Objective A detailed histochemical analysis of chemoarchitecture in the intraretinal (i) part of the rat optic nerve in order to create a new sub-division scheme, and to describe glial structures around the i part.
Background Our previous study showed that the rat optic nerve was divided into 3 parts: i, unmyelinated (u), and myelinated parts. The i part was further divided into 2 subparts: intraretinal parts 1 (i1) and 2 (i2; Neuroscience 2012, P2-a26). However, it is unclear whether chemoarchitecture is homogeneous in each subpart. Moreover, glial structures around the i part are also unclear.
Method Distribution of glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) was investigated by using fluorescent double-labeling immunohistochemistry.
Results The i part was further divided into 2 subparts: i1 and i2. Chemoarchitecture of the i2 part was almost homogeneously organized, while that of the i1 part was not homogeneously organized. Accordingly, the i1 part was divided into two sub-subparts: intraretinal parts 1a (i1a), and 1b (i1b). The density of astrocytic filaments was very high in the i2 part, while it was low in the i1a part. It was moderate in the i1b part. GS immunoreactivity was strong-to-moderate in the nerve fiber layer of the retina (NFL), and was weak in the i1a and i1b parts. Very weak GS immunoreactivity was detectable in the i2 part. As for glial structures around the i part, the inner limiting membrane of the optic nerve head [Elschnig] (ilm) was observed on the i part and on the medial-most part of the NFL. In addition, a high concentration of the intermediary tissue (hci) was seen beneath the surface of the optic nerve at the border between the i and u parts. Astrocytic filaments were densely packed and strongly GFAP-immunoreactive in both the ilm and hci. Weak GS immunoreactivity was observed in the ilm and hci.
Conclusion We created a new sub-division scheme in the i part which was divided into 3 subparts: i1a, i1b, and i2. Moreover, we described 2 glial structures around the i part: ilm and hci. The present study may help perform pathological analysis of rodent models of human optic nerve diseases such as glaucoma.