ABSTRACT

In-situ hybridization histochemistry was used to measure corticotrophin-releasing factor mRNA and proenkephalin A mRNA in the paraventricular nucleus (PVN), and pro-opiomelanocortin (POMC) mRNA in the anterior pituitary of the rat. Levels of message were determined at 1, 2, 4 and 8 h after exposure to a variety of physical and psychological stresses. Corticotrophin-releasing factor mRNA in the PVN and POMC mRNA in the anterior pituitary increased in response to i.p. hypertonic saline, restraint and swim stress but not to cold stress. Proenkephalin A mRNA was raised only in response to the physical stress of i.p. injection of hypertonic saline. These results suggest that different afferent pathways and hypothalamic neurotransmitters may be involved in mediating the hypothalamic response to different physical and psychological stresses.

Journal of Endocrinology (1989) 122, 705–711

Successful existence depends on the ability to cope with an immense variety of complex challenges or stressors and to mount an 'appropriate' response to any particular situation. While the concept of stress is readily understood, a definition acceptable to more than a handful of individuals remains elusive. It is necessary therefore at the outset to clarify the context within which we have written the current review. We will utilize a simple definition based on the neuroendocrine response to stressors and for this purpose we shall limit our discussion to those events resulting in the activation of the hypothalamo-pituitary-adrenal (HPA) axis. The final stage of this activation is the secretion of glucocorticoids from the adrenal cortex.

Glucocorticoids have a wide range of actions affecting many aspects of bodily function including metabolism, inflammation and immunity. Glucocorticoids also control their own synthesis and release by completing a negative feedback loop at the level

Serotonin re-uptake inhibitors (SSRIs) can affect the basal activity of the hypothalamic–pituitary–adrenal (HPA) axis in rats. A single injection of citalopram has been shown to stimulate the HPA axis while repeated administration leads to attenuation of the corticosterone response to the SSRI. The purpose of this work was to investigate the rodent HPA axis response to restraint stress, following acute and chronic treatment with the SSRI citalopram. We have demonstrated that a single injection of citalopram is able to prolong acute restraint-induced increases in plasma levels of corticosterone and adrenocorticotrophin (ACTH). This is possibly mediated by arginine vasopressin (AVP) in the parvocellular cells of the paraventricular nucleus (pPVN), as treatment with citalopram or restraint alone did not increase AVP mRNA in pPVN while the combination of treatments resulted in a significant increase in AVP mRNA in the pPVN. In contrast, the increase in corticotrophin-releasing factor (CRF) mRNA in the pPVN in response to acute restraint stress was not altered by citalopram. Oxytocin (OT) mRNA was also increased in the magnocellular PVN (mPVN) by the solo treatments of citalopram and restraint, and was not further enhanced by the dual treatment of restraint and citalopram. Chronic treatment with citalopram did not alter basal plasma levels of corticosterone or ACTH. However, the ACTH response to acute restraint was attenuated following chronic citalopram treatment. AVP mRNA in the pPVN was significantly elevated in response to chronic citalopram compared with saline controls suggesting an effect mediated through the AVP subset of pPVN neurones. The CRF mRNA response to acute restraint was not altered in rats treated chronically with citalopram. OT mRNA was not enhanced in the mPVN following chronic infusion of citalopram but was increased by acute restraint stress. We conclude from these data that both acute and chronic citalopram treatment has the potential to alter the rodent response to acute restraint stress. These effects appear to be regulated by the AVP-containing subset of CRF neurons in the pPVN and thus suggest that parvocellular AVP may have an important role in mediating the actions of SSRIs.

ABSTRACT

We have investigated the effects of recombinant human interleukin (IL)-1α, IL-1β and IL-6 on the activation of the hypothalamo-pituitary-adrenal axis. We have determined the effects of a single i.p. injection of cytokine on circulating ACTH and corticosterone levels, corticotrophin-releasing factor (CRF) mRNA in the parvocellular cells of the paraventricular nucleus and pro-opiomelanocortin (POMC) mRNA in the anterior pituitary at both 4 h and 24 h after injection. IL-1α had no effect on any of the parameters measured at either time-point. In contrast, IL-1β increased CRF mRNA in the parvocellular paraventricular nucleus and POMC mRNA in the anterior pituitary 4 h after injection. Plasma ACTH and corticosterone were increased at 4 h and circulating ACTH was still increased at 24 h after treatment with IL-1β. IL-6 had no effect on message levels but did increase circulating ACTH and corticosterone levels both 4 h and 24 h after injection. The mechanism responsible for the increase in circulating ACTH after IL-6 injection is unclear but would appear to be different from that which is activated by IL-1β which also results in increased CRF and POMC gene expression.

