Terahertz pulses induce segment renewal via cell proliferation and differentiation overriding the endogenous regeneration program of the earthworm Eisenia andrei

Abstract

Terahertz (THz) irradiation of excised Eisenia andrei earthworms is shown to cause overriding of the genetically determined, endogenously mediated segment renewing capacity of the model animal. Single-cycle THz pulses of 5 µJ energy, 0.30 THz mean frequency, 293 kV/cm peak electric field, and 1 kHz repetition rate stimulated the cell proliferation (indicated by the high number of mitotic cells) and both histogenesis and organogenesis, producing a significantly higher number of regenerated segments. The most conspicuous alteration in THz-treated animals was the more intense development of the new central nervous system and blood vessels. These results clearly demonstrate that THz pulses are capable to efficiently trigger biological processes and suggest potential applications in medicine.

Fig. 1.

Flowchart of the tail segments removal and regeneration in the earthworm showing the THz radiated body part.

Fig. 2.

Scheme of the irradiation setup. The E. andrei specimens of Group G were placed into the green laser beam. The specimens of Group T were placed into the focus of the THz beam. In this case the components within the green box were removed from the setup. DM: dichroic mirror, λ/2: half-wave retardation plate, OAP: off-axis parabolic mirror, EFL: effective focal length. The bottom left inset shows a photograph of an anaesthetized earthworm at the THz irradiation position.

Fig. 3.

(a) Image of the THz beam spot at the sample location. The inset in the top right shows in side view the nominal position of the Eisenia andrei sample along the x direction. (b) Measured temporal dependence of the THz electric field. The inset shows the amplitude spectrum calculated by Fourier transformation of the waveform.

Fig. 4.

Anatomical characteristics of the segments in freshly operated animals (a,b), and in the sixth postoperative hour (c,d). Note that in the freshly cut segment, a quick contraction of the body wall can be seen, whereas, in the 6^th postoperative hour, the fusion of the body wall and the midgut can be observed, forming a new internal opening. Abbreviations: mg - midgut, mg*: midgut is covered by thin layer of blast cells, s: segment, arrowheads label contracting body wall in (a,b), the arrow lines label the fusion of the tissues of body wall and midgut (c,d).

Fig. 5.

Comparison of the regenerated segment number of the control group (a,b) and THz-irradiated group (c,d) worms on the 7^th (a,c) and on the 21^st (b,d) postoperative day. Abbreviations: s: operated segment, s*: regenerating segments on the first postoperative week, Arabic numerals: regenerating segments on the third postoperative week, arrowheads: anus.

Fig. 6.

Kinetics of the segment regeneration in control (sham-exposed) and green light or THz irradiated E. andrei earthworms. Data represent mean ± SEM (n=45, *: p < 0.05, **: p < 0.01).

Fig. 7.

Histological characteristics of the regenerated segments of control (a), and THz-irradiated earthworms (b-e) on the 14^th postoperative day. Since group G animals are characterized by the same histological alterations than group C ones their sections are not presented in the figure. Abbreviations: ovnc: old ventral nerve cord, rvnc: regenerated ventral nerve cord, obw: old body wall, rbw: regenerated body wall, d: dissepiment, omg: old midgut muscular tissue rmg: regenerated midgut muscular tissue, bv: blood vessel, arrows: mitotic cells, circles: old epithelial body layer, stars: new epithelial layer.