Palatable Fluids Research Articles

Palatable solution overconsumption in the Cntnap2-/- murine model of autism: a link with oxytocin.

Dysregulated appetite is common in autism spectrum disorder (ASD) and it includes excessive interest in tasty foods. Overconsumption of palatable fluids has been found in the valproic acid-induced ASD rat. Though ASD has a strong genetic component, the link between ASD-related genes and appetite for palatable foods remains elusive. We focused on the CNTNAP2 gene whose deletion in mice recapitulates human ASD symptoms. We investigated whether Cntnap2-/- male mice consume greater amounts of palatable 10% sucrose, 0.1% saccharin, and 4.1% intralipid solutions offered in episodic meals either in a no-choice paradigm or a two-bottle choice test. We examined how sucrose intake affects c-Fos immunoreactivity in feeding-related brain areas. Finally, we determined doses at which intraperitoneal oxytocin decreases sucrose intake in mutants. In the single-bottle tests, Cntnap2-/- mice drank more sucrose, saccharin, and intralipid compared to WTs. Given a choice between two tastants, Cntnap2-/- mice had a higher preference for sucrose than intralipid. While the standard 1 mg/kg oxytocin dose reduced sucrose intake in WTs, a low oxytocin dose (0.1 mg/kg) decreased sucrose intake in Cntnap2-/- mice. Sucrose intake induced a more robust c-Fos response in wild-type (WT) than Cntnap2-/- mice in the reward and hypothalamic sites and it increased the percentage of Fos-immunoreactivity oxytocin neurons in WTs, but not in mutants. We conclude that Cntnap2-/- mice overconsume palatable solutions, especially sucrose, beyond levels seen in WTs. This excessive consumption is associated with blunted c-Fos immunoreactivity in feeding-related brain sites, and it can be reversed by low-dose oxytocin.

Characterization of Weight Gain and Motivation for Palatable Food in MAGEL2‐Deficient Rats

Disrupting expression of MAGEL2, part of the MAGE family, is associated with disorders such as Prader‐Willi syndrome (PWS). PWS involves changes to energy balance including hyperphagia and weight gain, but the neurohormonal mechanisms underlying these changes have not been fully elucidated. As energy balance is controlled by the central nervous system, rodent models represent an important tool in understanding the neurobiology of PWS and how gene expression changes such as MAGEL2 disruption may impact feeding, weight gain, and motivation for food. Here, we used a novel MAGEL2‐deficient rat to examine how disruption of MAGEL2 expression impacts weight gain and motivation for palatable food. We hypothesized that MAGEL2‐deficient rats would have increased body weight post‐weaning and would exhibit increased motivation to obtain palatable food. Ongoing studies suggest that, contrary to our hypothesis, MAGEL2‐deficient rats weigh less than wild type controls in the 6 weeks after weaning (p<0.05). When wild type and MAGEL2‐deficient rats were trained to lever press for a palatable sucrose solution or fat solution on a progressive ratio (PR) schedule of reinforcement, no significant genotype differences were observed for active lever responses, reinforcers earned, or breakpoint for sucrose self‐administration. For fat self‐administration, no significant effects of genotype were observed on these measures in the first day of PR testing; on a second day of PR testing, MAGEL2‐deficient rats had a lower breakpoint than did wild type counterparts (p<0.05), suggesting that they do not exhibit greater motivation to work for fat solution and may in fact be less motivated to obtain this palatable food compared to wild type rats. Interestingly, in ad libitum feeding studies, more MAGEL2‐deficient rats exhibited food hoarding than did wild type controls (p<0.05). Other studies in our lab are continuing to investigate meal patterns and palatable fluid intake in the MAGEL2‐deficient rat model. Collectively, these findings suggest that the MAGEL2‐deficient rat may be useful for assessing mechanisms of hoarding behavior in PWS, but may be less useful for examining the underpinnings of PWS‐associated weight gain as the MAGEL2‐deficient rat does not exhibit increased body weight like humans with PWS.

