Showing papers by "Patrick D. Wall published in 1986"

Relative effectiveness of C primary afferent fibers of different origins in evoking a prolonged facilitation of the flexor reflex in the rat

Abstract: Changes in the excitability of the hamstring flexor withdrawal reflex produced by conditioning stimuli applied to C-afferent fibers of different origins have been examined in the decerebrate spinal rat. In the absence of conditioning stimuli, the flexor reflex elicited by a standard suprathreshold mechanical stimulus to the toes is stable when tested repeatedly for hours. Three categories of conditioning stimuli have been used in an attempt to modify the excitability of the flexor reflex; electrical stimulation of a cutaneous (sural) nerve or a muscle (gastrocnemius-soleus) nerve at C-fiber strength; the application of mustard oil, a chemical irritant that activates chemosensitive C- afferents, to the skin or injected intramuscularly and intraarticularly; and the indirect activation of high-threshold muscle afferents by fused tetanic contractions of the tibial muscles. Conditioning stimuli of an intensity sufficient to activate C-afferent fibers result in a heterosynaptic facilitation of the flexor motoneuronal response to the standard test input, which lasts from 3 min to more than 3 hr, depending on the stimulus and the C-afferents activated. Pretreatment of the sciatic nerve with the C-fiber neurotoxin capsaicin abolishes all the postconditioning facilitations, which is an indication that it is likely that it is C-afferents that are primarily responsible for the facilitatory effects of the conditioning stimuli, although some A delta afferents may contribute. Capsaicin pretreatment does not modify the reflex response to the test stimulus. The most prolonged increase in the excitability of the flexor reflex resulted from intraarticular injections of 5 microliter mustard oil. Using the subsequent injection of lignocaine intraarticulary, it was found that the prolonged facilitation of the reflex is triggered by the afferent input generated by the conditioning stimulus and does not require an ongoing input for its maintenance. These results indicate that there is a spectrum of central changes in the stimulus response relations of the spinal cord resulting from the activation of C-fibers of different origins. The prolonged duration of some of these changes means that the peripheral activation of C-afferents will modify the functional response of the spinal cord to other inputs applied long after the conditioning input, and this may be responsible for some ofthe sensory and motor alterations found after peripheral tissue injury.

Acupuncture and transcutaneous electrical nerve stimulation

Abstract: The study of folk medicine by anthropologists and medical historians has revealed an astonishing array of ingenious methods to relieve pain (Brockbank, 1954). Every culture, it appears, has learned to fight pain with pain: in general, brief, moderate pain tends to abolish severe, prolonged pain. One of the oldest methods is cupping, in which a glass cup is heated up (by coals or flaming alcohol) and then inverted over the painful area and held against it. As the air in the cup cools and contracts, it creates a partial vacuum so that the skin is sucked up into the cup. The procedure produces bruising of the skin with concomitant pain and tenderness. Cupping was practised in ancient Greece and Rome as early as the 4th century B.C., and was also practised in ancient India and China. Over the centuries, the method spread to virtually all parts of the world, and cups of various sizes, shapes and materials have evolved. Cupping has been used-and is still widely practised-for a large variety of ailments, including headaches, backaches, and arthritic pains. Cauterization is yet another ancient method. Generally, the end of an iron rod was heated until it was red-hot, and was then placed on the painful area, such as the foot in the case of gout, or on the buttock, back or leg in patients with low back pain. Often, however, the cautery was applied to specifically prescribed sites distant from the painful area. The procedure, of course, produced pain and subsequent blistering of the area that was touched by the cautery, but reportedly also led to the relief of chronic pain (Elliott, 1962). The same effect was achieved by two other procedures: rubbing blistering fluids into the skin, or applying a cone ofmoxa (made from the leaves of the mugwort plant) to a site on the body, setting the tip of the cone aflame, and allowing it to burn slowly until it approached or reached the skin. Again, the procedure produced pain and, while used for all kinds of diseases, was often prescribed specifically for painful conditions (Brockbank, 1954; Elliott, 1962). There are countless other methods that resemble the ones just described, and which are usually labelled as 'counter-irritation'. It is evident that the one factor common to all ofthem is that they produce pain to abolish pain. The pain was usually brief and moderate but its effect was to relieve or abolish a much more severe, chronic pain. These methods, of course, did not always work, but they obviously worked well enough to have survived as procedures of folk medicine throughout the world for thousands of years. Do these procedures work better than a placebo? There are no experimental studies, but the evidence from studies of acupuncture suggests that they do.