Sucrose, ethanol, and sucrose/ethanol reinforced responding under variable-interval schedules of reinforcement

Adding sweeteners to ethanol solutions is a common method of inducing rats to consume ethanol. However, it has usually been assumed that it is the sweet taste and/or the calories contained in the sweet solution that controls consumption. The present experiment examined the role of ethanol in controlling responding reinforced by ethanol or an ethanol/sucrose mixture compared with sucrose solutions of various concentrations. After initiation to self-administer 10% (v/v) ethanol using the sucrose-substitution method, rats were trained to respond under a concurrent VI 5" VI 5" schedule. During one condition, responding on one lever was reinforced by the presentation of 10% ethanol, and responding on a second lever was reinforced by water or one of the following sucrose solutions: 1% (w/v), 1.5%, 2%, 2.5%, 3%, and 5%. During a subsequent condition, responding reinforced by a 10% ethanol/2% sucrose mixture was compared under the concurrent schedule with responding reinforced by water, 2%, 2.5%, 3%, 5%, or 10% sucrose (w/v). The results indicated that the ethanol or ethanol/sucrose mixture maintained more responding than did sucrose solutions that were sweeter. Data support the conclusion that, after initiation, the taste and/or pharmacological effects of ethanol had become an important component of the reinforcing stimulus independent of the sweetener.     

Human choice in concurrent ratio-interval schedules of reinforcement

Seven undergraduates participated in a concurrent-choice experiment with monetary reinforcers. Response-independent analogues of variable-interval and variable-ratio schedules were used to assess whether subjects would maximize reinforcement rate. The optimal pattern of behavior, in terms of maximizing reinforcement rate, involved a large bias toward the ratio alternative, with only occasional sampling of the interval schedule. Most experiments with pigeons, however, demonstrate matching of response rates to reinforcement rates, with only slight biases for the ratio schedule. Although subjects in the present experiment allocated more time to the ratio alternative than required by matching, the magnitude of the bias did not approximate that predicted by a maximizing account. After exposure to clock stimuli correlated with the operation of each schedule, 1 subject's behavior did show a substantial level of bias, increasing the total number of reinforcers obtained, and lay at a point between the predictions of matching and maximizing. The other subjects, however, continued to respond less optimally. The present results can be accounted for by a view of matching that incorporates the effects of delayed reinforcement.     

Choice between fixed and variable delays to reinforcement in the adjusting-delay procedure and concurrent chains.

A generalization of the contextual choice model ([CCM]; R. C. Grace, see record 1994-28397-001) is presented that describes preference between fixed and variable schedules in concurrent chains and the adjusting-delay procedure. In Exp 1A and 1B, fixed-delay indifference values for pigeons for a series of variable-delay schedules were obtained, using the adjusting-delay procedure, to test a Weber's law invariance and the effectiveness of several models. These data were then used to generate, in Exp 2, pairs of fixed and variable schedules that should have been equally preferred in concurrent chains. As predicted, deviation from indifference was small. These results indicate that (a) the determiners of value in the 2 procedures are the same, (b) the delay of reinforcement gradient is best represented as a power function with a delay threshold, and (c) a single model (CCM) can accurately describe data in the 3 most popular operant choice paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cannabinoid modulation of time estimation in the rat.

Cannabinoids have been implicated in a variety of cognitive processes in humans, including attention, learning, memory, and time estimation. However, studies of the effects of cannabinoids on rodent behavior have focused on motor, learning, and memory tasks. To assess cannabinoid effects on time perception, this study examined whether systemically administered cannabinoid receptor agonists and a cannabinoid receptor antagonist influenced rats' performance of a time interval estimation task based on a fixed-interval schedule (a "peak procedure"). Both cannabinoid agonists WIN 55,212-2 and Δ?-tetrahydrocannabinol shortened the modal response time, and cannabinoid antagonist SR 141716A lengthened the modal response time. Secondary measures of the shape of the response distribution were not influenced by any of the drugs, suggesting that the response distribution shifts were not artifacts of drug side effects. Therefore, these experiments argue for the involvement of endogenous cannabinoids in time estimation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of the self-administration of ethanol and ethanol/sucrose on rates of local cerebral glucose utilization in rats

