Altered preferences for sucrose, sodium chloride, urea and hydrochloric acid solutions in an animal model of cholestatic liver disease

Preferences for sucrose, sodium chloride (NaCl), urea and hydrochloric acid (HCl) solutions (representing sweet, salty, bitter and sour stimuli) were examined in rats with bile duct ligation using 24-hr two-bottle choice tests. Preferences in bile duct ligated rats for sucrose and NaCl solutions were decreased relative to control animals in the initial stages following ligation (Days 1-5) and then increased in the later stages (Days 11-20). Preferences for both HCl and urea solutions were decreased briefly compared to control animals but showed no consistent pattern. The results provide the first demonstration for altered ingestive behavior in an animal model of liver disease and suggest that the bile duct ligated rat may be useful in studying mechanisms of chemosensory disturbances in human liver disease.     

Holoturia arenicola extract modulates bile duct ligation-induced oxidative stress in rat kidney

Background: Acute Renal Failure (ARF) in patients with cirrhosis is one of the most frequently encountered complications of obstructive jaundice. Marine organisms from the Mediterranean Coast of Egypt are considered potential sources of bioactive molecules. The present study was undertaken to explore the curative effects of Holothuria arenicola extract (HaE) against renal injury induced by bile duct ligation in male albino rats. Methods: Fifty four male Wistar albino rats were assigned into two main groups, the Sham-operated control (received distilled water only for 28 days) and bile duct ligated (BDL) group, which divided into 2 subgroups, animals of these subgroups treated for 28 consecutive days as follow: Subgroup I (BDL), rats of this subgroup administered distilled water orally. Subgroup II, animals of this subgroup treated orally with HaE (200 mg/kg body weight). Results: BDL induced marked alteration on renal functions as manifested by a significant increase in the kidney function markers, serum creatinine, urea and uric acid. In addition, BDL caused significant increase in MDA level and significant decrease in GSH level as well as antioxidant enzymes activities (GST, SOD and CAT). However, administration of HaE for consecutive 28 days significantly reversed these changes, suggesting that the renal curative effect of HaE against oxidative stress- induced injury might be involved in decreasing lipid peroxide generation and stimulating antioxidant status. Conclusion: The present study revealed that HaE had a profound effect against BDL-induced oxidative stress in the kidney tissues which is the common feature of choestasis in the liver.     

Beneficial Effects of Glycocholic Acid (GCA) on Gut Mucosal Damage in Bile Duct Ligated Rats

In order to investigate the effect of bile acids on gastrointestinal inflammations, bile duct ligated rats (BDL) were treated with GCA (25 mM/ml, oral or colonic) or saline 1 h before ethanol challenge and twice daily for 3 days in the ileitis group, while GCA was given twice daily for 3 days in the colitis group. BDL reduced the macroscopic and microscopic damage scores in the ileitis group compared to sham operated group, while it had no significant effect on ulcer or colitis groups. However, GCA given in BDL group reduced the ulcer index and microscopic damage in colitis group compared to saline-treated groups, but had no effect in ileitis group. Both BDL and GCA administration in BDL group reduced ileitis- or colitis-induced elevations in MPO levels. GCA administration in BDL group inhibited gastric acid output and volume. Our results suggest that oral or colonic administration of primary bile acids may be useful for the treatment of gastrointestinal inflammations.     

Effects of bile duct ligation and captopril on salt appetite and renin-aldosterone axis in rats.

A ligation of the common bile duct (BDL) produces cholestasis and hypotension and increases the daily ingestion of sodium chloride solutions in rats. Low-dose captopril (CAP) treatment also modifies the ingestion of water and sodium in naive rats, and may do so in cholestatic rats. This study examined whether the elevated ingestion of saline by Long-Evans rats after BDL is associated with increased plasma renin activity (PRA), and whether treatment with a low dose of the angiotensin converting-enzyme inhibitor CAP further exacerbates fluid intake and PRA after BDL. In these experiments water and 0.3 M saline intake and PRA and plasma aldosterone (PA) were measured in naive and CAP-treated BDL and sham-ligated rats. We found that BDL elevated rats' daily saline intake 2 weeks after the ligation procedure but had no effect on PRA. CAP (0.1 mg/mL) placed in the drinking water of some BDL rats further increased saline intake. Both PA and hematocrits tended to be reduced in BDL rats, whereas PRA was elevated in both BDL and sham-ligated rats receiving CAP in the drinking water or by gavage (0.1 mg/mL in 10 mL/kg). The data suggest that the ingestion of saline by rats can be modified by BDL and CAP administration, but that exaggerated saline intake in BDL rats is not associated with excessive renin secretion.     

