A-delta fibers

Thermal nociceptors and mechanical nociceptors are associated with A-delta fibers. These are small myelinated fibers that transmit impulses at a rate of 5 to 30 m/sec. Polymodal nociceptors are associated with C fibers. These are small unmyelinated fibers that transmit impulses at a rate generally less than 1.0 m/sec (range of 0.5 to 2.0 m/sec). 

Rabben T. Effects of the NMD A receptor antagonist ketamine in electrically induced A delta-fiber pain. Methods Find Exp Clin Pharmacol 2000 22(3) 185-9. 

Opioid-induced analgesia is produced through the action of opioid receptors on presynaptic terminals of the C-fibers and A-delta fibers. These fibers, which transmit nociceptive messages, are inhibited by the indirect effects of opioids, which in turn reduce the release of neurotransmitters such as substance P, CGRP, and glutamate. This effect occurs in the peripheral nervous system as well as at the primary afferent terminals in the spinal cord. 

AD clinical trials, 1257 Addiction, 1207, 1375 Additive, 3983, 3984 A-delta fibers, 1371 Adenocarcinoma, 2421 Adenosine A2A receptor, 2682, 4115 Adenosine monophosphate-activated protein kinase (AMPK), 1304 Adenosine receptor, 946 Adenosine triphosphate (ATP), 3706 Adenylation protein, 51 Adenylyl cyclase, 3327 Adhatoda, 802 Adhatoda vasica, 4095... 

Acute pain is an adaptive physiological response that follows traumatic injuries and surgery. It has two primary components. (1) The sensory discriminative component describes the location and quality of the stimulus. It is characterized by rapid response, short latency to peak response, and short duration of action. Noxious information is conveyed by rapidly conducting A-delta fibers, and monosynaptic transmission to the sensory cortex [10,12]. This component rapidly identifies the site of injury or potential injury, and initiates reflexive/cognitive withdrawal responses. (2) The affective-motivational component underlies suffering and the emotional components of pain and is responsible for learned avoidance and other adaptative and non-adaptative behavioral responses. 

The purpose of PN is to act as an early warning system, with a sharp initial pain from the A-delta fibers followed by a dull pain from the slower C fibers. This mechanism prevents tissue damage by alerting the body to the presence of an intense, potentially damaging stimulus in the enviromnent The resulting pain protects tissue from being further damaged... 

Certain aspects of neural anatomy and ultrastructure favor LA blockade of noxious impulses [2-5]. To reduce conduction safely in sensory and motor fibers, at least three myelin inter-nodes must be blocked. This rule of three favors blockade of thin unmyelinated fibers and also A-delta fibers which have small inter-nodal distances. Larger A-alpha and A-beta fibers are more resistant to blockade because of their size and large distance between nodes of Ranvier (Figure 64.3). Unmyelinated C fibers are easiest to block since LAs can impede Na+ conductance and action potential propagation at any single site along the course of the nerve fiber. 

Smaller A-delta fibers have relatively small internodal distances, and three or more nodes can be more easily blocked (X). Unmyelinated C fibers do not employ salutatory conduction and are particularly vulnerable to local anesthetic blockade. Propagation of action potentials can be prevented by local anesthetic blockade at any point along the course of the nerve fiber. 

In mixed sensory nerves, noxious C fibers and A-delta fibers are generally localized to the outer regions of the nerve (Mantle), while greater numbers of larger motor and sensory fibers are localized in the center of the nerve (Core). Because of a concentration gradient from the site of local anesthetic deposition to the center of the nerve, the mantle fibers are first to be blocked and last to recover. 

The BioView sensor (DELTA Light Optics, Denmark) was developed especially for industrial applications. It is capable of completely automatic optical measurement for monitoring and control of different bioprocesses. The instrument is conceived to withstand harsh industrial environments (e.g., high temperature, moisture) and electromagnetic interference. For data transfer a single-fiber asynchronous modem is used, which allows a distance between the computer and spectrometer of up to several hundred meters. 

Another important reason for preferential blockade of sensory fibers follows directly from the state- and use-dependent mechanism of action of local anesthetics. Blockade by these drugs is more marked at higher frequencies of depolarization. Sensory (pain) fibers have a high firing rate and a relatively long action potential duration. Motor fibers fire at a slower rate and have a shorter action potential duration. Type A delta and C fibers are smaller-diameter fibers that participate in high-frequency pain transmission. Therefore, these fibers are blocked earlier and with lower concentrations of local anesthetics than are the large A alpha fibers. 

Tanelian DL, Maciver MB 1991 Analgesic concentrations of lidocaine suppress the tonic A-delta and C fiber discharges produced by acute injury. Anesthesiology 74 934-936... 

When the crystalloids and most of the globular proteins and enzymes are removed from the skeletal muscle fiber by extraction with glycerol-water, the tension developed in ATP-contraction remains as high as before, but the maximal shortening is now comparable to that of a muscle fiber in the delta state, and the velocity of shortening is even less. And finally, the thread model of purified, oriented actomyosin develops only a low tension of a few hundred grams per square centimeter, which is of the same order as that for some smooth muscles. 

Hyperalgesia is defined by the International Association for the Study of Pain (lASP) as an increased response to a stimulus which is normally painful . Primary hyperalgesia or peripheral sensitization reflects the activation and sensitization of nociceptive A delta and polymodal C-fiber terminal endings within the injured area. Secondary hyperalgesia, or central sensitization, involves spinal neuroplasticity and facilitation... 

The vegetable fibers were subjected to two different fiber extraction processes the alkaline treatment process, in which broom branches were heated to 40°C for 20 min in an aqueous solution of 4% (wt) sodium hydroxide. The fibers obtained were washed in water and dried, and the steam-explosion processes was applied whereby broom branches were steam heated at 190°C under a steam pressure of about 20 bar for 2 min using a Delta Lab EC 300. 

Bergersen, L., Waerhaug, O., Helm, J. et al. A novel postsyn-aptic density protein the monocarboxylate transporter MCT2 is co-localized with delta-glutamate receptors in postsynaptic densities of parallel fiber-Purkinje cell synapses. Exp. Brain Res. 136 523-34,2001. 

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