Effects of morphine sulfate on operant behavior in rhesus monkeys

Prenatal manganese biomarkers and operant test battery performance in Mexican children: Effect modification by child sex

BACKGROUND

Manganese (Mn) is essential to healthy neurodevelopment, but both Mn deficiency and over-exposure have been linked to prefrontal cortex (PFC) impairments, the brain region that regulates cognitive and neurobehavioral processes responsible for spatial memory, learning, motivation, and time perception. These processes facilitated by attention, inhibitory control, working memory, and cognitive flexibility are often sexually dimorphic and complex, driven by multiple interconnected neurologic and cognitive domains.

OBJECTIVE

We investigated the role of child sex as an effect modifier of the association between prenatal Mn exposure and performance in an operant testing battery (OTB) that assessed multiple cognitive and behavioral functional domains.

METHODS

Children (N = 575) aged 6-8 years completed five OTB tasks. Blood and urinary Mn measurements were collected from mothers in the 2nd and 3rd trimesters. Multiple regression models estimated the association between Mn biomarkers at each trimester with OTB performance while adjusting for socio-demographic covariates. Covariate-adjusted weighted quantile sum (WQS) regression models were used to estimate the association of a Mn multi-media biomarker (MMB) mixture with OTB performance. Interaction terms were used to estimate modification effect by child sex.

RESULTS

Higher blood Mn exposure was associated with better response rates (more motivation) on the progressive ratio task and higher overall accuracy on the delayed matching-to-sample task. In the WQS models, the MMB mixture was associated with better response rates (more motivation) on the progressive ratio task. Additionally, for the linear and WQS models, we observed a modification effect by child sex in the progressive ratio and delayed matching-to-sample tasks. Higher prenatal Mn biomarker levels were associated with improved task performance for girls and reduced performance in boys.

CONCLUSION

Higher prenatal blood Mn concentrations and the MMB mixture predicted improved performance on two of five operant tasks. Higher prenatal Mn concentrations regulated executive functions in children in a sexually dimorphic manner. Higher prenatal Mn exposure is associated with improved performance on spatial memory and motivation tasks in girls, suggesting that Mn's nutritional role is sexually dimorphic, and should be considered when making dietary and/or environmental intervention recommendations.

Morphine reduces the interest for natural rewards

RATIONALE

Alongside a pathological, excessive, motivation for substances of abuse, substance use disorder (SUD) patients often show a dramatic loss of interest for naturally rewarding activities, such as positive peer social interaction and food intake. Yet, pre-clinical evidence of the latter SUD features remains scarce and inconsistent.

OBJECTIVES

In the current study, we investigated the effect of non-rewarding and rewarding doses of morphine upon social behaviour, motivation for and intake of palatable food, in male and female C57BL/6J mice.

METHODS

First, the rewarding effects of two relatively low morphine doses (1.25 and 2.5 mg/kg) were assessed using a newly established single substance administration/conditioning trial conditioned place preference (CPP) paradigm. Then, morphine (1.25 and 2.5 mg/kg) effects upon social behaviour, motivation for and intake of palatable food were examined by the three-chamber (3-CH), an operant behaviour and a palatable food preference test, respectively.

RESULTS

Morphine (2.5 mg/kg) induced CPP in both male and female mice, whereas morphine (1.25 mg/kg) induced CPP only in female mice. Both morphine doses (1.25 and 2.5 mg/kg) reduced sociability, motivation for and intake of palatable food in male and female mice, independently of cognitive function or locomotor activity.

CONCLUSIONS

Female mice were more sensitive than male mice to the rewarding effects of morphine. Moreover, both a non-rewarding and a rewarding dose of morphine impaired the interest for naturally rewarding activities, indicating that brain reward systems might be more sensitive to the deleterious than to the rewarding effects of substances of abuse.

Remifentanil maintains lower initial delayed nonmatching-to-sample accuracy compared to food pellets in male rhesus monkeys

Emerging human laboratory and preclinical drug self-administration data suggest that a history of contingent abused drug exposure impairs performance in operant discrimination procedures, such as delayed nonmatching-to-sample (DNMTS), that are hypothesized to assess components of executive function. However, these preclinical discrimination studies have exclusively used food as the reinforcer and the effects of drugs as reinforcers in these operant procedures are unknown. The present study determined effects of contingent intravenous remifentanil injections on DNMTS performance hypothesized to assess 1 aspect of executive function, working memory. Daily behavioral sessions consisted of 2 components with sequential intravenous remifentanil (0, 0.01-1.0 μg/kg/injection) or food (0, 1-10 pellets) availability in nonopioid dependent male rhesus monkeys (n = 3). Remifentanil functioned as a reinforcer in the DNMTS procedure. Similar delay-dependent DNMTS accuracy was observed under both remifentanil- and food-maintained components, such that higher accuracies were maintained at shorter (0.1-1.0 s) delays and lower accuracies approaching chance performance were maintained at longer (10-32 s) delays. Remifentanil maintained significantly lower initial DNMTS accuracy compared to food. Reinforcer magnitude was not an important determinant of DNMTS accuracy for either remifentanil or food. These results extend the range of experimental procedures under which drugs function as reinforcers. Furthermore, the selective remifentanil-induced decrease in initial DNMTS accuracy is consistent with a selective impairment of attentional, but not memorial, processes. (PsycINFO Database Record

Effects of Morphine on Behavioral Task Performance in SIV-Infected Rhesus Macaques

The abuse of opiates such as morphine in synergy with HIV infection not only exacerbates neuropathogenesis but significantly impacts behavioral attributes in HIV infected subjects. Thus, the goal of the current study was to characterize behavioral perturbations in rhesus macaques subjected to chronic morphine and SIV infection. Specifically, we assessed three behavioral tasks: motor skill (MS), forelimb force (FFT) and progressive ratio (PR) tasks. After collecting baseline control data (44 weeks) and data during the morphine-only dependency period (26 weeks), a subset of animals were productively infected with neurovirulent strains of SIVmac (R71/E17) for an additional 33 weeks. A general pattern in the results is that behavioral decline occurred with high CSF viral loads but not necessarily with high plasma viral loads. Compared to saline controls, all treated animals showed significant decreases in performance on all three behavioral tasks during the morphine-only dependency period. During the post infection period, only the morphine plus SIV group showed a significant further decline and this only occurred for the MS task. Taken together, these data demonstrate a clear effect of morphine to produce behavioral deficits and also suggest that morphine can act synergistically with SIV/HIV to exacerbate behavioral deficits.

