The Nociception Regulator can be bought from Doctor Usanagi at the New Vegas Medical Clinic. Despite its advertised effect, it is not taken into account when Endurance is counted for the maximum implant limit. Only using the Intense Training perk to increase your Endurance will allow you to purchase additional implants.
With the Nociception Regulator implanted the user's cardiovascular system, the broadcasts of the user's nociceptiors are dulled and/or stops feelings of bodily harm and enhance the user's stamina as well adding +1 to Endurance.
Behind the scenes
Nociception is the process by which sensory nerve endings (called nociceptors) respond to damaging stimuli by signalling the brain and spinal cord - in other words, it's the sensation of pain.
- "The Nociception Regulator modifies your cardiovascular system, and you won't tire as quickly. The price is 4,000 caps, same as most other implants." - Dr. Usanagi