Bilateral reorganization of the rat optic tract following enucleation of one eye at birth.

In albino rats with one eye removed at birth (NE rats), electron microscopic studies were made on the optic tract (OT) to count the fibers and to measure their thickness. In addition, experiments were made in NE rats to know the physiological properties of the optic pathway such as conduction velocity, synaptic delay and so on. The number of fibers in the OT of NE rats was compared with that constituting the crossed and uncrossed pathways of normal adult rats. In NE rats the fiber count increased by about 30,000 in the OT ipsilateral to the remaining eye while it decreased by about the same amount in the contralateral OT. The axonal cross section area of OT fibers was measured as an index for fiber thickness. No marked abnormalities were found in the OTs of NE rats with regard to the morphological dimension. Relay cells (P-cells) of the LGN were recorded by electrical stimulation of the optic pathway. The uncrossed projection of NE rats to the LGN was characterized by the following points: (1) P-cells responding to stimulation of the uncrossed fibers were encountered in NE rats much more frequently than in normal adult rats. (2) Synaptic delays assumed to be involved in trans-synaptic activation of P-cells by the uncrossed fibers were calculated at larger values than for P-cells activated by the crossed fibers in NE rats and normally grown rats.