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To study effects of shifts in concentration of liquid reinforcers on licking behavior 4 experiments were performed. Depressed performance (relative to control groups) accompanied a shift from 32% to 4% sucrose solutions, but not a shift in saccharine concentrations. Various bases for this disparity were investigated, including type of deprivation and levels of deprivation. Depression in licking appears to result from shifts in sucrose concentration, with larger depressions accompanying increased amounts of preshift training, but this phenomenon does not occur following shifts in saccharine concentration.The effects of shifts in incentive magnitude have usually been studied in the instrumental running situation. A study by Collier, Knarr, and Marx (1961) has suggested that the licking response may be more sensitive to incentive effects than is running speed. The present experiments were designed to investigate the effects of shifts in incentive magnitude on the licking response.EXPERIMENT 1 Method Subjects and apparatus. Twenty adult male albino rats of the Sprague-Dawley strain were 60 days old at the start of the experiment. Two identical wire cages (8 X 934 X 7 in.) of the type used to house /Ss were used for experimental training. These cages were not housed in sound-attenuating chambers, although, in each of the other experiments reported here, training and test cages were enclosed in sound-attentuating chambers. Although this was originally viewed as a potentially important consideration, sound attenuation did not noticeably affect the results. By extending their tongues through the wire mesh Ss could lick from the glass drinking tubes mounted on the outside of the cages. A drinkometer was connected between the solution and the cage floor, so that S completed the circuit whenever it licked the tube.Procedure. All /Ss were maintained on a daily deprivation regimen of 10 gm. of powdered Purina chow (plus ad-lib water) given to each S 10-30

Drugs that reduce anxiety may be mediated by cyclic adenosine monophosphate in the brain because (i) potent anxiety-reducing drugs are also potent inhibitors of brain phosphodiesterase activity; (ii) dibutyryl cyclic adenosine monophosphate has the ability to reduce anxiety; (iii) the methylxanthines show significant anxiety-reducing effects; (iv) theophylline and chlordiazepoxide produce additive anxiety-reducing activity; and (v) there is a significant correlation between the anxiety-reducing property of drugs and their ability to inhibit phosphodiesterase activity in the brain.

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