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FIG. 1 A morphine-dependent chimpanzee pulling the experimenter, S. D. S. Spragg, toward the room in which morphine was to be administered. The photograph is from a movie made by Spragg and J. D. Bruhn. Reprinted with the permission of Dr. Spragg.
By the mid-1930s, tolerance to morphine and other opiates had been demonstrated in some animals, but no one had produced convincing data that any species other than man would work to produce a dose of a drug. The experimental evidence on this point was gathered by S. D. S. Spragg, who started his work in the fall of 1935 (Spragg, 1940). .....Spragg worked at the Yale Laboratories of Primate Biology, Orange Park, Florida, having just received his Ph.D. from Yale. ..... Spragg set up a procedure showing that a chimpanzee would actually do something to get a shot of morphine. R. M. Yerkes, Director at Orange Park, suggested that Spragg study chronic morphinism in chimpanzees in order to resolve the controversy concerning whether addiction was a peculiarly human phenomenon. (Spragg, 1940, p. 2) The prevailing viewpoint was that typified by the words of a sociologist, A. R. Lindesmith (see Spragg, 1940), who argued that "only those to whom the drug's effects can be explained can become addicts," and "Certainly from the point of view of social science it would be ridiculous to include animals and humans together in the concept of addiction" (Lindesmith quoted by Spragg, 1940, pp. 121-122). Spragg defined addiction to mean that "an actual desire or striving for the drug is clearly demonstrated in addition to the induced physiological dependence" (pp. 10-11). He took as his problem the measurement of "desire or striving." Note that the emphasis was not upon the morphine as a reinforcer; this language was not yet used routinely. Repeated injections of drug were supposed to increase "desire," which then led to some behavior. Spragg dosed chimpanzees regularly with morphine (usually twice daily) until physiological dependence developed (evidenced by the appearance of abstinence symptoms when the drug was withheld) and then tested his subjects in various ways.
Some of the most compelling evidence was captured in a short movie made of two subjects during the regimen on morphine. For instance, a chimp can be seen pulling Spragg toward the injection room, something he did if deprived of morphine for a time.
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Most important, morphine-deprived chimps would work to get their shots, having first learned what behavior produced the drug. This was the main measure of "desire" and demonstrated the similarity of addiction in chimp and man. Spragg set up a preference test, giving the animal access to two sticks, one black and one white, that would open different boxes (Fig. 2).
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FIG. 2. The apparatus used by Spragg to determine whether a chimpanzee ''desired" an injection of morphine or a banana. The choice boxes and associated keys (a white triangular stick that could open the white box, which contained a morphine-filled syringe and a black round stick that could open the black box, which contained a banana). Note the syringe and banana on top of the boxes in this illustrative photograph.
The following three stills are from the film. The first two are from
the viewpoint of the chimpanzee. The first photograph is the arrangement
of the two boxes in the preference-testing chamber. The animal was presented
with a choice of two keys on a sliding platform that was presented to the
animal behind a grillwork; the animal would reach in and take one of the
two keys, turn around and walk to the appropriate box containing either
the syringe or a banana.
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When food deprived but not morphine deprived, the chimp would choose
the black stick and open the black box, take out a banana and eat it. When
deprived of morphine, he would pick up the white stick, put it in the slot
of the white box to open it, take out a loaded syringe, and occasionally
even hand it to Spragg, who would then make the injection. The animal is
running off a perfectly fine chain of behavior that eventuates in a shot;
all the elements of self-administration are there but are not all under
the full control of the animal.
The obvious conclusion from this work was that the chimpanzee resembled man in its reaction to morphine and could serve as a model for man. But the flavor of the times is given by the way Spragg (1940) himself commented upon the possibility of the rat showing true evidence of addictive behavior. He did not believe that the rat would show morphine addiction, writing as follows:
"...Since morphine addiction seems to depend essentially upon forming an association between the administration of the drug and the alleviation of withdrawal symptoms, and since this sequence involves a time lag of 10-15 minutes or more, the value of using subjects high enough in the phyletic scale to be able to make a delayed association of this nature is obvious. By this token, animals such as the rat, for example, could probably never become addicted to morphine, simply because they are not capable of forming associations of this order..." (p 126)
Part III of the monograph comprises the
conclusion and summary of the monograph. The second part of this document
includes his observations on the value of infrahuman primates in drug addiction
research.
Reference
Spragg, S.D.S. Morphine Addiction in Chimpanzees. Comparative Psychology
Monographs. 15:1-132, 1940.
