Genetic influences on saccharin preference of mice

Preference for a 0.1% solution of sodium saccharin was assessed in a two-bottle, saccharin versus water, preference test. Animals were adult mice from four inbred strains (BAlb/cJ; C57BL/6J; I^s/Bi; 101BAg/Rl), both reciprocal F₁ crosses of BAlb with C57, and a hetergeneous generation formed by crossing F₁ with wild trapped mice. Individuals from the 101 strain demonstrated no preference for saccharin or water while the other inbred strains preferred saccharin. No sex or maternal effect was detected. Heritability (h²) and coefficient of genetic determination (CGD) was estimated by alternative methods. The CGD was between 0.81 and 0.94 ± 0.024; h² = 0.55 to 0.68. This high degree of genetic involvement suggests that genotype is a major determinant of individual differences in saccharin preference.     

Saccharin aversion in the rat following adrenalectomy

Changes in saccharin preference as a function of concentration were studied in rats after either adrenalectomy of sham surgery. A 48 hr two-bottle preference test was used. Under two different sets of testing conditions, adrenalectomized animals rejected saccharin solutions at concentrations that were highly acceptible to controls and did not show an appetitive behavior towards andy of the concentrations tested. This aversion pattern persisted even when preference tests were conducted for as long as 10 days. However, it was abolished when the adrenalectomized rats wre exposed to saccharin for 6 days prior to surgery, or when they were administered the glucocorticoid dexamethasone. Results are discussed with respect to the effects of adrenal hormones on sensory systems and to taste-aversion learning.     

Diminished taste reactivity to saccharin following chronic administration of theophylline in rats

Under a successive increase in the concentration of saccharin adulteration, a dual effect of facilitation and inhibition on food intake was observed in normal rats. At low concentrations (0.25 to 1.5%), saccharin adulterated diets were more acceptable than the normal one with a peak at 1.0% concentration. Food intake was conversely suppressed at a high concentration (3.0%). On exposure to either 1.0 or 3.0% saccharin diet, this facilitatory or inhibitory effect disappeared with chronic administration of theophylline. This diminution of acceptance or rejection response to saccharin was interpreted to be an impairment of taste discrimination induced by theophylline.     

Protein synthesis inhibition and amnesia for saccharin aversion memory in rats after intra-cisternal administration of cycloheximide

The series of experiments reported further investigated the time course relationship of the amnesia for saccharin aversion memory in rats and the inhibition of protein synthesis resulting from cycloheximide (CXM). The first experiment showed that intraventricular CXM injected rats which had been trained 7 hrs after injection had learned the contingency under a considerable inhibition of protein synthesis. However, 1 hr after CXM injection protein synthesis inhibition was 86% and yet there was no amnesia observed 24 hr after training. It was also apparent that there were no marked regional differences in the extent of protein synthesis inhibition after intraventricular CXM. Finally, intracisternal injection of CXM 1 hr before training resulted in amnesia 24 hrs after training although this effect was greater when the injection was performed 7 hr before training. The findings (1) are consistent with Day et al's [4] suggestion of maximal protein synthesis inhibition at 1 hr post CXM injection with an approximately linear decline thereafter, and (2) provide no support for the involvement of the brain stem nucleus solitarius in taste aversion learning.     

Conditioned saccharin aversion development following administration of hypotensive agents

Conditioned aversion was demonstrated in the rat following the pairing of 0.1% saccharin solution with intragastrically administered levo-α-methyldopa and hydralazine. Conditioned aversion was not observed following pairing of saccharin ingestion with intragastrically administered hydrochlorothiazide (maximum dose, 100 mg/kg). These data suggest that some hypotensives can condition an aversion. The data were interpreted as supporting a role for post-ingestion malaise or gastrointestinal illness in the clinically common observation of drug defaulting with hypotensive drugs.     

Comparison of circadian susceptibility to LiCl-induced taste aversion learning between preweanling and adult rats

Preweaning rats (18 days old) exhibited a definite circadian susceptibility to a LiCl-induced conditioned taste aversion with maximal susceptibility at the time just preceding light offset. Using the same procedure adults conditioned more readily during the light than the dark but appeared to be equally susceptible at all points examined in their light phase. Similiar dose-response conditioning curves were generated at each time of testing for both ages suggesting that the subjects' perceived intensity of LiCl's effects was not rhythmically altered.     

