Researchers' work from University of Sao Paulo focuses on behavior.

"The behavioral effects of the K-opioid receptor agonist U69593 were examined in lactating rats. On day 5 of lactation, animals were treated with 0.1 mg/kg of U69593 to determine whether it influences general activity and maternal latencies toward pups," scientists writing in the journal Pharmacology Biochemistry and Behavior report (see also Behavior).

"Because little attention has been given to the possibility that pre-mating treatment with morphine may modulate the response to K-opioid receptor stimulation, another group of animals was submitted to the same acute challenge after abrupt withdrawal from repeated treatment with morphine sulfate during the pre-mating period (5 mg/kg on alternate days for a total of five doses). Acute F;opioid stimulation reduced total locomotion, rearing frequency, and time spent self-grooming and increased immobility duration. These K agonist effects were not observed in animals pretreated with morphine. Similarly, latencies to retrieve pups were longer only in animals pretreated with saline and challenged acutely with U69593. None of these effects were observed in morphine sulfate-pretreated animals," wrote E. Teodorov and colleagues, University of Sao Paulo.

The ...