Confocal visualization of the effect of short-term locomotor exercise on BDNF and TrkB distribution in the lumbar spinal cord of the rat: The enhancement of BDNF in dendrites?

Locomotor exercise increases neurotrophin BDNF and its receptor TrkB F L expression in the lumbar spinal cord. Involvement of BDNF/TrkB F L in synaptic transmission raises the questions which intracellular compartments are involved in this upregulation and whether exercise leads to redistribution of these proteins related to the duration of exercise. We have investigated the influence of short-term (7 days) locomotor exercise (ST) on intracellular distribution of BDNF and TrkB F L in the rat lumbar spinal cord comparing it with the effects of long-term (28 days) exercise (LT) described earlier. Immunofluorescence (IF) of proteins was analyzed with confocal microscopy. ST exercise caused a redistribution of perikaryonal BDNF IF toward periphery resulting in an increase of dendritic signal. In contrast to an enhancement of perikaryonal BDNF staining following LT, no increase of BDNF IF in cell bodies was observed after ST. An increase of TrkB F L IF in oligodendrocytes was consistent with that caused by LT. The fibers of TrkB F L IF oligodendrocytes surrounding the largest neurons were in close apposition to neuronal membrane. We propose that ST exercise causes (1) BDNF translocation to dendrites and/or local dendritic synthesis to serve increased synaptic activity (2) sensitization of oligodendroglia to BDNF mediated responses.