Effects of phencyclidine, secobarbital and diazepam on eye tracking in rhesus monkeys

Towards improved animal models for evaluating social cognition and its disruption in schizophrenia: the CNTRICS initiative

Social cognition refers to processes used to monitor and interpret social signals from others, to decipher their state of mind, emotional status and intentions, and select appropriate social behaviour. Social cognition is sophisticated in humans, being embedded with verbal language and enacted in a complex cultural environment. Its disruption characterises the entire course of schizophrenia and is correlated with poor functional outcome. Further, deficits in social cognition are related to impairment in other cognitive domains, positive symptoms (paranoia and delusions) and negative symptoms (social withdrawal and reduced motivation). In light of the significance and inadequate management of social cognition deficits, there is a need for translatable experimental procedures for their study, and identification of effective pharmacotherapy. No single paradigm captures the multi-dimensional nature of social cognition, and procedures for assessing ability to infer mental states are not well-developed for experimental therapeutic settings. Accordingly, a recent CNTRICS meeting prioritised procedures for measuring a specific construct: "acquisition and recognition of affective (emotional) states", coupled to individual recognition. Two complementary paradigms for refinement were identified: social recognition/preference in rodents, and visual tracking of social scenes in non-human primates (NHPs). Social recognition is disrupted in genetic, developmental or pharmacological disease models for schizophrenia, and performance in both procedures is improved by the neuropeptide oxytocin. The present article surveys a broad range of procedures for studying social cognition in rodents and NHPs, discusses advantages and drawbacks, and focuses on development of social recognition/preference and gaze-following paradigms for improved study of social cognition deficits in schizophrenia and their potential treatment.

Pharmacological treatment effects on eye movement control

The increasing use of eye movement paradigms to assess the functional integrity of brain systems involved in sensorimotor and cognitive processing in clinical disorders requires greater attention to effects of pharmacological treatments on these systems. This is needed to better differentiate disease and medication effects in clinical samples, to learn about neurochemical systems relevant for identified disturbances, and to facilitate identification of oculomotor biomarkers of pharmacological effects. In this review, studies of pharmacologic treatment effects on eye movements in healthy individuals are summarized and the sensitivity of eye movements to a variety of pharmacological manipulations is established. Primary findings from these studies of healthy individuals involving mainly acute effects indicate that: (i) the most consistent finding across several classes of drugs, including benzodiazepines, first- and second- generation antipsychotics, anticholinergic agents, and anticonvulsant/mood stabilizing medications is a decrease in saccade and smooth pursuit velocity (or increase in saccades during pursuit); (ii) these oculomotor effects largely reflect the general sedating effects of these medications on central nervous system functioning and are often dose-dependent; (iii) in many cases changes in oculomotor functioning are more sensitive indicators of pharmacological effects than other measures; and (iv) other agents, including the antidepressant class of serotonergic reuptake inhibitors, direct serotonergic agonists, and stimulants including amphetamine and nicotine, do not appear to adversely impact oculomotor functions in healthy individuals and may well enhance aspects of saccade and pursuit performance. Pharmacological treatment effects on eye movements across several clinical disorders including schizophrenia, affective disorders, attention deficit hyperactivity disorder, Parkinson's disease, and Huntington's disease are also reviewed. While greater recognition and investigation into pharmacological treatment effects in these disorders is needed, both beneficial and adverse drug effects are identified. This raises the important caveat for oculomotor studies of neuropsychiatric disorders that performance differences from healthy individuals cannot be attributed to illness effects alone. In final sections of this review, studies are presented that illustrate the utility of eye movements for use as potential biomarkers in pharmacodynamic and pharmacogenetic studies. While more systematic studies are needed, we conclude that eye movement measurements hold significant promise as tools to investigate treatment effects on cognitive and sensorimotor processes in clinical populations and that their use may be helpful in speeding the drug development pathway for drugs targeting specific neural systems and in individualizing pharmacological treatments.

Primacy and recency effects in rhesus monkeys (Macaca mulatta) using a serial probe recognition task. I. Effects of diazepam

In this study, we evaluated the effects of diazepam (0.2, 0.8, 1.6 and 3.2 mg/kg; IM) on the primacy and recency memory effects in four rhesus monkeys trained on a six-item serial probe recognition (SPR) task. Only the highest dose of diazepam (3.2 mg/kg) consistently affected the shape of the monkeys' serial position curves. Accuracy on the probe trials was disrupted for list items which occurred in the middle portion and recency memory component of the serial position curve, without affecting the primacy component. Diazepam, however, also produced several nonspecific effects on SPR performance. Both the 1.6 and 3.2 mg/kg diazepam doses disrupted accuracy on the non-matching probe trials, and the 3.2 mg/kg dose caused an increase in response latencies which were unrelated to any one component of the serial position curve. This is the first demonstration in nonhuman primates showing that the primacy and recency memory effects can be differentiated on the basis of diazepam dose.

