5-HT(2a) receptors in the rabbit retina: Potential presynaptic modulators

Three 5-HT receptors have been implicated in retinal processing but positive identification of the receptors and the localization of receptor subtypes in the retina have not been achieved. In this study, molecular techniques were used to identify one class of 5-HT receptor-5-HT(2a)-in the retina, and immunohistochemical techniques were used to localize the receptor in the retinal network. Reverse transcription polymerase chain reaction (RT-PCR) techniques were used to identify a segment of the rabbit 5-HT(2a) gene; a 422 base fragment was identified, cloned, and sequenced. The fragment shows a high degree (ca. 90%) of nucleotide sequence identity with the 5-HT(2a) receptor gene from other mammals. 5-HT(2a) immunoreactivity was seen in both the inner and outer plexiform (synaptic) layers of the retina. Using cell-type-specific markers, the 5-HT(2a) immunoreactivity was shown to be on the terminals of photoreceptor and rod bipolar cells. This association of 5-HT(2a) receptors with these two synapses suggests that serotonin may be a modulator of synaptic function in the retina.