Hypothalamic paraventricular nucleus, but not vasopressin, participates in chronic hyperactivity of the HPA axis in diabetic rats

Medication Dosage Impact on Mortality in Old-Age Individuals with Schizophrenia: A National Cohort Study

As the prevalence of old-age individuals with schizophrenia (OAS) increases in a society undergoing demographic aging, the exploration of medication choices becomes increasingly crucial. Due to the current scarcity of literature on OAS, this study seeks to examine how the utilization and cumulative dosages of psychotropic medications influence both overall and cause-specific mortality risks within this population. A national cohort of 6433 individuals diagnosed with OAS was followed up for 5 years. This study involved comparing the mortality rates associated with low, moderate, and high dosages of antipsychotics, antidepressants, mood stabilizers, and sedative/hypnotic drugs against the 'no exposure' category, based on individual dosages. Cox regression was employed for survival analyses to compare overall mortality and specific-cause mortality across various dosage groups. The exposure variable examined was the dosage of a specific psychotropic medication. Covariates were adjusted accordingly. The analysis revealed that patients on low/moderate antipsychotic doses had improved survival compared to non-exposed individuals. Moderate antipsychotic use corresponded to reduced cardiovascular disease mortality risk. Similarly, those exposed to antidepressants had enhanced survival in low and moderate doses. Sedative-hypnotic exposure was linked to decreased mortality risk in low doses. This study observed that low/moderate antipsychotic doses in older adults with schizophrenia were associated with decreased all-cause mortality, emphasizing the significance of precise medication selection and dosing. It underscores the need for vigilant polypharmacy management and tailored medication strategies in addressing the complexities of treating OAS.

Pre-Test Manipulation by Intraperitoneal Saline Injection with or without Isoflurane Pre-Treatment Does Not Influence the Outcome of Social Test in Male Mice

Preclinical studies on rodents should follow the 3R principle minimising the suffering of the animals. To do so, some researchers use inhalation anaesthetic induction even before intraperitoneal injection. However, several studies suggested that both interventions might influence the behaviour of the animals. We aimed to test whether intraperitoneal injection alone or in combination with isoflurane anaesthesia is a preferable treatment method 30 min before a social test. Male C57BL/6 mice were studied using a behavioural test battery comparing three groups (one control group and intraperitoneal saline-treated groups with or without short isoflurane inhalation). Our results confirmed that both interventions had no profound influence on the conventionally measured parameters of social tests (interest in sociability, social discrimination memory, social interaction as well as resident–intruder test) and were not acutely stressful (measured by similar ACTH levels between the groups) not even after repeated administration (similar body weight gain during the one-week observation period). Taking into consideration the possible long-term harmful effect of isoflurane inhalation, we recommend using intraperitoneal injection without it as saline injection did not violate the 3R principle inducing only mild stress.

Bolus Injection of Liraglutide Raises Plasma Glucose in Normal Rats by Activating Glucagon-like Peptide 1 Receptor in the Brain

Diabetes is commonly treated with glucagon-like peptide-1 receptor (GLP-1R) agonists including liraglutide and others. However, liraglutide was found to raise plasma glucose levels in normal rats. The current study aims to determine how liraglutide causes this contentious condition in rats, both normal and diabetic. An adrenalectomy was performed to investigate the relationship between steroid hormone and liraglutide. To investigate the effect of central liraglutide infusion on blood glucose in rats, rats were intracerebroventricularly administrated with liraglutide with or without HPA axis inhibitors such as berberine and dexamethasone. The results showed that a single injection of liraglutide caused a temporary increase in blood glucose in healthy rats. Another GLP-1R agonist, Exendin-4 (Ex-4), increased blood sugar in a manner similar to that of liraglutide. The effects of liraglutide were also blocked by guanethidine pretreatment and vanished in normal rats with adrenalectomy. Additionally, central infusion of liraglutide via intracerebroventricular (icv) injection into normal rats also causes a temporary increase in blood glucose that was blocked by GLP-1R antagonists or the inhibitors such as berberine and dexamethasone. Similarly, central liraglutide treatment causes temporary increases in plasma glucose, adrenocorticotropic hormone (ACTH), and cortisol levels, which were reversed by inhibitors for the hypothalamic-pituitary-adrenal (HPA) axis. In normal rats, the temporary glucose-increasing effect of liraglutide was gradually eliminated during consecutive daily treatments, indicating tolerance formation. Additionally, liraglutide and Ex-4 cross-tolerance was also discovered in normal rats. Liraglutide was more effective in diabetic rats than in normal rats in activating GLP-1R gene expression in the isolated adrenal gland. Interestingly, the effect of liraglutide on glycemic control varied depending on whether the rats were diabetic or not. In normal rats, bolus injection of liraglutide, such as Ex-4, may stimulate the HPA axis, resulting in hyperglycemia. The cross-tolerance of liraglutide and Ex-4 provided a novel perspective on GLP-1R activation.

