Substance P (Sub P) is a neurotransmitter that was first identified in 1931. In the 1950s it was shown to play a major role in transmitting the pain signal to your brain.
Later work has shown it to have important roles in your brain related to your response to pain.
It has long been understood that the "Pain Experience" is a combination of the physical pain and your emotional response to it.
Recent studies are starting to show that Sub P plays an important part in both parts of your pain experience.
Along Nerve Pathways
Your body has special nerve pathways for conduction of the pain signal to your brain.
Sub P is the primary neurotransmitter transmitting the pain signal along these pathways in your spinal cord.
Increases and Decreases
Peripheral stimulation causes the release of Sub P in your spinal cord and studies have shown that this makes the nerves more sensitive to pain. Other studies have shown Sub P to have an inhibitory affect on the nerve signal.
Remember that neurotransmitters pass the signal from one nerve to another at the junctions where these nerves connect, and neurotransmitters can be excitatory (increasing the nerve signal) or inhibitory (suppressing the nerve signal).
Current thinking is that Sub P makes the nerves more sensitive to both excitatory and inhibitory signals. Exactly how these interactions work is still being studied. Scientists are looking for ways to manipulate or control your levels of Sub P to help control pain and manage other medical conditions.
Substance P is also found in your hypothalamus, your pituitary, and your amygdala which are areas of your brain associated with emotion and behavior responses to stress. Stimulation of the your amygdala in response to fear or anxiety leads to a stress response from your autonomic nervous system.
Other responses that involve substance P include your vomiting reflex, defensive behaviors, increased saliva production, and vasodilation.
Recent studies have started to show that that Sub P plays an important role in inflammation of nerves in response to pain or infection. It will increase local edema by making the blood vessels more permeable or "leaky". This is part of your inflammatory response that allows antibodies and inflammatory chemicals to seep out of blood vessels and into the injured tissue.
In your brain Sub P is released in response to stress or anxiety. Researchers are starting to show that it causes changes in your brain chemistry that make you more susceptible to depression. Studies with animals are starting to show that blocking Sub P in the brain can reduce anxiety and depression.
Capsaicin is an over the counter medication that is used for the treatment pain. Recently a high concentration patch has been introduced that is available by prescription.
Capsaicin is thought to relieve pain by depleting the supply of Sub P.
In some situations when Sub P is being used faster than your body can produce it the pain signal cannot be transmitted to your brain.
Capsaicin is derived from Chile peppers and its application is associated with a burning or stinging sensation. It is this stimulation that causes your body to release Sub P.
The Treatment may be Worse than the Disease
When the supply has been depleted the pain signal will no longer be transmitted.
Unfortunately, the burning pain from capsaicin may last for 2 to 4 weeks and it is sometimes a deterrent to continued use. Some people think that the treatment is worse than the disease.
Capsaicin has been shown to be helpful for the treatment of osteoarthritis pain and neuralgia.
Substance P is an important neurotransmitter involved in the sensation of pain. Efforts with attempting to directly control pain by manipulating or otherwise targeting Substance P have met with little success.
However, latest research is showing that Sub P plays a major part in your sensitivity to pain and in your emotional response to pain. There has been some success in animal models; blocking Sub P appears to lead to a reduction of this sensitivity and emotional response.
Further research is continuing for a better understanding and more effective ways to control pain and the pain experience.