Fixed-ratio Response Rates Research Articles

THE PERSISTENCE OF FIXED-RATIO AND DIFFERENTIAL-REINFORCEMENT-OF-LOW-RATE SCHEDULE PERFORMANCES

The effects of fixed-ratio (FR) and differential-reinforcement-of-low-rate (DRL) schedule histories on behavioral persistence were studied in three experiments with pigeons.After exposure to a multiple FR DRL schedule (baseline), either one of two prefeeding amounts were effected under the same schedule (test condition of Experiment 1), under extinction (test condition of Experiment 2), and under fixed-interval (FI) schedules (test condition of Experiment 3).FR response rates generally were less persistent than DRL response rates in Experiments 1 and 2, with the opposite occurring in Experiment 3. Regardless of the test schedules,FR response rates decreased and were less persistent under the large than under the small prefeeding amount.Rates under DRL schedules, however, were maintained when the test schedule was the same as in baseline (Experiment 1),and increased when the baseline schedule changed to an FI (Experiment 3),regardless of the prefeeding amount.Only when extinction was in effect during the test (Experiment 2)were the effects of prefeeding amounts on DRL rates observed consistently, such that these rates decreased with the larger prefeeding amount.These results suggest that the contingencies on response rates and patterns established by the baseline schedule affect the persistence of operant behavior to different prefeeding amounts and to changes in the test schedule.

The effects of pyridostigmine bromide, permethrin, and DEET alone, or in combination, on fixed-ratio and fixed-interval behavior in male and female rats

Concurrent exposure to pyridostigmine bromide (PB), permethrin (PERM) and/or N, N-diethyl- m-toluamide (DEET) may have contributed to the development of a syndrome that appears to have afflicted military personnel who served during the Gulf War. The present experiment sought to evaluate the behavioral effects of these compounds alone, or in various combinations, in male and female rats. Subjects were exposed to a multiple fixed-ratio (FR) 50, fixed-interval (FI) 2-min schedule of reinforcement. PB dose-dependently decreased FR and FI response rates. FR responding was disrupted by lower doses and there were no differences between the sexes. PERM vehicle administration decreased response rates maintained by both schedules of reinforcement; this was offset by an increase in response rate after the administration of the intermediate dose of PERM. The highest dose of PERM decreased both FR and FI response rates. FR rates in male rats were more disrupted than those in female rats. Only the highest dose of DEET decreased FR and FI response rates in male and female rats. FR rates were more disrupted in female rats than in male rats. Synergistic effects were only observed when FI response rates decreased in male rats upon exposure to half the low dose of PB with half the low dose of PERM or half the low dose of PB with half the low dose of DEET. The results of this experiment thus show that small doses of PB, PERM and DEET disrupt well-established, schedule-controlled behavior in male and female rats in a schedule- and gender-dependent manner; schedule-dependent and gender-dependent synergistic effects were also observed. The mechanism by which the compounds exert these behavioral effects remains to be determined.

Lead-Induced Decrements in Waiting Behavior: Involvement of D 2-Like Dopamine Receptors

Some behavioral changes produced by chronic postweaning lead (Pb) exposure have been linked to mesolimbic dopamine (DA) system alterations. This study sought to determine the role of DA systems in Pb-induced changes in a fixed ratio (FR) waiting-for-reward paradigm. Rats exposed chronically from weaning to 0, 50, or 150 ppm Pb acetate drinking solutions earned free reinforcers for waiting after completion of an FR, with increasing time between successive free reinforcers. Responses during the waiting period reset the FR requirement. Once performance stabilized, the effects of acute IP administration of the D 1 agonist SKF82958, the D 2 agonist quinpirole, the D 1 antagonist SCH23390, and the D 2 antagonist eticlopride were determined. Pb itself increased FR response rates and decreased mean waiting time, a pattern of behavior that increased the number of earned reinforcers, but doubled the number of responses/reinforcer. None of the DA compounds mimicked Pb effects when administered to controls. Only DA agonists altered waiting behavior and responses per reinforcer. Quinpirole, in particular, appeared to reverse Pb effects on the FR wait baseline by increasing waiting time and decreasing FR resets to control levels. These findings point to a particular role for D 2 DA function in Pb’s detrimental effects on waiting.

Operant analysis of chronic locoweed intoxication in sheep.

