Comparison Between Morphine and Feeding as Agents in Production of Conditioned Salivary Response.

Abstract

In a quantitative study of the conditioned salivation in the dog developed through daily injections of morphine 1 it was found that the flow of saliva was unusually copious. Thus the total quantity of saliva secreted conditionally by a 12 to 14 kilo dog would run as high as 400 cc. in one hour. The conditioned stimulus in this case consisted in placing the dog in a stand where it remained for a definite period of time (usually 30 minutes), before receiving a subcutaneous injection of morphine. In the work of Pavlov and others 1 where food or acid was employed as an unconditioned stimulus, the “delay” between the beginning of the action of the conditioned stimulus and the application of the unconditioned stimulus was a matter of 2 to 3 minutes or even less. This suggested the possibility that the long “delay” employed in the case of the morphine-produced response might be responsible for the large amounts of saliva secreted. To test this, 3 dogs, with fistulae of the submaxillary glands, were placed in a stand for 30 minutes daily, for periods of 22, 27, and 76 days respectively. Each day, at the end of the 30 minutes in the stand, they were fed a meal of ground beef heart. The unconditioned salivary response to feeding was greater than to the injection of morphine (3-6 cc. compared to 1-3 cc.), but none of the 3 dogs showed any conditioned secretion before feeding. All these dogs developed the conditioned salivary response to morphine on subsequent occasions in the course of a few days.

It seems that in the development of conditioned salivation, using the same conditioned stimulus, daily injections of morphine are efficacious, whereas daily feeding is not.