Shepard Siegel wasknown for conducting the paw lick latency test in order to examine the effectsof morphine when it’s administered into animals. After the morphine would beinjected into the rat, Siegel has observed how the animal’s paw lick latencyincreases, while the animal’s sensitivity would become lower. However, when themorphine injections become more frequent, the animal learns to adapt tolerance.
After the third trial of the training phase, Siegel injected two rat groupswith morphine and used the hot plate at the same testing room. The results cameout showing one group (M-HP) of the rats being tolerant towards morphine. On theother hand, the second group, M-CAGE, had a higher analgesic effect, although,they never displayed any signs of tolerance like the first group. Later on,Siegel flipped the experiment and gave the M-HP rats saline instead ofmorphine. They reacted by licking their paws much faster than when they were underthe influence of morphine.
Furthermore, this study has shown Siegel that therats were tolerant to morphine when the paw lick latency test was conducted inthe same room and they were injected earlier. The main idea of this experimentwas to clarify how conditional tolerance plays an important role in how themorphine or the saline would affect the rats when they are injected in eitherthe same room or a different one. Furthermore, conditional tolerance could beapplied to human beings as well. For instance, with drugs, Siegel and his colleagueshave concluded that the tolerance is correlated with the environment where it’staken through a series of experiments with rats. They were able to break downhow tolerance doesn’t only affect animals, but it affects in the same conditionsas well.