Hypothalamus is the highest center and the main crossroad of numerous homeostatic
regulatory pathways including reproduction and energy metabolism. Previous reports
indicate that some of these functions may be driven by the synchronized but distinct
functioning of the left and right hypothalamic sides. However, the nature of interplay
between the hemispheres with regard to distinct hypothalamic functions is still unclear.
Here we investigated the metabolic asymmetry between the left and right hypothalamic
sides of ovariectomized female rats by measuring mitochondrial respiration rates,
a parameter that reflects the intensity of cell and tissue metabolism. Ovariectomized
(saline injected) and ovariectomized+estrogen injected animals were fed ad libitum
or fasted to determine 1) the contribution of estrogen to metabolic asymmetry of hypothalamus;
and 2) whether the hypothalamic asymmetry is modulated by the satiety state. Results
show that estrogen-priming significantly increased both the proportion of animals
with detected hypothalamic lateralization and the degree of metabolic difference between
the hypothalamic sides causing a right-sided dominance during state 3 mitochondrial
respiration (St3) in ad libitum fed animals. After 24 hours of fasting, lateralization
in St3 values was clearly maintained; however, instead of the observed right-sided
dominance that was detected in ad libitum fed animals here appeared in form of either
right- or left-sidedness. In conclusion, our results revealed estrogen- and satiety
state-dependent metabolic differences between the two hypothalamic hemispheres in
female rats showing that the hypothalamic hemispheres drive the reproductive and satiety
state related functions in an asymmetric manner.