Cholera toxin-induced fluid secretion in rat gut ligated loops: influence of bile from normal or cholera toxin-immunized rats.

Fresh normal rat bile premixed with cholera toxin (CT) did not significantly affect the CT-induced fluid accumulation in rat jejunal ligated loops. Bile from rats intrajejunally (i.j.) immunized three times with CT definitely inhibited CT-induced fluid secretion. Bile duct ligature (BDL) for 1-4 days in unimmunized rats, in contrast with mice, did not significantly affect subsequent CT-elicited fluid secretion in their ligated loops. BDL for 4 days in rats i.j. immunized with CT, only slightly decreased the CT-neutralizing ability of their gut loops. Passive transfer during 24 hr of bile from i.j.-immunized rats, but not from normal rats, into gut of normal recipient rats with BDL, significantly protected loops made in such recipients. The affinity-purified antibodies of immune bile, mixed with CT, neutralized its effect. Our data show that, unlike mice, rat bile acids are not required for expression of the CT effect in gut loops. In addition, bile from i.j.-immunized rats contains enough anti-CT antibodies to be protective on its own, but is not necessary for substantial gut protection against CT in i.j.-immunized BDL rats. Our results confirm a major and complementary role of both biliary and intestinal secretory IgA antibodies in protection of the rat gut mucosa against CT-induced fluid secretion.     

The effect of obstructive jaundice on systemic concentrations of bile acids,histamine and antibodies to the core region of endotoxin glycolipid

Systemic endotoxaemia contributes to the high morbidity and mortality of jaundiced patiens undergoing surgery. In this study, correlations between systemic endotoxaemia (assessed by measuring antibodies to the core-glycolipid region of endotoxin, a-CGL), bile acids and blood histamine were investigated in a bile duct ligation (BDL) animal model of obstructive jaundice. Three weeks after BDL, systemic a-CGL (p<0.0001), total blood histamine (p<0.02) and bile acid concentrations (e.g. taurocholate,p<0.001) were significantly elevated in BDL animals compared to control or sham operated rats. Additionally, total blood histamine correlated significantly with plasma taurocholate (r=0.83,p=0.011). High circulating levels of endotoxin and bile acids may result in mast cell activation and/ or histamine synthesis in jaundiced animals, which may contribute to the pathophysiology of complications seen in cholestasis.     

Chronic bile duct obstruction induces changes in plasma and hepatic levels of cytokines and nitric oxide in the rat.

Chronic bile duct ligation (BDL) is a useful model of cirrhosis. However, its parallel plasma and liver changes in levels of cytokines and nitric oxide (NO), involved in liver damage, remain unknown. The aims of this work were to quantify both the plasma and hepatic levels of five cytokines and NO in cirrhotic rats, 28 days after bile BDL, and to analyze their relationship with liver damage markers. One group of male Wistar rats was bile duct ligated and another group was sham operated, both groups were sacrificed 28 days after BDL. Plasma and liver cytokines, tumor necrosis factor-alpha (TNF-alpha), interleukin-6, -1beta, -10 (IL-6, -1beta, -10) and interferon-gamma (IFN-gamma), were measured by ELISA. Plasma and hepatic NO was determined as NO(2)(-)+NO(3)(-) by an enzymatic method. Alkaline phosphatase, gamma-glutamyl transpeptidase, alanine aminotransferase and bilirubins were determined in plasma. Collagen, lipid peroxidation and glycogen were quantified in liver. Two histopathological staining techniques were performed. BDL-induced cirrhosis was corroborated by the elevated liver damage markers and histopathological analysis. Chronic BDL significantly increased (P<0.05) most of plasma and hepatic cytokine levels and diminished the hepatic IFN-gamma amount. NO was increased in both tissues, but such change was only significant in plasma. Biliary cirrhosis produces interesting changes in plasma and hepatic levels of cytokines and NO. This finding in chronic BDL model in rats has not been previously described in both tissues for such cytokines and NO. Cytokines and NO imbalance favor establishment and perpetuation of cirrhosis.     

