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WATER AND ELECTROLYTE HOMEOSTASIS

Estrogen receptor- expression in osmosensitive elements of the lamina terminalis: regulation by hypertonicity

¹Department of Physiology and Biophysics, University of Colorado Health Science Center, Denver, Colorado 80262; and ²Departments of Psychology and Pharmacology, University of Iowa, Iowa City, Iowa 52242

Submitted 27 February 2004 ; accepted in final form 30 April 2004

The subfornical organ (SFO), median preoptic nucleus (MnPO), and organum vasculosum lamina terminalis (OVLT), which are associated with the lamina terminalis, are important in the control of body fluid balance. Neurons in these regions express estrogen receptor (ER)-, but whether the ER- neurons are activated by hypertonicity and whether hypertonicity regulates ER- expression are not known. Using fluorescent, double-label immunocytochemistry, we examined the expression of ER--immunoreactivity (ir) and Fos-ir in control and water-deprived male rats. In control animals, numerous ER--positive neurons were expressed in the periphery of the SFO, in both the dorsal and ventral MnPO, and in the dorsal cap of the OVLT. Fos-positive neurons were sparse in euhydrated rats but were numerous in the SFO, MnPO, and the dorsal cap of the OVLT after 48-h water deprivation. Most ER--ir neurons in these areas were positive for Fos, indicating a significant degree of colocalization. To examine the effect of dehydration on ER- expression, animals with and without lesions surrounding the anterior and ventral portion of the 3rd ventricle (AV3V) were water deprived for 48 h. Water deprivation resulted in a moderate increase in ER--ir in the SFO of sham-lesioned rats (P = 0.03) and a dramatic elevation in AV3V-lesioned animals (P < 0.05). This was probably induced by the significant increase in plasma osmolality in both dehydrated groups (P < 0.001) rather than a decrease in blood volume, because hematocrit was significantly increased only in the dehydrated sham-lesioned animals. Thus these studies implicate the osmosensitive regions of the lamina terminalis as possible targets for sex steroid effects on body fluid homeostasis.

anteroventral third ventricle; Fos; organum vasculosum lamina terminalis; oxytocin; subfornical organ; water deprivation

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