Double dissociations of the effects of amygdala and insular cortex lesions on conditioned taste aversion, passive avoidance, and neophobia in the rat using the excitotoxin ibotenic acid

The results in this article show that although electrolytic amygdala lesions disrupt learning of a conditioned taste aversion (CTA), ibotenic acid-induced, axon-sparing lesions of the amygdala do not. However, ibotenic acid lesions of the insular cortex do disrupt learning of a CTA. Electrolytic, but not ibotenic acid lesions of the amygdala, interrupt axons running between the insular (gustatory) cortex and the brain stem/hypothalamus. It is the destruction of these projections which appear to underly CTA deficits after amygdala lesions. Other results revealed that ibotenic acid lesions of the insular cortex attenuated the reaction to the novel taste of saccharin in a familiar environment but failed to affect the ingestion of a novel food in a novel environment or passive avoidance learning. Conversely, ibotenic acid lesions of the amygdala did not affect the reaction to novel saccharin in a familiar environment but did impair both the reaction to novel food in a novel environment and passive avoidance learning. We conclude that the insular cortex is involved in reactions to the novelty and associative salience exclusively of taste stimuli, whereas the amygdala is probably more concerned with the reaction to more general aspects of novelty in the environment and in fear-motivated behavior.     

Preferences towards novel foods in Cebus apella: the role of nutrients and social influences

Information on the process of preference acquisition towards novel foods in nonhuman primates is lacking. This study aims to assess (1) whether nutrient and energy contents affect preferences towards novel foods encountered repeatedly by individuals when alone, (2) whether these preferences change after additional encounters with the novel foods, and (3) if the change is sensitive to social influences. We presented seven novel foods to 26 socially housed tufted capuchins. In Phase 1, each subject was presented individually with the 21 possible binary combinations of the seven novel foods. Afterwards, during treatment, 13 subjects received the novel foods ad libitum with their group members (social condition) and 13 subjects received the foods individually (individual condition); subjects assigned to the individual and social conditions had shown similar food preferences in Phase 1. Finally, in Phase 2, each subject was presented again with 21 binary choices between each of the novel foods. In Phases 1 and 2, the number of times each food was chosen differed among foods. In Phase 1, food preference correlated positively with glucose and fructose and negatively with total fiber content. In Phase 2, irrespective of social or individual prior experience in the treatment condition, food preference changed and became correlated with total energy content. Our results broaden the findings already available for familiar foods by demonstrating that individual experience based on the feedback obtained from novel foods guides the establishment of preferences towards them. Moreover, individual experience is sufficient to determine food preferences similar to those individuals may acquire when together with group members eating the same foods.     

Variations in food preference and consumption across the menstrual cycle

There is some evidence that food consumption changes across the menstrual cycle. However, archived studies tend to rely on self-report data and do not differentiate among types of food eaten. The present laboratory study was designed to measure women's taste preferences and specific food consumption across the menstrual cycle. Women came into the laboratory, consumed everyday foods, and rated them on taste judgment scales. The foods were weighed before and after the tasting session to determine amount eaten. After the tasting session, subjects completed several questionnaires (e.g., measures of affect, restrained eating, menstrual cycle and menstrual symptoms). Physical measurements (e.g., height, weight) were taken at the end of the session. Sweet food consumption and preference ratings were significantly higher during the premenstrual period. Consumption and ratings of other foods did not differ. There were no differences in levels of mood, obesity, or restrained eating across the menstrual cycle. Low restraint was associated with reporting fewer menstrual symptoms, in general, and slightly better mood. These results support the idea that specific taste preferences change over the menstrual cycle, and that endocrinological factors could be involved in this phenomenon.     

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.     

Polycose taste pre-exposure fails to influence behavioral and neural indices of taste novelty

Taste novelty can strongly modulate the speed and efficacy of taste aversion learning. Novel sweet tastes enhance c-Fos-like immunoreactivity (FLI) in the central amygdala and insular cortex. The present studies examined whether this neural correlate of novelty extends to different taste types by measuring FLI signals after exposure to novel and familiar polysaccharide (Polycose) and salt (NaCl) tastes. Novel Polycose not only failed to elevate FLI expression in central amygdala and insular cortex, but also failed to induce stronger taste aversion learning than familiar Polycose. Novel NaCl, on the other hand, showed patterns of FLI activation and aversion learning similar to that of novel sweet tastes. Possible reasons for the resistance of Polycose to typical pre-exposure effects are discussed.     

