The vasopressin deficient Brattleboro rats: a natural knockout model used in the search for CNS effects of vasopressin

Kidney collecting duct-derived vasopressin is not essential for appropriate concentration or dilution of urine

We have previously shown that kidney collecting ducts make vasopressin. However, the physiological role of collecting duct-derived vasopressin is uncertain. We hypothesized that collecting duct-derived vasopressin is required for the appropriate concentration of urine. We developed a vasopressin conditional knockout (KO) mouse model wherein Cre recombinase expression induces deletion of arginine vasopressin (Avp) exon 1 in the distal nephron. We then used age-matched 8- to 12-wk-old Avp fl/fl;Ksp-Cre(-) [wild type (WT)] and Avp fl/fl;Ksp-Cre(+) mice for all experiments. We collected urine, serum, and kidney lysates at baseline. We then challenged both WT and knockout (KO) mice with 24-h water restriction, water loading, and administration of the vasopressin type 2 receptor agonist desmopressin (1 µg/kg ip) followed by the vasopressin type 2 receptor antagonist OPC-31260 (10 mg/kg ip). We performed immunofluorescence and immunoblot analysis at baseline and confirmed vasopressin KO in the collecting duct. We found that urinary osmolality (UOsm), plasma Na+, K+, Cl-, blood urea nitrogen, and copeptin were similar in WT vs. KO mice at baseline. Immunoblots of the vasopressin-regulated proteins Na+-K+-2Cl- cotransporter, NaCl cotransporter, and water channel aquaporin-2 showed no difference in expression or phosphorylation at baseline. Following 24-h water restriction, WT and KO mice had no differences in UOsm, plasma Na+, K+, Cl-, blood urea nitrogen, or copeptin. In addition, there were no differences in the rate of urinary concentration or dilution as in WT and KO mice UOsm was nearly identical after desmopressin and OPC-31260 administration. We conclude that collecting duct-derived vasopressin is not essential to appropriately concentrate or dilute urine.NEW & NOTEWORTHY Hypothalamic vasopressin is required for appropriate urinary concentration. However, whether collecting duct-derived vasopressin is involved remains unknown. We developed a novel transgenic mouse model to induce tissue-specific deletion of vasopressin and showed that collecting duct-derived vasopressin is not required to concentrate or dilute urine.

Socio-behavioral dysfunction in disorders of hypothalamic-pituitary involvement: The potential role of disease-induced oxytocin and vasopressin signaling deficits

Disorders involving hypothalamic and pituitary (HPIT) structures-including craniopharyngioma, Langerhans cell histiocytosis, and intracranial germ cell tumors-can disrupt brain and endocrine function. An area of emerging clinical concern in patients with these disorders is the co-occurring socio-behavioral dysfunction that persists after standard hormone replacement therapy. Although the two neuropeptides most implicated in mammalian social functioning (oxytocin and arginine vasopressin) are of hypothalamic origin, little is known about how disease-induced damage to HPIT structures may disrupt neuropeptide signaling and, in turn, impact patients' socio-behavioral functioning. Here we provide a clinical primer on disorders of HPIT involvement and a review of neuropeptide signaling and socio-behavioral functioning in relevant animal models and patient populations. This collective evidence suggests that neuropeptide signaling disruptions contribute to socio-behavioral deficits experienced by patients with disorders of HPIT involvement. A better understanding of the biological underpinnings of patients' socio-behavioral symptoms is now needed to enable the development of the first targeted pharmacological strategies by which to manage patients' socio-behavioral dysfunction.

The Paraventricular Nucleus of the Hypothalamus in Control of Blood Pressure and Blood Pressure Variability

The paraventricular nucleus (PVN) is a highly organized structure of the hypothalamus that has a key role in regulating cardiovascular and osmotic homeostasis. Functionally, the PVN is divided into autonomic and neuroendocrine (neurosecretory) compartments, both equally important for maintaining blood pressure (BP) and body fluids in the physiological range. Neurosecretory magnocellular neurons (MCNs) of the PVN are the main source of the hormones vasopressin (VP), responsible for water conservation and hydromineral balance, and oxytocin (OT), involved in parturition and milk ejection during lactation. Further, neurosecretory parvocellular neurons (PCNs) take part in modulation of the hypothalamic–pituitary–adrenal axis and stress responses. Additionally, the PVN takes central place in autonomic adjustment of BP to environmental challenges and contributes to its variability (BPV), underpinning the PVN as an autonomic master controller of cardiovascular function. Autonomic PCNs of the PVN modulate sympathetic outflow toward heart, blood vessels and kidneys. These pre-autonomic neurons send projections to the vasomotor nucleus of rostral ventrolateral medulla and to intermediolateral column of the spinal cord, where postganglionic fibers toward target organs arise. Also, PVN PCNs synapse with NTS neurons which are the end-point of baroreceptor primary afferents, thus, enabling the PVN to modify the function of baroreflex. Neuroendocrine and autonomic parts of the PVN are segregated morphologically but they work in concert when the organism is exposed to environmental challenges via somatodendritically released VP and OT by MCNs. The purpose of this overview is to address both neuroendocrine and autonomic PVN roles in BP and BPV regulation.

Advances in novel molecular targets for antidepressants

Depression is the most common psychiatric illness affecting numerous people world-wide. The currently available antidepressant treatment presents low response and remission rates. Thus, new effective antidepressants need to be developed or discovered. Aiming to give an overview of novel possible antidepressant drug targets, we summarized the molecular targets of antidepressants and the underlying neurobiology of depression. We have also addressed the multidimensional perspectives on the progress in the psychopharmacological treatment of depression and on the new potential approaches with effective drug discovery.

Vasopressinergic control of stress-related behavior: studies in Brattleboro rats

Vasopressin, a nonapeptide, signaling both as hormone in the blood and neuromodulator/neurotransmitter in the brain is considered to be causally involved in the pathological changes underlying anxiety and depression. In the present review we summarize experimental data obtained with Brattleboro rats as a model of congenital vasopressin-deficiency to test the hypothesis that central vasopressin signaling contributes to anxiety- and depression-like behavior. Male, female and lactating rats were studied. We focused on the paraventricular nucleus of the hypothalamus (PVN) and the septum, two brain areas in which vasopressin is proposed to control the endocrine and behavioral stress response, respectively. The presented data support the hypothesis that the behavioral changes seen in these rats are brought about by an altered vasopressin signaling at the brain level. Whereas vasopressin synthesized and released within the hypothalamus is primarily involved in endocrine regulation, vasopressin signaling in other brain areas may contribute to anxiety- and depression-like behavioral parameters. Further studies in this context might focus particularly on the interplay between extra-hypothalamic brain areas such as the septum and the medial amygdala.

