HISTOLOGICAL-CHANGES DURING DEVELOPMENT OF THE CEREBELLUM IN THE CHICK-EMBRYO EXPOSED TO A STATIC MAGNETIC-FIELD

Few studies have been performed to evaluate the ultrastructural change s that exposure to static magnetic fields (SMF) can cause to the proce sses of cell migration and differentiation in the cerebellum during de velopment. Thus, we have studied the development of the cerebellum in the chick embryo (n = 144) under a uniform SMF (20 mT). All of our obs ervations were done on folium VIc of Larsell's classification. The cer ebella of chick embryos, which were exposed solely on day 6 of incubat ion and sacrificed at day 13 of incubation [short exposure (S)1; n = 2 4], showed an external granular layer (EGL) that was less dense than t he EGL in the control group (n = 24). The molecular layer (ML) exhibit ed a low number of migratory neuroblastic elements. Moreover, the inte rnal granular layer (IGL) was immature, with the cellular elements les s abundant and more dispersed than in controls. In chick embryos expos ed on day 6 of incubation and sacrificed at day 17 (S2; n = 24), the o utstanding feature was the regeneration of the different layers of the cerebellar cortex. The cerebellar cortex of chick embryos exposed con tinuously to an identical held from the beginning of the incubation up to day 13 [long exposure (L)1; n = 24] or day 17 (L2; n = 24) of incu bation showed a higher number of alterations than that of group S1. El ectron microscopy confirmed the findings from light microscopy and, at the same time, showed clear signs of cell degeneration and delay in t he process of neuronal differentiation. This was more apparent in grou ps L1 (100%) and L2 (100%) than in groups S1 (95.4%) and S2 (65.2%). I n conclusion, the present study showed that SMF can induce irreversibl e developmental effects on the processes of cell migration and differe ntiation of the chick cerebellar cortex. (C) 1997 Wiley-Liss, Inc.