CHANGES OF SYNAPSIN-I MESSENGER-RNA EXPRESSION DURING RAT-BRAIN DEVELOPMENT

Synapsin I is a synaptic phosphoprotein that is involved in the short- term regulation of neurotransmitter release. In this report we present the first extensive study of the developmental expression of its corr esponding messenger ribonucleic acid (mRNA) by in situ hybridization a nd northern blot analysis in rat brain. Synapsin I mRNA showed pronoun ced differences in expression in different brain regions during postna tal development. The early expression of synapsin I mRNA in ontogeneti cally older regions such as the thalamus, the piriform cortex and the hippocampus coincides with the earlier maturation of these regions, in contrast to its later expression in ontogenetically younger areas suc h as the cerebellum and the neocortex. An intriguing expression patter n was found in the hippocampus. In all hippocampal subregions synapsin I mRNA expression increased from postnatal day (PND) 1 to 17. After P ND 17, however, there was a marked dissociation between persisting hig h expression levels in CA3 and the dentate gyrus and a strong decline in synapsin I mRNA expression in CA1. The persistence of synapsin I in some adult rat brain regions indicates that it plays a part in synaps e formation during plastic adaption in neuronal connectivities.