Genetic Variants of Angiotensin-Converting Enzyme Are Linked to Autism: A Case-Control Study

Background

Autism is a disease of complex nature with a significant genetic component. The importance of renin-angiotensin system (RAS) elements in cognition and behavior besides the interaction of angiotensin II (Ang II), the main product of angiotensin-converting enzyme (ACE), with neurotransmitters in CNS, especially dopamine, proposes the involvement of RAS in autism. Since the genetic architecture of autism has remained elusive, here we postulated that genetic variations in RAS are associated with autism.

Methods

Considering the relation between the three polymorphisms of ACE (I/D, rs4343 and rs4291) with the level of ACE activity, we have investigated this association with autism, in a case-control study. Genotype and allele frequencies of polymorphisms were determined in DNAs extracted from venous blood of 120 autistic patients and their age and sex-matched healthy controls, using polymerase chain reaction (PCR) and PCR–restriction fragment length polymorphism (PCR–RFLP) methods.

Results

There were strong associations between both DD genotype of ACE I/D and the D allele, with autism (P = 0.006, OR = 2.9, 95% CI = 1.64–5.13 and P = 0.006, OR = 2.18, 95% CI = 1.37–3.48 respectively). Furthermore, a significant association between the G allele of rs4343 and autism was observed (P = 0.006, OR = 1.84, 95%CI = 1.26–2.67). Moreover, haplotype analysis revealed an association between DTG haplotype and autism (P = 0.008).

Conclusion

Our data suggests the involvement of RAS genetic diversity in increasing the risk of autism.

Antipsychotic drug-like facilitation of latent inhibition by a brain-penetrating neurotensin-1 receptor agonist

Latent inhibition (LI) is a measure of cognitive gating and refers to reduced conditioned learning when there is pre-exposure to the conditioned stimulus (CS) before it is paired with the unconditioned stimulus (US). Dysregulation of LI is associated with some neuropsychiatric disorders, including schizophrenia, and the ability to facilitate LI in rodents is a reasonably good predictive test for antipsychotic drugs. Converging evidence supports neurotensin-1 receptor (NTS1) agonists as novel drugs for schizophrenia. Therefore, we investigated the ability of a brain-penetrating, selective NTS1 agonist, PD149163, to facilitate LI in heterozygous Brattleboro rats, a strain that exhibits naturally low LI. Conditioned taste aversion to flavored water (FW; 0.1% saccharin) was induced by pairing it with malaise-inducing injections of lithium chloride (LiCl). Prior to LiCl-FW pairing, rats received subcutaneous injections of saline, or PD149163 (100 µg/kg or 200 µg/kg). Half the rats in each drug group had been allowed to drink FW the day before the LiCl-FW pairing (pre-exposed rats). Two days after pairing, the amount of FW each rat consumed was recorded. LI, defined as significantly greater FW drinking in the pre-exposed group compared with the non pre-exposed group, was exhibited only among rats that received 200 µg/kg of PD149163. These results further support NTS1 agonists as potentially novel drugs for the treatment of schizophrenia.

Anxiogenic role of vasopressin during the early postnatal period: maternal separation-induced ultrasound vocalization in vasopressin-deficient Brattleboro rats

Both animal and human studies suggest that in adulthood, plasma vasopressin level correlates well with anxiety. Little is known about the mood regulation during the perinatal period. Here, we aim to investigate the influence of vasopressin on anxiety during the early postnatal age. As a sign of distress, rat pups emit ultrasonic vocalizations (USVs) when they are separated from their mother. This USV was detected in 7- to 8-day-old vasopressin-deficient Brattleboro pups, and they were compared to their heterozygote littermates and wild-type pups. The results were confirmed by V1b antagonist treatment (SSR149415 10 mg/kg ip 30 min before test) in wild-types. Chlordiazepoxide (3 mg/kg ip 30 min before test)-an anxiolytic-was used to test the interaction with the GABAergic system. At the end of the test, stress-hormone levels were measured by radioimmunoassay. Vasopressin-deficient pups vocalized substantially less than non-deficient counterparts. Treatment with V1b antagonist resulted in similar effect. Chlordiazepoxide reduced the frequency and duration of the vocalization only in wild-types. Reduced vocalization was accompanied by smaller adrenocorticotropin levels but the level of corticosterone was variable. Our results indicate that the anxiolytic effect of vasopressin deficiency (both genetic and pharmacological) exists already during the early postnatal age. Vasopressin interacts with the GABAergic system. As mood regulation does not go parallel with glucocorticoid levels, we suggest that vasopressin might have a direct effect on special brain areas.

Restoration of peripheral V2 receptor vasopressin signaling fails to correct behavioral changes in Brattleboro rats

Beside its hormonal function in salt and water homeostasis, vasopressin released into distinct brain areas plays a crucial role in stress-related behavior resulting in the enhancement of an anxious/depressive-like state. We aimed to investigate whether correction of the peripheral symptoms of congenital absence of AVP also corrects the behavioral alterations in AVP-deficient Brattleboro rats. Wild type (WT) and vasopressin-deficient (KO) male Brattleboro rats were tested. Half of the KO animals were treated by desmopressin (V2-receptor agonist) via osmotic minipump (subcutaneous) to eliminate the peripheral symptoms of vasopressin-deficiency. Anxiety was studied by elevated plus maze (EPM), defensive withdrawal (DW) and marble burying (MB) tests, while depressive-like changes were monitored in forced swimming (FS) and anhedonia by sucrose preference test. Cell activity was examined in septum and amygdala by c-Fos immunohistochemistry after 10 min FS. KO rats spent more time in the open arm of the EPM, spent less time at the periphery of DW and showed less burying behavior in MB suggesting a reduced anxiety state. KO animals showed less floating behavior during FS revealing a less depressive phenotype. Desmopressin treatment compensated the peripheral effects of vasopressin-deficiency without a significant influence on the behavior. The FS-induced c-Fos immunoreactivity in the medial amygdala was different in WT and KO rats, with almost identical levels in KO and desmopressin treated animals. There were no differences in central and basolateral amygdala as well as in lateral septum. Our data confirmed the role of vasopressin in the development of affective disorders through central mechanisms. The involvement of the medial amygdala in the behavioral alterations of vasopressin deficient animals deserves further attention.

