This from the UFC rules on their site. I don't see pressure points or anything similar described as a no-no. #12 comes the closest.
1. Butting with the head.
2. Eye gouging of any kind.
4. Hair pulling.
5. Fish hooking.
6. Groin attacks of any kind.
7. Putting a finger into any orifice or into any cut or laceration on an opponent.
8. Small joint manipulation.
9. Striking to the spine or the back of the head.
10. Striking downward using the point of the elbow.
11. Throat strikes of any kind, including, without limitation, grabbing the trachea.
12. Clawing, pinching or twisting the flesh.
13. Grabbing the clavicle.
14. Kicking the head of a grounded opponent.
15. Kneeing the head of a grounded opponent.
16. Stomping a grounded opponent.
17. Kicking to the kidney with the heel.
18. Spiking an opponent to the canvas on his head or neck.
19. Throwing an opponent out of the ring or fenced area.
20. Holding the shorts or gloves of an opponent.
21. Spitting at an opponent.
22. Engaging in an unsportsmanlike conduct that causes an injury to an opponent.
23. Holding the ropes or the fence.
24. Using abusive language in the ring or fenced area.
25. Attacking an opponent on or during the break.
26. Attacking an opponent who is under the care of the referee.
27. Attacking an opponent after the bell has sounded the end of the period of unarmed combat.
28. Flagrantly disregarding the instructions of the referee.
29. Timidity, including, without limitation, avoiding contact with an opponent, intentionally or consistently dropping the mouthpiece or faking an injury.
30. Interference by the corner.
31. Throwing in the towel during competition.
“Courage is contagious. When a brave man takes a stand, the spines of others are often stiffened.”