In a previous study, the voluntary ingestion of ethanol by rats was found to be associated with a discrete pattern of changes in functional activity that included the nucleus accumbens, medial prefrontal cortex, basolateral and central nuclei of the amygdala, as well as the ventral midbrain. Rats in this study, however, consumed a combination of ethanol in a sucrose vehicle. The purpose of the present experiment was to characterize the role of sucrose in determining the effects of orally self-administered ethanol using the quantitative autoradiographic 2-[14C]deoxyglucose (2DG) method for measurement of rates of local cerebral glucose utilization. A modified sucrose-substitution procedure was employed to train three groups of Wistar rats to self-administer either water, 10% ethanol (10E), or a 10% ethanol/2% sucrose solution (10E/2S) in daily sessions. An additional group of rats was trained using a modified acclimation procedure (home cage) in order to determine if any exposure to sucrose would alter rates of glucose utilization. Once stable rates of consumption were established, the 2DG method was applied immediately following completion of the final test session. Rats received a dose of ethanol equivalent to 0.5 g kg-1 on the day of the procedure or a comparable volume of water. Rates of energy metabolism were significantly increased in all three groups of rats that consumed ethanol (10E/2S, 10E, and home cage), as compared to rates in rats that consumed water. The areas of significant change included the rostral pole and posterior shell of the nucleus accumbens, medial prefrontal cortex, the basolateral and central nuclei of the amygdala, the ventral tegmental area, and the substantia nigra pars compacta. Thus, the pattern of changes in functional brain activity that accompanies voluntary ingestion of ethanol is independent of the vehicle in which the ethanol is presented or the procedures used to initiate consumption. Furthermore, these data demonstrate that it is the simultaneous activation of an interrelated network of limbic brain regions that serves as the substrate of the effects of ethanol self-administration.     

Dietary lead increases ethanol consumption in the rat.

When 36 male Sprague-Dawley rats fed either a diet containing 500 parts per million Pb (as lead acetate) or an unadulterated control diet for 50 days were offered a 15% ethanol (ETOH) solution in a nonchoice (1-bottle) test situation, Pb-diet Ss consumed greater amounts of the ETOH solution than did controls. In a subsequent choice (3-bottle, 2-fluid) test situation offering a nonpreferred ETOH solution or tap water as alternatives, Pb-diet Ss again ingested greater amounts of the ETOH solution. Findings are discussed in terms of possible Pb-induced increases in emotionality and the potential stress-reduction properties of ETOH. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sardinian alcohol-preferring rats prefer chocolate and sucrose over ethanol

The purpose of this study was to evaluate the effect of sequential external counterpulsation (SECP) on cerebral and renal blood flow. The effect of SECP on carotid and renal artery blood flow was studied in 35 and 18 patients, respectively. With a portable unit, cuffs were applied to the calves and thighs, sequentially inflated with air at the onset of diastole, and deflated at the onset of systole. Carotid and renal artery Duplex studies were performed during intermittent SECP. Flow velocity and flow velocity integral were measured at baseline and during SECP. Diastolic augmentation of carotid and renal artery flow velocity was observed in all patients. The mean carotid flow velocity integral increased by 22% from 27.7 +/- 1.8 cm to 33.1 +/- 2.3 cm (P = 0.001). The mean renal artery flow velocity integral increased by 19% from 21 +/- 1 cm to 25 +/- 1 cm (P = 0.0001). With SECP, a new diastolic Doppler flow velocity wave was observed, with an average peak carotid diastolic flow velocity of 56 +/- 4 cm/sec and an average peak renal artery diastolic flow velocity of 40 +/- 2.5 cm/sec. This diastolic wave was 75% (carotid) and 68% (renal) as high as the systolic wave during SECP. In addition, with SECP the systolic wave increased by 6% and 8% in the carotid and renal artery, respectively (P = 0.02 and 0.006, respectively). In conclusion, SECP significantly increases carotid and renal blood flow. This noninvasive, harmless treatment may be useful to support patients with decreased cerebral and renal perfusion.     

Circadian modulation in the rat acoustic startle circuit.

The acoustic startle reflex (ASR) in rats exhibits robust circadian modulation, with ASR amplitudes greater during subjective night. To identify the location of this modulation, startle reactions were evoked either acoustically or electrically via electrodes implanted in the primary ASR circuit. Startle amplitudes were compared at different times in the circadian cycle. In constant environmental conditions, startle amplitudes were greater in subjective night for acoustically evolved and for electrically evoked reactions from the ventral lateral lemniscus and medial longitudinal fasciculus. The results show that at least 1 site of circadian modulation must occur at some point in the circuit after the last brainstem synapse in the caudal pontine reticular formation, at the level of spinal interneurons or motoneurons or at the neuromuscular junction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term ethanol administration enhances urinary ultraweak luminescence and age-dependent modulation of redox in central and peripheral organs of the rat

OBJECTIVES: The development of algorithms and computer programs for the analysis of screening performance in situations with multiple normally (Gaussian) distributed selection markers and a priori risks depending on a stratification of the population. METHODS: The S-PLUS programming language was used to construct programs producing distributions of log likelihood ratios based on the Monte Carlo simulation. These distributions were used to construct programs for the calculation of roc curves, including a possible stratification of the population. RESULTS: S-PLUS programs for the analysis of screening performance are listed and described. The programs can be used without any special knowledge of S-PLUS. An example of the use of the programs is given.     

