Claudia Di BerardinoSebastián F. EstayAlejandro AlcainoAndrés E. Chávez2026-02-252026-02-252025-03-0410.1186/s40659-025-00594-6https://cris-uv-2.scimago.es/handle/123456789/8601<jats:title>Abstract</jats:title> <jats:sec> <jats:title>Background</jats:title> <jats:p>Serotonin (5-HT) is known to be synthesized and accumulated in the vertebrate retina through the 5-HT transporter, SERT. While manipulation of the serotonergic system has been shown to impact visual processing, the role of 5-HT and SERT as modulators of retinal synaptic function remains poorly understood.</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Using mouse retinal slices, we show that acute application of 5-HT produces a cell-type specific reduction in light-evoked excitatory responses (L-EPSC) in ON–OFF retinal ganglion cells (RGCs), but not in ON RGCs. Similarly, increasing 5-HT tone by acute application of citalopram, a selective 5-HT reuptake inhibitor, also reduces L-EPSC in ON–OFF RGCs while not affecting ON RGCs. Importantly, citalopram-mediated reduction of L-EPSC was absent in ON–OFF RGCs recorded from SERT null retina, highlighting the role of SERT in regulating light-evoked responses in RGCs. The effects of both exogenous and endogenous 5-HT on L-EPSC in ON–OFF RGCs are likely due to a presynaptic reduction in excitatory synaptic strength as 5-HT and citalopram reduced the frequency but not the amplitude of spontaneous excitatory currents (sEPSCs) in ON–OFF RGCs. Moreover, 5-HT and citalopram had no effect on currents elicited by the direct activation of postsynaptic receptors in RGCs by brief application of glutamate in the inner retina.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Altogether these findings indicate that 5-HT modulates excitatory inputs onto RGCs in a cell-type specific manner and highlight that in the adult mouse retina, 5-HT-mediated effects onto RGCs are tightly controlled by the 5-HT transporter SERT.</jats:p> </jats:sec>journal-article