Interactive effects of morphine and dopaminergic compounds on spatial working memory in rhesus monkeys

Opiates and dopamine (DA) play key roles in learning and memory in humans and animals. Although interactions between these neurotransmitters have been found, their functional roles remain to be fully elucidated, and their dysfunction may contribute to human diseases and addiction. Here we investigated the interactions of morphine and dopaminergic neurotransmitter systems with respect to learning and memory in rhesus monkeys by using the Wisconsin General Test Apparatus (WGTA) delayed-response task. Morphine and DA agonists (SKF-38393, apomorphine and bromocriptine) or DA antagonists (SKF-83566, haloperidol and sulpiride) were co-administered to the monkeys 30 min prior to the task. We found that dose-patterned co-administration of morphine with D1 or D2 antagonists or agonists reversed the impaired spatial working memory induced by morphine or the compounds alone. For example, morphine at 0.01 mg/kg impaired spatial working memory, while morphine (0.01 mg/kg) and apomorphine (0.01 or 0.06 mg/kg) co-treatment ameliorated this effect. Our findings suggest that the interactions between morphine and dopaminergic compounds influence spatial working memory in rhesus monkeys. A better understanding of these interactive relationships may provide insights into human addiction.

Oxycodone lengthens reproductions of suprasecond time intervals in human research volunteers

Oxycodone, a popularly used opioid for treating pain, is widely abused. Other drugs of abuse have been shown to affect time perception, which, in turn, may affect sensitivity to future consequences. This may contribute to continued use. This study evaluated the effect of oxycodone on time perception in normal healthy volunteers. For this within-subject, double-blind design study, participants performed a temporal reproduction task before and after receiving placebo or oxycodone (15 mg, orally) over six outpatient sessions. Participants were first trained with feedback to reproduce three standard intervals (1.1, 2.2, and 3.3 s) in separate blocks by matching response latency from a start signal to the duration of that block's standard interval. During testing, participants were instructed to reproduce the three intervals from memory without feedback before and after drug administration. Oxycodone significantly lengthened time estimations for the two longer intervals relative to placebo. These results suggest that opioids alter temporal processing for intervals greater than 1 s, raising questions about the effect of these drugs on the valuation of future consequences.

The role of mediodorsal thalamus in temporal differentiation of reward-guided actions

The mediodorsal thalamus (MD) is a crucial component of the neural network involved in the learning and generation of goal-directed actions. A series of experiments reported here examined the contributions of MD to the temporal differentiation of reward-guided actions. In Experiment 1, we trained rats on a discrete-trial, fixed-criterion temporal differentiation task, in which only lever presses exceeding a threshold duration value were rewarded. Pre-training MD lesions impaired temporal differentiation of action duration, by increasing the dispersion of the duration distribution. Post-training MD lesions also impaired differentiation, but by reducing the average emitted press durations, thus shifting the distribution without increasing the dispersion. In Experiment 2, we trained rats to space their lever pressing above criterion inter-press-intervals in order to earn rewards. Both pre-training and post-training MD lesions impaired the differentiation of inter-press-intervals. These results show that MD plays an important role in the acquisition and expression of action differentiation.

Antidepressants alleviate the impact of reinforcer downshift

Depressive disorder is associated with problems of coping with life's difficulties, including episodes of frustration and disappointment, operationally defined as an unexpected reinforcer omission or a reduction of reinforcer magnitude. In a novel model aimed at detecting potential antidepressants, rats were trained in the operant task under progressive ratio schedule of reinforcement with the break point (BP, the value of the last completed response ratio) as a behavioral endpoint. In the main experiment, a 32% sucrose solution was initially used as the reinforcer. Once the stable responding was achieved, for the following 5 days animals were treated once daily with the experimental drugs, and were offered a 4% sucrose solution instead. In vehicle-treated controls, the reduction of sucrose concentration resulted in a decrease in responding from a BP of about 40 (totaling 166 responses) to a BP of about 9 (totaling 22 responses). Chlordiazepoxide (4 and 8 mg/kg), fluoxetine (3 mg/kg), citalopram (6 mg/kg) and cocaine (2.5 and 5 mg/kg) markedly inhibited this response decrement, while fluoxetine (6 mg/kg) augmented it. Neither desipramine (1-6 mg/kg) nor morphine (1-5 mg/kg) affected responding under the reduced sucrose concentration condition. In the control experiment, the rats have never been offered 32% sucrose solution but their responding was always maintained by 4% sucrose. Under these unchanged conditions, only cocaine (5 mg/kg) affected (increased) responding. The present results suggest that the antidepressants selectively inhibiting serotonin reuptake and a benzodiazepine anxiolytic but not psychostimulant cocaine may specifically protect animals from the effects of a reinforcer downshift.

