IMMUNOHISTOCHEMICAL LOCALIZATION OF CALRETININ IN THE RAT LATERAL GENICULATE-NUCLEUS AND ITS RETINOGENICULATE PROJECTION

In the present study, we examined the distribution of calretinin-immunoreactive neuronal cell bodies and fibers in the lateral geniculate nucleus of the rat. In normal rats, clusters of immunoreactive cell bodies were found in: (i) the rostral portion of the ventral lateral geniculate nucleus pars medialis (VLGM), (ii) the intergeniculate leaflet (IGL), (iii) the intermediate region between the VLGM and the ventral lateral geniculate nucleus pars lateralis (VLGL), (iv) the caudomedial portion of the VLGM, and (v) the caudolateral portion of the VLGM. In the dorsal lateral geniculate nucleus (DLG), immunoreactive cell bodies were rarely observed. After uni- or bilateral eye enucleation, no significant alteration in the morphological features or distribution of immunoreactive cell bodies was detected in the lateral geniculate nucleus. In normal rats, immunoreactive fibers formed dense plexuses in: (i) the DLG, (ii) the external layer of the VLGL, (iii) the internal layer of the VLGL, (iv) the IGL, (v) the caudomedial portion of the VLGM, and (vi) the optic tract. After unilateral eye enucleation, immunoreactive fibers in the external layer of the VLGL and in the optic tract almost totally disappeared on the contralateral side to the lesion. Unilateral eye enucleation caused a significant decrease of immunoreactive fibers in the DLG and in the internal layer of the VLGL, but a substantial number of immunoreactive fibers still remained there. In the IGL and the caudomedial portion of the VLGM, no observable alteration in the distribution of immunoreactive fibers was detected after uni- or bilateral eye enucleation. In conclusion, (i) subpopulations of neurons of the lateral geniculate nucleus are distinguished by the presence of calretinin immunoreactivity, and (ii) calretinin is a chemical component of subpopulations of the contralateral retino-geniculate pathway, which terminate in the DLG and in the external and internal layers of the VLGL.