A flexible technique for long term infusions in unrestrained rats

Adaptation to a high-protein diet progressively increases the postprandial accumulation of carbon skeletons from dietary amino acids in rats

We aimed to determine whether oxidative pathways adapt to the overproduction of carbon skeletons resulting from the progressive activation of amino acid (AA) deamination and ureagenesis under a high-protein (HP) diet. Ninety-four male Wistar rats, of which 54 were implanted with a permanent jugular catheter, were fed a normal protein diet for 1 wk and were then switched to an HP diet for 1, 3, 6, or 14 days. On the experimental day, they were given their meal containing a mixture of 20 U-[¹⁵N]-[¹³C] AA, whose metabolic fate was followed for 4 h. Gastric emptying tended to be slower during the first 3 days of adaptation. ¹⁵N excretion in urine increased progressively during the first 6 days, reaching 29% of ingested protein. ¹³CO₂ excretion was maximal, as early as the first day, and represented only 16% of the ingested proteins. Consequently, the amount of carbon skeletons remaining in the metabolic pools 4 h after the meal ingestion progressively increased to 42% of the deaminated dietary AA after 6 days of HP diet. In contrast, ¹³C enrichment of plasma glucose tended to increase from 1 to 14 days of the HP diet. We conclude that there is no oxidative adaptation in the early postprandial period to an excess of carbon skeletons resulting from AA deamination in HP diets. This leads to an increase in the postprandial accumulation of carbon skeletons throughout the adaptation to an HP diet, which can contribute to the sustainable satiating effect of this diet.

Increased dopamine and serotonin metabolites in CSF during severe insulin-induced hypoglycemia in freely moving rats

The effect of insulin on dopamine (DA) and serotonin (5-HT) metabolites was determined in the cerebrospinal fluid (CSF) of the rat and compared with glucose levels in blood and CSF. CSF was continuously withdrawn from the third ventricle of freely moving rats at a constant rate of 1 ?l/min. Liquid chromatography with electrochemical detection was used for the direct assay of DA and 5-HT metabolites in the CSF. The metabolites were stable during the first hour after insulin injection (6IU/Kg). A progressive increase occurred thereafter in animals which had no access to food during the time of the experiment. The maximal effect was observed 2.5 h after insulin, with respective mean increases of 80% for dihydroxyphenylacetic acid, 47% for homovanillic acid and 33% for 5-hydroxyindolacetic acid. These increases in monoamine metabolites were not observed when rats received glucose (5g/Kg ip) 45 min after insulin or when food was made available. The period for insulin-induced increase in DA and 5-HT metabolites corresponded to a maximal fall of glucose levels both in blood and CSF although the CSF glucose decrease was delayed when compared to the fall of blood glucose. The role of brain glucose and brain insulin in the control of central DA and 5-HT metabolism is discussed.

Increasing protein at the expense of carbohydrate in the diet down-regulates glucose utilization as glucose sparing effect in rats

High protein (HP) diet could serve as a good strategy against obesity, provoking the changes in energy metabolic pathways. However, those modifications differ during a dietary adaptation. To better understand the mechanisms involved in effect of high protein diet (HP) on limiting adiposity in rats we studied in parallel the gene expression of enzymes involved in protein and energy metabolism and the profiles of nutrients oxidation. Eighty male Wistar rats were fed a normal protein diet (NP, 14% of protein) for one week, then either maintained on NP diet or assigned to a HP diet (50% of protein) for 1, 3, 6 and 14 days. mRNA levels of genes involved in carbohydrate and lipid metabolism were measured in liver, adipose tissues, kidney and muscles by real time PCR. Energy expenditure (EE) and substrate oxidation were measured by indirect calorimetry. Liver glycogen and plasma glucose and hormones were assayed. In liver, HP feeding 1) decreased mRNA encoding glycolysis enzymes (GK, L-PK) and lipogenesis enzymes(ACC, FAS), 2) increased mRNA encoding gluconeogenesis enzymes (PEPCK), 3) first lowered, then restored mRNA encoding glycogen synthesis enzyme (GS), 4) did not change mRNA encoding β-oxidation enzymes (CPT1, ACOX1, βHAD). Few changes were seen in other organs. In parallel, indirect calorimetry confirmed that following HP feeding, glucose oxidation was reduced and fat oxidation was stable, except during the 1(st) day of adaptation where lipid oxidation was increased. Finally, this study showed that plasma insulin was lowered and hepatic glucose uptake was decreased. Taken together, these results demonstrate that following HP feeding, CHO utilization was increased above the increase in carbohydrate intake while lipogenesis was decreased thus giving a potential explanation for the fat lowering effect of HP diets.

The postprandial use of dietary amino acids as an energy substrate is delayed after the deamination process in rats adapted for 2 weeks to a high protein diet

The aim of this study was to determine the contribution of dietary amino acids (AA) to energy metabolism under high protein (HP) diets, using a double tracer method to follow simultaneously the metabolic fate of α-amino groups and carbon skeletons. Sixty-seven male Wistar rats were fed a normal (NP) or HP diet for 14 days. Fifteen of them were equipped with a permanent catheter. On day 15, after fasting overnight, they received a 4-g meal extrinsically labeled with a mixture of 20 U-[(15)N]-[(13)C] AA. Energy metabolism, dietary AA deamination and oxidation and their transfer to plasma glucose were measured kinetically for 4 h in the catheterized rats. The transfer of dietary AA to liver glycogen was determined at 4 h. The digestive kinetics of dietary AA, their transfer into liver AA and proteins and the liver glycogen content were measured in the 52 other rats that were killed sequentially hourly over a 4-h period. [(15)N] and [(13)C] kinetics in the splanchnic protein pools were perfectly similar. Deamination increased fivefold in HP rats compared to NP rats. In the latter, all deaminated AA were oxidized. In HP rats, the oxidation rate was slower than deamination, so that half of the deaminated AA was non-oxidized within 4 h. Non-oxidized carbon skeletons were poorly sequestrated in glycogen, although there was a significant postprandial production of hepatic glycogen. Our results strongly suggest that excess dietary AA-derived carbon skeletons above the ATP production capacity, are temporarily retained in intermediate metabolic pools until the oxidative capacities of the liver are no longer overwhelmed by an excess of substrates.

Postprandial nutrient partitioning but not energy expenditure is modified in growing rats during adaptation to a high-protein diet

It has been suggested that high-protein (HP) diets may favor weight management by lowering energy intake and reducing body fat. Whether these effects result from changes in energy metabolism remains unclear. We measured the adaptation of energy metabolism components during 2 wk of HP feeding. Fifty male Wistar rats were switched from a control diet to an HP diet (14 and 55% of protein, respectively) for 1, 3, 6, or 14 d. Energy expenditure (EE) and substrate oxidation were measured by indirect calorimetry in feed-deprived rats and after consumption of a test meal. EE components, including the thermic effect of feeding and activity, were not modified during adaptation to an HP diet. Nutrient oxidation in feed-deprived rats was not affected by HP feeding, except for an early increase in protein oxidation. After 1 d, the postprandial inhibition of lipid oxidation (Lox) was blunted, carbohydrate (CHO) oxidation decreased by one-half, and urea clearance decreased by 66%. Thereafter, CHO oxidation gradually rose, resulting in a null CHO balance. Lox and urea clearance recovered after 3 d of adaptation to an HP diet, while protein oxidation reached a plateau. The postprandial oxidation of CHO counterbalanced the amount of ingested CHO as soon as 3 d, leading to a null postprandial CHO balance. We conclude that the inhibition of de novo lipogenesis from dietary CHO, but not EE and Lox, may participate in limiting the adiposity induced by HP feeding. The transient changes occurring during the period of adaptation to the diet highlight that the duration of the diet is critical in HP diet studies.

