[Calcium-binding proteins and cytochrome oxidase activity in the turtle optic tectum characterzing the visual...

Using immunohistochemistry and tracer technique, we studied in the optic tectum of turtles (Emys orbicularis and Testudo horsfieldi) the distribution of CaBPr (parvalbumin, PV, calbindin, CB, calretinin, CR) before and after horseradish peroxidase delivery into nucleus rotundus (Rot). In parallel, activity of cytochrome oxidase (CO) was studied. In the main link of the tectofugal visual pathway (the central gray layer, SGC) in the both chelonian species rare PV-ir, as well CB- and CR-ir neurons were found to vary significantly both in the number and the immunoreactivity degree of their bodies and dendrites. The superficial (SGFS) and deep periventricular (SGP) tectal layers, on the contrary, contained numerous cells immunoreactive to all three CaBPr in different quantitative proportions. Only a small part of the retrogradely labeled tectorotundal neurons contained PV, CB or CR. Very large PV-ir neurons were not retrogradely labeled; by their morphological characteristics, they corresponded to efferent neurons with descending projections. SFC neurons of two chelonian species differed in the degree of CO activity. In SGFS, dense immunoreactivity of neuropil to all three CaBPr and the high CO activity were observed in both species with some differences in sublaminar distribution for every of proteins. Peculiarities of distribution of CaBPr-ir and of CO activity in various segments of SGC neurons are discussed with respect to laminar organization of the turtle tectum and to patterns of its retinal innervations. It was proposed that in projectional tectorotundal SGC neurons, the studied CaBPr are concentrated mainly in their distal dendrites contacting with retinal afferents in the superficial retinorecipient tectal layer.