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Previous studies of autoshaping of drinking report a positive relationship between experience with autoshaping procedures and drinking, but this effect was confounded with age, as the rats were older when they drank more. The present experiment evaluated the effects of the age of male Long-Evans hooded rats [90-days old (Younger group) vs. 135 days old (Older group)], at the beginning of the study, on drinking induced by Pavlovian autoshaping procedures. Autoshaping procedures consisted of pairings of sipper conditioned stimulus (CS) with food unconditioned stimulus (US). Rats were deprived of neither food or fluid, and sweeteners were not employed at any time during the study. For all rats (n = 32), during sessions 1-10, the sipper CS contained water. Thereafter, for rats in the Ethanol groups (n = 20), the sipper CS contained ethanol, with the concentration (1, 2, 3, 4, 5, 6%, v/v) increasing across autoshaping sessions. For rats in the Water groups (n = 12), throughout the experiment the sipper CS contained tap water (0% ethanol). Rats in the Younger group drank more ethanol and more water from the sipper CS than rats in the Older group, and across age groups there was more ethanol drinking than water drinking, an effect unlikely due to foraging for calories. Data support the hypothesis that ethanol’s pharmacological effect was to enhance autoshaping, resulting in a positive feedback loop inducing still more ethanol drinking. The younger rats were more vulnerable to autoshaping effects. Implications for models of addiction are discussed.

Effects of experience with Pavlovian autoshaping procedures on lever-press autoshaping conditioned response (CR) performance and 3H-8-OH-DPAT-labeled binding of 5-HT1a receptors as well as 125I-LSD-labeled binding of 5-HT2a receptors were evaluated in four groups of male Long-Evans hooded rats. Two groups of rats (Group Paired High CR and Group Paired Low CR) received Pavlovian autoshaping procedures wherein the presentation of a lever (conditioned stimulus, CS) was followed by the response-independent presentation of food (unconditioned stimulus, US). Rats in Group Paired High CR (n=12) showed more rapid CR acquisition and higher asymptotic levels of lever-press autoshaping CR performance relative to rats in Group Low CR (n=12). Group Omission (n=9) received autoshaping with an omission contingency, such that performing the lever-press autoshaping CR resulted in the cancellation the food US, while Group Random (n=9) received presentations of lever CS and food US randomly with respect to one another. Though Groups Omission and Random did not differ in lever-press autoshaping CR performance, Group Omission showed significantly lower levels of 3H-8-OH-DPAT-labeled 5-HT1a binding in post-synaptic areas (frontal cortex, septum, caudate putamen), as well as significantly higher plasma corticosterone levels than Group Random. In addition, Group Random showed higher levels of 3H-8-OH-DPAT-labeled 5-HT1a binding in pre-synaptic somatodendritic autoreceptors on dorsal raphe nucleus relative to each of the other three groups. Autoradiographic analysis of 125I-LSD-labeled 5-HT2a receptor binding revealed no significant differences between Groups Paired High CR and Paired Low CR or between Groups Omission and Random in any brain regions. [Copyright &y& Elsevier]