A tryptic hydrolysate from bovine milk alphaS1-casein improves sleep in rats subjected to chronic mild stress

The putative effects of a tryptic bovine alphaS1-casein hydrolysate on stress-induced sleep disorders were investigated and their possible link with typical blood stress parameters such as plasma corticosterone concentrations and glycaemia was assessed. Rats were subjected to chronic stress in the form of environmental disturbances, while receiving an oral administration of the alphaS1-casein hydrolysate (CH). Chronic stress significantly reduced sleep duration in control rats during the first 2 days of the stress period, but stress-induced sleep disturbance was prevented in CH-treated rats. Indeed, CH administration allowed the maintenance of slow wave sleep (SWS) duration and even a slight increase in paradoxical sleep (PS) duration in treated rats. Results on plasma corticosterone concentrations and on glycemia values were inconclusive with respect to the implication of the HPA axis in this study. However, the protective effect of the alphaS1-casein hydrolysate on sleep during exposure to our chronic mild stress conditions may be mediated by modulation of the central adrenergic response.

Restriction-refeeding of calories and protein induces changes to slow wave and paradoxical sleep that parallel changes in body lipid and protein levels in rats

Recent data have suggested that the activity of various brain nuclei is modulated during sleep. In this context, we developed the idea that sleep may participate in adapting brain responsiveness to feeding, so as to tune the control of peripheral energy metabolism. In order to characterize the nature of a possible link between sleep and peripheral energy metabolism, we have investigated the relationship between sleep parameters [wakefulness (W), slow wave sleep (SWS), paradoxical sleep (PS)] and the intensity of peripheral lipid and protein deposition processes. To achieve this, by manipulating the amount and quality of food available to rats, we induced states of energy or protein depletion/repletion which would specifically affect lean or fat body mass, which was quantified by an analysis of body composition. In parallel, using a permanently implanted cortical electrode, we measured electroencephalogram signals (EEG) to quantify the time spent in W, SWS and PS. Analysis of EEG changes in relation to the changes induced in body composition, showed that (1) the amount of sleep (PS and SWS) followed the evolution of energy supply levels, and (2) the time spent in PS relative to SWS varied to a considerable degree (14-23.5%) and followed the same trend as the ratio of lean body mass to fat mass. These results suggest the possible existence of quantitative and qualitative interactions between sleep quality and the anabolic and catabolic processes of peripheral fat and protein deposition.

A tryptophan-rich protein diet efficiently restores sleep after food deprivation in the rat

Sleep depends on the quantity and quality of the diet. Several studies have shown that food deprivation results in a reduction in sleep duration. It has also been demonstrated that in the newborn, the supply of certain essential amino acids improves sleep through their action on the synthesis of specific neurotransmitters. The aim of the present study was to test if the quantity and/or quality of dietary protein could improve the recovery of sleep during re-feeding after caloric deprivation. Sleep parameters were compared in rats fed ad libitum, food restricted during 4 days, or reefed isocalorically after food restriction with three dietary regimens varying in terms of the amount (14% versus 30%) or quality (milk protein or alpha-lactalbumin) of protein. The results showed that sleep recovery, in particular slow-wave sleep, was improved in rats re-fed with alpha-lactalbumin. This result confirms the close relationship between feeding and sleep and suggest that alpha-lactabumin could be used to improve sleep in adult submitted to nutritional disturbances such as food restriction, shift work, Ramadan.

Pharmacokinetics and feeding responses to muramyl dipeptide in rats

N-acetyl-muramyl-L-alanine-D-isoglutamine or muramyl dipeptide (MDP) is the minimally active subunit of bacterial peptidoglycan. During a systemic infection, the involvement of MDP has been demonstrated in food intake depression by the macrophage hydrolysis of Gram-positive bacteria. Under normal conditions, mammals are constantly exposed to the release of endogenous MDP from degraded gut flora and that of exogenous MDP from the diet. However, MDP digestion and absorption in the gastrointestinal tract are not fully understood, and their physiological significance needs to be clarified. After gavage (1.5 mg/kg), very low levels of MDP were found in the systemic circulation of rats and feeding patterns were not altered. In contrast, after the intraperitoneal injection of a similar dose, a depression in food intake was observed. The rats reduced their meal frequency and constant feeding rate, showing signs of satiety. The behavioral satiety sequence (BSS) was modified by behavioral changes, similar to those which appear during sickness, such as an increase in resting and a reduction in grooming. Our data suggest that the hypophagic effect of MDP may result from satiety and sickness behavior.

Peptide fragments released from Phe-caseinomacropeptide in vivo in the rat

The aim of this study was to investigate the pharmacokinetics of bovine Phe-caseinomacropeptide (Phe-CMP) in the rat after oral administration. This polypeptide was monophosphorylated and mainly nonglycosylated: Phe-CMP-1P. During gastrointestinal digestion and absorption, Phe-CMP-1P was degraded. Intact Phe-CMP-1P and CMP-1P were rapidly released from the stomach. In contrast, partial hydrolysis by pancreatic enzymes was observed. In vitro hydrolysis by brush-border membrane vesicles also indicated that the peptide was degraded. In the blood, "CMP-immunoreactive material" appeared rapidly, reaching a maximum level of 5.5 microg/ml at 60 min.

Effects of pure macronutrient ingestion on plasma tryptophan and large neutral amino acids

The role of tryptophan and its competitor large neutral amino acids, proposed earlier for serotonin synthesis following carbohydrate or protein ingestion, was reassessed in relation to a recent study investigating serotonin release, including the so far unknown effects of fats. In the present study, meals of either carbohydrates, casein, or lard, were supplied to rats for 30 min and blood samples collected every 15 min to follow the changes in plasma large neutral amino acids. In response to carbohydrates, amino acid levels fell and the ratio tryptophan over sum of other amino acids increased. Following casein ingestion, all amino acids were enhanced, tryptophan somewhat less, leading to a decreased ratio. The lard meal induced a slight decrease in some amino acids while the ratio remained constant. Only in response to casein, and partly to carbohydrates, did a consistent relation appear between the previously observed serotonin changes and the ratio. These data suggest that a relationship between the ratio and the previously observed serotonin changes is not always encountered because the release is not obligatorily coupled to synthesis and is subject to behavioral influences. It remains that serotonin release is affected by the composition of the meal through peripheral metabolic mechanisms.