Ethanol preloads increase ethanol preference under concurrent random-ratio schedules in social drinkers.

Ethanol (ETOH) preference was measured following ETOH preload doses in normal social drinkers. 11 Ss participated in a 5-session, double-blind choice study. In Session 1, Ss sampled an ETOH beverage (0.8 g/kg). In Sessions 2–5, they consumed a preload beverage containing placebo or ETOH (0.25 or 0.5 g/kg). One hour later, they responded on 2 concurrent random-ratio (RR) schedules. One schedule was associated with ETOH as the reinforcer and the other with money. When the probability of earning money was low, Ss responded more on the ETOH schedule following both ETOH preloads compared with placebo. Consistent with the increased responding for ETOH, Ss reported increased desire for ETOH. These data demonstrate a priming effect of ETOH preloads in normal social drinkers. They also illustrate the use of concurrent RR schedules to quantify ETOH preference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination behavior in the rat: Differential effects of reinforcement and nonreinforcement.

Gave information to a total of 12 male Sprague-Dawley albino rats in 3 experiments about the location of reinforcement and nonreinforcement. Ss then performed a discrimination task choosing among reinforced, nonreinforced, and a 3rd location. In all cases, avoidance of nonreinforcement was substantially greater than approach to reinforcement, indicating the crucial role of nonreinforcement in directing this discrimination behavior. Results of introducing a 50-min delay between information and discrimination trials and presenting other combinations of information confirm these conclusions. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postingestive modulation of the sweetness preference gradient in the rat.

Preference for a solution of a particular sweetness is increased by its previous association with postingestive effects of 10% glucose or polysaccharide solutions. Sweetness acceptance is decreased by previous association with 25%-50% glucose solutions. Conditioning in these two directions simultaneously by continuous access to a choice of solutions can reverse the usual gradient of preference for the sweeter of two solutions. This reversal is initially facilitated, but after some days attenuated, by a high proportion of carbohydrate in the diet. The reversal extinguishes over a few days without reinforcement. Expression of the relative aversion to the sweeter solution is not dependent on immediately prior carbohydrate ingestion (unlike sickly taste in man). Such conditioned attractions and aversions may assist normal caloric regulation. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Episodic excretion of ethanol during chronic intragastric ethanol infusion in the male rat: continuous vs. cyclic ethanol and nutrient infusions

Continuous intragastric infusion of ethanol has been reported to result in episodic daily blood alcohol concentrations in male rats (Tsukamoto et al., 1985). We have used a total enteral nutrition (TEN) model to study the effects of chronic alcohol exposure on blood and urine alcohol concentrations in adult male Sprague Dawley rats (300 g). Two TEN models were studied: 1) the continuous model in which a complete diet was infused i.g. for 24 h/day; or 2) the cyclic model in which TEN was infused intragastrically for 12 h/day (i.e., only during the dark phase of the lighting cycle). In the continuous model, blood alcohol concentrations (BACs) were determined at 0900 h each morning and were found to vary from day to day in an episodic fashion, with values ranging from less than 10 mg/dl to greater than 500 mg/dl. The urine alcohol concentrations (UACs) were also episodic and closely tracked those of serum, such that the 24-h UACs were excellent predictors of the BACs taken at 0900 h. Both BACs and UACs increased from values below 10 mg/dl to greater than 500 mg/dl, and then decreased back to below 10 mg/dl with a mean peak-to-peak interval of 6 +/- 0.9 days. In the cyclic model, daily UACs were also episodic (i.e., had a daily variation) and very closely resembled those of the continuous model. We have proposed that ethanol metabolism during experimental intragastric ethanol infusion in the rat occurs via a system characterized by time-dependent pharmacokinetics.     

Circadian modulation of the rat acoustic startle response.

The acoustic startle response (ASR) of male rats was measured during several sessions over a 24-hr period in both a light–dark cycle and a constant-dark condition. Each session consisted of 10 trials each at 80, 90, 100, 110, and 120 dB white noise. The results indicate robust daily and circadian modulation of ASR amplitude that consist of an approximately 2-fold nocturnal increase at eliciting-stimuli intensities above 80 dB. Similar results were observed in female rats in constant-dark conditions. To determine whether daily changes in auditory thresholds were responsible for the observed modulation, ASR reflex modification procedures were used. These procedures were designed to measure auditory thresholds at frequencies of 10 and 40 kHz at several times of day. The results suggest a lack of significant circadian differences in auditory thresholds at these frequencies. This study demonstrates a novel role of the rat circadian system in the modulation of ASR amplitude. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of signaled and unsignaled brain stimulation, water, and sucrose reinforcement on running behavior in rats.