Time to drink: Activating lateral hypothalamic area neurotensin neurons promotes intake of fluid over food in a time-dependent manner

The lateral hypothalamic area (LHA) is essential for ingestive behavior but has primarily been studied in modulating feeding, with comparatively scant attention on drinking. This is partly because most LHA neurons simultaneously promote feeding and drinking, suggesting that ingestive behaviors track together. A notable exception are LHA neurons expressing neurotensin (LHANts neurons): activating these neurons promotes water intake but modestly restrains feeding. Here we investigated the connectivity of LHANts neurons, their necessity and sufficiency for drinking and feeding, and how timing and resource availability influence their modulation of these behaviors. LHANts neurons project broadly throughout the brain, including to the lateral preoptic area (LPO), a brain region implicated in modulating drinking behavior. LHANts neurons also receive inputs from brain regions implicated in sensing hydration and energy status. While activation of LHANts neurons is not required to maintain homeostatic water or food intake, it selectively promotes drinking during the light cycle, when ingestive drive is low. Activating LHANts neurons during this period also increases willingness to work for water or palatable fluids, regardless of their caloric content. By contrast, LHANts neuronal activation during the dark cycle does not promote drinking, but suppresses feeding during this time. Finally, we demonstrate that the activation of the LHANts → LPO projection is sufficient to mediate drinking behavior, but does not suppress feeding as observed after generally activating all LHANts neurons. Overall, our work suggests how and when LHANts neurons oppositely modulate ingestive behaviors

Palatable Flavoured Fluids without Carbohydrates and Electrolytes Do Not Enhance Voluntary Fluid Consumption in Male Collegiate Basketball Players in the Heat.

Using palatable fluids to enhance drinking in athletes who display insufficient compensatory hydration behaviour may mitigate the risks of hypohydration and performance deficits. However, it is unclear whether flavour can independently enhance fluid consumption. This study examined the effects of a colourless, artificially sweetened flavoured water (FW), without carbohydrates and with negligible amounts of sodium, compared to plain water (W) on fluid consumption in male collegiate basketball players in a practical game setting. Eighteen male basketball players (age 23.1 ± 1.3 years) played a 3v3 basketball small-sided game. The players were randomly assigned to consume either FW or W. Pre-game urine-specific gravity, fluid consumption, body mass, and hedonic taste perceptions were assessed. Basketball performance was analysed through notational analysis. Ratings of perceived exertion and thirst were recorded at pre-, post-game, and at each rest period. Heart rate was recorded throughout the gameplay. Despite significantly higher hedonic ratings for FW than W (6.78 ± 0.83 vs. 5.56 ± 1.33, p = 0.033, d = 1.36), there were no significant differences in fluid consumption (1083 ± 32 mL vs. 1421 ± 403 mL, p = 0.068, d = 0.92). Our result highlighted that using palatable fluids as a strategy to increase fluid consumption during high-intensity gameplay in the heat may not be effective if used without carbohydrates and electrolytes. Practitioners could consider both fluid palatability and composition in establishing a hydration plan for athletes.

Manipulations of Central Amygdala Neurotensin Neurons Alter the Consumption of Ethanol and Sweet Fluids in Mice.

The central nucleus of the amygdala plays a significant role in alcohol use and other affective disorders; however, the genetically-defined neuronal subtypes and projections that govern these behaviors are not well known. Here we show that neurotensin neurons in the central nucleus of the amygdala of male mice are activated by in vivo ethanol consumption and that genetic ablation of these neurons decreases ethanol consumption and preference in non-ethanol-dependent animals. This ablation did not impact preference for sucrose, saccharin, or quinine. We found that the most robust projection of the central amygdala neurotensin neurons was to the parabrachial nucleus, a brain region known to be important in feeding behaviors, conditioned taste aversion, and alarm. Optogenetic stimulation of projections from these neurons to the parabrachial nucleus is reinforcing, and increases ethanol drinking as well as consumption of sucrose and saccharin solutions. These data suggest that this central amygdala to parabrachial nucleus projection influences the expression of reward-related phenotypes and is a novel circuit promoting consumption of ethanol and palatable fluids.SIGNIFICANCE STATEMENT Alcohol use disorder (AUD) is a major health burden worldwide. Although ethanol consumption is required for the development of AUD, much remains unknown regarding the underlying neural circuits that govern initial ethanol intake. Here we show that ablation of a population of neurotensin-expressing neurons in the central amygdala decreases intake of and preference for ethanol in non-dependent animals, whereas the projection of these neurons to the parabrachial nucleus promotes consumption of ethanol as well as other palatable fluids.

