CD206+ macrophages transventricularly infiltrate the early embryonic cerebral wall to differentiate into microglia.

The relationships between tissue-resident microglia and early macrophages, especially their lineage segregation outside the yolk sac, have been recently explored, providing a model in which a conversion from macrophages seeds microglia during brain development. However, spatiotemporal evidence to support such microglial seeding in situ and to explain how it occurs has not been obtained. By cell tracking via slice culture, intravital imaging, and Flash tag-mediated or genetic labeling, we find that intraventricular CD206+ macrophages, which are abundantly observed along the inner surface of the mouse cerebral wall, frequently enter the pallium at embryonic day 12. Immunofluorescence of the tracked cells show that postinfiltrative macrophages in the pallium acquire microglial properties while losing the CD206+ macrophage phenotype. We also find that intraventricular macrophages are supplied transepithelially from the roof plate. This study demonstrates that the "roof plate→ventricle→pallium" route is an essential path for microglial colonization into the embryonic mouse brain.

Laparoscopic resection of a paraganglioma in the greater omentum mimicking a peripancreatic neoplasm: a case report.

A paraganglioma is a tumor originating in the sympathetic or parasympathetic nervous system. Its diagnosis may sometimes be confusing if it occurs in an atypical site. We described herein a case of a peripancreatic paraganglioma originating in the greater omentum. An asymptomatic, 61-year-old, female patient was referred to our hospital for detailed examination of a peripancreatic mass detected incidentally on computed tomography (CT). The differential diagnosis was a neuroendocrine neoplasm (NEN), and a biopsy using EUS-FNA was performed. Histologically, the tumor cells showed proliferation in solid cell nests and were positive for CD56, chromogranin A, and synaptophysin. These findings and the hypervascularity of the tumor on imaging studies were compatible with NEN. Since the imaging studies did not clearly demonstrate the continuity of the tumor with the pancreas, laparoscopic tumor resection without a pancreatectomy and sampling of the enlarged peripancreatic lymph nodes were planned as treatment. The absence of continuity with the pancreas was later confirmed by intraoperative observation, and the resection was carried out as planned. The resected tumor was pathologically considered as NEN at first in agreement with the preoperative diagnosis. However, several histological findings (such as a zelleballen-like growth pattern, pseudo-inclusion, and strong nuclear atypia compared with the cells' proliferative ability) were atypical for NEN, and paraganglioma was included in the differential diagnosis. Additional immunostainings of S-100 and AE1/AE3 were performed, leading to the final diagnosis of paraganglioma. Paragangliomas should be included in the differential diagnosis of an intraperitoneal mass of uncertain identity with hypervascularity.

Transient microglial absence assists postmigratory cortical neurons in proper differentiation.

In the developing cortex, postmigratory neurons accumulate in the cortical plate (CP) to properly differentiate consolidating subtype identities. Microglia, despite their extensive surveying activity, temporarily disappear from the midembryonic CP. However, the mechanism and significance of this absence are unknown. Here, we show that microglia bidirectionally migrate via attraction by CXCL12 released from the meninges and subventricular zone and thereby exit the midembryonic CP. Upon nonphysiological excessive exposure to microglia in vivo or in vitro, young postmigratory and in vitro-grown CP neurons showed abnormal differentiation with disturbed expression of the subtype-associated transcription factors and genes implicated in functional neuronal maturation. Notably, this effect is primarily attributed to interleukin 6 and type I interferon secreted by microglia. These results suggest that "sanctuarization" from microglia in the midembryonic CP is required for neurons to appropriately fine-tune the expression of molecules needed for proper differentiation, thus securing the establishment of functional cortical circuit.