A detailed analysis of glucose and saccharin drinking in the rat

The drinking patterns of six adult male rats were monitored in an attempt to identify those parameters that change when rats are shifted from drinking water in a two bottle preference test, to a water vs glucose and saccharin solution preference test. Access to the palatable G and S solution not only increased total daily fluid intake relative to water, but disrupted the pattern established during water vs water baseline conditions by increasing the frequency and duration of drinking. Fluid intake per lick, and local licking rate were unaffected by the shift to the solution. A return to water vs water conditions demonstrated that all of these parameters were recoverable.     

Effect of gonadectomy on taste preference for glucose solutions in rats.

Mature male and female rats maintained on an ad lib diet were given a choice between tap water and glucose solutions of different concentrations (1, 5 and 12 percent). Both sexes exhibited a definite preference for the 12 percent glucose solution, but the females drank significantly more than males. Gonadectomy produced neither quantitative nor qualitative changes in the choice made by male rats. On the contrary, gonadectomized females showed a depression of the 12 percent glucose solution intake and an increase in the 5 percent glucose solution intake, resulting in a decrease of the total fluid intake. A comparison of ovariectomized and intact female rats in regard to the self-selection of tap water and a 5 percent glucose solution confirmed the stimulatory effect of ovariectomy on the 5 percent glucose solution intake. When a choice between tap water and 12 percent glucose solution was permitted the ovariectomized rats showed a weaker positive response to the sweet solution than the intact female rats.     

Reactivity to different saccharin concentrations as a function of testing procedure and alterations in body weight of intact and oophorectomized female rats

Two studies compared saccharin preference in oophorectomized and intact rats. Using a one bottle test, reliable preference difference between surgical groups were found at 0.1%, 0.4% and 0.75% saccharin concentrations. Using a two bottle test, reliable preference differences were found at the 0.4% and 0.75% concentrations. Although several differences were weight related, neither Marks' nor Zucker's hypotheses were supported.     

Role of novelty in the aversion for increasingly concentrated saccharin solutions

In Experiment 1, the role of novelty in the aversion response to increasingly concentrated flavored solutions was determined by repeatedly testing independent groups with 0.15, 0.5, 1.0, 2.0, and 3.0% saccharin. Initially, intakes quickly declined with increasing saccharin concentrations. However, animals drank more as they gained familiarity with the saccharin flavors, and their aversion to the more concentrated solutions became considerably attenuated. In Experiment 2, each animal was tested with 0.15, 0.5, 1.0, 2.0, and 3.0% saccharin in an irregular order following training with one of the saccharin solutions. Animals extensively familiarized with the high saccharin concentrations prior to the test sessions showed much less aversion to these solutions than animals for which the high saccharin concentrations were novel. These results demonstrate that the aversion response to increasingly concentrated flavored solutions is in part a function of the relative novelty of the flavors, and suggest that adequate control of relative novelty is necessary in studies of other variables regulating intake.     

Effects of periodic withdrawal on ethanol and saccharin selection in rats

When rats with continuous access to water are given periodic access to ethanol solutions, selection of the ethanol solutions is considerably higher than if the solutions of ethanol are continuously available. In Experiment 1 the same effect was demonstrated with solutions of sodium saccharin, thus showing that the basis of the effect is not related to the particular metabolic, intoxicating, or addictive properties of ethanol. In Experiment 2 the effects of periodic withdrawal on the selection of ethanol and sodium saccharin solutions were directly compared and several manipulations of the schedule of availability had the same effect in both the ethanol and sodium saccharin conditions. The results of Experiments 2 indicated that the basis for the facilitatory effects of periodic withdrawal on the selection of sapid solutions is a taste-related inhibitory factor which develops with consumption of a flavored substance and dissipates over periods when the substance is not consumed. Thus, selection is greater under conditions of periodic availability because of the lack of inhibition. This working hypothesis can not only account for the effects of periodic withdrawal but is also applicable to the alcohol-deprivation effect and the saccharin-elation effect, 2 phenomena which appear to be specific instances of the effects of periodic availability.     

Effects of water deprivation and prior LiCl exposure in conditioning taste aversions

The phenomenon of attenuated taste aversion conditioning following preexposure to a lithium chloride UCS was demonstrated in Experiment 1. The amount of fluid consumed during the preconditioning phase was shown to be a factor in the degree of attenuated conditioning. The pharmacological properties of LiCl, and the effects of either ad lib or restricted fluid intake in conjunction with state dependent variables were proposed to account for the results. In Experiment 2 the water scheduling and LiCl habituation procedures of Experiment 1 were replicated, and serum lithium was assessed in the various groups on conditioning day. The groups did not differ, ruling out an incremental illness hypothesis of attenuated conditioning.     

