Adolescent Ethanol Exposure Alters Cholinergic Function and Apical Dendritic Branching Within the Orbital Frontal Cortex.

During adolescence, heavy binge-like ethanol consumption can lead to frontocortical structural and functional impairments. These impairments are likely driven by adolescence being a critical time point for maturation of brain regions associated with higher-order cognitive functioning. Rodent models of heavy binge-like ethanol exposure show consistent disruptions to the typical development of the prefrontal cortex (PFC). All deep cortical layers receive cholinergic projections that originate from the Nucleus basalis of Meynert (NbM) complex. These cholinergic projections are highly involved in learning, memory, and attention. Adolescent intermittent ethanol exposure (AIE) induces cholinergic dysfunction as a result of an epigenetic suppression of the genes that drive the cholinergic phenotype. The current study used a model of AIE to assess structural and functional changes to the frontal cortex and NbM following binge-like ethanol exposure in adolescence. Western blot analysis revealed long-term disruptions of the cholinergic circuit following AIE: choline acetyltransferase (ChAT) was suppressed in the NbM and vesicular acetylcholine transporter (VAChT) was suppressed in the orbitofrontal cortex (OFC). In vivo microdialysis for acetylcholine efflux during a spatial memory task determined changes in cholinergic modulation within the PFC following AIE. However, AIE spared performance on the spatial memory task and on an operant reversal task. In a second study, Golgi-Cox staining determined that AIE increased apical dendritic complexity in the OFC, with sex influencing whether the increase in branching occurred near or away from the soma. Spine density or maturity was not affected, likely compensating for a disruption in neurotransmitter function following AIE.

Executive functioning-specific behavioral impairments in a rat model of human third trimester binge drinking implicate prefrontal-thalamo-hippocampal circuitry in Fetal Alcohol Spectrum Disorders.

Individuals diagnosed with Fetal Alcohol Spectrum Disorders (FASD) often display behavioral impairments in executive functioning (EF). Specifically, the domains of working memory, inhibition, and set shifting are frequently impacted by prenatal alcohol exposure. Coordination between prefrontal cortex and hippocampus appear to be essential for these domains of executive functioning. The current study uses a rodent model of human third-trimester binge drinking to identify the extent of persistent executive functioning deficits following developmental alcohol by using a behavioral battery of hippocampus- and prefrontal cortex-dependent behavioral assays in adulthood. Alcohol added to milk formula was administered to Long Evans rat pups on postnatal days 4-9 (5.25 g/kg/day of ethanol; intragastric intubation), a period when rodent brain development undergoes comparable processes to human third-trimester neurodevelopment. Procedural control animals underwent sham intubation, without administration of any liquids (i.e., alcohol, milk solution). In adulthood, male rats were run on a battery of behavioral assays: novel object recognition, object-in-place associative memory, spontaneous alternation, and behavioral flexibility tasks. Alcohol-exposed rats demonstrated behavioral impairment in object-in-place preference and performed worse when the rule was switched on a plus maze task. All rats showed similar levels of novel object recognition, spontaneous alternation, discrimination learning, and reversal learning, suggesting alcohol-induced behavioral alterations are selective to executive functioning domains of spatial working memory and set-shifting in this widely-utilized rodent model. These specific behavioral alterations support the hypothesis that behavioral impairments in EF following prenatal alcohol exposure are caused by distributed damage to the prefrontal-thalamo-hippocampal circuit consisting of the medial prefrontal cortex, thalamic nucleus reuniens, and CA1 of hippocampus.

Persistent Alterations of Accumbal Cholinergic Interneurons and Cognitive Dysfunction after Adolescent Intermittent Ethanol Exposure.

Adolescent binge drinking renders young drinkers vulnerable to alcohol use disorders in adulthood; therefore, understanding alcohol-induced brain damage and associated cognitive dysfunctions is of paramount importance. Here we investigated the effects of binge-like adolescent intermittent ethanol (AIE) exposure on nonspatial working memory, behavioral flexibility and cholinergic alterations in the nucleus accumbens (NAc) in male and female rats. On postnatal days P25-57 rats were intubated with water or ethanol (at a dose of 5 g/kg) on a 2-day-on/2-day-off cycle and were then tested in adulthood on social recognition and probabilistic reversal learning tasks. During the social recognition task AIE-treated rats spent similar amounts of time interacting with familiar and novel juveniles, indicating an impaired ability to sustain memory of the familiar juvenile. During probabilistic reversal learning, AIE-treated male and female rats showed behavioral inflexibility as indicated by a higher number of trials needed to complete three reversals within a session, longer response latencies for lever selection, and for males, a higher number of errors as compared to water-treated rats. AIE exposure also reduced the number of cholinergic interneurons in the NAc in males and females. These findings indicate AIE-related pathologies of accumbal cholinergic interneurons and long lasting cognitive-behavioral deficits, which may be associated with cortico-striatal hypofunction.

