IMMUNOHISTOCHEMICAL STUDY AND AN ELECTRON-MICROSCOPIC OBSERVATION OF THE NUCLEUS OF THE OPTIC TRACT IN THE RAT

In the present study, gamma aminobutyric acid (GABA)-positive cells an d terminals were detected in the nucleus of the optic tract (NOT) in t he rat. However, GABA-positive cells in the NOT receiving projections directly from retinal ganglion cells could not be identified. To deter mine the role of GABA in the projection from the retinal ganglion cell s to the NOT, we used electron microscopy to observe this nucleus of a rat in which one eyeball had been removed. In the nerve synapse bindi ng region of the NOT on the side opposite to the enucleated eyeball, t he symmetrical and asymmetrical types were recognized; the ratio betwe en the two was the same as before the eyeball was enucleated. From the se results, we conclude that the inhibitory axon terminals in the NOT do not have GABA activity. The GABA-positive cells seem to act indirec tly as intrinsic interneurons, when processing or transmitting the inf ormation from the retina to the inferior olivary nucleus.