Localization of mRNAs for trkB isoforms and p75 in rat retinal ganglion cells

Brain-derived neurotrophic factor (BDNF) plays an important role in the survival of retinal ganglion cells (RGCs). To better understand the potential role of BDNF receptors in the survival of RGCs, we studied the expression and localization of transcripts for trkB isoforms and p75, using reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization with digoxigenin-labeled RNA probes in the adult rat retina. We found that truncated trkB and p75 were expressed in RGCs, as well as full-length trkB, in the adult rat retina. The localization patterns of full-length and truncated trkB mRNAs suggest that a subpopulation of RGCs expresses both full-length and truncated trkB. The localization pattern of p75 mRNA suggests that it is expressed in a subpopulation of RGCs. Expression of both trkB isoforms in RGCs raises the possibility that truncated trkB lessens BDNF effect on RGCs by forming nonfunctional heterodimers with full-length trkB. This possibility was supported by our observation that apoptosis of RGCs detected by the TUNEL method followed close on the onset of truncated trkB mRNA expression in the ganglion cell layer of the developing rat retina.