Rat defensive behavior: burying noxious food.

In Experiment 1, rats living in chambers containing bedding material were injected with a toxicosis-producing dose of lithium chloride shortly after their initial taste of sweetened condensed milk. They consumed no additional milk and used the bedding to bury the spout through which the milk had been delivered, although they did not bury a concurrently available water spout. In another control condition, rats did not bury a spout containing a novel solution (saccharin) not paired with toxicosis. In Experiment 2, rats did not bury a milk spout until milk consumption was followed by toxicosis. In Experiment 3, rats buried a spout containing Tabasco pepper sauce but not a concurrently available water spout. Thus, burying the food source appears to be an integral component of the rat's defensive reaction to noxious food.     

The behavioral economics of production.

In two experiments, thirsty rats licked an empty spout instrumentally for water delivered at a neighboring spout. Each such pair of spouts constituted a work station, and one, two, or three stations were available in the test enclosure. In 1-hr sessions, the rats worked alone or in the company of 1 or 2 other rats, and performed either five, 10, or 40 licks at the empty spout for each water delivery. The total number of empty-spout licks, summed across rats and stations, increased with the empty-lick requirement and, with some exceptions, the number of rats in the enclosure and the number of work stations available. A Cobb-Douglas production function, with instrumental responding as an output and the three independent variables as inputs, accounted for a significant percentage of the variance. Contrary to that function, output failed to increase with additional rats (or work stations) when the number of work stations (or rats) was relatively small.     

Conservation, choice, and the concurrent fixed-ratio schedule

Five rats got all of their water in daily 60-minute sessions. Two levers and a water spout were freely available throughout baseline sessions. Contingency sessions offered a choice between two alternative fixed-ratio components, in the form of a choice between the two levers. Each component required a specified number of lever presses for access to the spout, and then a specified number of licks for another choice between components. Given the observed relative frequency, the absolute frequency of selecting each component was predicted accurately by assuming that the subject conserved between baseline and contingency the total amount of a dimension attributable to lever pressing and licking. Several quantitative models for predicting relative frequency were examined. The best of these assumed that the subject would show a nonexclusive preference for the component requiring fewer lever presses.     

Oral self-administration of pentobarbital by rhesus monkeys: relative reinforcing effects under concurrent fixed-ratio schedules.

During daily 3-hr sessions, orally delivered pentobarbital solutions and water, or two separate pentobarbital solutions, were concurrently available to rhesus monkeys according to fixed-ratio schedules of mouth contacts with a spout. First water, and then each of four "comparison-concentration" pentobarbital solutions (0.0625, 0.25, 1, and 4 mg/mL), was successively available from one spout for a block of sessions under a fixed-ratio-64 (three monkeys) or fixed-ratio-16 (one monkey) schedule. Under an identically sized fixed-ratio schedule, deliveries of a "standard-concentration" pentobarbital solution were concurrently available from a second spout. The concentration of the standard solution remained unchanged throughout testing of the series of comparison solutions. Each of three pentobarbital concentrations (4, 1, and 0.25 mg/mL) in turn served as the standard concentration. Within each pair of concurrently available solutions, the higher drug concentration maintained more behavior than the lower concentration. Thus when monkeys were provided with concurrent access to different pentobarbital concentrations, relative reinforcing effects were directly related to drug concentration. Further, the amount of behavior maintained by a particular drug concentration was dependent on the concentration of the concurrently available drug solution. Thus, the relative effectiveness of a reinforcer in maintaining behavior is a function of both the reinforcer's magnitude and the availability of alternative reinforcers in the environment.     

Polydipsia induced in rats by second-order schedules of reinforcement.

Three rats were exposed to a second-order schedule in which fixed-interval components ended either with food or with a brief stimulus that was never paired with food. Food and the brief stimulus occurred in a random sequence (variable-ratio 2 overall schedule). Another three rats were exposed to a similar second-order schedule, the only difference being that the food or the stimulus was presented independently of operant behavior (fixed-time components). The three rats exposed to the fixed-interval components licked at a water spout after each food presentation. These rats also licked in the intervals after the brief stimulus. Although the discriminative properties of food and of the brief stimulus were identical in relation to subsequent reinforcement, licking after the stimulus was less than after food. The three rats exposed to the second-order schedules with fixed-time components also licked at the water spout after food, but these rats did not lick consistently after brief stimulus presentations.     

