Asymmetric calmodulin distribution in the hypothalamus -: Role of sexual differentiation in the rat

The Ca2(+/)calmodulin (CaM) system plays important roles both in hypothalamic sexual differentiation and in the progesterone-induced facilitation of lordosis behavior in the adult rat. We recently showed sex-dependent differences in rat hypothalamic CaM levels, both in newborn and in adult animals. Here, we evaluated the presence of left-right hypothalamic asymmetries in CaM concentration in male and female rats, as well as the changes induced on these parameters by neonatal (1 h after birth) subcutaneous administration of tamoxifen (200 mug/rat) or testosterone (30 mug/rat). CaM measured by RIA in each half of the hypothalamus (at 2, 6, 12 and 24 h and at 90 days after birth) in both control and treated animals. In untreated young rats (2-24 h after birth), CaM concentration was significantly higher in the right half of the hypothalamus of males, whereas in females, it was higher in the hypothalamic left half. Treatment of females with testosterone of tamoxifen to males, consistently reversed these results. In the hypothalamus of treated animals, we found higher CaM levels in the left half of males, as well as in the right half of females. In control adult females, CaM concentration was also higher in the left half of the hypothalamus, as it was in the right half of adult males. However, this asymmetry was lost after neonatal hormone manipulation. These results reinforce the role of CaM in the development of sex-related hypothalamic functions. (C) 2002 Elsevier Science Inc. All rights reserved.