Identification of 5-HT3A and 5-HT3B receptor subunits in mammalian retinae: potential pre-synaptic modulators of photoreceptors

Although serotonin (5-HT) is found in the mammalian retina only at low leve ls, considerable evidence suggests that it plays a role in visual processin g. Pharmacological experiments indicate that numerous receptors for 5-HT ar e present in the mammalian retina. One of these is the ionotropic 5-HT3 rec eptor. So far, two subunits for this receptor have been identified in the n ervous system, 5-HT3A and 5-HT3B. Go-expression of these subunits in Xenopu s oocytes is sufficient to reconstitute native 5-MT3 receptor properties. T hus, it is believed that a native neuronal 5-HT3 receptor is multimeric sim ilar to the related acetylcholine receptor family. To determine whether thi s receptor is expressed in the mammalian retina, we first performed reverse transcription polymerase chain reaction and first demonstrated the presenc e of transcripts for both the 5-HT3A and 5-HT3B receptor subunits. Then usi ng a well-characterized polyclonal antiserum against the 5-HT3A receptor su bunit, we demonstrated 5-HT3A receptor immunoreactivity (IR) in the rabbit, rat, and human retina. This IR was localized specifically to the rod photo receptor terminals in all three species, suggesting that this receptor may modulate the rod signaling pathway by controlling the output at the rod ter minals. (C) 2001 Elsevier Science B.V. All rights reserved.