Developmental sex differences in calbindin-D28K 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 less than or equal to .001) and age (p less than or equal to .0001) and a significant interaction (p less than or equal to .02). Post-hoc Neuman-Keuls analysis revealed that PNO and PN2 males had significantly elevated calbindin levels over PN0 and PN2 females (p less than or equal to .05). ANOVA of mean calretinin levels from the same animals also indicated a significant effect of sex (p less than or equal to .002) and a significant interaction between sex and age (p less than or equal to .001). Post-hoc analysis indicated males had significantly elevated calretinin levels over PN0, PN4 (p less than or equal to .05) and PN6 (p less than or equal to .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. (C) 2000 John Wiley & Sons, Inc.