Age-dependent changes of p53 and p63 immunoreactivities in the mouse hippocampus / 한국실험동물학회지

P53 and its family member p63 play important roles in cellular senescence and organismal aging. In this study, p53 and p63 immunoreactivity were examined in the hippocampus of young, adult and aged mice by using immunohistochemistry. In addition, neuronal distribution and degeneration was examined by NeuN immunohistochemistry and fluoro-Jade B fluorescence staining. Strong p53 immunoreactivity was mainly expressed in pyramidal and granule cells of the hippocampus in young mice. p53 immunoreactivity in the pyramidal and granule cells was significantly reduced in the adult mice. In the aged mice, p53 immunoreactivity in the pyramidal and granule cells was more significantly decreased. p63 immunoreactivity was strong in the pyramidal and granule cells in the young mice. p63 immunoreactivity in these cells was apparently and gradually decreased with age, showing that p63 immunoreactivity in the aged granule cells was hardly shown. However, numbers of pyramidal neurons and granule cells were not significantly decreased in the aged mice with normal aging. Taken together, this study indicates that there are no degenerative neurons in the hippocampus during normal aging, showing that p53 and p63 immunoreactivity in hippocampal neurons was progressively reduced during normal aging, which might be closely related to the normal aging processes.

Developmental changes in GABAA tonic inhibition are compromised by multiple mechanisms in preadolescent dentate gyrus granule cells

The sustained tonic currents (I(tonic)) generated by γ-aminobutyric acid A receptors (GABA(A)Rs) are implicated in diverse age-dependent brain functions. While various mechanisms regulating I(tonic) in the hippocampus are known, their combined role in I(tonic) regulation is not well understood in different age groups. In this study, we demonstrated that a developmental increase in GABA transporter (GAT) expression, combined with gradual decrease in GABA(A)R α₅ subunit, resulted in various I(tonic) in the dentate gyrus granule cells (DGGCs) of preadolescent rats. Both GAT-1 and GAT-3 expression gradually increased at infantile (P₆₋₈ and P₁₃₋₁₅) and juvenile (P₂₀₋₂₂ and P₂₇₋₂₉) stages, with stabilization observed thereafter in adolescents (P₃₄₋₃₆) and young adults (P₄₁₋₄₃). I(tonic) facilitation of a selective GAT-1 blocker (NO-711) was significantly less at P₆₋₈ than after P₁₃₋₁₅. The facilitation of I(tonic) by SNAP-5114, a GAT-3 inhibitor, was negligible in the absence of exogenous GABA at all tested ages. In contrast, I(tonic) in the presence of a nonselective GAT blocker (nipecotic acid, NPA) gradually decreased with age during the preadolescent period, which was mimicked by I(tonic) changes in the presence of exogenous GABA. I(tonic) sensitivity to L-655,708, a GABA(A)R α₅ subunit inverse agonist, gradually decreased during the preadolescent period in the presence of NPA or exogenous GABA. Finally, Western blot analysis showed that the expression of the GABA(A)R α₅ subunit in the dentate gyrus gradually decreased with age. Collectively, our results suggested that the I(tonic) regulation of altered GATs is under the final tune of GABA(A)R α₅ subunit activation in DGGCs at different ages.

Early cerebellar granule cell migration in the mouse embryonic development / 대한해부학회지

Pax6, a paired homeobox DNA binding protein, has been found to be expressed in the cerebellum in both granule cells and their precursors in the external granular layer (EGL). In this study we have traced Pax6 expression through embryonic development in mice by using a polyclonal antibody against Pax6 and used it to study the cellular dispersal pattern of the EGL. During dispersal the EGL was thicker and Pax6 expression was more intense on the rostral side of the lateral corners of the cerebellum. Pax6 immunoreactive cells were found to be migrating from the EGL during the early stage of EGL dispersal, which suggested the early inward migration of granule cells. Double staining with various markers confirmed that the early-migrating cells are not Purkinje cells, interneurons or glia. Although the Pax6 immunoreactive cells within the cerebellum were not apparently proliferating, NeuN, a marker for postmitotic granule cells, was not expressed in these cells until E16. Furthermore, granule cells were observed migrating inwards from the EGL both during and after EGL dispersal. These early migrating granule cells populated the whole cerebellum. These findings offer novel views on specific stages of granule cell dispersal and migration.

Neurotoxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in cerebellar granule cells

An environmental pollutant, tetrachloro dibenzo dioxin (TCDD) is known to illicit the cognitive disability and motor dysfunction in the developing brain. TCDD induced effects leading to neurodevelopmental and neurobehavioral deficit may have been defined, however underlying molecular mechanism and possible intracellular targets remain to be elucidated. In this study, we attempted to analyze TCDD-induced neurotoxic effects in the granule cells from cerebellum where certain cognitive abilities and motor function command are known to be excuted. [3H]PDBu, (phorbol 12,13-dibutyrate) binding assay indicated that TCDD induced a dose-dependent increase of total PKC activity and its induction was the aryl hydrocarbon receptor (AhR) dependent and N-methyl-D-aspartate receptor (NMDAR) independent. TCDD also caused the translocation of both PKC-alpha and -epsilon in a dose-dependent manner but associated with different receptors; PKC-alpha via AhR but not PKC-epsilon indicating an isozyme-specific pattern of the induction. Increase of the ROS formation was also observed in the cells treated with TCDD in a dose-dependent and an AhR-dependent manner. The treatment of the cells with the diamino dicyano-bis(2-aminophenylthio) butadiene (U0126, MEK-1/2 inhibitor), dizocilpine maleate (MK-801, non-competitive N-methyl-D-aspartate glutamate receptor antagonist) and vitamin E attenuated the TCDD-induced ROS production indicating that TCDD-induced ROS formation may be associated with activation of ERK-1/2 in the MAP kinase pathway or the NMDA receptor. TCDD also increased [Ca2+]i, which is associated with ROS formation and PKC activation in the cerebellar granule cells. It is suggested that TCDD activates the NMDA receptor, which may induce a sustained increase of [Ca2+]i in neurons followed by the ROS formation. Our findings may contribute to understanding the mechanism of TCDD-related neurotoxicity, thereby improving the health risk assessment of neurotoxic compounds in humans.

