Biomedical subjects

S H Snodgrass

Publications and source records attributed to S H Snodgrass.

9 recordsLinked to original sources

PubMed1998

Effects of drugs on concurrent variable-interval variable-interval schedule performance.

According to the generalized matching law the ratio of responses between two alternatives matches the ratio of reinforcers produced by these responses. In these experiments using concurrent variable-interval variable-interval schedules in pigeons, responding occurred more frequently on the key associated with the lower reinforcement density (undermatching) than would be predicted by perfect matching. Under control conditions, there was no bias toward responding on either key. Pentobarbital, methamphetamine, morphine and phencylidine all increased bias toward responding on the left key with the exception of one 10 mg/kg dose of pentobarbital that increased bias toward responding on the right key. Higher doses of methamphetamine and morphine, and most doses of phencyclidine increased matching, but high doses of pentobarbital further decreased matching. Morphine increased bias toward responding on the left key at much lower doses than those that affected matching, while phencyclidine increased matching at lower doses than those that increased bias. Pentobarbital produced small increases in response rates that were sometimes accompanied by small increases in key switching. All other drugs only decreased response rate and decreased the number of key switches. These data suggest that drugs disrupt responding under concurrent schedules both by increasing bias and by changing baseline matching functions.

Animals↗

PubMed1997

Behavior of rats under fixed consecutive number schedules: effects of drugs of abuse.

Four rats responded under a simple fixed consecutive number schedule in which eight or more consecutive responses on the run lever, followed by a single response on the reinforcement lever, produced the food reinforcer. Under this simple schedule, dose-response curves were determined for diazepam, morphine, pentobarbital, and phencyclidine. The rats were then trained to respond under a multiple fixed consecutive number schedule in which a discriminative stimulus signaled when the response requirement on the run lever had been completed in one of the two fixed consecutive number component schedules. Under control conditions, the percentage of reinforced runs under the multiple-schedule component with the discriminative stimulus added was much higher than the percentage of reinforced runs under the multiple-schedule component without the discriminative stimulus. All of the drugs decreased the percentage of reinforced runs under each of the fixed consecutive number schedules by increasing the conditional probability of short run lengths. This effect was most consistently produced by morphine. The drugs produced few differences in responding between the multiple fixed consecutive number components. Responding under the simple fixed consecutive number schedule, however, was affected at lower doses of the drugs than was responding under the same fixed consecutive number schedule when it was a component of the multiple schedule. This result may be due to the difference in schedule context or, perhaps, to the order of the experiments.

Animals↗

PubMed1996

Drug discrimination under a concurrent schedule.

Three pigeons were trained to discriminate a 5.0 mg/kg dose of pentobarbital from saline under a two-key concurrent schedule with responding on the key associated with the presession injection, under both stimulus conditions, producing four times as many reinforcers as responding on the other key. This concurrent schedule resulted in approximately 70% responding to the higher reinforcement key under the pentobarbital stimulus and approximately 30% responding to that key under the saline stimulus. During testing, then, the pigeons were able to dose-dependently emit higher (>70%) or lower (<30%) values than were established under the control conditions. Dose-response curves were determined for pentobarbital (twice), methamphetamine, phencyclidine, chlordiazepoxide, and the combination of pentobarbital and the barbiturate antagonist bemegride. The results obtained with pentobarbital and chlordiazepoxide showed that, as the dose increased, pentobarbital-appropriate responding also increased. Methamphetamine produced relatively flat dose--response curves, whereas phencyclidine administration produced inconsistent effects on responding. The combination of the training dose of pentobarbital with increasing doses of bemegride produced a decrease in pentobarbital-appropriate responding. The results also showed that the dose-response curves for pentobarbital and chlordiazepoxide, instead of being all or none, were graded functions of the drug dose.

Animals↗

PubMed1991

Effects of acute and chronic administration of delta 9-tetrahy-drocannabinol or cocaine on ethanol intake in a rat model.

The acute and chronic administration of delta 9-tetrahydrocannabinol (delta 9-THC) or cocaine were studied in rats trained to obtain all of their daily food by lever pressing during four equally-spaced 30-min periods with water and 5% or 7.5% ethanol solutions freely available. With 5% ethanol available, rats consumed almost all of their daily fluid intake as ethanol, while with 7.5% ethanol available, rats consumed water and ethanol solution in approximately equal amounts. Rats consumed more food pellets with 7.5% ethanol available than with 5% ethanol available. Acute administration of delta 9-THC produced a dose-dependent decrease of 5% ethanol intake and food pellets consumed with a small increase in water intake, especially after the higher doses. Acute administration of delta 9-THC also depressed food intake when 7.5% ethanol was available, but decreases in ethanol solution intake were small. Chronic administration of delta 9-THC initially decreased ethanol intake, but tolerance occurred to this effect, so that during chronic delta 9-THC administration ethanol intake not only recovered, but increased above control levels. When the chronic administration of delta 9-THC was discontinued, ethanol intake was increased for 1 (5% ethanol) to 3 (7.5% ethanol) weeks. Animals with initially high, or initially low, but not with initially moderate ethanol intake, accounted for the increased ethanol intake during chronic delta 9-THC administration and withdrawal. Acute cocaine administration, at doses up to 30 mg/kg, had little effect on eating and drinking; however, during chronic cocaine administration, ethanol intake gradually increased, an increase which was sustained during cocaine withdrawal. The increased ethanol drinking was confined to the first 6-h period after cocaine administration. These data suggest that the chronic administration and withdrawal of other drugs can increase ethanol intake in this rat model.

