Administration of FGF-2 to embryonic mouse brain induces hydrocephalic brain morphology and aberrant differentiation of neurons in the postnatal cerebral cortex

Fibroblast growth factor-2 (FGF-2) was injected into mouse cerebral ventricles at embryonic day (E) 14 in utero and its effects on developing brain morphology and expression of various cell- or differentiation-associated protein markers in the cerebral cortex were examined. High doses of FGF-2 (200 or 300 ng) caused encephalic alternations such as deformation of the calvarium, enlargement of the ventricular spaces, and thinning of the cerebral cortex. There was no gross abnormality in the alignment of the cerebral neuronal layers, however, both cell number and cell density of the upper layers (II/III) and the lower layers (IV-VI) of the cerebral cortex were increased. Brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase, nestin, and microtubule-associated protein 2 were aberrantly or ectopically expressed in the deep areas of the cerebral cortex. A substantial number of these cells coexpressed these antigens. These observations demonstrate that a subpopulation of neurons in the cortical deep layer abnormally differentiated or partly sustained their immature state following a single administration of FGF-2 at E14. Developmental analysis of localization of BDNF-positive cells suggested that the abnormality started around P5. Furthermore, cell migration was not affected by FGF-2 administration. FGF-2 seems to play predominant roles in the proliferation of neuronal precursors and in neuronal differentiation in the developing mouse cerebral cortex even at relatively late stages of brain neurogenesis.