Effects of estradiol on the ontogenesis of striatal dopamine D1 and D2 receptor sites in male and female rats.

Since estradiol (E2) either increases or reduces the number of dopamine receptors in the corpus striatum of adult rats, depending on the dose and length of administration, the sensitivity of the two receptor subpopulations (D1 and D2) to E2 during ontogenesis was investigated. Rats of both sexes received either 10 micrograms/kg E2 for 3 days or 50 micrograms/kg for 6 days, and were sacrificed at the age of 15, 21, 40 and 120 days. D1 receptors (identified by [3H]SCH 23390 binding) displayed no changes in density and affinity in function of age, sex or E2 dose, whereas the D2 receptors (identified by [3H]spiperone binding) fell after the lower dose in all groups, and the higher dose resulted in supersensitivity in males of all ages, but only in the 15-day-old females. These findings show that the effect of E2 is bivalent on D2 density only. The effect of its brief administration at a low dose is not sex-dependent, whereas at higher doses administered for longer periods it appears to involve mechanisms linked to sexual differentiation after birth.