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The transgenic mouse technology is widespread in the analysis of physiological functions; however, until now 22.0% of the tested null mutations were found to be lethal. The complete lack of vasopressin (AVP) also resulted in preweaning lethality. It is surprising to take into consideration the viability of the AVP natural mutant Brattleboro rats. Thus, AVP is crucial for survival, but it remains unclear which of its different roles is the most important. AVP exerts its effect through specific plasma membrane receptors. The V1a receptors can induce vasoconstriction maintaining blood pressure during hypovolaemia. The V1b receptor on the anterior pituitary has a role in stress adaptation. The V2 subtype is located in the kidney and contributes to the antidiuresis. The avp gene consists of a signal peptide, AVP, neurophysin 2 and a C-terminal glycopeptide. The naturally occurring AVP-deficient Brattleboro rat has a framshift mutation in the neurophysin portion resulting in central insipidus diabetes. In its hypothalamus AVP is not produced, while in certain peripheral tissues, it may be expressed, suggesting the existence of a different synthetic pathway. The avp knockout mice can also be produced; they will be born, but without the peripheral AVP administration, they will not survive. Comparing the available knockout models, we can conclude that the combined V1a and V2 receptormediated effects, namely, hypotension and water loss, may together led to lethality. As in the Brattleboro and targeted knockout mice the local synthesis of AVP in the heart can be maintained and AVP can be released into the general circulation. Thus, in these animals vasoconstriction can compensate the hypovolemia. [ABSTRACT FROM AUTHOR]

Vasopressin ( AVP) regulates the body salt-water balance. Brattleboro rats carry an AVP gene mutation resulting in a recessive form of central diabetes insipidus, being ideal for AVP deficiency studies. Herein, we studied the water permeability of the apical and basolateral sides of outer medullary collecting duct ( OMCD) principal cells in response to dDAVP (a V2 receptor agonist) administration in Wistar and Brattleboro rats. Biophysical measurements of the water permeability ( Pf) of isolated OMCD principal cells were performed with the calcein quenching method with/without dDAVP (10−8 mol/L). mRNA transcripts and protein levels of AQP2, AQP3 and AQP4 were assessed by RT- PCR and western blot respectively. dDAVP increased the apical and basolateral Pf of OMCD principal cells in Wistar rats, while in Brattleboro rats this effect was present basolaterally. Long-term dDAVP administration in both strains resulted in a significant increase in mRNA expression of all assessed AQP's while only the protein levels of AQP2 and AQP3 were significantly increased. Short-term (20 minutes) dDAVP treatment of isolated OMCD fragments resulted in significantly increased plasma membrane expression of AQP2 in Wistar rats and of AQP2 and AQP3 in Brattleboro rats. In summary, dDAVP induces different expression of AQP2, AQP3 and AQP4 in Wistar and Brattleboro rats during short- and long-term treatment. In Wistar rats dDAVP mainly increased AQP2 expression while in Brattleboro rats it increased functional water permeability mainly by AQP3 expression. [ABSTRACT FROM AUTHOR]

We performed a complex functional study of the effects of prostaglandin synthesis blockage with diclofenac on manifestation of the hydroosmotic effect of vasopressin V-receptor agonist desmopressin in the kidneys of Wistar rats with normal synthesis of endogenous vasopressin and homozygous Brattleboro rats with hereditary impaired synthesis of neurohypophyseal hormone vasopressin. Blockage of prostaglandin synthesis led to more pronounced increase in urine osmolality in Brattleboro rats than in Wistar rats due to elevation of not only urine but also sodium gradient at the expense of elimination of the inhibitory effect of prostaglandins on sodium reabsorption and membrane permeability for urine. During combined treatment, the effects of the hormone predominated: the increase in urine osmolality in Wistar and Brattleboro rats did not differ from that after desmopressin administration. [ABSTRACT FROM AUTHOR]

Schizophrenia is a chronic and severe mental disorder with high heterogeneity in its symptoms clusters. The effectiveness of drug treatments for the disorder is far from satisfactory. It is widely accepted that research with valid animal models is essential if we aim at understanding its genetic/ neurobiological mechanisms and finding more effective treatments. The present article presents an overview of six genetically-based (selectively-bred) rat models/strains, which exhibit neurobehavioral schizophrenia-relevant features, i.e., the Apomorphine-susceptible (APO-SUS) rats, the Low-prepulse inhibition rats, the Brattleboro (BRAT) rats, the Spontaneously Hypertensive rats (SHR), the Wisket rats and the Roman High-Avoidance (RHA) rats. Strikingly, all the strains display impairments in prepulse inhibition of the startle response (PPI), which remarkably, in most cases are associated with novelty-induced hyperlocomotion, deficits of social behavior, impairment of latent inhibition and cognitive flexibility, or signs of impaired prefrontal cortex (PFC) function. However, only three of the strains share PPI deficits and dopaminergic (DAergic) psychostimulant-induced hyperlocomotion (together with prefrontal cortex dysfunction in two models, the APO-SUS and RHA), which points out that alterations of the mesolimbic DAergic circuit are a schizophrenia-linked trait that not all models reproduce, but it characterizes some strains that can be valid models of schizophrenia-relevant features and drug-addiction vulnerability (and thus, dual diagnosis). We conclude by putting the research based on these genetically-selected rat models in the context of the Research Domain Criteria (RDoC) framework, suggesting that RDoC-oriented research programs using selectively-bred strains might help to accelerate progress in the various aspects of the schizophrenia-related research agenda., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Walker 256 carcinosarcoma is a transplantable model of rat carcinoma that originally appeared spontaneously in mammary glands. The growth rate of Walker 256 carcinosarcoma in vasopressin-deficient Brattleboro rats is lower than in WAG rats and their congenic hybrids with normal vasopressin levels. Study of tumor proteins detected essential alterations. Tumor regression starting at the 14th day in Brattleboro rats was accompanied by changes in the laminin pattern. At the 21st day, the concentration of α-chains became twice as low, while β-chains of laminin showed a sixfold increase compared to the initial equimolar correlation of bands. Congenic hybrids having one active copy of the vasopressin gene to provide a physiological level of hormone against the genetic background of Brattleboro rats show the same laminin alterations as WAG rats. They demonstrated a similar moderate increase of γ-chains and threefold growth of α- and β-chains of laminin in tumor tissue. It is supposed that vasopressin may be involved in the regulation of relevant local stimuli to trigger renovation of the laminin composition in a course of growing Walker 256 carcinosarcoma. [ABSTRACT FROM AUTHOR]