The effects of morphine on the production and discrimination of interresponse times

Recent experiments suggest that the effects of drugs of abuse on the discrimination of the passage of time may differ for experimenter-imposed and subject-produced events. The current experiment examined this suggestion by determining the effects of morphine on the discrimination of interresponse times (IRTs). Pigeons pecked a center key on a random-interval 20-s schedule of matching-to-sample trials. Once the interval had timed out, a choice trial randomly followed either a short (2- to 3-s) or long (6- to 9-s) IRT on the center key. Pecking the side key lit one color produced food after a short IRT, and pecking the side key lit the other color produced food after a long IRT. Two experimental phases differed in the functional role of the different key colors. Under control conditions, the IRT distributions had two modes, one at the lower bound of the short category and a smaller one at the lower bound of the long category. Pigeons accurately categorized the duration of the IRTs: One key color was pecked following short IRTs and the other key color was pecked following long IRTs. Morphine flattened the IRT distribution and reduced the accuracy of categorizing IRTs. Categorization of long IRTs was particularly disrupted. Morphine did not produce overestimation of time as assessed by the production or categorization of IRTs. These results are similar to those obtained previously for the effects of morphine on the discrimination of the duration of experimenter-imposed events.

Low dose systemic morphine attenuates operant escape but facilitates innate reflex responses to thermal stimulation

Effects of systemic morphine on operant escape responses of rats to thermal stimulation were compared directly with effects on innate licking and guarding responses. For these independent tests, thermal stimulation was delivered via the floor of testing chambers with or without platforms that provided an escape option. The principal findings were (1) administration of 0.5 to 1.5 mg/kg morphine attenuated escape from nociceptive heat and (2) in distinct contrast, licking and guarding responses to heat were enhanced by these doses. When escape responding was calculated as time on the heated plate without licking or guarding, sensitivity to morphine was greater for 44 degrees C than for 47 degrees C or 50 degrees C. Also, escape responses to cold (0 degrees C or 10 degrees C) were unaffected by 1.5 mg/kg morphine. The preferential reduction of heat nociception by morphine was demonstrated also by an operant preference task that gave the animals the option of standing on a cold (10 degrees C) or a hot (45 degrees C) surface. Administration of 0.5 mg/kg morphine increased occupancy of the hot surface. Platform time during operant tests was low and variable for warm stimulation (36 degrees C) and was significantly increased by each level of heat, showing that platform occupancy represented escape from nociception rather than avoidance responses. A lack of significant effects of 1.5 mg/kg morphine on operant performance during cold or warm stimulation controls for effects of systemic morphine other than antinociception.

Enhanced attention in rhesus monkeys as a common factor for the cognitive effects of drugs with abuse potential

RATIONALE

One of the common neurochemical features of many drugs of abuse is their ability to directly or indirectly enhance dopaminergic activity in the brain, particularly within the ventral tegmental-nucleus accumbens pathway. Dopaminergic pathways in the frontal and limbic cortex also may be targets for these agents, where pharmacological effects could result in heightened attention and/or support self-administration behavior.

OBJECTIVES

The purpose of this study was to determine whether drugs from differing pharmacological classes that exhibit abuse potential would share the ability to counter distractability in the delayed matching task.

METHODS

Well trained mature macaques performed a computer-assisted delayed matching-to-sample task which included trials associated with three delay intervals and randomly interspersed task-relevant distractors. Drug regimens included four to five doses and subjects were tested no more than twice per week.

RESULTS

All but one of the six compounds (tomoxetine), on average, increased task accuracy for either non-distractor or distractor trials. It was evident that for several compounds, doses required to improve accuracy for non-distractor trials were routinely greater than the doses required to improve accuracy for distractor trials. Data for the individualized Best dose (based upon the subject's optimal level of accuracy during distractor trials) revealed statistically significant distractor-related improvements in task accuracy for the same five compounds. The relative efficacy for reversing distractor-induced decrements in task accuracy was estimated by the level of improvement with respect to baseline: nomifensine (31%)>nicotine (22%) approximately morphine (19%) approximately caffeine (19%) approximately methylphenidate (22%) >tomoxetine (9%). Tomoxetine (noradrenergic preferring) was the only compound that did not produce a significant improvement in accuracy.

CONCLUSIONS

These results provide pharmacological support for the concept that attentional mechanisms may play an important role in the "environmental" associative aspects of drug seeking behavior, and as such they may provide the basis for treatment strategies aimed at preventing relapse in detoxified addicts.

Effects of repeated exposure to JP-8 jet fuel vapor on learning of simple and difficult operant tasks by rats

Groups of 16 Sprague-Dawley rats each were exposed by whole-body inhalation methods to JP-8 jet fuel at the highest vapor concentration without formation of aerosol (1,000 +/- 10% mg/m3); to 50% of this concentration (500 +/- 10% mg/m3); or to treated room air (70 +/- 81 L/min) for 6 h/d, 5 d/wk, for 6 wk (180 h). Although two subjects died of apparent kidney complications during the study, no other change in the health status of exposed rats was observed, including rate of weight gain. Following a 65-d period of rest, rats were evaluated for their capacity to learn and perform a series of operant tasks. These tasks ranged in difficulty from learning of a simple food-reinforced lever pressing response, to learning a task in which subjects were required to emit up to four-response chains of pressing three different levers (e.g., press levers C, R, L, then C). It was shown that repeated exposure to 1,000 mg/m3 JP-8 vapor induced significant deficits in acquisition or performance of moderately difficult or difficult tasks, but not simple learning tasks, as compared to those animals exposed to 500 mg/m3. Learning/performance of complex tasks by the 500-mg/m3 exposure group generally exceeded the performance of control animals, while learning by the 1,000-mg/m3 group was nearly always inferior to controls, indicating possible "neurobehavioral" hormesis. These findings appear consistent with some previously reported data for operant performance following acute exposure to certain hydrocarbon constituents of JP-8 (i.e., toluene, xylenes). There has, however, been little previously published research demonstrating long-term learning effects for repeated hydrocarbon fuel exposures. Examination of regional brain tissues from vapor-exposed rats indicated significant changes in levels of dopamine in the cerebral cortex and DOPAC in the brainstem, measured as long as 180 d postexposure, as compared to controls.

