nt,ral characteristics of sympathetic actiitity in human skin nerues. Acta physiol. scand. 1972. 8.1.. 164-176. Synchronized bursts of efferent sympathetic impulses, appearing either spontaneously or triggered by various peripheral stimuli, were recorded with niicroelectrodes inserted percutaneously into skin nerve fascicles in alert, adult subjects. The signals were abolished by sympathetic ganglion blocking agents and by Lidocaine nerve blocks proximal to the recording site. Many of the sympathetic discharges were succeeded by skin resistance changes and plethysmographic vasoconstrictor responses within the innervation zone of the fascicle impaled. The sympathetic activity was not pulse synchronous as in muscle nerves and the spontaneous sympathetic volleys occurred largely indepmdently of spontaneous blood pressure variations, indicating a relative lack of baroreflex control of the vasoconstrictor outflow to the skin. A loose coupling was observed, however. between the resting respiratory rhl-thm and the spontaneous sympathetic bursts in the skin nerves.Sympathetic activity in human muscle nerves. appearing as spontaneous bursts of impulses grouped in the pulse rhythm, was first described by Hagbarth and Vallbo (1968). Their findings were recently confirmed by Delius c T t al. (1971 a ) . who noted in addition an inverse relationship between the strmgth of the pulsative sympathetic outflow in the muscle nenes and spontaneous blood pressure fluctuations. According to Hagbarth and \.'allbo a similar type of activity is not to be found in skin nerve fascicles. During an extended search for sympathetic signals in such fascicles, however, u.e now and then observed spontaneously occurring bursts of impulses which appeared in seemingly random fashion without any obvious relation to pulse rhythms or spontaneous blood pressure fluctuations. A systematic study of these neural phenomena in human skin nerve fascicles has now been undertaken. The results to b c a presented lead to the conclusion that the signals derive from groups of postganglionic sympathetic fibres which in awake relaxed subjects exhibit a fluctuating resting discharge of variable strength and which are easily activated by sudden arousal stimuli. A11 of the triggered and many of the spontaneously occurring sympa-I61
We have tested the effects of cutaneous application of noradrenaline in 35 patients presenting with neuropathic pain. Depending on the outcome of sympatholytic interventions the patients were considered to have sympathetically maintained pain (SMP; n = 25) or sympathetically independent pain (SIP; n = 10). Iontophoretic application or cutaneous injection of noradrenaline into symptomatic skin aggravated pain and mechanical or thermal hyperalgesia in 7/25 SMP patients. Results from differential nerve blocks suggested that noradrenaline-induced ongoing pain and heat hyperalgesia were signalled by unmyelinated afferents, while touch-evoked pain and cold hyperalgesia were signalled by myelinated afferents. In none of the remaining 18/25 SMP patients, 10 SIP patients or 18 normal subjects did application of noradrenaline result in any appreciable increase of pain. A follow-up of 12 patients (initially 9 SMP, 3 SIP) after 12-16 years showed that one individual (previously SMP) was healthy, while 3 patients still suffered from SMP and 8 from SIP. Of the 5 SMP patients who had noradrenaline-induced pain at the initial examination, only 1 SMP patient still responded to noradrenaline with pain and hyperalgesia. Three other patients had changed to SIP and 1 individual was healthy. None of these 4 and none of the 7 initially noradrenaline-unresponsive patients experienced pain to the noradrenaline challenge at follow-up. Thus, cutaneous noradrenaline application can aggravate the pain in some, but not all SMP patients. THe abnormal noradrenaline reaction can change over time as can the pain relieving effects of sympatholytic therapy.
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