Fos-like immunoreactivity in the rat hypothalamic-pituitary axis after immobilization stress.
The effect of immobilization stress on the expression of the protooncogene c-fos in the rat pituitary and hypothalamus was investigated immunohistochemically using different polyclonal antibodies raised against the c-fos protein (Fos). After a 4 h immobilization, Fos-like immunoreactivity (Fos-LI) increased substantially in the parvocellular part of the paraventricular nucleus and in the intermediate and anterior lobe of the pituitary. The majority of the Fos-immunoreactive cells in the pituitary contained corticotropin, which was demonstrated by immunohistochemical double-staining. Since the paraventricular nucleus contains a large number of glucocorticoid receptor immunoreactive cells, the effect of a synthetic glucocorticoid, dexamethasone, on the induction of Fos-LI was studied. Dexamethasone treatment before immobilization considerably reduced the stress-induced expression of Fos-LI in the anterior and intermediate lobe of the pituitary but did not alter the induction of Fos-LI in the paraventricular nucleus. The present results demonstrate that immobilization stress induces Fos-LI both in the hypothalamus and in the pituitary, suggesting that Fos may be involved in regulating the synthesis of different mediators of stress response, such as CRF- and POMC-derived peptides. Apparently glucocorticoids do not directly repress c-fos expression, since dexamethasone did not affect the induction of Fos-LI in the paraventricular nucleus. The reduction of stress-induced Fos-LI in the pituitary by dexamethasone is possibly due to the diminished release of CRF factor from the paraventricular neurons.
Kononen
J
J
Department of Biomedical Sciences, University of Tampere, Finland.
Honkaniemi
J
J
Alho
H
H
Koistinaho
J
J
Iadarola
M
M
Pelto-Huikko
M
M
D000324:Adrenocorticotropic Hormone / Q000032:analysis; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D003907:Dexamethasone / Q000494:pharmacology; D005508:Food Deprivation; D016762:Genes, fos; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology*; D007150:Immunohistochemistry; D008297:Male; D008969:Molecular Sequence Data; D010286:Paraventricular Hypothalamic Nucleus / Q000473:pathology / Q000503:physiopathology; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D010903:Pituitary Gland, Anterior / Q000473:pathology / Q000503:physiopathology; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D012149:Restraint, Physical; D013315:Stress, Psychological / Q000503:physiopathology*; D014868:Water Deprivation
D000906:Antibodies; D010455:Peptides; D016760:Proto-Oncogene Proteins c-fos; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone