Prolonged Water Deprivation Research Articles

Water deprivation modifies the metabolic profile of lavender (Lavandula angustifolia Mill.) leaves.

Lavender plantation is globally expanded due to the increasing demand of its essential oil and its popularity as an ornamental species. However, lavender plantations, and consequently essential oil industries, are threatened by more frequent and severe drought episodes in a globally changing climate. Still little is known about the changes in the general metabolome, which provides the precursors of essential oil production, by extended drought events. Prolonged drought fundamentally results in yield losses and changing essential oil composition. In the present study, the general metabolome of a main cultivated lavender species (Lavandula angustifolia Mill.) in response to water deprivation (WD) and re-watering was analyzed to identify the metabolomics responses. We found prolonged WD resulted in significant accumulations of glucose, 1,6-anhydro-β-D-glucose, sucrose, melezitose and raffinose, but declines of allulose, β-D-allose, altrose, fructose and D-cellobiose accompanied by decreased organic acids abundances. Amino acids and aromatic compounds of p-coumaric acid, hydrocaffeic acid and caffeic acid significantly accumulated at prolonged WD, whereas aromatics of cis-ferulic acid, taxifolin and two fatty acids (i.e., palmitic acid and stearic acid) significantly decreased. Prolonged WD also resulted in decreased abundances of polyols, particularly myo-inositol, galactinol and arabitol. The altered metabolite profiles by prolonged WD were mostly not recovered after re-watering, except for branched-chain amino acids, proline, serine and threonine. Our study illustrates the complex changes of leaf primary and secondary metabolic processes of L. angustifolia by drought events and highlights the potential impact of these precursors of essential oil production on the lavender industry.

Divergent Cross-Adaptation of Herbicide-Treated Wheat and Triticale Affected by Drought or Waterlogging.

Widely used agrochemicals that do not exert negative effects on crops and selectively target weeds could influence plant resilience under unfavorable conditions. The cross-adaptation of wheat (Triticum aestivum L.) and triticale (×Triticosecale Wittm.) exposed to two environmental abiotic stressors (drought and waterlogging) was evaluated after treatment with a selective herbicide (Serrate®, Syngenta). The ambivalent effects of the herbicide on the two studied crops were particularly distinct in waterlogged plants, showing a significant reduction in wheat growth and better performance of triticale individuals exposed to the same combined treatment. Histochemical staining for the detection of reactive oxygen species (ROS) confirmed that the herbicide treatment increased the accumulation of superoxide anion in the flooded wheat plants, and this effect persisted in the younger leaves of the recovered individuals. Comparative transcript profiling of ROS scavenging enzymes (superoxide dismutase, peroxidase, glutathione reductase, and catalase) in stressed and recovered plants revealed crop-specific variations resulting from the unfavorable water regimes in combination with the herbicide treatment. Short-term dehydration was relatively well tolerated by the hybrid crop triticale and this aligned with the considerable upregulation of genes for L-Proline biosynthesis. Its drought resilience was diminished by herbicide application, as evidenced by increased ROS accumulation after prolonged water deprivation.

Vasopressin and oxytocin expression in hypothalamic supraoptic nucleus and plasma electrolytes changes in water-deprived male Meriones libycus

ABSTRACT In mammals, plasmatic osmolality needs to be stable, and it is highly related to the hydric state of the animals which depends on the activity of the hypothalamic neurohypophysial system and more particularly by vasopressin secretion. Meriones, a desert rodent, can survive even without drinking for more than one month. The mechanism(s) by which they survive under these conditions remains poorly understood. In this study, we examine the water’s deprivation consequences on the: (1) anatomy, morphology, and physiology of the hypothalamic supraoptic nucleus, (2) body mass and plasma electrolytes changes in male desert rodents ‘Meriones libycus’ subjected to water deprivation for 30 days. The effect of water deprivation was evaluated on the structural and cellular organization of the supraoptic nucleus by morphological observations and immunohistochemical approaches, allowing the labeling of AVP but also oxytocin. Our finding demonstrated that upon water deprivation (1) the body weight decreased and reached a plateau after a month of water restriction. (2) The plasmatic osmolality began to decrease and return to values similar to control animals at day 30. (3) The SON, both in hydrated and water-deprived animals, is highly developed.(4) The AVP labeling in the SON increased upon dehydration at variance with OT. These changes observed in body mass and plasma osmolality reveal an important adaptive process of male Meriones in response to prolonged water deprivation. Overall, this animal represents an interesting model for the study of water body homeostasis and the mechanisms underlying the survival of desert rodents to xeric environments.