The role of conditioned taste aversion in the suppression of food intake by estradiol

In three experiments, ovariectomized rats were given a familiar or novel diet prior to treatment with a brain-enhanced estradiol-chemical delivery system (E2-CDS, 1 mg/kg). Experiment 1 showed that food intake was suppressed in subjects receiving either diet, but animals given a novel diet initially showed a profound anorexia which eventually recovered to the moderate suppression of animals given the familiar diet. In Experiment 2, rats showed an aversion to a novel diet paired with the E2-CDS in a two-choice preference test given on Day 2 after the injection, indicating that the initial large reduction in intake was mediated by a conditioned taste aversion. However, no aversion was observed seven days after the E2-CDS, suggesting that the residual intake suppression was mediated by unconditioned aversion or appetite suppression. Experiment 3 showed that lengthening the postovariectomy time resulted in a taste aversion that persisted for a longer duration.     

Microstructural analysis of chlordiazepoxide's effects on food preference behavior in roman high-, control- and low-avoidance rats

The effects of chlordiazepoxide (CDP) on feeding performance and on rearing activity were investigated using a food preference test in three Roman strains: Roman Low Avoidance (RLA), Roman Control Avoidance (RCA), and Roman High Avoidance (RHA). The aims of the study were to assess the responses of the three strains to a free choice of familiar and novel foods following a period of food deprivation, and to answer the important psychopharmacogenetic question of whether or not the strains would display differential responsivity to CDP challenges. No strain differences were discovered in relation to the latency to begin feeding, the response to familiar food, or the frequency of rearing in the 10 min food preference test. However, clear differences did emerge in relation to the animals' responses to novel foods. In contrast to the RCA and RHA lines, RLA rats sampled a greater variety of the available foodstuffs, and devoted a greater duration to the consumption of novel foods. Despite previous reports that under conditions of mild stress, RLA animals display greater emotionality, there was no evidence from the present study to show that RLA animals were more neophobic (a possible index of emotionality) than the other two Roman lines. Indeed, the evidence clearly suggests that RLA animals may under certain circumstances pay greater attention to novel cues. CDP treatments produced reductions in rearing, reductions in eating latency, and strongly potentiated the time devoted to feeding. Effects of CDP treatments on familiar and novel foods were dissociable. CDP at 10 mg/kg reliably increased the novel food feeding duration, an effect occurring mainly within the first 5 min of the test.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential effects of electrical stimulation of amygdala, caudate-putamen or substantia nigra pars compacta on taste aversion and passive avoidance in rats

The effect of unilateral, low-intensity subseizure electrical stimulation of the basolateral nucleus of the amygdala (ABL), caudate-putamen (CD) or substantia nigra pars compacta (SNC) on the acquisition and retention of a conditioned taste aversion and a step-down passive avoidance response were compared in two separate experiments. In Experiment 1 electrical stimulation of the ABL while rats were drinking saccharin prior to poisoning with LiCl disrupted conditioned taste aversion. Stimulation of the CD or SNC had no disruptive effect on taste aversion. In contrast, stimulation at all 3 brain loci disrupted the retention of a passive avoidance response in Experiment 2. The implications of these data for the hypothesis of dual neural control systems for shock avoidance behavior and taste aversion, are discussed.     

Estrogen increases the taste threshold for sucrose in rats

Anecdotal and empirical evidence suggests that females' preferences for sweet foods are affected by hormonal fluctuations across the reproductive cycle. In rats, the preference for sweet foods may involve estrogen-mediated changes in response to the taste of sweets. Our recent work showed that ovariectomized female rats lick less to dilute sucrose solutions when given estrogen than when given the oil vehicle. These findings suggest that estrogen decreases the preference for less concentrated sucrose solutions; however, an alternative explanation is that estrogen interferes with the ability to detect dilute sucrose solutions. To distinguish between these possibilities, we conditioned a taste aversion to 0.2 M sucrose in ovariectomized rats by pairing it with injection of LiCl and then examined the generalization of that taste aversion to 0.075 and 0.025 M sucrose solutions during estrogen or oil treatment. Oil-treated rats generalized the LiCl-induced aversion conditioned to 0.2 M sucrose to both 0.075 and 0.025 M sucrose. Estrogen-treated rats generalized the LiCl-induced taste aversion to 0.075 M sucrose but not to 0.025 M sucrose. Moreover, two weeks later, when estrogen had cleared the system, both groups generalized the aversion to both 0.075 and 0.025 M sucrose. These results show that estrogen affects the ability to discriminate dilute sucrose from water and suggest that estrogen may have short-term effects on the detection threshold for sucrose taste in rats.     

