Serotonergic Retinopetal Axons in the Monkey Retina

Abstract

Purpose-To describe serotonergic retinopetal axons in monkeys.Methods-Whole macaque and baboon retinas, fixed in 4% paraformaldehyde, were labeled with antisera raised against serotonin (5-HT).Results-Several large-diameter 5-HT-immunoreactive (IR) axons emerged from the optic disk. Most axons ran to the peripheral retina, where they branched extensively. Most terminated in the ganglion cell layer, but a few 5-HT-IR axons terminated in distal inner plexiform or within inner nuclear layer. Some axons branched extensively near the fovea, and a dense plexus of 5-HT-IR axons was also found around the optic disk. Varicose 5-HT-IR axons were also associated with blood vessels, especially in the central retina.Conclusions-Immunoreactive serotonin is present in a distinct population of retinopetal axons in the monkey retina. Receptors for serotonin are present in the primate retinas, and based on physiological studies in other mammals, these retinopetal axons are expected to modulate neuronal activity and regulate blood flow.

The electroretinogram as a method for studying circadian rhythms in the mammalian retina

“…Thus, the most direct route for exerting circadian control of retinal function is via local oscillators. However, the retina receives innervation, and hormonal inputs from the brain, including the SCN itself, providing an opportunity for central clocks to support rhythmicity (Smeraski et al 2004;Gastinger et al 2005Gastinger et al , 2006Korf and von Gall 2006). What then is the balance of central versus local clocks in providing temporal control of this tissue?…”

Olfaction and Vision Meet in the Retina

“…In primates, including man, the number given is no more than 25-30 such axons. These axons and their terminals do, however, spread widely across the retina, contain both histamine and serotonin, and are part of the arousal system that projects axons to many brain areas (Gastinger et al, 2005). The role of these centrifugal axons is not well understood; they are active when an animal is awake, but they also appear to play a role regulating blood vessels and blood flow in the retina.…”

Interactions between the Serotoninergic System and the Ionotropic GABA Receptors in Frog and Turtle Retina: An Immunofluorescent Study

“…Serotonin is also very richly expressed in the retina. In addition to its several retinal sources [7], retinopetal serotoninergic nerve fibers are also present [16,17]. These neurons enter the retina through the optic disc, branch extensively and release serotonin from their numerous varicosities, thus influencing the numerous retinal receptors.…”