Exercise-induced changes in brain glucose and serotonin revealed by microdialysis in rat hippocampus: effect of glucose supplementation

The aim of this study was to assess extracellular glucose changes in hippocampus in response to physical exercise and to determine the influence of glucose supplementation. In the same time, we have observed the changes in serotonin, in order to study the relationship between glucose and serotonin during exercise. Both glucose and serotonin were assessed using microdialysis. Exercise induced an increase in extracellular glucose levels over baseline during exercise to 121.1 +/- 3.0% (P < 0.001), then a decrease to baseline during recovery. The serotonin followed glucose changes during the first 90 min of exercise, but followed a different pattern during recovery, increasing to a maximum of 129.9 +/- 7.0% after 30 min of recovery (P < 0.001). When a 15% glucose solution was infused (10 microL x min(-1)) during exercise and recovery, blood glucose concentration was increased, but extracellular brain glucose decreased to reach a minimum of 73.3 +/- 4.6% after 90 min of recovery (P < 0.001). Serotonin was always the mirror-reflect of cerebral glucose, with a maximum increase of 142.0 +/- 6.9% after 90 min of recovery (P < 0.001). These results show that exercise induces changes in brain glucose and 5-hydroxytryptamine (5-HT) levels, which were dramatically modified by glucose infusion. Taking into account the implication of brain 5-HT in central fatigue, they suggest that if glucose supplementation, before and during exercise, undoubtedly increase performance because of its peripheral positive action, it would have a negative impact on the quality of recovery after the end of the exercise.

Effects of food texture change on metabolic parameters: short- and long-term feeding patterns and body weight

A complete diet was prepared with cooked pieces of meat, beans, cream starch, and water and presented to the rats in two different textures: a blended purée and a rough mixture that required a lot of chewing. We hypothesized that this texture modification might change both anticipatory reflexes and feeding behavior. Feeding rate, meal size, intermeal intervals, and their correlation were monitored in response to each texture. The long-term (6 wk) effect on body weight was assessed. Periprandial plasma glucose, insulin, glucagon, and lipid concentrations were assayed. Whole and background metabolism, respiratory quotient, and locomotion were measured using a computerized calorimeter of original design. In the short term, rats preferred the mixture. However, after 3 wk, they ingested more purée than mixture and gained more body weight per gram of food ingested as purée. Insulin response declined earlier with the mixture. During meals, glycerol and free fatty acid increased earlier with purée, whereas in the postprandial period, glycerol increased earlier with mixture. The metabolic rate, however, was not significantly affected. We concluded that texture, an everyday manipulation performed on food for human consumption, affects not only palatability of ingestants but also their metabolic management in the short and long term.

Postprandial metabolism and aversive response in rats fed a threonine-devoid diet

Lack of an indispensable amino acid in the diet induces a rapid reduction in food intake. In this study, we assessed whether the anorectic signal after ingestion of a meal lacking threonine originated from either direct perception of the decrease in plasma threonine or from an indirect effect related to increased postprandial amino acid catabolism and energy expenditure. We observed that 3 g of such a meal was sufficient to induce an aversive response to the diet within 2 h. Postprandial changes to plasma ammonia and urea, urinary urea, and energy metabolism did not differ from those measured after a control meal. In contrast, plasma threonine levels fell within 1 h after the meal. It is concluded that an increase in postprandial energy expenditure is not involved in the anorectic response to eating a threonine-devoid diet. The drop in plasma threonine levels may be a potential signal, but the fact that the decrease in food intake occurred 1 h after the decrease in plasma threonine questions a direct causal relationship.

Rapid fall in plasma threonine followed by increased intermeal interval in response to first ingestion of a threonine-devoid diet in rats

In most animals, ingestion of a diet lacking an essential amino acid (EAA) gives rise to anorexia within a few hours. The first signal in this feeding response may be the fall in plasma levels of the limiting EAA. In the present study, we measured plasma amino acid levels and food intake after the first exposure to either a threonine-devoid (THR-DEV) or corrected (COR) diet in 16 rats bearing a chronic jugular catheter for blood sampling. Food intake was reduced 165 min (p<0.05) after presentation of the THR-DEV diet. Analysis of the feeding pattern showed that intake was reduced via a four-fold lengthening of the second inter-meal interval. Plasma threonine levels started to fall between 30 and 60 min after onset of the meal (p<0.05). These results, observed in the same rats, lend further support for an early modification of the plasma amino acid pattern in relation to the decrease in feeding of a diet that is EAA deficient.

Brain insulin response to feeding in the rat is both macronutrient and area specific

Using microdialysis, we showed recently that hypothalamic immuno-reactive insulin (IRI) levels increased after a meal of chow and decreased in response to a fat meal. In the present study, we have compared extracellular hypothalamic and extrahypothalamic basal IRI levels and investigated the effect of meals composed exclusively of either carbohydrates (85% starch, 15% sucrose) or casein on both plasma and medial hypothalamic (PVN-VMH) insulin. The response of IRI to a carbohydrate meal was also investigated in the cerebellum. Basal hypothalamic IRI was twofold higher in the hypothalamus as compared to the cerebellum (33 +/- 4 and 15 +/- 2 pg/mL, respectively). Hypothalamic IRI increased twofold in response to the carbohydrate meal (72 +/- 15 pg/mL) but remained unchanged during the casein meal. No IRI change was found in the cerebellum after a meal of carbohydrates (16 +/- 2 pg/mL). Insulinemia was increased by both the carbohydrate and the casein meal. However, the protein-induced increase was less pronounced (maximum + 359% compared to 1650% for carbohydrates). The present data show a dual specificity of brain insulin response to feeding; in addition to the macronutrient specific variations, a regional specificity was also observed. Taken together with previous observations, the present data are in favor of an involvement of PVN-VMH insulin in the control of feeding and macronutrient-specific appetites.

Feeding enhances extracellular lactate of local origin in the rostromedial hypothalamus but not in the cerebellum

The use of brain microdialysis together with chronic vascular catheterization allowed us to assay extracellular fluid lactate (ECFL) in both the ventromedial-paraventricular (VMH-PVN) area of the hypothalamus and the cerebellum, in parallel with measures of plasma levels, and in relation to food intake. A 45 min scheduled meal increased VMH-PVN ECFL by 28%. This increase was not observed in the cerebellum. The prandial increase in plasma glucose (43%, from 4.74 to 6.77 mM) and lactate (84%, from 0.83 to 1.53 mM) showed a different temporal pattern and lasted longer than that of the ECFL. Glucose delivery by reverse dialysis for 45 min into the VMH-PVN area increased ECFL by 49%. When local glucose utilization was prevented by reverse dialysis-delivered 2-deoxy-d-glucose (2-DG), not only did VMH-PVN ECFL drop, but the feed-related increase in ECFL was blocked without affecting the normal rise in plasma glucose and in lactate. These results indicate that meal-related ECFL production and variations are independent of circulating lactate, but may depend on substrate availability in these hypothalamic structures.

Determination, using microdialysis, of hypothalamic serotonin variations in response to different macronutrients

In response to a chow meal in rats, we observed previously in PVN-VMH dialysates, an increase in serotonin (5-HT) that could be related to satiety or to metabolic consequences of the composition of the meal. Indeed, carbohydrates are admitted to increase 5-HT synthesis while proteins decrease it, but the time course and mechanisms of these effects were not known. For that purpose, pure carbohydrates, proteins, or fats were offered for 30 min and the changes in 5-HT from PVN-VMH dialysates were followed. Carbohydrates (85% starch + 15% sucrose) enhanced 5-HT levels as soon as the first 15 min of feeding, with a maximum 60 min later. Conversely, protein ingestion induced in the second 15 min of the meal, a decrease in 5-HT that lasted 2 h. During a fat meal (lard), 5-HT levels also decreased at the beginning of the meal and remained low during 45 min. The present data reassess the previous theories on the serotonergic effects of specific macronutrient ingestion. The effect of a fat meal on 5-HT levels had never been described so far. The increase in 5-HT in response to a carbohydrate meal is further specified. The 5-HT decrease induced by proteins, in agreement with the previous theories, is better explained now by using pure protein diets and extracellular 5-HT assay. However, all the changes observed start too early to be only metabolic in origin. Other mechanisms may occur, including the release of 5-HT in response to a meal to induce satiety.

