Salt and water intake in Brattleboro rats with hypothalamic diabetes insipidus

Brattleboro rats lacking vasopressin have an elevated plasma osmolality and a stimulated renin-angiotensin system relative to Long-Evans rats (LE). The current studies were performed to elucidate the factors controlling water and salt intake in the Brattleboro rat with diabetes insipidus (DI). DI and LE rats were given the choice of water and saline solutions ranging from 0.1-1.0% to assess palatability, dialyzed with isotonic glucose to test for sodium appetite after sodium depletion, and infused intracranially with an angiotensin II analogue (saralasin) to assess the role of angiotensin II in spontaneous salt and water intake. DI rats exhibited spontaneous salt intake which was not significantly different from LE rats and increased their intake of 3.0% NaCl following sodium depletion, although less reliably than LE rats. A significant proportion of those DI rats not developing a sodium appetite showed attenuation of their diabetes following dialysis. No evidence for involvement of angiotensin II in spontaneous salt and water intake was found.     

The behavior of vasopressin-deficient rats (Brattleboro strain)

Seven Brattleboro rats homozygous for diabetes insipidus (DI) and seven normal Long-Evans (LE) rats were tested on a neuropsychological test battery comprised of the following tasks: time-spent-eating in two adaptation boxes, time-to-emerge into an open field, adaptation to a T-maze, contingently reinforced T-maze alternation, olfactory and visual discrimination, runway learning, approach-avoidance conflict, step-through passive avoidance, prod burying, and stress-induced interference. It was found that DI rats adapted more slowly than LE rats to novel environments (e.g., adaptation box, T-maze, and runway), and DI rats were slower to emerge into an open field. However, DI rats performed as well as LE rats on all other tasks. These results suggest that DI rats have altered temperamental dispositions (timidity or cautiousness), normal working and reference memory, and similar susceptibility (compared to LE rats) to the interfering effects of inescapable stress.     

Conditioned taste aversion in vasopressin-deficient rats (Brattleboro strain)

Brattleboro rats are homozygous for diabetes insipidus (DI), lacking the ability to synthesize vasopressin. Previous studies reported learning deficits in DI rats on passive avoidance tasks using footshock. Other studies, however, could not replicate these results. In two experiments, we studied the learning of DI and control Long Evans (LE) rats in a different avoidance paradigm: conditioned taste aversion (CTA). In the first experiment a mild CTA to saccharin was established gradually using low levels of an illness-inducing agent (lithium chloride). In the second experiment a strong CTA was established in one acquisition trial and the extinction of the conditioned aversion was followed for 12 trials. The two experiments found no differences between the DI and LE rats in either the magnitude or the rate of acquisition and extinction of the CTA. These results suggest that vasopressin is not involved in the acquisition and retention of CTA, and support previous studies indicating that vasopressin may not be involved in avoidance learning.     

Salt preference in rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain)

Brattleboro rats are homozygous for diabetes insipidus (HO-DI), lacking the ability to synthesize vasopressin. Besides increasing water consumption, HO-DI rats may compensate for their excessive renal water loss by reducing their intake of and preference for substances that elevate plasma osmolarity. In two experiments we assessed this possibility. In Experiment 1, salt preference of HO-DI and control Long-Evans (LE) rats was measured by presenting the rats with two tubes: one filled with water and the other with NaCl. In the first part of the experiment, 18 NaCl concentrations were presented in increasing order (from 6 to 300 mM). In the second part, other groups of HO-DI and LE rats were presented with 6 concentrations of NaCl, ranging from 6 to 450 mM in either increasing or decreasing order of concentrations. In Experiment 2, preference for 6 concentrations of citric acid ranging from 0.1 to 6 mM was assessed. With NaCl concentrations greater than 100 mM, intake and preference declined rapidly for the HO-DI group but very gradually for the LE group. In contrast, the HO-DI rats preferred all citric acid solutions more than LE rats. The results suggest that HO-DI rats compensate for their inability to concentrate urine not only by increasing water consumption, but also by decreasing consumption of and preference for salty solutions.     

