Enhancement of taste intensity through pulsatile stimulation

Human magnitude estimates of a 500 mM NaCl solution increased with time when alternating pulses of NaCl and H₂O (2 sec-2 sec to 1 sec-1 sec) were deliverd to the tongue, but decreased with a continuous NaCl flow. Normal human drinking, and intermittant liquid intake in other species, may be similar enhancement situations.     

Drinking in the pigeon (Columba livia) in response to water deprivation and the influence of intracerebroventricular infusions of NaCl or sucrose solutions

Pigeons were deprived of fluid for 24 hours then allowed access to water and a 2.7% NaCl solution, the intakes of both solutions during the subsequent 60 min were observed. In a second experiment hypertonic or isotonic solutions of NaCl or sucrose were infused ICV, starting 5 min before access to the solutions and finishing 10 min after access, and the consummatory behaviour observed. Pigeons rehydrated themselves after the period of deprivation with a volume of water equal to the weight lost during the deprivation. Pigeons never drank the hypertonic NaCl solution. ICV infusions of hypertonic or isotonic sucrose attenuated drinking in response to 24 hours water deprivation. Isotonic or hypertonic NaCl infused ICV, on the other hand, had no significant effect. Thus, in the pigeon, drinking in response to 24 hours of water deprivation appears to be controlled by one mechanism, possibly osmoreceptor in nature (with the permissive control of CSF sodium concentration), since the birds drank a volume of water equal to their weight loss and changes in CSF sodium concentration influenced drinking in a manner similar to that described previously for osmotically induced drinking in pigeons.     

Release of hypothalamic norepinephrine during MSG intake in rats fed normal and nonprotein diet

Effects of monosodium L-glutamate (MSG) solution (0.06 M) on interstitial levels of norepinephrine (NE) were measured in the lateral hypothalamus (LH). Wistar male rats, housed in standard operant boxes, were fed either normal or nonprotein diet for 3 days. Beside a daily bar-mediated drinking session (75 min), animals were without access to fluids. Microdialysates, collected from the LH during the 75 min of drinking, were analyzed using high-pressure liquid chromatography. No significant responses of the LH NE to the drinking of distilled water, MSG, NaCl (0.06 M), and glucose solution (0.6 M) were found in normally fed rats. However, a specific decline in LH NE release was detected during MSG solution-drinking in rats fed nonprotein diet. As MSG preference indicates protein intake, it is possible that LH NE is, at least partially, one of the brain signals that relate MSG preference to dietary protein intake.     

Focal differences in lipid metabolism of the young pig aorta. III. Influence of insulin on lipogenesis from (1-14C)acetate.

Renal medullary necrosis was produced in rats by administration of 2-bromo-ethylamine hydrobromide and the resulting functional alterations of the kidneys, such as renal handling of sodium and potassium, response to salt-loading and glomerular filtration rate, and the effects of necrosis on the systolic blood pressure were investigated.The pair-fed rats drinking either distilled water or 0.9% NaCl solution had exaggerated natriuresis during the period examined. Glomerular filtration rate measured on day 2 and week 16 was significantly reduced. In addition, experimental rats consumed a large amount of 0.9% NaCl solution.Elevation of systolic blood pressure was seen in some of the experimental rats that drank 0.9% NaCl solution.In conclusion, the renal medullary necrosis in rats either primarily or secondarily influences the function of the kidneys. The renal medullary necrosis per se appears to have little effect on the systolic blood pressure unless it is coupled with NaCl loading.     

Taste avoidance, but not aversion, learning in rats lacking gustatory cortex.

Control rats rapidly learned to avoid drinking either a sucrose solution (Experiment 1) or a NaCl solution (Experiment 2) when the taste was paired with illness. These rats also produced aversive reactivity to each of these solutions in a taste reactivity test. Rats that lacked gustatory cortex (GC) learned to avoid drinking sucrose and NaCl, albeit at a slower rate than control rats. GC rats failed to display aversive reactivity to these tastes. The GC rats did show normal aversive reactivity to a strong quinine HCl solution during additional tests. It is suggested that the avoidance developed by GC rats did not entail a palatability shift of the conditional stimulus as it did in control rats. This altered learning strategy may account for the consistent learning deficits found in GC rats trained to avoid tastes.     

Effect of furosemide upon urinary kallikrein excretion

Having in mind the significant decrease of urinary kallikrein in rat with renal hypertension and in humans with essential hypertension, the effects of furosemide on kininogenase activity has been studied in urine of normal and hypertensive rats which received tap water or a 1% NaCl solution for drinking. Administration of 20 mg furosemide which produces maximal diuretic effect in normal rats, induced in these animals a 150–200% increase of the excretion of this enzyme after 8 hours, when compared to the activity measured before giving the drug. This increase which is observed in the normal rats drinking either water or a 1% NaCl solution shows a significant correlation with the excretion of sodium, potassium and water. In hypertensive rats, in 7 or 9 cases, an increase of kallikrein excretion (200–600%) is observed, which does not reach the levels of excretion in normal untreated rats. Furosemide did not produce increase of urinary kallikrein in hypertensive rats drinking 1% NaCl solution.     