Sex-specific enhancement of palatability-driven feeding in adolescent rats.

It has been hypothesized that brain development during adolescence perturbs reward processing in a way that may ultimately contribute to the risky decision making associated with this stage of life, particularly in young males. To investigate potential reward dysfunction during adolescence, Experiment 1 examined palatable fluid intake in rats as a function of age and sex. During a series of twice-weekly test sessions, non-food-deprived rats were given the opportunity to voluntarily consume a highly palatable sweetened condensed milk (SCM) solution. We found that adolescent male, but not female, rats exhibited a pronounced, transient increase in SCM intake (normalized by body weight) that was centered around puberty. Additionally, adult females consumed more SCM than adult males and adolescent females. Using a well-established analytical framework to parse the influences of reward palatability and satiety on the temporal structure of feeding behavior, we found that palatability-driven intake at the outset of the meal was significantly elevated in adolescent males, relative to the other groups. Furthermore, although we found that there were some group differences in the onset of satiety, they were unlikely to contribute to differences in intake. Experiment 2 confirmed that adolescent male rats exhibit elevated palatable fluid consumption, relative to adult males, even when a non-caloric saccharin solution was used as the taste stimulus, demonstrating that these results were unlikely to be related to age-related differences in metabolic need. These findings suggest that elevated palatable food intake during adolescence is sex specific and driven by a fundamental change in reward processing. As adolescent risk taking has been hypothesized as a potential result of hypersensitivity to and overvaluation of appetitive stimuli, individual differences in reward palatability may factor into individual differences in adolescent risky decision making.

A Phaseolus vulgaris Extract Reduces Cue-Induced Reinstatement of Chocolate Seeking in Rats

Previous evidence has suggested that treatment with a standardized dry extract of Phaseolus vulgaris reduced intake and operant self-administration of highly palatable foods and fluids in rats and mice. The present study was designed to assess whether such extract was also effective in reducing seeking behavior for a highly hedonic chocolate-flavored beverage, using a “reinstatement” procedure adopted from the drug addiction research field and modeling relapse behavior. Rats were initially trained to lever-respond for the chocolate-flavored beverage under the Fixed Ratio (FR) 10 schedule of reinforcement. Subsequently, rats were exposed to an extinction responding phase, during which lever-responding – being unreinforced – diminished progressively up to extinction. Lever-responding was then powerfully reinstated by the non-contingent presentation of a complex of gustatory, olfactory, auditory, and visual stimuli previously associated to the availability of the chocolate-flavored beverage. Acute, intragastric administration of P. vulgaris dry extract (100 and 500 mg/kg) reduced lever-responding by 40–45%, in comparison to vehicle condition. These results indicate the ability of P. vulgaris dry extract to reduce seeking behavior for a highly palatable nourishment in an experimental model of relapse into disordered eating of palatable foods. The unavailability of the chocolate-flavored beverage in the reinstatement session tends to exclude that the observed effect of the P. vulgaris dry extract was secondary to any inhibition of carbohydrate metabolism; conversely, it is the likely consequence on a central action on the rewarding and hedonic properties of food.

Gastric bypass in rats does not decrease appetitive behavior towards sweet or fatty fluids despite blunting preferential intake of sugar and fat

