AbstractThe goal of the present study was to elucidate the role of DARPP‐32 (dopamine‐ and cyclic adenosine 3′‐5′‐monophosphate‐regulated phosphoprotein, 32 kDa) in retinal function. We examined mouse and rat retinas for the presence of DARPP‐32 by immunocytochemistry. In both rodent retinas DARPP‐32 immunoreactivity was localized to horizontal and AII amacrine neurons and to the Mueller glial cells, using immuno‐double labelling. Additional unidentified neurons in the amacrine cell layer also showed DARPP‐32 immunoreactivity. Using mice entrained to a 12–12 h light–dark cycle, we found that exposure to light presented during the dark phase significantly enhanced phosphorylation of DARPP‐32 at threonine (Thr) 34 and phosphorylation of the ionotropic glutamate receptor subunit GluR1 at serine (Ser) 845, as measured by immunoblots. However, light also increased Ser 845‐GluR1 phosphorylation in DARPP‐32‐knockout mice. When a dopamine D1 receptor antagonist was injected into the eye prior to light exposure, phosphorylation of both Thr 34‐DARPP‐32 and Ser 845‐GluR1 was significantly reduced. These data indicate that DARPP‐32 participates in dopamine‐mediated modifications of retinal function. We also tested for a possible circadian rhythm of Thr 34‐ and Thr 75‐DARPP‐32 and Ser 845‐GluR1 expression. No significant circadian rhythm of either DARPP‐32 or GluR1 phosphorylation was found.