Lever-pressing Rates Research Articles

Rate dependent effects of imipramine. Effects of imipramine on operant behaviour in rats at various levels of water deprivation.

The behavioural effects of 1.0, 3.10 and 6.0 mg/kg imipramine injections on lever pressing of rats were studied. Lever pressing was reinforced according to a continuous reinforcement schedule at 0, 24, and 48 h of water deprivation, according to fixed ratio schedules with 22 1/2 h of water deprivation, and according to differential‐reinforcement‐of‐low‐rate schedules with 22 1/2 h of water deprivation. The mean rate of responding per min increased significantly at 1.0 mg/kg on the continuous reinforcement schedule at 24 h of deprivation. Otherwise, a dose‐related significant reduction in the mean response rate per min occurred on the fixed raito schedules and partly on the differential‐reinforcement‐of‐low‐rate schedules, thus lending support to the idea that rate dependent effects may be produced only on schedules of reinforcement such as the fixed ratio, the fixed interval and the variable interval. The results also indicate that depenent effects may be produced only at moderate levels of water deprivation. Some critical comments are made on concepts of rate dependency in view of the results and of previous finding.

TEMPORAL CONTROL IN A COMPLEX ENVIRONMENT: AN ANALYSIS OF SCHEDULE‐RELATED BEHAVIOR

Three experiments conducted in an automated ten-compartment chamber recorded collateral activities of rats reinforced for lever pressing on differential-reinforcement-of-low-rate schedules. In Experiment 1, the rate of lever pressing increased when stimulus support for collateral activities was removed, thus confirming earlier findings. However, there were no temporal or sequential patterns of collateral activities that predicted operant responding. In Experiment 2, the rate of lever pressing increased only if (a) access to all stimulus support for collateral activities was simultaneously prevented, and (b) the rat was forced to remain in the presence of the lever and food tray. The availability of any of the stimuli related to collateral activity was sufficient to keep lever-pressing rates from increasing. Experiment 3 examined collateral activities under a signaled differential-reinforcement-of-low-rate schedule. Preventing access to stimuli supporting collateral activities had little effect on stable lever pressing when the signal was maintained. When the signal was removed, collateral activities continued, but lever-pressing rates increased in three of the four rats and rates of food presentation declined in all rats. Hypotheses that collateral activities have (a) a timekeeping or discriminative function, or (b) directly inhibit operant responding were not supported. The results suggest that collateral activities may facilitate operant responding by simply removing the subject from the presence of reinforcement-related stimuli.

Increasing the work requirements lowers the threshold of naloxone for reducing self-stimulation in the midbrain of rats

Rats were trained to lever-press for intracranial self-stimulation (ICSS) with electrodes in the midbrain central gray area. The effects of naloxone (0.1–30.0 mg/kg, SC) on a continous reinforcement (CRF) schedule were determined. Rats were then re-trained on higher fixed-ratio (FR) schedules, and naloxone was re-tested at FR: 5, 10, 15 and 20. Only moderate reductions in lever-pressing rates were obtained at the highest dose of naloxone under CRF and FR: 5 schedules. In contrast, pronounced, dose-dependent reductions in ICSS rates occured at FR: 10, 15 and 20. The time-course for this reduction at FR: 20 was consistent with an opiate-antagonistic action of naloxone. The modest decrease in locomotor activity produced by naloxone in a matched group of control rats was not sufficient to account for the effects on ICSS. The threshold of naloxone for reducing the rate of ICSS lever-pressing was lowered by increasing the effort and/or time requirement for each reinforcement.

The effects of naloxone, diprenorphine, and diazepam on responding suppressed by pre-shock and pre-food stimuli

The lever-pressing of rats was reinforced with food according to a variable-interval 1-min schedule. In one group, occasional illumination of cue lights for 30-sec periods was followed by a brief electric shock; responding was suppressed during these periods. Naloxone (0.01–10 mg/kg) did not change the degree to which responding was suppressed during the pre-shock stimulus. Diprenorphine (0.1–10 mg/kg) slightly attenuated suppression, and diazepam (1.0–3.0 mg/kg) increased responding during the stimulus to normal levels. These results confirm that opiate antagonists do not always enhance the effects of shock on behavior. In a second group, occasional illumination of the cue lights for 20-sec periods was followed by delivery of free food pellets. Responding was also suppressed during the pre-food stimulus. Neither naloxone nor diprenorphine had any effect on response rate during this stimulus. In contrast to the results of earlier studies using benzodiazepines, diazepam (1.0–3.0 mg/kg) produced a marked attenuation of response suppression during the pre-food stimulus.