Five sheep were fed a 10% locoweed (Oxytropis sericea) pellet or alfalfa pellets for 3- to 5-wk periods to determine the effects of intermittent locoweed ingestion on operant responding; three controls were fed alfalfa pellets for 22 wk. Sheep were trained to respond to a multiple schedule with a fixed ratio (FR) 5 and fixed interval (FI) 50 s as major elements; performance was reinforced with rolled barley. Locoweed-treated sheep decreased (P < .05) FR response rate after 4 wk of locoweed feeding, but this decrease first appeared during the first recovery period (wk 6). The FR response rate of intoxicated sheep did not return to baseline during the remainder of the study and differed from controls during most of the study. Controls did not deviate (P > .05) from their FR baseline except during wk 2. Sheep did not stabilize on the FI component. As locoweed-treated sheep became progressively more intoxicated, they altered their pattern of FR responses, with longer post-reinforcement pauses, and a slower overall FR rate. Intoxicated sheep ingested an average of .21 mg swainsonine.kg-1.d-1. Overt signs of intoxication were noted when two sheep were stressed on wk 17. These two sheep had neuroviseral vacuolation typical of locoweed poisoning, whereas the three remaining locoweed-treated sheep that were euthanatized 5 wk later showed little histologic evidence of intoxication. Our findings indicate that "on-off" or cyclic grazing of locoweed ranges should be approached cautiously. Such a grazing program may be feasible because of the rapid resolution of histologic pathology; however, an initial toxic insult of 4 wk seems to be excessive, even at low doses, because sheep may exhibit persistent behavioral abnormalities that require > 6 wk to resolve.

Midazolam's dose effects on fixed-ratio response rate in rats depend on amount of prior training experience.

Midazolam's dose effects on fixed-ratio response rate in rats depend on amount of prior training experience.

Midazolam's dose effects on fixed-ratio response rate in rats depend on amount of prior training experience.

Midazolam's dose effects on fixed-ratio response rate in rats depend on amount of prior training experience.

Thermal stress modulates temporal patterns of responding on a multiple DRL-FR schedule

To investigate temporal changes in behavior induced by moderate cold temperatures, rats performing on a multiple differential-reinforcement-of-low-rate (DRL) fixed-ratio (FR) schedule were exposed to ambient temperatures of 2, 8, 16, and 24°C. DRL response rates markedly increased with decreasing cold temperatures, while FR response rates remained unchanged. In addition, as ambient temperatures decreased, the interresponse time (IRT) distribution of DRL responses shifted toward shorter times and short IRT bursts increased. Compared with cold effects, exposure to 38°C heat induced decreases in both DRL and FR response rates which were associated with increases in long IRTs. Decreases in reinforcement frequency were associated only with the DRL schedule in cold, and with both DRL and FR schedules during heat exposures. The distinct effects of cold and heat on both DRL and FR responding suggest that the increases in DRL response rates and shifts in IRT distribution are unique to cold, and are not due to general effects of nonspecific thermal change in the ambient environment.

Effects of terminating chronic phencyclidine on schedule-controlled behavior in rats

Six rats were trained to respond under a multiple fixed-ratio 30, fixed-interval 3-min schedule for food presentation. Acute administration of phencyclidine (0.1–3.2 mg/kg, IP) produced decreases in fixed-ratio response rates at doses above 0.3 mg/kg, but fixed-interval response rates were only decreased at the highest dose. However, the pattern of fixed-interval responding (as evidenced by quarter-life values) was affected at doses above 0.3 mg/kg. Osmotic minipumps were implanted, SC, which infused saline (2 rats) or phencyclidine (4 rats, 10.0 mg/kg/day) for 10 days, and then removed. Daily behavioral sessions were conducted during infusions and for 10 days afterwards. The effects of phencyclidine infusions on fixed-ratio responding were variable. Fixed-interval response rate and quarter-life values were only modestly affected during drug infusion. All three parameters were markedly affected upon cessation of chronic phencyclidine dosing, but there did not appear to be differential effects between the schedule components. No effects on responding were observed during or after saline infusions.

Nicotine and some related compounds: effects on schedule-controlled behaviour and discriminative properties in rats

Behavioural effects of d- and l-nicotine, d- and l-nornicotine and l-cotinine were studied in two paradigms. In experiment 1, rats responded under a multiple fixed-interval (FI) 5 min, fixed-ratio (FR) 20 schedule of food presentation. Aside from differences in potency and time course, l-nicotine and the stereoisomers of nornicotine produced qualitatively similar effects on rates of responding. With increasing doses of drugs, FI response rates first increased and then decreased, while FR response rates only decreased. In contrast, d-nicotine did not significantly increase FI response rates at lower doses, and only decreased FI and FR response rates at higher doses. At doses up to 100 mg/kg, cotinine produced only dose-dependent increases in FI response rates and had no effect on FR response rates. Rate-increasing effects of cotinine were not blocked by mecamylamine. In experiment 2, rats were trained to discriminate between l-nicotine (0.1 mg/kg SC) and saline (0.1 ml/kg SC) in a two-bar, operant conditioning procedure under a tandem variable-interval (VI) 1 min, FR 10 schedule of food presentation. Full generalization was obtained to d-nicotine and to l- and d-nornicotine. Generalization to cotinine occurred only with large doses that contained significant amounts of nicotine present as an impurity. There was no generalization to non-nicotinic drugs (morphine and clenbuterol), even at doses that reduced response rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of sublethal doses of ionizing radiation on schedule-controlled performance in rats