Peripheral ghrelin enhances sweet taste food consumption and preference, regardless of its caloric content

Aims

Ghrelin is one of the most potent orexigens known to date. While the prevailing view is that ghrelin participates in the homeostatic control of feeding, the question arose as to whether consummatory responses evoked by this compound could be related to search for reward. We therefore attempted to delineate the involvement of ghrelin in the modulation of non-caloric but highly rewarding consumption.

Methods

We tested the effect of intraperitoneally injected ghrelin on the acceptance and preference for a 0.3% saccharin solution using single bottle tests and free-choice preference test procedures in C57BL6/J mice, as well as in mice lacking the ghrelin receptor (GHSR1a −/−) and their wild-type (WT) littermates.

Results

In the single bottle tests, peripheral ghrelin consistently increased the consumption of saccharin, independently of availability of caloric food. In the free-choice preference test procedures, ghrelin increased the preference for saccharin in WT mice, while it did had not effect in GHSR1a −/−animals, indicating that the ghrelin receptor pathway is necessary to mediate this parameter.

Conclusions

Peripheral ghrelin enhances intake and preference for a sweet food, regardless of whether the food has caloric content. This effect, mediated through the ghrelin receptor pathway, may serve as additional enhancers of energy intake.     

Differential orexin/hypocretin expression in addiction-prone and -resistant rats selectively bred for high (HiS) and low (LoS) saccharin intake

Rats that have been selectively bred for high (HiS) saccharin intake demonstrate elevated drug-seeking behavior in several phases of addiction compared to those bred for low (LoS) saccharin intake. HiS rats also consume greater amounts of highly palatable substances compared to LoS rats; however, little is known about the neurobiological substrates moderating the divergent behaviors found between the HiS and LoS lines. Orexins are neuropeptides that have been implicated in the conditioned cue aspects of drug abuse and overconsumption of palatable substances, and differential orexin activity in the HiS and LoS phenotypes may enhance our understanding of the close relationship between food and drug reward, and ultimately food and drug addiction. The lateral hypothalamus (LH) and perifornical area (PFA) are brain regions that have been implicated in regulating feeding behavior and addiction processes, and they contain orexinergic neurons that project broadly throughout the brain. Thus, we investigated orexin and c-Fos expression in the LH and PFA using immunohistochemistry in HiS and LoS rats following either control or cocaine (15 mg/kg) injections. Results indicated that HiS rats have higher orexin-positive cell counts compared to LoS rats in both the LH and PFA, regardless of cocaine (vs. saline) treatment. In contrast, neuronal activity indicated by c-Fos expression did not differ in either of these brain areas in HiS vs. LoS rats. These results suggest that the orexin system may be involved in aspects of genetically-mediated differences in vulnerability to compulsive, reward-driven behaviors.     

Contingent and non-contingent actions of sucrose and saccharin reinforcers: effects on taste preference and memory

Preference curves were generated by comparing 14 concentrations each of sucrose and saccharin in a 20-minute test in which rats were presented with a choice of a sweet solution and water. The most preferred concentration and one concentration above and one below the most preferred for both substances were studied further. The sucrose and saccharin solutions were contingently paired with novel flavors in a conditioned taste preference (CTP) paradigm. All of the sweet solutions enhanced the animals' subsequent conditioned taste preferences for the flavors. The lack of difference between the effects of the solutions in this paradigm suggest that they had similar rewarding values and that CTP's are established mainly on the basis of taste cues. In another experiment, post-training ingestion of sucrose solutions, injection of glucose and, to a much lesser extent, ingestion of saccharin solutions retroactively and non- contingently improved retention of a previously formed, classically conditioned association. The results indicated that this effect was mainly due to the post- ingestional effects of the sucrose solutions, although taste factors also had a slight influence. This series of experiments parallels previous findings with self-stimulation as the reinforcer. The results support the hypothesis that reinforcers have a dual action on behavior: the elicitation of affective states that, when paired with environmental stimuli, can influence future behavior towards those stimuli; and a non-contingent retroactive enhancement of retention of previously formed associations.     

Taste preferences in rabbits for acids, sucrose, saccharin and quinine.