The role of ventral midline thalamus in cholinergic-based recovery in the amnestic rat.

The thalamus is a critical node for several pathways involved in learning and memory. Damage to the thalamus by trauma, disease or malnourishment can impact the effectiveness of the prefrontal cortex (PFC) and hippocampus (HPC) and lead to a profound amnesia state. Using the pyrithiamine-induced thiamine deficiency (PTD) rat model of human Wernicke-Korsakoff syndrome, we tested the hypothesis that co-infusion of the acetylcholinesterase inhibitor physostigmine across the PFC and HPC would recover spatial alternation performance in PTD rats. When cholinergic tone was increased by dual injections across the PFC-HPC, spontaneous alternation performance in PTD rats was recovered. In addition, we tested a second hypothesis that two ventral midline thalamic nuclei, the rhomboid nucleus and nucleus reuniens (Rh-Re), form a critical node needed for the recovery of function observed when cholinergic tone was increased across the PFC and HPC. By using the GABAA agonist muscimol to temporarily deactivate the Rh-Re the recovery of alternation behavior obtained in the PTD model by cholinergic stimulation across the PFC-HPC was blocked. In control pair-fed (PF) rats, inactivation of the Rh-Re impaired spontaneous alternation. However, when inactivation of the Rh-Re co-occurred with physostigmine infusions across the PFC-HPC, PF rats had normal performance. These results further demonstrate that the Rh-Re is critical in facilitating interactions between the HPC and PFC, but other redundant pathways also exist.

Differential cortical neurotrophin and cytogenetic adaptation after voluntary exercise in normal and amnestic rats.

Voluntary exercise (VEx) has profound effects on neural and behavioral plasticity, including recovery of CNS trauma and disease. However, the unique regional cortical adaption to VEx has not been elucidated. In a series of experiments, we first examined whether VEx would restore and retain neurotrophin levels in several cortical regions (frontal cortex [FC], retrosplenial cortex [RSC], occipital cortex [OC]) in an animal model (pyrithiamine-induced thiamine deficiency [PTD]) of the amnestic disorder Wernicke-Korsakoff syndrome. In addition, we assessed the time-dependent effect of VEx to rescue performance on a spontaneous alternation task. Following 2-weeks of VEx or stationary housing conditions (Stat), rats were behaviorally tested and brains were harvested either the day after VEx (24-h) or after an additional 2-week period (2-wk). In both control pair-fed (PF) rats and PTD rats, all neurotrophin levels (brain-derived neurotrophic factor [BDNF], nerve growth factor [NGF], and vascular endothelial growth factor) increased at the 24-h period after VEx in the FC and RSC, but not OC. Two-weeks following VEx, BDNF remained elevated in both FC and RSC, whereas NGF remained elevated in only the FC. Interestingly, VEx only recovered cognitive performance in amnestic rats when there was an additional 2-wk adaptation period after VEx. Given this unique temporal profile, Experiment 2 examined the cortical cytogenetic responses in all three cortical regions following a 2-wk adaptation period after VEx. In healthy (PF) rats, VEx increased the survival of progenitor cells in both the FC and RSC, but only increased oligodendrocyte precursor cells (OLPs) in the FC. Furthermore, VEx had a selective effect of only recovering OLPs in the FC in PTD rats. These data reveal the therapeutic potential of exercise to restore cortical plasticity in the amnestic brain, and that the FC is one of the most responsive cortical regions to VEx.

The role of cholinergic and GABAergic medial septal/diagonal band cell populations in the emergence of diencephalic amnesia.