Perinatal Exposure to Western Diet Programs Autonomic Dysfunction in the Male Offspring

Although the deleterious influence of protein deficiency on fetal programming is well documented, the impact of a Western diet on epigenetic mechanisms is less clear. We hypothesized that high-fat high-sucrose diet (HFHSD) consumption during pregnancy leads to epigenetic modifications within the progeny's compensatory renin-angiotensin system (RAS), affecting autonomic and metabolic functions. Dams were fed HFHSD (45% fat and 30% sucrose) or regular chow (RD) from mating until weaning of the pups (~7 weeks). Offspring from both groups were then maintained on chow and studied in adulthood (3-7 months). Offspring from HFHSD-exposed dams (OH) exhibited no difference in body weight or fasting blood glucose compared to controls (OR). In 3-month-old offspring, DNA methylation was significantly lower for the ACE2 gene (P < 0.05) in the brainstem, kidney and cecum. Moreover, ACE2 activity in the hypothalamus was increased at 7 months (OH: 91 ± 1 vs. OR: 74 ± 4 AFU/mg/min, P < 0.05). Although baseline blood pressure was not different between groups, vagal tone in OH was significantly impaired compared to OR. At the same time, OH offspring had a 1.7-fold increase in AT_1a receptor expression and a 1.3-fold increase in ADAM17 mRNA. DOCA-salt treatment further revealed and exacerbated hypertensive response in the OH progeny (OH: 130 ± 6 vs. OR: 108 ± 3 mmHg, P < 0.05). Taken together, our data suggest that perinatal exposure to HFHSD resulted in epigenetic modifications of the compensatory brain RAS, potentially affecting plasticity of neuronal networks leading to autonomic dysfunction in the male offspring.

The role of sigma-1 receptor and brain-derived neurotrophic factor in the development of diabetes and comorbid depression in streptozotocin-induced diabetic rats

RATIONALE

Depression is highly prevalent in diabetes (DM). Brain-derived neurotrophic factor (BDNF) which is mainly regulated by the endoplasmic reticulum chaperon sigma-1 receptor (S1R) plays a relevant role in the development of depression.

OBJECTIVES

We studied the dose-dependent efficacy of S1R agonist fluvoxamine (FLU) in the prevention of DM-induced depression and investigated the significance of the S1R-BDNF pathway.

METHODS

We used streptozotocin to induce DM in adult male rats that were treated for 2 weeks p.o. with either different doses of FLU (2 or 20 mg/bwkg) or FLU + S1R antagonist NE100 (1 mg/bwkg) or vehicle. Healthy controls were also enrolled. Metabolic, behaviour, and neuroendocrine changes were determined, and S1R and BDNF levels were measured in the different brain regions.

RESULTS

In DM rats, immobility time was increased, adrenal glands were enlarged, and thymuses were involuted. FLU in 20 mg/bwkg, but not in 2 mg/bwkg dosage, ameliorated depression-like behaviour. S1R and BDNF protein levels were decreased in DM, while FLU induced SIR-BDNF production. NE100 suspended all effects of FLU.

