effects of adenosine (Ad), or of various A1-receptor agonists is inhibitory,
leading to effects such as drowsiness, motor incoordination, analgesia and anticonvulsant
activity. Xanthines, such as caffeine, which are antagonists at A2-R, produce arousal and
Less is known about the function of ATP as a chemical mediator in the brain,
mainly because ATP itself is quickly metabolized to ADP and Ad. One of its roles may be in
nociception, since ATP is released by tissue damage, and causes pain by stimulating
unmyelinated afferent nerve terminals, which express P2X-R.