Astrocytic Fos expression in the rat posterior pituitary following LPS administration

Systemic lipopolysaccharide (LPS) administration has been shown to cause pr ofound Fos expression in multiple regions of the brain. In the present expe riment. Fos expression in the hypothalamic supraoptic nucleus (SON), poster ior pituitary, and anterior pituitary was investigated using quantitative i mmunohistochemistry. In the SON and anterior pituitary, a large number of F os-positive cells were observed by restraint stress, hyperosmotic administr ation (1.5, 3, and 9% NaCl), and LPS administration (5, 25, and 125 mug/kg) . In the posterior pituitary, LPS administration caused a significant incre ase in the number of Fos-positive nuclei in a dose-dependent manner, wherea s restraint stress and hyperosmotic stimulation (1.5 and 3% NaCl) did not i ncrease the number of Fos-positive cells and 9% NaCl administration induced weak Fos immunoreactivity. Moreover, a dual-labeling study using a confoca l microscope revealed that Fos-positive cells in the posterior pituitary we re astrocytes using MAP2, an astrocytic marker in the posterior pituitary. Here, we demonstrated that the astrocytes of the posterior pituitary expres sed Fos in response to LPS administration, which suggests that Fos expressi on participates in the activation of astrocytes juring acute-phase response s with LPS administration. (C) 2001 Elsevier Science B.V. All rights reserv ed.