The conduction velocity and central projections of retinofugal fibers in the rabbit.

IN anesthetized and paralyzed rabbits, action potentials were elicited antidromically following electrical stimulation of optic tract terminals at the geniculate level (LGN). The conduction velocity spectrum extended from 7 m.s-1 to 34 m.s-1. The distribution of conduction velocities indicated four major modes at 10, 18, 22 and 26 m.s-1. Antidromic compound action potentials exhibited good correlation between the conduction latency and the major modes of the distribution histogram. These results suggest that the rabbit optic tract is composed of four classes of fibers varying in their conduction velocities. The central projections of retinofugal axons were studied with electrical stimulations of the Superior Colliculus (CS) and the LGN while recording from the same optic tract fiber. Antidromic spikes could be elicited from all conduction velocity groups and 71% of axons responded to both sites of stimulation. This finding indicates that most retinofugal fibers branch to and innervate both CS and LGN. Further, there is a tendency for fast-conducting axons to have their receptive fields located eccentrically relative to the optic axis of the eye.