[Critical analysis of animal models of acute pain. II]

OBJECTIVE

To analyse models of acute pain in experimental animals.

DATA SOURCES

References were obtained from computerised bibliographic data banks (Medline and others) and the authors' personal documents.

DATA SYNTHESIS

The majority of tests permit only a measurement of threshold, whereas clinical pain is almost always prolonged. The relationships between tests of acute pain and motor activity are reviewed from a number of standpoints; in particular we consider the influence, which postural adjustments of the animal may exert on motor responses in the limbs and the significance of flexor and extensor reflexes. In analysing the problem of the sensitivity of tests, we raise the following questions: 1) what type(s) of fibres underlie the observed responses and might these be different depending on whether one is stimulating a healthy or an inflamed tissue; 2) what significance do measurements of "latency" have when a stimulus is increasing; 3) how valid are the methods of analysing the results? The influence of species and the genetic line used in tests and the specificity and predictivity of tests are considered. Finally, we review those factors, which may distort behavioural measurements in animals, notably--pharmacokinetics, interactions between heterotopic stimuli, environmental factors and related psychophysiological/psychological considerations (subjective "undesirable" phenomena, learning phenomena). We pay particular attention to related physiological functions (thermoregulation, vasomotricity, blood pressure). These considerations lead us to re-position nociception within a much larger homeostatic framework which in addition to pain, includes phenomena such as anxiety and vegetative functions. They also suggest that we should define an "effective stimulus" as one, which activates nociceptive nerve terminals after a physical stimulus, has passed through a "peripheral lens" which regulates its intensity for reasons, which are physical, albeit of biological origin. Finally they remind us that the "system of pain" forms part of a whole set of subsystems--sensory, motor, vegetative, emotional, motivational--which scientific method, being reductionist by nature, cannot study in its entirety. However one must consider results of nociceptive tests within this general context.

CONCLUSION

It is only by taking the approach described in this review, that fundamental and clinical research can interact usefully.

Morphine-induced spinal cholinergic activation: in vivo imaging with positron emission tomography

Positron emission tomography (PET) imaging of spinal cord in monkeys with a cholinergic tracer demonstrates increased spinal cholinergic activity in response to an analgesic dose of morphine, and this PET result correlates with measurement of acetylcholine spillover into spinal cord extracellular space induced by morphine, as measured by microdialysis. Previous studies in rats, mice, and sheep demonstrate activation of spinal cholinergic neurons by systemic opioid administration, and participation of this cholinergic activity in opioid-induced analgesia. Testing the relevance of this observation in humans has been limited to measurement of acetylcholine spillover into lumbar cerebrospinal fluid. The purpose of this study was to apply a recently developed method to image spinal cholinergic terminals non-invasively via PET and to test the hypothesis that the tracer utilized would reflect changes in local cholinergic activity. Following Animal Care and Use Committee approval, seven adult male rhesus monkeys were anesthetized on three separate occasions. On two of the occasions PET scans were performed using [(18)F] (+)-4-fluorobenzyltrozamicol ([(18)F]FBT), which selectively binds to the vesicular acetylcholine (ACh) transporter in the presynaptic cholinergic terminals. PET scans were preceded by injection of either saline or an analgesic dose of IV morphine (10 mg/kg). On the third occasion, microdialysis catheters were inserted in the spinal cord dorsal horn and acetylcholine concentrations in dialysates determined before and after IV morphine injection. Morphine increased cholinergic activity in the spinal cord, as determined by blood flow corrected distribution volume of [(18)F]FBT in the cervical cord compared to the cerebellum. Morphine also increased acetylcholine concentrations in microdialysates from the cervical cord dorsal horn. The one animal which did not show increased spinal cholinergic activity by PET from this dose of morphine also did not show increased acetylcholine from this morphine dose in the microdialysis experiment. These data confirm the ability to use PET to image spinal cholinergic terminals in the monkey spinal cord and suggest that acute changes in cholinergic activity can be imaged with this non-invasive technique. Following preclinical screening, PET scanning with [(18)F]FBT may be useful to investigate mechanisms of analgesic action in normal humans and in those with pain.

Effect of drugs on response-duration differentiation VII: response-force requirements

Rats were trained to press a lever for at least 1 s but for less than 1.3 s. The force required to press the lever was then increased or decreased by 10, 15, or 20 g. Increases in the force requirements for lever pressing decreased timing accuracy, but decreases in the force requirement had the opposite effect. Accuracy decreases at increasing force requirements were characterized by an increase in the relative frequency of responses that were too short to meet the reinforcement criterion. In contrast, increases in accuracy when the force requirements were decreased were characterized by increases in response durations that met the reinforcement criterion and decreases in the relative frequency of responses that were too short to produce the reinforcer. Phencyclidine (PCP) and methamphetamine produced dose-dependent decreases in accuracy that were associated primarily with increases in the relative frequency of short response durations, although methamphetamine also produced increases in long response durations at some doses. When the effects of PCP were determined with the force requirement increased by 10 g or decreased by 15 g, the cumulative response-duration distribution shifted toward even shorter response durations. When the effects of methamphetamine were determined with the force requirement on the lever increased by 10 g, the cumulative frequency distribution was shifted toward shorter response durations to about the same extent as it had been before force requirements increased; however, when the force required to press the lever was decreased by 15 g, these shifts toward shorter response durations almost completely disappeared. These results show that increases and decreases in the force requirements for lever pressing have different effects on the accuracy of temporal response differentiation.

