Competition Between Novelty and Cocaine Conditioned Reward Is Sensitive to Drug Dose and Retention Interval

The conditioned rewarding effects of novelty compete with those of cocaine for control over choice behavior using a place conditioning task. The purpose of the present study was to use multiple doses of cocaine to determine the extent of this competition and to determine whether novelty’s impact on cocaine reward was maintained over an abstinence period. In Experiment 1, rats were conditioned with cocaine (7.5, 20, or 30 mg/kg ip) to prefer one side of an unbiased place conditioning apparatus relative to the other. In a subsequent phase, all rats received alternating daily confinements to the previously cocaine paired and unpaired sides of the apparatus. During this phase, half the rats had access to a novel object on their initially unpaired side; the remaining rats did not receive objects. The ability of novelty to compete with cocaine in a drug free and cocaine challenge test was sensitive to cocaine dose. In Experiment 2, a place preference was established with 10 mg/kg cocaine and testing occurred after 1, 14, or 28 day retention intervals. Findings indicate that choice behaviors mediated by cocaine conditioning are reduced with the passing of time. Taken together, competition between cocaine and novelty conditioned rewards are sensitive to drug dose and retention interval.

Signaling via cAMP in Fungi: Interconnections with Mitogen-Activated Protein Kinase Pathways

The cAMP signal transduction pathway controls a wide variety of processes in fungi. For example, considerable progress has been made in describing the involvement of cAMP pathway components in the control of morphogenesis in Saccharomyces cerevisiae, Ustilago maydis, and Magnaporthe grisea. These morphological processes include the establishment of filamentous growth in S. cerevisiae and U. maydis, and the differentiation of an appressorial infection structure in M. grisea. The discovery that appressorium formation requires cAMP signaling provides an immediate connection to fungal virulence. This connection may have broader implications among fungal pathogens because recent work indicates that cAMP signaling controls the expression of virulence traits in the human pathogen Cryptococcus neoformans. In this fungus, cAMP also influences mating, as has been found for Schizosaccharomyces pombe and as may occur in U. maydis. Finally, cAMP and mitogen- activated protein kinase pathways appear to function coordinately to control the response of certain fungi, e.g., Saccharomyces cerevisiae and Schizosaccharomyces pombe, to environmental stress. There are clues that interconnections between these pathways may be common in the control of many fungal processes.