RESUMEN
Although serotonin (5-HT) is found in the mammalian retina only at low levels, considerable evidence suggests that it plays a role in visual processing. Pharmacological experiments indicate that numerous receptors for 5-HT are present in the mammalian retina. One of these is the ionotropic 5-HT(3) receptor. So far, two subunits for this receptor have been identified in the nervous system, 5-HT(3A) and 5-HT(3B). Co-expression of these subunits in Xenopus oocytes is sufficient to reconstitute native 5-HT(3) receptor properties. Thus, it is believed that a native neuronal 5-HT(3) receptor is multimeric similar to the related acetylcholine receptor family. To determine whether this receptor is expressed in the mammalian retina, we first performed reverse transcription polymerase chain reaction and first demonstrated the presence of transcripts for both the 5-HT(3A) and 5-HT(3B) receptor subunits. Then using a well-characterized polyclonal antiserum against the 5-HT(3A) receptor subunit, we demonstrated 5-HT(3A) receptor immunoreactivity (IR) in the rabbit, rat, and human retina. This IR was localized specifically to the rod photoreceptor terminals in all three species, suggesting that this receptor may modulate the rod signaling pathway by controlling the output at the rod terminals.
Asunto(s)
Receptores de Serotonina/análisis , Receptores de Serotonina/genética , Células Fotorreceptoras Retinianas Bastones/química , Células Fotorreceptoras Retinianas Bastones/fisiología , Secuencia de Aminoácidos , Animales , Anticuerpos , Clonación Molecular , Mamíferos , Datos de Secuencia Molecular , Hibridación de Ácido Nucleico , Oocitos/fisiología , Reacción en Cadena de la Polimerasa , Pruebas de Precipitina , Conejos , Ratas , Ratas Sprague-Dawley , Receptores Presinapticos/análisis , Receptores Presinapticos/genética , Receptores de Serotonina/inmunología , Receptores de Serotonina 5-HT3 , Especificidad de la Especie , XenopusRESUMEN
Serotonin or 5-hydroxytryptamine (5-HT) is a common neurotransmitter found widely in the nervous system. Here, using RT-PCR, we have identified both the 5-HT(1A) and 5-HT(7) receptor transcripts in the rabbit retina. Furthermore, we found the same two receptors in the rat retina which was previously believed not to have a serotoninergic system. These results confirm previous reports of 5-HT(7) gene expression in retina and together with other biochemical, physiological and anatomical studies, they support the presence of multiple 5-HT receptors in the mammalian retina and suggest that the action of serotonin in the retina may be more complicated than previously believed.
Asunto(s)
ARN Mensajero/metabolismo , Conejos/metabolismo , Ratas/metabolismo , Receptores de Serotonina/genética , Retina/metabolismo , Secuencia de Aminoácidos , Animales , Femenino , Datos de Secuencia Molecular , Ratas Sprague-Dawley , Receptores de Serotonina 5-HT1 , Reacción en Cadena de la Polimerasa de Transcriptasa InversaAsunto(s)
Clonación Molecular/métodos , Hibridación de Ácido Nucleico/métodos , ARN/genética , ARN/aislamiento & purificación , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/métodos , Animales , Biotecnología , ADN Complementario/genética , Pruebas de Precipitina , Sondas ARN , Conejos , Ratas , Receptores de Serotonina/genética , Receptores de Serotonina 5-HT3 , Retina/metabolismo , SolucionesRESUMEN
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-HT2a--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-HT2a 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-HT2a receptor gene from other mammals. 5-HT2a immunoreactivity was seen in both the inner and outer plexiform (synaptic) layers of the retina. Using cell-type-specific markers, the 5-HT2a immunoreactivity was shown to be on the terminals of photoreceptor and rod bipolar cells. This association of 5-HT2a receptors with these two synapses suggests that serotonin may be a modulator of synaptic function in the retina.