Methods for studying nonhuman primates in neurobehavioral toxicology and teratology

The behavioral repertoire of nonhuman primates is highly evolved and includes advanced problem-solving capabilities, complex social relationships, and sensory acuity equal or superior to humans. These factors make nonhuman primates valuable animal models for studies of the functional effects of neurotoxicants. This review provides descriptions of tests designed to study learning, memory, schedule-controlled behavior, information processing, social behavior, sensory functioning, and visual-motor coordination and/or visuospatial orientation in macaque monkeys. Whenever possible, the results of studies in primate behavioral toxicology are provided for individual test measures. The primate model is especially useful for studies of developmental exposures because monkeys, like humans, have relatively prolonged periods of gestation, infancy, and adolescence. In recognition of this, a special section is provided for tasks that are specifically designed to study behavioral processes in infant monkeys.

Similar effects of amphetamine and methylphenidate on the performance of complex operant tasks in rats

Methylphenidate and D-amphetamine are central nervous system stimulants that have been suggested to share certain behavioral and neurochemical effects. The current study was undertaken to determine whether methylphenidate and D-amphetamine have similar effects on the performance of a battery of complex operant tasks in rats. Thus, the effects of amphetamine (0.1-6.0 mg/kg, i.p.) and methylphenidate (1.12-18.0 mg/kg, i.p) on the performance of rats in three complex food-reinforced operant tasks were examined. The tasks (and the brain functions they are intended to model) included: (1) conditioned position responding (auditory/visual/position discrimination); (2) incremental repeated acquisition (learning); and (3) temporal response differentiation (time estimation). In addition, each of these tasks was paired with a progressive ratio task to assess drug effects on the rats' motivation to lever press for the food reinforcers used. Consistent with their effects in other behavioral paradigms, methylphenidate and D-amphetamine produced very similar patterns of disruption of the four tasks. Drug-induced changes in the endpoints of the progressive ratio task generally paralleled changes in the other three tasks, suggesting a major role for appetitive motivation in the effects of these agents. Several effects of these agents seen in the current study are consistent with their effects in children with attention-deficit-hyperactivity disorder. These data further validate the use of this battery of operant tasks for the characterization of pharmacological agents, and suggest that findings using these tasks may be predictive of what is seen in humans.

Adaptation of a primate operant test battery to the rat: effects of chlorpromazine

The National Center for Toxicological Research (NCTR) Operant Test Battery (OTB) has been used extensively in rhesus monkeys to characterize the effects of drugs and toxicants on the performance of tasks designed to model several cognitive functions. Recently, the majority of the OTB tasks have been adapted for use in rats. The current study is the first to examine the effects of a prototypic pharmacological agent previously assessed in monkeys on rat OTB performance. The effects of the dopamine antagonist chlorpromazine (0.56-5.6 mg/kg, i.p.) were assessed in rats performing tasks designed to model auditory-visual-position discrimination, learning, time estimation, and appetitive motivation. All four tasks were equally sensitive to the behavioral effects of chlorpromazine. This pattern of sensitivity was very similar to that obtained when chlorpromazine was tested in monkeys performing the OTB. These data thus suggest that operant tasks designed to model cognitive functions in monkeys can also be used in rats, and that the effects of chlorpromazine on the performance of these tasks may be predictive of results obtained with monkeys. Further characterization of the rat OTB using prototypic pharmacological agents will further determine the extent to which drug effects on rat OTB performance can be generalized to primates.

Operant test battery performance in children: correlation with IQ

The relationship between intelligence and money-(nickel-)reinforced operant behaviors were compared in 115 six year old children. The Operant Test Battery (OTB) consists of tasks thought to engender responses dependent upon specific brain functions that include motivation, color and position discrimination, learning, short-term memory, and time estimation. OTB endpoints were compared with Full Scale, Verbal and Performance IQ scores. Highly significant correlations were noted between several OTB measures (e.g., color and position discrimination accuracy) and IQ scores, but not in others (e.g., motivation task response rate). The results demonstrate the relevance of these measures as metrics of important brain functions. Additionally, since laboratory animals can readily perform these same tasks, these kinds of behaviors in laboratory animals should be useful in studying the effects of neuroactive/neurotoxic compounds on aspects of cognitive function in animals and in predicting adverse effects of such agents on related brain functions in humans.

Acute and chronic effects of morphine under a progressive-ratio 25 schedule of food delivery

The present study examined the effects of morphine in pigeons responding under a progressive-ratio 25 schedule of food delivery. Morphine initially reduced response rates and breaking points. With chronic exposure, tolerance developed to these effects. The magnitude of the observed tolerance was not obviously different from that previously reported under a PR 5 schedule of food delivery. In addition, when drug effects were compared under the fixed-ratio 25 and fixed-ratio 100 components comprised by the progressive-ratio schedule, comparable tolerance was observed. Although prior studies using other procedures have shown that ratio size modulates the development of tolerance to morphine and other drugs, the present data suggest that this relation is constrained, and is not easily observed under progressive-ratio schedules.

Acute and chronic effects of morphine in pigeons responding under a progressive-ratio schedule of food delivery

Although progressive-ratio schedules have often been used by behavioral pharmacologists to index the relative reinforcing effects of drugs of abuse, they have been ignored in the study of tolerance to opioids. The present study examined tolerance to morphine in pigeons responding under a progressive-ratio 5 schedule of food delivery. Acute administrations of morphine produced general dose-dependent reductions in response rates and breaking points. Dose-response curves for both measures shifted rightward substantially (roughly fivefold) following chronic (daily) exposure to morphine, indicating that tolerance developed to the drug's effects.

