Brain-derived neurotrophic factor promotes the differentiation of various hippocampal nonpyramidal neurons, including Cajal-Retzius cells, in organotypic slice cultures.

Brain-derived neurotrophic factor (BDNF) is widely expressed in the central nervous system, where its function is poorly understood. The aim of this study was to investigate the effects of BDNF on the differentiation of hippocampal nonpyramidal neurons using organotypic slice cultures prepared from postnatal rats. The application of BDNF induced an increase in immunostaining for the microtubule-associated protein (MAP)-2 in non-pyramidal neurons of the stratum oriens. BDNF promotes the elongation of the dendrites of these neurons, as demonstrated by analysis after biocytin labeling. Calbindin-D- and calretinin-containing subgroups of nonpyramidal cells in the stratum oriens were responsive to BDNF but not to nerve growth factor, as shown by an increase in the number of neurons immunostained for these proteins. BDNF also induced an increase in neuropeptide Y immunostaining of stratum oriens neurons. In contrast, BDNF had no effect on parvalbumin immunostaining, despite the fact that these cells express the BDNF receptor trkB. In addition, BDNF increased calretinin immunoreactivity in Cajal-Retzius cells situated around the hippocampal fissure. The Cajal-Retzius neurons persisted in slices beyond the time at which they degenerate in vivo. However, BDNF is not required for the survival of these cells, because they also persisted in slices from BDNF knock-out mice. The present results indicate that BDNF exerts an effect on the morphology of stratum oriens nonpyramidal cells and their calcium-binding protein levels. BDNF also regulates the calretinin content of Cajal-Retzius cells but is not necessary for their survival.