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Peripheral Nerve Sensations evoked by intraneural microstimulation of single mechanoreceptor unitsinnervating the human hand
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Note: A companion paper appears in the same journal issue: Haupt, P., Janig, W. and Kdhler, W., Response pattern of visceral afferent fibers, supplying the colon, upon chemical and mechanical stimuli. Pfhugers Arch. ges. Physiol., 398 (1983) 41-47. Prior collateral sprouting enhances axonal regeneration. - J. Sparrow and 3. Grafstein, Brain Res., 269 (1983) 133-136. Nerve regeneration after injury proceeds faster than normal if it follows a prior ‘conditioning’ lesion. In this paper it is shown that a ‘conditioning’ lesion that induces collateral sprouting of the test nerve, but does not injure it directly, also accelerates regeneration. In rats, the L, and L, spinal nerves were ligated and cut (the ‘conditioning’ lesion). This induces collateral sprouting of L, fibers in the periphery. Seven days later the ipsilateral sciatic nerve, which carries the L, fibers, was crushed. To measure the rate of regeneration of the crushed nerve fibers, [3H]proline was injected into the ventral horn 7 days after crushing, and the accumulation of label transported to the leading edge of the outgrowing fibers was determined by liquid scintillation counting. The conditioning lesion did not affect the most rapidly outgrowing fibers represented by the leading edge of transported label. In contrast, the advance of the bulk of outgrowing fibers, represented by the peak of transported label, was accelerated by 39%. The preferred explanation is that because of collateral sprouting induced by the ‘con~tioIling’ lesion, the metabolism of affected neurons is already primed for fiber growth at the time the nerve is crushed. Sensations evoked by intraneural microstimulation of single mechanoreceptor units innervating the human hand. - J. Ochoa and E. Torebjork, J. Physiol. (Lond.), 342 (1983) 633-654. Tungsten microelectrodes inserted into fascicles of the median and ulnar nerves of alert humans were used to record from, and to stimulate, single myelinated sensory axons. Evidence that single fibers were activated was 3-fold. First, low level stimulation evoked an ‘elementary sensation,’ the location, size and quality of which corresponded to the receptive field (RF) of the most prominent action potential that could be recorded from the electrode at that position. Second, in some experiments, a recording microelectrode was inserted into the same nerve fascicle that was microstimulated. As the stimulating current was gradually increased, individual action potentials were recruited on the recording electrode, and each was associated with a localized ‘elementary sensation.’ Furthermore, these referred sensations, and the shape of the electrically evoked action potential associated with each, corresponded to the cutaneous RF and the shape of the action potential evoked by cutaneous mechanical stimulation. Third, prolonged tetanic microstimulation increased the excitability of individual fibers whose RF had been characterized by recording. Electrical stimulation of Pacinian corpuscle (PC) afferents evoked a sensation of vibration or tickle the frequency of which depended on the stimulation frequency. Stimulation of fibers with rapidly adapting (RA) RFs evoked a sensation of
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intermittent tapping. Progressively increasing the stimulation frequency increased the rate of tapping and then evoked flutter and then vibration of gradually increasing intensity. Stimulation of type I slow adapting (SAI) fibers evoked a sensation of pressure which increased in force with increased stimulation frequency. Stimulation of type II SA fibers (SAII) did not evoke any recognizable sensation.
PSYCHIATRY Psychiatry and the cervical sprain syndrome, - H. Merskey (Dept. of Education and Research, London Psychiatric Hospital, P.O. Box 2532, Terminal A, London, Ont, N6A 4H1, Canada), Canad. med. Ass. J., 130 (1984) 1119-1121. This editorial discusses the relationship between injury, compensation, the whiplash (cervical sprain) syndrome and also the post-concussional syndrome. It is noted that expert evidence tends to favour the side which calls it. Nevertheless, follow-up studies have repeatedly shown that many patients fail to get better from compensable symptoms even after the legal proceedings are finished. An accumulation of other evidence is also listed to suggest that there is a significant organic basis both for the cervical sprain syndrome and the post-concussional syndrome after minor head injury. Psychiatric changes which develop are often secondary to pain and disability. The effects of dietary tryptophan on chronic maxillofacial pain and experimental pain tolerance. - S. Seltzer, D. Dewart, R.L. Pollack and E. Jackson (Ma~llofacial Pain Control Center, School of Dentistry, Temple University Hospital, 3223 N. Broad Street, Philadelphia, PA 19140, U.S.A.), J. psychiat. Res., 17 (1982/83) 181-186. This study investigated the effects of daily administration of 3 g of tryptophan in conjunction with a high carbohydrate, low fat, low protein diet on chronic maxillofacial pain, experimental pain thresholds, and anxiety and depression. In a double-blind study, 30 chronic pain patients were randomly assigned to a tryptophan or placebo group. At the initial appointment and 4 weeks later, the patients’ subjective ratings of their pain were recorded, electrical tooth pulp stimulation was used to measure pain thresholds, and psychological tests of depression and anxiety were administered. Over the 4 weeks of the study, there was a greater reduction in reported clinical pain and a greater increase in pain tolerance threshold in the tryptophan group than in the placebo group. The group did not differ in anxiety and depression - for all subjects there was lowered depression and anxiety over the 4 weeks of study. Sleepreiated myoclonus in rheumatic pain mutation disorder (fibrositis syndrome) and in excessive daytime somnolence. - H. Moldofsky, C. Tullis, F.A. Lue, G. Quance and J. Davidson (Edith Cave11 Wing, Toronto Western Hospital, 399 Bathurst Street, Toronto M5T 2S8, Canada), Psychosom. Med., 46 (1984) 145-151. A new syndrome, rheumatic pain modulation disorder (RPMD) (‘fibrositis syndrome’) with sleep-related myoclonus (involuntary periodic leg movements) is de-
