Hungry adult rats were tested in a 12-choice maze for their ability to find a reward of food 15 minutes after being injected peripherally with (D-Ala2)-β-endorphin. Injection of the endorphin analog in a dose of 80 μg/kg body weight resulted in rats running the maze significantly slower and with more errors than rats injected with diluent. Animals receiving a dose ten times larger (800 μg/kg) were indistinguishable from controls in both running speed and errors, thus making a toxic effect unlikely. Possible changes in appetite, thirst, olfaction, emotionality, and general motor activity did not seem to explain the results. The inverted U-shaped dose-related response seemed to represent a variant from previous observations with CNS-active peptides in that the smaller dose impaired rather than enhanced performance.
ASJC Scopus subject areas
- Experimental and Cognitive Psychology
- Behavioral Neuroscience