The Gate Theory of Pain

The Gate Theory of Pain

1. The gate theory of pain Ade Wijaya, MD – May 2019

2. Introduction The Gate Theory of Pain, published by Ronald Melzack and Patrick Wall in   Science   in 1965 A mechanism for coding the nociceptive component of cutaneous sensory input Mendell LM. Constructing and deconstructing the gate theory of pain. PAIN®. 2014 Feb 1;155(2):210-6.

3. Inhibition of cutaneous input to the spinal cord L arge fibers normally inhibit the effects of small fibers. The balance between the large and small fiber input was a major factor in determining the painfulness of a stimulus . L ong lasting presynaptic inhibition of input to motor neurons elicited by volleys in large afferent fibers Noordenbos W. Pain. Elsevier, Amsterdam; 1959. Frank K, Fuortes MGF. Presynaptic and postsynaptic inhibition of monosynaptic reflexes. Fed. Proc. 1957;16:3940.

4. Cells responsible for generating presynaptic inhibition of cutaneous sensory fibers An important component of the Gate Hypothesis was the suggestion by Wall that cells of the substantia gelatinosa (SG) were responsible for the presynaptic effects Szentagothai J. Neuronal and synaptic arrangement in the substantia gelatinosa rolandi. J Comp Neurol. 1964;122:219–239. Wall PD. The origin of a spinal-cord slow potential. J Physiol. 1962;164:508–526 . Wall PD. Presynaptic Control of Impulses at The First Central Synapse in The Cutaneous Pathway. Prog Brain Res. 1964;12:92–118

5. The Gate Theory of Pain model Melzack R, Wall PD. Pain mechanisms: a new theory. Science. 1965;150:971–979.

6. Tests of closing and opening the gate H igh frequency stimulation of the large fibers in that nerve (Transcutaneous Nerve Electrical Stimulation- TENS) produced tingling referred to the distribution of that nerve and relief of the pain for the duration of the stimulation, and for 30 min after cessation of the stimulation Reappearance of pain was attributed to gradual reopening the gate by ongoing small fiber activity which was less intense in cases where peripheral nerves had been damaged and therefore took longer to be re-established Wall PD, Sweet WH. Temporary abolition of pain in man. Science. 1967;155:108–109.

7. Windup phenomenon R epetitive discharge of spinal neurons exhibited a phenomenon called windup It became more prolonged in response to each successive C-fiber stimulus if it occurred within 4 seconds of the preceding one  due to the release of peptides by certain small diameter afferents which prolongs the synaptic potential thus allowing temporal summation over a period of seconds T his depolarization activates NMDA receptors whose blockade abolishes windup without eliminating the response to C-fiber stimulation Windup is an early event in a process leading to central sensitization Kumazawa T, Perl ER. Excitation of marginal and substantia gelatinosa neurons in the primate spinal cord: indications of their place in dorsal horn functional organization. J Comp Neurol. 1978;177:417–434 Mendell LM. Physiological properties of unmyelinated projection to the spinal cord. Exp. Neurol. 1966;16:316–324 Mendell LM, Wall PD. Response of single dorsal cord cells to peripheral cutaneous unmyelinated fibers. Nature. 1965;206:97–99. Woolf CJ. Windup and central sensitization are not equivalent. Pain. 1996;66:105–108.

8. Nociceptors Receptors activated by stimuli that were potentially damaging to the tissue in which they were embedded Nociceptors were later found to have important physiological properties such as sensitization, and to project into the superficial dorsal horn where they synapse upon a population of cells called marginal cells that respond exclusively to noxious stimuli These cells in the marginal zone were found to contribute to the spinothalamic tract which gave them access to forebrain structures and thus presumably to conscious sensation . A population of nociceptors was also observed to be peptidergic a nd thus able to promote Windup Mendell LM. Constructing and deconstructing the gate theory of pain. PAIN®. 2014 Feb 1;155(2):210-6.

9. Summary The Gate Theory of Pain was formulated using available physiological observations to explain certain behavioral and psychophysical observations related to pain A mechanism for coding the nociceptive component of cutaneous sensory input