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First published online August 31, 2007
Journal of Experimental Biology 210, 3179-3187 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.002394

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Serotonin and nitric oxide interaction in the control of bioluminescence in northern krill, Meganyctiphanes norvegica (M. Sars)

Jenny Krönström^1,*, Samuel Dupont², Jerome Mallefet³, Michael Thorndyke² and Susanne Holmgren¹

¹ Department of Zoophysiology, Göteborg University, Box 463, SE 405 30 Göteborg, Sweden
² Kristineberg Marine Research Station, SE 450 34 Fiskebäckskil, Sweden
³ Lab Marine Biology, Catholic University of Louvain, B-1348 Louvain-la-Neuve, Belgium

View larger version (74K): [in this window] [in a new window]   Fig. 1. Schematic picture of a longitudinal section through a ventral photophore from krill. Light is produced in the lantern (La) that is made up by processes from B-cells (possibly photocytes; B) and refractive rods. Light produced in the lantern is reflected against the inside of the organ wall (reflector; R) and passes through a lens (Le) before leaving the photophore. Apart from B-cells, three other cell types are present in the organ – large A-cells (A) and smaller C-cells (C) and D-cells (D). On both sides of the lens, photophore vessels (V) and nerves (N) enter the organ. Capillaries branch off from the arteries and pass both D- and C-cells before they empty in the lantern. Nerves follow the capillaries and end at a sphincter-like structure at the base of the C-cells. Modified from Herring and Locket (Herring and Locket, 1978) with permission.

View larger version (3K): [in this window] [in a new window]   Fig. 2. Parameters used to characterize the light response. An asymmetrical growth curve (Gompertz equation) was fitted to the accumulated original data from the luminometer recordings. L, cumulative value of light emitted (q s s–1); Ltot, the total amount of light (q s–1); RLPmax, rate of light production (q s–2) at inflection point (ip) and tip, time to the inflection point (s).

View larger version (161K): [in this window] [in a new window]   Fig. 3. Longitudinal sections of ventral photophores from M. norvegica. 5-HT-IR fibres are found throughout the light organ (A; for example, at the arrows) following capillaries and ending at the lantern (C; for example, at the arrows). Staining is abundant at the junction (D, arrow) between C-cells (D, arrowhead) and capillaries where the capillaries open into the lantern. Controls without primary antibody do not show any non-specific binding of the secondary antibodies (B). La, lantern; Le, lens; R, reflector. Scale bars, 50 µm in A,B; 10 µm in C,D.

View larger version (67K): [in this window] [in a new window]   Fig. 4. Transversal (A,B) and longitudinal (C) sections of ventral light organs from M. norvegica. NOS-like IR is detected around capillaries at the base of C-cells (A: staining at arrows, C-cells at arrowheads). IR against NOS is also detected along the capillaries in the peripheral parts of the light organ (B, arrows) and at both sides of the lens (C, arrows), possibly where the photophore arteries enter the light organ. La, lantern; Le, lens; R, reflector. Scale bars, 10 µm.

View larger version (4K): [in this window] [in a new window]   Fig. 5. Comparison of the total amount of light (Ltot) produced, as a response to 5-HT (0.03 mmol l–1), between the different months when experiments were performed. Some specimens tested in April and June were very bright, hence the large mean value of Ltot and the large variation in response in these months. Number of replicates (non-converging data in brackets, not included in the analysis): Sept., N=8 (1); Nov., N=9 (1); Dec., N=10; Apr., N=14 (4); June, N=10 (1); Sept., N=10 (2); error bars indicate s.e.m.

View larger version (14K): [in this window] [in a new window]   Fig. 6. Effect of the NO donors SNP and SNAP on the 5-HT-stimulated light response. White bars are 5-HT controls (0.03 mmol l–1 5-HT). Injection of either 5-HT and SNP (0.3 mmol l–1) or 5-HT and SNAP (0.3 mmol l–1) results in a significantly lower Ltot than injection of 5-HT per se (A, P<0.05). 5-HT controls from September (2004) and December (2004) were combined in the SNAP analysis. Injection of 5-HT and SNAP (0.3 mmol l–1) results in a significantly lower RLPmax (B) and a significantly higher tip (C) than injection of 5-HT per se (P<0.05). SNP did not affect these parameters. Number of replicates (non-converging data in brackets, not included in the analysis): SNP treatment: 5-HT, N=8 (1); 5-HT+SNP (0.03 mmol l–1), N=5; 5-HT+ SNP (0.3 mmol l–1), N=6 (2); SNAP treatment: 5-HT Ltot, N=18 (1); 5-HT RLPmax, tip, N=10; 5-HT+SNAP, N=8 (1); error bars indicate s.e.m.

View larger version (17K): [in this window] [in a new window]   Fig. 7. Effect of the NOS inhibitor L-NAME on the 5-HT-stimulated light response. White bars are 5-HT controls (0.03 mmol l–1 5-HT). Injection of L-NAME (3.0 mmol l–1) together with 5-HT gave a significantly higher Ltot (P<0.05), compared with the 5-HT control (A). As this treatment was performed in two different months (November and April) a two-factor ANOVA with `treatment' and `month' as factors was used to determine the effect of L-NAME. Month had no significant effect on Ltot. The lower concentrations of L-NAME used had no effect on the Ltot of the 5-HT response. In September and April the 5-HT and L-NAME treatment (0.3 and 3.0 mmol l–1 L-NAME, respectively) gave a slower response with longer tip (B) and a higher RLPmax (C) compared with the 5-HT control (P<0.05). Number of replicates (non-converging data in brackets, not included in the analysis): 5-HT, June, N=10 (1); 5-HT+L-NAME, June, N=8; 5-HT, Sept., N=10 (2); 5-HT+L-NAME, Sept., N=9; 5-HT, Nov., N=9 (1); 5-HT+L-NAME, Nov., N=9 (2); 5-HT, Apr., N=14 (4); 5-HT+L-NAME, Apr., N=15; error bars indicate s.e.m.

View larger version (9K): [in this window] [in a new window]   Fig. 8. Effects of the guanylyl cyclase inhibitor ODQ (0.01 mmol l–1) on the 5-HT-stimulated light response (A, Ltot; B, RLPmax; C, tip). ODQ had no effect on the 5-HT-stimulated light response. Numbers of replicates: 5-HT, N=10; 5-HT+ODQ, N=11; error bars indicate s.e.m.

View larger version (10K): [in this window] [in a new window]   Fig. 9. Effects of the cGMP analogue 8BrcGMP (0.3 mmol l–1) on the 5-HT-stimulated light response (A, Ltot; B, RLPmax; C, tip). Responses of specimens injected with both 5-HT and 8BrcGMP had a significantly lower RLPmax compared with the 5-HT control (B, P<0.05). Numbers of replicates: 5-HT, N=10; 5-HT+BrcGMP, N=10; error bars indicate s.e.m.