The effects of lactation on impulsive behavior in vasopressin-deficient Brattleboro rats

Vasopressin (AVP)-deficient Brattleboro rats develop a specific behavioral profile, which-among other things-include altered cognitive performance. This profile is markedly affected by alterations in neuroendocrine state of the animal such as during lactation. Given the links between AVP and cognition we hypothesized that AVP deficiency may lead to changes in impulsivity that is under cognitive control and the changes might be altered by lactation. Comparing virgin and lactating AVP-deficient female Brattleboro rats to their respective controls, we assessed the putative lactation-dependent effects of AVP deficiency on impulsivity in the delay discounting paradigm. Furthermore, to investigate the basis of such effects, we assessed possible interactions of AVP deficiency with GABAergic and serotonergic signaling and stress axis activity, systems playing important roles in impulse control. Our results showed that impulsivity was unaltered by AVP deficiency in virgin rats. In contrast a lactation-induced increase in impulsivity was abolished by AVP deficiency in lactating females. We also found that chlordiazepoxide-induced facilitation of GABAergic and imipramine-induced enhancement of serotonergic activity in virgins led to increased and decreased impulsivity, respectively. In contrast, during lactation these effects were visible only in AVP-deficient rats. These rats also exhibited increased stress axis activity compared to virgin animals, an effect that was abolished by AVP deficiency. Taken together, AVP appears to play a role in the regulation of impulsivity exclusively during lactation: it has an impulsivity increasing effect which is potentially mediated via stress axis-dependent mechanisms and fine-tuning of GABAergic and serotonergic function.

Intranasal desmopressin as an adjunct to risperidone for negative symptoms of schizophrenia: a randomized, double-blind, placebo-controlled, clinical trial

Considering the role of neurohypophyseal peptides in normal development and function of higher cortical processes along with their proven abnormalities in schizophrenic patients, these pathways have recently attracted greater attention as treatment targets for schizophrenia. Desmopressin (DDAVP) is a synthetic analog of vasopressin. This study aimed to evaluate the efficacy and safety of DDAVP nasal spray as an adjunct to risperidone in improving negative symptoms of schizophrenia. In this randomized double-blind placebo-controlled clinical trial, forty patients aged 18-50 years with a DSM IV-TR diagnosis of chronic schizophrenia and a minimum score of 60 on positive and negative syndrome scale (PANSS) were equally randomized to receive DDAVP nasal spray (20mcg/day) or placebo in addition to risperidone for 8 weeks. Patients were partially stabilized and treated with a stable dose of risperidone (5 or 6mg/day) for at least four weeks prior to entry. Participants were rated by PANSS every two weeks and decrease in the PANSS negative subscale score was considered as our primary outcome. By the study endpoint, DDAVP-treated patients showed significantly greater improvement in the negative symptoms (P=0.001) as well as the PANSS total and general psychopathology subscale scores (P=0.005 and P=0.003; respectively) compared to the placebo group. Treatment group was the strongest predictor of changes in negative symptoms (β=-0.48, t=-3.67, P=001). No serious adverse event or fluid/electrolyte imbalance was reported in this trial. In conclusion, DDAVP nasal spray showed to be an effective and safe medication for improving negative symptoms in patients with chronic schizophrenia.

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.

Association of angiotensin-converting enzyme (ACE) gene polymorphism with elevated serum ACE activity and major depression in an Iranian population

Genetic factors contribute substantially to the likelihood of developing major depressive disorder (MDD). The importance of renin-angiotensin system (RAS) elements in cognition and behaviour and their involvement in aetiology and treatment of depression imply that RAS gene polymorphism(s) associated with RAS overactivity might also be associated with depression. In the present study, genotype and allele frequencies of six common polymorphisms of genes encoding for RAS components were determined in DNAs extracted from venous blood of 191 depressed and 104 healthy individuals using polymerase chain reaction (PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and serum angiotensin-converting enzyme (ACE) activity was assayed using a high-performance liquid chromatography (HPLC) method. The results showed, for the first time, that GG genotype of ACE A2350G was significantly associated with MDD among Iranian participants (P=0.001; odds ratio (OR)=6.2; 95% confidence interval (CI)=2.1-18.3). Significant higher serum ACE activity (P=0.0001) as well as higher diastolic blood pressure (P=0.036) were observed in depressed patients compared to the healthy control group. Depressed patients carrying GG genotype of the A2350G polymorphism had a significantly higher serum ACE activity (P=0.02) than individuals with either AA or AG genotype. In conclusion, this study supports the hypothesis of RAS overactivity in depression in that the genotype associated with higher serum ACE activity in an Iranian population was also associated with MDD.

Maternal neglect with reduced depressive-like behavior and blunted c-fos activation in Brattleboro mothers, the role of central vasopressin

Early mother-infant relationships exert important long-term effects in offspring and are disturbed by factors such as postpartum depression. We aimed to clarify if lack of vasopressin influences maternal behavior paralleled by the development of a depressive-like phenotype. We compared vasopressin-deficient Brattleboro mothers with heterozygous and homozygous normal ones. The following parameters were measured: maternal behavior (undisturbed and separation-induced); anxiety by the elevated plus maze; sucrose and saccharin preference and forced swim behavior. Underlying brain areas were examined by c-fos immunocytochemistry among rest and after swim-stress. In another group of rats, vasopressin 2 receptor agonist was used peripherally to exclude secondary changes due to diabetes insipidus. Results showed that vasopressin-deficient rats spend less time licking-grooming their pups through a centrally driven mechanism. There was no difference between genotypes during the pup retrieval test. Vasopressin-deficient mothers tended to explore more the open arms of the plus maze, showed more preference for sucrose and saccharin and struggled more in the forced swim test, suggesting that they act as less depressive. Under basal conditions, vasopressin-deficient mothers had more c-fos expression in the medial preoptic area, shell of nucleus accumbens, paraventricular nucleus of the hypothalamus and amygdala, but not in other structures. In these areas the swim-stress-induced activation was smaller. In conclusion, vasopressin-deficiency resulted in maternal neglect due to a central effect and was protective against depressive-like behavior probably as a consequence of reduced activation of some stress-related brain structures. The conflicting behavioral data underscores the need for more sex specific studies.

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.

Further characterization of the predictive validity of the Brattleboro rat model for antipsychotic efficacy

Our laboratory and others have reported that Brattleboro (BRAT) rats, a Long Evans (LE) strain with a single gene mutation, have inherent deficits in prepulse inhibition (PPI) homologous to those observed in schizophrenia patients and that these deficits are reversed by antipsychotic drugs (APDs). To further evaluate the potential predictive validity of BRAT rat PPI for APDs, we compared the effects of acute subcutaneous administration of the typical APD chlorpromazine to that of three psychotropic drugs without antipsychotic efficacy, the antidepressant imipramine, the anxiolytic diazepam and the anticonvulsant mood stabilizer valproic acid on male and female BRAT rat PPI. Male and female BRAT rats exhibited baseline (saline treatment) PPI that was not different from each other (21.1% and 21.3%, respectively) and low compared with those historically exhibited by LE rats (approximately 59%). Chlorpromazine facilitated PPI in male and female BRAT rats, whereas imipramine, diazepam, and valproic acid had no significant effect on PPI. These results suggest that PPI in the BRAT rat responds specifically to drugs with APD efficacy but not psychotropic drugs of different therapeutic families.