Taste preferences of adult rabbits were investigated using a 4-hr two-bottle testing situation. Tastants presented for choice against double-distilled water included several concentrations each of citric, acetic and ascorbic acids and 2 concentrations each of sucrose, sodium saccharin, and quinine hydrochloride. Increasing concentrations of acids resulted in decreasing preferences. Sucrose was significantly preferred, and quinine rejected, to a degree comparable to results obtained in another laboratory using a 24-hr, two-bottle procedure [4]. Saccharin preferences were not exactly equivalent in the 2 studies. It is concluded that rabbits are not unlike other mammals in their rejection of sour taste stimuli and that results obtained in different laboratories may have validity across different breeds of rabbits and different testing durations.     

NaCl preference and water intake effects of food availability in median eminence polydipsia

Lesions in the median eminence (ME) produce a well-known neurological model of polydipsia and polyuria in rats. The effect of food availability (ad lib/deprivation) on the polydipsic/polyuric behaviour of animals was tested. As expected, all lesioned rats developed strong polyuria and polydipsia during the first postoperative 24 h. This effect was maintained during day 2 when food was available ad lib (experiment A), but both polyuria and polydipsia were abolished when animals were deprived of food during the next 24 h (day 3). Animals deprived of food from the first post-operative day (experiment B) showed a significant reduction in the initial polyuria and polydipsia (day 1) on day 2, but these effects were again observed on day 3 when food was available ad lib. Finally, when food-deprived animals were able to choose between a 1.5% sodium chloride solution and water (experiment C), they preferentially chose (82% of total liquid consumed) the hypertonic saline solution (day 1); during the next 24 h (day 2), when only water was available, the polyuric/polydipsic effect was abolished but returned when food became available ad lib on day 3. Hence, the polyuria/polydipsia effect produced by ME lesions appears to be consistent during the first 24 h but might later be related to the availability of standard food and is completely abolished under food deprivation conditions. Preference for the hypertonic solution supports the volemic component of this syndrome and demonstrates the need for appropriate amounts of hypertonic nutrients to be consumed during the first 24 h.     

Comparative effects of lesion of the basolateral nucleus and lateral nucleus of the amygdaloid body on neophobia and conditioned taste aversion in the rat

The effects of bilateral lesions of the basolateral and lateral nuclei of the amygdala on the neophobic response and LiCl-conditioned taste aversion to a saccharin solution were studied in rats. Compared to intact animals, rats with basolateral lesions did not exhibit neophobia to the novel stimulus, while rats with lateral lesions demonstrated an initial preference to the sweet solution over water. The LiCl-induced aversion was suppressed after basolateral lesions and was unchanged after lateral lesions. It is concluded that these two amygdaloid nuclei play an important but distinct role in neophobia and conditioned taste aversion.     

Taste preferences in a free-choice situation following electrical stimulation and lesion of septal area in rats

In the present study, electrical stimulation of medical or laternal septal areas and total or restricted lesions of these were conducted to observe the effect on ingestion of primary taste solutions in a free-choice situation. Stimulation induced a specific decrease in the intake of NaCl solution and had no effect on saccharin, acetic acid and quinine solutions and water. Total septal lesion or restricted lesions of medial or lateral septal areas induced hyperdipsia in rats. The lesioned rats, in a free-choice situation preferred NaCl, saccharin, as well as acetic acid solutions. This increase in acetic acid intake after lesion suggests that sour taste is also affected. Furthermore, there was no consumption of quinine solution before and after the lesion. This might be due to the presence of sweet tasting saccharin solution in this free-choice situation. These results indicate that the septal area causes aversion to NaCl intake, probably by inhibiting lateral hypothalamic neurons responsible for NaCl ingestion. The consumption of large quantities of saccharin, NaCl and acetic acid after the septal lesion suggests that the rats become overresponsive to taste factors in a free-choice situation.     

Ontogeny of urine preference and its relationship to NH4Cl preference and sodium hunger in suckling rat pups

We chart the postnatal ontogeny of urine preference in the suckling rat. Twelve-day-old sucklings, when offered urine, NH4Cl, or NaCl, ingest more urine and NH4Cl than NaCl. When rendered sodium hungry by ivc renin or by sodium depletion, these sucklings prefer urine and NH4Cl to NaCl, dilute urine, or an NaCl and KCl mineral mix equimolar to urine; however, by 18 days of age, urine and NH4Cl are no longer preferred to NaCl. Hence, urine preference in the suckling may be specific and preparatory for the variety of purposes urine preference serves in the adult rat, and it might guide the pup to urinary sodium in the nest. Since preference for urine and NH4Cl covary during postnatal development, the high preference for NH4Cl in midterm sucklings might be because its ammonium flavor is similar to urine.