Male rats responded under a fixed-ratio (FR) 50 or a fixed-interval (FI) 120 sec schedule of milk delivery. Separate groups were acutely exposed to 0.5, 1.5, 4.5 or 0 (FI only) Gray (Gy) of cobalt-60 gamma radiation 3 times at 43-day intervals. All rats received an acute dose of 6.5 Gy 64 days after the last of these exposures. One-half and 1.5 Gy did not alter FR or FI performance significantly. After 4.5 Gy, no observable changes in performance occurred within 1 hr of exposure. Maximal reductions in FR response rates occurred 24 hr after exposure and recovery followed over the subsequent 72 hr. Postreinforcement pause was increased and running response rate was decreased by 4.5 Gy. Similar effects were found after each 4.5 Gy exposure. In contrast, FI performance (overall response rate, postreinforcement pause, running response rate, index of curvature) was not altered reliably by 4.5 Gy. Both FR and FI response rates were reduced by 6.5 Gy beginning 24 hr after exposure; FR rates tended to be reduced more than FI rates 24–72 hr after exposure. Response rates under both schedules recovered gradually over 7 weeks. The behavioral effects of 6.5 Gy did not vary as a function of irradiation history. In contrast, irradiation history affected survival in that 4 9 rats previously exposed to 4.5 Gy died during weeks 4–5 after 6.5 Gy, whereas there were no deaths in the rats previously exposed to lower doses. Radiogenic disruption of operant performance was dose-related, reversible, noncumulative and dependent on the schedule of reinforcement.

Effects of repeated alcohol administration on human operant behaviour.

Nine human subjects were exposed to a multiple fixed-ratio (FR) differential-reinforcement-of-low-rate (DRL) schedule of monetary reinforcement. Presses on a manipulandum requiring relatively high force were occasionally followed by an increased money total displayed on a computer screen. Subjects were exposed to the schedule until their behaviour had stabilized. Prior to each of the next three sessions they were administered 0.85 g/kg alcohol. In eight of the nine subjects the initial effect of alcohol was to increase FR response rate and, consequently, reinforcement rate. Subsequent alcohol administration resulted in sensitization: even greater rate-increasing effects. In two further control sessions behaviour returned towards baseline level. DRL response rate was slightly increased by alcohol, but reinforcement rate remained unchanged. There was no consistent change in DRL response or reinforcement rates from the first to the third alcohol sessions. The effects of alcohol on human behaviour were similar to the effects found in studies with animals. The results were also consistent with the view that the changes in behaviour which occur with repeated drug administration depend in part on whether the initial effect of the drug is to increase, decrease or produce no change in reinforcement rate.

Behavioral effects of CGS 8216 alone, and in combination with diazepam and pentobarbital in dogs

Beagle dogs (N=3) responded under a multiple fixed-interval (FI) 300 sec, fixed-ratio (FR) 30 schedule of food presentation. The pyrazoloquinoline derivative CGS 8216, given either intravenously (0.01–3.0 mg/kg) or orally (0.1–30.0 mg/kg) had little effect on either the rate or temporal pattern of responding during either component. Both diazepam (0.3 to 17.5 mg/kg, PO) and pentobarbital (0.1–17.5 mg/kg, PO) produced qualitatively similar effects on behavior. Rates of responding during the FI components first increased, then decreased with increasing doses; both drugs produced only dose-related decreases in the rate of responding during the FR components. CGS 8216 antagonized some of the behavioral effects of diazepam; FI and FR response rates returned to baseline, however the effects of diazepam on quarter-life values were not appreciably altered by CGS 8216. The effects of pentobarbital on schedule-controlled responding were not antagonized by CGS 8216. These results indicate CGS 8216 is a selective benzodiazepine antagonist that does not produce benzodiazepine-like behavioral effects.