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.

Osmoregulation of vasopressin secretion is altered in the postacute phase of septic shock

OBJECTIVE

To determine whether septic shock patients have an abnormal reponse to increasing osmolarity.

DESIGN

Prospective interventional study.

SETTING

Intensive care unit at Raymond Poincaré and Etampes Hospitals.

PATIENTS

Normonatremic patients at > 72 hrs from septic shock onset.

INTERVENTION

Osmotic challenge consisting of infusing 500 mL of hypertonic saline solution (with cumulative amount of sodium not exceeding 24 g) over 120 mins.

MEASUREMENTS AND MAIN RESULTS

Plasma arginine vasopressin levels were measured 15 mins before the test and then four times every 30 mins. A slope of the relation between arginine vasopressin and plasma sodium levels of < 0.5 pg/mEq defined nonresponders. Among the 33 included patients, 17 (52%) were nonresponders. During osmotic challenge, variations throughout the test in plasma sodium levels, blood pressure, and central venous pressure were comparable between the two groups. Arginine vasopressin increased from 4.8 pg/mL [3.3-6.4 pg/mL] to 14.4 pg/mL [11.2-23.3 pg/mL] in responders but only from 2.8 pg/mL [2.3-4.0 pg/mL] to 4.0 pg/mL [3.1-5.3 pg/mL] in nonresponders (p < .0001). Responders had a higher plasma arginine vasopressin levels at baseline and a more severe hematosis alteration. Nonresponders had more frequently bacteremia and liver dysfunction, been referred from the ward and undergone surgery. Critical illness severity, hemodynamic alteration, hydroelectrolytic disturbances, treatment, and outcome did not differ between the two groups.

CONCLUSION

Osmoregulation is dramatically altered in half of patients with prolonged septic shock.

Neuroendocrinology of coping styles: towards understanding the biology of individual variation

Individual variation in behavior and physiology is a widespread and ecologically functional phenomenon in nature in virtually all vertebrate species. Due to domestication of laboratory animals, studies may suffer from a strong selection bias. This paper summarizes behavioral, neuroendocrine and neurobiological studies using the natural individual variation in rats and mice. Individual behavioral characteristics appear to be consistent over time and across situations. The individual variation has at least two dimensions in which the quality of the response to a challenging condition (coping style) is independent from the quantity of that response (stress reactivity). The neurobiology reveals important differences in the homeostatic control of the serotonergic neuron and the neuropeptides vasopressin and oxytocin in relation to coping style. It is argued that a careful exploitation of the broad natural and biologically functional individual variation in behavior and physiology may help in developing better animal models for understanding individual disease vulnerability.

A hypomorphic vasopressin allele prevents anxiety-related behavior

Background

To investigate neurobiological correlates of trait anxiety, CD1 mice were selectively bred for extremes in anxiety-related behavior, with high (HAB) and low (LAB) anxiety-related behavior mice additionally differing in behavioral tests reflecting depression-like behavior.

Methodology/ Principal Findings

In this study, microarray analysis, in situ hybridization, quantitative real-time PCR and immunohistochemistry revealed decreased expression of the vasopressin gene (Avp) in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei of adult LAB mice compared to HAB, NAB (normal anxiety-related behavior) and HABxLAB F1 intercross controls, without detecting differences in receptor expression or density. By sequencing the regions 2.5 kbp up- and downstream of the Avp gene locus, we could identify several polymorphic loci, differing between the HAB and LAB lines. In the gene promoter, a deletion of twelve bp Δ(−2180–2191) is particularly likely to contribute to the reduced Avp expression detected in LAB animals under basal conditions. Indeed, allele-specific transcription analysis of F1 animals revealed a hypomorphic LAB-specific Avp allele with a reduced transcription rate by 75% compared to the HAB-specific allele, thus explaining line-specific Avp expression profiles and phenotypic features. Accordingly, intra-PVN Avp mRNA levels were found to correlate with anxiety-related and depression-like behaviors. In addition to this correlative evidence, a significant, though moderate, genotype/phenotype association was demonstrated in 258 male mice of a freely-segregating F2 panel, suggesting a causal contribution of the Avp promoter deletion to anxiety-related behavior.

Discussion

Thus, the identification of polymorphisms in the Avp gene promoter explains gene expression differences in association with the observed phenotype, thus further strengthening the concept of the critical involvement of centrally released AVP in trait anxiety.

Postnatal development in vasopressin deficient Brattleboro rats with special attention to the hypothalamo-pituitary-adrenal axis function: the role of maternal genotype

Anomalies in hormonal and neurotransmitter status during perinatal period can lead to lifespan alterations in the central nervous system. Vasopressin is present early in the brain and has various mitogenic, metabolic and physiological actions, e.g. in water homeostasis or in the regulation of the hypothalamo-pituitary-adrenal (HPA) axis. Therefore we examine the possible role of vasopressin in perinatal development with special attention to the influence of maternal genotype and to the HPA axis regulation. We compared homozygous vasopressin deficient (di/di) Brattleboro rats to their heterozygous (di/+) littermates both from di/+ and di/di mother. Higher locomotion due to reduced adaptation was present at preweaning. During the first 10 days of life the di/di pups from di/di mother were the smallest, while in the later perinatal period the genotype of the pups became the more important determinant of the somatic development, namely the di/di pups from both mothers had reduced weight gain. Generally the lack of vasopressin in the pups fastened the somatic development (pinna detachment, eye and ear opening, incisor eruption) however the neurobehavioral development (palmar grasp reflex, righting reflex, negative geotaxis, etc.) was not influenced profoundly by either the mother's or the pup's genotype. The lack of vasopressin in pups abolished the 24 h maternal separation induced adrenocorticotrop hormone (ACTH) elevation while the accompanying corticosterone rises were even higher. The vasopressin deficiency of the mother reduced the resting ACTH and all corticosterone levels in all pups. So we can conclude that the lack of vasopressin speeds up the development, probably there is a greater drive for self-sufficiency in these animals. The mother's vasopressin deficiency reduced the HPA axis reactivity of the pups. The role of vasopressin in the HPA axis regulation is important during the perinatal period independently from the mother's genotype. The large discrepancy between ACTH and corticosterone regulation requires further studies.

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.

