Expression of synaptic proteins in the developing rat cerebellum following ionizing radiation

Various proteins regulating neurotransmission release and synaptic vesicle exocytosis have been implicated in axonal elongation and synaptic maturation. In the present study, immunohistochemistry to the presynaptic membrane proteins syntaxin-I and synaptosomal-associated protein of 25 kDa (SNAP-25) synaptic vesicle-associated proteins synaptophysin and synapsin-I and the neuronal maturation and axonal growth-related protein GAP-43, has been carried out in the normal developing cerebellum and following a single dose of ionizing radiation (2 Gy gamma-rays) at postnatal day 1. Our aim has been to learn about the morphological and possible functional modalities that occur during the progression of neuronal connectivity in normal and abnormal development. Expression of all these proteins is associated with the arrival of afferents in the subcortical white matter and with the maturation of the internal granule cell layer and molecular layer during normal development. In addition, SNAP-25 and GAP-43 are strongly expressed in granule cells of the external granule cell layer, thus suggesting that these proteins are involved in cell elongation of granule cells. Apoptosis appears at 3 h and peaks at 6 h following ionizing radiation. Radiation-induced apoptosis in the external granule cell layer produces a transient decrease in the expression of SNAP-25 and GAP-43 in the external granule cell layer. The external granule cell layer recovers at 48 h and external granule cells of proliferating cells also express SNAP-25 and GAP-43, thus indicating that proliferating cells in this layer are equipped with proteins involved in cell elongation. Furthermore, expression of synaptophysin, synapsin-I, syntaxin-I and SNAP-25 is the same in the cerebellum of irradiated and normal rats from this time to adulthood (3 months). These results point to the likelihood that recovery of the cerebellar cortex occurs following a single exposure of ionizing radiation during postnatal development.