Induction when rats lick for 1% liquid-sucrose reinforcement

Previous research reported that rats responding for 1% liquid-sucrose reinforcement when 32% sucrose reinforcement is upcoming will decrease their response rate (contrast) if licking is the dependent measure and increase their response rate (induction) if pressing a lever is the dependent measure. The present study investigated whether induction could be observed when licking served as the dependent measure and whether induction in lever pressing and contrast in licking behaviour could be concurrently observed. Experiment 1 found induction when rats licked to earn the rewards but consumed them at a location separate from the spout licked to earn them. Experiment 2 also found induction when rats earned (and consumed) rewards by licking the same spout throughout the session. Experiment 3 separately measured instrumental lever pressing for sucrose rewards and licking the sucrose during the reward period. We found that both measures increased for 1% sucrose when 32% sucrose reinforcement was upcoming. The present results indicate that the type of response is not the sole determinant of whether contrast or induction is observed. Rather, they suggest that other procedural details, such as the location of reinforcer delivery, influence which effect is observed. The results also indicate that associative processes underlie the appearance of induction in responding for 1% sucrose.     

Induction when rats lick for 1% liquid-sucrose reinforcement

Previous research reported that rats responding for 1% liquid-sucrose reinforcement when 32% sucrose reinforcement is upcoming will decrease their response rate (contrast) if licking is the dependent measure and increase their response rate (induction) if pressing a lever is the dependent measure. The present study investigated whether induction could be observed when licking served as the dependent measure and whether induction in lever pressing and contrast in licking behaviour could be concurrently observed. Experiment 1 found induction when rats licked to earn the rewards but consumed them at a location separate from the spout licked to earn them. Experiment 2 also found induction when rats earned (and consumed) rewards by licking the same spout throughout the session. Experiment 3 separately measured instrumental lever pressing for sucrose rewards and licking the sucrose during the reward period. We found that both measures increased for 1% sucrose when 32% sucrose reinforcement was upcoming. The present results indicate that the type of response is not the sole determinant of whether contrast or induction is observed. Rather, they suggest that other procedural details, such as the location of reinforcer delivery, influence which effect is observed. The results also indicate that associative processes underlie the appearance of induction in responding for 1% sucrose.     

Correspondence effects for objects with opposing left and right protrusions

Choice reactions to a property of an object stimulus are often faster when the location of a graspable part of the object corresponds with the location of a keypress response than when it does not, a phenomenon called the object-based Simon effect. Experiments 1-3 examined this effect for variants of teapot stimuli that were oriented to the left or right. Whether keypress responses were made with fingers within the same hand or between different hands was also manipulated. Experiment 1 showed that, for judgments of stimulus color and upright-inverted orientation, the Simon effect for intact teapots occurred in the direction of the spout location and was larger for within- than between-hand response modes. In Experiments 2 and 3, teapots with the handle or spout removed showed separate contributions of each component to the Simon effect. In Experiment 4, we clarified a discrepancy between our findings of object-based Simon effects and a previously reported absence of effect with color judgments for door-handle stimuli. We obtained an object-based Simon effect with respect to handle position when the bases of the door handles were centered but not when the handles were centered. The findings that object-based Simon effects occur with color judgments and when responses are fingers on the same hand are in closer agreement with a location coding account than with a grasping affordance account.     

Matching under nonindependent variable-ratio schedules of drug reinforcement.

Response-contingent deliveries of oral pentobarbital maintained responding of 3 rhesus monkeys during daily 3-hr sessions. Deliveries of pentobarbital were arranged under nonindependent concurrent variable-ratio variable-ratio schedules. Responses to either schedule counted toward completion of both variable-ratio schedule requirements. This schedule is similar in some respects to conventional concurrent variable-interval variable-interval schedules, in which passage of time counts toward completion of the interval value on both schedules. Restricted nonindependent concurrent variable-ratio variable-ratio schedules were also studied. On that schedule, when a drug delivery was assigned to one spout, it had to be collected before responses on the opposite spout again counted toward completion of the schedule requirements. Relative reinforcer magnitude was varied by changing the drug concentration on one schedule while keeping the drug concentration constant on the other variable-ratio schedule. Under both types of concurrent variable-ratio schedules, the relative rate of responding corresponded to the relative drug intake. Unlike earlier studies of concurrent variable-interval variable-interval intravenous cocaine reinforcement, preference was proportionate to concentration, and exclusive preferences did not develop. The relationship between relative rate of responding and relative drug intake was well described by the generalized matching law.     

