Distinct Modes of Neuron Addition in Adult Mouse Neurogenesis

Adult neurogenesis is restricted to two distinct areas of the mammalian brain: the olfactory bulb (OB) and the dentate gyrus (DG). Despite its spatial restriction, adult neurogenesis is of crucial importance for sensory processing and learning and memory. Although it has been shown that tens of thousands of new neurons arrive in the OB and DG every day with about half of them surviving after integration, the total contribution of adult neurogenesis to the pre-existing network remains mostly unknown. This is because of previous approaches labeling only a small proportion of adult-generated neurons. Here, we used genetic fate mapping to follow the majority of adult-generated neurons over long periods. Our data demonstrate two distinct modes of neuron addition to the pre-existing network. In the glomerular layer of the OB, there is a constant net addition of adult-generated neurons reaching a third of the total neuronal population within 9 months. In contrast, adult neurogenesis contributes to only a minor fraction of the entire neuronal network in the granular cell layer of the OB and the DG. Although the fraction of adult generated neurons can be further increased by an enriched environment, it still remains a minority of the neuronal network in the DG. Thus, neuron addition is distinct and tightly regulated in the neuronal networks that incorporate new neurons life long

c-jun is differentially expressed in embryonic and adult neural precursor cells

c-jun, a major component of AP-1 transcription factor, has a wide variety of functions. In the embryonic brain, c-jun mRNA is abundantly expressed in germinal layers around the ventricles. Although the subventricular zone (SVZ) of the adult brain is a derivative of embryonic germinal layers and contains neural precursor cells (NPCs), the c-jun expression pattern is not clear. To study the function of c-jun in adult neurogenesis, we analyzed c-jun expression in the adult SVZ by immunohistochemistry and compared it with that of the embryonic brain. We found that almost all proliferating embryonic NPCs expressed c-jun, but the number of c-jun immunopositive cells among proliferating adult NPCs was about half. In addition, c-jun was hardly expressed in post-mitotic migrating neurons in the embryonic brain, but the majority of c-jun immunopositive cells were tangentially migrating neuroblasts heading toward the olfactory bulb in the adult brain. In addition, status epilepticus is known to enhance the transient proliferation of adult NPCs, but the c-jun expression pattern was not significantly affected. These expression patterns suggest that c-jun has a pivotal role in the proliferation of embryonic NPCs, but it has also other roles in adult neurogenesis

Phenotype Analysis and Quantification of Proliferating Cells in the Cortical Gray Matter of the Adult Rat

In intact adult mammalian brains, there are two neurogenic regions: the subependymal zone and the subgranular layer of the hippocampus. Even outside these regions, small numbers of proliferating precursors do exist. Many studies suggest that the majority of these are oligodendrocyte precursors that express NG2, a chondroitin sulfate proteoglycan, and most of the residual proliferating cells seem to be endothelial cells. However, it is still unclear whether NG2-immunonegative proliferating precursors are present, because previous studies have neglected their possible existence. In this study, we systematically analyzed the phenotypes of the proliferating cells in the intact adult rat cortical gray matter. We improved our techniques and carefully characterized the proliferating cells, because there were several problems with identifying and quantifying the proliferating cells: the detection of NG2-expressing cells was dependent on the fixation condition; there were residual proliferating leukocytes in the blood vessels; and two anti-NG2 antibodies gave rise to different staining patterns. Moreover, we used two methods, BrdU and Ki67 immunostaining, to quantify the proliferating cells. Our results strongly suggest that in the intact adult cerebral cortical gray matter, there were only two types of proliferating cells: the majority were NG2-expressing cells, including pericytes, and the rest were endothelial cells

Differential expression of nuclear lamin subtypes in the neural cells of the adult rat cerebral cortex

Lamins are type V intermediate filament proteins that are located beneath the inner nuclear membrane. In mammalian somatic cells, LMNB1 and LMNB2 encode somatic lamins B1 and B2, respectively, and the LMNA gene is alternatively spliced to generate somatic lamins A and C. Mutations in lamin genes have been linked to many human hereditary diseases, including neurodegenerative disorders. Knowledge about lamins in the nervous system has been accumulated recently, but a precise analysis of lamin subtypes in glial cells has not yet been reported. In this study we investigated the composition of lamin subtypes in neurons, astrocytes, oligodendrocyte-lineage cells, and microglia in the adult rat cerebral cortex using an immunohistochemical staining method. Lamin A was not observed in neurons and glial cells. Lamin C was observed in astrocytes, mature oligodendrocytes and neurons, but not observed in oligodendrocyte progenitor cells. Microglia also did not stain positive for lamin C which differed from macrophages, with lamin C positive. Lamin B1 and B2 were observed in all glial cells and neurons. Lamin B1 was intensely positive in oligodendrocyte progenitor cells compared with other glial cells and neurons. Lamin B2 was weakly positive in all glial cells compared to neurons. Our current study might provide useful information to reveal how the onset mechanisms of human neurodegenerative diseases are associated with mutations in genes for nuclear lamin proteins

