SEROTONIN RECEPTORS MODULATE ROD SIGNALS - A NEUROPHARMACOLOGICAL COMPARISON OF LIGHT-ADAPTED AND DARK-ADAPTED RETINAS

Previous physiological studies have shown that serotonin (5-HT) recipr ocally modulates ON and OFF channels in the mammalian retina. This stu dy was undertaken to determine if the serotoninergic system is exclusi vely associated with the rod pathway. We tested drugs specific to 5-HT 3 receptor, a serotonin-gated ion channel, in both dark- and light-ada pted retina. Consistent with previous studies, we demonstrated that 5- HT3 receptors modulate the light-evoked responses of ganglion cells in the dark-adapted state, Moreover, we have extended these prior studie s and shown that activation of the 5-HT3 receptor is capable of comple tely blocking the light-evoked response of OFF-center cells whereas in activation of the 5-HT3 receptor is capable of completely blocking the light-evoked responses of ON-center cells. In contrast, in light-adap ted retinae, serotonin agents failed to have any effect on retinal pro cessing. These data suggest that the serotoninergic system in retina i s (1) specifically associated with rod-related pathways; and (2) exert s a powerful modulatory force over information transfer in the retina. Together these observations suggests that serotonin plays an importan t physiological role in modulating retinal processing.