Effects of corticotropin-releasing factor (CRF), tuftsin and dermorphin on behavior of squirrel monkeys maintained by different events

The effects of intracerebroventricular (ICV) administration of ovine CRF (0.1–30.0 μg/kg), dermorphin (0.3–30.0 μg/kg) and tuftsin (10–3000 μg/kg) were examined in squirrel monkeys trained to respond under a multiple 3-min fixed-interval schedule of food presentation and either shock presentation or stimulus-shock termination. Initial administration of the 41-amino acid polypeptide CRF increased food-maintained responding by 150–200% in 2 of 3 subjects. However, no other doses tested affected response rates, a result that may have been due to the rapid development of tolerance. The tetrapeptide tuftsin selectively increased responding maintained by food presentation at doses that decreased shock-maintained responding. The heptapeptide dermorphin selectively increased food-maintained responding when responding in the other component of the multiple schedule was maintained by shock presentation. When responding was maintained by a multiple food, stimulus-shock termination schedule, dermorphin decreased response rates in both components. Dermorphin's rate increases were blocked by the opiate antagonist naloxone, indicating that dermorphin's actions were mediated through the opiate receptor. These results indicate that the behavioral effects of tuftsin, dermorphin, and perhaps CRF, depend on the manner in which responding is controlled by its consequences. While the actions of tuftsin and dermorphin are believed to be mediated through the opiate system, the behavioral effects observed in primates appear different from the effects of morphine under similar schedule conditions.