Abstract
Abstract: :
Purpose:To investigate whether there is an anatomical pathway from short–wavelength sensitive (S) cones to flat (OFF) midget bipolar cells in the marmoset retina. Methods: Retinae of marmosets (Callithrix jacchus) were fixed with 4% paraformaldehyde in 0.1M PB for 2 or 3 hours. Retinal pieces or horizontal sections were processed for double immunofluorescence with antibodies to CD15 to stain flat midget bipolar (FMB) cells, and an antiserum to S–cone opsin (JH455) to stain S–cones including their pedicles. Some sections were additionally labelled with peanut agglutinin (PNA) coupled to a fluorescent marker to identify the pedicles of all cone types. Sections were analysed using a deconvolution microscope (Zeiss). Results: In all retinae analysed, CD15–labelled FMB cells formed distinct dendritic clusters located opposite M/L–cone but not opposite S–cone pedicles. In peripheral retina, 95 S–cone pedicles were analysed with respect to their connections to FMB cells. Only 22 (23%) of the S–cones contacted FMB cells. In central retina, 285 S–cone pedicles were analysed, of these, 66 (23%) contacted FMB cells. At all eccentricities the contacts made between S–cones and FMB cells were sparse, i.e. only a few FMB dendrites but no clusters were seen to contact S–cone pedicles. Conclusions: Our results suggest that in marmoset retina, S–cones do not provide strong OFF input to the midget–parvocellular pathway. Whether our results indicate a difference in the S–cone connectivity between Old World and New World primates remains to be determined.
Keywords: retinal connections, networks, circuitry • retina: distal (photoreceptors, horizontal cells, bipolar cells) • color vision