Caveolin (Cav)1 is expressed in the basolateral membrane domain of renal collecting duct (CD) principal cells (PCs), where it is associated with caveolae. To reveal any potential involvement of Cav1 in vasopressin signaling, we used specific monoclonal and polyclonal antibodies to examine its localization in CD PCs of Brattleboro (BB) rats treated with vasopressin (DDAVP). Compared with controls, immunofluorescence revealed a time-dependent increase in Cav1 expression in the apical membrane domain of PCs, where it overlapped with aquaporin-2 (AQP2). After 24 h of DDAVP treatment, Cav1 was visible as an increased number of small apical spots. The staining gradually became more extensive, and, after 2 wk of DDAVP, it occupied the majority of the apical membrane domain of many PCs. Cav1 also assumed an apical localization in PCs of DDAVP-treated Sprague-Dawley and Long-Evans rats. Similarly, Cav2 appeared at the apical pole of PCs after DDAVP treatment of BB, Sprague-Dawley, and Long-Evans rats. Immunogold electron microscopy confirmed bipolar Cav1 membrane expression in DDAVP-treated BB rats, whereas caveolae were only detected on the basolateral membrane. Immunoblot analysis of BB rat whole kidney homogenates revealed no significant increase in Cav1 levels in DDAVP-treated rats, suggesting that DDAVP induces Cav1 relocalization or modifies its targeting. We conclude that Cav1 and Cav2 trafficking and membrane localization are dramatically altered by the action of DDAVP. Importantly, the absence of apical caveolae indicates that while Cavs may have an as yet undetermined role in vasopressin-regulated signaling processes, this is probably unrelated to AQP2 internalization by caveolae. [ABSTRACT FROM AUTHOR]

Statins are 3-hydroxyl-3-methyglutaryl-CoA reductase inhibitors that are commonly used to inhibit cholesterol biosynthesis. Emerging data have suggested that they also have "pleotropic effects," including modulating actin cytoskeleton reorganization. Here, we report an effect of simvastatin on the trafficking of aquaporin-2 (AQP2). Specifically, simvastatin induced the membrane accumulation of AQP2 in cell cultures and kidneys in situ. The effect of simvastatin was independent of protein kinase A activation and phosphorylation at AQP2-Ser256, a critical event involved in vasopressin (VP)-regulated AQP2 trafficking. Further investigation showed that simvastatin inhibited endocytosis in parallel with downregulation of RhoA activity. Overexpression of active RhoA attenuated simvastatin's effect, suggesting the involvement of this small GTPase in simvastatin-mediated AQP2 trafficking. Finally, the effect of simvastatin on urinary concentration was investigated in VP-deficient Brattleboro rats. Simvastatin acutely (3-6 h) increased urinary concentration and decreased urine output in these animals. In summary, simvastatin regulates AQP2 trafficking in vitro and urinary concentration in vivo via events involving downregulation of Rho GTPase activity and inhibition of endocytosis. Our study provides an alternative mechanism to regulate AQP2 trafficking, bypassing the VP-vasopressin receptor signaling pathway. [ABSTRACT FROM AUTHOR]

The growth pattern of carcinosarcoma Walker 256 was studied in rats with different levels of vasopressin in the blood. The Brattleboro rats are unable to synthesize vasopressin in a consequence of deletion in the coding gene. Hybrids from crossbreeding of the mutant Brattleboro and normal WAG rats inherit the one intact vasopressin gene and hold nearly normal hormone level. It was found that non-strain-specific carcinosarcoma Walker 256 intensively grows in WAG rats and their offsprings from crossbreeding with Brattleboro rats, and tumor development is equally terminated in them by death. Carcinosarcoma grows less intensely in Brattleboro rats; the tumor nodes increased only within the first 2 weeks, after which, the tumor began to decrease and eventually disappeared. Infusion of exogenous vasopressin to Brattleboro rats intensifies a tumor growth in the first 2 weeks after the inoculation of Walker 256 cells; however, it does not prevent a following regression and resorption of tumors. [ABSTRACT FROM AUTHOR]

