Hannah Steinberg

Introduction to symposium on endorphins and behavioural processes; Review of literature on endorphins and exercise

The first symposium on endorphins and behavioural processes in Britain was held by the British Psychological Society in March 1985. Against a background of the explosive history of the discovery of endogenous opioids, problems of terminology, and basic mechanisms and concepts, five papers reflect the main fields in which outstanding progress has been made: analgesia, feeding, reward mechanisms, social behaviour and aggression, and addiction. A review of the literature on endorphins and exercise stresses both the value and limitations of trying to unravel a fashionable subject. Endorphin research is multi-disciplinary and highly complex, with tricky technical and conceptual problems and inevitable lack of consensus. Investigators should be more aware of the crucial role that outcomes of behaviour experiments play in the attribution of function to opioid systems.

Uses and Limitations of Photocell Activity Cages for Assessing Effects of Drugs

The behaviour of rats placed in a new environment was determined simultaneously by photocells and by direct observation. Predictably, a typical photocell activity cage did not measure a simple or homogeneous pattern of behaviour even in undrugged animals: two components of behaviour, the number of walks across the cage and of rears onto the hind feet, were correlated with photocell counts, but grooming was not. Even this agreement between observation and automation broke down if dexamphetamine was given; the correlation between rears and photocell counts was reduced by graded doses of dexamphetamine and by dexamphetamine-amylobarbitone mixtures, and the stimulant effect of dexamphetamine on walks was greatly exaggerated by the photocells. Such discrepancies were much smaller with amylobarbitone alone. For the testing of drugs, the use of activity cages seems to be more limited than has sometimes been supposed. Complex changes of behaviour are masked by the relatively crude photocell counts, but they may be detected by standardised observation. Watching the animals might also help with the development of improved automatic devices.

Selective effects of an anaesthetic drug on cognitive behaviour

The prediction has been tested that under the influence of an anaesthetic drug, nitrous oxide, cognitive performances undergo differential impairment, the extent of which is positively correlated with the “complexity” of the task, Ten kinds of performance were investigated, ranging from speed of finger tapping to reasoning by analogy. The relative complexity of each task was determined, in accordance with conventional criteria, from its respective qualitative category or “level”—relational, associative, and motor—and within each category from qualitative analysis of the component processes involved in its execution. A simple group difference design was used, involving two groups of 50 subjects each, matched for age and sex. Significant deterioration as a consequence of drug administration occurred in the performance of all tasks. On the whole, the more complex a task the more did it tend to be impaired. Motor performances were, however, impaired to a greater extent than had been predicted. The possible significance of these findings is discussed.

Lithium and alpha methyl p tyrosine prevent manic activity in rodents

Lithium in moderate doses seems to have little effect on the normal activities of laboratory rodents, but it does prevent some kinds of hyperactivity, especially repetitive movements which involve the whole body. High levels of such activities were induced by appropriately combining drug administrations, the animals previous experience and the kind of environment in which they were tested. Pretreatment with lithium and also with α-methyl-para-tyrosine blocked the hyperactivity withou taffecting controls. The possibility of using such artificially unbalanced states as animal models of manic-depressive disorders is discussed.

Inducing a preference for morphine in rats without premedication.

“ADDICTION” to morphine and morphine-type drugs can be shown in laboratory animals in several ways. Among the most convincing1 are experiments in which rats and monkeys are induced to administer the drug to themselves either by drinking solutions of it2,3 or by pressing levers which release intravenous injections through an implanted catheter4,5. Standard experimental procedures involve a period of premedication: daily injections of increasing doses of morphine are given for 2–3 weeks in order to make the animals “passively” dependent on the drug. Injections are then stopped and the animals have withdrawal symptoms6,7 which are only relieved by more morphine; so they learn to seek and self-administer the drug. Monkeys will, however, learn to press levers for intravenous injections even without premedication, though such learning is much slower. Some monkeys will also voluntarily drink morphine solutions, which are bitter, but others persistently reject them unless pre-medicated (personal communication from Seevers). In rats, premedication has usually been considered essential for learning either kind of self-administration, but even premedicated rats will initially reject morphine solutions if given a choice between them and water, probably because of the bitter taste.