Dietary modulation of oral amphetamine intake in rats

The interaction of sucrose availability and oral self-administration of amphetamine was examined in 23 male Sprague-Dawley rats. Fourteen rats were given a 0.075 mg/ml amphetamine sulfate solution as their sole source of fluid and 9 rats were given water. Feeding conditions were alternated between weeks with both granulated sucrose and chow available and weeks with only chow present. Rats drank significantly less of the amphetamine solution when consuming sucrose and chow than when eating chow alone. Sucrose intake had a slight effect on water intake. Rats drinking the amphetamine solution consumed significantly less food, gained significantly less weight, and were significantly less efficient at using calories for weight gain than rats drinking water. However, when given access to sucrose, rats drinking the amphetamine solution chose a significantly greater proportion of their daily caloric intake as sucrose (60%) than rats drinking water (42.5%). The present results demonstrate that 1) amphetamine intake alters nutrient choice and 2) that dietary variables can profoundly affect drug self-administration.     

Effects of chronically elevated intake of different concentrations of saccharin on morphine tolerance in genetically selected rats

Sixty-four LC2-Hi and LC2-Lo female rats were chronically supplied with either water or a solution of 1, 3 or 30 mM of sodium-saccharin. Pain sensitivity, as well as its reduction by a 2.5 mg/kg morphine injection, were measured in a hot-plate test. High saccharin consuming LC2-Hi rats did not exhibit significant morphine-induced analgesia (MIA) compared to baseline, after 38 days of drinking of saccharin, irrespective of concentration. MIA of those rats which were maintained on water was significant. In contrast, the low consuming LC2-Lo animals maintained either on water or on 1 and 30 mM saccharin showed significant MIA compared to baseline, following the same exposure period. The findings demonstrate that chronically elevated saccharin intake, activates an endogenous opiate system leading ultimately to cross-tolerance to the analgetic effects of morphine.     

Changes in gastrointestinal morphology associated with obstructive jaundice

Bacterial translocation has been consistently demonstrated in experimental models of obstructive jaundice. An important factor which promotes this phenomenon is physical injury of the intestinal mucosa. Some previous studies have presented suggestive evidence of this, following bile duct ligation. The aims of this study were to analyse objectively intestinal mucosal morphometric characteristics, to examine for evidence of bacterial translocation, and to assess enterocytes for ultrastructural abnormalities. Adult female Wistar rats were assigned to one of three groups: control (n=8), bile duct ligation (BDL; n=11), or sham operation (n=10). One week later, portal blood, mesenteric lymph nodes, liver, and spleen were harvested and cultured aerobically and anaerobically for evidence of bacterial translocation. Segments of jejunum, ileum, caecum, and large bowel were examined histologically, using light microscopy and morphometrically, using an image analysis system. Electron microscopy was performed on regions of the gastrointestinal tract where significant morphometric alterations had been identified. Significant bacterial translocation was identified following BDL (63. 6% BDL vs. 0% sham vs. 0% control, p<0.01, Fisher's exact test). There was a significant reduction in total mucosal thickness (standard error) [650 microm (23) BDL vs. 731 microm (27) sham vs. 744 microm (95) control] and villous height [451 microm (20) BDL vs. 515 microm (18) sham vs. 559 microm (79) control] in jaundiced animals, compared with sham-operated and control animals (p<0.02, Mann-Whitney U-test). Electron microscopy revealed oedematous change associated with mild inflammation, disruption of desmosomes, and the formation of lateral spaces between enterocytes. In addition, enterocytes showed vacuolation of their cytoplasm and mitochondrial swelling. Increased numbers of bacteria appeared to be attached to the mucosa. These data provide evidence of physical disruption of intestinal mucosa in jaundiced animals, most marked in the distal ileum. Significant bacterial translocation occurs following bile duct ligation and this supports the hypothesis of gut barrier dysfunction with obstructive jaundice.     

