Taste reactivity as a dependent measure of the rapid formation of conditioned taste aversion: A tool for the neural analysis of taste-visceral associations.

Investigated the ability of animals to form taste aversions following neural manipulations. In Exp 1, 10 rats received intraoral infusions of sucrose every 5 min starting immediately after the injection of LiCl. 12 controls were injected with NaCl. Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected Ss decreased their ingestive taste reactivity over time; aversive behavior increased. Controls maintained high levels of ingestive responding and demonstrated virtually no aversive behavior following sodium injection. Ss were tested several days later for a conditioned taste aversion (CTA). Rats previously injected with lithium demonstrated significantly more aversive behavior than controls. Exp 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, difference in the ingestive behavior was observed. In Exp 2, naive rats were injected with NaCl or LiCl but did not receive their 1st sucrose infusion for 20 min. Ss also received infusions at 25 and 30 min postinjection. There were no differences in the task reactivity behavior displayed. Rats dramatically changed their oromotor responses to sucrose during the period following LiCl administration, provided the infusions started immediately after injection, a change attributable to associative processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some effects of conditioned aversion on food intake and olfactory bulb electrical responses in the rat

Rats maintained on an unadulterated synthetic food, available from 8 a.m. to 10 a.m. everyday, were submitted to an aversive conditioning schedule on which a first ingestion of eucalyptol-flavored food (EF) was followed by an apomorphine injection (20 mg/kg, ip). In the first experiment the daily food intake was measured from Day 1 to 17, during the first and second hours of the meal. The EF was offered on Days 8, 9, and 17 during the first or the second hour of the meal (Series B or A). On Day 8, the meal was followed in a group of rats by the apomorphine injection. As compared with the intake of Day 8, the mean EF intake of Day 9 was significantly decreased in Series A and B, and of Day 17 in Series A only. No significant EF-intake modification could be observed in a saline-injected group or in an untreated control group. In the second experiment, rats bearing bulbar electrodes for the chronic recording of multiunit mitral cell responses received a 2-hr EF meal before the apomorphine injection. They were stimulated by puffs of odors of pure eucalyptol, unadulterated food, and EF and recorded in hungry and satiated states. Before the aversive conditioning, a significantly greater occurrence of positive responses to the odors of unadulterated food and EF was observed in hungry rats compared with satiated rats. The eucalyptol odor yielded equivalent patterns of responses in hungry and satiated rats before and after conditioning. Conditioning did not alter the modulated responses to unadulterated food odor (a greater occurrence of positive responses was still observed in hungry rats) but modified the responses to the odor of EF (the same high rate of positive responses was then observed in satiated and hungry rats). Electrophysiological data are discussed in terms of palatability changes and food-odor meaning.     

Perceptual characteristics of the amiloride-suppressed sodium chloride taste response in the rat.

Assessed the contribution of amiloride-sensitive membrane components to the perception of NaCl taste using a conditioned taste aversion procedure with 8 groups of adult rats conditioned to avoid either 0.1M NaCl, 0.5M NaCl, 0.1M NH?Cl, or 1.0M sucrose while their tongues were exposed either to water or to amiloride hydrochloride. Differences in the acquisition of taste aversions between the amiloride- and nonamiloride-treated groups were not apparent when the conditioned stimulus (CS) was 0.5M NaCl, 0.1M NH?Cl, or 1.0M sucrose. Although the magnitude of the 0.5M NaCl aversion was similar between amiloride- and nonamiloride-treated Ss, the perceptual characteristics of the CS differed between groups. Amiloride-treated Ss avoided monochloride salts after conditioning to 0.5M NaCl but not nonsodium salts or nonsalt stimuli. Ss not treated with amiloride only generalized the 0.5M NaCl aversion to sodium salts. The "salty" taste of NaCl is related to the amiloride-sensitive portion of the functional taste response in rats. The portion of the NaCl response insensitive to amiloride has "sour-salty" perceptual characteristics and is not perceived as being salty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sodium homeostasis in chronic decerebrate rats.