Trimethyltin-Induced Hippocampal Neurodegeneration is Possibly Mediated by Induction of Apoptosis

BACKGROUND: Trimethyltin (TMT) is a neurotoxicant which produces a distinct pattern of neuronal cell death in the hippocampus following systemic administration of a single dose. However, the mechanism of selective neuronal death remains unclear. We performed this study to elucidate the underlying mechanism of TMT-induced hippocampal neu-ronal death. METHODS: The effects of trimethyltin (8.0mg/kg, I.p., single dose) on the hippocampal neurons were investi-gated in terms of changes in the neurobehavioral status, histologic, and electron microscopc findings. RESULTS: Behaviorally, TMT treatment caused stereotypic limbic system dysfunction, i.e. tremors, spontaneous seizures, vocaliza-tion, hyperactivity, hyperexcitability, intraspecific aggression as described previously. Morphologically, TMT produced prominent neurodegeneration in the dentate gyrus. Widespread, strong glial fibrillary acidic protein (GFAP) immunore-activity, which was suggestive of reactive astrogliosis, was noted throughout the hippocampal subfields. Many degener-ating neurons were TUNEL positive. Electron microscopic findings revealed characteristic features of apoptosis in the dentate granule cells. NADPH-diaphorase positive cells were spared after TMT exposure. CONCLUSIONS: It is suggested that TMT-induced hippocampal degeneration might be a useful in vivo model for the study of learning and memory, neuronal-glial interactions, and selective neuronal apoptosis.

Trimethyltin-Induced Hippocampal Neurodegeneration is Possibly Mediated by Induction of Apoptosis

BACKGROUND: Trimethyltin (TMT) is a neurotoxicant which produces a distinct pattern of neuronal cell death in the hippocampus following systemic administration of a single dose. However, the mechanism of selective neuronal death remains unclear. We performed this study to elucidate the underlying mechanism of TMT-induced hippocampal neu-ronal death. METHODS: The effects of trimethyltin (8.0mg/kg, I.p., single dose) on the hippocampal neurons were investi-gated in terms of changes in the neurobehavioral status, histologic, and electron microscopc findings. RESULTS: Behaviorally, TMT treatment caused stereotypic limbic system dysfunction, i.e. tremors, spontaneous seizures, vocaliza-tion, hyperactivity, hyperexcitability, intraspecific aggression as described previously. Morphologically, TMT produced prominent neurodegeneration in the dentate gyrus. Widespread, strong glial fibrillary acidic protein (GFAP) immunore-activity, which was suggestive of reactive astrogliosis, was noted throughout the hippocampal subfields. Many degener-ating neurons were TUNEL positive. Electron microscopic findings revealed characteristic features of apoptosis in the dentate granule cells. NADPH-diaphorase positive cells were spared after TMT exposure. CONCLUSIONS: It is suggested that TMT-induced hippocampal degeneration might be a useful in vivo model for the study of learning and memory, neuronal-glial interactions, and selective neuronal apoptosis.

Effects of different membrane proteins and dimethylsulfoxide on neurite growth of cerebellum granule cells / 第三军医大学学报

Objective To observe the effects of different membrane proteins and dimethylsulfoxide on neurite outgrowth of cerebellum granule cells(CGC).Methods Membrane proteins were extracted from the liver,sciatic nerve and brain white matter of adult rats and coated on the cover slips.CGC were dissociated from newborn rats and inoculated on the coated cover slips,while dimethylsulfoxide(DMSO) was added into the CGC suspension.Results The neurite outgrowth was inhibited by membrane protein of brain white mater and the effect was concentration-dependent.Low concentration(

STUDIES ON THE RELATION BETWEEN INHIBITORY EFFECT OF MYELIN MEMBRANE PROTEINS ON NEURITE OUTGROWTH AND cAMP LEVELS IN NEURONS / 解剖学报

Objective To study the relationship between the inhibitory effects that myelin membrane proteins exerted on nerve regeneration and the changes of intracellular cAMP levels in neurons. Methods To observe the effects of myelin membrane proteins extracted from central nervous system(CNS) by density centrifugation on the outgrowth of neurite of cerebella granule cells in culture and detect the changes of intracellular cAMP levels of the neurons with radioimmunoassay. Results 1^Myelin membrane proteins of CNS inhibited neurite outgrowth of cultured cerebella granule cells. 2^The cAMP level in neurons decreased in 5 minutes after contacting myelin membrane proteins and reached to the lowest level in 12 hours of contacting. Conclusion The inhibitory effects of myelin membrane proteins on the outgrowth of neurites may be related to the inhibitory factors which cause the decrease of cAMP level in neuron through the passway of signal transduction pathway. [