Electrophysiological correlates of rapid escape reflexes in intact earthworms, Eisenia foetida. I. Functional development of giant nerve fibers during embryonic and postembryonic periods

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Abstract
Grids of recording electrodes etched onto printed circuit boards were used for noninvasive recording of medial (MGF) and lateral (LGF) giant nerve fiber spikes in developing earthworms, Eisenia foetida. Stereotyped patterns of throughconducted giant fiber spikes, evoked by light tactile stimulation, were first detectable in the normal crawling embryonic stage and continuned to be detectable throughout postembryonic development. Giant fiber spiking activity in normal crawling embryos was accompanied by stereotyped muscle activity and rapid escape withdrawal, suggesting that giant fiber reflex pathways are functionally intact before the worm hatches. For both the MGF and LFG, several age-de-pendent changes were noted, including the following: increases in spike conduction velocity, increases in giant fiber diameter, and decreases in spike duration. The MGF conduction velocity in normal crawling embryos was 1.1–1.6 m s−1 (6–7 μm diameter) and increased to 7.0–8.5 m s−1 (20–25 μm diameter) by 60 days after hatching. The LGF conduction velocity in normal crawling embryos was 0.7–1.1 m s−1 (2.5–4.0 μm diameter) and increased to 4.0–5.5 m s−1 (8–14 μm diameter) by 60 days after hatching. During postembryonic development MGF and LGF conduction velocities were linearly related to fiber diameter.