Conditioned taste preferences as a measure of brain-stimulation reward in rats

Conditioned taste preferences (CTPs) were demonstrated in rats after one, three or five pairings of a novel tasting solution with sessions of intracranial self-stimulation (ICSS). Control groups that experienced single or repeated unpaired presentations of the novel taste or the ICSS did not exhibit such preferences. Although there were no group differences in the absolute size of the CTPs, the resistance of those preferences to extinction reliably increased with the number of novel taste/ICSS pairings. A second experiment was devised to study the effects of changes in ICSS current intensity on the CTPs produced by that ICSS. There were statistically reliable differences in the CTPs produced by Low-Current and High-Current groups. A No-Current control group did not demonstrate a CTP. Taken together these data suggest that the conditioned taste preference is a learned phenomenon analogous to the conditioned taste aversion that occurs following novel taste/illness pairings. The use of the CTP paradigm as a measure of the rewarding nature of intracranial self-stimulation is proposed.     

Effects of amygdala lesions on body weight, conditioned taste aversion, and neophobia

Female rats with posterodorsal amygdala (PDA), basolateral amygdala (BLA), or sham lesions were compared regarding ad libitum food intake, weight gain, consumption of a novel food, and acquisition of a conditioned taste aversion (CTA). While only the rats with PDA lesions evidenced substantial weight gains at 10 days after surgery eating standard lab chow (25-45 g more than the other groups), only the rats with BLA lesions demonstrated significant deficits in the CTA and neophobia paradigms. Rats with basolateral lesions, on average, took less than 30 s to begin drinking the novel sweetened condensed milk after pairing with illness while the other groups took approximately 15 min to begin drinking. Also, rats with basolateral lesions ate, on average, 5 g of the novel Froot Loops while the other groups ate approximately 2 g. It is concluded that the changes in food-motivated behavioral tests frequently observed in animals with amygdala lesions do not coexist with the hyperphagia and weight gain of animals with PDA lesions.     

Mapping conditioned taste aversion associations using c-Fos reveals a dynamic role for insular cortex

Novel tastes are more effective than familiar tastes as conditioned stimuli (CSs) in taste aversion learning. Parallel to this, a novel CS-unconditioned stimulus (US) pairing induced stronger Fos-like immunoreactivity (FLI) in insular cortex (IC), amygdala, and brainstem than familiar CS-US pairing, suggesting a large circuit is recruited for acquisition. To better define the role of IC, the authors combined immunostaining with lesion or reversible inactivation of IC. Lesions abolished FLI increases to novel taste pairing in amygdala, suggesting a role in novelty detection. Reversible inactivation during taste preexposure increased FLI to familiar taste pairing in amygdala and brainstem. The difference between temporary inactivation, which blocked establishment of "safe" taste memory, and lesions points to a dual role for IC in taste learning.     

Nutritional supplementation in older adults: Pleasantness,preference and selection of sip‐feeds

Objectives: Malnourishment is common in older adults, and nutritional supplementation is used to improve body weight and well‐being. Clinical reports suggest, however, that patients routinely reject sip‐feeds. The present study examined the following questions: whether sip‐feeds are less preferred and less likely to be selected than other energy‐dense foods in healthy elders; and whether eating alone further reduces intake relative to eating in a social setting. Methods: Twenty‐one healthy older adults (aged 60‐79 years) attended the laboratory on three occasions. Subjects rated six different flavours of sip‐feed and then rated the pleasantness of the taste of the favoured flavour against five other energy‐dense familiar foods/drinks. Intake of these foods was measured when subjects ate alone or in a group of familiar others. Results: Favourite flavour of sip‐feed compared well with other more familiar foods and was selected as part of a snack. Snack intake increased by 60% when consumed in a group setting compared with eating alone. Conclusions: The study suggests that sip‐feeds are rated as pleasant and selected by free‐living elders. Rejection of sip‐feeds in hospitalized elders may relate more to loss of appetite than to the taste preference for sip‐feeds, and that eating alone rather than in groups of familiar others is likely to compound eating problems.     

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.     