Discriminative stimulus properties and schedule effects of fencamfamine in rats

The behavioral properties of fencamfamine, a sympathomimetic central stimulant recently identified in alleged cocaine samples, were studied in two different paradigms. In Experiment I, rats were trained to discriminate between injections of saline (0.1 ml/kg, IP) and cocaine (3.0 mg/kg, IP) in a two-lever drug discrimination task on a fixed-ratio (FR) 10 schedule of water presentation. Fencamfamine (0.3–3.0 mg/kg, IP) produced cocaine-appropriate choice behavior and was slightly more potent than cocaine in producing this effect. In Experiment II, rats responded under a multiple fixed-interval (FI) 300 sec, FR 20 schedule of water presentation. Fencamfamine (0.1–10.0 mg/kg, IP) and cocaine (0.1–30.0 mg/kg, IP) produced qualitatively similar effects on responding under this schedule. With increasing doses of either drug, FI response rates first increased, then decreased; FR response rates were only decreased. Fencamfamine was approximately three times more potent than cocaine in producing these effects. The results of these two experiments indicate that fencamfamine and cocaine have similar behavioral properties.

RATIO RESPONDING AS A FUNCTION OF CONCURRENT AVOIDANCE SCHEDULES, YOKED SHOCKS, AND RATIO VALUE

Fixed-ratio food-reinforced responding in rats was studied alone and with concurrent shock avoidance or with concurrent response-independent shocks matched to those that occurred in the avoidance condition. Under each condition, fixed-ratio size was increased over successive daily sessions. Fixed-ratio response rate generally passed through a maximum as a function of fixed-ratio size. Decreased fixed-ratio responding at values beyond the maximum occurred when (1) the time to complete a fixed ratio approximated the response-shock interval of the avoidance schedule, (2) the shock rate increased, and/or (3) the ratio requirements were so high that ratio strain occurred. Avoidance rates decreased slightly as fixed-ratio size increased.

Effects of phencyclidine, d-amphetamine and pentobarbital on schedule-controlled behavior in rats

The effects of phencyclidine, d-amphetamine, and pentobarbital on responding maintained under a multiple fixed interval (FI) 3-min fixed-ratio (FR) 30 schedule of food presentation were studied in rats. Phencyclidine (0.32–7.5 mg/kg) had a biphasic effect on overall response rate in both components; response rate increased and then decreased as the dose was increased. The FR was slightly more sensitive to the rate-decreasing effects of phencyclidine than the FI. The effects of d-amphetamine (0.1–7.5 mg/kg) on overall rate were qualitatively similar to those of phencyclidine. The FI tended to be slightly more sensitive than the FR to the rate-increasing effects of d-amphetamine. Pentobarbital (1–18 mg/kg) produced little or no rate-increasing effects in the FR at low doses and decreased FR response rate at higher doses. In the FI, pentobarbital produced small increases in overall rate at intermediate doses while decreasing response rate at higher doses. The FR tended to be more sensitive than the FI to the rate-decreasing effects of pentobarbital. Unlike d-amphetamine and pentobarbital, phencyclidine produced smaller rate-increasing effects when the dose-effect curves were redetermined. Within the FI, the effects of phencyclidine and d-amphetamine on response rate were generally independent of the control rate of responding.

Steady and transition states: effects of alternative activity on body-rocking in retarded children.

Two experiments are reported in which steady and transition states were observed for two independent operants (body-rocking and ball-manipulandum). First, stable fixed-ratio response rates were successively obtained for body-rocking and ball-manipulandum responding. Second, transition states were obtained for the two operants simultaneously. The results showed that the independent operants under standardized experimental conditions showed moderately correlated and stable response rates. The method of simultaneous operants provided a valid technique for analysis of transition states, i.e., the functional separation of stereotyped acts (e.g., body-rocking) and alternative activity (ball-manipulandum). Finally, the effects of experimental manipulations were reversible.

Actual versus potential shock in making shock situations function as negative reinforcers.

The relative importance of potential and actual shocks in making shock situations function as negative reinforcers was studied. Shocks were scheduled to occur at the same rate during two stimuli. During one, squirrel monkeys could avoid the shocks; during the other, they were unavoidable. For the two stimuli the potential rate of shocks was the same, but the actual rate was lower during avoidance because of avoidance responding. Fixed-ratio responding was maintained by the change from unavoidable shock to avoidance, indicating that the change was reinforcing when it resulted in a reduction in actual shock rate with no reduction in potential shock rate. Further increases in the rate of potential shock during avoidance had little effect upon the fixed-ratio responding until the rate was increased to the point that the actual shock rate during avoidance was comparable with that during unavoidable shock. At that point, the fixed-ratio response rate decreased nearly to zero. These findings show that actual shocks are more important than potential shocks in determining whether or not a shock situation will function as a negative reinforcer; this explains why the change from unavoidable shock to avoidable shock is reinforcing.