Schedule-induced Licking Research Articles

Response–food delay gradients for lever pressing and schedule-induced licking in rats

Eight food-deprived Wistar rats developed stable patterns of lever pressing and licking when exposed to a fixed-time 30-s schedule of food pellet presentation. The rats were trained to lever press by presenting the lever 10s before the programmed food delivery, with the food pellet being delivered immediately upon a lever press. The operant contingency was then removed and the lever was inserted through the entire interfood interval, being withdrawn with food delivery and reinserted 2s later. On successive phases of the study, a protective contingency postponed food delivery if responses (lever presses or licks) occurred within the last 1, 2, 5, 10, 20, or 25s of the interfood interval. Lever pressing was reduced at much shorter response-food delays than those that reduced licking. These results demonstrate that reinforcement contributes to the maintenance of different response patterns on periodic schedules, and that different responses are differentially sensitive to delays.

Level of response suppression and amphetamine effects on negatively punished adjunctive licking

The purpose of the present study was to investigate whether the level of response suppression is a major determinant of the effect of D-amphetamine on negatively punished adjunctive drinking. Rats were initially exposed to a multiple fixed-time (FT) 30-s FT 30-s food delivery schedule. They were then divided into two groups and subjected to one of two different multiple schedules, FT 30-s FT 45-s or FT 30-s FT 90-s. The FT 45-s and FT 90-s components were signalled by a tone. Comparably high levels of adjunctive licking were observed in both FT 30-s components, intermediate licking levels in the FT 45-s component, and little licking in the FT 90-s component. Licking during the FT 30-s components was subsequently punished by lick-contingent signalled delays (by a blackout) in food delivery. The duration of such delays was adjusted to reduce licking to levels obtained in the FT 45-s or FT 90-s components, respectively for each of the two groups. Punished licking was increased by 0.3 and 1.0 mg/kg of D-amphetamine, an effect that was greater in the FT 30-s FT 90-s group. No increase in licking was observed in the FT 45-s component, but the 1.0 mg/kg dose also increased responding in the FT 90-s component. In general, no statistically significant differences were found between the effects of D-amphetamine on punished and unpunished schedule-induced licking. As licking decreased during the FT 90-s component when the punishment contingency was introduced in the alternate component, the punishment procedure and FT 30-s component were entirely removed. On this occasion, D-amphetamine failed to increase licking induced by the FT 90-s schedule. These results indicate that the level of response suppression might be a good indicator of the degree to which D-amphetamine shows antipunishment effects on adjunctive licking reduced by negative punishment procedures.

Food Deprivation and Food-Delay Effects on the Development of Adjunctive Drinking

Lamas, E. and R. PellÓn. Food deprivation and food-delay effects on the development of adjunctive drinking. Physiol Behav 61(2) 153–158, 1997.—Twelve rats were food-deprived to 90% or 70% of their free-feeding weights. Food pellets were then delivered every 60 s (Fixed Time 60-s schedule), and the development of adjunctive drinking was measured by the water consumed and the number of licks. For “master” rats, each lick was followed by 10-s delays in food delivery. Yoked control rats received food at the same time as their master rats and independently of their own behavior. At 70% deprivation, both master and control rats developed similar levels of schedule-induced licking, but the master rats drank less water. At 90% deprivation, master animals showed little drinking and licking, but the development of adjunctive drinking was not completely prevented. Drinking by yoked control rats did not differ as a function of deprivation level. In showing that lick-dependent delays in food delivery reduce the asymptotic development of adjunctive drinking as a function of the rats' level of food deprivation, these results support the view that environmental influences on schedule-induced drinking are modulated by motivational factors.

Effects of cocaine on fixed-interval behavior and schedule-induced alcohol consumption in male and female rats

Three male and three female Wistar rats pressed a lever on a fixed-interval 60-s schedule of food reinforcement while they had simultaneous access to an alcohol solution. They were challenged with different doses of cocaine hydrochloride (vehicle, 1, 3, 10, and 30 mg/kg) once lever press rates and lick rates had stabilized. Low doses of cocaine (1 and 3 mg/kg) did not systematically affect lever press rates or lick rates. The administration of 10 and 30 mg/kg cocaine dose-dependently decreased lever press rates and schedule-induced licking to a greater extent in female than in male rats. Lick rates decreased even when cocaine administration did not affect the number of pellets obtained during an experimental session. Lever press rates accelerated throughout the interreinforcement interval during control sessions. Licking was mostly limited to the first 10 s (males) or 20 s (females) after pellet presentation. Cocaine administration did not affect the distribution of lever presses and licks during the interreinforcement interval. The results of the present experiment extend previous observations that cocaine's rate-dependent effects on lever press rates may be limited to situations in which changes in lever press frequency and/or distribution negatively affect reinforcement frequency and/or physiological consequences of schedule-induced behavior.

Effects of diazepam on schedule-controlled and schedule-induced behavior under signaled and unsignaled shock.

