Testosterone stimulated the expression of BDNF and its potential target genes in the HVC of female European robins. Sagittal sections of control (left panels) and testosterone-treated (right panels) female robins were hybridized with radioactive antisense-probes for BDNF (brain-derived neurotrophic factor), and potential target genes of BDNF including the ionotropic glutamate receptor GRIN2A, HOMER1 that binds to metabotropic glutamate receptors and SV2B (synaptic vesicle glycoprotein 2b), respectively. Hybridized sections were exposed to an autoradiography film and the resulting autoradiographic images were scanned for documentation. For both groups images were representative for three (BDNF probe) and two birds (other probes), respectively. White arrows point to HVC.