Journal of Endocrinology (1992) 133, 349–355

Abstract

While the effects of cytokines on the hypothalamo-pituitary-adrenal axis have received a great deal of attention in recent years the effects of cytokines on posterior pituitary hormone release has been less well characterized. In the present study we have investigated the effects of a single i.p. injection of interleukin (IL)-1β on circulating levels of vasopressin (AVP) in the rat. We have found that the ability of IL-1β to increase plasma AVP is strongly influenced by circulating levels of glucocorticoid steroids. IL-1β did not affect plasma AVP in sham-operated control animals over the 4 h period of study. In contrast, following adrenalectomy we were able to stimulate AVP substantially with increases over the 4 h period. This effect was reduced by treatment of adrenalectomized rats with a low dose of dexamethasone and abolished with a high dose. These data suggest an inverse relationship between circulating levels of glucocorticoids and the ability of IL-1β to stimulate plasma AVP.

Journal of Endocrinology (1994) 142, 361–366

ABSTRACT

In-situ hybridization with synthetic oligonucleotide probes was used to determine the mRNA content of corticotrophin-releasing factor (CRF) and proenkephalin A mRNA in the paraventricular nucleus, and of pro-opiomelanocortin (POMC) mRNA in the anterior pituitary gland of male rats immediately after, and during recovery from, chronic high-dose prednisolone treatment. Levels of transcripts for mRNA for both CRF and POMC were markedly reduced after the treatment, but there was a rapid return to control values for CRF mRNA within 18 h of steroid withdrawal.

In untreated animals, the stressful stimulus of i.p. hypertonic saline increased CRF and proenkephalin A mRNA within 4 h with no significant difference in response seen whether the tissues were removed at 13.00 or 20.00 h. The increase in POMC mRNA did not reach statistical significance in these animals. Although prednisolone resulted in a marked reduction of basal CRF mRNA, the stress-induced increment of CRF mRNA remained comparable with that found in untreated animals. On the day following cessation of prednisolone treatment at 09.00 h, basal and stress levels of CRF mRNA were significantly higher in rats killed at 20.00 h than at 13.00 h. Proenkephalin A mRNA transcripts were below quantifiable levels of detection in control or non-stressed prednisolone-treated animals at all the time-points studied. Stress, however, resulted in the accumulation of proenkephalin A mRNA in control animals. This response was inhibited by prednisolone treatment and only returned 18 h after withdrawal. Prednisolone treatment reduced POMC mRNA below the levels detected in untreated animals, with no detectable response to stress. However, 36 h after prednisolone withdrawal there was a significant increase in POMC mRNA in response to stress.

Prednisolone concentrations in the plasma on the morning of the day after the final administration of the steroid were very high (880 nmol/l), but these were halved by the evening of that day and had fallen to 60 nmol/l 72 h after withdrawal.

These data show that both CRF and POMC mRNA were profoundly reduced by long-term prednisolone treatment. Stress-induced accumulation of CRF mRNA, however, persisted although the proenkephalin A mRNA responses to this stress were inhibited. No increase in pituitary POMC mRNA in response to stress was apparent until 36 h after withdrawal of prednisolone.

Journal of Endocrinology (1990) 127, 407–415

Abstract

The expression of corticotropin releasing hormone (CRH) in the hypothalamic paraventricular nucleus (PVN) and CRH receptor mRNA in the PVN and anterior pituitary was studied during development of adjuvant-induced arthritis in Piebald–Viral–Glaxo rats, using in situ hybridization techniques. As previously shown with i.p. hypertonic saline injection, basal and immobilization stress-stimulated CRH mRNA levels in the PVN were significantly lower than in controls 14 days after adjuvant injection. However, 7 days after injection, preceding the onset of inflammation, the increase of CRH mRNA following immobilization was significantly higher than in control rats. In contrast to other chronic stress paradigms, inflammation stress failed to induce type-1 CRH receptor (CRH-R1) mRNA in the PVN, either at 7 days, or at 14 days after adjuvant injection, when inflammation is present. The ability of acute immobilization to induce CRH-R1 mRNA in the PVN was not affected 14 days after adjuvant injection but parallel to the CRH peptide mRNA response it was markedly potentiated at 7 days. Pro-opiomelanocorpin (POMC) mRNA levels in the anterior pituitary increased significantly 14 days after adjuvant injection, and they were unaffected by 1 h immobilization. While CRH binding in the pituitary decreased significantly 14 days after adjuvant injection, CRH-Rl mRNA was unchanged. This study shows biphasic hypothalamic responses to acute stress during development of adjuvant-induced arthritis, with enhanced CRH peptide and CRH-Rl mRNAs responses at 7 days, preceding the onset of inflammation, and blunted CRH mRNA responses at 14 days at the height of the inflammatory response. The lack of CRH receptor expression in the PVN in this model of chronic inflammation stress associated to low hypothalamic CRH peptide levels supports the view that positive feedback regulation by CRH is necessary to maintain enhanced CRH expression during chronic stress.

Journal of Endocrinology (1997) 153, 185–191