Schedule-controlled lever pressing and schedule-induced licking were studied in rats under a multiple fixed-interval fixed-interval schedule of food reinforcement upon which was superimposed a multiple variable-time variable-time schedule of electric-shock delivery. Shocks were signaled in one component of the multiple schedule and unsignaled in the other. The effects of diazepam upon the suppression of behavior during the signal (conditioned suppression) and during signaled and unsignaled shock (differential suppression) were studied under several shock intensities (Experiment 1) and at increased body weight (Experiment 2). In each study, diazepam led to dose-dependent increases in the rate of pressing and licking during signaled and unsignaled shock, but had little effect on conditioned suppression. the rate-enhancing effects of diazepam depended upon the intensity of shock, nature of the response, and whether or not shocks were signaled. The data was discussed in terms of (1) implications for understanding the effects of signaled and unsignaled shock on behavior, (2) the effects of diazepam on behavior suppressed by response-independent shock, and (3) comparison between operant and schedule-induced behavior.

EFFECTS OF SIGNALED AND UNSIGNALED SHOCK ON SCHEDULE‐CONTROLLED LEVER PRESSING AND SCHEDULE‐INDUCED LICKING: SHOCK INTENSITY AND BODY WEIGHT

Schedule-controlled lever pressing and schedule-induced licking were studied in rats under a multiple fixed-interval fixed-interval schedule of food reinforcement. Following acquisition of stable rates of pressing and licking, a multiple variable-time variable-time schedule of electric-shock delivery was superimposed upon the baseline schedule. In only one component of the multiple schedule, a 5-sec stimulus preceded each shock (signaled shock). In the other component shock was unsignaled. Several shock intensities (Experiment 1) and body weights (Experiment 2) were studied. Lever pressing and licking were affected similarly by experimental manipulations, although with parametric differences. Depending upon shock intensity and body weight, rates of lever pressing and licking were hardly suppressed, suppressed primarily in the unsignaled shock component (differential suppression), or markedly suppressed in both components. Differential suppression during components with signaled and unsignaled shock and conditioned suppression of responding during the preshock stimulus appeared not to be functionally related. Differential suppression depended more on the discriminability of shock-free time, and on shock intensity, body weight, and the type of response than on the "preparatory" behavior preceding shock.

Effects of d-amphetamine and caffeine on schedule-controlled and schedule-induced responding.

The effects of d-amphetamine and caffeine were studied on rates and patterns of lever pressing and schedule-induced licking under fixed-interval schedules of food pellet presentation. In addition, the effects of caffeine were studied on lever pressing and licking under a multiple fixed-ratio fixed-interval schedule. Caffeine reduced mean overall rates of licking at lower doses than it reduced mean overall rates of pressing under the fixed-interval schedules, but the effects of caffeine on both licking and lever pressing depended largely on the control rate of responding. d-Amphetamine reduced mean overall rates of lever pressing and licking at about the same dose, but the effects of d-amphetamine also were a function of the control rate of responding.

Effects of Signalled and Unsignalled Electric-Shock Delivery on Schedule-Controlled and Schedule-Induced Behavior

In Experiments 1 and 2, food pellets were delivered under a fixed-interval (Fi) 40-sec. schedule, with water freely available in an operant chamber. After acquisition of stable levels of lever pressing and schedule-induced water intake, electric shock was introduced under a variable-time (Vt) 70-sec. schedule. Each of four rats was studied under signalled and unsignalled electric shock. During signalled shock delivery, a 10-sec. stimulus preceded each shock. During unsignalled shock delivery, the preshock stimulus was not presented. More suppression of lever pressing was found for all of the animals during unsignalled than signalled shock. Three of four animals also suppressed schedule-induced licking more during unsignalled than signalled shock. For both lever pressing and licking, response suppression was a function of the intensity of shock. Depending upon the intensity of shock, responding was (a) relatively unaffected during signalled and unsignalled shock, (b) suppressed primarily during unsignalled shock, or (c) markedly suppressed under signalled as well as unsignalled shock. In Experiment 3, food pellets were delivered under a fixed-time (Ft) 40-sec. schedule. Schedule-induced licking was studied under signalled and unsignalled Vt 70-sec. shock delivery. More suppression of schedule-induced licking occurred during unsignalled than signalled shock for all of the animals. These data show that schedule-induced licking, like food-maintained lever pressing, is suppressed more by unsignalled than by signalled shock delivery.

