In the first phase of Experiment 3, a serial CS was explicitly unpaired with food. The second phase of this experiment was identical to that of Experiment 2. The results showed that lever contact was lowest during the Near element in Experiment 1, highest during the same element in Experiment 2, and indistinguishable among all the elements in Experiment 3. All rights of reproduction in any form reserved. Ann E.K. Kosobud, Norman C. Pec oraro, George V. Rebec, and William Timberlake.
Circadian activity precedes daily methamphetamine injections in the rat.
A circadian basis for pre-injection time activity was supported by its anticipatory timing in the apparent absence of reliable preceding external cues and by its persistence on a test day on which the rats remained undisturbed. Post-injection time locomotor activity also persisted on the test day, occurring from 24 to 29 h after the final MA injections. These results indicate that MA injections engage circadian processes underlying locomotor activity, and they raise the possibility that intake of drugs of abuse by humans may facilitate drug taking or relapse at times of day related to previous drug use. Elsevier Science Ireland Ltd. All rights reserved. Kathleen M. Silva and William Timberlake.