Sweet and fat taste preference in obesity have different associations with personality and eating behavior

The aim of this study was to test associations between self-reported attitudes of sweet and fat taste preferences and psychological constructs of eating behavior and personality in obesity. Sixty obese patients were included. The Three Factor Eating Questionnaire was used for the assessment of psychological constructs of eating behavior, and the Swedish universities Scales of Personality was used for measuring personality traits. A strong sweet taste preference was associated with more neurotic personality traits (P=.003), in particular lack of assertiveness (P=.001) and embitterment (P=.002). Strong fat taste preference was rather related to lower levels of the eating characteristic cognitive restraint (P=.017), implying less attempts to restrict and control food intake. Whereas strong sweet taste preference was linked to a personality style in obesity, strong fat preference could be more an aspect of eating behavior. A psychobiological stress model is discussed in relation to the results on sweet preference and hampered personality functioning.     

Rats with basolateral amygdala lesions show normal increases in conditioned stimulus processing but reduced conditioned potentiation of eating

Rats with neurotoxic lesions of basolateral amygdala (ABL) and control rats showed comparable enhancement of attentional processing of a visual stimulus when its predictive value was altered. In contrast, lesioned rats showed less potentiation of eating than did control rats when food was available during presentations of a conditioned stimulus that was previously paired with food. When considered together with previous data, these results indicate a double dissociation between effects of lesions of the ABL and of the amygdala central nucleus on phenomena related to attentional processing and the acquisition of motivational value.     

Chorda tympani nerve transection alters linoleic acid taste discrimination by male and female rats

Taste is intimately associated with food choice, yet little is known about the role of taste in preferences for dietary fat, a major component of many foods. We measured the taste threshold for linoleic acid (LA), an essential free fatty acid found in dietary fat, before and after bilateral transections of the chorda tympani nerve (CTX) in adult male and female rats. We conditioned a taste aversion to 88 microM LA and assessed the generalization of the aversion to lower LA concentrations to determine LA discrimination thresholds. We discovered that female rats had a lower LA discrimination threshold (approximately 2.75 microM LA) than did male rats (approximately 11 microM LA). In another set of animals, we performed CTX and found that CTX elevated LA threshold to the same level (approximately 22 microM LA) in male and female rats. Finally, we evaluated licking responses to 11, 22, 44 and 88 microM LA mixed in sucrose by male rats and ovariectomized (OVX) female rats treated with estradiol benzoate or oil vehicle. All rats increased licking to increasing LA concentrations, but OVX rats responded to a lower LA concentration (22 microM) than did males (44 microM) in 10-s trials. However, estradiol did not affect this outcome. Collectively, these experiments show that male and female rats use taste to discriminate LA and that the chorda tympani nerve, which innervates taste buds on the anterior tongue, plays a role in this discrimination. Furthermore, sex differences in fat preferences may depend on differences in fatty acid taste thresholds as well as on the taste stimuli with which fat is combined.     

Effects of central and basolateral amygdala lesions on conditioned taste aversion and latent inhibition

The present study examined the effects of neurotoxic lesions of the central nucleus (CNA) and basolateral complex (BLA) of the amygdala on conditioned taste aversion (CTA) in a latent inhibition design. In Experiment 1, lesions of the CNA were found to have no affect on CTA acquisition regardless of whether the taste conditioned stimulus (CS) was novel or familiar. Lesions of the BLA, although having no influence on performance when the CS was familiar, retarded CTA acquisition when the CS was novel in Experiment 2. The pattern of results suggests that the CTA deficit in rats with BLA lesions may be a secondary consequence of a disruption of perceived stimulus novelty.     

Some behavioral effects of microinjections of noradrenaline and serotonin into the amygdaloid body of the rat brain

The effects of microinjections of noradrenaline (NA) and serotonin (5HT) into the basomedial part of the amygdaloid body (BM AB) on various forms of behavior were studied in rats. NA as well as 5HT administered to the BM AB had dose-related and general inhibitory influence on the rats' behavior in the open field test. The reactivity of rats to pain (tail compression) was attenuated by 5HT injections. The effect of NA in this test was less clear, though some inhibitory tendency was also present. Pretrial injections of NA (40 micrograms) and 5HT (40 micrograms) significantly impaired the retention of a passive avoidance reaction. NA injections also produced some disinhibitory effects on shock-suppressed drinking in the conflict test. The effects of intra-amygdalar administration of NA and 5HT on open field behavior were potentiated by pretreatment of rats with nialamide, a monoaminooxidase inhibitor. The results are discussed in terms of an involvement of the amydalar NA and 5HT in the regulation of animal behavior.