Behavioral and endocrine responses of rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain)

Behavioral and endocrine profiles were established of homozygous (HO-DI) and heterozygous (HE-DI) rats with hereditary hypothalamic diabetes insipidus in comparison to Wistar strain rats. HO-DI rats were inferior in acquiring and maintaining active and passive avoidance behavior. Behavioral deficits were most obvious in a step-through one-trial learning passive avoidance test and least in multiple trial one way active avoidance test. Plasma corticosterone levels determined after the retention test appeared to be closely related to the passive avoidance behavior of the HO-DI rats. Passive avoidance immediately after the single learning trial was associated with elevated plasma corticosterone level; absence of avoidance and absence in plasma corticosterone elevation was observed 24 hr after learning. These observations are compatible with the hypothesis that vasopressin is involved in the consolidation and/or retrieval of learned responses. Differences between HO-DI and Wistar rats in open field behavior, in response threshold to electric footshock, and in a number of somatic endocrine parameters are reported and discussed.     

Hyperprolactinaemia alleviates behavioral alterations of rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain)

Male rats homozygous for hereditary hypothalamic diabetes insipidus (HO) and their heterozygous (HE) and normal (NO) variants (Brattleboro rats) were made hyperprolactinaemic by homografting two adenopituitaries under the kidney capsule. The high water intake and urine output of homozygous diabetic sham-operated rats (sham-HO) were similar to those of homografted HO animals. Also, hyperprolactinaemia failed to change the water intake and urine output of HE and NO rats, as compared to those of heterozygous (sham-HE) and normal (sham-NO) sham-operated animals. Compared to sham-HE and sham-NO animals, sham-HO rats showed a slow acquisition of active avoidance responses, a facilitated extinction of a pole jumping avoidance behavior and a reduced retention of a passive avoidance response. However, an improved performance of acquisition and retention behaviors up to the level of sham-HEs and sham-NOs was observed in homografted HO rats. Hyperprolactinaemia resulted in a reduced responsiveness to electrical footshock in HO, HE and NO animals, and in facilitated acquisition of active avoidance responses in HE and NO rats, but it failed to affect avoidance extinction and retention in the latter variants. These results suggest that the behavioral alterations shown by homozygous diabetes insipidus rats are alleviated by hyperprolactinaemia although high levels of plasma prolactin do not interfere with the mechanisms regulating water intake and urine output. In addition, hyperprolactinaemia affects the behavior of heterozygous and normal variants of Brattleboro strain but in a selective way.     

Lack of effect of Pitressin on the learning ability of Brattleboro rats with diabetes insipidus using positively reinforced operant conditioning

Brattleboro rats with hereditary hypothalamic diabetes insipidus (BDI) received daily subcutaneous injections of vasopressin in the form of Pitressin tannate (0.5 IU/24 hr). They were initially deprived of food and then trained to work for food reward in a Skinner box to a fixed ratio of ten presses for each pellet received. Once this schedule had been learned the rats were given a discrimination task daily for seven days. The performances of these BDI rats were compared with those of rats of the parent Long Evans (LE) strain receiving daily subcutaneous injections of vehicle (arachis oil). Comparisons were also made between these two groups of treated animals and untreated BDI and LE rats studied under similar conditions. In the initial learning trial, both control and Pitressin-treated BDI rats performed significantly better, and manifested less fear initially, than the control or vehicle-injected LE rats when first placed in the Skinner box. Once the initial task had been learned there was no marked difference in the discrimination learning between control or treated BDI and LE animals. These results support the view that vasopressin is not directly involved in all types of learning behaviour, particularly those involving positively reinforced operant conditioning.     

Histochemistry and ultrastructure of the interstitium of the renal papilla in rats with hereditary diabetes insipidus (brattleboro strain)

The Brattleboro strain of Long-Evans hooded rats has hereditary hypothalamic diabetes insipidus due to the inability to produce antidiuretic hormone. Animals homozygous for this autosomal recessive trait have extreme polyuria and polydipsia, whereas heterozygotes are less severely affected. Light and electron microscopy were used to study the interstitial tissue of the renal papilla of Brattleboro rats and normal Long-Evans rats. Staining with alcian blue or colloidal iron revealed that homozygous Brattleboro rats (DI) have greatly reduced quantities of glycosaminoglycans in the papillary interstitium. Heterozygotes showed staining similar but not identical to that of normal rats. The papillary interstitial cells of DI rats lacked the cytoplasmic processes seen in normal rats, and the normal relationship of these cells to the tubular elements of the papilla was absent. Electron microscopy revealed that the papillary interstitial cells of DI rats appeared less active than those of heterozygous or normal rats. In DI rats these cells displayed reduced numbers of lipid droplets and mitochondria, and the Golgi apparatus and rough endoplasmic reticulum were poorly developed. The altered ultrastructure of the papillary interstitial cells may be responsible for the reduction of interstitial glycosaminoglycans in DI rats. Glycosaminoglycans possess properties which may contribute to urinary concentration. It is suggested that the interstitial tissue of the renal papilla is influenced by antidiuretic hormone.     