Task-dependent properties of brain stimulation reward

Lawful relationships established between lever-pressing and parameters of brain stimulation reward (BSR) were examined for several tasks. Task-contingent BSR was given to the same rats at identical sites using identical stimulation parameters. Lengthening stimulation duration from 100 to 300 msec increased lever-press rates. Subsequent lengthening from 400 to 800 msec decreased lever-press rates. Wheel-turning rates increased linearly with lengthening duration. The form of the response-duration function depended on current for lever-pressing but not for wheel-turning. As duration lengthened, time between responses increased systematically for the lever and was invariant for the wheel. Stimulation of the substantia nigra, posterior medial forebrain bundle, and anterior hypothalamus produced similar relations. To further examine the generality of these findings, licking and barrier-jumping were tested. Licking decreased monotonically as stimulation duration lengthened. Barrier-jumping increased from 100 to 500 msec and subsequently remained stable despite lengthening duration to 900 msec. In all tasks examined BSR was rewarding, but the form of the response-duration function depended on task characteristics. Since identical sites were stimulated, task differences cannot be attributed to neurochemical substrates. Results provide evidence for behavioral constraints on BSR.

The effect of train duration of rewarding stimulation on food self-deprivation

In order to assess the effect of changes in brain-stimulation reward (BSR) on food intake, train duration of BSR was manipulated during food/BSR competition periods. Train duration, rather than intensity, was used in order to hold the area of stimulation about the electrode tip constant. Train duration had a significant effect on food intake, with longer durations decreasing intake. Increases in food deprivation increased feeding during food/BSR competition, and the tendency for subjects to self-deprive was reduced over the 4 weeks of successive competition testing. Further analyses of the data revealed that stimulation on-time (defined as the product of leverpresses and train duration) was a better predictor of food intake than was leverpressing rate. The results are interpreted as supporting the hypothesis that choices for food or BSR during competition reflect the relative reward value of the alternatives.

Effects of phenytoin on schedule-controlled performance of rats

The present study examined the effects of acute administrations of phenytoin on the lever pressing of rats maintained under fixed-ratio, fixed-interval, and interresponse-time-greater-than-T schedules of food delivery. The drug typically produced dose-dependent decreases in response rates under fixed-ratio and fixed-interval schedules, while response rates under the interresponse-time-greater-than-T schedule were affected little by the drug. These findings indicate that phenytoin effects on schedule-controlled responding differ from those of other anticonvulsants.

AUTOSHAPING IN THE RAT: EFFECTS OF OMISSION ON THE FORM OF THE RESPONSE

Two experiments were conducted to investigate the effect of an omission contingency on behavior related to and characterizing autoshaped lever contacts in the rat. In Experiment I an omission contingency imposed on autoshaped lever contacts forceful enough to produce a press (.078N) resulted in a significant decrease in lever presses, but had no effect on frequency of lever touches (contacts of insufficient force to produce a press) or rate of food tray entry during lever presentation. In contrast, rats which received a similar number of lever-food pairings, but whose behavior had no programmed consequences (yoked control subjects), showed an increase in lever press rate, a significant decrease in rate of food tray entry, and no change in rate of lever-touches. In Experiment II, the effect of a similar omission contingency on the topography of lever contact responses was investigated. Prior to omission training subjects contacted the lever primarily by pawing it. Following omission training this behavior was suppressed, with a subsequent increase in lever contacts characterized as nosing. Yoked control subjects showed no significant changes in lever contact topography. The results indicate that (1) an omission contingency does not simply eliminate wholesale those topographies which incur the contingency but produces subtle adaptive changes in lever contact topography; and (2) the nature of the autoshaped response in the rat does not appear to be rigid enough to depend solely upon the nature of the unconditioned stimulus or the conditioned stimulus, but can also be determined by the relationships existing between the animal's behavior and these stimuli.

A multivariate analysis of some operant variables used in behavioral pharmacology.

The classificatory power afforded by the conjoint measurement of lever-pressing response rate and response duration was compared with a univariate analysis based exclusively on response rate. Operant behavior was measured following chlorpromazine, haloperidol, chlordiazepoxide, and pentobarbital, all of which produce similar dose-related decreases in rate of responding on simple fixed-ratio schedules of reinforcement. The multivariate technique of linear discriminant analysis indicates that both response rate and response duration provide useful and nonredundant information regarding the drug effect, separating the four drugs into three distinct classes: neuroleptic, chlordiazepoxide, and pentobarbital.

