Reciprocal changes in the expression of neurotrophin mRNAs in target tissues and peripheral nerves of aged rats

trk receptors are downregulated in both dorsal root ganglion (DRG) and spin al motoneurons of aged rats with behavioral sensorimotor deficits, Here we provide evidence, using reverse transcription-polymerase chain reaction (RT -PCR), of decreased levels of neurotrophin (nerve growth factor, NGF; brain -derived neurotrophic factor, BDNF; neurotrophin-3, NT-3; and neurotrophin- 4, NT-4) mRNAs in target muscles. Moreover, the degree of neurotrophin mRNA decrease in target muscles seems to co-vary with the extent of sensorimoto r disturbances. In contrast, the peripheral nerve of aged rats showed a rec iprocal regulation of neurotrophins, with increased levels of NGF, BDNF, an d NT-4 mRNAs. Taken together, evidence suggest an aging-related attenuation of neurotrophin signaling between target tissues, on one hand, and DRG and motoneurons, on the other, and, furthermore, that target-derived neurotrop hins regulate the expression levels of trk mRNAs in both DRG and motoneuron s. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.