Anthony L. Riley

Conditioned taste aversions: A bibliography

A bibliographic list of 403 articles dealing specifically with conditioned taste aversions from 1950–1975 is provided. In addition, the references are classified according to six major categories in a topical index. The major categories are Parameters of Conditioning, Physiological Manipulations, Pharmacological Interventions, Methodology, Comparative, and General Information. References were obtained from individual journals in psychology, physiology, pharmacology, and animal behavior and were supplemented and extended byPsychological Abstracts. A final source of references was provided by individual researchers who contributed preprints and reprints.

Freezing as an avoidance response: Another look at the operant-respondent distinction

Abstract Groups of rats were trained with shock either contingent on freezing (punishment procedure) or contingent on not freezing (avoidance procedure). Although the different contingencies produced different levels of freezing behavior, these levels were attained immediately rather than over a number of trials. This result, together with the results of control rats, suggest that while freezing can be controlled by both punishment and avoidance procedures, in both cases the effects on freezing are due to elicitation rather than learning.

The paradox of drug taking: the role of the aversive effects of drugs.

In 1991, Woods described the paradoxical nature of eating, specifically, that it produced aversive and negative effects. He noted in this analysis the multiple physiological and behavior adaptations, both learned and unlearned, that were aimed at regulating food intake and reducing its aversive, disruptive effects. From this position, he argued that consumption reflected a balance of the positive and aversive effects of eating. The present review extends this analysis to drug use and abuse, i.e., that drug taking itself also is a balance of reward and aversion. Although traditionally the analysis of drug use and abuse has focused on a drugs positive and negative rewarding effects, the present review highlights the aversive effects of these same drugs, e.g., cocaine, morphine, alcohol, and describes such effects as protective in nature. This balance and the manner by which it can be impacted by subject and experiential factors are described with a focus on genetic models of drug abuse using the Lewis and Fischer inbred rat strains.

Conditioned Food Aversions: A Bibliography

As evidenced from the breadth of topics covered in the present collection of chapters, i t is clear that the area of conditioned food aversions has grown immensely since the early findings of John Garcia and his colleagues that x-irradiated rats would avoid consumption of flavored solutions that had been present during the irradiation episode. What began as an interesting biological response with clear implications for traditional models of learning has now become a broad research area in and of itself. Not only is attention being focused on understanding the associative, biological, physiological and pharmacological bases of food aversion learning, but the phenomenon itself has recently become an applied research tool in pharmacology, toxicology, predation control, and clinical treatment. This growing interest in conditioned food aversions has been reflected in the number of articles published over the past 30 years. While over 600 papers had been published on taste aversion learning as of 1977, this number now stands at 1,373. The present bibliography is an attempt to update our earlier reports (see Riley & B a d , 1976 and Riley & Clarke, 1977) and brings the literature from 1955 to 1985 into a workable list. In determining what topics are relevant for inclusion, some degree of arbitrariness is certain. The present list is no exception. Only articles directly related to conditioned food aversions are included. By this restriction, a number of interesting and important related topics have been excluded, e.g., conditioned preferences, mimicry, neophobia, and unconditioned drug effects. These topics are listed only if they are examined in relation to conditioned food aversions. Also, although every attempt was made to include every food aversion article, some are certain to be missed. We apologize in advance for these oversights. In compiling the bibliography, references were obtained from individual journals in the areas of psychology, physiology, pharmacology, and animal behavior and from computer searches from Medline and Psychological Abstracts. References were also obtained from the bibliographies of individual articles. A final source of references was provided by individual researchers in the field of conditioned food aversions who freely contributed both preprints and reprints of their work.

The UCS preexposure effect in taste aversion learning: Tolerance and blocking are drug specific

Following drug preexposure, rats were given taste aversion conditioning in either the preexposure environment or the home cage. For animals preexposed to LiCl, only the subjects conditioned in the preexposure environment showed the typical UCS preexposure effect, that is, an attenuated aversion, an effect consistent with a blocking interpretation of the LiCl-induced preexposure effect. On the other hand, all rats preexposed to morphine displayed attenuated aversions, independent of the preexposure and conditioning environments, an effect consistent with a pharmacological tolerance explanation of the UCS preexposure effect to morphine. The specific mechanism underlying the drug-induced attenuation appears to be drug-dependent.

Cocaine-induced conditioned taste aversions : comparisons between effects in LEW/N and F344/N rat strains

Recent studies have found the LEW/N rat self-administers drugs of abuse at higher rates than the F344/N rat, suggesting a genetic predisposition toward the abuse potential of drugs. The current study compared the acquisition of a conditioned taste aversion (CTA) to cocaine in these strains. During an initial 20-min daily session a 0.1% saccharin solution was available and a dose (0–50 mg/kg, SC) of cocaine was given immediately after that session. Water was available during sessions on the following 3 days. Fluid consumption was assessed over three saccharin/water cycles, and a final saccharin session. Vehicle injections (0 mg/kg) that followed exposure to saccharin had no effect on subsequent saccharin consumption. In contrast, when cocaine followed exposure to saccharin, rates of saccharin consumption decreased over successive saccharin sessions in a dose-related manner in both strains. The lowest dose (18 mg/kg) decreased consumption in LEW/N rats but not in F344/N rats. An intermediate dose (32 mg/kg) decreased consumption maximally in LEW/N rats and only marginally in F344/N rats. The highest dose (50 mg/kg) decreased consumption completely in LEW/N rats and almost completely in F344/N rats. These findings demonstrate that significant differences in sensitivity to stimuli paired with cocaine occur between these strains. These differences are consistent with previous reports that the LEW/N rat is uniquely sensitive to both behavioral and biochemical effects of drugs of abuse. The current report extends this sensitivity to the noxious effects of these drugs. To the extent that noxious and reinforcing effects of cocaine are unrelated, these results suggest that the LEW/N rat does not exhibit a genetic predisposition to factors related only to the abuse potential of drugs.

