EFFECT OF INTRAUTERINE POSITION ON THE METABOLIC CAPACITY OF THE HYPOTHALAMUS OF FEMALE GERBILS

The intrauterine position that a rodent fetus occupies relative to mem bers of the same or opposite gender affects both its reproductive phys iology and behavior when adult. Cytochrome oxidase histochemistry was used to assess regional differences in the oxidative metabolic capacit y of the hypothalamus of female Mongolian gerbils that developed in ut ero between 2 female fetuses (n = 15) or between 2 male fetuses (n = 1 4). Cytochrome oxidase reactivity was measured densitometrically by ex perimenters unaware of subject intrauterine position. Gray-to-white ma tter ratios of optical density in 11 brain regions were used as a norm alized index of metabolic capacity. Significant group differences in t he metabolic capacity of the medial and the posterior parts of the ant erior hypothalamus were revealed. Females that developed in utero betw een 2 male fetuses showed significant increases (19-22%) in cytochrome oxidase reactivity in these brain regions compared to that in females that developed between 2 female fetuses. The medial part of the anter ior hypothalamus contributes to copulatory behavior, whereas the poste rior part of the anterior hypothalamus may be involved in the control of pituitary gonadotropin secretion. Both these functions are influenc ed by intrauterine position during fetal life. To our knowledge, this is the first demonstration of metabolic changes in hypothalamic areas of the adult related to the differences in intrauterine position. (C) 1997 Elsevier Science Inc.