CONCLUSIONS

We suggest that disturbed S1R-BDNF signaling in the brain plays a relevant role in DM-induced depression. The activation of this cascade serves as an additional target in the prevention of DM-associated depression.

Vasopressin signaling at brain level controls stress hormone release: the vasopressin-deficient Brattleboro rat as a model

The nonapeptide arginine vasopressin (AVP) has long been suggested to play an important role as a secretagogue for triggering the activity of the endocrine stress response. Most recent studies employed mutant mice for analyzing the importance of AVP for endocrine regulation under stress. However, it is difficult to compare and draw overall conclusions from all these studies as mixing the genetic material from different mouse strains has consequences on the individual's stress response. Moreover, mice are not ideal subjects for several experimental procedures. Therefore, to get more insight, we used a rather old mutant rat model: the AVP-deficient Brattleboro rat. The present short review is aimed at providing the most interesting results of these studies within the last 8 years that allowed gaining new insights in the potential signal function of AVP in stress and endocrine regulation.

Vasopressin deficiency diminishes acute and long-term consequences of maternal deprivation in male rat pups

Early life events have special importance in the development as postnatal environmental alterations may permanently affect the lifetime vulnerability to diseases. For the interpretation of the long-term consequences it is important to understand the immediate effects. As the role of vasopressin in hypothalamic-pituitary-adrenal axis regulation as well as in affective disorders seem to be important we addressed the question whether the congenital lack of vasopressin will modify the stress reactivity of the pups and will influence the later consequences of single 24h maternal deprivation (MD) on both stress-reactivity and stress-related behavioral changes. Vasopressin-producing (di/+) and deficient (di/di) Brattleboro rat were used. In 10-day-old pups MD induced a remarkable corticosterone rise in both genotypes without adrenocorticotropin (ACTH) increase in di/di rats. Studying the later consequences at around weaning (25-35-day-old rats) we found somatic and hormonal alterations (body weight reduction, dysregulation of the stress axis) which were not that obvious in di/di rats. The more anxious state of MD rats was not detectable in di/di rats both at weaning and in adulthood (7-12-week-old). The lack of vasopressin abolished all chronic stress and anxiety-like tendencies both at weaning and in adulthood probably as a consequence of reduced ACTH rise immediately after MD in pups. This finding suggests that postnatal stress-induced ACTH rise may have long-term developmental consequences.

Blunted HPA axis response in lactating, vasopressin-deficient Brattleboro rats

Adaptation to stress is a basic phenomenon in mammalian life that is mandatorily associated with the activity of the hypothalamic-pituitary-adrenal (HPA) axis. An increased resting activity of the HPA axis can be measured during pregnancy and lactation, suggesting that these reproductive states lead to chronic load in females. In this study, we examined the consequences of the congenital lack of vasopressin on the activity of the HPA axis during lactation using vasopressin-deficient Brattleboro rats. Virgin and lactating, homozygous vasopressin-deficient rats were compared with control, heterozygous rats. In control dams compared with virgins, physiological changes similar to those observed in a chronic stress state (thymus involution, adrenal gland hyperplasia, elevation of proopiomelanocortin mRNA levels in the adenohypophysis, and resting plasma corticosterone levels) were observed. In vasopressin-deficient dams, adrenal gland hyperplasia and resting corticosterone level elevations were not observed. Corticotropin-releasing hormone (Crh) mRNA levels in the hypothalamic paraventricular nucleus were elevated in only the control dams, while oxytocin (OT) mRNA levels were higher in vasopressin-deficient virgins and lactation induced a further increase in both the genotypes. Suckling-induced ACTH and corticosterone level elevations were blunted in vasopressin-deficient dams. Anaphylactoid reaction (i.v. egg white) and insulin-induced hypoglycemia stimulated the HPA axis, which were blunted in lactating rats compared with the virgins and in vasopressin-deficient rats compared with the controls without interaction of the two factors. Vasopressin seems to contribute to the physiological changes observed during lactation mimicking a chronic stress state, but its role in acute HPA axis regulation during lactation seems to be similar to that observed in virgins. If vasopressin is congenitally absent, OT, but not the CRH, compensates for the missing vasopressin; however, the functional restitution remains incomplete.

