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Identification of magnetically responsive neurons in the marine mollusc Tritonia diomedea

John H. Wang^*, Shaun D. Cain and Kenneth J. Lohmann

Department of Biology, University of North Carolina, Chapel Hill, NC, 27599-3280, USA

View larger version (45K): [in a new window]   Fig. 1. The dorsal surface of the central nervous system of Tritonia diomedea showing the location of the bilaterally symmetric, visually identifiable neurons: left pedal 6 (LPd6), right pedal 6 (RPd6), left pedal 5 (LPd5) and right pedal 5 (RPd5). L, left; R, right; PdN, pedal nerve; CeN, cerebral nerve; PlN, pleural nerve.

View larger version (15K): [in a new window]   Fig. 2. The electrical responses of LPd6 to an earth-strength magnetic stimulus. (A) The electrical activity of two different LPd6 neurons during initial experiments. The white bar beneath each trace indicates the 20 min baseline period. The gray bars beneath each trace indicate the 26 min period in which the magnetic field was rotated 60° every minute (see text for details). The first gray bar represents the first 6 min while the subsequent gray bar represents the last 20 min of the magnetic stimulus (the period when data was collected). Action potentials are between 90 and 100 mV in amplitude. (B) Summary of results from initial magnetic experiments (see text). The numbers of action potentials during the baseline period and during the last 20 min of the stimulus period are plotted. Values are means ± S.E.M. (N=11).

View larger version (27K): [in a new window]   Fig. 3. Electrophysiological recordings of LPd6 from three different animals (A—C) during magnetic treatments (Ai,Bi,Ci) and during control treatments (Aii,Bii,Cii) in which the magnetic field was not changed. The bars beneath the magnetic treatment traces follow the convention in Fig. 2. The white bar beneath the control treatment indicates that the magnetic field remained unchanged. Action potentials are between 90 and 100 mV.

View larger version (10K): [in a new window]   Fig. 4. Summary of results from magnetic stimulus treatments and control treatments in which the magnetic field was not changed (see text). The change in action potentials between the baseline period and the magnetic stimulus period or the control period are plotted. Values are means ± S.E.M. (N=10).

View larger version (23K): [in a new window]   Fig. 5. Electrophysiological recordings of RPd6 from two different animals showing that this cell responds to rotations of the magnetic field with increased spiking. The bar beneath the traces follows the convention in Fig. 2.

View larger version (31K): [in a new window]   Fig. 6. Electrophysiological recordings from three cells (LPd1, RPd9, and an unidentified LPd neuron) that do not respond to rotations of the magnetic field. The third trace is from a small (50 µm) left pedal neuron located anterior of the LPdN2 trunk. The bars beneath the traces follow the conventions in Fig. 2.

View larger version (49K): [in a new window]   Fig. 7. Simultaneous electrophysiological recording of Pd6 and Pd5 neurons during a single 60° rotation. The white bar indicates a 15 min baseline before the magnetic field was rotated 60° clockwise. The arrow shows the point at which the field was rotated (see text for details). Action potentials are between 90 and 100 mV.

View larger version (22K): [in a new window]   Fig. 8. Simultaneous intracellular recording of LPd6, RPd6, LPd5 and RPd5 showing synchronous postsynaptic potentials over time.

View larger version (118K): [in a new window]   Fig. 9. Morphology and anatomy of Pd6 neurons. (A) Cobalt fill of LPd6 showing the large soma and primary neurite within the left pedal ganglion. Branches from the LPd6 primary neurite enter left pedal nerve 1 (LPdN1) and left pedal nerve 2 (LPdN2). Scale bar, 300 µm. (B) Cobalt fill of RPd6 showing branches from the primary neurite entering right pedal nerve 1 (RPdN1) and right pedal nerve 2 (RPdN2). Scale bar, 350 µm. (C) A schematic diagram of the innervation pattern LPdN1 and LPdN2 showing that these two nerves innervate the anterior regions of the foot. LPdN1 innervates the most anterior region of the foot, while LPdN2 innervates a more posterior region. There was little or no overlap between the areas of the foot innervated by the two nerves.

View larger version (13K): [in a new window]   Fig. 10. Action potential propagation in LPd6 through LPdN1 and LPdN2. Single units corresponding to LPd6 were identified in LPdN1 and LPdN2 (see text for details) (A,B) Simultaneous intracellular (LPd6) and extracellular (LPdN1 or LPdN2) recordings show spontaneous action potentials occurring in the cell soma before being recorded by the extracellular electrode.

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