Intragastric calcium infusions support flavor preference learning by calcium-deprived rats

We investigated whether rats can associate the flavor of ingested solutions with the postingestive delivery of calcium. In one series of experiments using the "electronic esophagus" preparation, calcium-deprived rats received pairs of daily one-bottle training trials in which they received intragastric infusions whenever they ingested an arbitrary flavor of Kool Aid. Rats later preferred the flavor associated with infusions of 50 mM CaCl(2) or 50 mM calcium lactate (CaLa), but not with water, 10, 100 or 250 mM CaCl(2) or 100 mM sodium lactate (NaLa). In another experiment, rats had simultaneous access to two arbitrary flavors, ingestion of one of which produced intragastric infusion of 50 mM CaCl(2), 75 mM NaCl or water. Only the rats given 50 mM CaCl(2) developed a preference for the flavor associated with the infusion. The preference for calcium infusions was not as large as that seen for orally ingested calcium. Nevertheless, these results show that 50 mM calcium infusions are rewarding to calcium-deprived rats. They thus suggest that rats can associate flavor ingestion with the postingestive benefits of consuming calcium.     

Separate mechanisms for central osmotically-induced drinking and vasopressin release in minipigs

Operant drinking and lysine vasopressin (LVP) release were investigated in minipigs following intracerebroventricular (ICV) injections of hypertonic equiosmolar (1.4 osM) solutions of NaCl and of sucrose and mannitol dissolved in 0.15 M NaCl or water, and of urea dissolved in 0.15 M NaCl. Hypertonic (0.74 M) NaCl produced significant drinking and LVP release in all minipigs tested whereas hypertonic equiosmolar (1.4 osM) solutions of sucrose and mannitol induced only drinking. Mannitol, both with and without NaCl, was more effective than sucrose. Hypertonic urea was ineffective both as an osmotic dipsogen and at stimulating the release of LVP. These results suggest that two independent mechanisms could be involved in drinking and LVP responses to ICV administration of hypertonic solutions in minipigs.     

Gadolinium chloride suppresses hepatic oval cell proliferation in rats with biliary obstruction.

Liver injury due to bile duct ligation (BDL) is histologically characterized by cholestasis, bile ductular proliferation, hepatocellular damage, portal fibrosis, and ultimately biliary cirrhosis. Stem cells within the liver may act as progenitor cells for small epithelial cells termed oval cells that can differentiate into bile duct cells or hepatocytes, whereas myofibroblasts are the principal source of collagen production in fibrosis. The aims of this study were to determine 1) whether BDL induces oval cell proliferation and 2) whether blockade of Kupffer cells affects oval cell proliferation, bile duct proliferation, and myofibroblast transformation in experimental biliary obstruction. Male Sprague-Dawley rats were divided into two groups to receive either a single dose of gadolinium chloride (a selective Kupffer cell blocking agent) or vehicle. One day later, the gadolinium- and vehicle-treated groups were further subdivided to receive either BDL or sham operation. The rats were sacrificed on day 7 postoperatively. Serum was collected for measurement of aspartate aminotransferase, gamma-glutamyl transpeptidase, and bilirubin levels. Liver tissue was taken for evaluation of fibrosis, bile ductular cells, oval cells, and myofibroblasts. BDL resulted in elevated aspartate aminotransferase, gamma-glutamyl transpeptidase, and bilirubin in serum, and gadolinium pretreatment did not modify these effects. BDL induced marked oval cell proliferation, which was completely prevented by gadolinium pretreatment. Gadolinium did not affect the induction of bile duct expansion or myofibroblasts after BDL. We conclude that experimental biliary obstruction induces oval cell proliferation, which can be prevented by gadolinium pretreatment. This suggests that bile ductular proliferation and myofibroblast transformation are not mediated by Kupffer cells and that ductular proliferation can proceed in the absence of oval cells. Alternatively, gadolinium may directly affect oval cell proliferation after BDL.     

