Examination of Acute Sensitivity to Morphine and Morphine Self- Administration Following Physical and Environmental Stressors in Fischer-344 and Lewis Female Rats.

摘要

The present experiments examined the effects of different environmental conditions on acute morphine sensitivity and morphine self- administration in two genetically diverse inbred strains of rats. Fischer-344 and Lewis rats were subjects because they are related to the commonly used Sprague-Dawley strain, but differ from each other in behavioral and biological responses to opioids and environmental conditions. It was hypothesized that differential behavioral and biological responses to morphine under the various environmental conditions would be strain dependent. In Experiment 1, behavioral and biological effects of acute morphine injections were examined in 96 Fischer- 344 and 96 Lewis rats that were either group housed, individually housed, or group housed and immobilized. F-344 rats were more sensitive to morphine's analgesic and locomotor effects, whereas Lewis rats were more sensitive to morphine's effects on body temperature, vertical movements, and rotarod performance. Strain-dependent environmental effects on the acoustic startle response, vertical activity, speed, and body temperature also were found. Further, environmental conditions interacted with strain of rat to produce differential effects of morphine on hot-plate and speed of locomotion. Specifically, F-344 rats had different responses to morphine under the different environmental conditions, whereas for Lewis rats the responses to morphine did not change on these measures. In addition to behavioral changes, strain-dependent environmental influences on peripheral and central morphine levels also were found. In Experiment 2, the effects of the same environmental conditions on subsequent morphine self-administration were examined in 30 Fischer-344 and 30 Lewis rats. Morphine self- administration of F-344 rats was more affected by the different environmental conditions than was the self- administration behavior of Lewis rats.