Use of the Urine-to-Plasma Urea Ratio to Predict ADPKD Progression.

Predicting disease progression in patients with autosomal dominant polycystic kidney disease (ADPKD) poses a challenge, especially in early-stage disease when kidney function is not yet affected. Ongoing growth of cysts causes maximal urine-concentrating capacity to decrease from early on. We therefore hypothesized that the urine-to-plasma urea ratio, as a reflection of the urine-concentrating capacity, can be used as a marker to predict ADPKD progression. The urine-to-plasma urea ratio was calculated by dividing concentrations of early morning fasting spot urine urea by plasma urea. First, this ratio was validated as surrogate marker in 30 patients with ADPKD who underwent a prolonged water deprivation test. Thereafter, association with kidney outcome was evaluated in 583 patients with ADPKD with a broad range of kidney function. Multivariable mixed-model regression was used to assess association with eGFR slope, and logarithmic regression to identify patients with rapidly progressive disease, using a cutoff of -3.0 ml/min per 1.73 m2 per year. The urine-to-plasma urea ratio was compared with established predictors, namely, sex, age, baseline eGFR, Mayo Clinic height-adjusted total kidney volume class, and PKD gene mutation. The maximal urine-concentrating capacity and urine-to-plasma urea ratio correlated strongly (R=0.90; P<0.001). Next, the urine-to-plasma urea ratio was significantly associated with rate of eGFR decline during a median follow-up of 4.0 (interquartile range, 2.6-5.0) years, both crude and after correction for established predictors (β=0.58; P=0.02). The odds ratio of rapidly progressive disease was 1.35 (95% confidence interval, 1.19 to 1.52; P<0.001) for every 10 units decrease in urine-to-plasma urea ratio, with adjustment for predictors. A combined risk score of the urine-to-plasma urea ratio, Mayo Clinic height-adjusted total kidney volume class, and PKD mutation predicted rapidly progressive disease better than each of the predictors separately. The urine-to-plasma urea ratio, which is calculated from routine laboratory measurements, predicts disease progression in ADPKD in addition to other risk markers. This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2021_01_27_CJN10470620_final.mp3.

SO091URINE-TO-PLASMA UREA RATIO, AS SURROGATE MARKER FOR URINE CONCENTRATING CAPACITY, IS ASSOCIATED WITH DISEASE PROGRESSION IN ADPKD