Vasopressin: behavioral roles of an "original" neuropeptide

Vasopressin (Avp) is mainly synthesized in the magnocellular cells of the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) whose axons project to the posterior pituitary. Avp is then released into the blood stream upon appropriate stimulation (e.g., hemorrhage or dehydration) to act at the kidneys and blood vessels. The brain also contains several populations of smaller, parvocellular neurons whose projections remain within the brain. These populations are located within the PVN, bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and suprachiasmatic nucleus (SCN). Since the 1950s, research examining the roles of Avp in the brain and periphery has intensified. The development of specific agonists and antagonists for Avp receptors has allowed for a better elucidation of its contributions to physiology and behavior. Anatomical, pharmacological and transgenic, including "knockout," animal studies have implicated Avp in the regulation of various social behaviors across species. Avp plays a prominent role in the regulation of aggression, generally of facilitating or promoting it. Affiliation and certain aspects of pair-bonding are also influenced by Avp. Memory, one of the first brain functions of Avp that was investigated, has been implicated especially strongly in social recognition. The roles of Avp in stress, anxiety, and depressive states are areas of active exploration. In this review, we concentrate on the scientific progress that has been made in understanding the role of Avp in regulating these and other behaviors across species. We also discuss the implications for human behavior.

A 'reverse' phylogenetic approach for identification of novel osmoregulatory and cardiovascular hormones in vertebrates

Vertebrates expanded their habitats from aquatic to terrestrial environments during the course of evolution. In parallel, osmoregulatory and cardiovascular systems evolved to counter the problems of desiccation and gravity on land. In our physiological studies on body fluid and blood pressure regulation in various vertebrate species, we found that osmoregulatory and cardiovascular hormones have changed their structure and function during the transition from aquatic to terrestrial life. In fact, Na(+)-regulating and vasodepressor hormones play essential roles in fishes, while water-regulating and vasopressor hormones are dominant in tetrapods. Accordingly, Na(+)-regulating and vasodepressor hormones, such as natriuretic peptide (NP) and adrenomedullin (AM), are much diversified in teleost fishes compared with mammals. Based on this finding, new NPs and AMs were identified in mammals and other tetrapods. These hormones have only minor roles in the maintenance of normal blood volume and pressure in mammals, but their importance seems to increase when homeostasis is disrupted. Therefore, such hormones can be used for diagnosis and treatment of body fluid and cardiovascular disorders such as cardiac/renal failure and hypertension. In this review, we introduce a new approach for identification of novel Na(+)-regulating and vasodepressor hormones in mammals based on fish studies. Until recently, new hormones were first discovered in mammals, and then identified and applied in fishes. However, chances are increasing in recent years to identify new hormones first in fishes then in mammals, based on the difference in the regulatory systems between fishes and tetrapods. As the direction is opposite from the traditional phylogenetic approach, we added 'reverse' to its name. The 'reverse' phylogenetic approach offers a typical example of how comparative fish studies can contribute to the general and clinical endocrinology.

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.

Diabetes insipidus and cognitive function

It has been well known that several neuropeptides may affect human behavior, and that some endocrinopathies are associated with impaired higher function of the brain. There have been increasing evidences that vasopressin has both peripheral and central effects, the latter of which is involved in memory. In experimental animals, male mice with a null mutation in the V1a receptor (V1aR) exhibit a profound impairment in social recognition and changes in anxiety-like behavior. An AVP fragment analog has been reported to facilitate memory retention and recall in mice through protein kinase C-independent pathways. In human, a few recent reports have suggested that a familial central diabetes insipidus, caused by a heterozygous mutation in the gene for vasopressin prohormone, have minor disturbances in central nervous system. Taken together, it is hypothesized that the subject with central diabetes insipidus may frequently present with an impaired cognitive ability. It is justified to examine the cognitive function, when we make a diagnosis of central diabetes insipidus and to perform a clinical study to investigate whether central diabetes insipidus may be associated with impairment of higher brain functions.

Upregulation of striatal dopamine-2 receptors in Brattleboro rats with prepulse inhibition deficits

BACKGROUND

Brattleboro rats (BRATs) have natural deficits in prepulse inhibition (PPI) of the startle response similar to those exhibited by schizophrenia patients, which are reversed by antipsychotics. We sought to determine whether they also have increases in striatal dopamine-2 (D2) receptors found in some studies examining the brains of schizophrenia patients.

METHODS

Several days after startle testing, the brains of BRAT and Long Evans (LE) rats were removed, and D1 and D2 receptor levels were measured by autoradiography.

RESULTS

PPI was lower in BRATs consistent with previous reports. D2, but not D1, receptor binding was significantly higher in the nucleus accumbens shell and the dorsomedial caudate of BRAT compared with LE rats, consistent with some findings in schizophrenia patients. Furthermore, individual rat PPI was inversely correlated with D2 binding density.

CONCLUSIONS

These findings suggest that the dopamine system in BRATs is dysregulated and these abnormalities may contribute to the PPI deficits observed in these rats.

The role of vasopressin in diabetes mellitus-induced hypothalamo-pituitary-adrenal axis activation: studies in Brattleboro rats

Chronic diabetes mellitus (DM) induces hyperactivity of the hypothalamo-pituitary-adrenal axis (HPA). Our present study addresses the role of vasopressin (AVP) in maintaining adrenocortical responsiveness during DM. AVP-deficient mutant Brattleboro rats were used with heterozygous controls and the V2 agonist, desmopressin was infused to replace peripheral AVP. To induce DM the rats were injected by streptozotocin (STZ, 60 mg/ml/kg i.v.) and studied 2 weeks later. The acute stress stimulus was 60 min restraint. The signs of DM (the increase in water consumption and in blood glucose levels) were discovered in all rats. The diuretic effect of the lack of AVP was additional to the DM-induced osmotic diuresis. DM induced significant, chronic stress-like somatic changes on which AVP-deficiency had no effect and although desmopressin infusion normalized the water consumption and the body weight gain in AVP-deficient rats, it had no effect on DM-induced changes. The acute stress-induced plasma ACTH elevation was smaller in AVP-deficient or DM rats but these effects were not additive. Desmopressin did not normalize the decreased ACTH-elevation of AVP-deficient animals. The resting morning plasma corticosterone level was elevated both in DM and AVP-deficient rats without interaction. The restraint-induced corticosterone rise was influenced neither by the lack of AVP nor by DM and the basal and stress-induced prolactin levels were smaller in DM rats without any effect of AVP-deficiency. In conclusion, our data suggest that AVP does not play a crucial role in HPA axis regulation during DM-induced chronic stress. In contrast, the role of AVP seems to be more important during acute stress, however, it is restricted to the ACTH regulation. According to the water consumption data diabetes insipidus seems to be an additional risk factor for DM.

