Expression of Corticosterone-binding Globulin in the Rat Hypothalamus

Abstract

We observed coexistence of corticosteroid-binding globulin (CBG) with vasopressin (VP) and oxytocin (OT) in magnocellular neurons in rat hypothalamus by combined immunoperoxidase staining and immunofluorescence. A portion of the supraoptic and of the paraventricular neurons showed double immunostaining of CBG with either VP or with OT. CBG staining was intensified by pretreating animals with colchicine to block axonal transport. CBG was also observed in widespread axonal projections throughout the lateral hypothalamus, the median eminence and the posterior pituitary lobe. Single ependymal cells and some of the endocrine cells in the anterior lobe contained specific CBG immunoreactivity. IN SITU hybridization of semithin sections with a synthetic oligonucleotide probe to CBG mRNA provided staining of magnocellular hypothalamic neurons, but not ependymal cells or anterior lobe cells. Western blots of CBG extracted by affinity chromatography from hypothalamus homogenates showed a band at approximately 50 kDa. Our observations indicate the intrinsic expression of CBG in peptidergic hypothalamus neurons in rat. The multiple locations of CBG-expressing neurons indicate multiple functional properties, probably exceeding the role of a mere steroid transporter. CBG is likely to be subject to axonal transport and secretion in a neuropeptide-like fashion, perhaps involved in neuroendocrine regulation, which may include stress responses.

Intrinsic expression of transcortin in neural cells of the mouse brain: a histochemical and molecular study

“…The expression of CBG in the brain has been reported before by various authors in rats (de Kloet et al, 1984;Perrot-Applanat et al, 1984;Möpert et al, 2006;Jirikowski et al, 2007) and humans (Sivukhina et al, 2006 coexpression of the steroid-binding globulin with the classical neuroendocrine peptides within the rat hypothalamus as well as intrinsic synthesis of Cbg mRNA in various brain regions. Here, we extend the data obtained previously by the use of a mouse model in which expression of the Cbg gene is totally abolished in each tissue of the animal.…”

“…In this culture system, CBG secretion could be rapidly induced after corticosterone stimulation in a doseand time-dependent manner whereas dexamethasone, a potent GC agonist that is not bound by CBG, was ineffective (Pusch et al, 2009). Previously, we described CBG in human magnocellular hypothalamic neurons as well as in neurons of the rat hypothalamohypophyseal system, partially co-localized with the two important peptides of stress response -vasopressin and oxytocin (Sivukhina et al, 2006;Möpert et al, 2006;Jirikowski et al, 2007). With immunohistochemistry and in situ hybridization methods, CBG has also been observed in a portion of the periventricular neurons, the ependymal cells lining the third ventricle and in the choroid plexus (Möpert et al, 2006;Jirikowski et al, 2007).…”

“…Previously, we described CBG in human magnocellular hypothalamic neurons as well as in neurons of the rat hypothalamohypophyseal system, partially co-localized with the two important peptides of stress response -vasopressin and oxytocin (Sivukhina et al, 2006;Möpert et al, 2006;Jirikowski et al, 2007). With immunohistochemistry and in situ hybridization methods, CBG has also been observed in a portion of the periventricular neurons, the ependymal cells lining the third ventricle and in the choroid plexus (Möpert et al, 2006;Jirikowski et al, 2007). However, detailed morphological analysis of CBG distribution in the different populations of brain cells has not been performed, and the brain Cbg structure has not been reported.…”

Corticosteroid-binding globulin contributes to the neuroendocrine phenotype of mice selected for extremes in stress reactivity

“…CBG is a monomeric glycoprotein synthesized and stored mainly by the liver (Rothschild et al 1972, Weiser et al 1979, Kuhn et al 1986, Hammond et al 1987, Henley & Lightman 2011. Evidence for an intracellular location of CBG in the CNS and the pituitary has been reported, but its role within the brain remains to be determined (de Kloet et al 1984, Mopert et al 2006, Sivukhina et al 2012. CBG is capable of binding GC with high affinity but with low capacity, in contrast to albumin, which binds GC with high capacity but with low affinity (Slaunwhite & Sandberg 1959, Sandberg et al 1964, Burton & Westphal 1972, Breuner & Orchinik 2002, Moisan 2010.…”

Identification of sex hormone binding globulin-interacting proteins in the brain using phage display screening

“…The same laboratory demonstrated the importance of binding globulins in mediating the effects of steroids. Mice lacking a corticosteroid-binding globulin, another steroid-binding globulin found in the brain (18,19), had more free steroids in the blood but showed fewer physiological responses to them, suggesting that the presence of this binding globulin was necessary in order to see the effects of corticosteroids (20).…”