Difference in PNA label intensity between short- and middle-wavelength sensitive cones in the ground squirrel retina

Purpose. Peanut agglutinin lectin (PNA) is known for its selective binding to cone cells and to the cone domains of the interphotoreceptor matrix. In the current study, the authors investigated whether there is any difference in PNA binding between color-specific cones of the cone-dominant ground squirrel. Methods. Consecutive serial sections of the retina of Spermophilus tridecemlineatus were reacted alternately with PNA and antivisual pigment antibodies. The PNA labels associated with short- and middle-wavelength- sensitive cones (S-cones and M-cones, respectively) were compared with fluorescent lectin cytochemistry. Results. Although all rod-like cells were left unstained, the cones exhibited a specific lectin label. There was, however, a significant difference between the two cone types; the intensity of the ring-like PNA label in the matrix sheath around S-cones significantly exceeded that of the M-cones. Conclusions. The difference in PNA label intensity indicates a difference in the composition of the matrix sheaths surrounding the two respective cone types. To the authors' knowledge, this is the first report on lectin-cytochemical discrimination of cone matrix sheaths and the first lectin study in the ground squirrel retina leading to the observation that PNA can distinguish the three characteristic photoreceptor types in this animal. In this respect, the rod-like cells of the ground squirrel retina were shown to be no different from rod cells of other species.