Genetic variants in the angiotensin I-converting-enzyme (ACE) and angiotensin II receptor (AT1) gene and clinical outcome in depression

The insertion/(I)/deletion (D) polymorphism of the angiotensin-converting enzyme gene (ACE) is of increasing interest in etiology and treatment of various neuropsychiatric disorders. The present study aimed to replicate own earlier findings that depressive patients with the ACE D-allele are responding better to treatment with antidepressants than those with the II genotype. We further investigated a common polymorphism (A1166C) in the angiotensin II receptor gene (AT1) to examine a possibly combined influence. A sample of 273 patients with major depression, being treated with different classes of antidepressants, was enrolled in the study. Genotyping was carried out using a polymerase chain reaction and snapshot method, respectively, and the severity of depression was monitored using the HAMD-17 scale before and after 4 weeks of treatment. The ACE II genotypes showed poorer improvement in HAMD-17 scale after 4 weeks of treatment (ANOVA: F=4.49, p=0.01) than carriers with one or two D-alleles. Similarly, more than 70% of the AT1 CC homozygotes had a 50% reduction in the HAMD-17 scale within 4 weeks of treatment. Our data might further suggest that patients with a haplotype combining the CC and DD/ID genotypes respond better to treatment than those with either single allele. These results should however be replicated in future research.

Peripheral vasopressin accelerates extinction of conditioned taste avoidance

Both peripheral and central administration of vasopressin improves retention and delays extinction when given before or after acquisition of shock avoidance learning. For conditioned taste avoidance, however, vasopressin prolongs extinction when injected peripherally before acquisition tests and accelerates extinction when infused intracerebroventricularly after acquisition. The following experiments were designed to determine whether this inconsistency is based on the route of administration or timing of vasopressin treatment. Because acquisition of conditioned taste avoidance is strengthened when an agent that is capable of inducing avoidance is administered after LiCl injection, it was determined in experiment 1 that a 6 microg/kg dose of vasopressin did not induce conditioned taste avoidance when administered 50 min after consumption of a sucrose solution. In experiment 2, it was determined that this dose of vasopressin accelerated extinction of a LiCl-induced conditioned taste avoidance when given 50 min after LiCl injection. These results suggest that the inconsistency is not based on route of administration. In experiment 3, it was determined that there was a tendency for animals to show prolonged extinction when vasopressin was administered 20 min before access to a sucrose solution. All of the results taken together suggest that the differential effects of vasopressin on extinction are due to the timing of administration. It was suggested that vasopressin accelerates extinction when given after acquisition by reducing the effectiveness of LiCl and it prolongs extinction when given before acquisition by altering neural responsiveness in areas mediating conditioned taste avoidance.

Dexamethasone induces different wheel running activity than corticosterone through vasopressin release from the suprachiasmatic nucleus

During the analysis of wheel running activity, we found that corticosterone (1 mg/100 g BW) injection decreased wheel activity, while dexamethasone (0.1 mg/100 g) increased the activity. To clarify the functional differences between corticosterone and dexamethasone, we measured Arg-vasopressin (AVP) release from the suprachiasmatic nucleus (SCN) slice culture in vitro and AVP coding mRNA in the SCN in vivo. The corticosterone (0.2 and 2 microg/ml, final concentration in medium) decreased the AVP release, while it increased by dexamethasone (0.2 and 2 microg/ml). An AVP mRNA in the SCN was decreased by both corticosterone (1 mg/100 g) and dexamethasone (0.1 mg/100 g). The differences in wheel activity by corticosterone and dexamethasone are discussed from the changes of AVP in the SCN.

Effects of repeated restraint stress on hypothalamo-pituitary-adrenocortical function in vasopressin deficient Brattleboro rats

Arginine-vasopressin (AVP) has been proposed to be an important mediator during chronic stress in the regulation of the hypothalamo-pituitary-adrenal axis. In the present study we addressed the role of AVP in maintaining adrenocortical responsiveness during chronic stress using the AVP deficient mutant Brattleboro rat. Heterozygous Brattleboro rats (di/+) served as controls and were compared to homozygous rats (di/di) with diabetes insipidus. Sixty minutes daily restraint was repeated for 5, 8, 11 or 15 days and organ weights, plasma adrenocorticotropin (ACTH) and corticosterone levels and anterior pituitary proopiomelanocortin (POMC) mRNA and ACTH content were measured. The body, adrenal and thymus weight changes induced by chronic stress became significant between 5 and 8 repetition and AVP deficiency had no effect on these parameters. The first indication that AVP has a role to play appears after 11 repetitions. In the di/di group at the end of 11th restraint, the plasma ACTH was decreased when compared to the di/+ rats. In animals with indwelling cannulas some adaptation could be seen in ACTH response without any difference between di/+ and di/di rats after 15 restraints. The corticosterone- and prolactin-elevations induced by restraint did not habituate in the di/+ and the di/di rats. Chronic stress increased POMC mRNA in the anterior pituitary similarly in di/+ and di/di rats. Although AVP seems to be necessary for a full ACTH response, most of the other signs of chronic stress after repeated restraint occur unchanged in the absence of AVP in both genders. This suggests that either AVP is not indispensable for activating the hypothalamo-pituitary-adrenocortical system by chronic stress or the absence of AVP is compensated by other mediators in Brattleboro rats.

The Role of Vasopressin in Hypothalamo-Pituitary-Adrenal Axis Activation during Stress: An Assessment of the Evidence

The hypothalamo-pituitary-adrenal (HPA) axis is a key component of the stress reaction. Most contemporary reviews mention the corticotropin-releasing hormone and arginine vasopressin (AVP)-containing parvocellular neurons of the hypothalamic paraventricular nucleus as the endocrinomotor component of the system. Although there are many studies about the role of AVP in the stress activation, there is evidence consistent and inconsistent with the general view on the importance of AVP. We propose a list of experiments that may provide critical evidence for or against the widely held opinion. The naturally AVP-deficient Brattleboro rat seems to be a good tool for studying the role of AVP. Our experiments on Brattleboro rats with restraint and ip hypertonic saline injection did not support the prominent role of AVP in acute stress, although in forced swim the lack of AVP influenced the HPA axis activation. Among different chronic stress situations (14 days' restraint, chronic morphine or ip hypertonic saline treatment, streptozotocin-induced diabetes mellitus), the role of AVP was not confirmed by changes in somatic parameter (i.e., body, thymus, and adrenal weight changes).

