So the second step was to give the drug to awake rats systemically and then do a microinjection into this brain region to inhibit all cell activity. Under those circumstances, the animals do not show an analgesic effect after the systemic cannabinoid. The activity of cells in this brain region is necessary for the cannabinoid to have its analgesic effect. So you're trying to figure out how cannabinoids work -you're not trying to prove that they do work. You recognize the existing evidence.
People know that they're analgesic.
But until fairly recently it hadn't been proven in animal studies that cannabinoids affect sensation. The anesthetized rat is placed on the box with its tail in a groove above a hole, so that the radiant heat from the bulb will reach the tail, which the animal then flicks out of the groove. If you give an analgesic drug, a cannabinoid, or morphine, then the animal will leave its tail on the heat source much longer. I also look at the actual transmission of pain signals through the central nervous system. I do single cell recording -looking at the activity of single neurons that are related to pain.