When an unconditioned stimulus, a reinforcer, or an innate releaser is repeatedly presented to human or animal subjects, three major affective phenomena are often observed. First, one often sees affective or hedonic contrast. Second, frequent repeti- tion of the unconditioned stimulus, reinforcer, or innate releaser often gives rise to affective or hedonic habitu- ation (tolerance). Finally, after frequent repetition of these stimuli, a withdrawal or abstinence syndrome often emerges directly following stimulus termination. These affective dynamics of organismicall y important stimuli generate new motives, new opportunities for reinforcing and energizing operant behaviors, based on the hedonic attributes of withdrawal or abstinence syndromes. This article describes the opponent-process theory of such new or experientiall y produced motives and discusses recent research testing the theory. The theory attempts to account for such diverse acquired motives as drug addiction, love, affection and social attachment, and cravings for sensory and aesthetic ex- periences (cases in which the initial reinforcers are posi- tive) and for such acquired motives as parachuting, jog- ging and "marathoning," sauna bathing, and a variety of self-administered, aversive stimuli like electric shocks (cases in which the initial reinforcers are negative). The empirical laws governing the establishment of these new motives are described. Crucial variables include the quality, intensity, and duration of each stimulus presentation and the time intervals between presenta-

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The opponent-process theory of acquired motivation: The costs of pleasure and the benefits of pain.

Drug reinforcement studied by the use of place conditioning in rat.

This chapter attempts to answer the following linked questions: 

1

What is the simplest adequate description of the effects of the “minor tranquilizers” on “emotional behavior” (terms I shall define below)?




2

What underlying psychological processes are altered by these drugs to produce these behavioral effects, and in what way are they altered?




3

On what brain structures or systems do these drugs act to produce these behavioral effects?

Drug Effects on Fear and Frustration: Possible Limbic Site of Action of Minor Tranquilizers

The open field test.

A novel means of measuring and analysing behavioural effects of dopamine agonists is described and illustrated by a comparison of the effects of d-amphetamine and apomorphine in the rat. d-Amphetamine (0–15 mg/kg IP) produced significant dose- and time-dependent changes in responses such as locomotion, rearing and sniffing, but not in licking or gnawing. In contrast, apomorphine (0–5 mg/kg SC) produced significant increases in licking and gnawing, as well as in locomotion and sniffing, but no changes in rearing. The results are discussed in comparison with those obtained by other methods, such as photocell beam interruptions or stereotypy rating scales, and may be of importance in elucidating the functions of the forebrain dopamine projections.

An observational method for quantifying the behavioural effects of dopamine agonists: contrasting effects of d-amphetamine and apomorphine.

Rats were induced to administer morphine to themselves by drinking solutions of it in preference to water; this behaviour was found to be a valid model of morphine dependence. Previous “passive” medication with morphine was not necessary; initial aversions for the bitter morphine solutions were converted into preferences after the rats were repeatedly given only morphine solutions to drink in order to relieve thirst. The consumption of solutions of quinine which were initially equally aversive did not increase, suggesting that the repeated pairing of a bitter taste with relief of thirst did not account for the preferences for the morphine solutions. It appeared that the post-ingestional effects of morphine provided primary reinforcement for the rats; they were able to regulate their daily intake of the drug after being injected with varying doses of it and they lost weight abruptly during enforced abstinence. There was also evidence that the bitter taste of morphine had become a secondary reinforcer for rats with established preferences.

Preferences for morphine in rats: validation of an experimental model of dependence.

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.

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

“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

Inducing a preference for morphine in rats without premedication.

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.

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

Rats were made dependent on morphine by training them to drink solutions of the drug even when water was available as an alternative Experiments were carried out to examine the reliability of the technique Drinking was recorded in two ways, and it was found that there was close agreement between the numbers of laps (“drinkometer” counts) and the volumes of fluids removed from the drinking bottles When dependent rats were allowed to partially satisfy their needs for morphine and/or water shortly before morphine: water choice trials, they made appropriate adjustments in their subsequent consummatory responses However, the value of using quinine solutions to control for effects due to the bitter taste of morphine was more limited than has sometimes been supposed; the relative palatabilities of the two drugs seemed to vary across experiments Considered as a whole, the results support the view that preferences for morphine in rats can provide a valid measure of their need for the drug

I. P. Stolerman

Papers

Preferences for morphine in rats: validation of an experimental model of dependence.

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

Inducing a preference for morphine in rats without premedication.

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

Regulation of drug and water intake in rats dependent on morphine.