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Visualization of modulatory effects of serotonin in the silkmoth antennal lobe

Evan S. Hill, Koutaroh Okada and Ryohei Kanzaki^*

Institute of Biological Sciences, University of Tsukuba, Ibaraki 305-8572, Japan

View larger version (30K): [in a new window]   Fig. 1. (A) Schematic illustration of electrical stimulation of the antennal nerve (AN). (B) Three-dimensional reconstruction of the Bombyx mori antennal lobe (AL). The two main compartments of the macroglomerular complex (MGC) — the cumulus and toroid — can be seen, as well as many ordinary glomeruli (Gs). The reconstruction of the AL represents the region in (A) outlined by the broken lines. Scale bar, 100µm. OL, optic lobe; Oe, oesophagus; PC, protocerebrum; SOG, suboesophageal ganglion; D, dorsal; L, lateral.

View larger version (24K): [in a new window]   Fig. 2. Serotonin enhances the optical response in the antennal lobe (AL) but not the antennal nerve (AN). (A) Real image of the brain demonstrating the regions from which measurements of the optical responses were made in the AN (100 pixels, representing an area of 70 µmx70 µm) and macroglomerular complex (MGC; 384 pixels, representing an area of 168 µmx112 µm). Scale bar, 200 µm. OL, optic lobe; Oe, oesophagus; PC, protocerebrum; SOG, suboesophageal ganglion; Gs, ordinary glomeruli. (B) Serotonin had virtually no effect on the optical response in the AN. Gray line, control optical response; black line, optical response following serotonin application. (C) The optical response in the MGC was greatly enhanced by serotonin. F, change in fluorescence; F, background fluorescence.

View larger version (52K): [in a new window]   Fig. 3. The optical response in the antennal lobe (AL) in response to electrical stimulation of the antennal nerve (AN) was greater and longer lasting following serotonin application. (A) The normalized control optical response is first in the macroglomerular complex (MGC) and, in later frames, throughout the AL. The time given in each frame represents the time (ms) following the stimulus; the same values apply to the corresponding frames in (B) and (C). (B) After 12 min bath application with serotonin (10-4 mol l-1), the normalized optical response is stronger throughout the AL and longer lasting. (C) The serotonin-effect images show that the enhancing effects are non-homogenously distributed throughout the AL. Arrows indicate two glomerulus-sized regions of the ordinary glomeruli (Gs) in which the enhancing effects of serotonin were particularly strong. Scale bar, 200 µm.

View larger version (25K): [in a new window]   Fig. 4. Serotonin application resulted in reversible enhancement of the optical responses in both the macroglomerular complex (MGC) and the ordinary glomeruli (Gs). The average peak percentage increase in the optical response in the MGC was 48.7±8.7% (N=7) and in the Gs was 40.0±8.0% (N=5). These both represent significant increases from the control values (P<0.001 and P<0.005, respectively). The enhancing effects reversed significantly with washing in both the MGC and Gs (P<0.05). Scale bar, 200 µm. OL, optic lobe; Oe, oesophagus; PC, protocerebrum; SOG, suboesophageal ganglion. Error bars represent S.E.M.

View larger version (10K): [in a new window]   Fig. 5. Serotonin increased the duration of the optical response in both the macroglomerular complex (MGC) and the ordinary glomeruli (Gs). Serotonin application significantly increased the duration of the optical response in the MGC from 6.6±0.2 ms to 8.3±0.2 ms (P<0.005, N=7) and in the Gs from 8.3±0.2 ms to 10.1±0.2 ms (P<0.005, N=5). Error bars represent S.E.M.

View larger version (31K): [in a new window]   Fig. 6. The enhancing effects of serotonin were non-homogenously distributed throughout the antennal lobe (AL). The inset shows a real image of the brain, demonstrating the regions from which measurements of optical responses were made in individual compartments of the macroglomerular complex (MGC; each compartment represents an area of 81 µmx81 µm) and the ordinary glomeruli (Gs; each compartment represents an area of 144 µmx144 µm). In this preparation, greater enhancing effects were observed in the toroid regions than in the cumulus regions of the MGC. Additionally, in some areas of the Gs, the enhancing effects of serotonin were stronger (i.e. Gs3) than in others (i.e. Gs2 and Gs4). The area-specific differences in the enhancing effects of serotonin varied among preparations. Scale bar, 200 µm. OL, optic lobe; Oe, oesophagus; PC, protocerebrum; SOG, suboesophageal ganglion; c, central; l, lateral; m, medial.

View larger version (15K): [in a new window]   Fig. 7. The enhancing effects of serotonin were greater in some antennal lobe (AL) regions than in others. (A) The average peak increase in the optical response was significantly greater in the toroid (54.9±8.0%, N=7) than in the cumulus (42.6%±10.2, P<0.05, N=7). (B) The enhancing effects of serotonin were significantly greater in the central cumulus than in the lateral cumulus (49.3±11.4% vs 39.0±11.4%; P<0.05, N=7). There were no significant differences in the enhancing effects of serotonin in the medial, central and lateral toroid. (C) The enhancing effects of serotonin were non-homogenously distributed in the Gs. The enhancing effects of serotonin in Gs3 were significantly greater than in Gs1, Gs4 and Gs5 (60.8±8.8% vs 32.0±11.8%, 37.7±5.8% and 21.2±13.8%, respectively; P<0.05, N=5). Error bars represent S.E.M.