After Roux-en-Y gastric bypass (RYGB) surgery, patients report consuming fewer fatty and dessert-like foods, and rats display blunted sugar and fat preferences. Here we used a progressive ratio (PR) task in our rat model to explicitly test whether RYGB decreases the willingness of rats to work for very small amounts of preferred sugar- and/or fat-containing fluids. In each of two studies, two groups of rats – one maintained on a high-fat diet (HFD) and standard chow (CHOW) and one given CHOW alone – were trained while water-deprived to work for water or either Ensure or 1.0M sucrose on increasingly difficult operant schedules. When tested before surgery while nondeprived, HFD rats had lower PR breakpoints (number of operant responses in the last reinforced ratio) for sucrose, but not for Ensure, than CHOW rats. After surgery, at no time did rats given RYGB show lower breakpoints than SHAM rats for Ensure, sucrose, or when 5% Intralipid served postoperatively as the reinforcer. Nevertheless, RYGB rats showed blunted preferences for these caloric fluids versus water in 2-bottle preference tests. Importantly, although the Intralipid and sucrose preferences of RYGB rats decreased further over time, subsequent breakpoints for them were not significantly impacted. Collectively, these data suggest that the observed lower preferences for normally palatable fluids after RYGB in rats may reflect a learned adjustment to altered postingestive feedback rather than a dampening of the reinforcing taste characteristics of such stimuli as measured by the PR task in which postingestive stimulation is negligible.

Reducing effect of aPhaseolus vulgarisdry extract on operant self-administration of a chocolate-flavoured beverage in rats

Extracts from or derivatives of Phaseolus vulgaris beans reduce body weight and food intake, including highly palatable foods and fluids, in multiple rodent models of overeating and obesity. The present study was designed to assess whether a standardised P. vulgaris dry extract was effective in reducing also the operant self-administration of a chocolate-flavoured beverage. To this end, rats were initially trained to lever-press for a chocolate-flavoured beverage under a fixed ratio 10 schedule of reinforcement in daily 60 min sessions. Once lever-responding reached stable levels, the effect of a P. vulgaris dry extract on the number of lever-responses for the chocolate-flavoured beverage was determined. Pretreatment with 50, 200 and 500 mg (intragastric) P. vulgaris dry extract per kg produced an approximate 15, 35 and 40 % reduction, respectively, in lever-responding for the chocolate-flavoured beverage. These results indicate the capacity of a P. vulgaris preparation to reduce the reinforcing properties of a highly palatable fluid in rats.

18-Methoxycoronaridine: a potential new treatment for obesity in rats?

Excessive eating often leads to obesity. Although a variety of neurotransmitters and brain regions are involved in modulating food intake, a role of accumbal dopamine is thought to be critical for several aspects of this behavior. Since 18-methoxycoronaridine (18-MC), a selective antagonist of alpha3beta4 nicotinic receptors, was previously shown to alter dopamine release in the nucleus accumbens in response to chronic injections of cocaine and morphine, this drug could be a promising therapy for abnormal eating behavior. Assess the effect of 18-MC on the consumption of sucrose (15%) vs. water in a self-administration paradigm and on the intake of freely available palatable fluids (i.e., 5% sucrose, 0.1% saccharin, and 0.6% saline solutions) as well as on water intake. Determine whether repeated administration of 18-MC (20 mg/kg i.p.) affects weight gain, food intake, and fat deposition in rats drinking 30% sucrose solution. Acute administration of 18-MC (10-40 mg/kg i.p.) reduced operant responding for sucrose and decreased ad libitum ingestion of sucrose, saccharin, and saline. The highest dose of 18-MC also reduced consumption of water when palatable fluids were not available. In rats having unlimited access to sucrose (30%), chronic treatment with 18-MC (20 mg/kg i.p.) prevented sucrose-induced increases in body weight, decreased fat deposition, and reduced consumption of sucrose while not altering food intake. These data suggest that antagonism of alpha3beta4 nicotinic receptors may be involved in the regulation of intake of palatable substances regardless of its caloric value and may participate in maintaining obesity.

