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First published online November 24, 2003
Journal of Experimental Biology 207, 179-188 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00718
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Visual learning in individually assayed Drosophila larvae

B. Gerber1,2,*, S. Scherer2, K. Neuser1, B. Michels1, T. Hendel1, R. F. Stocker2 and M. Heisenberg1

1 University of Würzburg, Department of Genetics and Neurobiology, Biocentre Am Hubland, D 970 74 Würzburg, Germany
2 University of Fribourg, Department of Biology and Program in Neuroscience, Ch. du Musée 10, CH 1700 Fribourg, Switzerland



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  		Fig. 1. (A-C) SEM images of the external chemosensory organs of the larval head. (A) Frontal overview; (B) enlarged view of the ventral organ (VO) and (C) dorsal (DO) and terminal (TO) organs. VO and TO probably have gustatory functions, whereas the DO serves both gustatory and olfactory functions. MH, mouth hook. The arrow in C points to one of the pores of the dome (DM). Scale bars, 20 µm. (D) Expression of the lacZ reporter in the Gal4 driver line MJ94, showing the position of the larval eye - the Bolwig's organ (BO) - in front of the cephalopharyngeal skeleton (dark brown). Further reporter expression also visualizes the positions of DO, TO and the dorsal, ventral and posterior pharyngeal gustatory sensilla (DPS, VPS, PPS). Scale bar, 100 µm. (E) Wiring diagram showing the central projections of the head sensory organs to the optic lobe (OL) tritocerebrum (TR), suboesophageal ganglion (SOG) and antennal lobe (AL) (modified from Python and Stocker, 2002aGo). AN, BN, LN, MN and LBN: antennal, Bolwig, labral, maxillary and labial nerves, respectively. LI, PN, local interneurons of the AL, projection neurons; LPR, lateral protocerebrum; MB, mushroom bodies; PH, pharynx.

 


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  		Fig. 2. Sketch of the experimental protocol for the learning experiments; for details see text. Please note that within each treatment condition, e.g. Light+/Dark-, half of the animals were trained with Light+ as the first trial and half of the animals with Dark- as the first trial.

 


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  		Fig. 3. Experiment 1, showing the test performance of individually assayed wild-type CS-F larvae, which had received either of two reciprocal training regimes: Light-/Dark+ (filled symbols) or Light+/Dark-(open symbols). (A) Percentage of animals located in a covered ('dark') quadrant of an X-plate photoresponse assay. Animals were observed every 10 s for 5 min. The 50% line indicates random distribution. (B) For each animal, a PREF value was calculated. Positive values indicate dark preference and negative values, light preference. The box plot represents the median as the middle line and 10 and 90 and 25 and 75% quantiles as whiskers and box boundaries, respectively. (C) A learning index (LI) was calculated for each pair of animals which underwent either Light-/Dark+ or Light+/Dark-training by subtracting the animals PREF values and dividing the result by two. Positive LIs indicate associative learning. The box plot represents the median as the middle line and 10 and 90, and 25 and 75% quantiles as whiskers and box boundaries, respectively. *P<0.0001 (significantly above chance level). Sample sizes are N=75, 75 for filled and open symbols, respectively; NLI=75.

 


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  		Fig. 4. Experiment 2, which is a repetition of Experiment 1, but uses the CS-W wild-type strain. All other details as in Fig. 1. Sample sizes are N=103, 110 for filled and open symbols, respectively; NLI=102.

 


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  		Fig. 5. Experiments 3 and 4, showing the photoresponse of individually assayed larvae, tested on either PURE agarose or on agarose plates containing gustatory stimuli. (A) Percentage of CS-F larvae located in a covered ('dark') quadrant in Experiment 3. Animals were observed every 10 s for 5 min in an X-plate photoresponse assay. The 50% line indicates random distribution. Animals were tested on either fructose (FRU; 1 mol l-1), quinine hemisulfate (QUI; 0.2%), sucrose (SUC; 1 mol l-1), or NaCl (2 mol l-1). (B) For each animal, a PREF value was calculated; positive values indicate dark preference and negative values, light preference. The box plot represents the median as the middle line and 10 and 90, and 25 and 75% quantiles as whiskers and box boundaries, respectively. No significant difference between the PREF values was found. Sample sizes were N=150, 150, 142, 146, and 144 for FRU, QUI, SUC, NaCl and PURE, respectively. (C) Experiment 4 is a repetition of Experiment 3, but using animals from the CS-W wild-type strain and employing the down-sized X-plate assay. PREF values were tested on either PURE agarose or on agarose plates, containing FRU (2 mol l-1) or NaCl (4 mol l-1). Sample sizes from left to right, N=88, 88, 72.

 


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  		Fig. 6. Experiment 5, showing the learning performance as measured by the LI values of individually assayed CS-W larvae from five learning experiments. Experiments use either NaCl only (PURE/NaCl), a combination of FRU and NaCl (FRU/NaCl), FRU only (FRU/PURE), a combination of FRU and QUI (FRU/QUI), or QUI only (PURE/QUI) as reinforcers. Positive LI values indicate associative learning. The box plot represents the median as the middle line and 10 and 90, and 25 and 75% quantiles as whiskers and box boundaries, respectively. *P<0.05. The test was performed in a down-sized X-plate assay. Please note the truncated axis. Sample sizes are from left to right NLI=108, 123, 111, 131, 117.

 

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© The Company of Biologists Ltd 2004