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Biomedical subjects

R Melzack

Publications and source records attributed to R Melzack.

At least 91 records · Page 5Linked to original sources
PubMed1982

Stimulation-produced analgesia: evidence for somatotopic organization in the midbrain.

The somatotopic organization of structures in the midbrain which mediate stimulation-produced analgesia (SPA) was studied by stimulating a series of neural loci using a movable electrode. The strength and distribution of analgesia at 7 fields on the body surface, as measured by the application of noxious pinch, was clearly related to the dorsoventral stimulation locus. SPA at dorsal sites was distributed at the ears and, to a lesser extent, at the forepaws. At progressively more ventral loci, maximal analgesia appeared successively at the forepaws, hindpaws and tail. This organization was maintained throughout the rostrocaudal extent of the midbrain. However, rostral stimulation sites tended to produce analgesia in smaller, more discrete fields than those produced by caudal stimulation sites. Further studies showed that the relationship between SPA and stimulation site is influenced by the electrical stimulation current level. Each site had an optimum current level, so that current intensities higher or lower than the optimum produced decreased analgesia. These results reveal a possible neural mechanism for somatotopic organization in hyperstimulation analgesia in which an intense somatic input at a body site produces analgesia in the same or adjacent segments.

Analgesia↗
PubMed1982

Brainstem lesions dissociate neural mechanisms of morphine analgesia in different kinds of pain.

The effects of brainstem lesions on morphine analgesia were examined using the formalin test which produces moderate pain that lasts about 2 h, and the tail-flick test which measures brief threshold-level pain. Lesions of the nucleus raphe magnus attenuated and small lesions of the central tegmental nucleus potentiated the effects of morphine in the tail-flick test. Lesions of the median raphe nucleus potentiated the effects of morphine in the formalin test. Large lesions of the pontine reticular formation had no effect in either pain test. These results indicate that the neural mechanisms underlying morphine analgesia are different in different kinds of pain.

Analgesia↗
PubMed1982

Morphine analgesia and tolerance in the tail-flick and formalin tests: dose-response relationships.

The dose-response relationships for morphine analgesia were studied in morphine-tolerant and non-tolerant rats using two pain tests: the tail-flick test which measures the threshold for an escape response, and the formalin test which assesses the behavioral response to continuous pain generated in injured tissue. The effects of prior experience with both pain tests on tolerance were also examined. In the formalin test, effective analgesia was obtained in non-tolerant rats at doses that produce minimal depression of locomotor behavior. Morphine tolerance was produced by 20 daily injections of morphine with increments that reached 16 mg/kg, a dose over the LD100 for barrier sustained Long Evans rats. This dose regimen produced a 1.8-fold increase in the ED50 in the tail-flick test and a 2.7-fold increase in the formalin test. Daily experience of the pain test, as well as the morphine regimen produced a 4.8-fold increase in the ED50 in the tail-flick test but did not affect the potency of morphine in the formalin test. The magnitude of tolerance in the absence of daily behavioral testing is consistent with recent clinical reports that little tolerance occurs after prolonged administration of morphine in cancer patients and that tolerance is not an important consideration in the management of pain.

Animals↗
PubMed1982

Recent concepts of pain.

Recent evidence shows that pain is not simply a function of the amount of bodily damage alone, but is influenced by attention, anxiety, suggestion, and other psychological variables. The gate control theory proposes than pain signals from the body are modulated by other, concurrent somatic inputs as well as by descending influences from the brain. It is now known that some kinds of pain can be diminished or abolished by anesthetic blocks of trigger points or by intense stimulation of the same points. These effects appear to be mediated by brainstem mechanisms that exert a tonic inhibitory effect on pain signals. Studies of paraplegic patients further elucidate the multiple neural interactions that occur in eliciting and alleviating pain. An example of interacting therapies for cancer pain is the significant augmentation of the effectiveness of the Brompton mixture by a psychologically supportive hospital environment.

Analgesia↗
PubMed1981

Labour is still painful after prepared childbirth training.

Labour pain was measured with the McGill Pain Questionnaire in 87 primiparas and 54 multiparas. The average intensity of labour pain ranked among the most intense pains recorded with the questionnaire. However, the pain scores had a wide range and were influenced by several medical and social variables. They were significantly higher for the primiparas than for the multiparas. Moreover, high pain levels were associated with a history of menstrual difficulties and lower socioeconomic status. The primiparas who had received prepared childbirth training had lower pain scores than those who had received no such training. Nevertheless, the effects of prepared childbirth training were relatively small, and most patients (81%) who received it requested epidural anesthesia. Because many women who received training suffered severe pain during labour, prepared childbirth training and epidural anesthesia should be regarded as compatible, complementary procedures.

Adolescent↗
PubMed1981

Apparent lack of tolerance in the formalin test suggests different mechanisms for morphine analgesia in different types of pain.

