DARK REARING BLOCKS THE DEVELOPMENTAL DOWN-REGULATION OF BRAIN-DERIVED NEUROTROPHIC FACTOR MESSENGER-RNA EXPRESSION IN LAYER-IV AND LAYER-VOF THE RAT VISUAL-CORTEX

In this study, we describe the distribution of brain-derived neurotrop hic factor messenger RNA in the binocular primary visual cortex of the rat during postnatal development, starting at postnatal day (P) 13. H igh-resolution non-isotopic in situ hybridization combined with Nissl staining were used to quantify the number of cells expressing brain-de rived neurotrophic factor messenger RNA. At P13, most of the cells exp ress brain-derived neurotrophic factor messenger RNA. after eye openin g (P14-P15), the relative number of brain-derived neurotrophic factor messenger RNA-positive cells decreases by a factor of two in layer IV, i.e. that receiving the visual input, and in layer V. To verify the h ypothesis that light could trigger this decrease, pups were kept in co mplete darkness from birth. At P22, pups reared in the dark were kille d and the visual cortex processed for in situ hybridization and northe rn blotting. The results obtained in dark-reared animals prove that li ght deprivation can: (i) decrease the general levels of brain-derived neurotrophic factor messenger RNA, and (ii) increase the relative numb er of brain-derived neurotrophic factor messenger RNA-positive cells i n layers IV and V with respect to control rats. Exposure to light for five days after the period of darkness restored the number of brain-de rived neurotrophic factor messenger RNA-positive cells. We conclude th at the expression of brain-derived neurotrophic factor messenger RNA i n the rat primary visual cortex is regulated during development and th at this process is under the control of visual input. (C) 1998 IBRO. P ublished by Elsevier Science Ltd.