Effects of prolonged exendin-4 administration on hypothalamic-pituitary-adrenal axis activity and water balance

Exendin-4 (Ex-4) is a natural agonist of the glucagon-like peptide-1 (GLP-1) receptor, currently being used as a treatment for type 2 diabetes mellitus due to its insulinotropic properties. Previous studies have revealed that acute administration of both GLP-1 and, in particular, Ex-4 potently stimulates hypothalamic-pituitary-adrenal (HPA) axis activity. In this work, the effects of prolonged Ex-4 exposure on HPA function were explored. To this end, Sprague-Dawley rats were subjected to a daily regimen of two Ex-4 injections (5 μg/kg sc) for a minimum of 7 days. We found that subchronic Ex-4 administration produced a number of effects that resemble chronic stress situations, including hyperactivation of the HPA axis during the trough hours, disruption of glucocorticoid circadian secretion, hypertrophy of the adrenal gland, decreased adrenal gland sensitivity, impaired pituitary-adrenal stress responses, and reductions in both food intake and body weight. In addition, a threefold increase in diuresis was observed followed by a 1.5-fold increase in water intake; these latter effects were abolished by adrenalectomy. Together, these findings indicate that Ex-4 induces a profound dysregulation of HPA axis activity that may also affect renal function.

Stress responsiveness of the hypothalamic-pituitary-adrenal axis: age-related features of the vasopressinergic regulation

The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in adaptation to environmental stresses. Parvicellular neurons of the hypothalamic paraventricular nucleus secrete corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) into pituitary portal system; CRH and AVP stimulate adrenocorticotropic hormone (ACTH) release through specific G-protein-coupled membrane receptors on pituitary corticotrophs, CRHR1 for CRH and V1b for AVP; the adrenal gland cortex secretes glucocorticoids in response to ACTH. The glucocorticoids activate specific receptors in brain and peripheral tissues thereby triggering the necessary metabolic, immune, neuromodulatory, and behavioral changes to resist stress. While importance of CRH, as a key hypothalamic factor of HPA axis regulation in basal and stress conditions in most species, is generally recognized, role of AVP remains to be clarified. This review focuses on the role of AVP in the regulation of stress responsiveness of the HPA axis with emphasis on the effects of aging on vasopressinergic regulation of HPA axis stress responsiveness. Under most of the known stressors, AVP is necessary for acute ACTH secretion but in a context-specific manner. The current data on the AVP role in regulation of HPA responsiveness to chronic stress in adulthood are rather contradictory. The importance of the vasopressinergic regulation of the HPA stress responsiveness is greatest during fetal development, in neonatal period, and in the lactating adult. Aging associated with increased variability in several parameters of HPA function including basal state, responsiveness to stressors, and special testing. Reports on the possible role of the AVP/V1b receptor system in the increase of HPA axis hyperactivity with aging are contradictory and requires further research. Many contradictory results may be due to age and species differences in the HPA function of rodents and primates.

High sensitivity of gastric mucosa to ulcerogenic effect of indomethacin in rats with diabetes

One week after injection of streptozotocin (60 mg/kg intravenously), rats developed diabetes associated with a significant increase of gastric mucosa sensitivity to the ulcerogenic effect of indomethacin (35 mg/kg subcutaneously). Since potentiation of the ulcerogenic effect of indomethacin was observed only in rats subjected to fasting before drug injection, we hypothesize that this effect was caused by a drop of high glucose level in the blood after fasting.