Brattleboro (BRAT) rats are a mutant variant of the Long-Evans (LE) strain deficient in the neurohormone vasopressin. BRAT rats show behavioural alterations relevant to schizophrenia. In particular, BRAT rats show deficits in prepulse inhibition (PPI) and alterations in various measures of cognition. The aim of this study was to replicate the reported PPI deficits in BRAT rats and its reversal by antipsychotic drugs and to investigate other behavioural and neurochemical characteristics. Acoustic startle reactivity, PPI, spontaneous and amphetamine-induced locomotor activity (LMA) and ex-vivo steady state neurochemistry were measured in male homozygous BRAT rats and LE rats. The effects of antipsychotics on PPI deficits were also determined. Relative to LE, BRAT rats showed enhanced startle reactivity, hyperactivity to a novel environment, PPI deficits and decreased levels of dopamine and DOPAC (dihydroxyphenylacetic acid) in the frontal cortex. BRAT and LE rats showed similar levels of hyperactivity following amphetamine (0.26 mg/kg s.c.). PPI deficits were attenuated by acute clozapine (5-10 mg/kg s.c.), risperidone (0.1-1 mg/kg i.p.), haloperidol (0.1-0.5 mg/kg p.o.) and less robustly by olanzapine (0.3-3 mg/kg s.c.). Chronic administration of clozapine (5 mg/kg s.c., once daily) attenuated baseline hyperactivity and elevated PPI of both strains. Clozapine concentrations were higher in BRAT brains compared with LE rats. These data confirm the reported PPI deficit in BRAT rats and its reversal by antipsychotic drugs, suggesting BRAT rats may represent a potential model for identifying novel antipsychotic drugs. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated behavioral differences between neonatal rats with vasopressin AVP deficiency (di/di) and those with little (+/di) or no deficiency (+/+) using a number of open field metrics. Infant rats (pups) at days 7 and 10 postpartum were videotaped in individual and group trials in a temperature-controlled arena for 12min. Pups were tracked every 5s for tip-of-the-nose and base-of-the-tail coordinate positions. These positional data were transformed, using computer algorithms, into measures of activity, change in orientation, distance moved, cells occupied, wall contact, number of corners visited, and degree of aggregation. Analysis of these data revealed some phenotypic differences among genotypes for 7-day-old pups in individual trials, but there was no clear pattern of genotypic differences. By day 10, however, there were dramatic differences. AVP deficient pups differed significantly from both +/+ and +/di pups on most individual and group metrics. As measured by effect size, group effects were especially large. The behavioral results were consistent with previous findings in adult di/di rats and indicated that 10-day-old di/di pups were hyperactive and had social deficits. AVP deficient pups also appeared to have accelerated locomotor development and to exhibit stereotypic behavior. These results suggest that Brattleboro, di/di, pups are a potentially important animal model for investigating the role of AVP in early locomoter and social development. These behavioral metrics are generalizable to infants of other rodent species and thus may allow early behavioral phenotyping and the assessment of behavioral deficits. [Copyright &y& Elsevier]

Vasopressin (AVP) deficient homozygous Brattleboro rats exhibit severe osmotic challenges due to waterless chronic hypernatremia and hyperosmolality. We investigated the effect of xylazine, an α2-adrenoceptor agonist, on the activity of oxytocinergic (OXY) neurons in the supraoptic nucleus (SON) of homozygous (di/di), heterozygous (di/+), and control (+/+) rats. Ninety minutes after saline (0.1 mL/100 g b.w., i.p.) or xylazine injection (10 mg/kg, i.p.) rats were anaesthetized with pentobarbital (50 mg/kg i.p.) and sacrificed by transcardial perfusion with fixative. Activity of OXY neurons was evidenced by nuclear Fos protein immunoreactivity. Fos/OXY colabelings were analyzed on 40-μm thick coronal sections using computerized light microscope. As expected, plasma osmolality and water intake revealed high heterogenity within the di/di group of rats. Fos expression in SON of di/di rats was correlated with osmolality of each rat. In saline-treated rats, maximum activation of Fos reached around 4% in +/+, 20% in di/+ rats, and as much as 60% in di/di rats. Xylazine activated in SON about 70% of OXY-ergic neurons in +/+, 60% in di/+ rats, and more than 80% in di/di rats. The present findings indicate that in spite of the high spontaneous activity of SON OXY-ergic neurons due to the AVP deficiency in di/di rats, many of the silent OXY-ergic neurons in the SON remained acceptable for α2-adrenoceptor stimulation. [ABSTRACT FROM AUTHOR]

Prepulse inhibition (PPI) of the startle reflex is an operational measure of sensorimotor gating, a process critical to normal cognitive function. Researchers (D. Feifel & K. Priebe, 2001) have identified PPI deficits in the Brattleboro rat, a genetically vasopressindeficient strain that is derived from the Long Evans rat. The absence of vasopressin, a neuropeptide involved in affiliative behaviors, may adversely affect the rearing of offspring by Brattleboro dams, perhaps accounting for their attenuated PPI. Cross-fostering of Long Evans and Brattleboro pups did not alter the PPI deficits in Brattleboro rats. However, the magnitude and habituation of the startle response, which normally differs between Brattleboro and Long Evans rats, was not different in cross-fostered rats. The authors' results indicated that abnormal rearing by Brattleboro dams may contribute to the startle magnitude and habituation abnormalities in Brattleboro Rats but not to their PPI deficits, suggesting that their sensorimotor gating deficits result from their genetic deviation from Long Evans rats. [ABSTRACT FROM AUTHOR]