Cloning of a Putative Vesicle Transport-related Protein, RA410, from Cultured Rat Astrocytes and Its Expression in Ischemic Rat Brain

To elucidate the role of astrocytes in the stress response of the central nervous system to ischemia, early gene expression was evaluated in cultured rat astrocytes subjected to hypoxia/reoxygenation. Using differential display, a novel putative vesicle transport-related factor (RA410) was cloned from reoxygenated astrocytes. Analysis of the deduced amino acid sequence showed RA410 to be composed of domains common to vesicle transport-related proteins of the Sec1/Unc18 family, including Sly1p and Sec1p (yeast), Rop (Drosophila), Unc18 (Caenorhabditis elegans), and Munc18 (mammalian), suggesting its possible role in vesicular transport. Northern analysis of normal rat tissues showed the highest expression of RA410 transcripts in testis. When astrocyte cultures were subjected to a period of hypoxia followed by reoxygenation, induction of RA410 mRNA was observed within 15 min of reoxygenation, reaching a maximum by 60 min. At the start of reoxygenation, the addition of diphenyl iodonium, an NADPH oxidase inhibitor, blocked in parallel astrocyte generation of reactive oxygen intermediates and expression of RA410 message. In contrast, cycloheximide did not affect RA410 mRNA levels, indicating that RA410 is an immediate-early gene in the setting of reoxygenation. Using polyclonal antibody raised against an RA410-derived synthetic peptide, Western blotting of lysates from reoxygenated astrocytes displayed an immunoreactive band of ≈70 kDa, the expression of which followed induction of the mRNA. Fractionation of astrocyte lysates on sucrose gradients showed RA410 antigen to be predominantly in the plasma membrane. Immunoelectron microscopic analysis demonstrated RA410 in large vesicles associated with the Golgi, but not in the Golgi apparatus itself, consistent with its participation in post-Golgi transport. Consistent with thesein vitro data, RA410 expression was observed in rat brain astrocytes following transient occlusion of the middle cerebral artery. These data provide insight into a new protein (RA410) that participates in the ischemia-related stress response in astrocytes

Impact of Hands-on Experience of a Cadaver Dissection on the Professional Identity Formation of Health Sciences Students

[Background] In Japan, some nursing and health science universities that train nurses and/or clinical laboratory technicians have a curriculum in which students observe medical students performing a cadaver dissection. Observing a cadaver dissection is believed to affect the formation of a student’s professional identity. This study aimed to investigate the effects of observing a cadaver dissection on the professional identity of nursing and clinical laboratory science students to find an effective educational support system for developing professional identity. [Methods] Sophomores majoring in nursing science or clinical laboratory science were asked to complete a questionnaire with a professional identity scale before and after hands-on experience of a cadaver dissection performed by medical students. After their hands-on session was complete, they responded to a free-answer question about acquiring a professional identity. [Results] The professional identity score of nursing students significantly decreased after the hands-on experience of the cadaver dissection. No significant change in professional identity score was observed in the clinical laboratory science students. However, the effect size (r) was moderate. [Conclusion] Although professional identity formation fluctuates immediately after the experience of the hands-on experience of a cadaver dissection, the findings do suggest that these hands-on sessions will be effective for developing their professional identity if educational support is provided to help them utilize what they learned through reflection

Huge splenic epidermoid cyst with elevation of serum CA19-9 level

A 30-year-old female was referred to our hospital for further examination of liver dysfunction. A huge, soft mass was noted in her left upper quadrant on physical examination. Abdominal ultrasonography and computed tomography revealed a huge cystic tumor of 20 cm in the hilus of the spleen. Serum CA19-9 was 491 U/ml, and splenectomy was performed under suspicion of a malignant cystic tumor. The inner surface of the cyst was lined by squamous epithelial cells that were immunohistochemically positive for CA19-9. Serum CA19-9 level was normalized after the surgery. Our case of a very rare, huge epidermoid cyst of the spleen suggests that measurement of the serum CA19-9 level is useful for evaluating therapeutic efficacy of a splenic epidermoid cyst