Endogenous opioids modulate the cardiovascular response to mental stress

The role of endogenous opioids in the cardiovascular response to mental stress was investigated in two controlled studies. In the first, cardiovascular, hormonal and psychological measures were made in a group of subjects before, during and after presentation of either a mental stress task or a non-stressful control task in the presence of naloxone (8 mg), an opiate antagonist, or an equal volume of saline. The study was carried out in random order and single(subject)-blind. Naloxone specifically enhanced the heart rate response to the stressful task but had no effect on blood pressure, plasma epinephrine or norepinephrine, or feelings of anxiety. Naloxone increased plasma cortisol and ACTH in both stressful and control tasks. A second, double-blind, study replicated the effect on heart rate. An endogenous opioid mechanism thus appears to inhibit the cardiovascular response to stress.

Development of morphine dependence in rats: lack of effect of previous ingestion of other drugs.

It has often been observed that periods of abuse of non-narcotic drugs precede the development of dependence on opiates, but this correlation does not necessarily imply that there is a simple causal relationship. We have previously described a procedure for inducing rats to drink solutions of morphine in preference to water; self-administration of the drug in this way seems to be a valid model of dependence. For the first 46 days of the experiment described here, solutions of alcohol, amylobarbitone, chlordiazepoxide, cocaine or dexamphetamine were made available to different groups of rats. Most of these drugs were ingested in substantial doses, had clear effects on behaviour and produced characteristic patterns of drinking over the repeated trials. However, there was no unequivocal evidence of dependence, and indeed the rats learned to reject the solutions of dexamphetamine. Ingestion of these drugs did not affect the eventual development of dependence when solutions of morphine were substituted at a later stage, although the avoidance of dexamphetamine seemed to temporarily transfer to morphine. Further studies using other methods and species are needed before inferences can be made about “escalation” to dependence on opioids in man.

Reducing interference in forgetting

According to interference theories forgetting results from the intervention of extraneous associations which disturb the patterns built up during learning. It also seems that the period immediately following learning is critical for forgetting. The experiment which is described was carried out to investigate whether administration of the central-depressant drug nitrous oxide immediately after learning would reduce forgetting, since it had been shown to impair the formation of associations and ought therefore to reduce interference. This expectation was borne out, significantly less forgetting occurring when nitrous oxide was given than when air was given. A possible physiological basis, relating these results to those for sleep is discussed.

Exercise enhances creativity independently of mood

Objectives It has been widely accepted in the literature that various forms of physical exercise, even in a single session, enhance positive mood. It has also been shown that physical exercise may sometimes enhance creative thinking, but the evidence is inconclusive. Positive moods can favour creative thinking, but the opposite has also been reported and these relations are unclear. There is a large anecdotal literature suggesting that creative people sometimes use bodily movement to help overcome “blocks”. The aim of this study was to establish whether post-exercise creative thinking was attributable to improved mood. Methods The responses of 63 participants to an exercise (aerobic workout or aerobic dance) and a “neutral” video watching condition were compared. Mood was measured using an adjective list, and creative thinking was tested by three measures of the Torrance test. Results Analysis of variance showed a large and significant increase in positive mood after exercise (P<0.001) and a significant decrease in positive mood after video watching (P<0.001). A significant increase between the creative thinking scores of the two conditions was found on the flexibility (variety of responses) measure (P<0.05). A multifactorial analysis of all data failed to show a significant covariance of creative thinking with the two measures of mood (P>0.05). Conclusions These results suggest that mood and creativity were improved by physical exercise independently of each other.

Influence of a depressant drug on acquisition in rote learning

Central depressant drugs have been shown to impair performance during learning and at recall. The experiment which is described was carried out to investigate whether the effect during learning is primarily on the availability of associations or on their formation. The learning decrement attributable to the drug used (30 per cent. nitrous oxide in oxygen) persisted on recovery from the drug and during subsequent learning under normal conditions. It is concluded that the effect of the drug is on acquisition rather than performance; that is, it acts so as to impede the formative process and does not merely obscure the progress of learning by blocking responses.