EXPRESSION OF PLATELET-DERIVED GROWTH-FACTOR B-CHAIN IN THE MATURE RAT-BRAIN AND PITUITARY-GLAND

For better understanding of the role of platelet-derived growth factor (PDGF) B-chain in the brain, the expression of PDGF B-chain was studi ed in the mature rat brain at both protein and mRNA levels, by assay o f PDGF B-chain-related mitogenic activity, Northern blot, in situ hybr idization and immuohistochemistry. It was shown that (1) mature rat br ain contained substantial PDGF B-chain-related mitogenic activity, (2) significant amounts of two sizes of transcripts (3.5 kb, widely, and 2.6 kb, weakly and in narrower areas) were expressed in the brain, and (3) the transcripts were localized in ubiquitous neurons by in situ h ybridization, with the strongest signal in hippocampal pyramidal cells , which distribution almost corresponded with that of the immunoreacti ve products. The abundant neuronal localization of the transcript and protein, as well as the neuronal expression of the receptor reported e lsewhere, suggests the role of the growth factor in neuronal cells as a neuronal regulatory and/or trophic agent acting by autocrine loop or by neuron to neuron interaction. However, there was an apparent discr epancy in part, in the distribution between transcripts and immunoreac tivity; that is, transcripts were expressed intensely in the intermedi ate pituitary lobe with only a scattered immunoreactivity, and the opp osite situation was observed in the accessory olfactory nerve and post erior pituitary lobe. This might suggest that PDGF B-chain is transpor ted or secreted in these foci.