Neurology Reversible inactivation of raphe magnus neurons: effects on nociceptive threshold and morphine-induced analgesia

an image intensifier and 2 ml of air was injected through each to confirm that the tip lay in the correct fascial plain; 4 ml 7.5% aqueous phenol were injected through each needle. It is often necessary to repeat it before a fully successful result is obtained. The possible reasons for this success are discussed. Firstly, the original pain could have been a neuralgia caused by trauma or infection and subsequent surgery was the result of misdiagnosis. Secondly, damage to nervous tissue could have occurred during initial or subsequent necessary surgery. Thirdly, sympathetic lysis could also successfully relieve the pain in these circumstances. And also the utilities of diagnosis block are discussed.

ANESTHESIOLOGY Failure of transcutaneous electrical stimulation to alleviate experimental tourniquet pain. - R.M. Rosenblatt and A. Hetherington, Anesth. Analg. Curr. Res., 60 (1981) 720-722 The authors evaluated the effectiveness of transcutaneous electrical nerve stimulation (TENS) in alleviating ischemic pain produced experimentally during a submaximal-effort tourniquet test. Ten subjects were studied on 3 separate occasions. Cutaneous electrodes were placed proximal to the tourniquet and TENS was begun before ‘exsanguination’ of the arm by temporary tight application of an elastic bandage. The subjects then exercised the ischemic arm by repetitively squeezing a hand-held dynamometer. The time from inflation of the tourniquet to the onset of intolerable pain was noted; the subjects were also asked to indicate the pain intensity on a visual analog scale. TENS did not prolong the tolerated duration of ischemia or cause any reduction in the subjective intensity of pain. Effects of local anesthetic infiltration on brain potentials evoked by painful dental stimulation. - J.D. Gehrig, Y.H. Colpitts and C.R. Chapman, Anesth. Analg. Curr. Res., 60 (1981) 7799782 Painful electrical stimulation was applied to the pulp of healthy unfilled lateral incisor teeth. In 10 volunteers both the cerebral evoked potential wave form and the subjective pain were eliminated by infiltrating lidocaine 2% over the apex of the tooth. Saline infiltration under identical conditions in 10 other volunteers had no effect. The results support the claim that cerebral evoked potentials recorded during painful dental stimulation are a reliable physiologic correlate of human pain.

NEUROLOGY Reversible inactivation of raphe magnus neurons: effects on nociceptive threshold and morphine-induced analgesia. - H.K. Proudfit, Brain Res., 201 (1980) 459-464 Electrolytic lesions made in raphe magnus of the rat caused a decrease in nociceptive threshold on the tail-flick test but no alteration in the capacity of morphine to produce analgesia. The same result was obtained with injecting tetra-

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Caine into the nucleus. ‘These data support the suggestion that raphe magnus neurons exert a tonic inhibitory influence on the transmission of nociceptive information, that they do not support the participation of these neurons in the expression of opiate-induced analgesia.’ Specific sensations evoked by activity in single identified sensory units in man. - H.E. Torebjork and J.L. Ochoa, Acta physiol. stand., 110 (1980) 445-447 Single nerve fibers of human peripheral nerves were both stimulated and recorded from. The subject refers the sensation to the field of the stimulated nerve fiber and that skin area was then stimulated. When this field was then stimulated by natural stimuli, usually only the nerve fiber that ‘was in focus for the electrode’ produced action potentials that could be recorded. The nerve fiber could also be identified by ‘physiolo~cal marking.’ It was found that ‘prolonged, ~~-frequency intraneural microstimulation rendered that single myelinated sensory fiber hyperexcitable. Upon intraneural recording this fiber will either discharge spontaneously or will generate a burst in response to a triggering pulse.’ Trains of impulses in single rapidly adapting units in the glabrous skin of the hand usually reached consciousness, whereas activity in single slowly adapting II units practically never did. The sensations evoked are reported. Human nociceptive reactions: effects of spatial summation of afferent input from relatively large diameter fibers. - J.C. Willer, F. Boureau and D. Albe-Fessard, Brain Res., 201 (1980) 465-470 In man, the peroneal and sural nerves were stimulated to cause an ipsilateral spinal flexor reflex and pain; the afferent nerve fibers were cutaneous AP fibers conducting at 55 m/set. Spatial summation was obtained by stimulating the two nerves simultaneously, there being no increase in pain nor reflex activity. But spatial and temporal summation together produced either facilitation or inhibition. The changes in amplitude of the flexor reflex correlated with the pain sensation. Both the facilitation and inhibition were maximal with 60-160 msec between the stimuli to the two nerves; the effect then decreased so that there were no effects with intervals of 230-300 msec. From the neurogram it was seen that AS fibers were not excited, all afferent effects being due to the Aevb components. To obtain facilitation, it was necessary to evoke at least 80% of the maximal amplitude of the first peak of the compound action potential of the conditioning stimulus and to obtain inhibition 50% of the first peak; the test stimulus had to be adequate to produce pain and the flexor reflex.

HEADACHE Local anesthetic blocks of the second cervical ganglion: a technique with application in occipital headache. - N. Bogduk, Cephalalgia, 1 (198 1) 41-50 By dissections of 5 human adult corpses, the author has demonstrated that the C2 spinal ganglion bears a constant relationship to the dorsal aspect of the lateral