Water drinking caused by intracerebroventricular infusions of hypertonic solutions in cattle

Infusions into the lateral cerebral ventricle of hypertonic solutions of NaCl, mannitol or sucrose all induced water drinking in cattle. However, infusion of hypertonic NaCl caused a significantly greater water drinking response than did the infusions of mannitol or sucrose, despite the fact that CSF osmolality increase was similar. In contrast, hypertonic solutions of NaCl or mannitol had similar dipsogenic effects when infused intravenously. The intracerebroventricular infusions of hypertonic NaCl or mannitol did not affect the intakes of food or Na solution. The results are consistent with the hypothesis that both cerebral osmoreceptors and Na sensors are involved in regulating thirst in cows.     

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.     

Liquid lost during drinking

Rats fail to transfer into their mouth all liquid removed from the drinking tube when they lick water in a licking environment which permits only the anterior portion of the tongue to contact the drinking tube. To quantitatively measure the liquid splattered during 10 sec licking trials in this high restriction licking environment, the red-dyed water observed on the surfaces of the environment was collected with 1 μl pipettes. Data were corrected for evaporation occurring before collection. Median volume lost per lick was 0.07 μl, corresponding to 1.2% of the median initial volume removed by a lick, 5.88 μl. Such loss can probably be considered negligible. Consequently, estimates of lick-volume parameters which are based upon amount of liquid removed from a drinking tube reservoir divided by number of licks, can have almost 1% accuracy.     

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.     

Increased and decreased preference for saccharin immediately following injections of various agents

Rats pretrained for preference testing and injected with LiCl showed a reduction of saccharin preference in a test with a novel saccharin solution paired with water given 15 min following the injection. Previous exposure to the saccharin solution precluded this selective depression of drinking. In a second experiment, using rats naive to saccharin, insulin injection produced an increase, 2-DG and hypertonic NaCl produced a decrease, and saccharin injection produced no change in saccharin preference.     

Depression of lingual tactile sensation during chemical stimulation of the human tongue

The subjectively estimated magnitude of human tactile sensation elicited by tapping the tongue was depressed during taste stimulation by 3 and 6% NaCl solution, 0.1% quinine and 0.5% acetic acid. No significant change in the tactile sensation occurred during flow of 2–20% sucrose solution. The result may be attributed to presynaptic inhibition exerted by gustatory onto lingual tactile afferents.     

The relation of feeding and activity following septal lesions in rats

The patterns of intake of liquid diet and water were recorded in diet-deprived rats with septal lesions and neurologically intact controls during the first hour of diet access. The occurrences of grooming, resting/sleeping, and exploring were also recorded. Both groups of rats consumed similar amounts of diet in one meal during the 1-hr diet access period. Control rats consumed the meal in one prolonged bout of eating, whereas rats with septal lesions consumed the meal in numerous small bouts of eating. Rats with septal lesions were active for longer periods, exhibiting continuous alternation of brief bouts of eating, drinking, exploring, and resting throughout the meal. In tests in which water was not available during the diet access period, both groups of rats increased their intrameal bout size, but rats with septal lesions still showed much smaller bouts of ingestion than did controls. These data suggest that the small-bout pattern of ingestion may reflect a general disruption in the control of behavioral sequences, rather than processes uniquely related to the regulation of eating or drinking.     

The influence of central infusions on drinking due to peripheral osmotic stimuli in the pigeon (Columba livia)

The drinking responses of pigeons infused simultaneously IV (0.334 ml/min) and ICV (2 microliters/min) for 15 min with various osmotic solutions were observed during, and for 60 min after, the combined infusions. Drinking in response to IV infusion of 0.5 M NaCl or 1.0 M sucrose was unaffected by simultaneous ICV infusion of 0.15 M NaCl, enhanced by ICV 0.3 M NaCl, inhibited during the infusion of water ICV and attenuated by ICV infusion of 0.9 M sucrose. Drinking in response to IV infusion of 1.0 M NaCl or 1.5 M sucrose, two solutions that would have greatly increased CSF sodium concentration, was only slightly affected by simultaneous ICV infusions of NaCl, sucrose or water. These results show that drinking following IV administration of osmotic stimuli can be affected by ICV infusions that may have further increased or decreased CSF sodium concentration thereby suggesting that CSF sodium concentration may play a "permissive role" in osmotically induced drinking.     