Two experiments examined physiological and behavioral concomitants of sodium need in supracollicularly transected and pair-fed intact male Sprague-Dawley rats. Chronic decerebrate Ss, like intact Ss, reduced their urine sodium output when placed on a sodium-deficient diet. Similarly, 24 hrs after sodium loading, decerebrate and intact Ss excreted comparable levels of the excess sodium. In the 2 hrs immediately following loading, decerebrate Ss excreted less sodium. In contrast, behavioral aspects of sodium homeostasis were completely absent in chronic decerebrate Ss. In separate experiments, intraoral intake and taste-reactivity responses elicited by intraoral infusions of NaCl were measured during sodium-replete and sodium-deficient conditions. In response to oral infusions of NaCl, intact Ss consumed significantly more and produced greater numbers of ingestive taste-reactivity responses when they were sodium deficient than when they were sodium replete. The same sodium-depletion treatments in chronic decerebrate Ss, however, altered neither the intraoral intake of NaCl nor the frequency of NaCl-elicited ingestive taste-reactivity responses. Results suggest that the behavioral compensatory responses that follow changes in the internal sodium state depend on forebrain mechanisms. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motivational state regulates the content of learned flavor preferences.

Rats acquired a preference for an aqueous odor (almond) presented in simultaneous compound with sucrose. Separate presentations of saccharin reduced this preference in rats with ad-lib access to food during training or at test, but not in rats that were hungry during both training and test. In contrast, separate presentations of sucrose reduced the preference for the almond irrespective of deprivation state during training and test. We interpret the results to mean that a hungry rat forms odor–taste and odor–calorie associations, and its motivational state on test determines which of these associations controls the preference. In contrast, a rat that is not hungry during training only forms an odor-taste association, and its performance on test is independent of its level of hunger. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Area postrema mediates the formation of rapid, conditioned palatability shifts in lithium-treated rats.

The rapid acquisition and subsequent retention of lithium-induced conditioned changes in taste reactivity responses to sucrose were examined in rats with the area postrema (AP) either ablated or intact. On 2 conditioning days, a series of brief intraoral sucrose infusions was paired with the effects of LiCl or NaCl injections. Repeated associations of the sucrose taste with the effects of lithium significantly reduced ingestive responses and increased aversive responses only in the AP-intact group. AP-ablated rats treated with LiCl and rats injected with NaCl displayed an ingestive pattern of responses. Only the AP-intact rats, previously injected with LiCl, subsequently displayed evidence of a conditioned taste aversion. We conclude that toxin activation of the AP is required to produce the conditioned shift in taste reactivity responses and subsequent expression of a taste aversion in rats treated with lithium. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social facilitation of operant behavior in satiated rats.

Tested 24 male, Long-Evans hooded rats in 2 motivational states (hungry and satiated) and 2 social conditions (single and paired) in adjacent and communicating Skinner boxes for the effect of a social stimulus on operant behavior. The social stimulus interfered in all conditions except 1: satiated Ss paired with hungry Ss pressed the bar significantly more often than in any other condition. It is concluded that the social facilitation effect is produced by progressive changes in the motivational state of the S as well as by a set of stimuli triggering the operant behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of dietary NaCl deprivation during early development on behavioral and neurophysiological taste responses.

Investigated whether the gustatory system can be modified by restricting dietary NaCl during early development by recording neurophysiological taste responses in Sprague-Dawley rats at various times after deprivation (Exp I), and by measuring behavioral taste preferences in 3 groups of 7 NaCl deprived adult rats (Exp II). Overall findings indicate that Ss deprived of dietary NaCl from the 3rd day of gestation to 12 days postnatally and then placed on a NaCl-replete diet had chorda tympani nerve responses similar to those of nondeprived Ss when recordings were made at 28 days of age and older; however, preferences for NaCl solutions over water were significantly less than those of controls when tested at adulthood. NaCl deprivation in Ss from the 3rd day of gestation to approximately 35 days postnatally resulted in altered chorda tympani nerve responses to NaCl but not to other stimuli such as NH?Cl and KCl. Thus, it is concluded that restriction of dietary NaCl at a period in the rat's development when peripheral and central taste responses are changing results in short-term alterations in peripheral neural responses and in long-term changes in preference behaviors. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intraoral intake and taste reactivity responses elicited by sucrose and sodium chloride in chronic decerebrate rats.

