Microneurographical approach to physiological mechanism of itching

Microneurographical approach to physiological mechanism of itching

WS5-D-1-05 MICRONEUROGRAPHICAL APPROACH TO PHYSIOLOGICAL MECHANISM OF ITCHING M. Kunimoto Dept. of Neurol., Yokohama Rosai Hospital, Yokohama, Japan I...

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WS5-D-1-05 MICRONEUROGRAPHICAL APPROACH TO PHYSIOLOGICAL MECHANISM OF ITCHING M. Kunimoto Dept. of Neurol., Yokohama Rosai Hospital, Yokohama, Japan Introduction : Itching has been considered to be conducted by C-fibers. There were important works in the past by Dr. Torebjoerk and Dr. Handwerker. However, there are still some unresolved problems in the mechanism of itching. One problem is that, if itching is conducted by C-fibers, can micro-stimulation to C-fibers evoke itching by electrical impulse sequences? Another problem is whether the impulse amount of C-fiber discharge evoked by chemical stimuli may be correlated to the itching sensation. In order to solve these two questions, following experiments were planned. Subjects and Methods : 48 healthy male(I) and females(47)(age from 20 to 33 years old). Insert a tungsten micro-electrnde to a peroneal nerve at the lateral surface of knee directly through skin without any anesthetics. Proper site for C-fibers was searched by confirming the conduction velocity of around 1 m/sec. Electrical micro-stimulation was given to the C-fibers through the micrtyelectrnde. Stimulation pulse was 0.2 msec duration and the strength varied from sub- to supra-threshold. The subject was asked to answer the sensation evoked by it. Stimulation patterns were 1,2,5,10,20,40,80 Hz for 4 sec or 30 sec. Different stimulation frequencies were also combined together like 1 and 5 Hz each for 30 sec consecutively, Another plan was histamine application to the receptive field of the C-fibers. It was injected into epidermis (0.01-0.02%, 0.020.03 ml) or by electrophoretic technique(0.02%, 0.5-1.0mA). Evoked impulses were counted by pulse counter and the discharge rate was compared to the subjective itching sensation. Results : The mean value of threshold of electrical stimulation to C-fibers was 0.33mV. Itching was never evoked by electrical microstimulation with any frequency and strength. Itching sensation was well correlated to the impulse amount of C-fiber discharge stimulated with histamine application. Conclusions : Our data supported the past result that C-fiber conducts itching. However, direct electrical stimulation to the C-fiber axon did not evoke itching. This means that some environmental conditions to the C-fiber terminal in the epidermis(e.g.: amount of histamine, blood flow, skin temperature and so on) is quite important to generate the itching sensation.

WS5-D-1-06 SYMPATHETIC NERVOUS ACTIVITY IN PATIENTS WITH CHRONIC RENAL FAILURE E-Gotoh I, T.Matsukawa 2, S.Sumita I, K.Ashino I, N.Takagi I, T.Mano 2, and M.Ishii I. i) Second Dept of Internal Medicine, Yokohama City University, 2) Department of Autonomic and Behavioral Neurosciences, Research Institute of Environmental Medicine, Nagoya University. Objective: The pathophysiological role of sympathetic nervous activity in hypertension associated with chronic renal failure (CRF) and effects of hemodialysis on the activity were investigated by measuring muscle sympathetic nerve activity (MSNA). Design and Methods: Fourteen patients with CRF (age;50.3 ± 4.2 ( S E ) years, serum creatinine {Cr);8.6 ± 1.2 mg/dl) and seven normal controls (51.5 ± 3 )were used as the subjects of this study. All patients with CRF had mild to moderate hypertension {mean blood pressure (MBP);II8 ± 4 mmHg), eight patients received furosemide 40-120 mg/day and ant±hypertensive medications except furosemide were d i s c o n t i n u e d three days before predialysis study. Hemodialysis was performed after the construction of vascular access in six of these patients with CRF. Four weeks after the start of hemodialysis, c a r d i o v a s c u l a r stability was m a i n t a i n e d and p o s t d i a l y s i s study was conducted on the interdialysis day. After a 30-minute rest in the prone position, we measured the rate of postganglionic sympathetic-nerve discharge to the blood vessels in skeletal muscle by m e a n s of m i c r o e l e c t r o d e s i n s e r t e d into the tibial nerve. B l o o d pressure, heart rate, electrocardiogram, respiration, and neurogram were continuously monitored for 30 minutes in both the pre- and postdialysis studies. MSNA was assessed by the number of bursts per minute obtained from mean voltage of the neurogram. Results: In the p r e d i a l y s i s study, MBP and serum Cr were s i g n i f i c a n t l y (p<0.05) higher in patients with CRF than those in normal controls. MSNA were markedly increased (52 ± 5 bursts/min) in the patients with CRF regardless of receiving furosemide, compared with normal controls (26 ± 3). On the other hand, MSNA reduced significantly after hemodialysis in the patients (38 ± 4 ). Significant decreases in MBP and serum Cr were also shown after hemodialysis. Conclusions: Sympathetic nervous activity is increased in patients with chronic renal failure, and the increase is reduced with hemodialysis. Since the changes in sympathetic activity are closely related to those in b l o o d pressure, the sympathetic activity may participate in the regulation of blood pressure in the patients with end stage renal disease.

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