Electrical stimulation of the PAG
a. produces changes in sensations of touch and pressure.
b. produces a type of analgesia that is not blocked by naloxone.
c. activates dopamine cells in the medulla, which in turn inhibit spinal cord pain transmission.
d. most likely releases endogenous opiates that act on m- and k- receptors.
e. is more effective at treating chronic pain than morphine because tolerance does not occur.