Differential regulation of brain-derived neurotrophic factor messenger RNAcellular expression in the adult rat visual cortex

In this study, we report a comparative analysis of the distribution of brai n-derived neurotrophic factor messenger RNA in the binocular primary visual cortex of rats analysed at the end of the critical period for monocular de privation (postnatal day 35) and during adulthood (postnatal day 90). High- resolution non-isotopic ia situ hybridization coupled with Nissl staining a llowed to determine the relative number of neurons expressing brain-derived neurotrophic factor messenger RNA. In postnatal day 90 rats, the relative number of neurons positive for brain-derived neurotrophic factor messenger RNA significantly decreases in layer II/III with respect to postnatal day 3 5 animals, being constant in all the other cortical layers. Moreover, we de monstrate that dark rearing for 22 days, starting from postnatal day 90, de termines: (i) a decrease of the overall level of brain-derived neurotrophic factor messenger RNA with a consequent reduction of labelling intensity in all cells throughout cortical layers II-VI; (ii) an increase of cell numbe rs expressing brain-derived neurotrophic factor messenger RNA in layers IV and V; and (iii) a decreased intensity of staining for brain-derived neurot rophic factor messenger RNA in dendrites after dark rearing. A re-exposure to light for 2 h after the period of darkness almost restores the number of brain-derived neurotrophic factor RNA-positive neurons. We conclude that t he maturation of brain-derived neurotrophic factor messenger RNA in neurons of layer II/III goes beyond postnatal days 35-40, which can be considered the end of the critical period [Fagiolini M. et al. (1994) Vis. Res., 34, 7 09-720]. Moreover, we show that the cellular expression of brain-derived ne urotrophic factor messenger RNA is regulated by light in adult rats as well as during development. (C) 1999 IBRO. Published by Elsevier Science Ltd.