Ultrastructural localization of glucocorticoid receptor (GR) in hypothalamic paraventricular neurons synthesizing corticotropin releasing factor (CRF)

Abstract

Corticotropin releasing factor (CRF) synthesizing neurons, located in the hypothalamic paraventricular nucleus (PVN), are the main central regulators of the pituitary-adrenal cortex endocrine axis. The hormone production and release of CRF-synthesizing neurons is regulated by neuronal messages and feedback action(s) of glucocorticoids secreted by the adrenal gland. In order to characterize the latter mechanism, glucocorticoid receptor (GR)-immunoreactive (IR) sites were studied in hypothalamic paraventricular neurons of intact, long-term adrenalectomized, and adrenalectomized plus glucocorticoid treated animals, by means of ultrastructural immunocytochemical labelling. In intact animals, glucocorticoid receptor immunoreactivity was found predominantly in the nuclei of parvocellular neurons. Following adrenalectomy GR-immunoreactivity was localized in the cytoplasm of the cells, and there was a concomitant disappearance of the label from the nuclei. After corticosterone administration to adrenalectomized animals, GR-IR sites were again concentrated within the cell nuclei. Immunocytochemical double labelling studies performed on adrenalectomized plus corticosterone-replaced animals demonstrated glucocorticoid receptor-IR sites in the cell nuclei of parvocellular paraventricular neurons that expressed CRF-immunoreactivity in their cytoplasm. These ultrastructural data indicate that the intracellular location of glucocorticoid receptor is dependent on the availability of glucocorticoids by the neurons. The simultaneous expression of GR- and CRF-immunoreactivity in parvocellular paraventricular neurons supports the concept of a direct feedback action of glucocorticoids upon CRF-synthesizing neurons.

Type II Corticosteroid Receptor-Like Immunoreactivity in the Rat Cerebellar Cortex: Differential Regulation by Corticosterone

“…In intact rats, type ll-ir was local ized predominantly in nuclei. This was in agreement with previous reports on type ll-ir in other regions of the CNS [6][7][8][9]17], Nucleoli were clearly devoid of immunoreactiv ity, in contrast to a previous ultrastructural study in the hypothalamic paraventricular nucleus [24], Fuxe et al [8] did not observe type ll-ir Purkinje cells in intact rats, even though neighbouring glial cells were immunoreactive. The antibody used in that study, IgG2a nr 7, crossreacts with an epitope in the variable domain of the type II re ceptor [8,9], distinct from the BUGR epitope [9], Despite a good degree of correspondence between the distribu tion of type ll-ir cells labeled by these two antibodies, there are differences in the hippocampus, septum and hy pothalamus [9].…”

“…The activated type II re ceptor is translocated to the nucleus where it binds to spe cific DNA sequences (glucocorticoid response elements) and regulates various gene networks [29], With increasing duration of adx, nuclear type II-ir was reduced in all bas ket, stellate and Golgi cells in all lobules. There was no apparent increase in cytoplasmic type II-ir, as has been reported for the paraventricular hypothalamic nucleus and hippocampal pyramidal cells [8,24], The majority of Purkinje cells showed nuclear type II-ir in the presence of corticosterone. Like basket, stellate, granule and Golgi cells, most Purkinje cells showed reduced nuclear type IIir in response to adx.…”

Central actions of glucocorticoids in the control of body fluid homeostasis: Review

“…The expression of GR in CRF-expressing neurons in the parvocellular PVN reinforces the direct feedback action of glucocorticoid in the control of CRF synthesis and release (14,29). Co-localization of mineralocorticoid receptor (MR) and GR was also observed in the parvocellular region, but not in the magnocellular region of the PVN (30).…”

“…There is growing evidence for the participation of the hypothalamic-pituitary-adrenal (HPA) axis in the adaptive responses following changes in blood volume and osmolality. The presence of the cytoplasmic glucocorticoid receptor (GR) has already been reported in the SON (13) and also in the parvocellular portion of the PVN, where this receptor is predominantly co-expressed with corticotrophin-releasing factor (CRF) (14). Furthermore, AVP and OT are weak secretagogues of adrenocorticotropic hormone (15)(16)(17), strongly suggesting an interaction between the HPA axis and the secretion of neurohypophyseal hormones.…”

Estrogen Receptor (ER)β Isoforms Rather Than ERα Regulate Corticotropin-Releasing Hormone Promoter Activity through an Alternate Pathway

“…These neurons synthesize and secrete corticotropin-releasing hormone (CRH) (Vale et al, 1981) in response to numerous stimuli (for review, see Pacak and Palkovits, 2001). Because CRH neurons contain glucocorticoid receptors (GR) (Cintra et al, 1987;Liposits et al, 1987;Uht et al, 1988), and because glucocorticoids downregulate cAMPactivated CRH transcription (Guardiola-Diaz et al, 1996), it may be that a component of downregulation occurs at the level of CRH transcription.…”