The septohippocampal pathway, which is mostly composed of cholinergic and GABAergic projections between the medial septum/diagonal band (MS/DB) and the hippocampus, has an established role in learning, memory and disorders of cognition. In Wernicke-Korsakoff's syndrome (WKS) and the animal model of the disorder, pyrithiamine-induced thiamine deficiency (PTD), there is both diencephalic damage and basal forebrain cell loss that could contribute to the amnesic state. In the current experiment, we used the PTD animal model to access both cholinergic (choline acetyltransferase [ChAT] immunopositive) and GABAergic (parvalbumin [PV]; calbindin [CaBP]) neuronal loss in the MS/DB in relationship to midline-thalamic pathology. In addition, to gain an understanding about the role of such neuropathology in behavioral dysfunction, animals were tested on a non-rewarded spontaneous alternation task and behavioral performance was correlated to neuropathology. Unbiased stereological assessment of neuronal populations revealed that ChAT-positive neurons were significantly reduced in PTD rats, relative to control pair-fed rats, and thalamic mass and behavioral performance correlated with ChAT neuronal estimates. In contrast, both the PV- and CaBP-positive neurons in the MS/DB were not affected by PTD treatment. These results support an interactive role of both thalamic pathology and cholinergic cell loss in diencephalic amnesia.

Psoriatic arthritis and psoriasis: role of patient advocacy organisations in the twenty first century.

All the psoriatic arthritis and psoriasis patient advocacy organisations are devoted to promoting public awareness and patient education; supporting access to effective treatments and physicians committed to the welfare of patients; working with physicians and other organisations to facilitate development of new treatments; and supporting research for more effective treatments and a cure for psoriasis and psoriatic arthritis. They have participated in the remaking of health politics in the late twentieth century. This was an era in which small patient support and advocacy groups were transformed into sophisticated national health organisations integral to the formation of national health policy and research, treatment, and education funding by working with physicians, legislators, pharmaceutical companies, third party payors, and the media. As we enter the twenty first century, some of these groups have done critical surveys of patients and physicians to discern needs that are redirecting their programming and reshaping directions in the field. Many national leagues have united to form international organisations. Although differences in their national healthcare systems, the age of their organisations, and the diseases they cover are reflected in the focus of their individual activities, much unites them. Whatever their size, as their roles have come to be recognised in the healthcare community, the patient advocacy organisations welcome being invited to the decision making table. This report describes a sampling of these organisations.

Aging potentiates the acute and chronic neurological symptoms of pyrithiamine-induced thiamine deficiency in the rodent.

The present study aimed to assess the role of advanced age in the development and manifestation of thiamine deficiency using an animal model of Wernicke-Korsakoff syndrome (WKS). Interactions between pyrithiamine-induced thiamine deficiency (PTD) and age were examined relative to working memory impairment and neuropathology in Fischer 344 rats. Young (2-3 months) and aged (22-23 months) F344 rats were assigned to one of two treatment conditions: PTD or pair-fed control (PF). Rats in the former group were further divided into three groups according to duration of PTD treatment. Working memory was assessed with an operant matching-to-position (MTP) task; after testing, animals were sacrificed and both gross and immunocytochemical measures of brain pathology were obtained. Aged rats exhibited acute neurological disturbances during the PTD treatment regime earlier than did young rats, and also developed more extensive neuropathology with a shorter duration of PTD. Aged rats displayed increased brain shrinkage (smaller frontal cortical and callosal thickness) as well as enhanced astrocytic activity in the thalamus and a decrease in ChAT-positive cell numbers in the medial septum; the latter two measures of neuropathology were potentiated by PTD. In both young and aged rats, and to a greater degree in the latter group, PTD reduced thalamic volume. Behaviorally, aged rats displayed impaired choice accuracy on the delayed MTP task. Regardless of age, rats with lesions centered on the internal medullary lamina of the thalamus also displayed impaired choice accuracy. Moreover, increased PTD treatment duration led to increased response times on the delayed MTP task. These results suggest that aging does indeed potentiate the neuropathology associated with experimental thiamine deficiency, supporting an age coupling hypothesis of alcohol-related neurological disorders.

In search of the neurobiological underpinnings of the differential outcomes effect.

Correlating unique rewards with to-be-remembered events (the Differential Outcomes Procedure [DOP]) enhances learning and memory performance in a range of species. Recently, we have demonstrated that the DOP can be used to reduce or eliminate the learning and memory impairments associated with animal models of amnesia and dementia. This powerful phenomenon, the Differential Outcomes Effect (DOE), has led to the question: How does such a simple manipulation exert such dramatic influence on learning and memory performance? A revised two-process account of the DOE states that using the DOP results in the activation of reward expectancies through Pavlovian mechanisms. The use of unique reward expectancies alters the nature of cognitive processing used to solve discrimination tasks. The change in cognitive processing is represented by utilization of a different memory system than that commonly used to acquire and remember information when a Nondifferential Outcomes Procedure (NOP) is used. Using neurochemical manipulations, it has been demonstrated that different, potentially independent, brain systems modulate memory performance when subjects are trained with a NOP versus a DOP. This memory-based DOP/NOP distinction resembles other dissociative memory theories in which two psychological processes are purportedly served by distinct neurobiological mechanisms. In addition, such results have important ramifications for the treatment of memory disorders because they demonstrate that stimulus and behavioral manipulations, like drugs, can influence neurotransmitter functioning.