Oral stimulating effects of sucrose and NaCl were assessed in chronic decerebrate and pair-fed intact control rats by measuring oral motor taste-reactivity responses (TRRs) and intraoral intake (II) volume. TRRs were videotaped during the 1st minute of the intraoral taste infusion. The infusion continued until the taste solution was rejected from the mouth, and the intake volume was computed accordingly. The number of ingestive TRRs and the volume of II consumed by pair-fed control and decerebrate rats increased with increasing sucrose concentration. Sucrose intake increased as concentration increased, then plateaued for both groups. For controls, intraoral NaCl elicited an inverted U-shaped function for both TRRs and intake. TRRs of chronic decerebrate rats varied with NaCl concentration. In contrast with controls, intake of NaCl did not differ from that of water for decerebrate rats. Data indicate that caudal brain-stem mechanisms are sufficient to control sucrose intake but not adequate for the concentration dependent intake of NaCl. Data indicate it is possible for taste-elicited oral motor responses to be dissociated from intake. Roles of taste and postingestive factors in sucrose and NaCl intake are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Restraint and internal responsiveness: Effects of placebo manipulations of hunger state on eating.

Restrained and unrestrained subjects were given a "vitamin" (placebo) prior to an ad-lib taste test. Subjects were either told nothing about the placebo or told that previous subjects had reported that the vitamin had made them feel either hungry or full. As predicted, restrained subjects, in two separate studies, behaved in accordance with placebo messages, eating more when given "hungry" messages than when given "full" messages. Unrestrained subjects showed an apparent reverse-placebo effect; they ate less ice cream when given "hungry" information than when given "full" information. Hunger ratings did not parallel eating behavior; possible explanations for this discrepancy are considered. We conclude that unresponsiveness to internal hunger state, and an overreliance on external cognitive cues, characterizes restrained but not unrestrained individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nutritive expectancies mediate cholecystokinin's suppression-of-intake effect.

In previous studies of cholecystokinin's (CCK's) effect on consumption, physical features (e.g., taste, texture, and odor) of test meals were confounded with the nutritive expectancies elicited by those features. To separately assess the role of these two factors in supporting CCK's suppression-of-intake effect, we varied the caloric expectancies elicited by a flavored test solution, while holding constant its actual caloric density, as well as all other unconditioned stimulus features. On alternate days for a 12-day period, hungry rats drank grape or orange Kool-Aid (noncaloric) mixed with a caloric 5% ethanol solution; on the other days, they drank the alternate flavor mixed with plain water. In a subsequent choice test between the flavored solutions without ethanol, the ethanol-associated flavor (Ef) was preferred over the water-associated flavor (Wf). Two days later, the rats were injected with either cholecystokinin octapeptide (CCK-8; ip, 2 μg/kg) or isotonic saline, and then given access to their Ef or their Wf for 1 hr. Consumption of the Ef was supressed by CCK-8; intake of the Wf was unaffected. These results suggest that CCK-8's effectiveness in suppressing intake of a test meal may be treated not to the unconditioned stimulus features of that meal but to the nutritive expectations elicited by those features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oral somatosensory factors in dietary self-selection after food deprivation and supplementation.

In 2 experiments with 72 male albino Sprague-Dawley rats, trigeminally deafferented Ss were subjected to nutritional stresses while being allowed to balance protein and carbohydrate intake from 3 separate dietary fractions. Partially trigeminally deafferented Ss that had recovered a normal protein ratio (protein/total intake) underwent total food deprivation (Exp I) or intragastric (IG) supplementation of protein or carbohydrate suspensions (Exp II). In response to deprivation, control Ss increased protein intake above ad-lib levels, but not carbohydrate intake. In response to IG supplementation, they decreased protein intake disproportionately more than carbohydrate intake when the fluid consisted of protein and vice versa when the fluid consisted of carbohydrate. The recovered deafferented Ss showed no selective increase in protein intake after deprivation and no differential compensation to nutrient supplementation. This suggested that recovery of the protein ratio after partial trigeminal deafferentation could not fully replace the function of trigeminal somatosensory input. The possible roles of other orosensory and of postingestional factors for recovery are discussed. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heredity and experience: Their relative importance in the development of taste preference in man.

