Examination of Acute Sensitivity to Morphine and Morphine Self-Administration Following Physical and Environmental Stressors in Fischer-344 and Lewis Female Rats
Uniformed Services University Of The Health Sciences Bethesda United States
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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 morphines analgesic and locomotor effects, whereas Lewis rats were more sensitive to morphines 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.