Somatostatin modulates dopamine release in rat retina

The aim of the present study was to determine the possible role of somatostatin as a modulator of dopamine release in rat retina. Basal release of dopamine, and how this is influenced by somatostatin receptor (sst) selective ligands, was examined ex vivo in rat retinal explants. Dopamine levels were quantified by high-pressure liquid chromatography (HPLC) with electrochemical detection. Basal levels of dopamine were measured over 120 min of tissue incubation and found to be 1.17 ± 0.35 ng/ml. Somatostatin (10−6, 10−5, 10−4 M) increased dopamine levels in a concentration-dependent manner, while the sst2 antagonist CYN154806 (10−4 M) reversed its actions. BIM23014 (sst2 agonist) increased dopamine levels in a statistically significant manner only at the concentration of 10−5 M. The sst1 agonist L797.591 (10−5, 10−4 M) also increased dopamine levels, while activation of the sst3 receptor (sst3 agonist, L796.778, 10−4 M) had no effect. These data substantiate a neuromodulatory role for sst1 and sst2 somatostatin receptors in the retina and show for the first time somatostatin's influence on dopamine release.