Note: A companion paper appears in the same journal issue: Haupt, P., Janig, W. and Kdhler, W., Response pattern of visceral afferent fibers, supplying the colon, upon chemical and mechanical stimuli. Pfhugers Arch. ges. Physiol., 398 (1983) 41-47. Prior collateral sprouting enhances axonal regeneration. - J. Sparrow and 3. Grafstein, Brain Res., 269 (1983) 133-136. Nerve regeneration after injury proceeds faster than normal if it follows a prior ‘conditioning’ lesion. In this paper it is shown that a ‘conditioning’ lesion that induces collateral sprouting of the test nerve, but does not injure it directly, also accelerates regeneration. In rats, the L, and L, spinal nerves were ligated and cut (the ‘conditioning’ lesion). This induces collateral sprouting of L, fibers in the periphery. Seven days later the ipsilateral sciatic nerve, which carries the L, fibers, was crushed. To measure the rate of regeneration of the crushed nerve fibers, [3H]proline was injected into the ventral horn 7 days after crushing, and the accumulation of label transported to the leading edge of the outgrowing fibers was determined by liquid scintillation counting. The conditioning lesion did not affect the most rapidly outgrowing fibers represented by the leading edge of transported label. In contrast, the advance of the bulk of outgrowing fibers, represented by the peak of transported label, was accelerated by 39%. The preferred explanation is that because of collateral sprouting induced by the ‘con~tioIling’ lesion, the metabolism of affected neurons is already primed for fiber growth at the time the nerve is crushed. Sensations evoked by intraneural microstimulation of single mechanoreceptor units innervating the human hand. - J. Ochoa and E. Torebjork, J. Physiol. (Lond.), 342 (1983) 633-654. Tungsten microelectrodes inserted into fascicles of the median and ulnar nerves of alert humans were used to record from, and to stimulate, single myelinated sensory axons. Evidence that single fibers were activated was 3-fold. First, low level stimulation evoked an ‘elementary sensation,’ the location, size and quality of which corresponded to the receptive field (RF) of the most prominent action potential that could be recorded from the electrode at that position. Second, in some experiments, a recording microelectrode was inserted into the same nerve fascicle that was microstimulated. As the stimulating current was gradually increased, individual action potentials were recruited on the recording electrode, and each was associated with a localized ‘elementary sensation.’ Furthermore, these referred sensations, and the shape of the electrically evoked action potential associated with each, corresponded to the cutaneous RF and the shape of the action potential evoked by cutaneous mechanical stimulation. Third, prolonged tetanic microstimulation increased the excitability of individual fibers whose RF had been characterized by recording. Electrical stimulation of Pacinian corpuscle (PC) afferents evoked a sensation of vibration or tickle the frequency of which depended on the stimulation frequency. Stimulation of fibers with rapidly adapting (RA) RFs evoked a sensation of
202
intermittent tapping. Progressively increasing the stimulation frequency increased the rate of tapping and then evoked flutter and then vibration of gradually increasing intensity. Stimulation of type I slow adapting (SAI) fibers evoked a sensation of pressure which increased in force with increased stimulation frequency. Stimulation of type II SA fibers (SAII) did not evoke any recognizable sensation.
PSYCHIATRY Psychiatry and the cervical sprain syndrome, - H. Merskey (Dept. of Education and Research, London Psychiatric Hospital, P.O. Box 2532, Terminal A, London, Ont, N6A 4H1, Canada), Canad. med. Ass. J., 130 (1984) 1119-1121. This editorial discusses the relationship between injury, compensation, the whiplash (cervical sprain) syndrome and also the post-concussional syndrome. It is noted that expert evidence tends to favour the side which calls it. Nevertheless, follow-up studies have repeatedly shown that many patients fail to get better from compensable symptoms even after the legal proceedings are finished. An accumulation of other evidence is also listed to suggest that there is a significant organic basis both for the cervical sprain syndrome and the post-concussional syndrome after minor head injury. Psychiatric changes which develop are often secondary to pain and disability. The effects of dietary tryptophan on chronic maxillofacial pain and experimental pain tolerance. - S. Seltzer, D. Dewart, R.L. Pollack and E. Jackson (Ma~llofacial Pain Control Center, School of Dentistry, Temple University Hospital, 3223 N. Broad Street, Philadelphia, PA 19140, U.S.A.), J. psychiat. Res., 17 (1982/83) 181-186. This study investigated the effects of daily administration of 3 g of tryptophan in conjunction with a high carbohydrate, low fat, low protein diet on chronic maxillofacial pain, experimental pain thresholds, and anxiety and depression. In a double-blind study, 30 chronic pain patients were randomly assigned to a tryptophan or placebo group. At the initial appointment and 4 weeks later, the patients’ subjective ratings of their pain were recorded, electrical tooth pulp stimulation was used to measure pain thresholds, and psychological tests of depression and anxiety were administered. Over the 4 weeks of the study, there was a greater reduction in reported clinical pain and a greater increase in pain tolerance threshold in the tryptophan group than in the placebo group. The group did not differ in anxiety and depression - for all subjects there was lowered depression and anxiety over the 4 weeks of study. Sleepreiated myoclonus in rheumatic pain mutation disorder (fibrositis syndrome) and in excessive daytime somnolence. - H. Moldofsky, C. Tullis, F.A. Lue, G. Quance and J. Davidson (Edith Cave11 Wing, Toronto Western Hospital, 399 Bathurst Street, Toronto M5T 2S8, Canada), Psychosom. Med., 46 (1984) 145-151. A new syndrome, rheumatic pain modulation disorder (RPMD) (‘fibrositis syndrome’) with sleep-related myoclonus (involuntary periodic leg movements) is de-