ISSN:
1365-2826
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Corticotropin releasing hormone (CRH), a major regulator of pituitary ACTH secretion, also acts as a neurotransmitter in the brain. To determine whether CRH is involved in the regulation of hypothalamic function during stress, CRH receptor binding and CRH receptor mRNA levels were studied in the hypothalamus of rats subjected to different stress paradigms: immobilization, a physical-psychological model; water deprivation and 2% saline intake, osmotic models; and i.p. hypertonic saline injection, a combined physical-psychological and osmotic model. In agreement with the distribution of CRH receptor binding in the brain, in situ hybridization studies using 35S-labeled cRNA probes revealed low levels of CRH receptor mRNA in the anterior hypothalamic area, which were unaffected after acute or chronic exposure to any of the stress paradigms used. Under basal conditions, there was no CRH binding or CRH receptor mRNA in the supraoptic (SON) or paraventricular (PVN) nuclei. However, 2 h after the initiation of acute immobilization, CRH receptor mRNA hybridization became evident in the parvicellular division of the PVN, with levels substantially increasing from 2 to 4 h, decreasing at 8 h and disappearing by 24 h. Identical hybridization patterns of CRH receptor mRNA were found in the parvicellular PVN after repeated immobilization; levels were similar to those after 2 h single stress following immobilization at 8-hourly intervals for 24 h (3 times), and very low, but clearly detectable 24 h after 8 or 14 days daily immobilization for 2 h. On the other hand, water deprivation for 24 or 60 h and intake of 2% NaCI for 12 days induced expression of CRH receptor mRNA in the SON and magnocellular PVN, but not in the parvicellular pars of the PVN. Both parvicellular and magnocellular hypothalamic areas showed CRH receptor mRNA following i.p. hypertonic saline injection, single (4 h after) or repeated at 8-hourly intervals for 24 h (3 injections), or one injection daily for 8 or 14 days. Consistent with the expression of CRH receptor mRNA, autoradiographic studies showed binding of 125I-Tyr-oCRH in the parvicellular division of the PVN after immobilization; in the magnocellular division of the PVN after osmotic stimulation, and in the PVN and SON after i.p. hypertonic saline injection. The data show that stress-specific activation of the parvicellular and magnocellular systems is associated with CRH receptor expression, and suggest a role for CRH in the autoregulation of hypothalamic function.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2826.1994.tb00636.x
Permalink