Fear and power-dominance motivation: proposed contributions of peptide hormones present in cerebrospinal fluid and plasma

We propose that fear and power-dominance drive motivation are generated by the presence of elevated plasma and cerebrospinal fluid (CSF) levels of certain peptide hormones. For the fear drive, the controlling hormone is corticotropin releasing factor, and we argue that elevated CSF and plasma levels of this peptide which occur as a result of fear-evoking and other stressful experiences in the recent past are detected and transduced into neuronal activities by neurons in the vicinity of the third ventricle, primarily in the periventricular and arcuate hypothalamic nuclei. For the power-dominance drive, we propose that the primary signal is the CSF concentration of vasopressin, which is detected in two circumventricular organs, the subfornical organ and organum vasculosum of the lamina terminalis. We suggest that the peptide-generated signals detected in periventricular structures are transmitted to four areas in which neuronal activities represent fear and power-dominance: one in the medial hypothalamus, one in the dorsolateral quadrant of the periaqueductal gray matter, a third in the midline thalamic nuclei, and the fourth within medial prefrontal cortex. The probable purpose of this system is to maintain a state of fear or anger and consequent vigilant or aggressive behavior after the initial fear- or anger-inducing stimulus is no longer perceptible. We further propose that all the motivational drives, including thirst, hunger and sexual desire are generated in part by non-steroidal hormonal signals, and that the unstimulated motivational status of an individual is determined by the relative CSF and plasma levels of several peptide hormones.

The role of angiotensin II in cognition and behaviour

Polymorphisms of the renin-angiotensin system are associated with cardiovascular disorders, possibly as a consequence of increased brain angiotensin II activity. Within the brain, angiotensin controls blood pressure, fluid balance and hormone secretion; it also influences behaviour: reduction of central angiotensin function has both antidepressant-like and axiolytic-like actions. Evidence concerning the role of the renin-angiotensin system in learning and memory is contradictory, although more studies support the proposal that angiotensin reduces cognitive function. Studies of renin-angiotensin system genotype and psychological status have suggested an association between the angiotensin-converting enzyme deletion allele and age related cognitive decline, but a greater prevalence of the insertion allele in Alzheimer's disease. The deletion allele has also been associated with depressive illness, as has the M allele of the angiotensinogen gene although other studies have failed to replicate these findings. The role of the brain renin-angiotensin system in human psychopathology remains to be fully explored.

The molecular neurobiology of stress--evidence from genetic and epigenetic models

Knowledge of the genetic and molecular events underlying the neuroendocrine and behavioural sequelae of the response to stress has advanced rapidly over recent years. The response of an individual to a stressful experience is a polygenic trait, but also involves non-genetic sources of variance. Using a combination of top-down (quantitative trait locus [QTL] and microarray analysis) and bottom-up (gene targeting, transgenesis, antisense technology and random mutagenesis) strategies, we are beginning to dissect the molecular players in the mediation of the stress response. Given the wealth of the data obtained from mouse mutants, this review will primarily focus on the contributions made by transgenesis and knockout studies, but the relative contribution of QTL studies and microarray studies will also be briefly addressed. From these studies it is evident that several neuroendocrine and behavioural alterations induced by stress can be modelled in mouse mutants with alterations in hypothalamic-pituitary-adrenal axis activity or other, extrahypothalamic, neurotransmitter systems known to be involved in the stress response. The relative contribution of these models to understanding the stress response and their limitations will be discussed.

Vasopressin-deficient rats exhibit sensorimotor gating deficits that are reversed by subchronic haloperidol

BACKGROUND

Brattleboro (BB) rats are Long Evans rats with a single base pair genetic mutation that impairs their ability to synthesize vasopressin, a neurotransmitter and neurohormone. Brattleboro rats are known to have deficits in memory, emotional reactivity, motivation, attention, and social recognition, abnormalities associated with schizophrenia. Prepulse inhibition (PPI) of the acoustic startle reflex (ASR) is a measure of sensorimotor gating. Prepulse inhibition is deficient in unmedicated schizophrenia patients, and PPI deficits in schizophrenia may be related to the cognitive and behavioral abnormalities associated with this disorder. In this study we tested the hypothesis that BB rats exhibit PPI deficits analogous to those exhibited by schizophrenia patients.

METHODS

In one experiment, BB rats homozygous (BB-Ho) or heterozygous (BB-Hz) for the mutated vasopressin gene were compared with normal Long Evans (LE) rats from the same breeder source. In separate studies, BB-Ho and LE rats were treated with acute or subchronic (22 days) injections of haloperidol.

RESULTS

Both BB-Ho and BB-Hz rats had significantly higher ASR and significantly lower PPI compared with LE rats, with BB-Ho rats exhibiting the lowest PPI among all three genotypes. Furthermore, a single subcutaneous (SC) injection of haloperidol (0.5 mg/kg) did not reverse the PPI deficits in BB rats. In contrast, daily SC administration of haloperidol for 22 days reversed PPI deficits in BB rats.

CONCLUSIONS

These results suggest that PPI deficient BB rats may be an important genetic model of PPI deficits, which may help elucidate genetic, pharmacologic, and pathophysiologic mechanisms underlying PPI deficits and the effects of antipsychotic drugs on PPI.

Electrophysiological evidence for vasopressin V(1) receptors on neonatal motoneurons, premotor and other ventral horn neurons

Prominent arginine-vasopressin (AVP) binding and AVP V(1) type receptors are expressed early in the developing rat spinal cord. We sought to characterize their influence on neural excitability by using patch-clamp techniques to record AVP-induced responses from a population of motoneurons and interneurons in neonatal (5-18 days) rat spinal cord slices. Data were obtained from 58 thoracolumbar (T(7)-L(5)) motoneurons and 166 local interneurons. A majority (>90%) of neurons responded to bath applied AVP (10 nM to 3 microM) and (Phe(2), Orn(8))-vasotocin, a V(1) receptor agonist, but not V(2) or oxytocin receptor agonists. In voltage-clamp, postsynaptic responses in motoneurons were characterized by slowly rising, prolonged (7-10 min) and tetrodotoxin-resistant inward currents associated with a 25% reduction in a membrane potassium conductance that reversed near -100 mV. In interneurons, net AVP-induced inward currents displayed three patterns: decreasing membrane conductance with reversal near -100 mV, i.e., similar to that in motoneurons (24 cells); increasing conductance with reversal near -40 mV (21 cells); small reduction in conductance with no reversal within the current range tested (41 cells). A presynaptic component recorded in most neurons was evident as an increase in the frequency but not amplitude (in motoneurons) of inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs), in large part due to AVP-induced firing in inhibitory (mainly glycinergic) and excitatory (glutamatergic) neurons synapsing on the recorded cells. An increase in frequency but not amplitude of miniature IPSCs and EPSCs also indicated an AVP enhancement of neurotransmitter release from axon terminals of inhibitory and excitatory interneurons. These observations provide support for a broad presynaptic and postsynaptic distribution of AVP V(1) type receptors and indicate that their activation can enhance the excitability of a majority of neurons in neonatal ventral spinal cord.