Arginine vasopressin (AVP) expressional changes in the hypothalamic paraventricular and supraoptic nuclei of stroke-prone spontaneously hypertensive rats

Arginine vasopressin (AVP) is a neuropeptide with vasoconstrictive, antidiuretic, cardiovascular regulative and hepatic glycogenolysis effects, that also affects other behaviors including modulating learning. A number of studies on AVP regulation have been conducted in various metabolic diseases (disorders). In this study, the immunoreactivities of AVP in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) and mRNA expressions in the hypothalamus were investigated by immunohistochemistry and quantitative real-time PCR (RT-qPCR) in stroke-prone spontaneously hypertensive rats at different ages (i.e., at postnatal months [PM] 1, 8, and 12). Blood glucose levels in the PM 8 group were higher than in the other groups. However, cresyl violet positive neurons were detected in the PVN and SON of all animals, and numbers of cresyl violet positive neurons were similar in all aged groups. In addition, AVP immunoreactivity was detected in the PVN and SON of all age groups, and AVP immunoreactivity and mRNA expression levels were found to be increased in proportion to age by immunohistochemistry and RT-qPCR. These results suggest that the diabetic condition is temporally generated after hypertension has developed. Furthermore, our findings suggest that increased AVP expressions in the hypothalamic PVN and SON are associated with hypertension by age.

Congenital absence of vasopressin and age-dependent changes in ACTH and corticosterone stress responses in rats

The hypothalamic components of the hypothalamo-pituitary-adrenal axis (HPA) are corticotropin-releasing hormone (CRH) and vasopressin. To test the hypothesis that HPA regulation changes with age, we compared ether and bacterial lipopolysaccharide (LPS) injection induced stress reactions in adult and 10-day-old Brattleboro rats, which naturally lack vasopressin owing to mutation of the gene (di/di). The LPS stimulus was used also with V(1b) receptor antagonist pretreatment (SSR149415). In adult di/di or V(1b) pretreated rats, we observed normal pituitary and adrenocortical secretory responses, while in all 10-day-old rats stress-induced serum corticosterone increases were marked, but adrenocorticotropin (ACTH) increases were significantly smaller. Compared to control pups the adenohypophysis of the 10-day-old di/di rats responded normally to CRH, but their adrenal glands were hyper-responsive to ACTH, while in adults there was greater secretion at both levels with no difference between the genotypes. The serum transcortin level was higher in adults than pups, with the di/di pups having higher transcortin levels than controls. Hence, using the same stressors in adults and pups with both a genetic model and pharmacological pretreatment, we have shown that the role of vasopressin in ACTH regulation is more important during the neonatal period than in adulthood. Blunted hypophysial sensitivity to CRH and similar adrenal gland sensitivity to ACTH in the pups compared to adults suggest that hypothalamic factors could be responsible for the neonatal stress hyporesponsive period.

Enhanced glucose tolerance in the Brattleboro rat

[Arg(8)]-vasopressin (AVP) plays a crucial role in regulating body fluid retention, which is mediated through the vasopressin V(2) receptor in the kidney. In addition, AVP is involved in the regulation of glucose homeostasis via vasopressin V(1A) and vasopressin V(1B) receptors. Our previous studies demonstrated that vasopressin V(1A) receptor-deficient (V(1A)R-/-) and V(1B) receptor-deficient (V(1B)R-/-) mice exhibited hyperglycemia and hypoglycemia with hypoinsulinemia, respectively. These findings indicate that vasopressin V(1A) receptor deficiency results in decreased insulin sensitivity whereas vasopressin V(1B) receptor deficiency results in increased insulin sensitivity. In addition, vasopressin V(1A) and vasopressin V(1B) receptor double-deficient (V(1AB)R-/-) mice exhibited impaired glucose tolerance, suggesting that the effects of vasopressin V(1B) receptor deficiency do not influence the development of hyperglycemia promoted by vasopressin V(1A) receptor deficiency, and that the blockage of both receptors could lead to impaired glucose tolerance. However, the contributions of the entire AVP/vasopressin receptors system to the regulation of blood glucose have not yet been clarified. In this study, to further understand the role of AVP/vasopressin receptors signaling in blood glucose regulation, we assessed the glucose tolerance of AVP-deficient homozygous Brattleboro (di/di) rats using an oral glucose tolerance test (GTT). Plasma glucose and insulin levels were consistently lower in homozygous di/di rats than in heterozygous di/+ rats during the GTT, suggesting that the blockage of all AVP/vasopressin receptors resulting from the AVP deficiency could lead to enhanced glucose tolerance.