Brain insulin response to feeding in the rat is both macronutrient and area specific

Using microdialysis, we showed recently that hypothalamic immunoreactive insulin (IRI) levels increased after a meal of chow and decreased in response to a fat meal. In the present study, we have compared extracellular hypothalamic and extrahypothalamic basal IRI levels and investigated the effect of meals composed exclusively of either carbohydrates (85% starch, 15% sucrose) or casein on both plasma and medial hypothalamic (PVN-VMH) insulin. The response of IRI to a carbohydrate meal was also investigated in the cerebellum. Basal hypothalamic IRI was twofold higher in the hypothalamus as compared to the cerebellum (33 +/- 4 and 15 +/- 2 pg/mL, respectively). Hypothalamic IRI increased twofold in response to the carbohydrate meal (72 +/- 15 pg/mL) but remained unchanged during the casein meal. No IRI change was found in the cerebellum after a meal of carbohydrates (16 +/- 2 pg/mL). Insulinemia was increased by both the carbohydrate and the casein meal. However, the protein-induced increase was less pronounced (maximum + 359% compared to 1650% for carbohydrates). The present data show a dual specificity of brain insulin response to feeding; in addition to the macronutrient specific variations, a regional specificity was also observed. Taken together with previous observations, the present data are in favor of an involvement of PVN-VMH insulin in the control of feeding and macronutrient-specific appetites.

Pharmacologic restoration of suppressed temperature rhythms in rats by melatonin, melatonin receptor agonist, S20242, or 8-OH-DPAT

Endogenous circadian rhythms in body temperature and locomotor activity rhythms are suppressed in Sprague-Dawley rats exposed to prolonged continuous light, possibly as a result of a profound alteration of the melatonin secretion rhythm. The ability to restore circadian system function with either exogenous melatonin, or melatonin receptor agonist S20242 (N-[2-(7-methoxy napth-1-yl)ethyl] propionamide), or 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), was investigated under these conditions. Seven rats received a daily 6-h intravenous infusion of melatonin (0.01 mg kg(-1)) for 10 days, which generates a nearly physiological circadian rhythm of urinary 6-sulfatoxy-melatonin, the main urinary metabolite of melatonin. Nevertheless, there was no effect on body temperature or locomotor activity rhythms. Then, 49 rats received daily subcutaneous melatonin (0.01, 1 or 5 mg kg(-1) day(-1)), S20242 (1 or 5 mg kg(-1) day(-1)) or 8-OH-DPAT (5 mg kg(-1) day(-1)) for 30 days. The circadian rhythm in body temperature was restored by subcutaneous melatonin or by S20242 as a function of the dose or by 8-OH-DPAT. The effect started within the first 10 days of treatment and persisted for I to 3 weeks following the end of treatment in 8 of 10 rats receiving melatonin, in 9 of 11 rats treated with S20242 and in 1 of 4 rats treated with 8-OH-DPAT. Activity was less susceptible to entrainment than temperature with these drugs, since circadian rhythmicity was restored in only 2 of 6 rats treated with melatonin and in 1 of 4 rats treated with 8-OH-DPAT. These data demonstrate a specific action of subcutaneous melatonin, S20242 or 8-OH-DPAT on temperature rather than on activity rhythms. This differential effect on two major outputs of the suprachiasmatic nucleus further supports the existence of two independent oscillators in this hypothalamic circadian clock, which may be considered as separate pharmacological targets in the circadian system.

Effects of muscimol or homotaurine on sleep-wake states in alcohol-dependent rats during withdrawal

Sleep-wake states were studied following withdrawal in 36 adult male wistar alcohol-dependent rats, after chronic administration of ethanol (10 g/kg/24 h) for 13 days. In the light phase of the withdrawal day, 12 alcohol-dependent rats received muscimol (0.25 mg/kg), 12 received homotaurine (140 mg/kg), and 12 received 0.9% physiological saline (10 ml/kg). The results have been compared with a control group of 36 rats that received water during the treatment phase of the experiment, and the 14th day received intraperitoneal muscimol or homotaurine. Muscimol significantly improves the alterations of sleep-wake states in alcohol-withdrawn rats, decreasing the percentage of active wakefulness and increasing the percentage of REMS, but without any action on the latency of appearance of REMS, which remains shortened. The effects of homotaurine are less important on the wakefulness, but it also increases the percentage of REMS without influencing its latency of appearance. The influence of these GABA(A) agonists is not identical during the whole period of survey in the light phase, as there are important differences in the temporal sequences for each of them. We conclude that the stimulation of GABA(A) receptors, of which the activity is decreased during alcohol withdrawal, significantly improves the disturbances in the sleep-wake states in the alcohol-dependent rats, in a time-related manner, and there are significant pharmacodynamic differences between muscimol and homotaurine.

Spatial cues are relevant for learned preference/aversion shifts due to amino-acid deficiencies

Rats are able to choose appropriately between two versions of a novel diet, when one is amino-acid devoid and the other corrected. Recognition of the deficiency has been reported to occur within hours and to initiate a strong conditioned aversion. For that purpose the rat can use either oro-sensory cues or another alternative as the conditioned stimulus (CS) with which to associate the unconditioned stimuli (US) of either the adequate diet or the devoid diet. The present investigation was designed to determine whether rats have the ability to use place as a cue in amino-acid preference/aversion. In order to avoid interfering with any other than spatial sensory discrimination between the devoid diet and its corrected version, rats were offered two food cups containing an identical threonine-devoid diet. This was supplemented with an intra-gastric delivery of either threonine or its vehicle, that varied according to the position of the feeder from which the rats had chosen to eat. After three choice sessions, rats chose the food container on the side corresponding to the threonine load. Our results showed that rats use place as a cue for an amino-acid replete nutritional state by learning a conditioned place preference/aversion and that they achieve this type of learning in spite of the long delay elapsing between CS and US.

Insulin responses to a fat meal in hypothalamic microdialysates and plasma

In a recent microdialysis study in freely-behaving rats, we observed changes in immunoreactive insulin (IRI) in hypothalamic dialysates after a meal of standard laboratory chow. These changes did not always parallel plasma insulin variations, suggesting a partial independence from peripheral insulin. In the present study, we have attempted to assess the profile of medial hypothalamus (VMPH-PVN) extracellular insulin and peripheral insulin before and after a fat meal (lard). In contrast to the increase we previously observed with chow meals, hypothalamic extracellular IRI decreased during the fat meal and fell to 60% 30 min after the meal. Plasma insulin levels did not change. The intake of the lard meal, provided in unlimited amounts, was much larger in calories than the intake of a chow meal under the same conditions. However, when rats were offered a meal of chow after they had eaten a meal averaging 6.7 g of fat (61 calories), they immediately began eating the chow. Thus, the meal of fat produced no general satiation. On the contrary, the rats consumed a second chow meal only after a delay of approximately 40 min after the first one. The present data, in conjunction with our previous observations with chow fed rats, suggest that the level of extracellular hypothalamic IRI may decrease independently of plasma insulin levels and may, at least partially, account for the observed lack of satiation.