Flavor preferences conditioned by sucrose depend upon training and testing methods: two-bottle tests revisited

In confirmation of prior work, rats given one-bottle training with flavored 5% and 30% sucrose solutions (CS5 and CS30) strongly preferred the CS5 when both flavors were presented in intermediate 17.5% sucrose solutions. The CS5 preference has been attributed to a conditioned satiety response to the CS30 flavor, but equal intakes of CS5 and CS30 in one-bottle tests did not support this view. To determine if sweetness differences between training and test solutions contributed to the CS5 preference, new rats were trained and tested with flavored 10% sucrose solutions. One flavor (CS5) was paired with matched intragastric (ig) water infusions (=net 5% solution) and another flavor (CS30) was paired with matched infusions of 50% sucrose (=net 30% solution) during one-bottle training. In two-bottle tests with both flavors paired with an intermediate infusion (25%=net 17.5%), the rats initially showed no overall preference for the CS5 or CS30. Following additional training, the rats significantly preferred the CS30 to the CS5. The intragastric data suggested that a change in sweet taste context between training and testing might have accounted for the strong CS5 preference obtained in the first experiment. This was confirmed in a third experiment in which rats were trained with flavored 5% and 30% sucrose solutions and then given two-bottle tests with both flavors presented either in 5% sucrose or 30% sucrose. Rats tested with 30% sucrose strongly preferred the CS5 flavor, whereas rats tested with 5% sucrose significantly preferred the CS30 flavor. Thus, the outcome of two-bottle flavor preference tests and presumably other tests of conditioned flavor reward may be greatly influenced by the solutions used in the tests. The impact of this variable may be greatest when the training solutions do not substantially differ in their net postingestive reinforcing actions. This appears to be the case with 5% and 30% sucrose solutions because the satiating effect of the concentrated solution tends to counteract its nutrient reinforcing action.     

Kupffer cell phagocytosis blockade decreases morbidity in endotoxemic rats with obstructive jaundice

OBJECTIVE AND DESIGN: The consequences of Kupffer cell phagocytosis blockade were studied in endotoxemic rats with obstructive jaundice. MATERIAL OR SUBJECTS: 159 male Wistar rats. TREATMENT: Obstructive jaundice was induced by bile duct ligation (BDL). Gadolinium chloride (1 mg/100 g iv) was given 6 days after BDL to inhibit Kupffer cell activity and the animals were challenged with 1 microg/g endotoxin 24 h later. METHODS: Endotoxin sensitivity, tumor necrosis factor-alpha and interleukin-6 production were studied, liver and lung injury were assessed by neutrophil infiltration assay, tissue adenosine triphosphate, aspartate aminotransferase, alanine aminotransferase level determinations and histology, respectively. For statistics non-parametric methods were used. RESULTS: BDL sensitized the animals to endotoxin, increased endotoxin-induced tumor necrosis factor-alpha and interleukin-6 production and reduced ATP contents of the liver and the lung. Kupffer cell blockade significantly increased the resistance against endotoxin, diminished the inflammatory cytokine release and reduced endotoxin-induced tissue injury in BDL animals. CONCLUSION: Attenuation of Kupffer cell function decreases endotoxin-induced lethality and morbidity in obstructive jaundice.     

