IMMUNOHISTOCHEMICAL LOCALIZATION OF DOPAMINE D-1 RECEPTORS IN RAT RETINA

We have localized the dopamine D-1 receptor in rat retina using a subt ype-specific monoclonal antibody. Immunolabelling can be detected in t he inner and outer plexiform layers and in a number of cells in the in ner nuclear layer. In the inner plexiform layer, labelled processes fo rm four distinct horizontal bands and a series of patches. In order fu rther to characterize the labelling pattern of the D-1 receptor antibo dy, double-labelling experiments were performed with antibodies agains t population-specific neuronal markers in the retina, Antibodies again st tyrosine hydroxylase, choline acetyltransferase, calretinin, calbin din, the glutamate transporter GLT-1, protein kinase C, recoverin and parvalbumin were co-applied with the D-1 receptor antibody. With these cell markers we demonstrate that horizontal cells, at least three typ es of cone bipolar cells and a small number of amacrine cells are immu nolabelled for the D-1 receptor, In the inner plexiform layer, process es labelled by the D-1 receptor antibody are co-stratified with proces ses labelled by the GLT-1 antibody, D-1 receptor-labelled processes ar e not co-localized with the processes of amacrine cells and ganglion c ells labelled by antibodies against tyrosine hydroxylase, choline acet yltransferase or calretinin, Our results indicate that dopamine D-1 re ceptors are localized predominantly to horizontal cells and cone bipol ar cells. Furthermore, the spatial disparity between dopaminergic proc esses and the site of the majority of D-1 receptors supports the idea that in the retina dopamine acts as a neuromodulator that diffuses thr ough extracellular space. The localization of D-1 receptors to a numbe r of identified cell types enables future physiological work to be dir ected towards specific synaptic circuits within the retina.