5-HT2a receptors in the rabbit retina: Potential presynaptic modulators

Three 5-HT receptors have been implicated in retinal processing but positiv e 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-HT2a-in the retina, and immunohistochemical techniques were used to localize the receptor in the re tinal network. Reverse transcription polymerase chain reaction (RT-PCR) tec hniques were used to identify a segment of the rabbit 5-HT2a gene; a 422 ba se fragment was identified, cloned, and sequenced. The fragment shows a hig h degree (ca. 90%) of nucleotide sequence identity with the 5-HT2a receptor gene from other mammals. 5-HT2a immunoreactivity was seen in both the inne r and outer plexiform (synaptic) layers of the retina. Using cell-type-spec ific markers, the 5-HT2a immunoreactivity was shown to be on the terminals of photoreceptor and rod bipolar cells. This association of 5-HT2a receptor s with these two synapses suggests that serotonin may be a modulator of syn aptic function in the retina.