Effects of Estradiol on Glucoprivic Transactivation of Catecholaminergic Neurons in the Female Rat Caudal Brainstem

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Hyperphagic and hypothalamic neuroendocrine responses to acute glucose deprivation are modified by the ovarian steroid estradiol (E). Observations of genomic activation of catecholaminergic (CA) neurons in the hindbrain lateral reticular nucleus, nucleus of the solitary tract, and area postrema (AP) by glucopenia support their potential function in pathways mediating regulatory effects of this metabolic challenge within the brain. Expression of E receptors by these cells suggests that their activity may be sensitive to steroid modulation during glucopenia. The present studies investigated the role of E on transcriptional activation of caudal brainstem CA neurons by the glucose antimetabolite, 2-deoxy-D-glucose (2DG). Ovariectomized rats were implanted with s.c. Silastic capsules containing E (30 or 250 µg/ml) or sesame oil, and injected i.p. 7 days later with 400 mg 2DG/kg or saline. Tyrosine hydroxylase (TH)-immunoreactive (-ir) neurons in the C₁/A₁, C₂, C₃, A₂, A₅, and A₆ cell groups and AP were colabeled for Fos following antimetabolite administration, whereas vehicle injection resulted in negligible nuclear staining of these cells. With the exception of A₂, A₆, and AP cells, mean numbers of Fos- and TH-/Fos-ir-positive neurons in these brain sites did not differ between E- and sesame oil-implanted groups. Numbers of TH-positive A₂ and A₆ neurons that expressed Fos in response to 2DG were significantly greater in rats implanted with the high E dose vs. either the low steroid dose or sesame oil. These results show that the magnitude of cellular Fos labeling within discrete hindbrain CA neuron populations varies in accordance with circulating E levels. These findings suggest that E may exert potential modulatory effects on glucoprivic activation of the Fos stimulus/transcription cascade and consequent compensatory genomic responses within specific areas of the female rat caudal brainstem.