Chronic sucrose intake reduces the antagonist effect of β-funaltrexamine on morphine-induced antinociception in female but not in male rats

Chronic ingestion of a sweet-tasting sucrose solution enhances the pain relieving actions of opioid agonists. These results, taken in conjunction with research demonstrating that sucrose stimulates the production and release of endogenous opioid peptides, have led to the hypothesis that the effects of palatable foods and fluids on pain sensitivity are mediated by the endogenous opioid system. To assess this hypothesis, two studies determined if chronic sucrose intake would block the antagonist effects of the μ-selective opioid antagonist β-funaltrexamine (β-FNA) on morphine-induced antinociception. Female and male Long-Evans rats were maintained on chow and water, or chow, water and a 32% sucrose solution. In Experiment 1, after four weeks on the diets, female rats received 0 or 10mg/kg (subcutaneously (sc)) β-FNA, while in Experiment 2, male and female rats received 0, 5 or 20 mg/kg β-FNA. Six days later, rats were tested for morphine-induced antinociception using the hot-water tail-withdrawal test. Morphine, administered using a cumulative dose regime (1.0, 3.0, 5.6, 10.0 and 31.0 mg/kg sc), led to dose-dependent increases in tail-withdrawal latencies in male and female rats. Males were more sensitive to the pain relieving properties of morphine than females. Sucrose intake increased, while β-FNA decreased the analgesic actions of morphine in males and females. β-FNA was less effective in blocking the antinociceptive actions of morphine in sucrose-fed female rats than in females fed only chow. In contrast, diet had minimal effects on responses to β-FNA in male rats.

Sex Differences in Voluntary Fluid Intake by Older Adults during Exercise

This study compared the voluntary fluid intake behavior of older men and women (54-70 yr) when provided cold, palatable beverages and ample opportunity to drink between repeated bouts of exercise in the heat. Thirteen men and 14 women performed four bouts of 15-min cycling at 65% VO2peak followed by 15 min of rest at 30 degrees C and 50% relative humidity. In separate trials, subjects drank either a carbohydrate-electrolyte solution (CES) or water ad libitum during the rest periods and were unaware that their fluid intake was being measured. Fluid intake behavior was repeatable (intraclass correlation coefficient = 0.75), and subjects drank enough of either beverage to match sweating rates and maintain their body mass (BM). Fluid intake per kilogram of BM was greater with CES (18.7 +/- 2.2 vs 15.1 +/- 2.1 mL x kg(-1); P < 0.05), and plasma volume (PV) was better maintained during the CES trials (-1.3 +/- 1.1 vs -4.2 +/- 1.1% during the second half of the session). Women drank significantly more water than the men on a per kilogram basis (17.2 +/- 2.9 vs 12.8 +/- 1.7 mL x kg(-1) BM), and one woman (BM = 45.7 kg) became hyponatremic (S(NA) = 126 mmol x L(-1)) with symptoms during the water trial. Older adults drank enough to maintain fluid balance when palatable fluid was readily available; however, CES promoted greater voluntary fluid intake and restored PV losses faster than water. In addition, older women drank more water than men during interval exercise in the heat, which may put smaller women at an increased risk for developing hyponatremia.

Sex Differences In Voluntary Fluid Intake By Older Adults During Exercise

Older adults are particularly susceptible to fluid/electrolyte imbalances due to impaired thirst sensitivity and renal sodium- and water-conserving ability. In addition, anecdotal evidence suggests that hyponatremia, which usually occurs due to over-consumption of sodium- free fluids such as water, most commonly occurs in women; however, little data exists on actual sex-related differences in fluid intake behavior of older adults during exercise-heat stress. PURPOSE This study compared the voluntary fluid intake behavior of older men and women (54–70 yrs) when provided cold, palatable beverages and ample opportunity to drink between repeated bouts of exercise in the heat. METHODS Thirteen men and 14 women performed 4 bouts of 15 min cycling at 65% VO2peak followed by 15 min rest, all at 30°C and 50% rh. In separate trials, subjects drank either a carbohydrate-electrolyte solution (CES) or water ad libitum during the rest periods and were unaware that their fluid intake was being measured. RESULTS Fluid intake behavior was repeatable (r=0.75, p< 0.05) and subjects drank enough of either beverage to match sweating rates and maintain their body mass (BM). Fluid intake per kg BM was greater with CES (18.7±2.2 vs. 15.1±2.1 mL/kg; p< 0.05) and plasma volume (PV) was better maintained during the CES trials (−1.3±1.1 vs. −4.2±1.1% during the second half of the session). Women drank significantly more water than the men on a per kg basis (17.2±2.9 vs. 12.8±1.7 mL/kg BM) and one woman (BM = 45.7 kg) became hyponatremic (Na+ = 126 mmol/L) with symptoms during the water trial. CONCLUSIONS Older adults drink enough to maintain fluid balance when palatable fluid is readily available; however, CES promotes greater voluntary fluid intake and restores PV losses faster than water. In addition, older women drink more water than men during interval exercise in the heat which may put smaller women at an increased risk for developing hyponatremia. Funded by the Gatorade Sports Science Institute

