Central projections of Limulus photoreceptor cells revealed by a photoreceptor‐specific monoclonal antibody

Abstract

Studies of lateral, median, and ventral eyes of the chelicerate arthropod Limulus polyphemus (the common American horseshoe crab) are providing important basic information about mechanisms for information processing in the peripheral visual system and for the modulation of visual responses by light and circadian rhythms. The processing of visual information in Limulus brain is less well understood in part because the specific central projections of the various classes of visual neurons are not known. This study describes a mouse monoclonal antibody, 3C6A3, which binds to Limulus photoreceptor cell bodies, their axons, and terminals, but not to any other cell type in the central nervous system. This antibody, and intracellular injection of biocytin, are used to demonstrate the central projections of each type of photoreceptor. Our main conclusions are that: 1) the photoreceptors (retinular cells) of the lateral eye project only to the lamina; 2) the photoreceptors of the lateral rudimentary eye project to both the lamina and medulla; 3) the photoreceptors of the median ocellus project only to the ocellar ganglion; and 4) the photoreceptors of the rudimentary median (endoparietal) eye project to the ocellar ganglion and also into the optic tract. These results, along with previous studies, allow us to infer the projections of the secondary cells. The eccentric cells of the lateral eye project to the lamina, medulla, optic tract, and ocellar ganglion. The arhabdomeral cells of the median ocellus project through the ocellar ganglion and to optic tract to the medulla.

Dissecting a neuron network: FIB-SEM-based 3D-reconstruction of the visual neuropils in the sea spider Achelia langi (Dohrn, 1881) (Pycnogonida)

“…Hence, the pycnogonid visual system is composed of a thickening dorsolateral to the protocerebrum where the nerve fibers from the two eyes of one hemisphere concentrate, a bifurcated visual tract and two successive distinct visual neuropils. This innervation pattern is very similar to that of the eyes in Euperipatoides rowelli (Onychophora) [50] and the median rudimentary eye in Limulus polyphemus (Xiphosura) [51,52]. …”

Wiring a Periscope – Ocelli, Retinula Axons, Visual Neuropils and the Ancestrality of Sea Spiders

“…Deeper knowledge of, e.g., R-cell projections and visual neuropil architecture is missing, hence there is no stable basis on which to compare visual system features among pycnogonids and to those of their putative arthropod outgroups. In Chelicerata other than Pycnogonida, the visual systems of Limulus polyphemus [15],[16],[17] and Cupiennius salei [18],[19], which are important model organisms in the field of visual neuroscience, are especially well studied. In scorpions the only study of the visual neuropils is that of Hanström [13].…”

The visual system of harvestmen (Opiliones, Arachnida, Chelicerata) – a re-examination

“…Furthermore, the second median and the second lateral eye visual neuropils overlap each other; this means that there is a region with axon terminals from both eye types [15, 31]. A similar situation is found in the normal median and lateral eyes of Xiphosura [17, 18, 20], indicating close evolutionary relationships, at least of the visual systems. A chiasma in the median eye visual system is found neither in Pycnogonida, nor in Xiphosura, nor in Scorpiones.…”