Serotonin and its receptor agonists stimulate the release of arginine vasopressin (AVP) into peripheral blood under intraventricular injection. To test the hypothesis that brain serotonin can modulate the development of natural osmoregulatory responses, the effect of an increase in endogenous brain serotonin on the response to an intragastric hypo- or hyperosmotic loading was studied in Wistar and AVP-deficient Brattleboro rats. 5-Hydroxytryptophan (5-HTP), the rate-limiting serotonin biosynthesis precursor known to increase the brain level of serotonin, was injected intraperitoneally (5 mg/100 g body weight). The renal functional parameters (glomerular filtration rate [GFR], free water reabsorption, and urine flow rate) were monitored during the 4 h after intragastric infusion of water or a 2% NaCl solution (5% of body weight). Plasma AVP was measured by radioimmunoassay. In Wistar rats, intraperitoneal injection of 5-HTP at the same time as water loading prevented the development of the renal diuretic response: there was no increase in urine flow rate and GFR, and free water reabsorption remained at the high level. In AVP-deficient Brattleboro rats, unlike Wistar rats, 5-HTP treatment was without effect on the renal function parameters. In Wistar rats, injection of 5-HTP at the peak of water diuresis produced an abrogation of the diuretic response to water loading due to the increase in free water reabsorption. Plasma AVP increased from 1.2 ± 0.4 to 4.2 ± 1.6 pg/ml (n = 8 in each group, p < 0.01). Hyperosmotic treatment of Wistar rats with a 2% NaCl solution stimulated AVP secretion compared to baseline (from 3.2 ± 0.1, n = 7 to 5.6 ± 0.9, n = 7, p < 0.01), and the saluretic response developed on the background of high free water reabsorption. When injected concomitantly with NaCl solution, 5-HTP revealed no additive effect on plasma AVP and on free water reabsorption. We conclude that the 5-HTP-caused increase in brain serotonin contributed significantly to the dynamics of changes in the osmoregulatory response to the hypo-osmotic challenge due to stimulation of AVP secretion. 5-HTP had no additive effect on the osmoregulatory response to hyperosmotic loading. Peripherally injected 5-HTP had no effect on the renal function, being absent in AVP-deficient Brattleboro rats. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Diabetes mellitus (DM), as chronic stress activates the hypothalamo-pituitary-adrenocortical axis. We examined whether arginine vasopressin (AVP) and the hypothalamic paraventricular nucleus (PVN) participate in DM-induced chronic stress symptoms. AVP-deficient Brattleboro or PVN-lesioned Wistar rats were used with heterozygous or sham-operated controls. The rats were studied 2 wk after a single injection of streptozotocin. The appearance of DM (enhanced water consumption and blood glucose elevation) and the chronic stress-like somatic changes (body weight decrease, thymus involution, adrenal gland hypertrophy) were not influenced by the lack of AVP. By contrast, PVN lesion significantly attenuated DM-induced thymus involution and adrenal gland hypertrophy as well as the increase in water consumption. The corticotropin-releasing hormone mRNA in PVN was diminished by DM and elevated by the lack of AVP without interaction. DM elevated the proopiomelanocortin (POMC) mRNA in the anterior lobe of the pituitary. The lack of AVP had no effect, whereas lesioning the PVN significantly diminished the elevation. The elevated basal corticosterone plasma levels detectable in DM were influenced neither by the lack of AVP nor by lesioning the PVN. Thus the lack of AVP had no influence on DM-induced chronic stress symptoms, but lesioning the PVN attenuated part of them. However, the lack of elevation in POMC mRNA after PVN lesion, together with the maintained corticosterone elevation, suggests that direct adrenal gland activation occurs in untreated DM. [ABSTRACT FROM AUTHOR]

This study compared the renal metabolism of arachidonic acid in Brattleboro (BB) (vasopressin deficient) and Long-Evans (LE) control rats and the effects of a cytochrome P-450 (CYP) inhibitor 1-aminobenzotriazole (ABT) on renal function in these animals. The production of 20-hydroxyeicosa-tetraenoic acid (20-HETE) by renal cortical and outer medullary microsomes was significantly greater in BB than in LE rats (155 ± 16 vs. 92 ± 13 and 59 ± 7 vs. 33 ± 3 pmoI·min-1·mg protein-1). Renal cortical epoxygenase activity was not different in these strains. The expression of CYP4A proteins was 58 and 78% higher in the renal cortex and outer medulla of BB than in LE rats. Chronic treatment of BB rats with a vasopressin type 2 receptor agonist for 1 wk normalized the renal production of 20-HETE. Chronic blockade of the formation of 20-HETE and EETs with ABT had little effect on renal function in LE rats. However, urine flow increased by 54% and urine osmolarity decreased by 33% in BB rats treated with ABT. Plasma levels of oxytocin fell significantly from 7.2 ± 1.3 to 3.9 ± 1.0 pg/ml. The effects of ABT in BB rats were attenuated by chronic infusion of oxytocin (0.7 ng·min-1·100 g-1) to maintain fixed high plasma levels of this hormone. These results indicate that the expression of CYP4A protein and the renal formation of 20-HETE are elevated in the kidney of BB rats due to a lack of vasopressin and that chronic blockade of the formation of 20-HETE and EETs with ABT promotes water excretion in vasopressin-deficient BB rats by reducing the circulating levels of oxytocin, which is a weak vasopressin agonist. [ABSTRACT FROM AUTHOR]

Vasopressin-stimulated insertion of the aquaporin 2 (AQP2) water channel into the plasma membrane of kidney collecting duct principal cells is a key event in the urinary concentrating mechanism. The paradigm for vasopressin-receptor signaling involves cAMP-mediated protein kinase A activation, which results in the functionally critical phosphorylation of AQP2 on amino acid serine 256. We previously showed that a parallel cGMP-mediated signaling pathway also leads to AQP2 membrane insertion in AQP2-transfected LLC-PK1 (LLC-AQP2) cells and in outer medullary collecting duct principal cells in situ (Bouley R. Breton S. Sun T, McLaughlin M, Nsumu MN, Lin HY, Ausiello DA, and Brown D. J Clin Invest 106: 1115-1126, 2000). In the present report, we show by immunofluorescence microscopy, and Western blotting of plasma membrane fractions, that 45-mm exposure of LLC-AQP2 cells to the cGMP phosphodiesterase type 5 (PDES) inhibitors sildenafil citrate (Viagra) or 4-{[3',4'-methylene-dioxybenzyl] amino }-6-methoxyquinazoline elevates intracellular cGMP levels and results in the plasma membrane accumulation of AQP2; i.e., they mimic the vasopressin effect. Importantly, our data also show that acute exposure to PDE5 inhibitors for 60 mm induces apical accumulation of AQP2 in kidney medullary collecting duct principal cells both in tissue slices incubated in vitro as well as in vivo after intravenous injection of Viagra into rats. These data suggest that AQP2 membrane insertion can be induced independently of vasopressin-receptor activation by activating a parallel cGMP-mediated signal transduction pathway with cGMP PDE inhibitors. These results pro- vide proof-of-principle that pharmacological activation of vasopressin-independent, cGMP signaling pathways could aid in the treatment of those forms of nephrogenic diabetes insipidus that are due to vasopressin-2 receptor dysfunction. [ABSTRACT FROM AUTHOR]