Heritability estimates for sucrose, lactose, and sodium chloride taste preferences were uniformly low in a total of 311 pairs of monozygotic and like-sex dizygotic twins between 9 and 15 yrs of age. Black Ss preferred more concentrated solutions of all 3 tastants than did Caucasian Ss. This effect was independent of socioeconomic status in the total sample. Males preferred more concentrated solutions of sucrose and lactose than did females, but there were no sex differences in sodium chloride preference. The possibility that early intake experiences may play a role in the determination of enduring taste preferences in humans is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intraventricular injection of tachykinin NK? receptor agonists suppresses the ingestion of NaCl-associated tastes.

The present experiments evaluated whether a salty taste was required for injections of a neurokinin-3 (NK?) receptor agonist (senktide) to suppress intake or whether senktide would reduce the intake of tastes that are predictive of NaCl. During training, different groups of rats were given access to 1% almond + water, 1% almond + 0.3 M NaCl, or 1% almond + 0.1 M sucrose. On the test day, rats were administered intraventricular injections of either saline or 200 ng senktide and then given access to 1% almond + water. Senktide had no effect on the intake of the water-associated or sucrose-associated almond. In contrast, senktide significantly reduced the intake of NaCl-associated almond. Senktide had no effect on almond intake by water-deprived rats. These results show that activation of NK? receptors reduces the intake of NaCl and of a neutral taste that is predictive of sodium but not of calories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ontogeny of feeding in rats: I. Ingestive and behavioral responses to oral infusions.

Reports on 3 experiments with Charles River rat pups. When milk infusions were made through oral cannulas in the front of their mouths, 1–20 day old Ss actively ingested the diet, and their intake was related to the length of deprivation. Ss decreased their ingestive responding after they had consumed large volumes of milk. In addition, 1-, 3-, and 6-day-old Ss, when 24-hr deprived, exhibited an intense behavioral activation in response to milk infusion. The behavioral activation appeared to be stimulated primarily by taste and the opportunity to swallow. Milk infusions did not produce activation in older Ss; their behavior was more exclusively ingestive and food directed. Results demonstrate that (a) from birth, rat pups are capable of an active form of ingestion, independent of normal suckling from the mother; (b) such ingestion is controlled by physiological factors; (c) food has arousing properties in young animals; and (d) as pups grow older, their ingestive responding is refined from a generalized and nondirected activation to specific and directed feeding responses. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sodium depletion enhances salt palatability in rats.

Stereotyped fixed action patterns (FAPs) elicited in rats by oral infusions of taste solutions can be classified as either ingestive or aversive. They reflect the palatability of the taste and can be modified by learning and by the physiological state of the animal. The present 2 experiments, with 5 male Sprague-Dawley rats, demonstrated that when the physiological state of the S was altered by sodium depletion, the pattern of FAPs elicited by oral infusions of 0.5 M NaCl shifted from a mixture of ingestive and aversive components (while sodium replete) to exclusively ingestive ones (while sodium deplete). This shift in taste reactivity occurred the 1st time the Ss were made sodium deplete. A similar shift did not accompany infusions of 0.01 M HCl, a taste solution that also elicited mixed ingestive and aversive FAPs. This result suggests that the shift in response to NaCl was not due to a general change in ingestive bias or to a general taste deficit. On the basis of the change in FAPs, it is concluded that the palatability of highly concentrated salt solutions increases in sodium-deplete rats. Such a shift in salt palatability may be instrumental in directing the appetitive behavior of the animal. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acute effects of exercise or sauna on appetite in obese and nonobese men

