Normal CTA in D2r-/- mice.

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These data were collected in concert with our studies of CTA in D1r-/- mice, published in the European Journal of Neuroscience. You will find below 1) the caption to the figure above and 2) Material and Methods

1) Figure.

Both D2r +/+ (open symbols) and D2r -/- (filled symbols) mice demonstrated dose-dependent CTA to 0.2 M NaCl after LiCl. A, At the lowest dose of LiCl, 40 mg/kg, aversion was minimal, and no difference was observed between the response of the D2r +/+ (n = eight) and D2r -/- (n = eight) mice. B, 150 mg/kg LiCl reduced intake of the salty solution on subsequent trials, and no difference was observed between the response of the D2r +/+ (n = eight) and D2r -/- (n = eight) mice. C, After a single exposure to the salty solution followed by 254 mg/kg LiCl, thirsty D2r +/+ (n = five) and D2r -/- (n = six) mice manifested strong aversion. Values plotted are the average % baseline intake +/- SEM.

2) Materials and methods

Animal Handling and Care
All procedures were in accordance with protocols approved by the IACUC at the University of Washington. Mutant mice lacking the dopamine D2 receptor gene (D2r-/-) were generated as described and maintained on a congenic C57BL/6J background in a specific pathogen free facility. Heterozygous mice were bred to obtain mutant and wildtype littermates. After weaning, mice were housed in sex-segregated groups of 2 to 5 mice in polycarbonate mouse cage with 1/8 inch BED-O-COB bedding (Animal Specialties, Hubbard OR, USA) and nesting material (“nestlet” block, Ancare Corp., N. Belmore NY, USA). Food (5LJ5, “hi-energy breeder diet”, 11% fat, PMI Nutritional Inc., Brentwood MO, USA) and water were available ad libitum, except as noted below.

Testing Procedures
For CTA studies with salt as the conditioned flavor, water deprivation was used to increase the motivation to consume the mildly salty test solution. Forty-three D2r +/+ and D2r -/- mice mice were individually housed, and acclimated to IP injections and 22-h daily water deprivation over eight days. Mice were then tested every other day. On a test day, mice were given access to a solution of 0.2 M NaCl for one hour at 10:30 AM, at the same time and in the same type of bottle that they were usually presented with water. This was followed by injection of LiCl (doses of 40, 150 or 254 mg/kg were administered by injecting 10 microliter / g body weight of a solution of 4, 15 or 25.4 mg/ml) at 11:30 AM. Mice that did not drink any of the test solution on subsequent trials were not injected with LiCl. To avoid dehydration on LiCl-pairing days, water was given for one hour at 4:30 PM.

Data Analysis
Intake data collected as grams were converted to a percentage of baseline (Trial 0) for each mouse as follows: [100 / intake of mouse A during Trial 0 (ml)] X intake of mouse A during Trial B (ml) = % of baseline intake for mouse A during Trial B. The data were analyzed by repeated measures ANOVA using the program STATISTICA 6.0 (StatSoft, Tulsa OK, USA). Tukey?s post-hoc analysis revealed no significant effect of LiCl dose in either genotype and the doses were pooled for further analysis. Comparisons of volume intake were made by Student’s T-tests.