Splenectomy ameliorates portal pressure and anemia in animal models of cirrhotic and non-cirrhotic portal hypertension

PurposePortal hypertension (PH)-associated splenomegaly is caused by portal venous congestion and splanchnic hyperemia. This can trigger hypersplenism, which favors the development of cytopenia. We investigated the time-dependent impact of splenectomy on portal pressure and blood cell counts in animal models of non-cirrhotic and cirrhotic PH.Materials and methodsNinety-six rats underwent either partial portal vein ligation (PPVL), bile duct ligation (BDL), or sham operation (SO), with subgroups undergoing additional splenectomy. Portal pressure, mean arterial pressure, heart rate, blood cell counts and hemoglobin concentrations were evaluated throughout 5 weeks following surgery.ResultsFollowing PPVL or BDL surgery, the animals presented a progressive rise in portal pressure, paralleled by decreased mean arterial pressure and accelerated heart rate. Splenectomy curbed the development of PH in both models (PPVL: 16.25 vs. 17.93 ?mmHg, p ?= ?0.083; BDL: 13.55 vs. 15.23 ?mmHg, p ?= ?0.028), increased mean arterial pressure (PPVL: +7%; BDL: +9%), and reduced heart rate (PPVL: ?10%; BDL: ?13%). Accordingly, splenectomized rats had lower von Willebrand factor plasma levels (PPVL: ?22%; BDL: ?25%). Splenectomy resulted in higher hemoglobin levels in PPVL (14.15 vs. 13.08 ?g/dL, p ?< ?0.001) and BDL (13.20 vs. 12.39 ?g/dL, p ?= ?0.097) animals, and significantly increased mean corpuscular hemoglobin concentrations (PPVL: +9%; BDL: +15%). Thrombocytopenia only developed in the PPVL model and was alleviated in the splenectomized subgroup. Conversely, BDL rats presented with thrombocytosis, which was not affected by splenectomy.ConclusionsSplenectomy improves both cirrhotic and non-cirrhotic PH, and ameliorates the hyperdynamic circulation. Hypersplenism related anemia and thrombocytopenia were only significantly improved in the non-cirrhotic PH model.     

Flavor learning in weanling rats and its retention

The present study examined whether weanling animals can acquire associative memory for reward and retain it several weeks later. Three-week-old Wistar male rats were trained in a flavor learning task. Half of the rats received unsweetened grape-flavored water on odd-numbered days and sweetened (sucrose) cherry-flavored solution on even-numbered days. The remaining rats received sweetened grape-flavored solution on odd-numbered days and unsweetened cherry-flavored water on even-numbered days. During the acquisition session, the liquid was presented to each rat for 15 min daily for 6 consecutive days. In the following test session, each rat was presented with unsweetened cherry-flavored water and grape-flavored water simultaneously for 15 min daily for 4 consecutive days. The rats showed significant preferences for the flavor previously associated with 2% and 10% sucrose, significant aversion to the flavor associated with 30% sucrose, and no particular preference or aversion to the flavor associated with 20% sucrose, indicating a hedonic shift from positive to negative with an increasing concentration of sucrose. The association learning acquired at the age of 3 weeks was retained when re-tested in adulthood at the age of 20 weeks. In contrast to the conditioned flavor aversion associated with 30% sucrose, 20-week-old rats showed a preference for this flavor. In accordance with these learning effects, 3-week-old rats preferred 2% sucrose to 30% sucrose, and the reverse was true in 20-week-old rats. The reasons for rejection of high-concentration sucrose by weanling rats are also discussed. The present study showed that weanling rats established a conditioned flavor preference or aversion depending on the concentration of associated sucrose and retained it in adulthood, indicating that feeding experience in the weanling period is important in influencing later dietary preferences.     

SAPID Solutions and Food Intake in Repeated Dehydration and Rehydration Periods in Rats

