Functional PET/MR Discloses Gender Differences in Color Processing in Mice

OBJECTIVES: Color processing is a central component of human vision. There has been much debate about the existence of color vision in animals. Mice have two types of cone pigments, one with a peak sensitivity at about 510 nm, and the other with a peak at 370 nm in the ultraviolet range. Most studies of color vision have used behavioral experiments, and hence uncertainties remain whether the two cone types yield color vision. Since PET has been used to measure changes of rCBF of rhesus monkeys performing color discrimination we have hypothesized that FDG-PET combined with anatomical MR can be used to study color processing in mice. Here we demonstrate gender differences in color processing in mice.
METHODS: Ten anaesthetized CD-1 mice were repeatedly injected on different days with 12 MBq 18F-FDG and subjected in random order to separate monocular stimulation of the left and right eye with white, blue and yellow lights, respectively, for 20 min using gelatin-(Wratten)-filters affixed within a viewing device (Chromatoscope) specially designed for small animals. The SUV of 18F-FDG was determined at 27.5, 32.5, 37.5 and 42.5 min p.i. in the whole cortex and in the left and right visual cortex. Data were analyzed with MANOVA and t-test.
RESULTS: In both genders no hemispheric differences are revealed in dark baseline condition and during stimulation with white light of either eye. Male mice have 13-16% higher SUV (p< 0.001) than female mice in the cortical area, right and left visual cortex in dark baseline condition and during stimulation with white, blue and yellow lights through the right eye but not the left. In male mice, the SUV was higher in the left visual cortex (1.53 ± 0.08) during Blue stimulation through the right eye compared to the right visual cortex (1.47 ± 0.10, p<0.05) (Fig. left) while the SUV did not differ during Blue stimulation through the left eye. Conversely, in female mice, the SUV was higher in the right visual cortex (1.34 ± 0.08) during Blue stimulation through the left eye compared to the left visual cortex (1.30 ± 0.11, p<0.01) (Fig. right) while there was no change during stimulation with Blue through the right eye. Yellow stimulation through the right eye revealed hemispheric differences only in female mice, while Yellow stimulation through the left eye revealed hemispheric differences only in male mice.
CONCLUSION: The experimental setup using FDG-PET combined with anatomical MR is suitable to study color processing in mice. As previously has been shown for human in a functional transcranial Doppler study (Njemanze 2011) gender differences in the perception of blue and yellow colors appear to exist also in rodents. In both species Blue provided the highest stimulation. In opposite to human the visual cortex in male mice revealed higher metabolism than in female.
REFERENCE
Njemanze PC. Gender-related differences in physiologic color space: a functional transcranial Doppler (fTCD) study. Exp. Transl Stroke Med. 2011; 3: 1.