The hippocampal corticosterone receptor system of the homozygous diabetes insipidus (Brattleboro) rat

The binding of [³H] corticosterone to hippocampal cytosol receptors of Brattleboro rats homozygous for diabetes insipidus (Ho-Di) and of normal Brattleboro rats (Ho-No) was investigated at 24 h after removal of the adrenals. The apparent maximal binding capacity of the Ho-Di hippocampal corticosterone receptor system was about 30% less than that of the Ho-No rats. Substitution of the vasopressin deficient rats with 1E pitressin tannate in oil partially restores the hippocampal corticosterone receptor level towards that of the control animals.     

Hydronephrosis: prevention by restoration of urinary concentrating ability using desamino-8D-arginine vasopressin (DDAVP) in Brattleboro rats.

Male Brattleboro rats with hereditary diabetes insipidus (BDI) were lifetime-treated with the vasopressin V2 receptor agonist desamino-8D-arginine vasopressin (DDAVP), given daily in the drinking fluid. The DDAVP-treated adult male BDI rats drank 34 +/- 6 ml/24 h (mean +/- s.e.m.) and excreted urine volumes of 22 +/- 5 ml/24 h compared with their age-matched untreated controls of 142 +/- 12 and 115 +/- 7 ml/24 h respectively. There was no significant difference between the mean body weights of chronically DDAVP-treated BDI rats (198 +/- 9 g) and untreated animals (207 +/- 9 g). Morphometry of sections of kidney confirmed extensive hydronephrosis in the right kidneys of the control untreated Brattleboro rats only. This was quantified as the area of pelvis expressed as a percentage of total cross-sectional area of kidney (17 +/- 3 compared with 5 +/- 1% in the chronically DDAVP-treated rats; P less than 0.002). Medium-term treatment of adult BDI rats with DDAVP reduced daily fluid output towards normal rat values but hydronephrosis was still present. These observations indicate that the restoration of fluid balance in adult BDI rats by treatment from conception with DDAVP may be an important factor in preventing the development of hydronephrosis in these animals.     

Hydruric response in Wistar and vasopressin-deficient Brattleboro rats to water load under conditions of increased brain serotonin level

The hydruric response to water load in Wistar rats and homozygous Brattleboro rats with a hereditary defect in the synthesis of vasopressin was studied under conditions of increased brain serotonin level. Serotonin prevented the reduction in reabsorption of osmotically free water in normal rats, but had no effect in vasopressin-deficient Brattleboro rats. Our results suggest that serotonin stimulates vasopressin secretion and interacts with the vasopressinergic system during the realization of osmotic regulation. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 141, No. 2, pp. 137–139, February, 2006     

A comparison of micropuncture and lithium clearance methods in the assessment of renal tubular function in rats with diabetes insipidus

The lithium clearance technique has been proposed as a non-invasive method whereby fluid delivery from the pars recta and pars convoluta of proximal tubules can be measured as C_Li and C_IN [0.78 C_Li/C_IN+0.22], respectively [12], C_Li being the clearance of lithium and C_IN that of inulin. In the present study, fluid delivery from proximal tubules was estimated simultaneously by micropuncture and lithium clearance techniques in anaesthetized Brattleboro rats with diabetes insipidus, under control conditions and following chronic treatment with hydrochlorothiazide. Absolute deliveries from the proximal convoluted tubules as determined by the micropuncture and lithium clearance methods were 437 and 427 μl/min, respectively, in untreated animals and 348 and 355 μl/min, respectively, in thiazide-treated animals. The individual results obtained by the two methods showed a high degree of correlation (r=0.85,P<0.001). In untreated Brattleboro rats, proximal fluid delivery as estimated by both the micropuncture and lithium clearance techniques showed significant (P<0.001) correlations with urine flow rate. These results provide further evidence for the acceptance of lithium clearance as a valid estimate of proximal tubular fluid delivery.     