Involvement of the Mesolimbic System in Palatability-induced Ingestion

The pleasantness of taste powerfully influences the preference for food and fluids. Particularly palatable tastes can lead to considerable overconsumption. Because palatable foods and fluids are potentially nutritive, animals are highly motivated to ingest them. The brain regions along the taste pathway and its anatomical interfacing with the brain reward system are thought to be involved in palatabilitydependent consumption (Kelley et al., 2002). However, the role of the mesolimbic system in the behavioral expression induced by taste pleasantness is still unclear. Our previous studies (Shimura et al., 2002) demonstrated that lesions of the ventral tegmental area (VTA), the origin of the mesolimbic dopamine system, selectively affected the consumption of highly palatable solutions in rats. To obtain further information concerning the mechanisms of the reward system for palatability-driven ingestion, we recorded single neuron activities from the mesolimbic system during the licking of water and taste solutions in freely behaving rats.

Influence of sweet tasting solutions on opioid withdrawal

The effect of the ingestion of palatable fluids on the suppression of opioid withdrawals in the opioid-dependent rats was studied. Physical dependence was induced by administration of morphine over a period of 6 days. Withdrawals were precipitated with naloxone (1 mg/kg, s.c.) 4 h after the last morphine injection on the 6th day. Test drugs (10–30% sucrose solution) were given orally for 2 h prior to naloxone-induced withdrawal in 14 h water deprived rats. Somatic signs of withdrawals were scored by using the global Gellert–Holtzman rating scale. Animals pretreated with low doses of sucrose solution (10–15%) did not produce any effect on the global withdrawal scale whereas a significant decrease on the global withdrawal scores was observed at higher doses of sucrose solution (20–30%) as compared to the controls. All the individual behavioral signs of withdrawals were significantly suppressed in a dose-related manner at higher doses of sucrose solutions whereas minimal suppression was observed for facial fasciculation/teeth chattering. These findings provide support that ingestion of high concentrations of sucrose solutions for shorter duration may activate the endogenous opioid system and appears to have an important role in modifying morphine withdrawals.

Palatable solutions during paradoxical sleep deprivation: reduction of hypothalamic-pituitary-adrenal axis activity and lack of effect on energy imbalance.

Paradoxical sleep deprivation (PSD) induces increased energy expenditure in rats, insofar as rats eat more but loose weight throughout the deprivation period. In the present study, rats were offered water, saccharin or sucrose to drink during the deprivation period, since it has been proposed that carbohydrates reduce the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Rats were submitted to the flower pot technique for 96 h. During the PSD period, they were weighed daily and food and fluid intake was assessed twice a day. At the end of the PSD period, rats were killed and plasma concentrations of glucose, adrenocorticotropic hormone (ACTH) and corticosterone were assayed. Compared to their control counterparts, all paradoxical sleep-deprived rats consumed more food, but lost weight. Paradoxical sleep-deprived rats given sucrose drank more than their control counterparts (especially in the light phase of the light/dark cycle). Paradoxical sleep-deprived rats showed increased food intake during all periods throughout the experiment, with peak intake during the dark phase and nadir during the light phase of the light/dark cycle. All paradoxical sleep-deprived rats showed lower glucose plasma levels than control rats and increased relative adrenal weight. However, when given saccharin or sucrose, paradoxical sleep-deprived rats showed lower concentrations of ACTH and corticosterone than their water-provided counterparts, indicating that palatable fluids were capable of lowering HPA axis activation produced by PSD. The fact that PSD induced energy imbalance regardless of the relative attenuation of the HPA axis activity produced by saccharin or sucrose suggests that the HPA axis may play only a secondary role in this phenomenon, and that other mechanisms may account for this effect. The data also suggest that supply of palatable fluids can be an additional modification to reduce the stress of the flower pot method.

