Histological changes in the olfactory bulb and rostral migratory stream due to interruption of olfactory input.

OBJECTIVE: Periglomerular and granule cells in the adult mammalian olfactory bulb modulate olfactory signal transmission. These cells originate from the subventricular zone, migrate to the olfactory bulb via the Rostral Migratory Stream (RMS), and differentiate into mature cells within the olfactory bulb throughout postnatal life. While the regulation of neuroblast development is known to be affected by external stimuli, there is a lack of information concerning changes that occur during the recovery process after injury caused by external stimuli. To address this gap in research, the present study conducted histological observations to investigate changes in the olfactory bulb and RMS occurring after the degeneration and regeneration of olfactory neurons. METHODS: To create a model of olfactory neurodegeneration, adult mice were administered methimazole intraperitoneally. Nasal tissue and whole brains were removed 3, 7, 14 and 28 days after methimazole administration, and EdU was administered 2 and 4 h before removal of these tissues to monitor dividing cells in the RMS. Methimazole-untreated mice were used as controls. Olfactory nerve fibers entering the olfactory glomerulus were observed immunohistochemically using anti-olfactory marker protein. In the brain tissue, the entire RMS was observed and the volume and total number of cells in the RMS were measured. In addition, the number of neuroblasts and dividing neuroblasts passing through the RMS were measured using anti-doublecortin and anti-EdU antibodies, respectively. Statistical analysis was performed using the Tukey test. RESULTS: Olfactory epithelium degenerated was observed after methimazole administration, and recovered after 28 days. In the olfactory glomeruli, degeneration of OMP fibers began after methimazole administration, and after day 14, OMP fibers were reduced or absent by day 28, and overall OMP positive fibers were less than 20%. Glomerular volume tended to decrease after methimazole administration and did not appear to recover, even 28 days after recovery of the olfactory epithelium. In the RMS, EdU-positive cells decreased on day 3 and began to increase on day 7. However, they did not recover to the same levels as the control methimazole-untreated mice even after 28 days. CONCLUSION: These results suggest that the division and maturation of neuroblasts migrating from the RMS was suppressed by olfactory nerve degeneration or the disruption of olfactory input.

Glycolytic activity is required for the onset of neural plate folding during neural tube closure in mouse embryos.

Physiological hypoxia is critical for placental mammalian development. However, the underlying mechanisms by which hypoxia regulates embryonic development remain unclear. We discovered that the expression of glycolytic genes partially depends on hypoxia in neuroepithelial cells of E8.25 mouse embryos. Consistent with this finding, inhibiting glycolysis during the early phase of neural tube closure (E8.0-8.5) resulted in a neural tube closure defect. In contrast, inhibiting the electron transport chain did not affect neural tube formation. Furthermore, inhibiting glycolysis affected cell proliferation, but not differentiation and survival. Inhibiting glycolysis repressed the phosphorylation of myosin light chain 2, and consequent neural plate folding. Our findings revealed that anaerobic glycolysis regulates neuroepithelial cell proliferation and apical constriction during the early phase of neural tube closure.

A three-dimensional single-cell-resolution whole-brain atlas using CUBIC-X expansion microscopy and tissue clearing.

A three-dimensional single-cell-resolution mammalian brain atlas will accelerate systems-level identification and analysis of cellular circuits underlying various brain functions. However, its construction requires efficient subcellular-resolution imaging throughout the entire brain. To address this challenge, we developed a fluorescent-protein-compatible, whole-organ clearing and homogeneous expansion protocol based on an aqueous chemical solution (CUBIC-X). The expanded, well-cleared brain enabled us to construct a point-based mouse brain atlas with single-cell annotation (CUBIC-Atlas). CUBIC-Atlas reflects inhomogeneous whole-brain development, revealing a significant decrease in the cerebral visual and somatosensory cortical areas during postnatal development. Probabilistic activity mapping of pharmacologically stimulated Arc-dVenus reporter mouse brains onto CUBIC-Atlas revealed the existence of distinct functional structures in the hippocampal dentate gyrus. CUBIC-Atlas is shareable by an open-source web-based viewer, providing a new platform for whole-brain cell profiling.

Expression of steroidogenic enzymes and metabolism of steroids in COS-7 cells known as non-steroidogenic cells.

The COS-7 (CV-1 in Origin with SV40 genes) cells are known as non-steroidogenic cells because they are derived from kidney cells and the kidney is defined as a non-steroidogenic organ. Therefore, COS-7 cells are used for transfection experiments to analyze the actions of functional molecules including steroids. However, a preliminary study suggested that COS-7 cells metabolize [3H]testosterone to [3H]androstenedione. These results suggest that COS-7 cells are able to metabolize steroids. Therefore, the present study investigated the expression of steroidogenic enzymes and the metabolism of steroids in COS-7 cells. RT-PCR analyses demonstrated the expressions of several kinds of steroidogenic enzymes, such as cytochrome P450 side-chain cleavage enzyme, 3ß-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase, cytochrome P450 7α-hydroxylase, cytochrome P450 17α-hydroxylase/17,20-lyase, 17ß-hydroxysteroid dehydrogenase, 5α-reductase, cytochrome P450 21-hydroxylase, cytochrome P450 11ß-hydroxylase, and cytochrome P450 aromatase in COS-7 cells. In addition, steroidogenic enzymes 3ß-HSD, P4507α, 5α-reductase, P450c17, P450c21, P450c11ß, and 17ß-HSD actively metabolized various steroids in cultured COS-7 cells. Finally, we demonstrated that 17ß-HSD activity toward androstenedione formation was greater than other steroidogenic enzyme activities. Our results provide new evidence that COS-7 cells express a series of steroidogenic enzyme mRNAs and actively metabolize a variety of steroids.