Potentiation and overshadowing in odor-aversion learning: Role of method of odor presentation,the distal-proximal cue distinction,and the conditionability of odor

Four experiments with rat subjects examined interactions between odors and tastes in compound aversion conditioning. In Experiments 1 and 2, a saccharin taste potentiated the conditioning of an almond odorant presented on a cup near the location of the drinking spout, but overshadowed the same odorant when it was mixed in drinking water. This difference depended on the type of odor administered during conditioning rather than testing (Experiment 2). Experiments 3 and 4 examined implications of two other differences between the cup and drink odors: (1) while the cup odor was a distal cue that suppressed approach to the spout, the drink odor was primarily a proximal cue that suppressed consumption, and (2) the cup odor was less conditionable than the drink odor when the stimuli were conditioned alone. In Experiment 3, unlike the proximal saccharin taste, the proximal drink odor failed to potentiate the conditioning of a different distal odor. In Experiment 4, substantial dilution of the proximal drink's concentration resulted in both weaker conditioning of the stimulus alone, and potentiation of its conditioning by saccharin. The results suggest that the difference in the conditionability of the cup and drink odors, and not their status as distal and proximal cues, may be critical in the production of potentiation. Weakly conditionable target stimuli are uniquely potentiated by saccharin.     

Oral self-administration of pentobarbital by rhesus monkeys: maintenance of behavior by different concurrently available volumes of drug solution.

For 4 rhesus monkeys, mouth-contact responses with either of two brass spouts were reinforced according to fixed-ratio schedules by 0.65-mL liquid deliveries during daily 3-hr sessions. Three experiments were conducted. In each experiment, independent fixed-ratio schedules were concurrently in effect at the two spouts. Following completion of each fixed ratio on a spout, a specified number of liquid deliveries were available from that spout under a continuous-reinforcement schedule. The number of such deliveries available at each spout was manipulated independently. In Experiment 1, a 1-mg/mL pentobarbital solution was simultaneously available with water (the drug vehicle) under concurrent fixed-ratio schedules of 32 responses for 3 subjects and 64 responses for the remaining subject. The number (N) of liquid deliveries that were available after completion of each fixed ratio was varied in the following order: 8, 4, 2, 1, and 8 (retest). For each subject at each condition, drug maintained more responding than water. The number of drug deliveries obtained per session was directly related to the amount of drug available per fixed ratio (i.e., to N), whereas the number of fixed ratios completed per session generally was inversely related to the value of N. In Experiment 2, fixed-ratio size was the same for each subject as in Experiment 1, but deliveries of a 1-mg/mL pentobarbital solution were available at both spouts. The number of drug deliveries available under one fixed-ratio schedule (Ns, the "standard" reinforcer amount) was held at eight, and the number of drug deliveries available under the second schedule (Nc, the "comparison" reinforcer amount) was changed across blocks of six sessions of stable responding in the following order: 1, 2, 4, 8, 4, 2, and 1. The identical series of comparison reinforcer amounts (Nc) was then tested twice more, but with the standard reinforcer (Ns) held first at four and then at two deliveries. Across the three choice series, reinforcing effects were directly related to reinforcer magnitude. In Experiment 3, deliveries of a 1-mg/mL pentobarbital solution again were available at both spouts. However, the two reinforcer amounts were held constant at N = 8 deliveries under one schedule and N = 4 deliveries under the second schedule, and fixed-ratio size was systematically varied. Across the range of fixed-ratio sizes from low to high, the degree to which behavior was better maintained by the larger of the two drug quantities was an inverted U-shaped function of fixed-ratio size.(ABSTRACT TRUNCATED AT 400 WORDS)     

Interactions between brainstem noradrenergic neurons and the nucleus accumbens shell in modulating memory for emotionally arousing events

