Level of corticosterone replacement determines body weight gain in adrenalectomized rats with VMH lesions

Injection of Urocortin 3 into the ventromedial hypothalamus modulates feeding, blood glucose levels, and hypothalamic POMC gene expression but not the HPA axis

Urocortin 3 (Ucn 3) is a corticotropin-releasing factor (CRF)-related peptide with high affinity for the type 2 CRF receptor (CRFR2). Central administration of Ucn 3 stimulates the hypothalamic-pituitary-adrenal axis, suppresses feeding, and elevates blood glucose levels, suggesting that activation of brain CRFR2 promotes stress-like responses. Several CRFR2-expressing brain areas, including the ventromedial hypothalamus (VMH) and the posterior amygdala (PA), may be potential sites mediating the effects of Ucn 3. In the present study, Ucn 3 or vehicle was bilaterally injected into the VMH or PA, and food intake and plasma levels of ACTH, corticosterone, glucose, and insulin were determined. Food intake was greatly reduced in rats following Ucn 3 injection into the VMH. Ucn 3 injection into the VMH rapidly elevated plasma levels of glucose and insulin but did not affect ACTH and corticosterone secretion. Injection of Ucn 3 into the PA did not alter any of the parameters measured. We determined that the majority of CRFR2-positive neurons in the VMH were excitatory glutamatergic, and a subset of these neurons project to the arcuate nucleus of the hypothalamus (ARH). Importantly, stimulation of CRFR2 in the VMH increased proopiomelanocortin mRNA expression in the ARH. In conclusion, the present study demonstrates that CRFR2 in the VMH mediates some of the central effects of Ucn 3, and the ARH melanocortin system may be a downstream target of VMH CRFR2 neurons.

On the mechanisms and putative pathways involving neuroimmune interactions

Bidirectional interdependence between the immune system and the CNS involves the intervention of common cofactors. Cytokines are endogenous to the brain, endocrine and immune systems. These shared ligands are used as a chemical language for communication. Such interaction suggests an immunoregulatory role for the brain, and a sensory function for the immune system. Interplay between the immune, nervous and endocrine systems is associated with effects of stress on immunity. Cytokines are thus capable of modulating responses in the CNS, while neuropeptides can exert their effects over cellular groups in the immune system. One way is controlled by the HPA axis, a coordinator of neuroimmune interactions that is essential to unravel in order to elucidate vital communications in a manner that this crosstalk remains a cornerstone in perpetuating a stance of homeostasis.

Interaction of corticosterone and gonadal steroids on lipid deposition in the female rat

The present study was designed to evaluate the interaction of corticosterone (CORT) and female gonadal steroids on energy balance and lipid metabolism. To this end, a 2 x 4 factorial experiment was carried out in which two cohorts of rats differing in their ovary status [OV status: intact (INT) and ovariectomy (OVX)] were each divided into four groups defined by their CORT status [CORT status: nonadrenalectomized (non-ADX), ADX without CORT replacement (placebo subcutaneous pellet), ADX with low-dose CORT replacement, and ADX with high-dose CORT replacement]. After 3 wk of treatment and a 12-h fast, rats were killed and their carcasses analyzed for energy (lipid and protein) content. In addition, indexes of endogenous triglyceride (TRIG) production (liver TRIG content), transport into plasma (triglyceridemia), and incorporation into fat stores [lipoprotein lipase (LPL) activity in adipose tissue (AT)] were assessed. OV and CORT status interacted on body weight gain, total energy, and fat gains. The interactions arose from the fact that the twofold increase in these variables brought on by OVX was abolished by ADX and restored by CORT replacement. Although in ADX groups there was a dose-related restoration of total energy and fat gain by CORT replacement in both INT and OVX cohorts, the impact thereupon of OVX observed in the non-ADX group reappeared only in ADX animals receiving the high dose of CORT. Protein gain was increased by OVX solely in non-ADX rats, whereas the high dose of CORT prevented any net protein gain independently of the OV status. Consistent with treatment effects on total body fat gain, OVX resulted in an increase in liver TRIG content, AT weight, AT LPL activity, and plasma insulin. All these effects of OVX were abolished by ADX and restored by the high dose of CORT. Plasma TRIG were unaffected by OV status but were highly responsive to CORT status. All treatment effects were highly correlated with cumulative food intake. This study shows that the presence of CORT is required for OVX to exert its action on global energy balance and the concomitant, closely integrated adaptations of lipid metabolism.

Abnormal corticosterone regulation in an immature rat model of continuous chronic stress

Neuroendocrine correlates of chronic stress in human infants have not been established. The goal of the present study was to create an animal model of continuous chronic stress using the immature rat to measure basal plasma corticosterone, and secretion of plasma corticosterone in response to an acute stress. This was achieved by modulation of the cage environment for rat pups and their mothers. During postnatal days 2-9, pups were maintained in three groups: (1) handled, (2) not handled and with ample bedding; and (3) not handled with limited bedding. On postnatal day 9, some pups from each group were subjected to acute cold-separation stress and were killed 90, 240, or 360 min later along with unstressed controls. The group not handled and with limited bedding manifested increased plasma corticosterone output even without cold exposure and a sustained increase of plasma corticosterone after cold-separation stress. Plasma corticosterone interanimal variability was increased and body weight was decreased in these pups, typical of a state of chronic stress. The first model of continuous stress in infant rats in which upregulation of hypothalamic-pituitary-adrenal axis is achieved without maternal separation is presented. This paradigm may more closely approximate the human situation of chronically stressed, neglected infants.