Nicotinamide Adenine Dinucleotide Phosphate-Diaphorase (NADPH-d) expressing neurons in the retina of golden hamsters have been identified to be a subset of amacrine cells that provide a major source of Nitric Oxide (NO) in retina. This subset of amacrine cells in mouse retina was recently proved to contain the circadian clock gene Per1 (D.Q. Zhang, T. Zhou, G.X. Ruan, D.G. McMahon, Circadian rhythm of Period 1 clock gene expression in NOS amacrine cells of the mouse retina, Brain Res., 1050 (2005) 101-109). However, it remains unknown whether these clock-related NADPH-d amacrine cells can be regulated by light stimulation and thus synchronized to ambient day/night cycle. A previous study has reported that NADPH-d expressing amacrine cells in postnatal hamsters exhibited a surge after eye-opening (D. Tay, Y.C. Diao, Y.M. Xiao, K.F. So, Postnatal development of nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons in the retina of the golden hamster, J. Comp. Neurol., 446 (2002) 342-348) suggesting a possible effect of light on the NADPH-d amacrine cells. In order to further reveal the relationship between NADPH-d amacrine cells and light stimulation, the present study focuses on the changes of the expression of NADPH-d in the retina of postnatal hamsters reared in completely deprived light conditions. Prior to eye opening, P12 hamster pups were subjected to either bilateral eyelid suturing or dark rearing. On P28 a subgroup of light deprived hamsters was returned to lighting conditions and the expression of NADPH-d activities in the retina was assessed. In hamsters reared in the 12:12 light-dark cycle, the number of NADPH-d amacrine cells in the ganglion cell layer (GCL) increased right after eye-opening and reached the adult level gradually. However, hamsters subjected to both bilateral eyelid suturing and dark rearing, the number of NADPH-d amacrine cells in GCL was maintained at a low level but increased again upon returning to the 12:12 light-dark condition. In contrast, the number of NADPH-d expressing amacrine cells in the inner nuclear layer (INL) remained low and unaltered regardless of the lighting environment. This study demonstrates that there are two subpopulations of NADPH-d expressing amacrine cells with respect to different locations in the retina of hamsters. Different from those in INL, the NADPH-d amacrine cells in GCL of postnatal hamsters are dependent on the lighting environment implicating that these clock-related amacrine cells and the production of NO might be under a modulation of light stimulation.