NGF is known to up-regulate neuropeptides, especially substance P. Substance P has been found to have an important role in inducing pain; however, there is no confirmation that substance P directly causes acute sensitization. Instead, substance P may contribute to itch by increasing neuronal sensitization and may affect release of mast cells, which contain many granules rich in histamine, during long-term interaction. Central sensitization
Noxious input to the spinal cord is known to produce central sensitization, which consists of allodynia, exaggeration of pain, and punctuate hyperalgesia, extreme sensitivity to pain. Two types of mechanical hyperalgesia can occur: 1) touch that is normally painless in the uninjured surroundings of a cut or tear can trigger painful sensations (touch-evoked hyperalgesia), and 2) a slightly painful pin prick stimulation is perceived as more painful around a focused area of inflammation (punctuate hyperalgesia). Touch-evoked hyperalgesia requires continuous firing of primary afferent nociceptors, and punctuate hyperalgesia does not require continuous firing which means it can persist for hours after a trauma and can be stronger than normally experienced. In addition, it was found that patients with neuropathic pain, histamine ionophoresis resulted in a sensation of burning pain rather than itch, which would be induced in normal healthy patients. This shows that there is spinal hypersensitivity to C-fiber input in chronic pain. Treatment
A variety of over-the-counter and prescription anti-itch drugs are available. Some plant products have been found to be effective anti-pruritics, others not. Non-chemical remedies include cooling, warming, soft stimulation.
Many people who habitually use cocaine develop a transient, manic-like condition similar to amphetamine psychosis and schizophrenia, whose symptoms include aggression, severe paranoia, restlessness, confusion and tactile hallucinations; which can include the feeling of something crawling under the skin (formication), also known as "coke bugs", during binges. Different ingestion techniques have their own symptoms that accompany them. Snorting it can cause a loss of sense of smell, nose bleeds, problems swallowing and an inflamed, runny nose. Smoking it causes lung damage and injecting it puts users at risk of contracting infectious diseases like HIV and hepatitis C. Heavy users of cocaine have also reported having thoughts of suicide, unusual weight loss, trouble maintaining relationships, and an unhealthy, pale appearance. Withdrawal symptoms
When used habitually, cocaine, because of its highly addictive nature, can change brain structure and function. Circuits within the brain structure, that play a part in stress signals become more sensitive. When cocaine is not being used this increases an individuals displeasure and negative moods. In 1986, Gawin and Kleber led an important study on the withdrawal symptoms of cocaine users. In this study, three distinct phases were reported. These phases are the crash, withdrawal and extinction. The crash phase or phase 1 occurs directly after cocaine is not being used anymore. Withdrawal symptoms for this phase are exhaustion, hypersomnia, no cravings to use, dysthymia, increased appetite, restlessness, and irritability.