A phase advance of the light‐dark cycle stimulates production of BDNF, but not of other neurotrophins, in the adult rat cerebral cortex: association with the activation of CREB

Abstract

Circadian variation in the expression of brain-derived neurotrophic factor (BDNF) indicates that BDNF is involved in the regulation of diurnal rhythms in a variety of biological processes. However, it is still unclear which brain regions alter their BDNF levels in response to external light input. Therefore, in selected brain regions of adult male rats, we investigated diurnal variation, as well as the effects of a single eight-hour phase advance of the light-dark cycle, on the levels of BDNF and of other neurotrophins. The cerebellum, hippocampus and cerebral cortex containing visual cortex (VCX) showed diurnal variation in BDNF protein levels and the VCX also in NT-3 levels. In the VCX and the region containing the entorhinal cortex and amygdala (ECX), BDNF protein levels were increased 12 h after the phase advance, while BDNF mRNA levels were increased significantly in the VCX and slightly in the ECX after 4 h. After one week, however, BDNF protein levels were reduced in eight brain regions out of 13 examined. BDNF levels in the ECX and VCX were significantly different between light rearing and dark rearing, while a hypothyroid status did not produce an effect. Cyclic AMP responsive element-binding protein (CREB), a transcription factor for BDNF, was greatly activated by the phase advance in the ECX and VCX, suggesting the existence of CREB-mediated pathways of BDNF synthesis that are responsive to external light input.