Diurnal metabolism of dopamine in the mouse retina

Dopamine is an important retinal neurotransmitter and neuromodulator that r egulates key diurnal cellular and physiological functions. In the present s tudy we carried out a comprehensive analysis of dopamine metabolism during the light phase of the diurnal cycle and evaluated the presence of diurnal and circadian rhythms of dopaminergic activity in the mouse retina. Steady- state levels of dopamine did not change significantly between the dark phas e (night) and the light phase (day) of the diurnal cycle, nor did they chan ge between early and late points in the day. Dopamine synthesis and utiliza tion, however, revealed significant;alterations between the night and day a nd between early and late time points in the day. A spike in synthesis and utilization was measured immediately after light onset at the end of the ni ght. Subsequently, dopamine synthesis and utilization partially declined an d remained stable throughout the remainder of the day at a level that was s ignificantly higher than that at night. The burst of dopamine synthesis and utilization at the beginning of the day is entirely light evoked and not d riven by a circadian clock. Similarly, there was no circadian rhythm in dop amine synthesis and utilization in mice kept in constant darkness. This dai ly pattern of dopaminergic activity may impact upon a variety of temporally regulated retinal events. Moreover, these data will provide a basis for ev aluating the role of dopamine in retinal pathology in mouse models of retin al degeneration where mutations affect light perception. (C) 2000 Elsevier Science B.V. All rights reserved.