Developmental increase in (3)H-muscimol binding to the gamma-aminobutyric acid(A) receptor in hypothalamic and limbic areas of the rat: why is the ventromedial nucleus of the hypothalamus an exception?

Using in vitro autoradiography to measure binding of the gamma-aminobutyric acid(A) (GABA(A)) receptor agonist, muscimol, we examined male and female rats on postnatal days 1, 5, 10, and 20. There were no sex differences in muscimol binding in any hypothalamic or limbic regions examined. However, all regions exhibited a developmental increase in the density of binding, except the ventromedial nucleus (VMN) of the hypothalamus. We have previously shown that the adult VMN is the only hypothalamic nucleus containing an abundance of the alpha2 subunit of the GABA(A) receptor and lack of the alpha1 subunit. We hypothesize that the lack of alpha1 may be causally related to the lack of increase in muscimol binding.