Alcohol-induced brain pathology and behavioral dysfunction: using an animal model to examine sex differences.

BACKGROUND: Human epidemiological studies suggest that the female brain may be more susceptible to the toxic effects of alcohol and that this is the reason why women show greater behavioral dysfunction after chronic alcohol exposure. This hypothesis was tested by using a rat model of chronic alcoholism [chronic ethanol treatment (CET)]. The investigation assessed sex differences in neuropathology and behavior after chronic exposure and subsequent withdrawal from alcohol. METHODS: Young male and female rats (approximately 3 months old) were assigned to either a CET group, which received a 20% ethanol drinking solution for 20 weeks, or a pair-fed control group, which received ad libitum tap water and a restricted diet for 20 weeks. After the CET groups were phased off the 20% alcohol solution, learning and memory abilities were examined by using matching-to-position and nonmatching-to-position tasks. Neuropathology was assessed in the frontal cortex and medial septal region. RESULTS: CET was shown to cause behavioral deficits. The behavioral dysfunction was sex, task, and process dependent; i.e., CET-female rats displayed a delay-dependent impairment on delayed matching-to-position, whereas CET-male rats displayed a delay-independent impairment on delayed nonmatching-to-position. CET resulted in a significant reduction in the frontal cortical (FR1) and collosal thickness, as well as a decrease in cells staining immunopositive for choline acetyltransferase in the medial septal region. However, relative to male rats exposed to CET, female rats did not show any accelerated neuropathology after CET. CONCLUSIONS: Chronic exposure to ethanol does result in both brain and behavior dysfunction in male and female rats. The results demonstrate that different cognitive processes are altered by chronic ethanol exposure in male and female rats. However, the neurobiological mechanisms responsible for these differences remain to be determined.

Memory enhancement in aged rats: the differential outcomes effect.

Aged (23 months) and young (3 months) rats were trained on an operant Matching-To-Position (MTP) task that had either (a) specific outcomes (reinforcers) correlated (differential groups), or (b) outcomes uncorrelated (nondifferential groups) for each correct sample-choice sequence. The traditional version of MTP uses a common outcome and is thought to assess spatial working memory. Aged rats are impaired on the traditional version of MTP. However, aged animals trained with the Differential Outcomes Procedure (DOP) did not display the typical age-related decline in spatial working memory. Differences in choice accuracy between old and young rats reached significance only if the subjects were trained with a nondifferential outcomes procedure (NOP)-similar to when a common outcome is used. These data demonstrate that employing behavioral procedures to tap intact cognitive functions is an effective means of enhancing spatial working memory in normal as well as aged subjects.

Rats exposed to acute pyrithiamine-induced thiamine deficiency are more sensitive to the amnestic effects of scopolamine and MK-801: examination of working memory, response selection, and reinforcement contingencies.

Pyrithiamine-induced thiamine deficiency (PTD), which has been used as a model of Wernicke-Korsakoff syndrome (WKS), produces a range of neuropathological and behavioral abnormalities in rodents. The extent of the diencephalic damage produced by this treatment varies from moderate to extreme cell loss. The magnitude of working memory impairment tends to correlate with the degree of neuropathology. In this study a PTD protocol that produces moderate thalamic pathology was used to gain further insight into the neurobehavioral consequences of thiamine deficiency. Towards this end, two distinct manipulations were conducted. First, the differential outcomes procedure (DOP), which correlates specific reinforcers with specific to-be-remembered events, was applied to an operant version of matching-to-position (MTP). This behavioral manipulation was conducted to determine if the DOP would improve memory performance in PTD-treated rats, demonstrating some intact cognitive functions. Additionally, to assess the functional integrity of the cholinergic and glutamatergic systems, normal and PTD-treated rats were administered i.p. injections of scopolamine and MK-801. It was found that the DOP enhanced memory, but not acquisition performance, in both normal and PTD-treated rats. Furthermore, when administered scopolamine, but not MK-801, rats trained with the DOP continued to outperform rats trained with a non-differential outcomes procedure (NOP). However, PTD-treated rats, regardless of training procedure (DOP, NOP), were more disrupted by the 'amnestic' effects of both scopolamine and MK-801. The differential sensitivity of treatment groups to the amnestic effects of scopolamine and MK-801 reveals insights into the neurochemical correlates of memory processes and WKS.