To study the effect of exercise on appetite in men, hunger, thirst, taste perception, energy intake, and macronutrient choice were assessed in relation to exercise and to sauna; the latter was done to correct for dehydration and rise in body temperature. Since exercise is used to prevent and cure obesity, subjects included obese as well as nonobese men. Thirty subjects (25 +/- 7 years, BMI 22.8 +/- 1.6 and 28.5 +/- 1.9) were given twice, in random order before and after 2 h of cycling at 60% of Wmax, 2 h of sauna, or 2 h of rest, an ample choice from solid and liquid almost single-macronutrient food items and a taste perception test with solutions of sucrose, citric acid, NaCl, quinine, a mixture of these, and a carbohydrate electrolyte solution. After cycling as well as after sauna, in comparison to after rest, subjects lost 3 +/- 0.5% of body mass, while thirst, fluid intake, perception of sweet at relatively low concentrations, and percentage of energy coming from carbohydrate increased significantly. Only after cycling compared to after rest did perception of bitterness at a low concentration increase and hunger and energy intake decrease. We conclude that exercise induced a short-term reduction in hunger and energy intake, whereas exercise and sauna induced a short-term increase in taste perception of sweet at the lower concentration, while macronutrient preference of carbohydrate increased.     

Toxin-induced conditioned changes in taste reactivity and the role of the chemosensitive area postrema

Conditioned taste avoidances (CTAs) are an important component of behavioral regulation of ingestion. In the laboratory CTAs can be produced by pairing a novel taste stimulus with the physiological feedback produced by a toxin, such as lithium. Such toxins putatively activate a chemosensitive brainstem structure, the area postrema, which ultimately results in the production of a CTA. The present review describes a series of studies which examined conditioned changes in taste reactivity responses (TRRs) when a novel intraoral sucrose taste was paired with the effects of an intraperitoneal (IP) injection of LiCl, and the role of the area postrema in the formation of conditioned palatability shifts. It was first of all necessary to examine the effects of area postrema ablations on TRRs to a range of intraoral sucrose and quinine stimulus intensities. In the first study area postrema lesioned rats exhibited concentration dependent changes in TRRs to these taste stimuli that were very similar to those exhibited by sham lesioned rats. The second study demonstrated that 30 s intraoral infusions of sucrose (0.3 M), presented at 5 or 10 min intervals following an IP injection of LiCl (3.0 meq), resulted in conditioned changes in TRRs. These were characterized by orderly, gradual reductions in ingestive responses and increases in aversive responses. Finally, when area postrema lesioned rats (Study 3) were subjected to this conditioning procedure (brief sucrose presentations paired with the effects of LiCl) no evidence for conditioned or unconditioned changes in TRRs to sucrose were obtained. Lesioned rats injected with LiCl behaved similarly to sham lesioned rats injected with NaCl. These series of studies provide evidence indicating that the chemosensitive area postrema mediates the formation of conditioned palatability shifts induced by treatment with a toxin such as lithium.     

Contribution of the rat's neocortex to ingestive control: I. Latent learning for the taste of sodium chloride.

Conducted 3 experiments with 13 decorticate and 12 control male Sprague-Dawley rats to investigate whether some permanent ingestive control deficit would be revealed in a latent learning paradigm for salt taste. The ability of Ss to associate how they obtained the taste of NaCl when Na-replete was assessed by examining barpresses during extinction when Na-depleted. Intact Ss exposed to 4–6 hrs of NaCl taste training retained the association after decortication; decorticate Ss exposed to the same training acquired the association. Decorticate Ss exposed to as little as 2 min of NaCl taste training demonstrated the ability to associate barpressing with NaCl by their resistance to extinction. This association was specific to NaCl training. It is concluded that subcortical structures are adequate for latent learning involving NaCl taste. Conversely, previous research has shown that the neocortex is required for the retention of taste-aversion learning for the same taste. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Circadian rhythms and partial recovery of regulatory drinking in rats after lateral hypothalamic lesions.

Eight sighted male albino rats that had recovered spontaneous ingestive behavior after lesions of the lateral hypothalamus were challenged with acute injections of hypertonic NaCl administered at different times during the day-night cycle. Nine intact controls were also studied. Following these injections, drinking was observed only during the nighttime. After morning injections Ss frequently waited until nightfall before drinking, whereas Ss injected at night showed much shorter delays in the behavioral response; a similar nocturnal predominance of drinking was seen after food deprivation and in the ad-lib situation. Studies in 6 blind lesioned Ss suggest that these effects were due to an endogenous circadian rhythm. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)