Conditioned leg-flexion responses in dogs were developed with electric shock as an unconditioned stimulus and intestinal stimulation or the effects of injections of various drugs as conditioned stimuli. It is concluded that physiological effects can play a role in the development and maintenance of conditioned avoidance behavior.

Acquisition of a behavioral response motivated by shock was enhanced in rats chronically treated with yeast ribonucleic acid, and resistance to extinction was greater in rats so treated than in controls. This extends the role of ribonucleic acid to include a behavioral effect in laboratory mammals treated with a purified preparation from yeast.

Experimentally naive rats were trained to key press on a fixed-ratio 10 schedule of food reinforcement by a completely automatic procedure within a single, 1-hr session. Control procedures demonstrated that the resulting behavior was an operant, under control of the schedule of reinforcement and the specified reinforcing stimulus (food). A simple, combination food-tray operandum, also described, was used as the basis for the training technique. Teichner (1952) and Bremner and Trowill (1962) described combined operandum-reinforcement devices for use with food pellets, which facilitated lever-press training of rats and which did not require response shaping by an experimenter. Procedures in which responding was automatically acquired have also been used with rhesus monkeys (Sidman and Fletcher, 1968) and bobwhite quail (Gardner, 1969), based on the procedure developed by Brown and Jenkins (1968) used in these experiments was based on the species-specific tendency of hungry rats to sniff the area in which food was obtained and to "'nose" objects. METHOD SubjectsIn the present experiments, the weights of experimentally naive male Charles River rats (Sprague-Dawley) were decreased to approximately 80% of original weight (150 to 190 g) by 48 hr of food deprivation followed, on the next day, by 6 g per day of the food pellets used as reinforcers in the experimental procedures. Three different rats were used in each of the five experiments reported and all rats were housed in individual home cages with free access to water. ApparatusThe rats were tested in three cubic chambers (230 mm, each dimension) with grid floors, housed in sound-attenuating, ventilated, wood boxes. Conventional scheduling and recording equipment was used. Noyes food pellets (0.045 g) were delivered into a recessed food tray (Gerbrands Recessed Tray for Model D-1 Feeder; Cat. No. G-7020), modified for use as an operandum.As illustrated in Fig. 1

d-Amphetamine (1-4 mg/kg) significantly decreased responding for food in the presence of free food. This effect is opposite to that obtained in experiments on motor activity and responding for stimulus change but is in agreement with predictions based on its anorectic activity. Fenfluramine (2-8 mg/kg), an anorectic with qualitatively different effects on motor activity at anorectic doses, similarly decreased responding for food in the presence of free food. These results suggest that the appetitive properties of response contingent food play a major role in the maintenance of responding in the presence of free food, even if only as part of a stimulus complex whose significance was established during early training.