Electromyographic activity of the lip muscle as a measure of puffing on a cigarette

The electromyographic activity (EMG) of the upper lip muscle (m. orbicularis oris) during sucking on a cigarette was examined as a potential new measure of smoking behaviour. This parameter was examined under conditions of actual smoking, sham smoking and sucking on a straw. We applied psychophysical procedures (methods of magnitude production), normal and paced smoking, two conventional means to confirm puffing (video recording and changes in air pressure in a cigarette holder) on different groups of smokers (heavy and light). The data revealed that lip-EMG is a valid and reliable means to quantify sucking on a cigarette in a variety of situations common to the study of smoking. It was concluded that lip-EMG may be a sensitive and selective measure of motor activity associated with smoking. The lip-EMG may also be applied together with hand activity and breathing to identify individual puffing, particularly in heavy smokers and during actual smoking. Discussed were several applications of this method to the study of smoking and other motivated behaviour such as consumption of water and palatable fluids.

Selective effects of vagal deafferentation and celiac–superior mesenteric ganglionectomy on the reinforcing and satiating action of intestinal nutrients

The role of vagal afferents and splanchnic fibers in nutrient-induced flavor conditioning and feeding suppression was determined. Male rats were fitted with intraduodenal (ID) catheters and given subdiaphragmatic vagal deafferentation (SDA), celiac–superior mesenteric ganglionectomy (CGX), combined (COM) treatments, or sham surgery. In separate conditioning trials, they were trained to drink (30 min/day) flavored saccharin solutions paired with concurrent ID infusions of 8% maltodextrin or water and 3.55% corn oil or water. Experiment 1 revealed that SDA and sham rats showed equal preferences for the nutrient-paired flavors over the water-paired flavors. In contrast, SDA rats, unlike sham rats, failed to suppress their intake of a palatable fluid when infused intraduodenally with maltodextrin or corn oil. Experiment 2 revealed that CGX, COM and sham rats all developed preferences for the maltodextrin-paired flavor, although CGX alone or COM attenuated the conditioned preference. CGX and COM treatments also attenuated or blocked the feeding inhibitory actions of ID nutrient infusions. These findings along with prior data indicate that gut vagal afferents and splanchnic nerves are not essential for flavor–nutrient preference conditioning, whereas both vagal afferents and splanchnic nerves are implicated in carbohydrate- and fat-induced satiation.

Palatable fluids do not affect alcohol intake and its reduction by serotonergic compounds in alcohol-preferring cAA rats

1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI) decreases alcohol intake by alcohol-preferring cAA rats more selectively than fluoxetine in a two-bottle alcohol vs. water paradigm. We report now that availability of sucrose or saccharin in a 3rd bottle does not affect (1) alcohol intake, supporting further the validity of this model of alcoholism, nor (2) the selectivity profile of the alcohol intake-reducing effects of these compounds. It is hypothesized that reduction of alcohol intake by DOI is not simply due to decreased intake of palatable fluids.

Intraaccumbens baclofen selectively enhances feeding behavior in the rat

Intraaccumbens infusions of the GABA B agonist baclofen are known to stimulate food intake in the rat. The aim of the present study was to evaluate the effects of baclofen infusion on nonfood-related chewing and on the consumption of a palatable fluid. Rats were bilaterally infused with baclofen (188 ng in 1 μL) or saline, and tested in a situation in which food was available in one or two locations and wood blocks might also be present. Baclofen-infused animals showed no enhancement of chewing directed at the wood blocks, but showed increased food consumption regardless of food location. In a second, separate test we recorded the microstructural parameters for drinking of a palatable glucose/saccharin mixture. Baclofen infusion had no effect on overall intake, although bout size was reduced and the number of bouts was increased. These data confirm that baclofen-stimulated food intake following accumbens infusion is a robust and substantial phenomenon that appears to be selective to solid food. It is likely to result from relatively direct activation of neural circuits for feeding, rather than an indirect facilitation consequent upon changes in taste processings, as has been suggested for some other examples of drug-induced hyperphagia.