Vasopressin- and oxytocin-induced activity in the central nervous system: electrophysiological studies using in-vitro systems

During the last two decades, it has become apparent that vasopressin and oxytocin, in addition to playing a role as peptide hormones, also act as neurotransmitters/neuromodulators. A number of arguments support this notion: (i) vasopressin and oxytocin are synthesized not only in hypothalamo-neurohypophysial cells, but also in other hypothalamic and extrahypothalamic cell bodies, whose axon projects to the limbic system, the brainstem and the spinal cord. (ii) Vasopressin and oxytocin can be shed from central axons as are classical neurotransmitters. (iii) Specific binding sites, i.e. membrane receptors having high affinity for vasopressin and oxytocin are present in the central nervous system. (iv) Vasopressin and oxytocin can alter the firing rate of selected neuronal populations. (v) In-situ injection of vasopressin and oxytocin receptor agonists and antagonists can interfere with behavior or physiological regulations. Morphological studies and electrophysiological recordings have evidenced a close anatomical correlation between the presence of vasopressin and oxytocin receptors in the brain and the neuronal responsiveness to vasopressin or oxytocin. These compounds have been found to affect membrane excitability in neurons located in the limbic system, hypothalamus, circumventricular organs, brainstem, and spinal cord. Sharp electrode intracellular recordings and whole-cell recordings, done in brainstem motoneurons or in spinal cord neurons, have revealed that vasopressin and oxytocin can directly affect neuronal excitability by opening non-specific cationic channels or by closing K(+) channels. These neuropeptides can also influence synaptic transmission, by acting either postsynaptically or upon presynaptic target neurons or axon terminals. Whereas, in cultured neurons, vasopressin and oxytocin appear to mobilize intracellular Ca(++), in brainstem slices, the action of oxytocin is mediated by a second messenger that is distinct from the second messenger activated in peripheral target cells. In this review, we will summarize studies carried out at the cellular level, i.e. we will concentrate on in-vitro approaches. Vasopressin and oxytocin will be treated together. Though acting via distinct receptors in distinct brain areas, these two neuropeptides appear to exert similar effects upon neuronal excitability.

Vasopressin reverses aluminum-induced impairment of synaptic plasticity in the rat dentate gyrus in vivo

Aluminum (Al), an important neurotoxin, contributes to a variety of cognitive dysfunction and mental diseases. Previous studies have demonstrated that Al impairs hippocampal long-term potentiation (LTP) in vitro and in vivo. In the present study, both LTP and LTD (long-term depression) were recorded in the same animal to investigate the Al-induced impairment of synaptic plasticity. Another aim of the present research was to verify whether the impairment of synaptic plasticity induced by Al could be reversed by vasopressin (VP) treatment. Neonatal Wistar rats were exposed to Al from parturition through adulthood (pre- and post-weaning) by the drinking of 0.3% aluminum chloride (AlCl(3)) solution. The input-output (I/O) function, paired-pulse reaction (PPR), excitatory postsynaptic potential (EPSP) and population spike (PS) amplitude were measured in the dentate gyrus (DG) of adult rats (60-90 days) in response to stimulation applied to the lateral perforant path. The results showed: (1) Al reduced the amplitudes of both EPSP LTP (control: 132+/-7%, n=7; Al-exposed: 115+/-10%, n=8, P<0.05) and PS LTP (control: 242+/-18%, n=7; Al-exposed: 136+/-7%, n=8, P<0.01) significantly. The amplitudes of EPSP LTD (control: 82+/-6%, n=7; Al-exposed: 92+/-7%, n=8, P<0.05) and PS LTD (control: 81+/-4%, n=7; Al-exposed: 98+/-5%, n=8, P<0.05) were also decreased by Al treatment. The Al-induced impairments of PS LTP and PS LTD were more serious than that of EPSP LTP and EPSP LTD. (2) In control rats, VP had an increase in the PS LTP amplitude (control: 242+/-18%, n=7; control+VP: 358+/-23%, n=6, P<0.01), while it had no significant effects on PS LTD (control: 81+/-4%, n=7; control+VP: 76+/-7%, n=6, P>0.05). (3) In Al-exposed rats, VP had a significant increase in the amplitudes of both PS LTP (Al-exposed: 136+/-7%, n=8, Al-exposed+VP: 255+/-16%, n=6, P<0.01) and PS LTD (Al-exposed: 98+/-5%, n=8; Al-exposed+VP: 81+/-6%, n=6, P<0.05). After the application of VP, the range of synaptic plasticity (PS LTP+PS LTD) in Al-exposed rats increased from 38% to 174%, which surpassed that in control rats (161%). It was suggested that VP could reverse Al-induced impairment of synaptic plasticity and might be an effective medicine to cure Al-induced neurological disorders.

Prolonged hypoxia during cell development protects mature manganese superoxide dismutase-deficient astrocytes from damage by oxidative stress

Mouse astrocytes deficient in the mitochondrial form of superoxide dismutase do not grow in culture under 20% atmospheric O2 levels. By flow cytometry, immunocytochemistry, and enzymatic analysis we have shown that the oxygen block of cell division is due to a decrease in the number of cells entering the S phase of the cell cycle and is concomitant with higher DNA oxidation and impairment of mitochondrial functions. Seeding the cells under 5% O2 until the cultures become confluent can circumvent this problem. An initial hypoxic environment increases the resistance of manganese superoxide dismutase-deficient astrocytes to superoxide radicals artificially produced by paraquat treatment, preserves respiratory activity, and allows normoxic division during a subsequent passage. DNA oxidation is then not higher than in wild-type control cells. However, the adaptation of the cells is not due to compensation by other enzymes of the antioxidant defense system and is specific to cells totally lacking manganese superoxide dismutase. Alteration of the phenotype by prior hypoxia exposure in the SOD2-deficient mutant provide a unique model to study adaptative mechanisms of cellular resistance to oxygen toxicity.

Melanocortins and the brain: from effects via receptors to drug targets

The lack of specific receptors (and antagonists) has hampered the research on the neural mechanism of action of adrenocorticotropic hormone (ACTH)- and melanocyte-stimulating hormone (MSH)-like peptides. Yet the original observations in the 1970s already pointed to cAMP as a possible mediator of ACTH/MSH effects in neurons. The cloning of melanocortin receptors since 1992, the identification of at least two subtypes (melanocortin MC(3) and MC(4) receptors) that are present in neural tissue and the development of selective and potent agonists as well as antagonists have markedly furthered the position of melanocortins as important neuropeptides. In this paper we discuss the role of especially the receptor subtype melanocortin MC(4) in various behaviors including grooming behavior and feeding behavior and consider new insights in the interaction between the opioid and the melanocortin system at the level of the spinal cord (i.e. pain perception). Finally, based on new data obtained in molecular pharmacological studies on brain melanocortin receptors, we suggest a general concept for selective receptor-ligand interaction: ligand residues outside the peptide core-sequence may direct the conformation of the residues in the ligand core-sequence that interact directly with the receptor-binding pocket and thereby determine selectivity.