Interactions between intracranial electrical self-stimulation behavior and cardiovascular responses

Interactions between electrical self-stimulating behavior, cardiovascular state and reactions were studied in a series of chronically prepared cats. Pressor responses were found to be the most common cardiovascular concomitants of intracranial electrical self-stimulating behavior in cats. The leverpressing rate for brain stimulation decreased under the effect of both dibenzyline, an adrenergic blocking agent, and local anesthesia of the cervical vago-sympathetic trunk by procaine. Bilateral vagotomy resulted in an acceleration in lever-pressing responses. The depression and the acceleration in the lever-pressings for brain stimulation were associated with an increase and a decrease in pulse pressure, respectively. It is suggested that peripheral autonomic modifications exert a regulatory feedback effect on the rewarding property of brain stimulation.

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.

Intracranial self-administration of morphine into the ventral tegmental area in rats

The rewarding properties of morphine injected directly into the ventral tegmental area were investigated using a self-administration procedure. Experimentally naive rats demonstrated rapid acquisition of a lever-pressing response which produced a 100 ng infusion of morphine sulfate solution. Response rates were relatively stable and markedly exceeded lever-press rates of rats passively receiving the same pattern of infusions (i.e., yoked control procedure). Intracranial self-administration was effectively blocked by naloxone suggesting that this behavior is mediated through opiate receptors and is not the consequence of mechanical trauma, or changes in osmolarity or pH.

Comparison of morphine, meperidine, anileridine, and alphaprodine on schedule-controlled responding and analgesia

The effects of morphine, meperidine, alphaprodine, and anileridine were studied alone and in the presence of 1 mg/kg of naloxone in rats on level pressing under a fixed-ratio 20-response schedule of food presentation and on tail-withdraw al latency from warm water (55°C) as a measure of analgesia. All four narcotics decreased rates of lever pressing and increased tail-withdrawal latencies. Naloxone antagonized the effects of all four narcotics on tail-withdrawal, but did not antagonize the rate-decreasing effect of meperidine on lever pressing. Naloxone shifted the morphine dose-effect for lever-pressing by a factor of 4–8; the alphaprodine dose-effect curve by a factor of 4–8; and the anileridine dose-effect curve by a factor of 2. These results strengthen the interpretation that meperidine's effect on schedule-controlled responding is not mediated by a narcotic action whereas the analgesic effect is. The results also suggest that anileridine has significant non-narcotic actions like meperidine.

Response-reinforcer relations and the hippocampus

The operant performance of intact rats is guided by response-reinforcer contingency but that of animals with hippocampal lesions is not. Despite this impairment, lesioned animals perform a number of tasks without difficulty. This experiment examines the possibility that response-reinforcer contiguity is the relationship upon which the operant performance of hippocampals is exclusively based. This hypothesis is tested in a yoked-control design where pellets are dispensed freely and responses are without effect on pellet delivery rate. The temporal patterning of deliveries is rearranged such that they become unpaired, paired, or random with respect to lever presses. Thus, contiguity is manipulated independently of contingency. The behavior of rats with hippocampal lesions was robustly superstitious, and contiguity effects were strong. Pairing channeled superstition into the lever press topography, while noncontiguity displaced the activities away from the lever. Random delivery resulted in intermediate rates of lever pressing.

CHOICE OF TIMEOUT DURING RESPONSE INDEPENDENT FOOD SCHEDULES

Rats' lever pressing terminated visual or auditory stimuli associated with fixed-time or variable-time schedules of food delivery and produced a timeout period during which food delivery could not occur. Lever pressing during a timeout period reinstated the food-associated stimuli and again permitted food delivery according to the fixed-time or variable-time schedules. The mean interfood interval ranged from 1 minute to 16 minutes (variable-time schedules) or 32 minutes (fixed-time schedules); the timer controlling schedule intervals did not stop during timeout periods. The percentage of session time spent in timeout increased when the mean interfood intervals were lengthened and decreased when the mean interfood intervals were shortened. Timeouts were initiated most frequently about half way between successive food deliveries (fixed-time schedules) or after 15 seconds or more had lapsed since the last food delivery (variable-time schedules). Elimination of food delivery increased the percentage of session time spent in timeout, and elimination of the timeout contingency decreased lever press rates. When timeout was produced only when the lever was held in the depressed position, little time was spent in timeout. The main determinants of timeout initiation and termination appeared to be the rate of food delivery, freedom of movement during timeout, and the stimulus change associated with initiation and termination of timeout.