Effect of hyperglycemia on the polyol pathway in rat kidney during the perinatal period

The activity of the polyol pathway was studied in developing rat kidney. For this purpose, sorbitol content, aldose-reductase activity and sorbitol-dehydrogenase activity were determined in papilla from fetuses and 24-h-old neonates. After birth, no significant difference was observed in sorbitol content, whereas sorbitol-dehydrogenase activity decreased and aldose-reductase activity doubled. Changes in aldose-reductase activity were due to an increased number of enzymatic sites but not with a change in affinity. Low levels of sorbitol were found in fetal and neonatal medulla together with low levels of urine osmolarity. In neonates, sorbitol contents were tenfold lower than in the adult, probably as a result of a lower affinity and a lower number of enzymatic aldose-reductase sites. Attempts to increase the activity of polyol pathway in fetal kidney were made by means of hyperglycemic animals; this approach resulted in an increase of aldose-reductase activity without any change in sorbitol content. Our results indicate that, in fetal and neonatal kidneys, aldose-reductase activity is probably not the limiting factor for sorbitol synthesis; another parameter, such as the availability of NADPH, might explain the low efficiency of the polyol pathway during the perinatal period.

Pharmacokinetically guided melatonin scheduling in rats with circadian system suppression

To obtain a pharmacologic effect of melatonin in rats kept under prolonged continuous light exposure, conditions known to produce functional suppression of the circadian system, mimicking of the physiologic 24-h pattern of melatonin secretion, a hormonal signal of darkness exposure may be needed. The delivery scheme for melatonin was established in rats in the present studies. First, the plasma pharmacokinetics of [3H]melatonin were determined in rats kept under continuous light and in rats synchronized by exposure to alternating 12 h light and 12 h darkness (LD 12:12) in the early light span. The pharmacokinetics of total radioactivity were similar in both groups. Further quantitation of melatonin by thin-layer chromatography revealed differences dependent on light conditions. The mean plasma clearance and steady-state distribution volume were approximately twice as low with continuous light as with LD 12:12. Plasma protein binding of melatonin was approximately 33%, irrespective of group or sampling time. These pharmacokinetic parameters were used to devise a 24-h periodic delivery schedule consisting of a 6-h constant infusion of exogenous melatonin, followed by an 18-h melatonin-free interval. In a second study, the melatonin 24-h pattern was estimated from the measurement of 2-h fractions of urinary 6-sulfatoxymelatonin excretion for 4 days. 6 unrestrained rats kept under continuous light received melatonin for 2 days from 22:00 to 04:00 h through an indwelling jugular catheter, connected to a reservoir from a programmable pump. Only the administration of low doses (0.01 mg/kg/day) resulted in both a circadian pattern for 6-sulfatoxymelatonin excretion and normal physiological values during the infusion-free intervals. The resynchronizing efficacy of this schedule should be tested in rats with functional suppression of the circadian system.

Melanin-concentrating hormone is a potent anorectic peptide regulated by food-deprivation and glucopenia in the rat

Melanin-concentrating hormone is a cyclic nonadecapeptide that is produced almost exclusively in neurons of the lateral hypothalamus and sub zona incerta areas while fibers are widespread in the rat brain. Such a localization strongly suggests that this peptide might participate as neurotransmitter/neuromodulator in the control of feeding behavior. In this study we examined first the influence of rat melanin-concentrating hormone on feeding behavior at different times either in the light or in the dark period (light off at 18.00 h) of the day in fed Wistar rats. Intracerebroventricular injection of rat melanin-concentrating hormone (1-100 ng per rat) at 18.00 h reduced food consumption as early as 2 h after injection and for the next 24 h. In addition, similar anorectic effect was noted after bilateral administration of 1 ng melanin-concentrating hormone into the lateral hypothalamic area at 11.30 h but not at 16.30 h. These findings strongly suggest that rat melanin-concentrating hormone may exert inhibitory control over food intake behavior depending on the circadian rhythm. Second, we investigated the modifications induced by food deprivation/refeeding on melanin-concentrating hormone messenger RNA levels in Wistar rats. Total RNA was isolated from whole hypothalamic dissections and the contents of melanin-concentrating hormone messenger RNA, beta-actin messenger RNA (taken as sample control) and neuropeptide Y messenger RNA (taken as control of food-deprivation paradigms) were assessed by using northern blotting. The time-course of messenger RNA expression was determined in groups of rats deprived for 24, 48 and 72 h and revealed a three-fold induction of melanin-concentrating hormone messenger RNA by 24 and 48 h, with reduced increase at 72 h. As expected, the same treatment led to a three-fold increase in neuropeptide Y messenger RNA content by 48 and 72 h. Refeeding groups of animals for up to 72 h after 24 h of food deprivation resulted in full restoration of melanin-concentrating hormone messenger RNA levels by 24 h. Strikingly, a large range of variations in melanin-concentrating hormone messenger RNA content between individuals was observed in food-deprived versus controls or refed rats suggesting that genetic or environmental factors may alter response in melanin-concentrating hormone gene activity after food deprivation. Finally, we investigated the effects of short-term glucoprivation induced by intraperitoneal administration of either 2-deoxy-D-glucose or insulin on melanin-concentrating hormone messenger RNA expression. A transitory increase in melanin-concentrating hormone messenger RNA content was noted 1 h after 2-deoxy-D-glucose injection while melanin-concentrating hormone messenger RNA levels rose two-fold only 5 h after insulin treatment. These results indicate that 2-deoxy-D-glucose and insulin activate melanin-concentrating hormone gene expression through likely distinct regulatory pathways.

Water versus salty taste and Iontophoretic ANGII responses of septopreoptic neurons in dehydrated and euhydrated awake rats

Little is known of the influence of gustatory, particularly salt, input on neurons of the forebrain and if the same neurons are sensitive to hydromineral balance humoral stimuli. In awake, nonpremedicated rats we recorded the activity of spontaneously active neurons in the preoptic/anterior hypothalamic area of dehydrated and euhydrated rats while allowing them to ingest water or a hypertonic salt solution (1.6% NaCl) administered to the tongue. The hormones angiotensin and aldosterone, both implicated in hydromineral balance, were applied by iontophoresis to the same neurons. In the dehydrated rats, 27% (15/55) of the spontaneously active neurons responded to a liquid (either water or the NaCl) applied to the tongue; in the euhydrated rats 23% (18/78) responded to the same stimuli. In the dehydrated rats, however, 33% (5/15) of the responding neurons were inhibited when the NaCl solution was applied to the tongue compared with only 5% (1/18) in the euhydrated rats. Iontophoretic application of angiotensin increased the spontaneous activity in 21% of those neurons tested that responded to taste. These results suggest that the state of hydration of an animal is able to change the neuronal response to substances applied to the tongue. Furthermore, it appears that these gustatory-sensitive neurons may also be related to hydromineral balance regulation since they are able to respond to angiotensin.