Abstract Introduction Predicting disease progression in autosomal dominant polycystic kidney disease (ADPKD) patients poses a challenge, especially in early stage disease when renal function is not yet affected. The ongoing formation and growth of cysts causes the urine concentrating capacity to decrease from early on in the disease. We therefore hypothesized that the easy and inexpensive to measure urine-to-plasma urea ratio (UPU ratio), which is assumed to be surrogate for maximal urine concentrating capacity, can be used as marker to predict disease progression in ADPKD. Methods The UPU ratio was calculated by dividing urea concentration in a fasting morning spot urine sample by plasma urea concentration adjusted for plasma creatinine concentration. First, we validated the UPU ratio in 30 ADPKD patients who underwent a prolonged water deprivation test to measure the maximal urine concentrating capacity. Thereafter, the association of the UPU ratio with renal outcome was evaluated in 583 ADPKD patients participating in the DIPAK observational cohort (inclusion criteria: age&amp;gt;18 years, eGFR &amp;gt;15 mL/min/1.73m2, no concomitant diseases affecting eGFR, without V2 receptor antagonist prescription). Kidney function was assessed as eGFR by the creatinine based CKD-EPI formula, height adjusted total kidney volume (htTKV) by MRI and copeptin (surrogate for vasopressin) by ELISA. Results In the water deprivation test participants (n=30), the UPU ratio was strongly correlated with maximal urine concentrating capacity (R = 0.67, p&amp;lt;0.001). This association remained significant after correcting for sex, age, htTKV and eGFR (st. β = 0.53, p = 0.007). In these subjects maximal urine concentrating capacity as well as UPU ratio were associated with the rate of eGFR decline during a median follow-up of 6.3 yr (12 eGFR assessments per patient) assessed using linear mixed modeling, also when corrected for sex, baseline age and eGFR (β = 0.009, p = 0.04, and β = 5.56, p&amp;lt;0.001, resp.). We subsequently corroborated in the larger DIPAK observational cohort (n=583, 58% female, mean age 47 yr median eGFR 60 mL/min/1.73m2 and htTKV 898 ml/m), that the UPU ratio was significantly associated with rate of eGFR decline during a median follow-up of 4.0 yr (6 eGFR assessments per patient): β = 0.23, p = 0.005. This association remained significant when corrected for sex, baseline age and eGFR (β = 0.32, p&amp;lt;0.001) and even when additionally corrected for Mayo class, PDK mutation and copeptin (β = 0.40, p &amp;lt;0.001). Stepwise backward multivariate regression analysis resulted in a final model including the UPU ratio, PKD mutation, Mayo Class and copeptin. Cox survival analysis showed that a lower baseline UPU ratio (indicating less urine concentrating capacity) was significantly associated with a higher risk to develop the combined renal endpoint of incidence of start of kidney replacement therapy, eGFR &amp;lt;15 mL/min/1.73m2 or eGFR decrease &amp;gt;40% during follow-up (adjusted Hazard Ratio per SD = 1.39, p = 0.007). Limiting the aforementioned analyses to the subgroup of patients with relative early stage disease (n=122, age &amp;lt;40 yr and eGFR &amp;gt;60 mL/min/1.73m2) rendered essentially similar results, with an adjusted β for UPU ratio in the final model of 0.33 (p = 0.04). In this subgroup with a limited number of events (n=10), Cox survival analysis did not reach formal significance (adjusted HR per SD: 2.67, p = 0.055). Conclusion The UPU ratio, which is calculated from routine laboratory measurements, predicts renal prognosis in ADPKD in addition to other, more laborious to measure and expensive risk markers. Notably, this marker of urine concentrating capacity also shows promise in early-stage disease.

Neurobehavioral and neurophysiological effects of prolonged osmotic stress in rats: A focus on anxiety state and pain perception

This study examined the effect of prolonged water deprivation, in rat, on 5-HT and TH- immuno-expression in Dorsal Raphe Nucleus (DRN), Substantia Nigra pars compacta (SNc), Ventral Tegmental Area (VTA), and Magnus Raphe Nucleus (MRN). In parallel, we evaluated the anxiety state and pain perception in dehydrated rats. Our Findings revealed that dehydrated rats exhibited more preference for the dark compartment, suggesting that prolonged water deprivation is associated to an anxiogenic effect. After one week, 5 H T IR in the DRN of dehydrated rates showed a significant decrease. This was reversed to a significant increase post week 2 of dehydration. Our findings also demonstrated that TH-IR in DRN, MRN, SNc and VTA neuronal systems is significantly and gradually enhanced after 1-and-2-week osmotic stress. In addition, our results proved that all dehydrated rats were characterized by a significant and proportional rise of the reaction time to the nociceptive response in the hot plate test, as water deprivation duration increased, suggesting that dehydration caused a significant decrease in pain perception. Finally, the data described here clearly showed the implication of serotonin and dopamine neurotransmitter systems in the resistance to osmotic stress. Therefore, in this study, such central impairments were traduced by a few peripheral outcomes manifested by changes in mood state and nociception.

Prolonged Fasting Increases DNA Methylation in Northern Elephant Seal Pups

Northern elephant seals (NES) are naturally exposed to extreme conditions, including prolonged food and water deprivation (fasting). NES pups initially nurse for a month before they are weaned and fast for two months. During this fasting period NES pups lose about 25% of their body mass, while maintaining biochemical homeostasis and supporting muscle development. The environment, especially stressful environmental conditions, can modify the methylation status of DNA, consequently regulating gene expression. We compared global DNA methylation between early (1–2 weeks) and late (7–8 weeks) fasting NES pups. DNA was extracted from white blood cells collected from fasting NES pups. Global DNA methylation was measured using a MethylFlash™ Global DNA Methylation (5‐mC) Kit. Prolonged fasting significantly increased global DNA methylation (p = 0.0463) in NES pups, suggesting a decrease in transcription activity. We are in the process of identifying changes in specific genes involved in growth, hypoxia tolerance, and metabolism between early and late fasting pups by analyzing the methylation status of CpG islands in putative promoter region sequences. Our initial results suggest that DNA methylation is an important regulator of gene expression during natural, prolonged food deprivation.