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 acetone and toluene vapors on multiple schedule performance of rats

Six rats were trained to press a lever for a liquid food reward on a multiple fixed ratio-fixed interval (FR-FI) schedule of reinforcement. When lever-pressing rates became relatively stable, the animals were exposed to 150 ppm of either acetone or toluene for duration times of 1 2 , 1, 2 and 4 hr. Exposures were conducted at least three weeks apart. Acetone produced minimal changes on the FR-FI responding during the 1 2 hr exposure. During the 1 hr exposure period, both FR and FI rates increased while during the 2 hr exposure, both FR and FI responses decreased below control levels. During the 4 hr exposure FI responses approximated control levels for 2 rats and were above the control level for the third animal while FR rates were below controls for 2 of the 3 subjects. Rate changes under toluene were generally qualitatively similar to those produced by acetone. An initial enhancement of FR and FI rates occurred during the shorter exposure periods followed by a decrease in rates during the longer exposure periods.

The effects of fenfluramine on schedule-induced drinking in rats

The lever pressing of rats was maintained by a fixed-interval 60 sec schedule of food reinforcement. Water bottles were available during sessions and high levels of schedule-induced drinking developed. Both fenfluramine (0.5, 1.0, 2.0, 4.0, 8.0 mg/kg) and d-amphetamine (0.25, 0.5, 1.0, 2.0 mg/kg) produced dose related decreases in this drinking with d-amphetamine approximately four times as potent as fenfluramine. d-Amphetamine produced large increases in overall rates of lever pressing and greatly decreased the duration of postreinforcement pauses. Fenfluramine exerted similar actions but all doses studied these effects were much less than the effects of d-amphetamine on these measures.

Within-session variations in pellet composition and schedule-induced drinking

Rats were given fixed-interval 1 min training for standard formula 45 mg Noyes food pellets with water freely available. Sessions consisted of 60 reinforcements and each pellet was paired with brief stimuli. The rate of licking and lever pressing was measured for successive 10 sec intervals in each fixed-interval 1 min component. Within session probes were made on randomly selected components and consisted of: omitting the food pellet, omitting brief stimuli, substituting sugarless, 30% dextrose, 90% dextrose, 7.5% NaCl, or 30% NaCl 45 mg Noyes pellets for the standard pellet. Results showed that lick rates did not differ from baseline for omission of brief stimuli or substituting sugarless pellets, that omitting the standard pellet or substituting 90% dextrose virtually eliminated drinking, and that lick rates were of intermediate level for 7.5% NaCl, 30% NaCl pellet compositions. Results for lever pressing showed that operant responding was not similarly affected by probes, with only the pellet omission probe producing responding that differed from baseline. Results indicate that immediate within-session effects on lick rates are consistent with between-group or session comparisons for pellet omission and dextrose conditions, but not for NaCl conditions. These findings further support that compositions of food reinforcers per se as well as acquired discriminative properties of food reinforcers are important variables in the maintenance of schedule-induced drinking.

Effects of response-contingent clock stimuli on behavior maintained by intravenous codeine in the rhesus monkey

Response-contingent brief presentations of clock stimuli differentially correlated with food availability altered rates of codeine-maintained lever pressing. Rhesus monkeys performed under a two lever multiple schedule: Multiple fixed interval clock 5 min variable interval 2 min. Different colored lights were presented during successive 75 sec periods of the fixed-interval clock component. Lever pressing under the FI Clock schedule was maintained by presentation of 1 g Noyes pellets, and lever pressing under the VI schedule by 0.05 mg/kg infusions of codeine PO 4. Characteristic schedule-controlled performance developed in both schedule components. When the clock stimulus from the first or the final period of the FI Clock schedule was presented contigent upon completion of a short fixed ratio of responses during the variable-interval schedule component, the first clock stimulus decreased and the final clock stimulus increased rates of codeine-maintained lever pressing. Neither the first nor the final clock stimulus altered the frequency of codeine injection. The effect of each clock stimulus was accentuated by increasing the duration of stimulus presentation and by decreasing the response requirement for stimulus illumination. These rate-altering effects of the clock stimuli were most pronounced when different reinforcers were presented in the two components of the multiple schedule when either food or intravenous codeine injection was available under both components of the multiple schedule, response-contingent clock stimulus presentation did not alter response rates under the VI schedule.