Atrial natriuretic peptide and its mRNA in heart and brain of vasopressin-deficient Brattleboro rats

To understand the secretion and synthesis of atrial natriuretic peptide we measured immunoreactive atrial natriuretic peptide from plasma, heart tissues and brain areas, and ANP mRNA was determined from heart auricles and ventricles of vasopressin-deficient Brattleboro rats (DI) and from desmopressin treated Brattleboro rats (DI + DDAVP). Long-Evans rats (LE) served as controls. DI + DDAVP rats were given for 3 days sc. injections of 0.5/g l-desamino-8-D-arginine vasopressin in 1 ml. saline twice a day. The rats were housed in single metabolic cages and urinary output and water intake were measured daily. All the body and organ weight parameters were similar in the three groups when the rats were killed. No change was seen in the plasma ANP level between the groups. The right ventricle of DI + DDAVP rats had significantly (P < 0.05) higher concentration of ANP than LE rats (15.8 + 4.4 vs. 3.4 + 0.6 ng mg“¹ tissue). The left ventricle of DI and DI+DDAVP had significantly (P < 0.05) lower amounts of ANP mRNA than LE rats (0.5 ± 0.2 vs. 1.3 + 0.2 and 0.5 + 0.1 vs. 1.3 + 0.2 arbitrary units). In the hypothalamus, the ANP concentration was significantly (P < 0.05) lower both in DI and in DI + DDAVP rats than in LE rats (9.3 ±1.3 vs. 14.5 ±±1.6 and 6.1+0.6 vs. 14.5 ± 1.6 pg mg^-1 tissue). To conclude, although the water intake and urinary output of DI rats were changed towards normal with desmopressin treatment, the heart ventricular and hypothalamic ANP did not parallel the change. Desmopressin increased the ANP concentration in the right ventricle of DI rats. Thus the correction of the complete vasopressin deficiency-does not appear to associate with synthesis or release of atrial natriuretic peptide in heart or hypothalamus.     

Radioautographic study of glycoprotein synthesis and fate in the hypothalamo-neurohypophyseal system of vasopressin-deficient Brattleboro rats

Summary L-3H-fucose was injected into the lateral cerebral ventricle of vasopressin-deficient Brattleboro and control Long-Evans rats which were subsequently killed at several time intervals after the injection. The hypothalamus and the neurohypophysis were processed for light- and electronmicroscopic radioautography. Other complementary experiments using immunocytochemical and enzyme-histochemical techniques were also undertaken. L-3H-fucose was incorporated into newly synthesized glycoproteins in the Golgi apparatus of supraoptic and paraventricular neurons, and later on labelled glycoproteins migrated to lysosomes and the plasma membrane surrounding the perikaryon. The Golgi apparatus of the vasopressin-deficient neurons remained heavily labelled as long as 3 days after injection, in sharp contrast with the normal neurons in which there was a remarkable decrease of label in the Golgi region between 4 and 24 h after the isotope administration. Labelled glycoproteins also migrated to the neurohypophysis and were mainly found in the axonal plasma membrane, vesicles and axoplasm. The renewal of glycoproteins in the neurohypophysis of Brattleboro rats was faster than in the normal rats and this was attributed to the lack of formation of products which are normally packaged in secretory granules in the perikaryon and released at the axon terminal in the neurohypophysis. Colchicine caused a disturbance in the topography of the organelles of the perikaryon and the most striking features were the displacement of Golgi stacks to the periphery of the perikaryon and an accumulation of mitochondria in this neuronal region. No secretory granules were observed in the vasopressin-deficient neurons of untreated or colchicine-treated Brattleboro rats. By contrast, secretory granules (most of them labelled with 3H-fucose) were concentrated in the perikaryon of colchicinetreated Long-Evans rats. In these rats, colchicine caused a severe block in the migration of 3H-fucose-labelled glycoproteins to the neurohypophysis, but this did not occur in the Brattleboro rats. The results of the experiments were interpreted in the light of the genetic defect known to occur in Brattleboro rats which causes the inability to produce vasopressin and also remarkable morphological and physiological changes in the affected neurons.