Oral irritation by sodium chloride: sensitization, self-desensitization, and cross-sensitization to capsaicin

Psychophysical methods were used to investigate the irritant sensory properties of concentrated NaCl. The first experiment investigated potential sensitization and desensitization properties. Subjects rated the intensity of the irritation elicited by 10 successive applications of 5 M NaCl on one side of the dorsal surface of the tongue. The mean irritant sensation increased significantly across trials, consistent with sensitization. To test for self- and cross-desensitization effects of unilateral sequential stimulation with NaCl followed by a 10-min rest period, either 5 M NaCl or 10 microM capsaicin was applied bilaterally. In a two-alternative forced-choice (2-AFC) test, subjects indicated which side of the tongue had a stronger irritant sensation. They also rated the intensity of irritation on each side separately. When NaCl was applied bilaterally, the side not previously receiving NaCl was chosen as stronger by a significant majority of subjects and was given significantly higher intensity ratings, consistent with self-desensitization. In contrast, when capsaicin was applied bilaterally, the side that had previously received sequential NaCl was perceived as having a significantly more intense irritation, consistent with cross-sensitization. In a second experiment, the effect of amiloride on NaCl-evoked irritation was studied. One side of the tongue was treated with 1 mM amiloride, after which 5 M NaCl was applied bilaterally and subjects performed the same 2-AFC and rating procedures. Since amiloride significantly reduced the intensity of the irritant sensation, the contribution of amiloride-sensitive ionic currents or the Na+/H+ exchange pump (NHE) are suggested as possible transduction mechanisms in lingual nociceptors mediating NaCl-evoked oral irritation.     

Drinking characteristics of normal rats and rats heterozygous or homozygous for diabetes insipidus

Rats heterozygous for the mutant gene for diabetes insipidus did not drink more water than normal rats without the mutant, but did drink more of dilute quinine solutions (0.03% or less) and ingested more 3% NaCl. Heterozygous rats were the same as normal controls in regard to intake of 20% sucrose and the shape of the circadian rhythm function of drinking. In heterozygous and normal rats, but not rats, homozygous for the mutant, the addition of food deprivation to water deprivation sharply reduced drinking during a subsequent test period. Compared to heterozygous and normal rats, homozygous rats drank more water, more dilute QHCl solution (0.03% or less), but the same amount of concentrated QHCl (0.06 and 0.12%) and approximately the same amount of 20% sucrose. Homozygous rats, in spite of their renal defect, ingested less 3% NaCl than heterozygous rats, but approximately the same amount as normals. Half the homozygous rats died following the self-imposed NaCl load indicating that there is no protective taste-mediated rejection mechanism for NaCl. The circadian rhythm function of drinking was approximately the same shape for all three groups of rats, but the homozygous rats consumed a larger proportion of their daily intake during the light cycle than do the two other genotypes. Water intakes for all three types of rats are less during fasting than during ad lib feeding suggesting that a large segment of the water intakes of the 3 groups probably is utilized to facilitate the feeding and digestion of food.     

Drinking by dogs during and after running.

1. Drinking by dogs has been studied during and after running on a treadmill, and compared with the drinking produced by NaCl given by stomach tube or intravenously. 2. When water was offered with a delay of more than 5 min after the end of a run producing loss of 30-90 g water by panting, the drinking was similar to that produced by NaCl, assuming that loss of 100 g water produces the same increase in plasma sodium as 15 m-mole NaCl. It is thus possible to explain drinking with a delay after the run as due to loss of water. 3. When water was offered immediately after a run or during pauses in the running there was drinking which cannot be explained as due to loss of water. Although the immediate stimulus to drinking is small, it may cause repeated small drinks by which the evaporative loss of water during running is matched by water intake. 4. Water (10-20 ml./kg body wt.) given by stomach tube before the run reduced or abolished drinking during running. Doses of water sufficient to stop drinking did not cause an increase in urine volume. 5. From these results a figure is produced placing in order mechanisms which may contribute to the control of water balance.     

Drinking in goats as effect of simultaneous intravenous infusions of angiotensin (I or II) and hypertonic NaCl or mannitol

Drinking during the simultaneous intravenous infusion of angiotensin I (Al) or II (AII) and hypertonic NaCl or mannitol was studied in the goat, and was compared to the dipsogenic responses to the separate infusion of each of these four factors. Approximately the same amount of water was drunk during the infusion of AI/NaCl, AI/mannitol and AII/NaCl. The amount was roughly equal to the sum of the amounts taken when each of two paired stimuli was infused separately. Significantly less water was drunk in response to AII/mannitol. Somewhat more water was drunk during the separate AI than during the separate AII infusion. Administration of an AI converting enzyme inhibitor completely abolished the AI contribution to drinking during the AI/NaCl infusion but did not reduce AII/NaCl drinking, indicating that the response to Al was entirely due to its conversion into AII. The possibility is discussed that the considerable difference between AI/mannitol and AII/mannitol drinking might have been the result of choroidal and/or ependymal AI converting enzyme activity.     

Ontogeny of renin-induced salt appetite in the rat pup

Intracerebroventricular injections of renin in suckling rat pups increased intake of NaCl solutions when they were orally infused 5 hr after injection. The appetite for saline solution was evident in pups as young as 3 days, was greater in females, and was specific insofar as intake of milk, either by suckling or by oral infusion, was not affected. Three-day-old pups increased intake only to 12% NaCl, the acceptable concentration of NaCl becoming lower in older pups. These results suggest, first, that, as is true for feeding and drinking, the brain mechanism for salt appetite is competent for expression of the behavior in the very young rat pup, and second, that its angiotensinergic neural substrate is distinct from that which mediates the dipsogenic effect of the hormone.