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First published online February 6, 2004
Journal of Experimental Biology 207, 1043-1049 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00864

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Identifiable neurons inhibited by Earth-strength magnetic stimuli in the mollusc Tritonia diomedea

John H. Wang^1,*, Shaun D. Cain² and Kenneth J. Lohmann¹

¹ Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
² Friday Harbor Laboratories, University of Washington, Friday Harbor, Washington 98250, USA

View larger version (41K): [in a new window]   Fig. 1. Diagram of the central ganglia of Tritonia diomedea indicating the location of the identifiable neurons LPd7, RPd7, LPd6, RPd6, LPd5 and RPd5. L/R, left/right; Ce N, cerebral nerve; Pd N, pedal nerve; Pl N, pleural nerve.

View larger version (44K): [in a new window]   Fig. 2. Representative electrophysiological recordings of LPd7 from three different animals during control treatments (Ai–Ci) and magnetic treatments (Aii–Cii). Traces in the same row (A–C) are from the same animal. Action potentials are between 90 and 100 mV in amplitude. The brackets beneath each trace indicate the 15 min baseline period and the 30 min control or magnetic stimulus period.

View larger version (11K): [in a new window]   Fig. 3. Summary of LPd7 responses during control treatments (in which the magnetic field was not changed) and magnetic stimulus treatments (see text). (A) Results from control treatments. Bar graphs indicate the mean spike frequencies during the baseline and control periods (no significant difference; Wilcoxon Signed Ranks Test, P>0.30, N=9). (B) Results from the magnetic stimulus treatments. Bar graphs indicate the mean spike frequencies during the baseline and magnetic stimulus periods (*significant difference, Wilcoxon Signed Ranks Test, P<0.01, N=9). (C) Bar graphs indicate the mean changes in action potentials between the baseline period and the control period or magnetic stimulus period (*significant difference, Wilcoxon Signed Ranks Test, P<0.01, N=9). Values are means ± S.E.M. AP, action potential.

View larger version (21K): [in a new window]   Fig. 4. (A) Electrophysiological recording of RPd7 during a magnetic stimulus treatment. Conventions as in Fig. 2. (B) Recordings of LPd7 (Bi) and RPd7 (Bii) before and after a single 60° clockwise rotation of the magnetic field. The white and black bars indicate a period of 900 s. In both traces, the number of spikes decreased after the 60° rotation. Action potentials are between 90 and 100 mV in amplitude.

View larger version (27K): [in a new window]   Fig. 5. Simultaneous intracellular recordings of LPd5, LPd6 and LPd7 neurons during a magnetic stimulus treatment. Action potentials are between 90 and 100 mV in amplitude. Conventions as in Fig. 2. Spiking in LPd5 and LPd6 increased in response to the magnetic stimulus while spiking in LPd7 decreased. (B) Representative simultaneous intracellular recordings of LPd5, LPd6 and LPd7 showing common postsynaptic potentials (PSPs). The first two vertical lines indicate times at which common synaptic input occurred in all three neurons. Subsequent vertical lines indicate times at which synchronous PSPs occurred in LPd5 and LPd6 but not in LPd7. In this and many other recordings, LPd5 and LPd6 shared more synchronous PSPs with each other than with LPd7.

View larger version (132K): [in a new window]   Fig. 6. Cobalt fill of LPd7 showing the large soma and primary neurite within the left pedal ganglion. The primary neurite extends into the left cerebral ganglion before entering left cerebral nerve 3 (LCeN3). At the left pedal–cerebral connective, a small neurite branches off and enters left cerebral nerve 6 (LCeN6). Scale bar, 250 µm.

View larger version (13K): [in a new window]   Fig. 7. Action potential propagation in LPd7 through LCeN3 and LCeN6. Single units corresponding to LPd7 were identified in LCeN3 and LCeN6 (see text for details). Simultaneous intracellular (LPd7) and extracellular (LCeN3 or LCeN6) recordings indicate that spontaneous action potentials were detected in the cell soma before they were detected in the cerebral nerves. Thus, action potentials propagate from the cell body toward the periphery of the animal.