The effect of chronic cocaine exposure during pregnancy on the acquisition of operant behaviors by rhesus monkey offspring

To explore possible long-term effects of gestational cocaine exposure in a nonhuman primate model, pregnant rhesus monkeys were treated from about 1 month of gestation until term with either 0 (N = 3), 0.3 (N = 3), 1.0 (N = 3), or escalating doses up to 8.5 (N = 3) mg/kg (IM), three times per day, 5 consecutive days per week. Despite these differences in cocaine exposure, the experimental groups did not differ significantly with respect to the postnatal growth of offspring over an 18-month period following birth. Beginning at 6 months of age, the behavior of offspring was monitored using an operant test battery that included five food-reinforced tasks designed to model aspects of learning, color and position discrimination, time estimation, short-term memory and attention, and motivation. Although the acquisition of each operant behavior by offspring progressed significantly during training between 6 and 18 months of age, this acquisition was not differentially affected by gestational cocaine exposure. It was concluded that, in a rhesus monkey model, chronic cocaine exposure during pregnancy had no significant effect on the offsprings' acquisition of operant behaviors.

Acute behavioral effects of phencyclidine on rhesus monkey performance in an operant test battery

The effects of phencyclidine (PCP; a noncompetitive NMDA antagonist) were assessed in rhesus monkeys using performance in an operant test battery (OTB) consisting of five food-reinforced tasks thought to engender responses dependent upon aspects of time estimation, short-term memory, motivation, learning, and color and position discrimination. End-points included percent task completed (PTC), response rate or latency, and response accuracy. Testing occurred 15 min after IV injections of PCP (0.00, 0.003, 0.01, 0.03, 0.1, 0.13, 0.18, and 0.3 mg/kg). PCP disrupted performance of all tasks at 0.30 mg/kg. PTC was significantly decreased in the time estimation, motivation, and learning tasks at doses > or = 0.13 mg/kg. PTC for the short-term memory and color and position discrimination tasks was significantly decreased at 0.18 mg/kg and above. Response rate was significantly decreased at 0.13 mg/kg and above in the motivation and learning tasks and at 0.18 mg/kg and above in the time estimation, short-term memory, and color and position discrimination tasks. Response accuracy was significantly decreased in the time estimation, short-term memory, and learning tasks at doses > or = 0.13 mg/kg, while accuracy in the color and position discrimination task was decreased only at 0.30 mg/kg. PCP's effects on OTB performance were generally nonspecific, in that the time estimation, short-term memory, learning, and motivation tasks were all equally sensitive, with the color and position discrimination task being the least sensitive. These results are different than those obtained from earlier studies on the effects of MK-801, a more selective noncompetitive NMDA antagonist.

Behavioral and neurochemical effects of chronic methylenedioxymethamphetamine (MDMA) treatment in rhesus monkeys

Effects of chronic treatment with the putative serotonergic neurotoxicant MDMA were assessed in rhesus macaques using behavior in an operant test battery (OTB) designed to model aspects of time estimation, short-term memory, motivation, learning, and color and position discrimination. After an initial acute dose-response assessment, escalating doses of MDMA (0.10-20.0 mg/kg, im, twice daily, for 14 consecutive days at each dose) were administered, followed by three additional acute dose-response assessments. In general, tolerance to MDMA's acute effects was evident in all OTB tasks by the second week of repeated exposure to each individual MDMA dose and as doses escalated. Baseline OTB performance after chronic treatment was not significantly altered. Residual behavioral tolerance to MDMA's acute effects, however, was evident in all OTB tasks but was least pronounced in the motivation task. Monkeys were sacrificed (21 months after chronic treatment) and brains were dissected into several regions for neurochemical analyses. Serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were analyzed via HPLC. Although MDMA-treated monkeys tended to have lower 5-HT concentrations in the frontal cortex, chronic MDMA treatment had no significant effects on 5-HT concentrations in any brain area sampled. Hippocampal 5-HIAA concentration, 5-HT uptake sites, and turnover of 5-HT of MDMA-treated monkeys were significantly lower than control values. DA concentrations in the CN of MDMA-treated monkeys were significantly greater than control values. No significant effects on DA concentrations were noted in any other brain area sampled. The absence of significant decreases in 5-HT and the general increase in DA concentrations are dissimilar to neurochemical effects reported after a short course of MDMA treatment at relatively high doses. These data suggest that chronic administration of gradually increasing doses of MDMA results in long-lasting tolerance to the drugs acute effects on the complex brain functions modeled in the OTB. It is uncertain, however, if such tolerance is related to the observed decreases in uptake sites and turnover of 5-HT in the hippocampus of these monkeys.

Acute effects of methylenedioxymethamphetamine (MDMA) on several complex brain functions in monkeys

The effects of MDMA were assessed in rhesus macaques using behavior in an operant test battery (OTB) consisting of five food-reinforced tasks designed to model aspects of time estimation, short-term memory, and attention, motivation, learning, and color and position discrimination. Testing occurred 30 min after intramuscular, injections of MDMA (0.0, 0.1, 0.3, and 1.0 mg/kg). The behavioral endpoints monitored included percent task completed, response rate or latency, and response accuracy. Percent task completed was significantly decreased in the time estimation, learning, and motivation tasks at 1.0 mg/kg as compared to saline controls. Response accuracies in the time estimation and learning tasks were also decreased at 1.0 mg/kg. Response rate was decreased at 1.0 mg/kg in the motivation task but was not significantly affected in any other tasks. No behavioral endpoints were significantly affected in the short-term memory and attention and color and position discrimination tasks at any dose tested. Results indicate that time estimation, motivation, and learning are more sensitive to the acute effects of MDMA than are short-term memory and attention and color and position discrimination.