Abstract: The tachykinin neuropeptides acting at NK3 receptors affect mean arterial pressure (MAP) through both neuroendocrine and neural mechanisms. NK3 receptors are found in brainstem nuclei that mediate the baroreflex, but the effects of NK3 receptor stimulation on baroreflex function are unknown. The present study tests the effects of intraventricular injections of senktide, a selective NK3 receptor agonist, on the sensitivity of the baroreflex in three stains of rats: Charles River Laboratory, Long–Evans, and Brattleboro rats, which lack the ability to synthesize vasopressin. Rats with lateral ventricle cannulas were administered injections of isotonic saline, 100 ng, or 200 ng senktide, and 5 min later arterial baroreceptor–heart rate (HR) function was examined by constructing full-range blood pressure–HR curves using alternating doses (5–20 μg kg min) of phenylephrine and nitroprusside to raise and decrease blood pressure approximately 50 mm Hg over a period of 1 min, respectively. Intraventricular injections of 200 ng senktide had no significant effect on baseline MAP, but significantly decreased the gain of the baroreflex in all three rat strains whereas the 100 ng dose had no effect on the baroreflex. These results show that NK3 receptor stimulation modulates the baroreflex that is independent of any action of vasopressin. [Copyright &y& Elsevier]

Prepulse inhibition (PPI) of acoustic startle is decreased in unmedicated schizophrenia patients and similar deficits can be induced in rats through pharmacological, environmental, or neuroanatomical manipulations. Recently, we reported that Brattleboro (BB) rats, a Long Evans (LE) strain with a single gene mutation, have inherent deficits in PPI homologous to those observed in schizophrenia patients. We also reported that PPI deficits in BB rats could be reversed by chronic but not acute administration of 0.5 mg/kg haloperidol. No other dose or drug was tested in that experiment. In this study, we tested the effects of acute subcutaneous administration of several doses of haloperidol as well as the second-generation antipsychotic, clozapine, and the putative novel antipsychotic, PD 149163, a neurotensin mimetic that crosses the blood-brain barrier. Consistent with our previous report, BB rats exhibited PPI deficits, compared to LE rats and none of the doses of haloperidol produced a significant effect on this PPI deficit. In contrast, 10 and 15 mg/kg of clozapine and all the doses of PD 149163 tested reversed the PPI deficits in BB rats. In addition, haloperidol, but not clozapine or PD 149163 produced significant catalepsy in BB rats, supporting the notion that PD 149163 has a profile consistent with atypical antipsychotics and providing support for the predictive validity of the PPI results. These results further strengthen the notion that the BB rat is a useful predictive model of antipsychotic efficacy and suggest that this model may differentiate between antipsychotics belonging to different therapeutic categories, for example, first- and second-generation agents. [ABSTRACT FROM AUTHOR]

The presence of both CFTR and ClC-2 proteins in the kidney suggest that they are involved in chloride transport along the nephron but their physiological roles in this organ are not known. To further understand the role of these chloride channels we studied Wistar rats subjected to dehydration for 2 days and also the homozygous Brattleboro rats, a strain of Long-Evans rats carrying an autosomal recessive mutation that leads to a deficiency of arginine-vasopressin (AVP) secretion in the plasma. The expression of CFTR was increased in the medulla of dehydrated Wistar rats and no variation was observed in the cortex. The expression of both ClC-2 and CFTR mRNAs was low in the renal cortex and medulla of the homozygous Brattleboro rats but returned to normal levels after AVP reposition. By the use of Madine-Darby canine kidney (MDCK) type I epithelial cells, it was observed that AVP (10–8, 10–7 and 10–6 M) increased CFTR mRNA expression "in vitro" but no effect was observed when changes in the medium tonicity were caused by the addition of sucrose, NaCl, manitol or urea. The modulation of both CFTR and ClC-2 mRNA by AVP, the main hormone involved in the regulation of body fluid osmolality, suggests the participation of these two chloride channels in the renal tubule transcellular chloride transport modulated by AVP. [ABSTRACT FROM AUTHOR]