Lack of vasopressin does not prevent the behavioural and endocrine changes induced by chronic unpredictable stress

Vasopressin (VP) plays an important role in hypothalamo-pituitary-adrenal (HPA) axis regulation and in stress-related disorders. Our previous studies confirmed the role of VP in acute situations, where VP-deficient Brattleboro rats had less depression-like behaviour compared to animals that express VP. In this study, we test the hypothesis that VP-deficient rats are more resistant to the development of chronic HPA axis hyperactivity and depression-like symptoms after chronic unpredictable stress (CUS). Male VP-deficient Brattleboro rats were compared to their heterozygous littermates (controls). CUS consisted of different mild stimuli for 5 weeks. Elevated plus maze and forced swim test were used for behavioural characterization, while organs and blood for HPA axis parameters were collected at the end of the experiment. In controls, CUS resulted in the development of chronic stress state characterized by typical somatic (body weight reduction, thymus involution) and endocrine changes (resting plasma ACTH and corticosterone elevation and POMC mRNA elevation in anterior lobe of the pituitary). Floating time in the forced swim test was enhanced together with reduced open arm entries on elevated plus maze and a reduction in daily food intake. Unexpectedly, the lack of VP did not alter the effect of CUS on the somatic and behavioural measures, but only prevented CUS-induced corticosterone changes. In conclusion, lifelong VP-deficiency has a positive effect on corticosterone elevation following CUS but does not affect the behavioural consequences of CUS. It is likely that the interplay of several related factors, rather than an alteration in a single neuropeptide, modulates behaviour and disease pathogenesis.

Stress-related endocrinological and psychopathological effects of short- and long-term 50Hz electromagnetic field exposure in rats

It is believed that different electromagnetic fields do have beneficial and harmful biological effects. The aim of the present work was to study the long-term consequences of 50 Hz electromagnetic field (ELF-EMF) exposure with special focus on the development of chronic stress and stress-induced psychopathology. Adult male Sprague-Dawley rats were exposed to ELF-EMF (50 Hz, 0.5 mT) for 5 days, 8h daily (short) or for 4-6 weeks, 24h daily (long). Anxiety was studied in elevated plus maze test, whereas depression-like behavior of the long-treated group was examined in the forced swim test. Some days after behavioral examination, the animals were decapitated among resting conditions and organ weights, blood hormone levels as well as proopiomelanocortin mRNA level from the anterior lobe of the pituitary gland were measured. Both treatments were ineffective on somatic parameters, namely none of the changes characteristic to chronic stress (body weight reduction, thymus involution and adrenal gland hypertrophy) were present. An enhanced blood glucose level was found after prolonged ELF-EMF exposure (p=0.013). The hormonal stress reaction was similar in control and short-term exposed rats, but significant proopiomelanocortin elevation (p<0.000) and depressive-like behavior (enhanced floating time; p=0.006) were found following long-term ELF-EMF exposure. Taken together, long and continuous exposure to relatively high intensity electromagnetic field may count as a mild stress situation and could be a factor in the development of depressive state or metabolic disturbances. Although we should stress that the average intensity of the human exposure is normally much smaller than in the present experiment.

