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

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 through-conducted giant fiber spikes, evoked by light tactile stimulation, were first detectable in the normal crawling embryonic stage and continued 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-dependent 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 micrometers diameter) and increased to 7.0-8.5 m s-1 (20-25 micrograms 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 micrometers diameter) and increased to 4.0-5.5 m s-1 (8-14 micrometers diameter) by 60 days after hatching. During postembryonic development MGF and LGF conduction velocities were linearly related to fiber diameter.

Electrophysiological correlates of rapid escape reflexes in intact earthworms, Eisenia foetida. II. Effects of food deprivation on the functional development of giant nerve fibers

“…At hatching (day 0) the mean body weight for each group ranged from 4-7 mg. increases in body weight continued after day 56. These patterns of somatic growth were comparable to those obtained in previous studies of normal earthworm development (Neuhauser et al, 1980b;O'Gara, Vining, and Drewes, 1982).…”

“…Fig. 9, O'Gara, Vining, and Drewes, 1982). Therefore, we conclude that although severe levels of food deprivation stunted rates of giant fiber conduction, there was no apparent alteration in the predicted velocity-versus-diameter relationship in these animals.…”

“…Nevertheless, the values for velocity and diameter in these animals appear to fit the predicted velocity-versus-diameter relationship for normally developing animals (O'Gara, Vining, and Drewes, 1982). Therefore, the effect of extreme food deprivation may simply be a stunting of giant fiber diameter.…”

“…Procedures for obtaining these measurements have been described previously (O'Gara, Vining, and Drewes, 1982).…”

Environmental determinants of escape reflex performance in a freshwater oligochaete

“…This was first demonstrated in earthworm giant fibers by Bullock (1951), who noted during twin-pulse electrical stimulation of isolated ventral nerve cords that the second giant fiber spike in a pair of spikes was conducted 10-20% faster than the first. This phenomenon, termed "facilitation of conduction velocity," and hereafter abbreviated FCV, also was observed in vivo by means of non-invasive recordings of giant fiber spiking in earthworms (Drewes et al, 1978;Drewes and McFall, 1980;O'Gara et al, 1982). However, the potential relevance of this unusual phenomenon to oligochaete escape behavior has never been established.…”