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Oxytocin, Corticosterone, ACTH, Stress, HPA axis, Adrenalectomy
Abstract:
The oxytocin (OXT) system is functionally linked to the HPA axis in a
reciprocal and complex manner. Certain stressors are known to cause the
simultaneous release of OXT and adrenocorticotrophic hormone (ACTH)
followed by corticosterone (CORT). Furthermore, brain OXT attenuates
ACTH and CORT responses. Although there are some indications of CORT
influencing OXT neurotransmission, specific effects of CORT on
neurohypophyseal or intra-hypothalamic release of OXT have not been
studied in detail.
In the present set of experiments, adult male rats were adrenalectomized
(ADX) or sham-operated and fitted with a jugular vein catheter and/or
microdialysis probe targeting the hypothalamic paraventricular nucleus
(PVN). Blood samples and dialysates were collected before and after
forced swimming (FS) and analyzed for CORT, ACTH and AVP concentrations
(in plasma) and OXT concentrations (in plasma and dialysates).
Experimental treatments included acute infusion of CORT (70 or 175 mu
g/kg i.v.) 5 min prior to FS, or subcutaneous placement of 40% CORT
pellets resulting in stable CORT levels in the normal basal range.
Although ADX did not alter basal OXT concentrations either in plasma or
in microdialysates from the PVN, it did cause an exaggerated peripheral
secretion of OXT and a blunted intra-PVN release of OXT in response to
FS. CORT pellets did not influence either of these ADX-induced effects,
while acute infusion of 175 mu g/kg CORT rescued the stress-induced rise
in OXT release within the PVN and modestly increased peripheral OXT
secretion.
In conclusion, these results indicate that CORT regulates both
peripheral and intracerebral OXT release, but in an independent manner.
Whereas the peripheral secretion of OXT occurs simultaneously to HPA
axis activation in response to FS and is modestly influenced by CORT,
HPA axis activation and circulating CORT strongly contribute to the
stress-induced stimulation of OXT release within the PVN. (C) 2016
Elsevier Ltd. All rights reserved.
