The role of corticotropin-releasing factor in pain and analgesia.

Corticotropin-releasing factor (CRF) is a peptide that is released from the hypothalamus and in widespread areas of the brain following exposure to stressors. It is considered to be a mediator of many of the effects of stress, and its analgesic properties have been demonstrated in many studies. However, for primarily methodological reasons, the effects of CRF in the central nervous system have been neglected whereas the peripheral effects of CRF have been overemphasized. We present evidence that: (1) CRF can act at all levels of the neuraxis to produce analgesia; (2) the release of beta-endorphin does not explain the analgesia following intravenous or intracranial CRF administration; (3) inflammation must be present for local CRF to evoke analgesia and (4) the analgesic effects of CRF show specificity for prolonged pain. These findings suggest that CRF may have a significant role in chronic pain syndromes associated with hypothalamic-pituitary-adrenal axis abnormalities. Furthermore, CRF may represent a new class of analgesics that merits further study. Implications for the relationship between stress and pain are discussed.

An association between phantom limb sensations and stump skin conductance during transcutaneous electrical nerve stimulation (TENS) applied to the contralateral leg: a case study.

This report describes a placebo-controlled study of transcutaneous electrical nerve stimulation (TENS) applied to the contralateral lower leg and outer ears of an amputee with non-painful phantom sensations. The subject received TENS or placebo stimulation on separate sessions in which baseline periods of no stimulation alternated with periods of TENS (or placebo). Throughout the two sessions, continuous measures of stump skin conductance, surface skin temperature and phantom intensity were obtained. The results showed that TENS applied to the contralateral leg was significantly more effective than a placebo in decreasing the intensity of phantom sensations, whereas stimulation of the outer ears led to a non-significant increase. The pattern of electrodermal activity on the TENS session was consistently linear during baseline periods, indicating a progressive increase in sympathetic sudomotor activity. In contrast, during periods of electrical stimulation the pattern of electrodermal activity was consistently curvilinear indicating an initial decrease followed by an increase in sudomotor responses. Changes in stump skin conductance correlated significantly with changes in phantom sensations both in TENS and placebo sessions suggesting a relationship between sympathetic activity at the stump and paresthesias referred to the phantom. Two hypotheses are presented to account for these findings.

Trigger points and acupuncture points for pain: correlations and implications.

Trigger points associated with myofascial and visceral pains often lie within the areas of referred pain but many are located at a distance from them. Furthermore, brief, intense stimulation of trigger points frequently produces prolonged relief of pain. These properties of trigger points--their widespread distribution and the pain relief produced by stimulating them--resemble those of acupuncture points for the relief of pain. The purpose of this study was to determine the correlation between trigger points and acupuncture points for pain on the basis of two criteria: spatial distribution and the associated pain pattern. A remarkably high degree (71%) of correspondence was found. This close correlation suggests that trigger points and acupuncture points for pain, though discovered independently and labeled differently, represent the same phenomenon and can be explained in terms of the same underlying neural mechanisms. The mechanisms that play a role in the genesis of trigger points and possible underlying neural processes are discussed.

Prolonged relief of pain by brief, intense transcutaneous somatic stimulation.

The purpose of this study was to examine the effects of brief, intense transcutaneous electrical stimulations at trigger points or acupuncture points on severe clinical pain. The McGill Pain Questionnaire was used to measure the change in pain quality and intensity produced by stimulation. The data indicate that the procedure provides a powerful method for the control of some forms of severe pathological pain. The average pain decrease during stimulation sessions was 75% for pain due to peripheral nerve injury, 66% for phantom limb pain, 62% for shoulder-arm pain, and 60% for low-back pain. The duration of relief frequently outlasted the period of stimulation by several hours, occasionally for days or weeks. Different patterns of the amount and duration of pain relief were observed. Daily stimulation carried out at home by the patient sometimes provided gradually increasing relief over periods of weeks or months. Control experiments, which included two forms of placebo stimulation, showed that brief, intense electrical stimulation is significantly more effective than placebo contributions. Possible neural mechanisms that underlie these patterns of pain relief by brief, intense stimulation are discussed.