Hypothalamic monoamines and insulin in relation to feeding in the genetically obese Zucker rat as revealed by microdialysis

Dynamic changes in VMH and PVN monoamines and immunoreactive insulin (IRI) were investigated by microdialysis in freely-moving genetically obese Zucker rats in order to relate possible disturbances to the impaired regulation of food intake of this model. Serotonin (5-HT), 5-HIAA and dopamine (DA) increased at the beginning of spontaneous meals while DOPAC decreased. Although similar in normal and obese rats, these changes were much more dramatic in the latter, as if more "signal" for satiety were necessary at the VMH-PVN level. Glucoprivic feeding or satiety are induced in normal rats by intravenous infusions of insulin or insulin+glucose respectively. The Zucker rat is resistant to these treatments. The monoaminergic changes brought about by these infusions were similar in obese and normal rats (decreases in 5-HT and DA and increases in 5-HIAA and DOPAC), but the occurrence of meals, in the obese, showed a superim-position of monoaminergic changes resembling those related to spontaneous feeding. The monoaminergic effects of insulin must therefore be dissociated from its effects on feeding. Hypothalamic insulin itself might be the brain signal. At the beginning of meals presented for the first time, VMH-PVN IRI increased earlier and with a smaller magnitude in the obese. When the rats were accustomed to scheduled meals, a similar anticipatory increase in IRI was found in both obese and lean rats. This suggests that brain insulin is more than a satiety signal. In addition, in response to an i.v. insulin infusion, IRI increased twice as much in obese rats despite lower basal levels. Whatever the origin of hypothalamic insulin, the larger response of the obese Zucker rat, known to be insulin resistant, may reflect the inefficiency of the peptide in reducing feeding and body weight in this pathological model.

Changes in hypothalamic prostaglandin E2 may predict the occurrence of sleep or wakefulness as assessed by parallel EEG and microdialysis in the rat

Prostaglandin (PG) E2 is produced by mammalian hypothalamus and when administered exogenously prolongs wakefulness. In order to study the relation of endogenous hypothalamic PGE2 to sleep and wakefulness, we have used microdialysis in freely moving rats associated with EEG recording. Male Wistar rats were implanted with three cortical electrodes and with a guide cannula for microdialysis in the space between the paraventricular nucleus (PVN) and the ventromedial hypothalamus (VMH). PGE2 was measured by RIA in 3- or 6-min dialysates 15 days after surgery, when sleep patterns were normal again and PGE2 production stabilised. PGE2 levels were significantly higher during wakefulness (601 +/- 35 pg/ml, 5 experiments, 35 samples) than during slow-wave sleep (487 +/- 24 pg/ml, 5 experiments, 49 samples). Samples corresponding to paradoxical sleep showed a tendency towards higher PGE2 values compared to slow-wave sleep but lower compared to wakefulness. In epochs of wakefulness or sleep lasting at least 12 min, high PGE2 levels in the middle of wakefulness regularly dropped, thus announcing the occurrence of sleep. During sleep, PGE2 first went on dropping and then reincreased towards the values that characterize early periods of wakefulness. In its turn, this reincrease in PGE2 announced the end of sleep and the imminent occurrence of wakefulness. It is the first study to our knowledge showing that the evolvement in endogenous PG profile may predict the occurrence of sleep or wakefulness.

Spontaneous feeding-related monoamine changes in rostromedial hypothalamus of the obese Zucker rat: a microdialysis study

Using microdialysis in freely moving rats, we have been able to observe changes in monoamines from the ventromedial and paraventricular hypothalamic nuclei before, during, and after spontaneous feeding. Because the genetically obese Zucker rat shows abnormalities related both to feeding and monoamines, it was of interest to investigate possible particularities in the monoaminergic variations around spontaneous feeding. The profile of changes in Zucker rats was grossly similar to that of Wistar rats: increases in 5-hydroxy-tryptamine (5-HT), 5-hydroxyindolacetic acid (5-HIAA), and dopamine (DA), and decrease in dihydroxyphenylacetic acid (DOPAC). However, the release in monoamines (5-HT and DA) was more dramatic and longer-lasting than in Wistar rats, while the changes in the metabolites were proportionnally less pronounced. This suggests that high concentrations of these feeding-related amines are released and remain in the synaptic cleft of the obese rat, possibly because they are required in larger amounts to bring about satiety. The hyperphagia of the obese Zucker rat may therefore be the result of a resistance to these prandially released satiety-promoting neurosubstances.

Effect of mefenorex on 5-HT release: studies in vitro on rat hypothalamic slices and in vivo by microdialysis

Mefenorex, used for 20 years as an anorexic drug, has not been studied so far with regard to its central mechanism of action, although its chemical structure suggests a serotonergic mechanism. In the present study, the effect of mefenorex on serotonin (5-HT) release was investigated both in vitro, on rat hypothalamic slices and in vivo, using microdialysis in the paraventricular (PVN)-ventromedian (VMH) hypothalamic area while mefenorex was applied locally by means of counterdialysis. In vitro, mefenorex increased the spontaneous release of 3H 5-HT from hypothalamic slices but not the electrically evoked release. This suggests a 5-HT releasing action of mefenorex not mediated through the terminal autoreceptor. The in vivo study confirmed the enhanced release and provided additional information. The delayed and modest increase of the 5-HT intracellular metabolite 5-HIAA may be indicative of an inhibition of reuptake. The dopaminergic system was also, but more modestly, activated by mefenorex. The increase in 5-HT release together with the inhibition of its reuptake may represent the main mechanism of action of mefenorex, and the secondary activation of the dopaminergic system may contribute in its anorexigenic effect at the level of the PVN-VMH area.

Feeding-related immunoreactive insulin changes in the PVN-VMH revealed by microdialysis

The presence of insulin in the brain and its anorectic effect when centrally infused are well-established today. The question of physiological and dynamic changes in brain insulin in relation to meals is still unanswered and addressed here. Immunoreactive insulin (IRI) was measured using a sensitized RIA in 30-min microdialysates from VMH and PVN nuclei during and after a scheduled meal in male Wistar rats. We indeed observed elevations in hypothalamic IRI during the first 30 min of 1-h meals with a progressive return towards premeal levels in spite of a robust satiety. When the rats were accustomed to the scheduled meals, an anticipatory rise in IRI was found in the hypothalamus, but not in the plasma, during the 30 min preceding the due time of the meal whether the meal was presented or not. This anticipatory rise was proportional to the number of repeated scheduled meals. These results first suggest that hypothalamic IRI changes reflect in some instances those in the plasma although there are exceptions that cannot be accounted for by a simple plasma-brain tissue delivery. Besides, hypothalamic IRI can hardly be proposed as a satiety signal. The present data suggest a role in satiation rather than in satiety or, perhaps, in the inhibition of the behavioral response of feeding that can include the anticipatory rise.

In vivo effects of hyperinsulinemia on lipogenic enzymes and glucose transporter expression in rat liver and adipose tissues

Chronic hyperinsulinemia with maintenance of euglycemia was imposed on normal rats for 4 days. In white adipose tissue, hyperinsulinemia resulted in a twofold increase in GLUT4 protein and mRNA and a sixfold to 15-fold increase in fatty acid synthase (FAS) and acetyl coenzyme A (CoA) carboxylase (ACC) activity, respectively. Lipogenic enzyme mRNA was also markedly increased (20- to 30-fold). This was specific for white adipose tissue and was not observed in brown adipose tissue. In the liver, hyperinsulinemia was accompanied by a threefold increase in glucokinase (GK) activity and mRNA and by a threefold to fivefold increase in lipogenic enzyme activities and mRNA. In agreement with the changes in lipogenic activities, lipogenesis was markedly increased in white adipose tissue and liver of hyperinsulinemic rats. The data strongly suggest that in the rat, insulin is a driving force leading to increased lipid synthesis in liver and white adipose tissue.

