Independent and overlapping effects of corticosterone and testosterone on corticotropin-releasing hormone and arginine vasopressin mRNA expression in the paraventricular nucleus of the hypothalamus and stress-induced adrenocorticotropic hormone release

Abstract

Adrenocorticotropin (ACTH) release is regulated by both glucocorticoids and androgens; however, the precise interactions are unclear. We have controlled circulating corticosterone (B) and testosterone (T) by adrenalectomy (ADX) +/- B replacement and gonadectomy (GDX) +/- T replacement, comparing these to sham-operated groups. We hoped to reveal how and where these neuroendocrine systems interact to affect resting and stress-induced ACTH secretion. ADX responses. In gonadal-intact rats, ADX increased corticotropin-releasing factor (CRH) and vasopressin (AVP) mRNA in hypothalamic parvocellular paraventricular nuclei (PVN) and ACTH in pituitary and plasma. B restored these toward normal. GDX blocked the increase in AVP but not CRH mRNA and reduced plasma, but not pituitary ACTH in ADX rats. GDX+T restored increased AVP mRNA in ADX rats, although plasma ACTH remained decreased. Stress responses. Restraint-induced ACTH responses were elevated in ADX gonadally intact rats, and B reduced these toward normal. GDX in adrenal-intact and ADX+B rats increased ACTH responses. Without B, T did not affect ACTH; together with B, T restored ACTH responses to normal. The magnitude of ACTH responses to stress was paralleled by similar effects on the number of c-fos staining neurons in the hypophysiotropic PVN. We conclude that gonadal regulation of ACTH responses to ADX is determined by T dependent effects on AVP biosynthesis, whereas CRH biosynthesis is B-dependent. Stress-induced ACTH release is not explained by B and T interactions at the PVN, but is determined by B- and T-dependent changes in drive to PVN motorneurons.

Fig. 1.

Mean ± SEM plasma (top) and pituitary (bottom) ACTH levels in adrenal-intact, ADX, and ADX+B rats as a function of gonadal status (n = 6 per group). **p < 0.01 versus INTACT; †p < 0.01 versus INTACT. ADX,^ap < 0.01;^bp > 0.05 versus ADX.

Fig. 2.

CRH expression in the PVH is dominated by ADX and B. Dark-field photomicrographs of CRH mRNA through a common level of the PVH comparing the effects of ADX ± B and GDX ± T. ADX produced reliable increases in CRH mRNA levels, reversible with B replacement (left to right). Similar response patterns were also seen in GDX and GDX+T-replaced animals (top to bottom).

Fig. 3.

AVP mRNA responses to ADX vary as a function of gonadal status. Dark-field photomicrographs of AVP mRNA in the PVH illustrating the effects of GDX and T replacement on ADX-induced elevations in AVP expression. ADX increased AVP mRNA levels in gonadal intact animals (top). This response was abolished in GDX rats (middle), and reversed by T replacement (bottom).

Fig. 4.

Mean ± SEM medial parvocellular CRH (left) and AVP mRNA (right) responses to ADX and B-replacement as a function of gonadal status. Data are expressed as a percentage of INT. INT values (n = 6 per group). **p < 0.01 versus INTACT;^bp < 0.05;^cp > 0.05 versus ADX.

Fig. 5.

Mean ± SEM plasma ACTH responses to 30 min restraint in adrenal-INTACT, ADX, and ADX+B animals as a function of gonadal status (n = 6 per group). **p < 0.01; *p < 0.05 versus INTACT.

Fig. 6.

Mean ± SEM plasma ACTH responses to 30 min restraint in gonadal-INTACT, GDX, and GDX+T animals as a function of adrenal status (n = 6 per group). **p < 0.01; *p < 0.05 versus INTACT.

Fig. 7.

Mean ± SEM number of Fos-IR cells in the mpPVH induced by 30 min restraint as a function of gonadal and adrenal status (n = 3 per group; experiment 3). **p < 0.01 versus INTACT;^ap < 0.01;^cp > 0.05 versus ADX (see Table 2). Note the parallel effects of B and T on plasma ACTH responses in Figure8.

Fig. 8.

Mean ± SEM peak change in ACTH responses to restraint as a function of gonadal and adrenal status (n = 6 per group; experiment 2). Peak Δs were derived from ACTH values in Figures 5 and 6. **p < 0.01 versus INTACT; ^bp < 0.05;^cp > 0.05 versus ADX (see Table2).