Journal of Neuroscience, Vol 10, 1513-1521, Copyright © 1990 by Society for Neuroscience
Steroid hormone regulation of ribosomal RNA in rat hypothalamus: early detection using in situ hybridization and precursor-product ribosomal DNA probes
KJ Jones, CA Harrington, DM Chikaraishi and DW Pfaff
Department of Cell Biology and Anatomy, Chicago Medical School, Illinois 60064.
In the female rat, behavioral and endocrine aspects of reproduction are
controlled, in part, by the action of the steroid hormone estradiol on
several regions of the brain, including the ventrolateral portion of the
ventromedial hypothalamus (VL-VMN) and the arcuate nucleus of the
hypothalamus (ARC). Quantitative assessment of the effects of estradiol on
the regulation of ribosomal RNA in rat hypothalamus was accomplished in
this study by tandem in situ hybridization experiments with 2 ribosomal DNA
probes specific to the initial transcript (precursor) or mature, stable
(product) rRNA. This novel approach allowed the regulation of RNA
processing by steroid hormones to be analyzed in the individual neuron, a
particularly important concern in heterogeneous tissue such as the brain.
Estradiol was administered subcutaneously to ovariectomized rats for 15
min, 30 min, or 2 hr, or a discontinuous schedule of 2 hr on/7 hr off/2 hr
on. Levels of precursor and product rRNA were measured in VL-VMN and ARC
neurons using a computerized image- analysis system. Significant increases
in the levels of precursor rRNA were observed only in the VL-VMN as early
as 30 min after hormone exposure, with a doubling in the amount of
precursor rRNA occurring at 2 hr. No changes in product rRNA were observed
in either brain region at these early times. These data, in conjunction
with our previous findings of increases in product rRNA after longer
hormone exposure times, lead us to conclude that rRNA gene transcription is
activated in rat hypothalamic neurons within 30 min.(ABSTRACT TRUNCATED AT
250 WORDS)