A new triple-channel swivel for fluid delivery in the range of intracranial (10 nl) and intravenous (100 microliters) self-administration volumes and also suitable for microdialysis

This paper describes a new low-torque, bubble-free and multiple-channel swivel of easy construction. This swivel combined with the use of fused silica capillary tubing to connect syringes and injectors, as we recently proposed, allow the accurate and repeated microinjection of low nanoliter volumes (10 nl) in freely moving rats, as required in the intracranial self-administration paradigm. Microinjections can be simultaneously performed in 3 different brain regions. Relatively large volumes in the 10-100 microliters range can be repeatedly administered, as in intravenous self-administration, using the traditional connections with polyethylene (PE) tubing. This swivel allows the execution of experiments involving in vivo microdialysis in up to 3 different brain areas. The internal channel has a very low dead space (4 microliters) and can be used to withdraw small liquid samples and perform on-line microdialysis in freely moving animals. This versatility makes the present swivel appropriate for sophisticated experimental designs involving combinations of intracranial, intravenous and/or intragastric self-administration with microdialysis.

Insulin and glucose-induced changes in feeding and medial hypothalamic monoamines revealed by microdialysis in rats

Microdialysis from the ventromedian (VMH) and paraventricular (PVN) regions and simultaneous infusion of insulin alone (orexigenic) or with glucose (anorexigenic) was performed in the free-feeding rat. Intravenous insulin infusion (1 IU in 1 ml over 1 h) resulted in the expected glucoprivic feeding and a decrease in dopamine (DA) and serotonin (5-hydroxytryptamine [5-HT]) with an increase in their respective metabolites, dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5-HIAA). These data are quite different from those observed in spontaneous ad lib feeding: increase in DA, 5-HT and 5-HIAA and decrease in DOPAC. These last changes were not superimposed on insulin effects when insulin-induced meals occurred. When food was not available, insulin infusion induced the same changes except an increase in DA levels which could probably be ascribed to stress. When insulin was infused together with a sufficient amount of glucose to prevent hypoglycemia, we observed the usual anorexigenic effect. Although this treatment had an effect on induced-feeding opposite to that following insulin alone, the changes in hypothalamic monoamines were similar. The only consistent overall change is finally the rise in 5-HIAA found in both spontaneous and induced feeding conditions. These data suggest that monoaminergic changes in the VMH and PVN are not directly implicated in the control of feeding but they rather reflect metabolic events that accompany this behavior.

Chronic vascular catheterization in the mouse

A method is described for stress-free periodic sampling of blood and/or intravenous infusions in the normal awake and behaving mouse. The surgical procedure consists of the permanent implantation of a Silastic-rubber catheter in the right external jugular vein. The free end of the catheter is then pulled subcutaneously up to the skull and fixed on the skull with a form of dental acrylic that sticks firmly on the bone and thus does not require anchor screws in the skull. This technique allowed us to perform glucose tolerance tests in the mouse, and to follow the time course of blood glucose levels in individuals.

Intravenous administration of inorganic selenium compounds, inhibitors of prostaglandin D synthase, inhibits sleep in freely moving rats

Prostaglandin (PG) D2 has been postulated to be an endogenous sleep-promoting factor. Biosynthesis of PGD2 is catalyzed by PGD synthase (prostaglandin-H2 D-isomerase, EC 5.3.99.2), the activity of which is inhibited by inorganic selenium compounds such as SeCl4 and Na2SeO3. We recently examined the effect of intracerebroventricular administration of these selenium compounds on sleep in rats, and demonstrated time- and dose-dependent sleep inhibition. To establish whether this effect of selenium is also produced when the compound is administered systemically, we devised a procedure for intravenous catheterization and examined the effect of these selenocompounds on sleep-wake activity in freely moving rats (n = 35). Each test compound was administered into the inferior vena cava continuously between 11.00 and 17.00 h on the experimental day. SeCl4 time- and dose-dependently inhibited sleep at infusion rates of 5, 7.5, 10 and 20 nmol/microliters per min. During the SeCl4 infusion at 20 nmol/microliters per min, slow-wave sleep and paradoxical sleep were reduced to 63% and 50% of their respective baseline values. Na2SeO3 exhibited a similar sleep inhibition, though Na2SO3 was ineffective. Infusion of SeCl4 at 10 nmol/microliters per min or below produced no consistent changes in the mean brain temperature, or food and water intake during the infusion period. During the nocturnal period subsequent to SeCl4 infusion, sleep was increased by a rebound phenomenon, while a decrease in brain temperature and inhibition of food and water intake dose-dependently occurred. We conclude that systemic administration of these PGD synthase inhibitors has a sleep-reducing potency.

Basal and hyperinsulinemia-induced immunoreactive hypothalamic insulin changes in lean and genetically obese Zucker rats revealed by microdialysis

Lean and genetically obese Zucker rats were implanted with permanent intravenous catheters and a guide cannula was aimed at the region of the ventromedial (VMH) and paraventricular (PVN) nuclei to measure immunoreactive insulin collected by means of microdialysis. Preliminary experiments assessed the validity of a novel assay of insulin in microdialysates by a sensitized radioimmunoassay technique. This method was then used to measure basal levels of insulin and those induced by i.v. infusion of 0.5 U of insulin over 30 min in both lean and obese rats. Basal hypothalamic immunoreactive insulin levels were lower in the obese rats than in the lean Zucker rats. When insulin was infused i.v. for 30 min, hypothalamic immunoreactive insulin showed an increase in the 30-60 min sample, which was twice as great in the obese rats. Two facts suggest that the insulin found in the microdialysates was of cerebral, not vascular origin: the short latency in the response and the finding that the response was greater in obese rats.

Spontaneous feeding-related monoaminergic changes in the rostromedial hypothalamus revealed by microdialysis

The activity of hypothalamic monoamines in response spontaneous feeding was investigated using the in vivo technique of brain microdialysis together with the instrumental recording of feeding pattern. The simultaneous variations of dopamine (DA), serotonin (5-HT), and their respective metabolites, DOPAC and 5-HIAA, were measured in the rostromedian hypothalamus, where the probe was located between the PVN and VMH. Throughout the experiment, the changes in DOPAC followed a mirror image of those in DA: DA regularly increased, reaching its zenith within the 15-min sample collected during the meal before returning to the same level as just before the meal. Following a premeal plateau, both 5-HT and 5-HIAA increased as soon as the beginning of feeding; 5-HT reached its zenith during the meal while 5-HIAA showed a more delayed and prolonged increase. When a new meal was initiated, 60 to 70 min later, a similar monoaminergic pattern was observed again. These data suggest that building up hunger is announced by an ascending slope of DA and setting up of satiation is concomitant with a descending slope of DA. Concerning serotonergic changes, the sharp 5-HT release during the meal would be a signal of satiation (transient preabsorptive fullness) while the longer-lasting increase in 5-HIAA, reflecting 5-HT synthesis, would be associated with satiety (more persistent postabsorptive state substituting satiation). These data partially confirm and extend previous pharmacological studies as well as the findings on deprivation-induced, imposed meals. They suggest a possible causal relation between monoaminergic changes and behavioral initiatives.

Effects of alcohol dependence on shock-induced fighting: action of muscimol and homotaurine

We have applied the electroshock-induced fighting behavior to the study of experimental alcohol dependence. Adult Wistar rats were intoxicated chronically with ethanol (10 g/kg/24 h) for 13 days. Electroshock-induced fighting behavior was studied during chronic intoxication and withdrawal in comparison with normal rats receiving a water-carbohydrate solution isocaloric to ethanol. Rats were divided into groups receiving respectively muscimol (0.25 mg/kg), a GABAA agonist; homotaurine (140 mg/kg) a GABA mimetic; and physiological saline (10 ml/kg), intraperitoneally. During chronic intoxication, rats showed an increase in defensive-fighting behavior. Withdrawal accentuated the aggressive behavior and muscimol and homotaurine inhibited it. These results confirm the relevance of the electroshock-induced defensive fighting behavior test in chronic intoxication with alcohol, but to show the involvement of GABAergic transmission in the behavioral effects of alcohol withdrawal, additional experiments with other GABA mimetics and with GABA antagonists should be considered.

