A transgenic screen and method for screening biological and chemical test substances or molecules for their ability to influence or modulate the production of BDNF in cells, includes a fusion gene having a zebrafish BDNF gene fragment (promoter) and a fluorescent marker gene inserted downstream of the BDNF gene fragment. When the fusion gene is injected into a zebrafish embryo, the BDNF promoter causes the production of fluorescent protein in various cell types. The embryo is exposed to a test substance for determining the effect thereof on the production of the fluorescent marker protein.