Slow potentials in nonspiking optic nerve fibers in the peripheral visual system ofLimulus

Abstract

This study was undertaken to determine whether nonspiking fibers in the peripheral visual system of adultLimulus polyphemus can transmit information to the brain. Light-initiated slow potentials were detected in singly impaled nonspiking fibers in the ventral optic nerve (2–15 mV, 3–16 mm from photoreceptor cell somata), the median optic nerve (8 mV, 15–20 mm from the photoreceptor cell soma, and the lateral optic nerve (28.5 mV, 7–12 mm from the photoreceptor cell soma; 1 mV, about 8 cm from the eye) (Fig. 1, Tables 1, 2). Using the equations for passive conductance along a semi-infinite cable and an assumed value for the magnitude of the voltage at the beginning of the axon (60 mV), space constants of non-spiking fibers in the ventral, median and lateral optic nerves were estimated to be 4–6 mm, 7–10 mm and 8–21 mm, respectively (Table 2). The results of experiments using multiply impaled ventral photoreceptor somata and axons indicate that the decrement in the magnitude of light-initiated slow potentials is greater in the transitional soma-to-axon region than in more distal axonal regions and that decrement of theC2 component of the receptor potential is greater than that of theC1 component (Figs. 2, 3, 4; Table 3). The results suggest it is likely that nonspiking fibers in theLimulus peripheral visual system can transmit information to centrally located optic ganglia via graded slow potentials.