Effect of chlordiazepoxide on schedule-controlled responding and schedule-induced drinking

Lever pressing of four rats was maintained under a multiple fixed ratio 80, fixed interval 2-min schedule of food presentation. Water was concurrently available from a drinking tube. Overall rates of lever pressing were highest under the fixed ratio schedule and, for three rats, most drinking occurred during the pause preceding responding under the fixed interval schedule. Chlordiazepoxide increased the lower rates of lever pressing maintained under the fixed interval schedule but generally decreased the higher response rates under the fixed ratio schedule. The effects of chlordiazepoxide on schedule-induced licking also depended on the extent to which this response occurred in each schedule component. Typically, chlordiazepoxide produced relatively greater increases in the lower levels of licking and either increased less or decreased licking in that component where, under control conditions, this response was more extensive. Chlordiazepoxide also produced overall increases in the total amount of water consumed during the session. When the number of food pellets obtained during the experimental session was given all at one time in the home cage, the amount of water ingested over a period of time equivalent to the session duration was substantially less than that consumed during the experimental session. Chlordiazepoxide did not increase home cage water consumption under this condition.

Interactive effects of interpellet interval and pellet composition on schedule-induced licking and drinking behavior

Three groups of rats received different formulae of Noyes 45-mg dry food pellets (sugarless, 7.5% sucrose, 7.5% glucose) on fixed time reinforcement schedules with interpellet intervals of 30, 60, and 90 sec. For all groups, as interpellet interval increased, water consumed and licks per session increased to a maximum and then decreased. Licks per pellet increased across sessions. There was a significant interaction between pellet formula and interpellet interval. The type of sugar contained in the food pellet affected the number of licks and the number of mls consumed.

Suppression of operant behavior and schedule-induced licking in rats.

The first experiment studied the effects of punishment on rats' lever pressing maintained by a fixed-interval schedule of food reinforcement and on the associated schedule-induced licking. When licking was followed by shock, licking was suppressed but lever pressing was largely unaffected. When lever pressing was followed by shock, lever pressing was suppressed but licking was unaffected. In both cases, the punished behavior recovered its previous unpunished level when the shocks were discontinued. In a second experiment, the rats' lever pressing was maintained by a variable-interval schedule of food reinforcement under which polydipsic licking also developed. Both lever pressing and licking were partially suppressed during a stimulus correlated with occasional unavoidable electric shocks. With a higher shock intensity, both behaviors were suppressed further. Both lever pressing and licking recovered their previous levels when shocks were discontinued. These results show that schedule-induced licking, which has been described as adjunctive behavior, can be suppressed by procedures that suppress reinforced lever pressing, an operant behavior.

Effects of trihexyphenidyl on schedule-induced alcohol drinking by rats

Three rats from the Maudsley reactive strains and three rats from the Maudsley nonreactive strain were trained to barpress with food reinforcement scheduled at fixed intervals of 1 min. With various alcohol concentrations, schedule-induced licking was higher in the nonreactive animals but there was little difference in intake between the strains. Injections of trihexyphenidyl attenuated alcohol consumption by all animals, with 3.0 mg/kg being the most effective dose.

SCHEDULE‐INDUCED LICKING DURING MULTIPLE SCHEDULES1

Schedule-induced polydipsia was studied in rats bar pressing under two-component multiple schedules of food reinforcement. The first component of the multiple schedule was a variable-interval 1-min schedule throughout the experiment. The schedule comprising the second component was varied over blocks of sessions in terms of rate and magnitude of reinforcement, and was either variable-interval 3-min (one pellet), variable-interval 3-min (three pellets), variable-interval 1-min (one pellet), or extinction. Water intake per session varied with the rate of reinforcement in the schedule comprising the second component and was highest when the schedule was variable-interval 1-min. Both bar-pressing behavior and licking behavior showed behavioral interactions between the two components of the multiple schedules. With magnitude of reinforcement held constant, a matching relationship was observed between lick rate and reinforcement rate; the relative frequency of licks in the constant component matched the relative frequency of reinforcement in that component. Bar pressing, however, showed only a moderate degree of relativity matching. During the schedule-induced licking, a burst of licking followed each delivery of a pellet (post-prandial drinking). The duration of these bursts of licking was observed to be a function of the inter-reinforcement interval.

Schedule-Induced Licking and Polydipsia

Detailed observations were made of the eating and drinking behavior of a pair of hooded rats under a VI 1 min schedule of food reinforcement after one of them (executive) had been trained alone to bar-press. Reinforcements could be consumed by either rat. The executive nearly always drank after eating, the other (control) never did. Eventually the control acquired the bar-press response. When it was then run alone it too came to drink after eating. It is argued that as drinking after eating is a result of reinforcement scheduling it is improper to ascribe schedule-induced polydipsia to a tendency of rats to drink after eating. Instead it is suggested that a wet mouth becomes a discriminative or otherwise favorable stimulus for bar-pressing with food reinforcement.

Schedule-induced polydipsia: A partial reinforcement effect

Several degrees of polydipsia were induced in three pairs of rats fed on VI 20-, 45-, or 120-sec free-pellet schedules. The number of licks to extinction was proportional to the number of licks per pellet emitted during training trials. The results are consistent with the assumption that schedule-induced licking is maintained (superstitiously) as an operant for food and not simply as a function of meal termination or thirst.