Osmolyte Depletion and Thirst Suppression Allow Hibernators to Survive for Months without Water.

Thirteen-lined ground squirrels (Ictidomys tridecemlineatus) are obligatory hibernators who can survive over 6months of the year in underground burrows or laboratory hibernaculum without access to food or water [1]. Hibernation consists of prolonged periods of torpor, lasting up to 18days, which are characterized by low body temperature and suppressed metabolism. This torpidity is interspersed with short periods of interbout arousal, lasting up to 48 h, during which squirrels temporarily return to an active-like state and lose small amounts of water to urination and evaporation [2]. Water is also lost during torpor due to a positive vapor pressure difference created by the slightly higher temperature of the body compared to its surroundings [2, 3]. Here, we investigate the physiological mechanism of survival during prolonged water loss and deprivation throughout hibernation. By measuring hydration status during hibernation, we show that squirrels remain hydrated during torpor by depleting osmolytes from the extracellular fluid. During brief periods of arousal, serum osmolality and antidiuretic hormone levels are restored, but thirst remains suppressed. This decoupling of thirst and diuresis enables water retention by the kidney while suppressing the drive to leave the safety of the underground burrow in search of water. An acute increase in serum osmolality reinstates water-seeking behavior, demonstrating preservation of the physiological thirst circuit during hibernation. Better mechanistic understanding of internal osmolyte regulation and thirst suppression could translate to advancements in human medicine and long-term manned spaceflight. VIDEO ABSTRACT.

Long term osmotic stress exposure outcomes on rat dopaminergic innervations and the associated motor behavior.

The osmotic stress is a powerful stimulus that elicits profound peripheral and central disturbances. In the mammalian brain, osmotic stress has been associated to several glial and neuronal changes. The lack of data regarding the impact on the dopaminergic system and locomotion led us to investigate the effect of prolonged water deprivation in rat on the midbrain dopaminergic system and locomotor performance by dehydrating rats for one and two weeks. Locomotor activity and tyrosine hydroxylase (TH) expression were assessed using the open field test and immunohistochemistry respectively. Water deprivation was accompanied with a significant increment of TH expression within substantia nigra compacta (SNc) and ventral tegmental area (VTA) gradually as the duration of dehydration increases. While locomotor activity showed the inverse tendency manifested by a drop of crossed boxes number following one and two weeks of water deprivation. Our data suggest a substantial implication of midbrain dopaminergic system in the central response to the osmotic stimuli accompanied with locomotor deficiencies.

The underlying physiological basis of the desert rodent Meriones shawi's survival to prolonged water deprivation: Central vasopressin regulation on peripheral kidney water channels AQPs-2

Meriones shawi (M. shawi) is a particular semi-desert rodent known by its resistance to long periods of thirst. The aim of the present investigation is to clarify the underlying mechanisms allowing M. shawi to resist to hard conditions of dehydration. For this reason we used two different approaches: i) a morphometric study, which consists in measuring the effect of dehydration on body and kidneys weights as well as the report kidney weight/body weight, ii) By immunohistochemistry, we proceed to study the effect of dehydration on the immunoreactivity of central vasopressin (AVP) and the kidney aquaporin-2 (AQP-2) which is a channel protein that allows water to permeate across cell membranes. Our results showed both a body mass decrease accompanied by a remarkable kidneys hypertrophy. The immunohistochemical study showed a significant increase of AQP-2 immunoreactivity in the medullar part of Meriones kidneys allowing probably to Meriones a great ability to water retention. Consistently, we demonstrate that the increased AQP-2 expression occurred together with an increase in vasopressin (AVP) expression in both hypothalamic supraoptic (SON) and paraventricular nucleus (PVN), which are a major hub in the osmotic control circuitry.These various changes seen either in body weight and kidneys or at the cellular level might be the basis of peripheral control of body water homeostasis, providing to M. shawia strong resistance against chronic dehydration.

