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Biomedical subjects

R C Bolles

Publications and source records attributed to R C Bolles.

8 recordsLinked to original sources
PubMed1988

Nutritive expectancies mediate cholecystokinin's suppression-of-intake effect.

In previous studies of cholecystokinin's (CCK's) effect on consumption, physical features (e.g., taste, texture, and odor) of test meals were confounded with the nutritive expectancies elicited by those features. To separately assess the role of these two factors in supporting CCK's suppression-of-intake effect, we varied the caloric expectancies elicited by a flavored test solution, while holding constant its actual caloric density, as well as all other unconditioned stimulus features. On alternate days for a 12-day period, hungry rats drank grape or orange Kool-Aid (noncaloric) mixed with a caloric 5% ethanol solution; on the other days, they drank the alternate flavor mixed with plain water. In a subsequent choice test between the flavored solutions without ethanol, the ethanol-associated flavor (Ef) was preferred over the water-associated flavor (Wf). Two days later, the rats were injected with either cholecystokinin octapeptide (CCK-8; ip, 2 micrograms/kg) or isotonic saline, and then given access to their Ef or their Wf for 1 hr. Consumption of the Ef was suppressed by CCK-8; intake of the Wf was unaffected. These results suggest that CCK-8's effectiveness in suppressing intake of a test meal may be related not to the unconditioned stimulus features of that meal but to the nutritive expectations elicited by those features.

Animals↗
PubMed1987

Hunger enhances the expression of calorie- but not taste-mediated conditioned flavor preferences.

Rats learned to associate one flavor conditioned stimulus (CS; grape or orange) with an ethanol (caloric) or saccharin (sweet but noncaloric) solution unconditioned stimulus (US), and the other flavor CS with either the other US or plain tap water. They were then given two-bottle choice tests between the flavor CSs apart from the USs. Flavors associated with 5% ethanol were preferred over saccharin-paired and water-paired flavors by sated rats, and food deprivation during the choice test enhanced this preference. The ethanol-paired flavor preference was not affected by feeding conditions (deprived vs. ad lib) during CS-US conditioning. Flavors associated with 8% sucrose (caloric + sweet tasting) were preferred over water-paired flavors during ad lib testing, and this preferences was also enhanced by food deprivation. Flavors associated with 0.028% or 0.25% saccharin were preferred over flavors paired with water; however, these preferences were not enhanced by deprivation at test time. In all cases, calorie-mediated preferences, at their highest levels, were stronger than taste-mediated preferences. These experiments indicate that preferences for flavors associated with caloric substances are positively related to hunger level at test time, but preferences mediated by a prior preferred taste are independent of test-time hunger level.

Alcohol Drinking↗
PubMed1979

Role of conditioned contextual stimuli in reinstatement of extinguished fear.

If the unconditioned stimulus (US) is presented independently of the conditioned stimulus (CS) following extinction, the conditioned response may be reinstated to the CS. Three experiments are reported that suggest that reinstatement is mediated by conditioning to contextual stimuli that are present during both US presentation and testing. Shocks presented to rats following the extinction of conditioned suppression reliably reinstated suppression to the CS, but only when they were presented in the context in which testing was later to occur. Reinstatement was also reversed by extinguishing fear to the context through nonreinforced exposure to the context between shock presentation and testing. Reinstatement was obtained in these experiments in spite of procedures that have been used in the past to minimize the influence of context conditioning. Moreover, fear of the context was never detected directly by depressed bar-press rates in the absence of the CS. The results do not support the hypothesis that reinstatement results from an increment in the strength of a memory of the US that has been weakened during extinction. Problems inherent in controlling and detecting levels of context conditioning that may influence behavior toward nominal CSs are discussed.

Animals↗
PubMed1979

Naloxone and shock-elicited freezing in the rat.

The freezing behavior of the rat that occurs following painful electric shock was found to increase when the animal was pretreated with the opiate antagonist naloxone. Freezing was a positive linear function of drug dose and shock intensity (Experiment 2). Naloxone pretreatment enhanced freezing only when the animal was given two or three shocks but did not affect freezing when the animal was given only one shock or not shocked at all (Experiments 3, 4, and 5). Naloxone must be present during shock, nor just during the observation period, in order to increase freezing (Experiment 6). These results suggest that when an animal is shocked, it releases endogenous analgesics (endorphins) that make a subsequent shock less aversive. Naloxone, by blocking the endorphin system, makes the shock more aversive than it would normally be.

Animals↗