Aspartic acid asp

Dopamine (DA), norepinephrine hydrochloride (NE), 5-hydroxytryptamine (5-HT), acetyl- choline (Ach), l-tryptophan (Trp), γ-aminobutyric acid (GABA), glutamic acid (Glu) and aspartic acid (Asp) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Isoproterenol hydrochloride (internal standard, IS) was supplied by the National Institute for Food and Drug Control (Beijing, China). Heptafluorobutyric acid (HFBA) was obtained from Sigma-Aldrich. The purity of these reference standards were all more than 98%. Methanol and acetonitrile (HPLC grade) were purchased from Fisher Scientific (Fair Lawn, NJ, USA). Distilled water prepared with demineralized water was used throughout the study. Other reagent and solvent of analytical grade, were provided by the department of pharmaceutics, Shenyang Pharmaceutical University (Shenyang, China).

We used third-instar feeding-stage larvae from the Canton-Special wild-type strain, aged 5 days after egg laying. Flies were maintained on standard medium, in mass culture at 25°C, 60–70% relative humidity and a 12/12 hr light/dark cycle. Before each experiment, we removed a spoonful of food medium from a food vial, collected the desired number of larvae, briefly rinsed them in distilled water, and started the experiment.
For experiments, we used Petri dishes of 90-mm inner diameter (Sarstedt, Nümbrecht, Germany) filled with 1% agarose (electrophoresis grade; Roth, Karlsruhe, Germany). As reinforcers fructose (FRU; CAS: 57-48-7; Roth, Karlsruhe, Germany), aspartic acid (ASP; CAS: 56-84-8; Sigma–Aldrich, Seelze, Germany), quinine (QUI; CAS: 6119-70-6; Sigma–Aldrich), or sodium chloride (SAL; 7647-14-5; Roth, Karlsruhe, Germany) were used in concentrations given in the results section. As odors, we used n-amyl acetate (AM; CAS: 628-63-7; Merck, Darmstadt, Germany), diluted 1:50 in paraffin oil (Merck, Darmstadt, Germany) and 1-octanol (OCT; CAS: 111-87-5; Sigma–Aldrich).