Characterization of the C-MYC amplicon in a case of acute myeloid leukemia with double minute chromosomes.

We have characterized the double minute chromosomes in a case of acute myeloid leukemia (AML). Southern blot analysis showed that the C-MYC was amplified. Further analysis with probes located both 3' and 5' of MYC indicated that the amplicon was at least 700 kb in size, extending from the papilloma virus integration site situated 500 kb 5' of MYC to the PVT gene located 280 kb 3' of MYC. This appears to be the largest MYC-containing amplicon in human leukemia.

Effects of lesions of thalamic intralaminar and midline nuclei and internal medullary lamina on spatial memory and object discrimination.

Male Sprague-Dawley rats received either radiofrequency lesions of the lateral internal medullary lamina (IML) or ibotenic acid lesions of the lateral intralaminar nuclei (ILN) and midline nuclei (MLN) or sham treatment. Neither lesion group was impaired in the retention of 3 object pair discriminations acquired before surgery nor in the acquisition of a new object pair after surgery. Rats with ILN, but not IML, lesions were impaired in acquiring an initial and 5 subsequent hidden platform locations in a water maze task. These results suggest that damage to both ILN and MLN are needed to produce spatial learning deficits and that extensive damage to the IML or ILN has no detectable effects on retrograde or anterograde memory of object discriminations.

The effects of lesions to thalamic lateral internal medullary lamina and posterior nuclei on learning, memory and habituation in the rat.

The behavioral effects of radiofrequency lesions to the lateral internal medullary lamina region (IML) or the posterior region (Po: containing the parafascicular and posterior nuclei) of the thalamus were compared to sham operated controls. Subjects were pre-operatively trained and then tested for post-operative retention of a NMTP task. Whereas the Po-lesion group was impaired only on long delays (60, 90 s), the IML-lesion group was impaired on retention and re-acquisition and demonstrated lower performance at all delays (5-90 s) of the NMTP task. Post-operative training and testing was conducted on three additional tasks: Morris water maze, acoustic startle, and passive avoidance. The IML-lesion group was impaired in finding a hidden and visual platform in the Morris water maze, demonstrated a blunted response but normal habituation to an acoustic startle stimulus, and showed normal retention of a passive avoidance task. On those three tasks, the performance of the Po-lesion group was similar to controls. In the IML-lesion group, neuronal loss resulting from axotomy and/or transneuronal degeneration was observed within nuclei of the midline and anterior thalamus and the mammillary body. These results suggest that lesions to the IML region disrupt a range of cognitive functions and produce pathological destruction in distant brain regions; whereas damage to the posterior thalamus causes spatial delay-sensitive deficits.

Neuropathology of thiamine deficiency: an update on the comparative analysis of human disorders and experimental models.

This paper provides a re-examination of the neuroanatomical consequences of thiamine deficiency in light of more recent studies of human disorders and models of experimental thiamine deficiency. A major goal is to elucidate the relative roles of thiamine deficiency and chronic alcohol consumption in the pathogenesis of Wernicke-Korsakoff syndrome (WKS). Particular emphasis is placed on the role of thiamine deficiency in lesions to basal forebrain, raphe, locus coeruleus, white matter and cortex and their role in the cognitive and memory disturbances of human WKS and experimental models of thiamine deficiency.

Thiamine deficiency in rats produces cognitive and memory deficits on spatial tasks that correlate with tissue loss in diencephalon, cortex and white matter.

Exploratory activity, spontaneous alternation, learning and memory abilities were examined in the pyrithiamine-induced thiamine deficiency (PTD) rat model of Wernicke-Korsakoff's syndrome and pair-fed controls (CT). PTD and CT animals showed normal retention of a single trial of a passive avoidance task acquired prior to the acute stages of thiamine deficiency. While there were no significant group differences in spontaneous activity, PTD animals with extensive damage to internal medullary lamina (IML-lesioned) of thalamus and mammillary body nuclei demonstrated a significant decrease in spontaneous alternation and were significantly impaired in learning both the initial spatial non-matching-to-position (NMTP) task and the reverse MTP task. PTD animals without IML damage (IML-spared) were only impaired on the acquisition of NMTP. Examination of response patterns suggest that the learning impairment was related to an inability to adopt or shift to the appropriate response rule. Performance of PTD IML-lesioned animals on NMTP mixed-delay sessions (4, 30, 60, 90 s) was similar to controls and PTD IML-spared, but was significantly lower on MTP delay trials. These IML-lesioned rats also had significant reductions in thickness of frontal and parietal cortex, corpus callosum and severe neuronal loss in anterior and reticular thalamic nucleic. Four PTD IML-lesioned animals that were unable to learn the NMTP task had more extensive cortical, white matter and thalamic damage than the PTD IML-lesioned animals that did learn the task. These results demonstrate that thiamine deficiency in the rat produces behavioral changes ranging from mild cognitive deficits to severe learning and memory impairments. Pathologic damage following a bout of thiamine deficiency also varies from neuronal loss in select thalamic nuclei to tissue loss in large regions of thalamus, mammillary bodies and cortex. Learning and memory deficits are closely related to the degree of cortical and diencephalic damage.

