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First published online November 17, 2006
Journal of Experimental Biology 209, 4676-4689 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02556

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Neural control of the velum in larvae of the gastropod, Ilyanassa obsoleta

Oliver R. Braubach, Amanda J. G. Dickinson^*, Carol C. E. Evans and Roger P. Croll

Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, B3H 4H7, Canada

View larger version (79K): [in a new window]   Fig. 1. Anatomy and innervation of ciliated cells on the velum. (A) Lateral view of a velar lobe showing tubulin-like immunoreactivity in cell bodies and cilia along the pre- and post-oral bands. Scale bar, 20 µm. (B) Lateral view of the velum at a slightly deeper focal plane showing details of the pre-oral ciliated cells and a bundle of tubulin-like immunoreactive axons (arrows) at their bases. Scale bar, 20 µm. (C) At higher magnifications, serotonin-immunoreactive fibres and varicosities (arrows) can be seen near the bases of the pre-oral ciliated cells. Scale bar, 10 µm. (D) Lines of varicosities (arrows) exhibit Leu-enkephalin immunoreactivity. Pre-oral cells possess slender nuclei at their bases. Scale bar, 10 µm.

View larger version (113K): [in a new window]   Fig. 2. Immunocytochemical localization of neural elements (green) and F-actin labelling of muscle (red) in the velum. (A) Lateral view of a velar lobe showing 5-HT-immunoreactive axons (green) with varicosities along the muscles and concentrated distally near the pre-oral cells. Scale bar, 30 µm. (B) Lateral view of a velar lobe showing FMRFamide-immunoreactive axons (green) and muscle fibres (red). Scale bar, 30 µm. (C) High magnification of the edge of a velar lobe showing FMRFamide immunoreactive axons (green) and muscle fibbers (red). Scale bar, 25 µm. (D) Lateral view of a velar lobe showing Leu-enkephalin-immunoreactive axons (green) and muscle fibres (red). Scale bar, 30 µm. (E) Lateral view of a velar lobe showing TH-like immunoreactive cells and axons. Scale bar, 10 µm. (F) High magnification of the edge of a velar lobe showing TH-like immunoreactive cells and axons and cells containing pre-oral and post-oral cilia. Scale bar, 10 µm.

View larger version (8K): [in a new window]   Fig. 3. Effects of transmitters on pre-oral ciliary beating. (A) Under control conditions, cilia beat at approximately 8-9 Hz and all three phases are evident. (B) Perfusions of 10-6 mol l-1 serotonin caused a threefold increase in ciliary beat frequency (CBF). Different phases are no longer evident in this recording (but see Fig. 5). (C) Perfusion of 10-7 mol l-1 dopamine slowed the ciliary beat frequency. All three phases of activity are apparent, but additional, irregular peaks (arrows) were also observed. (D) Perfusion of 10-7 mol l-1 Leu-enkephalin did not alter ciliary beat frequency but change the waveform of the beat cycle, with the normal three-phase form no longer evident. Scale bar, 150 ms.

View larger version (12K): [in a new window]   Fig. 4. Summarized effects of putative transmitters (serotonin, dopamine, norepinephrine, FMRFamide and Leu-enkephalin) at different concentrations (10-6 mol l-1 to 10-9 mol l-1) on ciliary beat frequency (CBF) of the pre-oral cilia. Asterisks indicate significant difference when compared to the respective control groups (P<0.001).

View larger version (5K): [in a new window]   Fig. 5. Serotonin affects both the frequency and the waveform of the ciliary beat as seen at higher temporal resolution. (A) Control trace of cilia in seawater without serotonin. Both the phases 1 and 2 are evident. The subsequent phase 3 is not shown. Perfusion with 10-7 mol l-1 (B) and 10-6 mol l-1 (C) serotonin increases the speed of ciliary beating. Phase 2 is less regular and phase 3 is no longer apparent. Scale bar, 50 ms for all traces.

View larger version (3K): [in a new window]   Fig. 6. Photodiode recordings from post-oral ciliary activity during perfusion with 10-6 mol l-1 dopamine. Different phases of the beat waveform are not as distinct as those recorded in large pre-oral cilia. Scale bar, 150 ms.

View larger version (2K): [in a new window]   Fig. 7. Photodiode recordings of ciliary arrests along the pre-oral band. (A) Brief, isolated ciliary arrest (onset and offset indicated by arrows). (B) Longer duration contractile arrest, which occurred during muscular contraction (onset indicted by arrow) and often repositioned the entire velum and prevented further recordings. Scale bar, 150 ms.

View larger version (11K): [in a new window]   Fig. 8. Summarized effects of putative transmitters (serotonin, dopamine, norepinephrine, FMRFamide and Leu-enkephalin) at different concentrations (10-6 mol l-1 to 10-9 mol l-1) on the frequency of isolated ciliary arrests. Asterisks indicate significant difference when compared with the control group (P<0.05).

View larger version (10K): [in a new window]   Fig. 9. Summarized effects of putative transmitters (serotonin, dopamine, norepinephrine, FMRFamide and Leu-enkephalin) at different concentrations (10-6 mol l-1 to 10-9 mol l-1) on the frequency of contractile ciliary arrests. Asterisks indicate significant difference when compared with the control group (P<0.05).

View larger version (12K): [in a new window]   Fig. 10. Summarized effects of putative transmitters and respective analogues on swimming behaviour, expressed as the average percentage of larvae in the top of the water column. Tested compounds included serotonin (10-4 mol l-1 to 10-6 mol l-1), fluoxetine and mianserin (both at 10-5 mol l-1), dopamine and norepinephrine (both from 10-4 mol l-1 to 10-6 mol l-1), haloperidol, alprenolol and spiperone (all at 10-5 mol l-1). Asterisks indicate significant difference when compared with the control group (P<0.05).

View larger version (8K): [in a new window]   Fig. 11. Summarized effects of putative transmitters on algal intake of I. obsoleta larvae expressed as percentage of the control (100%). Tested compounds included serotonin (from 10-4 mol l-1 to 10-6 mol l-1), dopamine and norepinephrine (from 10-4 mol l-1 to 10-6 mol l-1). Asterisks indicate significant difference when compared with the control group (P<0.05).

View larger version (10K): [in a new window]   Fig. 12. Summarized effects of putative transmitters on the number of locomotor arrests per minute during exposure of free swimming larvae to the following compounds: serotonin (from 10-4 mol l-1 to 10-6 mol l-1), dopamine and norepineprhine (from 10-4 mol l-1 to 10-6 mol l-1), FMRFamide and Leu-enkephalin (from 10-4 mol l-1 to 10-6 mol l-1). Asterisks indicate significant difference when compared with the control group (P<0.05).