Alcohol Drinking↗

PubMed1991

Effects of schedule of reinforcement on a pentobarbital discrimination in rats.

The purpose of this study was to determine the effects of the schedule of reinforcement on a pentobarbital discrimination in rats. Five rats were trained to discriminate 10 mg/kg pentobarbital from saline under a multiple fixed-interval 180-s fixed-ratio 20 schedule of reinforcement. During both saline and pentobarbital training sessions, subjects emitted a higher percentage of correct responses under the fixed-ratio component as compared to the fixed-interval component of the multiple schedule. Determination of the pentobarbital dose-response curve under the fixed-ratio component resulted in a steep curve characterized by responding on the saline lever at low doses and on the drug lever at higher doses. Under the fixed-interval component, a graded dose-effect curve was produced, with considerable responding on both levers after intermediate doses of pentobarbital. The administration of phencyclidine and MK-801 resulted in an intermediate level of drug-lever responding for some subjects. Administration of d-amphetamine resulted in saline (nondrug) appropriate responding. The results of this study demonstrate that the schedule of reinforcement is a determinant of drug stimulus control, just as it is a determinant of other drug effects.

Animals↗

PubMed1989

Time-response effects of pimozide on operant behavior and schedule-induced polydipsia.

Previous research has indicated that the administration of specific doses of pimozide results in the suppression of the acquisition of schedule-induced polydipsia in rats while not affecting operant behavior. The purpose of this study was to determine if these results were due to a specific action of pimozide on schedule-induced polydipsia or if they were due to an insufficient presession time of drug administration. Pimozide at 1.0 mg/kg was administered to three groups of rats at either 30, 60 or 120 minutes presession with control subjects receiving administration of the drug vehicle also at these times. The results of the study were that both operant behavior and the acquisition of schedule-induced polydipsia were affected in a nondifferential and time-dependent manner by pimozide. It was also found that pimozide caused an alteration in the temporal pattern of both schedule-induced polydipsia and operant responding. This latter result appears to have been caused by a disruption in sensorimotor integration due to the dopamine blocking properties of pimozide.

Animals↗

PubMed1989

Repeated acquisition of behavioral chains: response sequences or conditional discriminations?

The purpose of this study was to determine whether pigeons learn a sequence of positional responses or a series of conditional discriminations under a repeated-acquisition-of-behavioral-chains procedure. Three pigeons were trained under a repeated-acquisition procedure in which three different key colors served as stimuli correlated with the three steps in a chain. The order of presentation of the three stimuli was altered during the latter part of each test session after acquisition had occurred. If the pigeons had acquired a response sequence, the pattern of responding should remain the same as in the initial portion of the test session. However, if the pigeons had acquired a conditional discrimination, the response pattern should change in accordance with the changed order of the key colors. Although the results of this study do not rule out the possibility that the subjects acquired, to some degree, a response sequence, the results suggest that the behavior of pigeons under a repeated-acquisition-of-behavioral-chains procedure is controlled primarily by conditional discriminative stimuli.

Animals↗

PubMed1988

The effects of apomorphine on the acquisition of schedule-induced polydipsia in rats.

Injections of the dopamine agent, apomorphine, at the doses of 0.05, 0.50 and 1.0 mg/kg were given to three different groups of rats while a fourth group received an injection of the drug vehicle. The injections preceded each of 15 schedule-induced polydipsia (SIP) acquisition sessions in which the subjects bar-pressed for food pellets on a fixed interval 60-sec schedule of reinforcement. The vehicle-injected group developed SIP over sessions while each dose of apomorphine suppressed the acquisition of SIP. Bar-press rates were also depressed at the higher doses, while response patterning was affected at the lower dose. The results support the contention that a normally functioning dopamine system is necessary for the acquisition of SIP, but they do not support the view that this neurotransmitter system is specifically involved in the generation of SIP.

Animals↗

PubMed1987

Effect of dopamine agents on schedule- and deprivation-induced drinking in rats.

The dopamine agonist, apomorphine, or its antagonist, haloperidol, was administered to rats whose drinking was induced by fixed-interval schedules of pellet delivery or by water deprivation. The first study revealed that both drugs produced dose-dependent decreases in bar-pressing and schedule-induced polydipsia (SIP). At higher doses, haloperidol also depressed the rate of pellet delivery. The second study demonstrated that the suppression in SIP obtained in the first study was primarily due to the direct effect of the drugs and not to changes they produced on the underlying food reinforcement schedule. The third study showed that both drugs suppressed water deprivation-induced drinking during a ten-minute session. Apomorphine delayed the onset of drinking, while haloperidol accelerated the cessation of drinking. The results indicated that apomorphine produced motor deficits that interfered with consummatory behavior, and that haloperidol interfered with the sensory feedback necessary to sustain consummatory behavior.

Animals↗