Morphine preexposure facilitates morphine place preference and attenuates morphine taste aversion

Repeated morphine preexposure has been reported to enhance measures of morphine reward (conditioned place preference; CPP) and attenuate measures of morphine aversion (conditioned taste aversion; CTA). These effects are generally independently assessed, limiting the ability to determine if the enhancing and attenuating effects of morphine exposure are mediated by a common factor. To assess any potential relationship between these two effects, the present study examined the impact of morphine preexposure on these motivational properties of morphine using a combined CTA/CPP procedure in which the same animals receive concurrent taste and place conditioning. Specifically, male Sprague-Dawley rats were preexposed to morphine [5 mg/kg; subcutaneously (sc)] or equivolume drug vehicle. Following preexposure, animals were given saccharin to drink and injected with morphine sulfate (1 or 5 mg/kg sc) or drug vehicle (CTA). Immediately thereafter, they were placed on one side of a two-compartment chamber (CPP). On the next day, they were given water followed by injections of the drugs vehicle and then placed in the other compartment. There were four such conditioning cycles after each of which a CTA and CPP test were given. While preexposure to morphine attenuated morphine-induced CTAs, morphine-induced CPPs were enhanced within the same animals. These effects of morphine preexposure were dose- and time-dependent and parallel. These data indicate that the attenuating and sensitizing effects of morphine preexposure on taste aversions and place preferences, respectively, could be mediated by a common mechanism, although other possibilities for these effects of morphine preexposure remain.

Effects of Cross Fostering on Open-Field Behavior, Acoustic Startle, Lipopolysaccharide-Induced Corticosterone Release, and Body Weight in Lewis and Fischer Rats

Lewis (LEW/N) and Fischer (F344/N) rats differ on a myriad of behavioral and physiological endpoints, some of which have been reported to be affected by maternal experience in outbred rats and other strains. To assess whether epigenetic factors contribute to the differential behavioral responses to stress and pro-inflammatory challenges in these strains, the effects of cross fostering on open-field, acoustic startle, and glucocorticoid reactivity to lipopolysaccharide (LPS) were examined in the present experiment. In the open-field test, although in-fostered female LEW/N and F344/N strains did not differ, female LEW/N rats displayed significantly greater activity than female F344/N rats in the cross-fostered condition. Differences between males of the two strains were increased by cross fostering, with the LEW/N strain displaying greater total activity. In acoustic startle, there was little strain difference between in-fostered or cross-fostered female rats. On the other hand, in-fostered male LEW/N rats had a significantly greater startle response than in-fostered male F344/N rats, an effect that was dramatically reduced by cross fostering. In-fostered female LEW/N rats displayed a blunted corticosterone response relative to in-fostered female F344/N rats, an effect that was reduced by cross fostering. Conversely, although there was no strain difference between male in-fostered rats, cross-fostered male F344/N rats displayed a significantly greater corticosterone response to LPS than cross-fostered male LEW/N rats. Finally, body weight differences between in-fostered LEW/N and F344/N rats were reduced by cross fostering. Together, these data illustrate that maternal factors play a role in the behavioral and physiological responses to stress between the two strains.

Cocaine-induced taste aversions: effect of route of administration.

Female Long-Evans rats were given 20-min access to saccharin followed by either intraperitoneal (IP) or subcutaneous (SC) cocaine (18, 32 or 50 mg/kg) or vehicle. Aversions induced by IP-administered cocaine were relatively weak, with subjects at all doses decreasing consumption by only 35% after four conditioning trials. On the other hand, aversions induced by SC-administered cocaine were robust, with subjects at the two highest doses (32 and 50 mg/kg) decreasing saccharin consumption by 95 and 98%, respectively, on the final aversion test. Although several possibilities exist for the differential ability of IP and SC cocaine to induce taste aversions (e.g., longer duration of action with SC cocaine and the convulsant property of IP cocaine), the basis for this difference remains unknown. A secondary finding was the effect of route of administration on body weight. While all subjects receiving IP cocaine maintained or increased in body weight, subjects receiving the two highest doses of SC cocaine decreased in body weight by 3 and 5%, respectively. The differential effect of IP and SC cocaine on body weight may be due to cocaines action on drinking and feeding or cocaines leptogenic property. Independent of the mechanism underlying the differential ability of IP and SC administration to induce taste aversions and affect body weight, it is clear that route of administration may play an important role in the effects of cocaine.

Morphine-induced taste aversions: A consideration of parameters

Following consumption of saccharin, groups of rats were injected with various doses of morphine sulfate. Although no aversion was found after one conditioning trial, repeated saccharin-morphine pairings resulted in decreases in consumption of the saccharin solution. On the average, however, the groups of rats showed only a moderate aversion, independent of the dose of morphine. Although there was little variability in consumption among rats that received the smallest dose of morphine, there was considerable individual variability among subjects receiving the larger doses. The differences between morphine-based conditioned taste aversions and aversions based on emetic USs were discussed.