Tolerance to morphine analgesia was examined using the Formalin test in which pain lasting about 2 hrs associated with minor tissue injury is produced by subcutaneous injection of dilute Formalin. To distinguish behavioral from pharmacological tolerance, different groups of rats received their daily morphine injection (7 mg/kg) in the test environment or in their home environment for 5 days. Another group of rats was given morphine for 15 days in the home cage followed by 5 days in the test environment. None of the morphine injected groups differed from saline injected control groups in the amount of analgesia. These findings add to previous evidence that the Formalin test measures a type of pain which is different from that assessed in withdrawal reflex tests, and which more closely resembles clinical pain in man. Moreover, the fact that analgesia in the Formalin test shows little tolerance while analgesia in withdrawal tests shows rapid tolerance suggests that the underlying neural mechanisms are different.

Animals↗
PubMed1981

Myofascial trigger points: relation to acupuncture and mechanisms of pain.

The gate control theory of pain describes the modulation of sensory nerve impulses by inhibitory mechanisms in the central nervous system. One of the oldest methods of pain relief is hyperstimulation analgesia produced by stimulating myofascial trigger points by dry needling, acupuncture, intense cold, intense heat, or chemical irritation of the skin. The moderate-to-intense sensory input of hyperstimulation analgesia is applied to sites over, or sometimes distant from, the pain. A brief painful stimulus may relieve chronic pain for long periods, sometimes permanently. Pain may be relieved by "closing the gate" by means of a central biasing mechanism possibly located in the brainstem reticular formation. Prolonged relief may require the disruption of reverberatory neural circuits responsible for the "memory" of pain. The termination of pain by either hyperstimulation, or by local injection of an anesthetic, normalizes function, which helps to prevent recurrence of abnormal neural activity. Thus, modulation of sensory inputs by use of many techniques may reduce pain more than by surgically interrupting the sensory input.

Acupuncture Therapy↗
PubMed1980

Relief of dental pain by ice massage of the hand.

Patients suffering from acute dental pain were treated with ice massage of the web between the thumb and index finger of the hand on the same side as the painful region. Control groups received tactile massage alone or with explicit suggestion that the massage was intended to alleviate their pain. Changes in pain intensity produced by the procedures were measured with the McGill Pain Questionnaire. Ice massage decreased the intensity of the dental pain by 50% or more in the majority of patients. Furthermore, the pain reductions produced by ice massage were significantly larger than those produced by tactile massage alone or with explicit suggestion. The results indicate that ice massage has pain-reducing effects comparable to those of transcutaneous electrical stimulation and acupuncture. The fact that cold signals are transmitted to the spinal cord exclusively by A-delta fibres and not by C fibres provides a potential method for differentiating the various feedback systems that mediate analgesia produced by different forms of intense sensory input. Ice massage provides a simple method for the palliative control of pain in dental clinics.

Adolescent↗
PubMed1980

Ice massage and transcutaneous electrical stimulation: comparison of treatment for low-back pain.

It has recently been shown that ice massage of the web between the thumb and index finger produces significantly greater relief of dental pain than a placebo control procedure. These results indicate that ice massage may be comparable to transcutaneous electrical stimulation (TES) and acupuncture, and may be mediated by similar neural mechanisms. The purpose of this study was to examine the relative effectiveness of ice massage and TES for the relief of low-back pain. Patients suffering chronic low-back pain were treated with both ice massage and TES. The order of treatments was balanced, and changes in the intensity of pain were measured with the McGill Pain Questionnaire (MPQ). The results show that both methods are equally effective: based on the Pain Rating Index of the MPQ, 67-69% of patients obtained pain relief greater than 33% with each method. The results indicate that ice massage is an effective therapeutic tool, and appears to be more effective than TES for some patients. It may also serve as an additional sensory-modulation method to alternate with TES to overcome adaptation effects. Evidence that cold signals are transmitted to the spinal cord exclusively by A-delta fibers and not by C fibers suggests that ice massage provides a potential method for differentiating among the multiple feedback systems that mediate analgesia produced by different forms of intense sensory input.

Adolescent↗
PubMed1979

The Brompton mixture versus morphine solution given orally: effects on pain.

The Brompton mixture is widely used as an effective method for controlling pain in cancer patients. In a double-blind crossover trial a standard Brompton mixture containing morphine, cocaine, ethyl alcohol, syrup BP and chloroform water was compared with morphine alone in a flavoured aqueous solution; both were administered orally. Pain was measured by means of the pain intensity index of the McGill Pain Questionnaire. Ratings of confusion, nausea and drowsiness were obtained from both the patients and their nurses and relatives. The data showed that there was no significant difference between the Brompton mixture and morphine administered orally for any of the variables. Both relieved pain effectively in about 85% of the patients.

Administration, Oral↗