The rat SCO responsiveness to prolonged water deprivation: Implication of Reissner�s fiber and serotonin system

The rat SCO responsiveness to prolonged water deprivation: Implication of Reissner�s fiber and serotonin system

Vasopressin, Copeptin, and Renal Concentrating Capacity in Patients with Autosomal Dominant Polycystic Kidney Disease without Renal Impairment

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent hereditary renal disease, characterized by cyst formation in the kidneys leading to end stage kidney failure. It is clinically acknowledged that ADPKD patients have impaired urine concentrating capacity, but the mechanism behind this observation is unknown. Fifteen ADPKD patients (estimated GFR ≥60 ml/min per 1.73 m(2)) and 15 age- and sex-matched healthy controls underwent a standard prolonged water deprivation test in which urine and plasma osmolality, vasopressin, and copeptin were measured. The effect of a synthetic vasopressin analog (desmopressin) injected at the moment of maximal urine concentrating capacity was also studied. After 14 hours of water deprivation, ADPKD patients tended to have higher plasma osmolality (P=0.07) and significantly higher vasopressin and copeptin levels (both P<0.05), whereas urine osmolality was similar in ADPKD patients and controls (710 versus 742 mOsmol/kg; P=0.61). Maximal urine concentrating capacity was lower in ADPKD patients (758 versus 915 mOsmol/kg in controls; P<0.001). At maximal urine concentrating capacity, plasma osmolality, vasopressin, and copeptin levels were significantly higher in ADPKD patients. The median increase in urine osmolality after desmopressin administration in ADPKD patients was less than in healthy controls. Already early in their disease, ADPKD patients have impaired maximal urine concentrating capacity brought out upon dehydration, with no evidence of impaired hypothalamic response. To maintain fluid balance, vasopressin concentration increases, which is hypothesized to play a role in ADPKD disease progression.

The rat SCO responsiveness to prolonged water deprivation: Implication of Reissner's fiber and serotonin system

The osmotic stress is a potent stimulus that can trigger several peripheral as well as central impairments. The brain is a vulnerable target of the osmotic stress and particularly circumventricular organs (CVOs) regarding their strategic localization as sensory organs of biochemical changes in the blood and cerebrospinal fluid circulations. The subcommissural organ (SCO) is a CVO which releases doubly in the CSF and blood circulation a glycoprotein called Reissner's fiber (RF) that has been associated to several functions including electrolyte and water balances. The present work was aimed on the assessment of the secretory activity of the SCO and its serotoninergic innervation following 2weeks of total water restriction in Wistar rat. Using the immunohistochemistry of RF and serotonin (5HT), our data showed a significant overall reduction of RF immunoreactivity within both ependymal and hypendymal cells of the SCO of dehydrated rats compared to their corresponding controls, this decrease was concomitant with an enhancement of fibers 5HT immunoreactivity in the SCO as well as in the classical ependyma and in the dorsal raphe nucleus (DRN), constituting the origin of this innervation. The present findings support the possible involvement of the SCO in the response to prolonged water deprivation by decreasing its secretory materials which may result from either a direct peripheral hormonal control and/or the consequence of the enhanced 5HT innervation of the SCO.

Aquaporin-4 Gene Disruption in Mice Reduces Brain Swelling and Mortality in Pneumococcal Meningitis

The astroglial water channel aquaporin-4 (AQP4) facilitates water movement into and out of brain parenchyma. To investigate the role of AQP4 in meningitis-induced brain edema, Streptococcus pneumoniae was injected into cerebrospinal fluid (CSF) in wild type and AQP4 null mice. AQP4-deficient mice had remarkably lower intracranial pressure (9 +/- 1 versus 25 +/- 5 cm H2O) and brain water accumulation (2 +/- 1 versus 9 +/- 1 microl) at 30 h, and improved survival (80 versus 0% survival) at 60 h, through comparable CSF bacterial and white cell counts. Meningitis produced marked astrocyte foot process swelling in wild type but not AQP4 null mice, and slowed diffusion of an inert macromolecule in brain extracellular space. AQP4 protein was strongly up-regulated in meningitis, resulting in a approximately 5-fold higher water permeability (P(f)) across the blood-brain barrier compared with non-infected wild type mice. Mathematical modeling using measured P(f) and CSF dynamics accurately simulated the elevated lower intracranial pressure and brain water produced by meningitis and predicted a beneficial effect of prevention of AQP4 upregulation. Our findings provide a novel molecular mechanism for the pathogenesis of brain edema in acute bacterial meningitis, and suggest that inhibition of AQP4 function or up-regulation may dramatically improve clinical outcome.

