Fig. 2

Fos activation pattern of accumbal and lateral hypothalamic neurons following intake of highly rewarding food. a Top: Brain regions of interest (ROIs) for counting Fos-labeled cell nuclei in the accumbens nucleus. The diagram was adopted from the Atlas of Paxinos and Watson [24] and illustrates a sampling frontal section level of 2.28 mm to Bregma. ROIs (200 µm × 200 µm) were overlaid on microphotographs in the different areas: 1–2, core; 3, medial shell hedonic hot spot; 4, control area in the ventral part of the shell. Bottom: The number of Fos-positive cells per area/animal. No significant difference existed between the experimental groups, n = 8-9. b Fos activation in the accumbens nucleus in relation to the amount of consumed sweet milk. Strong correlations were found in the medial shell (top) in both control (left, open circle) and PR (right, filled circle) groups and in the core (bottom) in PR rats only. Note that Fos-counts are in the same range in the individual areas, but there is a shift toward higher quantities of consumed milk in PR rats. Solid and dashed lines show the regression lines and the 95% confidence intervals, respectively, see correlation coefficients (R) on the graphs, *p < 0.05, n = 8–9. c Top: a similar diagram as in A, showing location of ROIs (400 µm × 400 µm) for counting Fos-labeled cell nuclei in the rostral lateral hypothalamic area at a sampling frontal section level of −1.92 mm caudal from Bregma. ROIs were placed: 5, laterally to fornix (PF), 6, on the lateral hypothalamus (LH). Bottom: The number of Fos+ cells per area/animal. A higher Fos-count was detected in the PF area in PR rats, but there was no significant difference in the LH region. Fos+ cell nuclei appear as black dots on the representative pictures (left the PF, right the LH regions, respectively, n = 7,*p < 0.05 vs. controls. : d Palatable food intake-activated neurons in the rostral LHA were non-MCH, non-orexin cells. Double immunostainings from control animals. Fos+ nuclei are seen as dark dots. Scale: 50 µm. e Fos induction in the caudal part of the hypothalamus. Many Fos+ cells were seen caudal to the analyzed area (white arrowheads). MCH cells were Fos-negative. Orexin cells lateral to the fornix were also Fos-negative. Many of orexin cells were double-labeled medial to the fornix. Black arrows: Fos-negative MCH or orexin cells, black arrowheads: orexin and Fos double-labeled cells. Control animals. Scale: 50 µm. Data are presented as means ± SEM. ac anterior commissure, f fornix, LH lateral hypothalamic, and PF perifornical regions of the lateral hypothalamic area (LHA), opt optic tract, PR intrauterine protein-restricted