Control of the hypothalamo-pituitary-adrenal axis in the neonatal period: adrenocorticotropin and corticosterone stress responses dissociate in vasopressin-deficient brattleboro rats

In adulthood the hypothalamo-pituitary-adrenal axis is controlled by both CRH and arginine vasopressin (AVP). However, in neonates CRH secretion is very low, whereas AVP secretion is fully functional. This suggests that the role of AVP is more pronounced in young than in adult rats. We investigated the role of AVP by studying stress responses in 5, 10, and 20-d-old AVP-deficient Brattleboro rats. Two different stressors were applied: 24-h maternal separation and Hypnorm Grove Oxford UK injections. In heterozygous controls (that do express AVP), both stressors increased plasma ACTH and corticosterone. The ACTH stress response disappeared in AVP-deficient rats, demonstrating that during the perinatal period, the secretion of this hormone is controlled by AVP. Surprisingly, corticosterone responses remained intact in AVP-deficient rats. Similar findings were obtained after 1-, 4-, 12-, and 24-h long maternal separations. Thus, preserved corticosterone stress responses were not explained by changes in the timing of ACTH secretion. In vitro experiments suggested that the dissociation of ACTH and corticosterone stress responses can only be partly explained by higher ACTH responsiveness of the adrenal cortex in AVP-deficient rats. Together, our results show that in neonatal periods, AVP is crucial for the expression of ACTH stress responses, but neither AVP nor ACTH is necessary for the induction of corticosterone stress responses. Discrepant ACTH and corticosterone stress responses may reflect compensatory mechanisms activated by AVP deficiency, but disparate findings suggest that they rather depict a neonate-specific mechanism of hypothalamo-pituitary-adrenal-axis control.

Enhanced expressions of arginine vasopressin (Avp) in the hypothalamic paraventricular and supraoptic nuclei of type 2 diabetic rats

Arginine vasopressin (AVP) is known to a neuropeptide that plays important roles in water conservation, sodium homeostasis, and in the regulation of serum osmolality. Several studies have reported that the elevated AVP level is related with diabetes mellitus as an acute or chronic stressor using type 1 diabetes mellitus animal models. However, it is unclear as to how the immunoreactivity and protein level of AVP in the brain is regulated in animal models of type 2 diabetes mellitus. In the present study, Zucker diabetic fatty (ZDF) rats were employed as a type 2 diabetes mellitus model and were compared with Zucker lean control (ZLC) rats with respect to AVP protein expression. Furthermore, in order to verify the regulation of AVP expression before and after the onset of diabetes mellitus, pre-diabetic rats (4 week-old) and obese-diabetic rats (12 week-old) were used. Blood glucose levels and water consumption were also measured and the results showed significantly high in 12 week-old ZDF than any other groups. AVP expression levels in the paraventricular nucleus and supraoptic nucleus were found to be significantly higher in 12 week-old ZDF rats than in 12 week-old ZLC rats and than in 4 week-old rats by immunostaining and western blotting. Enhanced expression of AVP in these animals may be associated with type 2 diabetes mellitus.

Signs of attenuated depression-like behavior in vasopressin deficient Brattleboro rats

Vasopressin, a peptide hormone functioning also as a neurotransmitter, neuromodulator and regulator of the stress response is considered to be one of the factors related to the development and course of depression. In the present study, we have tested the hypothesis that congenital deficit of vasopressin in Brattleboro rats leads to attenuated depression-like behavior in tests modeling different symptoms of depression. In addition, hypothalamic-pituitary-adrenocortical axis activity was investigated. Vasopressin deficient rats showed signs of attenuated depression-like behavior in forced swimming and sucrose preference tests, while their behavior on elevated plus maze was unchanged. Vasopressin deficiency had no influence on basal levels of ACTH and corticosterone and had only mild impact on hormonal activation in response to forced swimming and plus-maze exposure. However, vasopressin deficient animals showed higher level of dexamethasone induced suppression of corticosterone response to restraint stress and higher basal levels of corticotropin-releasing hormone mRNA in the hypothalamic paraventricular nucleus. In conclusion, present data obtained in vasopressin deficient rats show that vasopressin is involved in the development of depression-like behavior, in particular of the coping style and anhedonia. Moreover, behavioral and endocrine responses were found to be dissociated. We suggest that brain vasopressinergic circuits distinct from those regulating the HPA axis are involved in generating depression-like behavior.