Figure 1

Study design, behavioral study and differences in brain glucose metabolism between rat strains. (A) Representative diagram of the chronology of the experimental procedures performed during the study according to the age of the animals. Abbrev.: ¹⁸FDG, [18F]-Fluorodeoxyglucose; PET, positron emission tomography. (B) MSA study in LEW and F344 rats. Morphine (1 mg/kg) or saline self-administration in adult LEW and F344 rats under an FR1 schedule of reinforcement. The values are expressed as the mean ± SEM: LEW-saline (n = 6), LEW-morphine (n = 8), F344-saline (n = 6), and F344-morphine (n = 7). The number of morphine injections per session was greater for LEW animals than for F344 animals. 3-way ANOVA followed by Bonferroni’s multiple comparisons test [*p < 0.05 and **p < 0.01 vs saline animals]. (C) PET results in T-maps overlaid on aT2-MRI reference showing increased FDG uptake (hot colors) or decreased FDG uptake (cold colors) in Saline-LEW animals compared with Saline-F344 animals in the first scan (PND 115). Similar results were obtained for the second scan (PND 130) (data not shown). Saline-LEW animals showed higher FDG uptake in the hypothalamus and the cerebral cortex and lower FDG uptake in the brainstem, cerebellum and PAG than Saline-F344 animals. Statistics corrected for multiple comparisons (FWE, p < 0.05). Region of interest (BS: brainstem, Cb: Cerebellum, Hypoth: hypothalamus, PAG: periaqueductal gray matter). Side: left (L) and right (R). k: cluster size, T: Student t. FDG uptake: increase (↑) and decrease (↓). p: p value (unc: uncorrected, FWE: family-wise error).