Gene therapy, the transfer of genetic material for therapeutic purposes, has undergone an explosive development in the last few years. Within this context, development of gene therapy approaches for the neuroendocrine system, while incipient, has already generated a core of results which emerge as a promising area of research in neuroendocrinology. The present review presents a brief description of the viral vector-based gene delivery systems being currently used in neuroendocrinology, namely the adenoviral and herpes simplex type-1 (HSV-1)-derived vector systems, as well as an updated account of neuroendocrine pathologies for which gene therapy approaches in animal models are being implemented is provided. Current research efforts include treatment of experimental pituitary tumors by adenoviral vector-mediated transfer of the suicide gene for the HSV-1 thymidine kinase, which converts the prodrug ganciclovir into a toxic metabolite. An adenoviral vector encoding the human retinoblastoma suppressor oncogene has also been successfully used to rescue the phenotype of spontaneous pituitary tumors of the pars intermedia in mice. At the hypothalamic level, an adenovirus harboring the cDNA for arginine vasopressin has been used in Brattleboro rats to correct diabetes insipidus for several weeks. The last part of the review outlines the potential of gene therapy to correct age-associated neurodegenerative processes at the neuroendocrine level. Although effective implementation of gene therapy strategies still faces significant technical obstacles, these are likely to be progressively overcome as gene delivery systems are being improved.Copyright © 2001 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The renal vascular response to vasopressin and its modulation were evaluated in vivo by infusing the peptide directly into the renal artery of anaesthetized rats. The intra-renal artery (i.r.a) infusion of vasopressin induced a dose-dependent decrease in renal blood flow. Vasoconstriction was obvious at a dose of 3 ng/kg per min and reached a maximum at 100 ng/kg per min. The dose required for a half-maximal response (ED50) was 24±4 ng/kg per min (mean±SEM, n=8), corresponding to an estimated concentration in renal arterial blood required for a half-maximal response (EC50) of 1.9±0.6 nM. Thiobutabarbitone anaesthesia markedly increased plasma vasopressin concentration. This increase was prevented partially by hypotonic hydration of the rats without any change in the renal vascular response to exogenous vasopressin. Vasopressin-induced vasoconstriction dose/response curves were similar in homozygous and heterozygous Brattleboro rats. Infusion of desmopressin (1–1000 ng/kg per min, i.r.a.), a vasopressin V2 receptor-selective agonist, failed to induce renal vasodilation or vasoconstriction. In the presence of SR 49059 (1 mg/kg i.v.), a vasopressin V1A receptor antagonist that completely abolished the vasopressin-induced renal vasoconstriction, desmopressin again failed to induce vasodilation. Inhibition of nitric oxide synthase by Nω-nitro-l-arginine (L-NNA, 100 µg/kg for 10 min and 7.5 µg/kg per min, i.r.a.) enhanced vasopressin-induced renal vasoconstriction (EC50 0.6±0.1 nM, P<0.05). In contrast, cyclooxygenase blockade by indomethacin (5 mg/kg, i.v.) neither modified the vasopressin-induced decrease in renal blood flow nor altered the potentiation of vasoconstriction by L-NNA. These results show that the constrictor response of the rat renal vascular bed in vivo is observed only with high local concentrations of vasopressin. This hyporeactivity in vivo was not explained by an anaesthesia-elicited increase in endogenous vasopressin, nor by a modulatory effect linked to V2 receptor activation or prostanoid release. In contrast, NO release contributed to the attenuation of vasopressin-induced renal vasoconstriction. [ABSTRACT FROM AUTHOR]

Hyperviscosity syndrome was described in Brattleboro rats. The aim of this study was to investigate the possibility of Brattleboro rats using, as a test system for the study of agents with hemorheological activity. Under conditions of this model of high blood viscosity syndrome in Brattleboro rats, Lychnis chalcedonica L. extract (150 mg/kg) administered intragastrically for 10 days exhibited hemorheological activity by modulating macro- (plasma viscosity, fibrinogen concentration) and microrheological (erythrocyte aggregation and deformability parameters. Hence, Brattleboro rats are an adequate model of hyperviscosity syndrome that can be used for search and testing of substances with hemorheological activity. [ABSTRACT FROM AUTHOR]

The 3-layer immunoperoxidase-bridge technique was used to study the distribution of neurophysin and vasopressin in the neurosecretory neurons of rats homozygous and heterozygous for diabetes insipidus (Brattleboro strain). In the homozygous rats there was a marked hypertrophy of the hypothalamic magnocellular structures when stained either for neurosecretory material or neurophysin-like antigens. Neurophysin was present in both the paraventricular (PVN) and supraoptic nuclei (SON) of homozygous and heterozygous animals. Less than half of the cells in the PVN and SON were stained for neurophysin. This observation was less apparent when histochemical stains were used to visualize the distribution of neurosecretory material. Although it is generally considered that the homozygous Brattleboro rat does not synthesize vasopressin, a positive reaction was observed in the PVN and SON when anti-[8-lysine]vasopressin serum was employed in the immunohistochemical procedure. [ABSTRACT FROM AUTHOR]

Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals. In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation. [ABSTRACT FROM AUTHOR]

The renal response to iso-oncotic blood volume expansion with bovine serum albumin was studied in anaesthetized homozygous Brattleboro (DI) rats after acute (1 day) pretreatment with 1 U arginine-vasopressin (AVP) compared to heterozygous controls. In AVP-treated DI (DI+AVP) rats, basal urine flow as well as urinary sodium, chloride, and potassium excretion, were not different from controls. Diuresis and kaliuresis induced by volume expansion were blunted in DI+AVP rats. However, natriuresis and chloruresis were exaggerated in DI+AVP rats. They increased faster, reached a higher maximum, but declined earlier, compared to controls. The blunted diuresis resulted in a positive volume balance by the end of the experiment in DI+AVP rats, whereas the controls showed restoration of normal balance. Significant retention of sodium and chloride was observed in controls, but not in DI+AVP rats, over the time of the experiment. DI+AVP rats lost significantly less potassium than controls during the experiment. As judged from the lithium clearance method, the exaggerated saluresis in DI+AVP rats was mainly due to a reduced proximal sodium reabsorption. Plasma immunoreactivity of atrial natriuretic peptide (ANP) rose during blood volume expansion and fell in the recovery period. It was not different between AVP-treated DI rats and controls at any time of the experiment. Inulin clearance was slightly, but not significantly, lower in DI+AVP rats and increased after blood volume expansion in DI+AVP rats only. The results indicate that acute AVP substitution may abolish the exaggerated volume loss, but not the increased saluresis known to occur in DI rats after blood volume expansion. [ABSTRACT FROM AUTHOR]

The following study was designed to test the hypothesis that peripheral blood vessels of vasopressin deficient (Di/Di) rats are less responsive to pressor substances than normal rats. To address this question, pithed Di/Di and normal Long-Evans rats (LE) were exposed to intravenous injections of arginine-vasopressin, angiotensin II and noradrenaline. In addition, blood pressure increments and noradrenaline release in response to spinal cord stimulation in pithed Di/Di and LE rats were studied. The results show no abnormalities in peripheral vascular sensitivity to any of the pressor substances administered, nor was there any change in blood pressure and sympatho-adrenomedullary response to graded stimulation of the sympathetic outflow from the spinal cord. This study suggests that the failure of vasopressin deficient rats to recover from acute hemorrhage is not due to hyporesponsiveness of the peripheral vasculature to pressor agents but, rather, to the deficiency in the direct pressor effect of vasopressin. [ABSTRACT FROM AUTHOR]

