No abstract

The neural crest is a migratory population of cells that originates from the dorsal neural tube in vertebrates. Recently, the existence of a group of ventrally emigrating neural tube (VENT) cells has been proposed, based upon cell labelling studies in the hindbrain of avian embryos. Like crest cells, these VENT cells have been reported to give rise to numerous cell types. VENT cell emigration is thought to occur after embryonic day (E) 3, when neural crest cell production has ceased. Migration of cells from the ventral neural tube into the periphery was inferred retrospectively after examining numerous embryos harvested at different stages. We have attempted to label VENT cells in vivo by using a green fluorescent protein (GFP) expression vector, electroporated into the ventral neural tube after crest cell migration and before the putative migration of the ventrally localised cells. Because GFP can be visualised strongly in living tissue a few hours after electroporation, the migration of labelled cells within the same embryo can be followed. Fluorescent cells labelled in the mid-hindbrain region were examined in ovo and in explant culture. No GFP-expressing cells were detected emigrating from the ventral neural tube from E3 to E5. Our findings are, thus, in disagreement with those of previous studies, which have indicated the existence of VENT cells in the cranial region.

Methotrexate is reasonably effective in clinical practice as a steroid sparing agent in inflammatory bowel disease. The efficacy in fistulating Crohn's disease justifies its use as an immunomodulator in these patients. Combined azathioprine and methotrexate treatment appears to offer no advantage over methotrexate alone.