Orexins increase mRNA expressions of neurotrophin-3 in rat primary cortical neuron cultures

Orexins and melanin-concentrating hormone (MCH) as orexigenic neuropeptides are present in the lateral hypothalamus, and their receptors are distributed in the cerebral cortex and hippocampus. In the present study, the regulatory effects of orexin-A, orexin-B and MCH on neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) expressions were examined in primary cortical neuron cultures using quantitative real-time PCR. Both orexin-A and orexin-B on 6-day exposure significantly increased the NT-3 mRNA at concentrations of 0.01, 0.1 and 1 μM. Orexin-A and B at 1 μM led to an increase of twofold or more over the control. However, no such NT-s mRNA increase occurred with exposure to MCH at the same concentrations as orexins. The mRNA expression of BDNF was significantly increased only by orexin-B at 1 μM. These findings suggest that orexins, but not MCH, may be an inducer of NT-3 in the cerebral cortex.