The medullary thick ascending limb (MAL), but not the medullary collecting tubule (MCT), has been shown to have an impaired adenylate cyclase (AC) responsiveness to ADH and a selective hypoplasia in Brattleboro diabetes insipidus (DI) rats. Since chronic ADH administration has been found to increase epithelium volume and basolateral membrane surface area in MAL but not in MCT, we investigated whether chronic ADH infusion would affect the hormone-sensitive AC and the Na−K-ATPase activity - two markers of the basolateral membrane - in single microdissected portions of thick ascending limb and collecting tubule in DI rats. Results indicate that 1. in MAL of ADH-treated rats, AC resposes to in vitro AVP and glucagon and Na−K-ATPase activity increased to the same extent as did epithelium volume (60-80%); 2. changes in the other segments were independent of any morphological alteration. In the cortical thick ascending limb, AVP and glucagonsensitive AC decreased by 30-40% whereas Na−K-ATPase activity did not change. In the collecting tubule, AC response to in vitro AVP was not altered by ADH-treatment but glucagon-sensitive AC dropped by 50% and Na−K-ATPase activity doubled, independently of any variation in plasma aldosterone and glucagon levels. These results show that, in the MAL, the ADH-induced variations in enzyme activity are a reflection of the enlargement of the basolateral membrane surface area. Further studies are needed to clarify the origin of enzymatic alterations in the other segments. [ABSTRACT FROM AUTHOR]

The effect of antidiuretic hormone on urinary electrolyte excretion was investigated by clearance techniques in conscious rats in metabolic cages. Brattleboro rats with hereditary diabetes insipidus (DI) (no ADH) were studied in the absence of exogenous ADH (control group = C, n=4), and after several weeks of continuous dDAVP infusion (period A) followed by discontinuation of dDAVP (period B) (experimental group = E, n=6). dDAVP, a non-pressor antidiuretic analogue to ADH, induced 1) a high urine concentration (2,645±44 (SEM) in group E vs 131±6 mosmol/kg HO in group C), P<0.001; 2) no significant change in plasma osmolality (288±2 vs 297±7 mosmol/kg HO respectively) and in plasma concentration of major electrolytes, Na, K, Cl, Mg, and Ca; 3) a large decrease in urinary excretion of calcium and magnesium and no change in other electrolyte or total osmolar excretion. Fractional excretions in rats of groups C and E during period A were, respectively, for Na: 0.59±0.03 (SEM) and 0.51±0.33% (NS), for Ca: 2.92±0.62 and 0.34±0.05% ( P<0.001) and for Mg: 7.75±0.83 and 1.38±0.28% ( P<0.001). After treatment discontinuation, plasma osmolality in group E rose to 304±2 mosmol/kg HO ( P<0.01 compared to period A) with slight increases in plasma Na and Cl concentrations. Urine osmolality fell below, and urine flow rate rose above values observed in the control group. Fractional excretion of Ca and Mg rose to values seen in DI rats (3.30±0.37%, NS, for Ca) or above (26.95±0.65%, P<0.001, for Mg), with no change in other solute fractional excretion. Other works, from our and other's groups have shown that 1) long-term exposure to dDAVP induces a marked hypertrophy of the epithelium of the thick ascending limb of Henle's loop in its medullary part (MTAL) and 2) dDAVP induces an increase in Ca and Mg tubular reabsorption between end proximal and early distal sites of micropuncture. Taken together, these results suggest that the effects of ADH on divalent cation fractional excretion, seen in the present study, probably results from an increased Ca and Mg voltage-dependent reabsorption in the MTAL. This reabsorption is linked to the increased salt transport induced in this segment, both by a direct effect of ADH and by an indirect effect resulting from the increased solute delivery to the MTAL in the concentrating kidney. [ABSTRACT FROM AUTHOR]

Prostaglandin (PG) production by the kidney is known to be reduced both in vivo and in vitro in rats with hereditary diabetes insipidus (DI), totally lacking ADH. Exogenous ADH restores normal PG excretion in these rats. On the other hand, osmolality in vitro, and urine flow rate in vivo have been shown to influence PG synthesis rate. In order to determine whether the decreased PG synthesis of DI rats is due to the lack of antidiuretic hormone itself or to low tissue osmolality, we studied in vivo and in vitro PG production in DI rats in which urine osmolality had been raised either with ADG (infused by Alzet minipumps), or without ADH (by dehydratation) and in control DI rats. PGE and PGF were measured by radioimmunoassay in the urines and in supernatants of papillary homogenates incubated at 37°C for 15-120 min. ADH administration and dehydration led to similar urine osmolalities (≅900-1,000 mosmol/kg HO versus 150 in controls). However, only ADH administration but not dehydration increased PG urinary excretion (×5, P<0.001) and subsequent in vitro papillary synthesis (×1.6, P<0.01). These results show that antidiuretic hormone increases PG-synthesis of the renal papilla directly and not through its effects on papillary osmolality. [ABSTRACT FROM AUTHOR]

The effects of human calcitonin (HCT) on the distal tubule were investigated by micropuncture in hormone-deprived rats, i.e. in the absence of parathyroid hormone, antidiuretic hormone and glucagon, which might have masked these effects. Two groups of rats were studied: hormone-deprived and hormone-deprived+HCT, infused at 1.0 mU/min\100 g b.w. In the urine, HCT markedly reduced Ca and Mg excretion whereas excretion of water, Na and K was not significantly affected. Along the distal tubule, HCT strongly enhanced Na, Cl, Mg, Ca and total solute reabsorption, decreased K secretion but did not alter water or phosphate transport. It is concluded that HCT stimulated Na, Cl, Ca and Mg reabsorption. If, as suggested, HCT also stimulated the reabsorptive component of K transport, the hormone should therefore elicit the same physiological effects in the distal tubule and the thick ascending limb. [ABSTRACT FROM AUTHOR]

