Pii: S0306-4522(01)00003-3

ÐBrain-speci®c cytoplasmic RNA 1 (BC1-RNA), a non-coding RNA polymerase III transcript, is a neuronal RNA that is speci®cally targeted to dendritic domains. It is co-localized with components of the dendritic protein synthetic machinery, and it has been suggested to operate in the regulation of local translation-related processes in postsynaptic microdomains, thus subserving long-term synaptic plasticity in neurons. To probe the relevance of BC1 expression in neuronal plasticity, we have analyzed the expression pattern of BC1 RNA in the rat nervous system. We found that BC1 RNA is expressed by a speci®c subset of neurons (but not by non-neuronal cells) in the central and peripheral nervous system of the adult rat. The BC1 labeling pattern indicates that the subcellular location of the RNA is typically postsynaptic which, depending on cell type, manifests itself in a predominantly somatic, somatodendritic, or dendritic location. Our results further show that BC1-expressing neurons typically co-express the messenger RNA for growth-associated protein-43 (GAP43). Such co-expression was observed in diverse brain areas, including the olfactory bulb, neocortex, and hippocampus, among others. While BC1 RNA was in many neuronal cell types detectable in distal dendritic domains, GAP-43 messenger RNA was typically more restricted to neuronal perikarya. In the mature nervous system, expression of GAP-43 has been described as an intrinsic determinant of predominantly presynaptic plasticity, while BC1 RNA has been implicated in postsynaptic plasticity. Co-expression of both RNAs, as reported here, thus identi®es a distinct subset of neurons in the rat nervous system that exhibits both types of plasticity. q 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.