34 male Long-Evans hooded rats in 4 groups, reinforced with signaled electrical stimulation of the brain (S-ESB), immediate ESB (I-ESB), water, or sucrose, were run for 20 10-trial sessions in a runway. For 10 sessions the intertrial interval (ITI) was 60 sec, and for 10 sessions the ITI was 5 sec. Both ESB groups ran faster with the shorter ITI, but the ITI effect was significantly smaller for the S-ESB group. The water group showed no significant ITI effect, and the sucrose group ran faster with the longer ITI. All groups showed overnight decrements in running speed. It may be that all reinforcing stimuli have a response-facilitating effect on behavior and that this effect alone can account for both the overnight decrements and the differences in the ITI effect from group to group. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Competition and summation between rewarding effects of sucrose and lateral hypothalamic stimulation in the rat.

Rats were offered a forced choice between a train of brain stimulation that varied in strength from trial to trial and a fixed standard reward. This standard reward consisted of an intraoral sucrose infusion presented either alone or paired with an equipreferred train of brain stimulation. Postingestional effects were minimized by opening a gastric cannula. The presence of a sucrose standard led the Ss to forgo trains of brain stimulation for which they had responded when the sucrose was absent. The strength of the brain stimulation required to balance the compound reward exceeded the stimulation strength required to balance a reward consisting of sucrose alone. These results imply that the rewarding effects of brain stimulation and intraoral sucrose can be evaluated in a common system of measurement and combined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of ethanol and nicotine in the pregnant rat

Treatment of pregnant Sprague-Dawley rats on day 9 of gestation with both ethanol (0.02 ml/gm of a 12.5% or 25% solution, i.p.) and nicotine (5 mg/kg, s.c.) resulted in no significant adverse effects on embryonic development and fetal viability.     

Effects of nicotine and mecamylamine microinjections into the nucleus accumbens on ethanol and sucrose self-administration

Nicotine (NIC) and ethanol (ETOH) are both drugs of abuse that can affect similar pathways in the central nervous system. However, the role of nicotinic processes in ETOH's reinforcing actions is unclear. Although the mesolimbic dopamine systems are known to be involved in the reinforcing effects of ETOH, the role of nicotinic receptors within the nucleus accumbens (NAc) in ETOH reinforcement has not been studied. To address this issue, adult male Long-Evans rats were initiated to self-administer ETOH (10% v/v, n = 14) using the sucrose-substitution procedure or sucrose (5% w/v, n = 8) in a 30-min operant session. They were then surgically implanted with bilateral stainless-steel guide cannulae to allow for microinjection into the core of the NAc. After recovery from surgery, presession microinjections of NIC (0.3, 3.3, 10, 30, and 60 microg/1 microl/brain) or the antagonist mecamylamine (MEC) (1, 3, 10, 30, and 60 microg/1 microl/brain) were performed prior to an ETOH or sucrose self-administration session. NIC (3.3 and 60 microg/microl) and MEC (30 microg/microl) both reduced ETOH self-administration behavior, without affecting sucrose-reinforced behavior. A reduction in the total duration of ETOH responding (termination) was also observed after either 60 microg/microl of NIC and 30 microg/microl of MEC. The lack of a clear dose-response relationship for the agonist and the antagonist indicates that the interaction between the NAc nicotinic system and ETOH self-administration is complex.     

Stress controllability influences the ataxic properties of both ethanol and midazolam in the rat.

Rats were administered either 80 escapable shocks or yoked inescapable shocks, were then injected with saline or several ataxic doses of either ethanol or midazolam, and then had their motoric impairment assessed by Rotarod performance. No motoric impairment was observed following saline injection. However, inescapable shock impaired Rotarod performance in response to both ethanol and midazolam at 2 hr, but not immediately poststress. Conversely, escapable shock reduced the ataxic potency of ethanol, although it had no influence on midazolam-induced ataxia. These results indicate functional alterations in behavioral reactivity to low doses of several classes of central nervous system depressants by psychological dynamics of stress exposure. Our findings demonstrate the impact of stress controllability on behavioral reactivity to two classes of drugs of abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The consequences of gustatory nerve transection on taste-guided licking of sucrose and maltose in the rat.

Lick responses to sucrose and maltose (0.01–1.0 M) were measured in nondeprived rats during brief-access taste trials before and after histologically confirmed gustatory neurotomy. Pronounced decreases in sugar responsiveness occurred after combined section of the chorda tympani (CT) and greater superficial petrosal nerves. The additional section of the glossopharyngeal nerve (GL) flattened the sucrose concentration-response function. Extirpation of the sublingual and submaxillary salivary glands also attenuated sugar responsiveness. Section of the CT or GL alone or in combination caused less severe or no decreases in sugar licking. There were signs of licking impairments after some of these neurotomies, but the data suggest that changes in sugar responsiveness were not solely motor in origin. Thus the 7th nerve is necessary and most likely sufficient for the maintenance of normal unconditioned appetitive responsiveness to sucrose and maltose. (PsycINFO Database Record (c) 2010 APA, all rights reserved)