The nucleus accumbens shell (NAC) receives axons containing dopamine-β-hydroxylase that originate from brainstem neurons in the nucleus of the solitary tract (NTS). Recent findings show that memory enhancement produced by stimulating NTS neurons after learning may involve interactions with the NAC. However, it is unclear whether these mnemonic effects are mediated by norepinephrine (NE) release from NTS terminals onto NAC neurons. The present studies approached this question by examining the contribution of NAC α-noradrenergic receptors in mediating this effect and assessed whether glutamatergic activation of the NTS alters NE concentrations in the NAC. Rats were trained for 6 d to drink from a water spout located at the end of an inhibitory avoidance chamber. On day 7, a 0.35-mA footshock was initiated once the rat approached the spout and remained active until it escaped into the neutral compartment. Blockade of α-noradrenergic receptors in the NAC with phentolamine (0.5 μg/0.5 μL) attenuated memory enhancement produced by glutamatergic (50 ng/0.5 μL) infusion on NTS neurons (P < 0.01). Experiment 2 used in vivo microdialysis to assess whether glutamate activation of NTS alters NAC NE concentrations. NE levels were unchanged by NTS infusion of phosphate-buffered saline (PBS) or low dose glutamate (50 ng/0.5 μL) but elevated significantly (P < 0.05) by combining the same dose with the footshock (0.35 mA, 2 sec) given in Study 1 or infusion of (100 ng/0.5 μL) glutamate alone. Findings demonstrate that NE released from NTS terminals enhances representations in memory by acting on α-noradrenergic receptors within the NAC.     

Electric shock produced drinking in the squirrel monkey.

Squirrel monkeys were periodically exposed to brief electric tail shocks in a test environment containing a rubber hose, response lever, and a water spout. Shock delivery produced preshock lever pressing and postshock hose biting. Additionally, all subjects displayed licking responses following postshock biting-attack episodes. Further experiments showed that licking was: (1) influenced by hours of water deprivation; (2) drinking behavior; (3) the direct result of shock delivery; and (4) developed spontaneously in naive subjects with or without opportunities for hose biting or lever pressing. Removing the opportunity to attack increased postshock drinking. A noxious environmental stimulus that causes aggression can also produce drinking.     

Orogastric, hydrational, and behavioral controls of drinking following water deprivation in rats.

Drinking and its associated behaviors were studied in rats deprived of fluid for 8,24, or 48 hr. The behavior of rats drinking water could be divided into three successive stages: (a) an initial intense burst of drinking that could not be easily disrupted; (b) intermittent drinking, often distinguished by the brief appearance of conflict behavior directed at the drinking spout; and (c) termination of drinking. Drinking stopped well before the fluid loss, reflected in a sizable extracellular deficit, was restored. Intake of water was terminated when serum hyponatremia and hypoosmolality (and presumably cellular overhydration) developed in temporal continguity with drinking. These and other considerations suggest that the cellular fluid phase exerts significant inhibitory as well as excitatory control over drinking.     

Within-Session Changes in Adjunctive and Instrumental Responding

Rats pressed levers for food delivered by several fixed interval schedules. A drinking spout or running wheel was also available during some conditions, but not during others. The rate of lever pressing, drinking and running often changed within experimental sessions. The within-session patterns of lever pressing did not differ when drinking or running was available and when it was not. The correlation between the amount of lever pressing and the amount of drinking or running at a particular time in the session was inconsistently positive or negative. Finding within-session changes in responding for adjunctive behaviors implies that the factors that produce these changes are present for both adjunctive and instrumental behavior. Finding inconsistent correlations between instrumental responding and adjunctive behaviors questions arousal and interference from adjunctive behaviors as explanations for within-session changes in instrumental responding.     

A high-sensitivity drinkometer circuit with 60-Hz filtering

This article describes a drinkometer circuit designed to (1) detect licks even if the resistance of the skin on the animal’s feet becomes quite high due to low humidity, (2) automatically adjust its triggering threshold and increase its gain so that it will continue to detect licks when the water delivery spout is partially shorted to ground by high ambient humidity, (3) reject 60-Hz signals so they will not be treated as rapid licks by the data-recording system, and (4) tolerate the high voltages that can occur if the subject receives an electric shock while drinking. This lickometer will be especially useful in situations where it is not practical to monitor for possible signal failure due to high or low humidity, or where 60-Hz artifacts may contaminate the signal provided to a recording computer.     

