Electron-dense Material of Nematosomes in Teleost Retinas Has Aboundant Phosphorous Compatible with the Presence of RNA

Abstract

Abstract: : Purpose: Spinules and nematosomes of Horizontal Cells (HCs) are retinal structures exclusive of teleosts fish. Its functions are still not well known today. Nematosomes were larger and more numerous in dark-adapted retinas than in light-adapted ones. Number and size of nematosomes are inverse-correlated with the spinules number. Data suggest that nematosomes should be the source of the electron-dense material observed in spinules and viceverse. In other locations it has been suggested that RNA is a component of electron-dense material of the nematosomes. The aim of this work is to determine the presence of RNA in nematosome electron-dense material. Methods: Micropterus salmoides and Roccus americana were adapted (>2h) to dark at midnight. The retinas were processed for transmission electron microscopy and thin vertical sections were obtained. Using the Electron Spectroscopy Imaging (ESI) methodology we determine the amount of phosphorous (P) atoms in electron-dense material of nematosomes. Results: Electron-dense material in nematosomes presents larger amounts of P similar to that existing in ribosomes and compatible with the presence of ribonucleoproteins (RNP). Also, we observed nematosomel material "traveling" through the dendrites of HCs near cone pedicles. Conclusions: 1) Nematosomes and spinules may be the over-expression of a more general process normally not detectable in other cells. 2) We think that the spinule's electron-dense material is originates in nematosomes, and may represent a RNP storage needed for synapse modulation.

Keywords: plasticity • synapse • retina