The Partitioning of Water and Solutes during Evaporative Water Loss in Three Terrestrial Crabs

Water contents, hemolymph volumes, and hemolymph composition were measured during dehydration in three terrestrial crabs. Holthuisana transversa, which is able to survive prolonged water deprivation, had a higher hydrated water content (72.3% total mass) and a relatively higher hemolymph volume (48.9% total water) than the supralittoral crabs Ocypode cordimanus (hydrated water content, 665% total mass; hemolymph volume, 35.0% total water) and Leptograpsus variegatus (hydrated water content, 67.2% total mass; hemolymph volume, 32.6% total water). Water was lost from both vascular and nonvascular fluids in all crabs. However, this loss was primarily at the expense of the hemolymph in Ocypode but at the expense of nonvascular fluids in Leptograpsus. With increasing desiccation of Holthuisana, water was lost first from the nonvascular fluids and then mainly from the hemocoel. These results differ from previous studies where water loss was either exclusively vascular (Birgus) or extravascular (Gecarcoidea). We suggest that these apparently different patterns may result from differences in the quantities of water initially stored in the gut or bladder rather than from fundamentally different processes. These differences in turn may depend partly on different basic morphologies of Brachyura and Anomura and partly on differing requirements to store water in their normal habitats. Unlike many insects, none of the crabs osmoregulated by excretion or sequestration of salts. Osmolality and ion concentrations in the hemolymph increased, but the total quantity of each ion in the hemolymph did not change greatly. Small shifts of Na, Cl, and Mg in Holthuisana, and of K in Leptograpsus, were consistent with the above partitioning and maintenance of internal osmotic equilibrium. Increases in hemolymph pools of Ca and total CO₂ in dehydrated and emersed Holthuisana and Leltograpsus were considered to result from acid-base regulation associated with air breathing rather than from dehydration. Dehydration of Holthuisana depressed the urine filtration rate to less than half of the rate in emersed hydrated crabs. Hemolymph ammonia concentrations were reduced by a factor of three during emersion of both hydrated and dehydrated (fasting) Holthuisana.

Haemoconcentration in Yankasa sheep exposed to prolonged water deprivation

Five non-pregnant healthy Yankasa ewes were deprived of water for 10 d with only one watering period during hot dry weather. On d 5, the mean body weight significantly ( P<0.05) decreased, while mean packed cell volume (PCV) and plasma potassium (K), bicarbonate, glucose concentrations and albumin-to-globulin ratio did not vary significantly. However, mean plasma total protein and albumin concentrations were slightly increased ( P>0.05) and mean plasma globulin, sodium (Na), chloride, urea, creatinine and cholesterol concentrations and urea-to-creatinine and cholesterol-to-glucose ratios were significantly ( P<0.05) increased. Sheep were watered on an ad libitum basis for only 12 h after sample collection on d 5. On d 10, the mean body weight was only slightly decreased ( P>0.05), mean PCV and plasma K, bicarbonate and glucose concentrations and albumin-to-globulin ratio still did not vary significantly. Significant increases ( P<0.05) in mean plasma Na, chloride, creatinine and cholesterol concentrations and cholesterol-to-glucose ratio were sustained, while mean plasma total protein, albumin, globulin and urea concentrations, and urea-to-creatinine ratio returned to normal. In conclusion, when assessing haemoconcentration during prolonged dehydration, PCV may not be increased and plasma total protein, albumin, globulin and urea concentrations may be initially increased, but later return to normal, whereas increases in plasma Na, chloride, creatinine and cholesterol are sustained. With this information, misleading interpretations of blood data from clinically dehydrated Yankasa sheep may be avoided.

The Controlled Water Access Paradigm

The following contribution, The Controlled Water Access Paradigm, was submitted in response to Prolonged Water Deprivation: A Case Study (ILAR News 33[3]:48-52, 1991), by F. Barbara Orlans. It is followed by a rejoinder from Dr. Orlans. In considering Prolonged Water Deprivation: A Case Study for publication, the ILAR News Editorial Panel understood the term case study used by Dr. Orlans to mean an account of a single institutional animal care and use committee's (IACUC's) deliberations concerning a single protocol. However, as Dr. Orlans acknowledges in her rejoinder, certain additions were made (thus making it a 'composite'). It is ILAR's editorial policy to use the term case study only when referring to a true record of circumstances surrounding a single event. ILAR News strives to stimulate discussion within IACUCs by providing material from a variety of sources. Contributions such as these are not intended to be used as policy or precedent. The opinions expressed in author-attributed articles in ILAR News do not necessarily reflect those of ILAR or the National Research Council, National Academy of Sciences.