Monologue speech: effects of d-amphetamine, secobarbital and diazepam

Drugs of abuse from different pharmacological classes increase social conversation. Alcohol and d-amphetamine also increase rates of talking in subjects producing speech monologues in an isolated context. This latter finding suggests that the increases observed during dyadic social conversation may represent general increases in talking and not specific effects on social interaction. The present study was conducted to assess whether other abused drugs also increase monologue speaking. The acute effects of secobarbital (0, 50, 150, 250 mg), d-amphetamine (0, 25 mg) (Experiment 1), and diazepam (0, 10, 20, 40 mg) (Experiment 2) were investigated in healthy, adult volunteers. Secobarbital and d-amphetamine both increased the total amount of speech emitted, while diazepam generally had no effect or decreased talking. Experiment 3 was conducted to further compare the effects of secobarbital (0, 50, 150, 250 mg) and diazepam (0, 5, 15, 25 mg) using a within-subject, crossover design. Secobarbital increased talking in three of the four subjects studied, while diazepam, again, had no effect or decreased talking. In contrast to the differences noted with talking, secobarbital and diazepam both decreased response rates in a nonverbal performance task (i.e., circular-lights procedure); they also produced many similar effects on various subject-rated measures of drug effect. Thus, the differences in the effects of these two compounds on talking are not the result of a general difference in their overall profile of behavioral effects. In summary, the results obtained with secobarbital and d-amphetamine further demonstrate that an explicitly social context is not a necessary condition to observe drug-produced increases in speech quantity. The failure of diazepam to reliably increase talking in the present study illustrates the existence of some pharmacological specificity in the effect of drugs on human speech, and suggests another way in which the behavioral effects of the barbiturates and benzodiazepines may differ.

The effects of ethanol on eye tracking in rhesus monkeys and humans

The effects of ethanol on eye tracking function were compared in rhesus monkeys and humans using a similar experimental procedure. In Experiment 1, 3 rhesus monkeys were trained to visually track a projected image of a disk that oscillated sinusoidally along a horizontal plane on a screen. This training was accomplished using a procedure in which responses on a lever resulted in the delivery of water when the central area of the projected disk image was dimmed for a brief period. Intragastric administrations of ethanol at doses of 0.25 to 2 g/kg were tested during one-day test sessions using a cumulative dose procedure. Pursuit eye movements were disrupted at doses of 0.5 g/kg while lever pressing behavior was not disrupted until a dose of 2 g/kg was reached. In Experiment 2, pursuit eye movements of 6 humans were not disrupted when ethanol was given orally at cumulative doses of 0.25 to 1 g/kg, while microswitch pressing behavior was disrupted in some of the subjects at a dose of 0.5 g/kg. Blood ethanol levels increased in a dose-dependent manner in both species with higher levels in humans than in monkeys. The dose dependent effects observed in both species and qualitative similarities in some of the effects such as saccadic pursuit eye movements suggest that the eye tracking method employing monkeys is useful for predicting drug effects on sensory motor function in humans.

Effects of benzodiazepines on acquisition and performance: a critical assessment

Evidence related to the effects of benzodiazepines on learning and memory is reviewed in the contexts of human verbal learning studies and animal studies using both aversive and non-aversive paradigms. While the impairment of acquisition by benzodiazepines appears to be a robust phenomenon generalizing across species and experimental conditions, the impairment in the performance of an already-learned task by such drugs appears to be more restrictive and highly dependent upon experimental contingencies. Thus far, performance impairment appears to be found mainly in animal studies using non-aversive, food-motivated tasks, with such tasks being particularly well suited for investigating such a phenomenon. At present, there is a noticeable lack of knowledge regarding the neurochemical substrates underlying BDZ-induced impairment. Finally, some issues that may contribute to the presence or absence of a BDZ-induced performance impairment in published studies are briefly considered.

Effects of dopaminergic agents on eye tracking before and after repeated methamphetamine

The effects of methamphetamine (MA), apomorphine (AP) and haloperidol (HAL) on eye tracking function were tested in rhesus monkeys. Three rhesus monkeys were trained to track with their eyes a disk-shaped projected image that oscillated along a horizontal plane on a screen, using a training procedure in which responses on a lever were reinforced with water only when the center of the disk dimmed for a brief period. Eye movements were recorded by electrooculography (EOG). The effects of intramusuclar administration of MA, APO and HAL on responding were compared before and after a 8-14 day period of repeated MA administration. During this regimen, MA was given in 4 divided doses starting at a total daily dose of 4 mg/kg/day and increasing to 16-40 mg/kg/day. All three drugs disrupted performance during both the initial dose-response determination as well as during the redetermination following the regimen. However, tolerance to MA in 3 monkeys and to APO in 2 monkeys was observed after the regimen, while no marked sensitivity change was observed to haloperidol. Since other data reported elsewhere have shown that dopamine is depleted in the caudate after similar repeated administration regimens, long lasting brain dopaminergic changes are likely present in these monkeys. Therefore, these results suggest that the changes in sensitivity to the drugs that were observed in terms of eye tracking function are related to dopamine depletion in the brain.