one of the main contributors in AGE-albumin accumulation, deleterious to DA neurons in human and animal PD brains. Finally, activated microglial AGE-albumin could be used as a diagnostic and therapeutic biomarker with high sensitivity for neurodegenerative disorders, including PD.

Comparative Studies on the Distribution of Glutamate Transporters in the Retinae of the Mongolian Gerbil and the Rat

Glutamate is the major excitatory amino acid transmitter in vertebrate retinae. Glutamate transporters therefore play an important role in the precise control of glutamate concentration in the synaptic cleft by regulating extracellular glutamate concentration. In the present study, we performed an analysis of the expressions of three glutamate transporters in gerbil retina using immunohistochemistry. In the gerbil retina, excitatory amino acid carrier 1 and glutamate transporter 1 immunoreactivity was predominant in the ganglion cells but not amacrine or bipolar cells. Glutamate/aspartate transporter (GLAST) immunoreactivity was observed in the radial gliocytes of which the dense network of fine processes was localized in the inner and outer plexiform layers. GLAST immunoreactivity was also detected in astrocytes in the nerve fibre layer. These results demonstrate that three glutamate transporters show specific distributions in the gerbil retina and suggest that the glutamate re‐uptake system in the gerbil retina may be different from that of the rat.

Voltage-gated Na+ channel II immunoreactivity is selectively up-regulated in hippocampal interneurons of seizure sensitive gerbils

In the present study, we investigated the distribution of voltage-gated Na(+) channels (VGSCs) in the normal and epileptic hippocampus of gerbils (a genetic epilepsy model) in order to confirm the relationship between VGSC and seizure activity in these animals. There was no difference of VGSC I immunoreactivity in the hippocampus between seizure-resistant (SR) and seizure sensitive (SS) gerbils. VGSC II immunoreactivity was rarely detected in the perikarya of principal neurons and interneurons in the SR gerbil hippocampus. However, in the SS gerbil hippocampus, VGSC II immunoreactivity was densely observed in the somata of interneurons located in the stratum radiatum and stratum lacunosum-moleculare. Double immunofluorescent study showed immunoreactivity for calretinin (approximately 80% in VGSC II-positive neurons) or calbindin D-28k (approximately 20% in VGSC II-positive neurons) in VGSC II-immunoreactive neurons. VGSC II-immunoreactive neurons did not show parvalbumin immunoreactivity. These findings suggest that seizure activity in SS gerbils may be related to the selective hyperactivation of interneurons in stratum lacunosum-moleculare via the up-regulation of VGSC II expression, which leads to the disinhibition of CA1 pyramidal cells.