Developmental sex differences in calbindin-D(28K) and calretinin immunoreactivity in the neonatal rat hypothalamus.

The proteins calbindin-D(28K) and calretinin buffer intracellular calcium and are speculated to be involved in the integration of neuronal signaling. Using Western blot analysis, we compared the levels of calbindin-D(28K) and calretinin in the developing male and female rat hypothalamus on postnatal days (PN) 0, PN2, PN4, PN6, PN8, and PN10. Analysis of variance (ANOVA) of mean calbindin levels indicated a significant effect of sex (p </=.001) and age (p </=. 0001) and a significant interaction (p </=.02). Post-hoc Neuman-Keuls analysis revealed that PN0 and PN2 males had significantly elevated calbindin levels over PN0 and PN2 females (p </=.05). ANOVA of mean calretinin levels from the same animals also indicated a significant effect of sex (p </=.002) and a significant interaction between sex and age (p </=.001). Post-hoc analysis indicated males had significantly elevated calretinin levels over PN0, PN4 (p </=.05) and PN6 (p </=.01) females. Immunocytochemical analyses indicated calbindin-immunopositive staining for cell bodies in the central subdivision of the medial preoptic nucleus, paraventricular nucleus, arcuate nucleus, and dorsomedial nucleus, and an area immediately surrounding the ventromedial nucleus (VMN). Calbindin immunoreactivity was absent from the ventrolateral VMN, but lightly stained cell bodies were observed in the dorsomedial VMN. The sex differences observed in calcium binding proteins parallel our previously observed sex differences in excitatory gamma-aminobutyric acid and glutamate early in development and may be related to mechanisms of sexual differentiation of the brain. Copyright 2000 John Wiley & Sons, Inc.