Allopregnanolone reduces neuroendocrine response to acute stressful stimuli in sheep

Abstract

The verified hypothesis assumed that centrally administered neurosteroid, allopregnanolone (AL), could affect basal and/or stress-induced activity of the hypothalamic-pituitary-adrenal (HPA) axis in sheep. Four groups (n = 6 each) of luteal-phase sheep were intracerebroventricularly infused for 3 days with a vehicle without stress (control); a vehicle treated with stressful stimuli (isolation and partial movement restriction) on the third day; AL (4 × 15 µg/60 µL/30 min, at 30-min intervals) treated with stressful stimuli, and AL alone. Simultaneously, the push-pull perfusion of the infundibular nucleus/median eminence and plasma sample collection were performed. After the experiment, the sheep were killed to collect the hypothalamic and anterior pituitary (AP) tissues. Stressful stimuli evoked an increase in the expression of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA in the hypothalamic paraventricular nucleus (PVN), and AVP receptor (V1b) and proopiomelanocortin (POMC) mRNA in the AP; the concentrations of perfusate CRH, and plasma adrenocorticotropic hormone (ACTH) and cortisol compared to controls. Conversely, the expression of the CRH receptor (CRHR1) mRNA in the AP was downregulated. AL decreased the expression of CRH and AVP mRNA in the PVN, and AVPRV1b and POMC mRNA in the AP in stressed sheep, compared to only stressed ones. There was also a reduction in perfusate CRH, and plasma ACTH and cortisol concentrations. AL alone decreased the expression of CRHR1 mRNA in the AP, and plasma cortisol concentration at the beginning of the collection period compared to controls. In conclusion, AL may function centrally as a suppressor of HPA axis activity in stressed sheep.

The Effect of Allopregnanolone on Enzymatic Activity of the DNA Base Excision Repair Pathway in the Sheep Hippocampus and Amygdala under Natural and Stressful Conditions

“…Studies on adult rats have shown that in response to stress, the bed nucleus of the stria terminalis sends an axonal projection into neuroendocrine cell regions of the paraventricular nucleus (PVN) [ 33 ] and relays hippocampal cholinergic signals activating the HPA axis [ 34 ]. The results described in our earlier work [ 25 ] showed that the acute stressful stimuli used, i.e., isolation in combination with partial movement restriction, induced strong neuroendocrine stress response in experimental sheep. This was reflected by an increase in the concentration of corticotropin-releasing hormone (CRH) in the cerebrospinal fluid (CSF), as well as the concentration of adrenocorticotropic hormone (ACTH) and cortisol in the blood.…”

“…This was reflected by an increase in the concentration of corticotropin-releasing hormone (CRH) in the cerebrospinal fluid (CSF), as well as the concentration of adrenocorticotropic hormone (ACTH) and cortisol in the blood. In addition, increased abundance of the CRH and arginine vasopressin mRNA in the PVN was observed [ 25 ]. Considering more broadly the consequences of such types of stress at the molecular level, the results of this study showed the strong stimulation of DNA defense mechanisms in all tissues examined.…”

“…Moreover, Concas et al [ 65 ] suggested that the rate of AP synthesis in the brain was greater than in peripheral blood-supplying tissues. By examining earlier the central effect of AL on HPA axis activity in the same sheep, we found that this neurosteroid reduced numerous aspects of neuroendocrine stress response when administered into the IIIv [ 25 ]. This was reflected, among other factors, by a decrease in the concentration of CRH in the CSF, as well as of ACTH and cortisol in plasma.…”

“…The experiment was performed during the reproductive season from mid-October to mid-December. Estrus synchronization was performed using the Chronogest CR method [ 25 ]. The sheep were randomly divided into four groups ( n = 6 each) and were treated over three consecutive days of the late luteal phase (days 12–14) of the estrous cycle as follows: (1) intracerebroventricular (icv.)…”

“…The main goal was to investigate whether these processes were affected by AL administered directly to the CNS. We used the sheep, a large animal model whose brain has a high structural similarity to the human brain and is highly susceptible to stress [ 25 ].…”