Papillary plasma flow (PPF) was measured by the albumin accumulation technique in rats of the Brattleboro strain with or without diabetes insipidus (DI and HZ respectively) and in Wistar rats. Measurements were also performed in DI rats receiving antidiuretic hormone for 30 min or 5 days and in dehydrated Wistar rats. PPF in HZ control and Wistar control rats was similar to previously published measurements. In contrast PPF was significantly higher in DI rats (461±26μl/min·g versus 263±28 in HZ) and decreased significantly after acute ADH administration. It returned to control values after prolonged ADH administration (262±40). Plasma flow entering the papilla was inversely correlated with urine osmolality up to 1000 mosmol/kg HO. Further increases in urine concentration (dehydration of Wistar rats) did not modify further PPF (255±28 versus 270±16 in non dehydrated Wistar). PPF might be influenced indirectly by ADH or prostaglandins and seems to depend on the osmotic environment of the papilla up to a certain limit. The factors which maintain PPF at a given minimum level with further increases in urine concentration are not known. [ABSTRACT FROM AUTHOR]

In Brattleboro rats, many more supraoptic neurones are baroresponsive than in normal rats. This may reflect the more widespread noradrenergic innervation of the supraoptic nucleus in Brattleboro rats. If so, the present data suggest that baroreceptor influences on vasopressin secretion are mediated by a noradrenergic pathway and that the altered responsiveness reflects the altered innervation. [ABSTRACT FROM AUTHOR]

In order to evaluate the role played by vasopressin on pressor responses elicited by stimulation of the periaqueductal gray (PAG) area by excitatory amino acids we carried out in vivo studies in genetically vasopressin deficient rats (Brattleboro). Microinjections of l-glutamic acid (glutamate, 0.6 to 60 nmol/rat) or N-methyl-d-aspartic acid (NMDA, 0.07 to 7 nmol/rat) into the PAG area of freely moving Brattleboro rats induced increases of arterial blood pressure values significantly lower than those obtained in Long Evans rats (control) (glutamate in Brattleboro rats: from +2±1 mmHg to 16±3 mmHg; glutamate in Long Evans rats: from +16±2 mmHg to +36±4 mmHg; NMDA in Brattleboro rats: from +5±2 mmHg to +34 ±8 mmHg; NMDA in Long Evans rats: from +18±7 mmHg to 80±9 mmHg; n=5). Similarly, in anaesthetized Brattleboro rats (urethane 1.2 g/kg i.p.) pressor responses to NMDA microinjections (0.7 nmol/rat) into the PAG area were significantly lower than in Long Evans rats (controls) (+15±3 mmHg vs +24±4 mmHg). In Long Evans rats NMDA injection also reversed blood pressure decrease induced by ganglionic blocker, hexamethonium and/or losartan (3 mg/kg i.v.), an AT1 receptor antagonist. In Brattleboro rats, NMDA injection did not reverse blood pressure decreases induced by hexamethonium (5 mg/kg i.v.). Moreover, hexamethonium induced blood pressure decrease was not reversed by acetylcholine injection (137 nmol/rat) into the PAG area of anaesthetized Long Evans rats, but if injected before hexamethonium, acetylcholine was able to increase blood pressure (+25±3 mmHg). Our results document: i) the importance of the PAG area in the control of cardiovascular system; ii) the involvement of excitatory amino acids in the neural control of vasopressin release; iii) the close relationship between glutamate and vasopressin in the central blood pressure regulation. [ABSTRACT FROM AUTHOR]

We studied the effect of vasopressin V receptor agonist (desmopressin, 5 μg/100 g body weight for 2 days) on the efficiency of osmotic concentration in Wistar rats and homozygous Brattleboro rats defective by the synthesis of antidiuretic hormone. Specific differences in the reaction of the osmotic concentration system components (urine osmolality and urea, sodium, and potassium content in the renal tissue) involved in the realization of the hydroosmotic effect of the hormone depend on genetically determined capacity to vasopressin synthesis in these animals. [ABSTRACT FROM AUTHOR]

The characteristics of the osmotic concentration system under conditions of sodium diclofenac treatment were studied in Wistar rats with normally functioning vasopressin gene and homozygotic Brattleboro rats completely lacking endogenous vasopressin. Blockade of prostaglandin synthesis in rats with different neurohypophyseal status stimulated urinary osmolality to a different degree. Different contribution of sodium cations and urea to osmotic concentration was revealed. [ABSTRACT FROM AUTHOR]

Serotonin 5-HT1A receptor agonist 8-OH DPAT suppressed drinking behavior in Brattleboro and Wistar rats. 5-HT1B agonist CGS-12066A and 5-HT2A antagonist ketanserin did not affect drinking behavior in Brattleboro rats; 5-HT3 antagonist ondansetron suppressed water consumption and 5-HT1A agonist stimulated salt appetite in Brattleboro, but not in Wistar rats. Presumably, vasopressin regulates thirst and salt appetite by modulating sensitivity/density of various types of 5-HT receptors. [ABSTRACT FROM AUTHOR]

The antidiuretic activity of oxytocin (OT) was measured in Brattleboro rats with congenital diabetes insipidus. A dose dependent antidiuretic response was found in animals receiving chronic infusions of 0.1 μg/h, 1.0 μg/h, and 5 μg/h of OT. OT infused at the rate of 5 μg/h over a 7-day period completely reversed the symptoms of diabetes insipidus. The results support the concept that OT serves as a weak agonist of vasopressin at the level of the kidney and at pharmacological levels exhibits antidiuretic activity. [ABSTRACT FROM AUTHOR]