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First published online June 29, 2007
Journal of Experimental Biology 210, 2563-2573 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004283

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Effects of two bitter substances on olfactory conditioning in the moth Heliothis virescens

Kari Jørgensen^1,*, Marit Stranden¹, Jean-Christophe Sandoz², Randolf Menzel³ and Hanna Mustaparta¹

¹ Neuroscience Unit, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway,
² Research Center on Animal Cognition, University Paul Sabatier, Toulouse, France
³ Department of Biology, Freie Universität, Berlin, Germany

View larger version (37K): [in this window] [in a new window]   Fig. 1. The effect of US concentration on acquisition, retention and extinction of the conditioned PER, and the effect of time on retention and extinction in H. virescens. The proportion (%) of moths showing CR in each of the acquisition, retention and extinction trials is shown. (A) Average acquisition curves obtained in classical conditioning experiments with racemic linalool as CS and 2 mol l–1 and 3 mol l–1 sucrose as US. The letters NS indicate no significant between-group differences (Mann–Whitney test, P<0.05). (B) Retention in moths receiving 2 mol l–1 or 3 mol l–1 sucrose reward tested at different times after acquisition. Retention decreased significantly from 15 min to 48 h. N>31 in all retention groups. Different letters indicate significant between-group differences (Fisher's exact tests, P<0.0127). (C) Acquisition and extinction curves for the five retention times and the two sucrose concentrations. The extinction curves were obtained by stimulating with CS alone. No significant between-group differences were found, indicated by the letters NS (2 mol l–1: Kruskal–Wallis test, P>0.05; 3 mol l–1: Kruskal–Wallis test, P>0.05). (D) Extinction curves for moths tested after 15 min, 2 h, 8 h, 24 h or 48 h. Only moths showing CR at the first extinction test were included. Extinction was slower in the moths tested after 48 h. Different letters indicate significant between-group differences (Noether tests, P<0.0127).

View larger version (33K): [in this window] [in a new window]   Fig. 2. Typical responses obtained by tip recordings from gustatory receptor neurons in s. chaetica on the flagellum of the H. virescens antennae. Stimulation and recording starts simultaneously when the electrode is applied and ends when the electrode is removed, meaning that only the stimulation period is shown. (A) Responses to 1 mmol l–1 quinine, 1 mmol l–1 sinigrin, 100 mmol l–1 sinigrin, and the electrolyte 10 mmol l–1 KCl in the same s. chaeticum. (B) Responses to 1 mmol l–1 quinine in four different s. chaetica. (C) Responses to 100 mmol l–1 sinigrin in four other sensilla.

View larger version (14K): [in this window] [in a new window]   Fig. 3. (A) Average dose–response curves for quinine and sinigrin obtained during 5 s recordings from single s. chaetica. The average response to the electrolyte 0.01 mol l–1 KCl is indicated as a reference. (B) Average temporal response patterns for KCl, quinine and two concentrations of sinigrin, counted in 0.5 s bins in 75 s. chaetica during 5 s recordings. Whereas 100 mmol l–1 sinigrin elicited a high-response frequency very shortly after application, responses to 1 mmol l–1 quinine were bursts of activity distributed over the whole 5 s recordings. Different letters indicate significant between-group differences. The dotted areas show tests within the first and the third time bin, respectively. Letters behind the captions in B indicate differences between the average spiking activity during 5 s (Scheffé tests after ANOVA, P<0.01).

View larger version (16K): [in this window] [in a new window]   Fig. 4. Inhibitory learning effects of pre-exposure to linalool paired with a mechanosensory control, quinine or sinigrin on acquisition and retention. (A) Responses to the mechanosensory stimulus, quinine and sinigrin during pre-exposure. The odorant linalool alone elicited no responses. Different letters indicate significant between-group differences (Mann–Whitney tests, P<0.05). (B) Effect of pre-exposure on acquisition in moths. The group of moths receiving quinine treatment showed lower acquisition than the control group, suggesting an aversive effect of quinine. Such an aversive effect appeared only as a tendency for sinigrin. The untreated group of moths was not pre-exposed. The control group showed reduced acquisition compared with the untreated group, corresponding to a latent inhibition effect. Different letters indicate significant between-group differences (Mann–Whitney tests, P<0.05). (C) The control group showed higher retention than the quinine treatment group, but not the sinigrin treatment group. The control group was not different from the untreated group in retention. Different letters indicate significant between-group differences (Fisher's exact tests, P<0.05).

View larger version (16K): [in this window] [in a new window]   Fig. 5. Acquisition, extinction and facilitated extinction of CRs in moths receiving different treatments during the extinction phase. (A) Acquisition and extinction in moths receiving different extinction treatments. No significant between-group differences were found, indicated by the letters NS (Mann–Whitney tests, P>0.05). (B) Extinction curves for moths that have learned the CS. Only moths showing CR at the first extinction test were included. Pairing of linalool with quinine or sinigrin induced a more rapidly decreasing number of responses than the control. Different letters indicate significant between-group differences (Mann–Whitney tests, P<0.05).