BRAIN-DERIVED NEUROTROPHIC FACTOR AND TRKB RECEPTOR MESSENGER-RNAS INGRAFTS OF CORTEX CEREBRI

Trophic factors are expressed by neurons throughout several areas of t he CNS. We studied the mRNA expression of a member of the neurotrophin family, brain-derived neurotrophic factor (BDNF), and of the two rece ptor transcripts, full-length trkB and truncated trkB in single intrao cular cortex cerebri grafts and in double cortex cerebri grafts. All s ingle as well as double intraocular cortex grafts grew well, reaching a maximal size 4 weeks postgrafting. BDNF mRNA was moderately expresse d in neurons in all intraocular grafts and significantly increased com pared to that in adult rat cortex. Truncated trkB mRNA was strongly ex pressed in neurons and glia, while full-length trkB mRNA was moderatel y expressed only in neurons in the intraocular cortical grafts. The ex pression of the two trkB transcripts in the grafted cortex did not dif fer from that of adult rat cortex. No difference in the expression of mRNAs for full-length or truncated trkB was found between single graft s grown for 4 or 8 weeks or between single and double grafts. Similarl y, no difference in expression of BDNF mRNA in single grafts grown for 4 or 8 weeks was detected. However, BDNF mRNA levels were significant ly lower in grafts which were placed in close contact with previously grafted cortex in the eye chamber. Moreover, contact with a second gra ft led to downregulation of BDNF mRNA in the first graft. We conclude that BDNF mRNA expression is increased in isolated intraocular cortex cerebri grafts when compared to the normal adult rat cortex and abnorm ally high levels of BDNF mRNA in isolated adult cortex tissue can be n ormalized by contact with fetal brain tissue, suggesting a role for BD NF in the developing cortex cerebri. (C) 1994 Academic Press, Inc.