The effects of scopolamine, diazepam, and lorazepam on working memory in pigeons: an analysis of reinforcement procedures and sample problem type.

Two groups of pigeons were trained on a delayed-matching-to-sample (DMTS) task with both identity and symbolic problems, that had either a) specific outcomes correlated (differential group) or b) outcomes uncorrelated (nondifferential group), for each correct sample-choice sequence. After reaching a criterion of 90% correct at the 0 s delay, subjects were tested under saline, methylscopolamine (0.03 mg/kg), scopolamine (0.007, 0.015, 0.03 mg/kg), diazepam (0.0, 1.0, 1.75, 2.5 mg/kg), and lorazepam (0.0, 0.5, 0.75, 1.0 mg/kg) at delays of 0 to 8 s. Scopolamine, diazepam, and lorazepam at all doses impaired performance in the nondifferential group; however, in the differential group, the medium and high doses of both scopolamine and lorazepam, and only the high dose of diazepam impaired performance. The differential outcomes procedure, relative to the nondifferential procedure, enhanced retention in the non-drug state and under these amnestic drugs. Impairments observed in the differential group were a result of decreased performance only on samples correlated with a secondary reinforcer (flashing hopper light); there was no decreased performance on samples correlated with a primary reinforcer (grain). Neither group showed any differences in performance as a function of identity versus symbolic problems in a nondrug or drug state.

Electrophysiology of newt skin: responses to salt-depletion, aldosterone, arginine vasotocin and epinephrine.

1. Newts (Taricha granulosa), salt-depleted by 3 weeks' immersion in distilled water, showed significantly higher in vitro integumental short-circuit current (SCC) than control newts immersed in dilute saline. 2. Isolated, in vitro preparations of newt skin responded to aldosterone (10(-6) M), arginine vasotocin (10(-9)-10(-8) M), and epinephrine (10(-7)-10(-5) M) by increasing SCC. 3. The hormonal response of the skin of this salamandrid urodele, as judged from in vitro (Ussing chamber) measurements, is similar to that seen in classical anuran ("frog skin") preparations.

Changes in body water and plasma constituents during bullfrog development: effects of temperature and hormones.

The osmoregulatory responses to warmer temperatures and hormone treatment in cold-adapted (5 degrees C) Rana catesbeiana tadpoles and newly metamorphosed frogs were examined. Tadpoles transferred to 11 degrees C and 18 degrees C and left for 5 days lost 7% and 10% of their body weight. Plasma [Na+] was elevated 28% and 21%, respectively. Control (5 degrees C) animals maintained their body weight and plasma [Na+] constant. Daily treatment with either ovine prolactin (oPRL) or ovine growth hormone (oGH) prevented the weight loss and the increase in extracellular [Na+] that occurred when tadpoles were transferred to 18 degrees C. Neither propylthiouracil (PTU) nor arginine vasotocin (AVT) were effective in countering temperature-induced weight loss in tadpoles. Newly metamorphosed frogs transferred to 18 degrees C also lost weight; this was not prevented by daily treatment with saline, oPRL, oGH or PTU. However, in frogs treated daily with AVT, initial BW was regained by day 6. When warm-adapted (18 degrees C) tadpoles were treated daily for 18 days with saline, bPRL, bGH, thyroxine (T4), ergocornine, cortisol, or cortisol + T4, bPRL was most effective in retarding weight loss and maintaining body water content, whereas T4 + cortisol caused the greatest loss of weight and body water. By day 20, the correlations between weight loss and both body water content and hematocrit were highly significant. These data suggest that reported increases in plasma solute concentrations in larval amphibians may actually reflect decreases in extracellular fluid volume, rather than increased amounts of solutes, per se.