Tryptophan Hydroxylase and Serotonin Receptors 5-HT1A, 5-HT2A, 5-HT3A, 5-HT4, 5-HT5A, 5-HT6 and 5-HT7 in Frog and Turtle Retina: an Immunofluorescence Study

Serotonin (5-HT) is one of the major monoamines in the brain. It is also found in the retina, a part of the brain, where a subgroup of amacrine cells are considered to be the sole retinal source of 5-HT. The data, obtained so far, about the serotonin receptors’ function are contradictory. Therefore, our aim was to study the distribution of the 5-HT synthesizing neurons and the serotonin receptors from 5-HT1A to 5-HT7 in frog and turtle retinas, using the indirect immunofluorescent method. We found strong Tryptophan hydroxylase immunoreactivity in many amacrine and bipolar cells. Some horizontal, ganglion and glial cells were also stained, as well as a bundle of parallel axons in the proximal retina. All 5-HT receptors were also very well expressed. Our data show that the serotonin retinal sources are more numerous than was previously thought. The great variety of receptors expressed implies that serotonin may fulfill different functions, serving both as neuroand glio-transmitter/modulator.