Vole retina is a target for gonadotropin-releasing hormone

Gonadotropin-releasing hormone (GnRH) projections from the terminal nerve to the retina are common in fish, but have not been reported in mammals. However, GnRH fibers have been seen previously in the optic nerves (but not retinas) of rats and monkeys. Using prairie voles, we tested the hypotheses that (1) GnRH-immunoreactive (-ir) neurons project into the optic nerve and (2) the retina expresses GnRH receptor mRNA as determined by reverse transcription-polymerase chain reaction (RT-PCR) combined with Southern blotting. In both adult and postnatal-day-2 voles, GnRH-ir fibers were observed within the optic nerve. In adult voles, GnRH-ir fibers projected only a short distance into the optic nerve compared with the much longer length of projections in neonates. Fibers immunoreactive for GnRH were not seen in the retinas of neonates or adults. However, RT-PCR-Southern blotting demonstrated GnRH receptor expression in the retina of adult voles. This study supports the hypothesis that GnRH has the potential of modulating visual processing in the retina of mammals.