Limited protection by small unilamellar liposomes against the renal tubular toxicity induced by repeated amphotericin B infusions in rats

Amphotericin B (AMB), either alone or incorporated into small unilamellar vesicles of pure dipalmitoylphosphatidyl choline (DPPC SUV-AMB), was administered intravenously to male Sprague-Dawley rats once daily for 5 days. Either 1.5 or 3.5 mg of AMB or DPPC SUV-AMB per kg was given, since these concentrations corresponded, respectively, to the lowest nephrotoxic dose and the sublethal dose of AMB in our model. Tubular functions were evaluated daily, and AMB concentrations in plasma, urine, and tissues were measured by high-performance liquid chromatography. AMB at both doses induced tubular toxicity, hyposthenuria being the earliest symptom. DPPC SUV-AMB at 1.5 mg/kg/day was atoxic, but the tubular alterations induced by 3.5 mg of DPPC SUV-AMB per kg were similar to those observed with 3.5 mg of AMB per kg, except that the ability to concentrate urine was partly restored 72 h after the last infusion. Incorporating AMB into DPPC SUV did not influence the pharmacokinetics of the drug. Using this lipidic AMB formulation, we thus observed a beneficial effect toward limiting the renal tubular toxicity of repeated low doses of AMB but, unexpectedly, not that of high doses. These results indicate that tubular renal functions and electrolyte serum values should be closely monitored in patients treated with AMB liposomal formulations, especially high-dose regimens.

Effects on metabolic and hormonal parameters of monosodium glutamate (umami taste) ingestion in the rat

Umami taste appears to signal, at the gustatory level, the intake of proteins, therefore the working hypothesis was: does umami taste of a monosodium glutamate (MSG) solution elicit changes in both glucagon and insulin release, similar to those elicited by amino acids, and consequently, changes in plasma glucose and in overall cellular metabolism? In a first experiment, rats were equipped with indwelling jugular and oral catheter and serial samplings were made in the free moving, undisturbed rat before and after an oral or IV infusion of MSG (0.05 M). None of the plasma parameters showed any significant response. In a second experiment, energy expenditure was monitored by means of an original computer-based calorimeter capable of calculating, besides the classical parameters, resting metabolism in a moving animal (designated by background metabolism). The addition of MSG to a low calorie, low-protein meal did not modify background metabolism or respiratory quotient. Therefore MSG ingestion does not by itself affect plasma levels of hormones of glucose and protein metabolism, total metabolism rate, or nutrient utilization. However, examination of individual data and those from a pilot experiment for future work suggests that MSG becomes an efficient metabolic effector if added to a caloric diet, and so enhances proper thermogenesis of macronutrients.

Corticotropin-releasing factor enhances sodium and water intake/excretion in rabbits

Sodium and water intake and excretion of wild rabbits was studied during intracerebroventricular (icv) infusion of corticotropin-releasing factor (CRF). Icv infusion of 200 and 600 pmol/h for 22 h induced changes in the ingestive and general behavior of animals. Increased consumption of 0.5 M NaCl solution was observed during the day of infusion, accompanied by increased sodium excretion, and food intake was decreased. The rabbits maintained the high sodium turnover, together with a high water turnover, for 2-3 days after the icv infusion stopped. Icv infusion of CRF induced strange behaviour in wild rabbits, they appeared to react with fright to normal daily events around them. The strange behaviour started about two hours after the beginning of icv infusion and disappeared immediately after the infusion stopped. On the basis of present and earlier observations, that systemic administration of adrenocorticotropin (ACTH) and adrenal steroid hormones induce increased sodium turnover, it is proposed that changes in the sodium and water metabolism might constitute part of the general stress reaction of the body.

Circadian variations in vigilance states in the alcohol-dependent rat

Waking and sleep states were studied in the alcohol-dependent rat after administration of ethanol (416 mg/kg/hr) by indwelling intragastric catheter (IGC) for 13 days. Electropolygraphic recordings performed for a total of 24 hr from the start of withdrawal were compared with those of control rats receiving water by IGC and showed 1) that rapid eye movement sleep was the most sensitive of the four vigilance states studied. A decrease was noted both for the total duration of recording and for the light period; 2) that nonactive wakefulness was the only vigilance state to show an inversion of percentages between the light and dark period; 3) that the light period was the best time for studying changes in vigilance states. Changes included increased percentages of active and nonactive wakefulness and decreased percentages of slow-wave and rapid eye movement sleep. This was due to a change in the number of episodes rather to a change in their mean duration. No significant change occurred during the dark period.

Does alcohol promote reactive hypoglycemia in the rat?

Alcohol induces a reactive hypoglycemia in man, but divergent results have been reported, in man and rats, on the effects of ethanol plus a carbohydrate load. The interactions between ethanol and glucose metabolism are complex. In the present study isocaloric solutions of glucose alone (A) or glucose plus alcohol (B) were administered in rats at the beginning of nighttime. Their effects were compared on blood glucose (BG) levels. Since rats don't drink alcohol spontaneously, glucose was given by mouth and alcohol through an intragastric catheter (IG); in the case of glucose alone half the load was ingested by mouth, and half IG. After administration, BG level was continuously determined in freely moving rats. It was shown that the latency to eat after the ingestion of glucose plus alcohol was significantly shorter and the size of the meal smaller. The postabsorptive hyperglycemia was significantly decreased in B as compared to A. The following hypoglycemia was more severe in B and it appeared earlier. In addition, a stress was applied after both A and B. It is well known that stress are potent stimuli of the sympathetic nervous system which inhibits insulin secretion. In both situations (A and B) with stress, the small preabsorptive hypoglycemia which appeared 4 min after the ingestion was suppressed. The hyperglycemia was higher in situation A with, than without, stress. The subsequent hypoglycemia was significantly lower. After stress in B, there was no difference in the peak of hyperglycemia but it appeared later. So, in rat the ingestion of alcohol together with an oral glucose load could trigger a reactive hypoglycemia. Stress greatly enhanced the phenomenon.

Sham drinking in rats: osmotic and volumetric manipulations

Male rats, fitted with indwelling gastric fistulas, were tested with either a closed fistula (normal drinking) or an open fistula (sham drinking) following either intracellular dehydration (with NaCl), extracellular dehydration (with PEG), or the combination of the two stimuli. In normal drinking tests, the combined stimulus induced an intake of water that was the sum of the individual effects. In sham-drinking tests, both NaCl- and PEG-treated rats drank up to twice that of their normal drinking counterparts, but those given NaCl + PEG showed no such increase. Various body fluid measurements confirmed the persistence of the respective dehydration states at the end of sham-drinking sessions. The relatively poor or absent sham drinks after these stimuli are contrasted with vigorous sham drinking following fluid deprivation. In a second experiment, sham drinking following NaCl injections did not improve with repeated testing, but intake after intravenous infusion of NaCl did show some increase but was still modest and slow compared with that after fluid deprivation.