In a previous report, it has been shown that water deprivation significantly affects the two-bottle taste preferences and one-bottle taste acceptance in rats when no food was available during tests. Since no food was available, the course of drinking was never interrupted by eating. Theoretically, if a rat faces a simultaneous choice between food and fluid, and if the course of drinking is interrupted by eating, these conditions might interfere with taste preferences, total fluid intake and eating in thirsty rats. The aims of the present experiments were: to ascertain whether food intake during both two-bottle preference and one-bottle acceptance tests in thirsty rats might be influenced by the palatability of the solutions; to verify whether the availability of food during tests influences taste preference and acceptance, and total fluid intake; to detect variations induced by dehydration on body weight and some plasma and urinary parameters that might interfere with food and fluid intake, taste preference and acceptance. Using naive rats, five groups of rats showing the same taste preferences for one of four prototypical tastes and water were selected. Then, both two-bottle preference (Expt 1) and one-bottle acceptance tests (Expt 2) were performed in rats deprived of water for either 12, 24, 36 or 48 h. The results showed that in both Expt 1 and Expt 2, inhibition of feeding and decrease of body weight during dehydration was very similar in all rats. The presence of food during the tests did not affect taste preference and acceptance. During Expt 1, after severe water deprivation (36 and 48 h), food intake was related to the palatability of the solution paired with water. When rats drank either NaCl or sucrose, they ate less food than rats drinking HCl, quinine, or water. In Expt 2, rats drinking NaCl solution as the only source of fluid ate significantly less food than all other groups. The intake of sucrose and/or NaCl solutions be may explained by two different post-ingestion effects (energetic and osmotic). Since rats drinking either sucrose or NaCl ate less food but drank more fluid, they had a significantly higher fluid/food intake ratio than that of rats who drank water, quinine, or HCl, who ate more food but drank less fluid. The increase of the fluid/food intake ratio in rats drinking sucrose or NaCl was directly correlated with the length of dehydration. Self-denial of food during dehydration may be responsible for overeating and overdrinking during the recovery period after tests. After dehydration lasting for 24 and 48 h, plasma [Na(+)], [protein], osmolality and haematocrit values increased but [K(+)] decreased. Urinary volume decreased but urinary [Na(+)] increased. These results are related to food and fluid intake, taste preference and acceptance after dehydration periods. Experimental Physiology (2001) 86.4, 489-498.     

Effects of gustatory deafferentation on ingestion of taste solutions as seen by licking behavior in rats

The role of the taste nerves in licking behavior to various taste solutions was examined in rats. The study consisted of two experiments. In the electrophysiological experiment, the whole nerve recording of the anterior palatine nerve (PN) was performed to examine the response properties of this nerve to taste stimulation applied to the taste buds in the nasoincisal duct. When the moderate concentrations of solutions were used, the PN responded best to HCl, followed by sucrose and NaCl. Quinine hydrochloride elicited the smallest response. In the behavioral experiment, the number of licks/20 sec was measured for each of the test solutions such as 0.5 M sucrose, 0.01-1.0 M NaCl, 0.03 M HCl and 0.0005 M-0.01 M quinine in normal control and experimental rats. The experimental animals received bilateral deafferentation of the PN, chorda tympani (CT) and glossopharyngeal nerve (GN) alone or in various combinations. Rats without one of the 3 taste nerves still rejected the aversive HCl and quinine solutions. However, after lesions of both CT and GN, or all the 3 taste nerves, the rats showed a significant increase in the number of licks to these aversive solutions. These results suggest that taste aversion disappears after denervation of more than 80% of the total taste buds. The interlick interval, lick duration and the amount of intake per lick did not change significantly after sections of the taste nerves in any combinations.     

Naloxone modifies sugar-water intake in rats drinking with open gastric fistulas

The effects of the opiate antagonist naloxone (NX) on fluid preference and intake were determined in rats drinking with chronically indwelling gastric fistulas. The subjects were tested both after 22.5 hr fluid deprivation, and no deprivation, with open fistulas (sham drinking), as well as with closed fistulas. Following an injection of either saline or NX (0.5–10.0 mg/kg, administered SC), or no injection, the subjects were given the choice to drink water or 10% sucrose, in a two-bottle test, for 1 hr/day. With open fistulas, and following fluid deprivation, the animals sham drank both sucrose and water, but had a strong preference for sucrose. When not fluid deprived, the same animals sham drank sucrose almost exclusively. NX significantly reduced sucrose intake by the sham drinking animals, in both the deprived and not deprived conditions, but did not modify fluid preference. These data support the idea that NX modifies affective reactivity to palatable solutions, and that NX's antidipsogenic actions are not due to feedback from post-absorptional events.