Adaptations of the reed frogHyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment

Ofall amphibians living in arid habitats, reed frogs (belonging to the super species Hyperolius viridiflavus) are the most peculiar. Froglets are able to tolerate dry periods of up to 35 days or longer immediately after metamorphosis, in climatically exposed positions. They face similar problems to estivating juveniles, i.e. enduranee of long periods of high temperature and low RH with rather limited energy and water reserves. In addition, they must have had to develop meehanisms to prevent poisoning by nitrogenous wastes that rapidly accumulate during dry periods as a metabolie consequenee of maintaining a non-torpid state. During dry periods, plasma osmolarity of H. v. taeniatus froglets strongly increased, mainly through urea accumulation. Urea accumulation was also observed during metamorphic climax. During postmetamorphic growth, chromatophores develop with the density and morphology typical of the adult pigmentary pattern. The dermal iridophore layer, which is still incomplete at this time, is fully developed within 4-8 days after metamorphosis, irrespective of maintenance conditions. These iridophores mainly contain the purines guanine and hypoxanthine. The ability of these purines to reflect light provides an excellent basis for the role of iridophores in temperature regulation. In individuals experiencing dehydration stress, the initial rate of purine synthesis is doubled in eomparison to specimens continuously maintained under wet season conditions. This increase in synthesis rate leads to a rapid increase in the thiekness of the iridophore layer, thereby effectively reducing radiation absorption. Thus, the danger of overheating is diminished during periods of water shortage when evaporative cooling must be avoided. After the development of an iridophore layer of sufficient thickness for effective radiation reflectance, synthesis of iridophore pigments does not cease. Rather, this pathway is further used during the remaining dry season for solving osmotic problems eaused by accumulation of nitrogenous wastes. During prolonged water deprivation, in spite of reduced metabolic rates, purine pigments are produced at the same rate as in wet season conditions. This leads to a higher relative proportion of nitrogen end products being stored in skin pigments under dry season conditions. At the end of an experimental dry season lasting 35 days, up to 38% of the accrued nitrogen is stored in the form of osmotically inactive purines in thc skin. Thus the osmotic problems caused by evaporative water loss and urea production are greatly reduced.

Effet d'une carence hydrique prolongée sur la croissance pondérale et sur le métabolisme hydrique chez un rongeur Gerbillidé (Meriones shawi shawi)

The effect of prolonged water deprivation, applied progressively since weaning, was studied on body weight in growing sub-desert rodents (Meriones shawi). Then, water metabolism, food consumption and kidney weight were measured in these adults animals. During partial water deprivation the weight curve was similar to that of controls, whereas with total water deprivation three different stages were noticed: a decrease, a stabilization and an increase in body weight as a function of age. At the end of the experiment, the body water volume was similar in dehydrated and in control animals. However, in water deprived animals, there was a lower rate of water influx and efflux compared to controls. Their food consumption was two-fold that of controls. Dehydrated meriones showed a significant increase in kidney weight as compared to controls.

Activity, startle magnitude, and prolonged food and water deprivation: Two further failures to duplicate

Studies from one laboratory have shown deprivation-induced attenuation of startle response magnitudes, but another laboratory has reported failures to show any relationship between these variables. In an attempt to locate possible procedural contributions to this discrepancy in outcomes, our Experiment 1 involved 20 massed startle-stimulus presentations (30-sec ISI) to rats that had gone either 43 h or 1 h since eating (80% body weights equated for groups). Experiment 2 entailed spaced presentations (four trials per five bidaily sessions, 20-min ISI) to rats that had gone either 43 h or 1 h since drinking (80% weights also equated). Activity prior to, during, and after startle presentations also was recorded. Although group startle magnitudes differed on some trial blocks of both experiments, these differences were not systematically related to either of the deprivation conditions. Mean activity level was sensitive to startle-stimulus presentations, and showed systematic trial-block rates of decline for periods prior to, during, and following startle presentations that were identical for all groups.