GABAergic stimulation regulates the phenotype of hippocampal interneurons through the regulation of brain-derived neurotrophic factor

gamma-Aminobutyric acid (GABA) switches from enhancing to repressing brain-derived neurotrophic factor (BDNF) mRNA synthesis during the maturation of hippocampal neurons in vitro. Interneurons do not produce BDNF themselves, but BDNF enhances their differentiation. Therefore, the question arose whether hippocampal interneurons regulate their phenotype by regulating BDNF expression and release from adjacent cells. The GABA(A) receptor agonist muscimol and BDNF increased the size and neuropeptide Y (NPY) immunoreactivity of hippocampal interneurons. However, GABAergic stimulation failed to increase NPY immunoreactivity in cultures from BDNF knockout embryos. At later developmental stages, when GABA represses BDNF synthesis, treatment with muscimol induced a decrease in cell size and NPY immunoreactivity of interneurons. Interneurons might thus control their phenotype through the regulation of BDNF synthesis in, and release from, their target neurons.