Urocortin II (Ucn II) is a novel corticotropin-releasing hormone (CRH)-related peptide discovered as a selective agonist for type-2 CRH receptor. In the rat or mouse brain, Ucn II mRNA shows weak expression mainly in the hypothalamic paraventricular nucleus (PVN) and the locus coeruleus (LC). Understanding the regulation of Ucn II mRNA expression under varying conditions provides new insights into central stress response. We examined expression of Ucn II mRNA in the PVN and LC following immobilization stress, water deprivation, and adrenalectomy. Rats subjected to immobilization stress exhibited a dramatic induction of Ucn II mRNA expression in the parvocellular part of the PVN at the end of 2 h of immobilization. In contrast, water deprivation for 3 days induced Ucn II mRNA expression mainly in the magnocellular part of the PVN. Although water-deprived rats showed a marked decrease in their food intake, pair-fed rats failed to alter PVN Ucn II mRNA expression, suggesting that osmotic stimuli per se, but not reduced food consumption during water deprivation, caused Ucn II mRNA induction in the magnocellular part of the PVN. Adrenalectomized rats failed to show an increase in Ucn II mRNA in the PVN when compared to sham-operated rats. Double-label in situ hybridization revealed colocalization of Ucn II mRNA in approximately 45% of the CRH mRNA-expressing cells in the parvocellular part of the PVN following immobilization, or colocalization in most of the vasopressin mRNA-expressing cells in the magnocellular part of the PVN following water deprivation. In the LC, no induction of Ucn II mRNA was observed in any of the three experimental conditions, indicating that the regulation of Ucn II mRNA expression was site-specific. The results show a stressor-specific regulation of Ucn II mRNA expression in the PVN and raise the possibility that Ucn II mRNA plays a modulatory role in stress-induced alteration of anterior and posterior pituitary function, depending on the type of stress.

In our previous study, apparent reduction of glucocorticoid receptor (GR) mRNA was seen in the hippocampus and the hypothalamic paraventricular nucleus (PVN) during repeated immobilization (IMO) stress, but not following starvation. Our laboratory has also shown that the sp1 activates, whereas tumour suppressor p53 represses the promoter activity of GR gene. In an attempt to reveal the possibility that transcription factors such as sp1 and/or p53 are involved in the regulation of GR mRNA expression in the hippocampus and in the PVN in vivo, we examined the expression of GR mRNA, p53 mRNA, and sp1 mRNA in the hippocampus and in the PVN during repeated IMO and following starvation. In addition, the expression of these mRNAs was examined in the anterior pituitary, another GR-rich area. GR mRNA in all subfields of the hippocampus was robustly decreased, while GR mRNA in the anterior pituitary was increased, 24 h following 4 x IMO (2 h daily, for 4 consecutive days) and immediately after 5 x IMO. GR mRNA in the PVN was significantly decreased immediately after 5 x IMO, but not at 24 h after 4 x IMO. Conversely, p53 mRNA in the PVN and hippocampus was increased, whereas p53 mRNA in the anterior pituitary was decreased, 24 h following 4 x IMO and immediately after 5 x IMO. Sp1 mRNA was unchanged in all areas examined following repeated IMO. Following 4 days of starvation, neither GR mRNA, p53 mRNA nor sp1 mRNA showed any changes in the PVN and the hippocampus, except there was a minor decrease in GR mRNA in CA1-2. In the anterior pituitary, 4 days of starvation induced a minor, but significant increase in GR mRNA, whereas it decreased p53 mRNA. Overall, regression analyses revealed a negative correlation between GR mRNA levels and p53 mRNA levels in CA1-2 and dentate gyrus of the hippocampus and in the anterior pituitary. GR mRNA in the PVN also showed a tendency towards the negative correlation with p53 mRNA levels. The results raise the possibility that p53 negatively regulates GR mRNA expression in the PVN, the hippocampus and the anterior pituitary during repeated immobilization stress.

We have shown in a previous study that high corticosterone levels during repeated immobilization stress result in a reduction of glucocorticoid receptor (GR) mRNA in the hypothalamic paraventricular nucleus (PVN) and the hippocampus. The reduction of GR presumably accounts for loss of or decrease in glucocorticoid-negative feedback, and thus hyperfunction of the hypothalamic-pituitary-adrenocortical (HPA) axis persists during chronic stress. Starvation is a stress state in which the counterregulatory responses against the loss of food occur in the central nervous system. We explored the impact of starvation on the HPA axis, GR and mineralocorticoid receptor (MR) mRNAs in the hippocampus, the PVN, and the anterior pituitary (AP) of rats. Rats were starved for 4 days and sacrificed in the morning. Starved rats showed high levels of plasma corticosterone, whereas neither plasma corticotropin (ACTH), AP proopiomelanocortin (POMC) mRNA nor AP type-1 corticotropin-releasing hormone (CRH) receptor mRNA was altered in the starved rats. In the presence of high corticosterone, starvation resulted in a decrease in both CRH mRNA and type-1 CRH receptor mRNA in the PVN. Consistently, the starved rats did not show any changes in GR mRNA in the hippocampus (CA1-2, CA3, and dentate gyrus), the PVN or the AP despite the elevation of plasma corticosterone. A significant decrease in MR mRNA was seen in the dentate gyrus and the AP, but not in CA1–2, CA3 or PVN. The lack of reduction of GR may be one of the organism’s counterregulatory responses during starvation, which allows an intact glucocorticoid negative feedback, thereby resulting in decreased anorectic neuropeptide levels, namely CRH, in the PVN. The results also indicate that GR mRNA in the hippocampus and other brain regions is not solely regulated by circulating glucocorticoids. The mechanism underlying the regulation of GR mRNA in the central nervous system remains to be clarified.

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During starvation, counterregulatory responses to loss of food (i.e. responses that lead to an increase in appetite) occur in the central nervous system (CNS). This study was designed to examine whether middle-aged rats show greater or smaller behavioural, peripheral and central hormonal responses during starvation compared to young rats. In experiment 1, refeeding following 4 days of starvation was measured in both middle-aged (72-week-old) and young (9-week-old) rats. The level of refeeding was similar to each prestarved level until 3 days after the end of starvation in both groups. From the 4th day, the level of refeeding in young rats increased and reached beyond the prestarved level, whereas refeeding in middle-aged rats remained similar to the prestarved level. Thus, overall refeeding throughout 7 days was greater in young rats than in middle-aged rats. In experiment 2, middle-aged and young rats were starved for 4 days and were killed in the morning. Middle-aged rats showed a smaller plasma corticosterone response than that of young rats. The magnitude of decreases in plasma glucose, insulin and leptin was similar in both groups. In the arcuate nucleus, the starvation-induced increase in neuropeptide Y (NPY) mRNA and the decrease in proopiomelanocortin (POMC) mRNA were smaller in middle-aged rats than in young rats. In contrast, the starvation-induced decrease in corticotrophin-releasing hormone (CRH) mRNA in the hypothalamic paraventricular nucleus was greater in middle-aged rats than young rats. The magnitude of decrease in type-2 CRH receptor mRNA in the ventromedial hypothalamus was similar in both groups. The results indicate that (a) ageing impaired refeeding response (b), middle-aged rats showed the same directional neuropeptide mRNA responses as seen in young rats during starvation and (c) the magnitude of these counterregulatory responses in the CNS in middle-aged versus young rats was not uniform, but rather was site-specific or neuropeptide-specific. This study suggests the importance of NPY and POMC responsiveness in the arcuate nucleus in the age-related differences resulting from starvation-induced refeeding.