Ratio size and cocaine concentration effects on oral cocaine-reinforced behavior.

Monkeys were given a choice between cocaine solutions and water under concurrent fixed-ratio reinforcement schedules. The operant response was spout contact. Six rhesus monkeys served as subjects. The cocaine concentration was varied from 0.0125 to 0.8 mg/ml, and the fixed-ratio value was varied from 8 to 128. Cocaine maintained higher response rates than did water over a wide range of conditions. Response rate and number of cocaine deliveries per session were inverted U-shaped functions of concentration. These functions were shifted to the right as the fixed ratio was increased. The number of cocaine deliveries was more persistent as fixed-ratio value was increased when the unit dose was larger rather than smaller. Cocaine consumption was analyzed as a function of unit price (fixed-ratio value divided by cocaine concentration), and unit price accounted for between 77% and 92% of the variance in cocaine consumption for individual monkeys. The current data support the claim that a drug's reinforcing effects increase directly with dose and underscore the need to gather parametric data when examining the effects of experimental manipulations on a drug-reinforced baseline.     

Contrast, induction, facilitation, suppression, and conservation

Ten rats received all of their water in daily 1-hr sessions. Following a baseline phase in which lever and water spout were freely available throughout each session, subjects were trained to press the lever for water on mixed schedules composed of two alternating components. Each component gave access to water for a fixed cumulation of drinking time every time the rat cumulated a fixed amount of lever-pressing time. Changes in one component produced contrast and induction effects, both positive and negative, with respect to both lever pressing and drinking in the unchanged component. All schedules facilitated lever pressing relative to baseline. All schedules suppressed drinking relative to baseline, even though contingency sessions allowed ample time to perform the baseline amount of drinking. The entire pattern of results was predicted in quantitative detail by assuming that the total amount of a dimension apportioned to lever pressing and drinking is conserved between baseline and contingency sessions. Conservation theory was shown to predict several effects produced by simple fixed-ratio schedules, and was compared favorably with probability-differential (Premack, 1971) and response-deprivation (Timberlake and Allison, 1974) theory.     

Deficient passive and one-way active avoidance acquisition following medial forebrain bundle lesions in rats.

Cathodal electrolytic lesions of the medial forebrain bundle (MFB) at posterior hypothalamic levels in male hooded rats produced a mild, transient hypodipsia and lowered jump thresholds to footshock. The lesions produced marked deficits in passive avoidance performance in a paradigm that paired discrete, linearly incrementing footshock intensities with contact of a water spout following 48 hr of water deprivation. Intraperitoneal injections of DL-5-hydroxytryptophan (75 mg/kg), the immediate metabolic precursor of serotonin, had no effect on the passive avoidance performance of either experimental or operated control subjects. Lesions of the MFB also resulted in deficient acquisition in a one-trial step-through passive avoidance paradigm not using motivation to drink and caused a severe acquisition deficit in a one-way active avoidance task. Lesions of the septal nuclei produced lowered jump thresholds but did not affect acquisition in the first passive avoidance task. The results are interpreted as indicating a lesion-induced deficiency in fear learning, independent of the serotonergic functions of the MFB.     

Diversity and substitutability of adjunctive activities under fixed-interval schedules of food reinforcement

Six rats received food contingent on pressing a lever on fixed-ratio 1, fixed-interval 30-second, and fixed-interval 60-second schedules, with concurrent access to a drinking spout, a running wheel, and a block of wood. Drinking, running, and chewing were monitored automatically, and these and other activities were observed directly during selected sessions. Because all sessions ended after delivery of 60 pellets, total time available for activities other than eating increased over the three schedules. Time spent contacting the lever and visiting the food tray increased in proportion to total available time, whereas the time spent in other activities changed in a complex manner such that drinking was the dominant adjunctive behavior in the 30-second condition, and running or chewing the dominant adjunctive behavior in five of six rats in the 60-second condition. General activity and grooming also occupied significant amounts of time. In a subsequent part of the experiment, running and chewing were prevented, and the majority of other activities, especially drinking and grooming, increased. The results show that (a) FI schedules of food reinforcement are accompanied by a wide variety of adjunctive activities; (b) the preferred activity differs according to the schedule duration; and (c) the extent to which activities substitute for one another is limited by the tendency for different activities to occupy different parts of the interreinforcement interval.