Effects of cocaine in pigeons responding under a progressive-ratio schedule of food delivery

Although the progressive-ratio schedule has been used frequently to quantify the reinforcing effectiveness of self-administered drugs, it has seldom been used to examine the effects of drugs on food-maintained behavior and has never been used to evaluate the effects of cocaine on such behavior. In the present study, the effects of acute administrations of cocaine were evaluated in pigeons responding under a progressive-ratio 5 schedule of food delivery that continued for 1 h or until responding ceased for 5 consecutive min, whichever occurred first. The largest ratio completed each session (breaking point) was the primary dependent variable. In general, acute administrations of cocaine at 0.56 to 3.2 mg/kg increased breaking points, whereas doses above 5.6 mg/kg decreased breaking points. Although cocaine reduces food intake and subjective hunger for food, the present data indicate that the drug reduces the reinforcing effectiveness of food only at high doses.

Acute effects of physostigmine on complex operant behavior in rhesus monkeys

The effects of physostigmine were assessed in rhesus macaques using behavior in several complex tasks designed to model aspects of time estimation [temporal response differentiation (TRD)], short-term memory [delayed matching-to-sample (DMTS)], motivation [progressive ratio (PR)], learning [incremental repeated acquisition (IRA)], and color and position discrimination [conditioned position responding (CPR)]. The endpoints monitored included percent task completed, response rate, and accuracy. Physostigmine sulphate (0.001-0.056 mg/kg) significantly decreased the percentage of task completed and response rate in each task at 0.03 and 0.056 mg/kg. Accuracy in the TRD task was significantly decreased at 0.03 and 0.056 mg/kg, whereas accuracy in the CPR and IRA tasks was significantly decreased only at 0.056 mg/kg. DMTS accuracy was not significantly affected at any dose tested. A significant increase in accuracy was noted in learning task performance at the 0.01 mg/kg dose, although only for one-lever response sequences. Performance enhancements were not seen in any other task. These results indicate that in monkeys, low doses of physostigmine may facilitate acquisition or learning of simple one-lever spatial tasks while not significantly altering the acquisition of similar but more complex tasks. Impaired task performance at high doses may be more reflective of cholinomimetic side effects (tremor and hypothermia) that affect response rate than a central or "cognitive" impairment.

Comparisons of dose-dependent effects of systemic morphine on flexion reflex components and operant avoidance responses of awake non-human primates

Electromyographic activity and the force of reflex and operant responses were recorded following administration of morphine. Low doses facilitated reflex responses to input from A-delta afferents but not from A-beta input. Higher doses inhibited A-delta responses but not A-beta responses. Operant avoidance responses to visual cues were unchanged. Thus, depending on the dose, nociceptive reflexes were facilitated or inhibited, without associated effects on non-nociceptive input or on motor output.

Acute behavioral effects of MK-801 in rhesus monkeys: assessment using an operant test battery

The acute effects of MK-801, a selective, noncompetitive NMDA receptor antagonist, were assessed using an operant test battery (OTB) of complex food-reinforced tasks that are thought to depend upon relatively specific brain functions such as motivation to work for food (progressive ratio, PR), learning (incremental repeated acquisition, IRA), color and position discrimination (conditioned position responding, CPR), time estimation (temporal response differentiation, TRD), and short-term memory and attention (delayed matching-to-sample, DMTS). Endpoints included response rates (RR), accuracies (ACC), and percent task completed (PTC). MK-801 (0.003-0.075 mg/kg, IV), given 15 min pretesting, produced significant dose-dependent decreases in measures of IRA and TRD performance at doses > or = 0.03 mg/kg. In both tasks, MK-801 produced significant decreases in accuracy at doses lower than those required to affect response rate. MK-801 also produced statistically significant decreases in PR, CPR, and DMTS measures, but only at higher doses (> or = 0.056 mg/kg) that caused significant decreases in both response rates and accuracies. These results indicate that, in monkeys, performance of operant tasks designed to model learning and time estimation is more sensitive to the disruptive effects of MK-801 than performance of tasks that model motivation, color, and position discrimination, and short-term memory and attention.

Effects of drugs on response duration differentiation. III. Acute variation of reinforced duration

Rats trained to hold a lever down for at least 1.0 s but less than 1.3 s could differentiate the reinforced response duration on about 50% of the trials. The response duration frequency distribution was a normal distribution with a peak near the minimum reinforced response duration. Dose-effect curves were determined for the effects of phencyclidine (PCP) and methamphetamine. Subsequently, rats continued to be trained for 3 days a week with responses between 1.0 and 1.3 s reinforced, but on days when injections were given either the maximum reinforced duration was increased to 2.3 s, or the minimum reinforced duration was lowered to 0.5. When the maximum duration was increased to 2.3 s, the percentage of reinforced responses increased to 60% and when the minimum reinforced duration was decreased to 0.5 s, the percentage of reinforced responses increased to 89%. Despite the increased percentage of reinforced responses when the time window was widened, the effects of PCP and methamphetamine were not changed. These data suggest that the effects of drugs on response duration differentiation are not greatly influenced by transient changes in reinforcement frequency.

Drug effects on response duration differentiation. I: Differential effects of drugs of abuse

Rats were trained to respond under a response duration differentiation schedule in which responses on a lever were reinforced if lever press durations were greater than or equal to 1.00 s but were also less than 1.30 s. Dose-effect curves were generated for cocaine, methamphetamine, pentobarbital, phencyclidine, delta-9-tetrahydrocanninabol (delta 9-THC), and morphine. All drugs produced dose-dependent decreases in accuracy (the percentage of total response durations that were reinforced); however, the degree to which changes in accuracy were accompanied by changes in response rates varied among drugs. Pentobarbital and morphine affected primarily longer (> 1.3 s) response durations, phencyclidine and delta 9-THC affected primarily shorter response durations, whereas cocaine and methamphetamine affected both shorter and longer response durations. High doses of methamphetamine and cocaine increased the dispersion of response duration distributions with increasing dose, whereas higher doses of pentobarbital, delta 9-THC and morphine did not increase dispersion of response duration distributions as much. These data show that behavior under this novel schedule is differentially sensitive to a number of pharmacologic manipulations, and that the schedule can provide a useful addition to the analysis of drug effects upon behavior.

