| Abstract: | Previous results show that endogenous opioid systems mediate affective responses in neonatal rats. Opioids modulate isolation-induced ultrasonic vocalizations and analgesia. This study further examines the behavioral effects of κ-receptor-system stimulation on 10-day-old rats. With the agonist U50,488, response to isolation in terms of vocalizations, activity levels, and pain sensitivity was tested. In contrast to morphine's effects (primarily a μ-agonist), the κ-agonist U50,488 produced increased vocalizing and hyperactivity, although both opioid agonists caused analgesia. Isolation adds to the U50,488-mediated increase in the latency for paw withdrawal from heat. This study suggests that the kappa system provokes calling and activity as opposed to the quieting effects of μ-agonists found in previous studies. These differential effects may be due in part to the interaction of the opioid and dopamine systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved) |
