Quantitative autoradiographic analysis of estradiol retention by cells in the preoptic area,hypothalamus and amygdala

Summary These experiments were done to compare quantitatively, on a cell-by-cell basis, estradiol retention by cells in the medial preoptic area, arcuate nucleus, ventrolateral subdivision of the ventromedial nucleus, and the caudal half of the medial nucleus of the amygdala. The steroid autoradiograms were prepared from 2 sections of brains from ovariectomized, adrenalectomized adult female rats that had been infused intravenously with [³H] estradiol (E₂) in a regimen which kept circulating hormone concentration at or above proestrus levels for 3–4 h. Even in these brain regions, containing the most dense collections of E₂-concentrating cells, a maximum of only 27–61% of the cells concentrated E₂. Therefore, in these regions only a particular subset of the cells retain hormone; other cells in the region do not retain hormone. Frequency distribution histograms of the number of grains per cell versus the number of cells in each region showed a wide range in the amount of E₂ retained per cell, and no modes among E₂retaining cells. The data followed a distribution markedly different from that predicted by a simple Poisson distribution, confirming that E₂-retention does not result from a random, passive process such as diffusion. The overall quantitative characteristics of the frequency distribution histograms were similar across the four brain areas. Therefore, we propose that the different E₂-sensitive functions of these brain areas must depend on differences in the neural connectivity or differences in hormone regulated peptide content of the areas.