Immunohistochemical characterization of the suprachiasmatic nucleus and the intergeniculate leaflet in the hereditary bilaterally microphthalmic rat.

Immunohistochemical observation was performed in the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) of hereditary bilaterally microphthalmic rats without the optic nerve on both sides. In the microphthalmic rats, volume of the SCN reduced to ca. 70% of the normal and numbers of the vasoactive intestinal polypeptide (VIP)-like immunoreactive (lir) neurons were significantly decreased. Although the arginine vasopressin (aVP)- and the VIP-lir neurons distributed in the dorsomedial and the ventrolateral part of the SCN, respectively, as reported in the normal one, somatostatin-lir neurons, localizing mainly in a border area between the dorsomedial and the ventrolateral region of the normal SCN, were shifted to the ventral part of the SCN in the microphthalmic rats. The ventral part of the SCN was covered with neuropeptide Y (NPY)-lir fibers in both normal and mutant rats. The IGL was hardly delineated cytologically in the lateral geniculate nucleus (LGN) of the mutant rats. NPY-lir neurons were found in the dorsal part of the ventral LGN, in contrast to their even distribution in the normal IGL. These findings suggest that the IGL-SCN tract remains in the hereditary microphthalmic rats without the retinal projections.