Acute effects of caffeine on several operant behaviors in rhesus monkeys

The acute effects of 1,3-trimethylxanthine (caffeine) were assessed using an operant test battery (OTB) of complex food-reinforced tasks that are thought to depend upon relatively specific brain functions, such as motivation to work for food (progressive ratio, PR), learning (incremental repeated acquisition, IRA), color and position discrimination (conditioned position responding, CPR), time estimation (temporal response differentiation, TRD), and short-term memory and attention (delayed matching-to-sample, DMTS). Endpoints included response rates (RR), accuracies (ACC), and percent task completed (PTC). Caffeine sulfate (0.175-20.0 mg/kg, IV), given 15 min pretesting, produced significant dose-dependent decreases in TRD percent task completed and accuracy at doses > or = 5.6 mg/kg. Caffeine produced no systematic effects on either DMTS or PR responding, but low doses tended to enhance performance in both IRA and CPR tasks. Thus, in monkeys, performance of an operant task designed to model time estimation is more sensitive to the disruptive effects of caffeine than is performance of the other tasks in the OTB.

Acute effects of pentobarbital in a monkey operant behavioral test battery

The effects of acute pentobarbital treatment were assessed using a complex operant test battery containing five tasks in which correct performance is thought to depend upon processes associated with short-term memory and attention [delayed-matching-to-sample (DMTS)], color and position discrimination [conditioned position responding (CPR)], motivation [progressive ratio (PR)], time perception [temporal response differentiation (TRD)], and learning [incremental repeated acquisition (IRA)]. Adult, male rhesus monkeys were tested 15 min after IV injection of saline or pentobarbital (1, 3, 5.6, 10, or 15 mg/kg). Behavioral endpoints measured included percent task completed, response rate or latency, and response accuracy. The order of task sensitivity to disruption by PBT was TRD > IRA = DMTS = PR > CPR, in which sensitivity was defined as a significant disruption in any aspect of task performance. PBT slowed response rates at 10.0 and/or 15.0 mg/kg in all tasks. Accuracy was decreased in the TRD task at > or = 5.6 mg/kg but doses of > or = 10.0 mg/kg were required to decrease accuracy in the IRA, DMTS, and CPR tasks. Thus, behavior thought to model time perception (TRD) was more sensitive than behavior modeling learning (IRA), short-term memory and attention (DMTS), and motivation (PR). CPR was the least sensitive behavior. Because pentobarbital exerts its effects at least in part via GABA systems, the effects in the current study were compared with those of a previous study of the acute effects of diazepam. The two compounds exerted fundamentally different effects on operant test battery performance.

Acute effects of chlorpromazine in a monkey operant behavioral test battery

The effects of acute chlorpromazine treatment were assessed using a complex operant test battery (OTB) containing five tasks thought to depend upon processes associated with short-term memory and attention [delayed-matching-to-sample (DMTS)], color and position discrimination [conditioned position responding (CPR)], motivation [progressive ratio (PR)], time perception [temporal response differentiation (TRD)], and learning [incremental repeated acquisition (IRA)]. Adult male rhesus monkeys were tested 15 min after IV injection of saline or chlorpromazine (0.010, 0.030, 0.100, or 0.175 mg/kg). Behavioral endpoints measured included percent task completed, response rate or latency, and response accuracy. The order of task sensitivity to disruption by chlorpromazine was TRD = PR = IRA = DMTS = CPR in which sensitivity was defined as a significant alteration in any aspect of task performance. Chlorpromazine slowed response rates in all tasks except TRD but did decrease accuracy in that task. These effects were similar to those noted in previous studies of acute chlorpromazine treatment. Specific motoric effects suggested decreased task initiation at doses that left general motor ability intact. This finding is similar to that noted in parkinsonism caused by chronic chlorpromazine treatment.

Effects of atropine on operant test battery performance in rhesus monkeys

The acute behavioral effects of atropine sulfate were assessed using a battery of complex food-reinforced operant tasks that included: temporal response differentiation (TRD, n = 7); delayed matching-to-sample (DMTS, n = 6), progressive ratio (PR, n = 8), incremental repeated acquisition (IRA, n = 8), and conditioned position responding (CPR, n = 8). Performance in these tasks is thought to depend primarily upon specific brain functions such as time perception, short-term memory and attention, motivation, learning, and color and position discrimination, respectively. Atropine sulfate (0.01-0.56 mg/kg iv), given 15-min pretesting, produced significant dose-dependent decreases in the number of reinforcers obtained in all tasks. Response rates decreased significantly at greater than or equal to 0.03 mg/kg for the learning and discrimination tasks, at greater than or equal to 0.10 mg/kg for the motivation and short-term memory and attention tasks, and at greater than or equal to 0.30 mg/kg for the time perception task. Response accuracies were significantly decreased at doses greater than or equal to 0.10 mg/kg for the learning, discrimination, and short-term memory and attention tasks, and at greater than or equal to 0.30 mg/kg for the time perception task. Thus, the order of task sensitivity to any disruption by atropine is learning = color and position discrimination greater than time perception = short-term memory and attention = motivation (IRA = CPR greater than TRD = DMTS = PR). Thus in monkeys, the rates of responding in operant tasks designed to model learning and color and position discrimination were the most sensitive measures to atropine's behavioral effects. Accuracy in these same task was also disrupted but at higher doses. These data support the hypothesis that cholinergic systems play a greater role in the speed (but not accuracy) of performance of our learning and discrimination tasks compared to all other tasks. Accuracy of responding in these and the short-term memory task, all of which involve the use of lights as visual stimuli, was more sensitive to disruption by atropine than those tasks which did not utilize such strong visual stimuli.