Journal of the Neurological Sciences, 1977, 33:353 374 ~) Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
353
A C R Y L A M I D E A U T O N O M I C N E U R O P A T H Y 1N T H E CAT Part I. Neurophysiological and Histological Studies
ELIZABETH J. POST and J. G. McLEOD Department of Medicine, University of Sydney, N.S.W. 2006 (Australia)
(Received 1 March, 1977)
SUMMARY Neurophysiological and histological studies have been performed on the sympathetic nervous system of cats poisoned with acrylamide. The neurophysiological studies indicate that the large and small diameter myelinated fibres are damaged in the sympathetic nervous system in association with damage to the fibres of the peripheral nervous system. Quantative histological studies confirmed and extended the neurophysiological findings; there was a loss of myelinated fibres of all diameters from the sympathetic, parasympathetic and peripheral nervous system.
INTRODUCTION Disturbances of autonomic function occur in association with peripheral neuropathy, and are most commonly recognised clinically in diabetic neuropathy, (Rundles 1945; Sharpey-Schafer and Taylor 1960; Low, Walsh, Huang and McLeod 1975) and in the Guillain-Barr6 syndrome (Parker and Adams 1947; Matsuyama and H a y m a k e r 1967). However, the relationship between the disturbances of physiological function and the pathological changes in the autonomic nervous system has been largely overlooked. Since the physiological studies which may be performed in man in these conditions are of necessity limited, and often the conclusions to be drawn from them about the nature and sites of the abnormalities in the autonomic nervous system are imprecise, an autonomic disorder associated with a peripheral neuropathy has been produced experimentally in cats in order to investigate the mechanism of the physiological abnormalities which result.
Elizabeth J. Post was supported by a Commonwealth Post-Graduate Student Award. The work was also supported by grants from the Postgraduate Medical Foundation, University of Sydney, the National Heart Foundation and the National Health and Medical Research Council of Australia.
354 Acrylamide, a plastic monomer, is known to damage peripheral myelinated nerve fibres and to cause a dying-back type of degeneration (Fullerton and Barnes 1966: Prineas 1969; Hopkins 1970; Hopkins and Gilliatt 1971 ; Schaumburg, Wi~niewski and Spencer 1974). There is an extensive literature on the generalised acrylamide peripheral neuropathy and although brief mention of autonomic dysfunction has been made in some publications (Fullerton and Barnes 1966; Auld and Bedwell 1967; Leswing and Ribelin 1969; Prineas 1969; Hopkins 1970), little attention has been focused on the autonomic disturbances accompanying acrylamide peripheral neuropathy. In a previous study, Hopkins and Lambert (1972) investigated conduction in the unmyelinated fibres of the cervical sympathetic trunk of rats poisoned with acrylamide. In the present paper, the results of electrophysiological and histological studies on the sympathetic nervous system of cats poisoned with acrylamide are presented, and in the subsequent paper the effects of acrylamide on vasomotor control are reported (Post and McLeod 1977). METHODS
Animals Experiments were carried out on adult cats of weight 2-3 kg. Seventeen animals were given, with their food, 15 mg/kg acrylamide ( > 98 % pure) dissolved in 0.9% sodium chloride daily for periods of up to 16 weeks. The animals in the present study were described as mildly poisoned when they displayed weakness of the hind limbs only and severely poisoned where they were unable to walk because of severe paralysis of the fore- and hind-limbs. The severely poisoned cats also suffered from weight loss and occasionally mild diarrhoea in the final days of intoxication. The duration of poisoning was 4-6 weeks in mildly poisoned animals, and 12-16 weeks in the severely poisoned. Motor conduction studies were performed in 7 mildly acrylamide poisoned cats, and histological studies were subsequently carried out on 6 of them. Motor conduction studies were carried out in 10 severely acrylamide poisoned cats; 5 of these animals were also used for neurophysiological studies on the sympathetic nervous system and the remaining 5 were used for histological studies. Twenty-three control cats fed on a normal diet and housed in the same conditions as the poisoned animals were also studied. Neurophysiological studies of the peripheral nervous system were performed in 17 cats, and of these, neurophysiological studies of the sympathetic nervous system were performed in 9 animals. Six control cats were used for histological studies only.
Neurophysiological techniques Anaesthesia was induced and subsequently maintained after intubation, with 1% halothane/oxygen gas mixture. The body temperature, which was monitored with a rectal thermometer, was maintained at 37.5 4- 0.5 °C and an intramuscular thermistor measured limb temperature which was maintained at 33.4 4- 1.9 °C by means of a heated stage and radiant heat.
355 Peripheral nervous system Ten severely poisoned, 7 mildly poisoned and 17 control cats were studied. The motor conduction velocity (CV) of the fastest conducting fibres in the posterior tibial nerve was measured using a technique similar to that described by Kaeser and Lambert (1962) for the guinea pig. The compound muscle action potential was recorded from the flexor digitorum brevis and lumbrical muscles of the foot with a pair of stainless steel needle electrodes. The supramaximal stimulus was a square wave of 0.1 msec derived from a Devices stimulator and delivered at a rate of 1 pulse per second (pps). The nerve was stimulated at two sites through stainless steel electrodes inserted at the knee and at the ankle respectively. The preparation was earthed through another stainless steel needle inserted between the stimulating and recording electrodes. The paired recording electrodes were connected to a Tektronix FM 122 preamplifier with a 10 kilocycle high frequency response and time constant 0.02 msec. Compound muscle action potentials were displayed on the upper beam of a Tektronix 502A dual beam oscilloscope; a time scale derived from a Devices Digitimer was displayed on the lower beam. Photographic records were made on 35 m m film using a Grass oscilloscope camera. The distance between the cathodes at the two sites of stimulation was measured on the skin to the nearest 1 ram. Before measurement, the leg was straightened to ensure that the linear distance along the skin between the two points approximated closely to that along the nerve. The latency of the action potential was always measured from the stimulus artefact to the first negative deflection of the wave. Sympathetic nervous system Five severely poisoned and 9 control cats were used in this part of the study. The compound action potential was recorded and the conduction velocity of each of its component waves was measured in the greater splanchnic nerve and thoracic sympathetic nerve trunk. The left greater splanchnic nerve was exposed retro-peritoneally through an incision in the flank of anaesthetised animals. The four or five lowermost ribs were removed to expose the thoracic sympathetic trunk. The cat was maintained with an open thorax by a Palmer respiratory pressure pump with a tidal volume of 20-50 ml and a rate of 15/rain. The nerve trunk was bathed in warm paraffin oil and the temperature, which was monitored by means of a thermistor, was maintained at 34-37 °C. The experimental technique employed was a modification of that used by McLeod (1958) in the cat and baboon (Fig. 1). The compound nerve action potential was recorded from the greater splanchnic nerve l0 m m from the coeliac ganglion. The overlying connective tissue and pleura were removed from at least 3 regions of the thoracic sympathetic trunk and paired silver wire stimulating electrodes were placed in position. The distance between the cathode and the proximal recording electrode was measured to the nearest 0.5 ram. The nerve was stimulated supramaximally at a rate of 0.5 pps for several minutes and the resulting nerve action potentials were recorded on an F.M. analogue data tape recorder. To determine the amount, if any, by which the compound action potential was dispersed, photographs of the action potential from 4 control and 5 severely poisoned
356
, i 13
B lO00~V IIII
.
-"
-
-
4m$
AI3
B 2OOMV
toms
......
.
.
.
.
.
GREATER SPLANCHNIC NERVE
.
.
~/.A~ ~COELIAC
GANGLION
Fig. 1. Experimental arrangement for the measurement of conduction velocity in the greater splanchnic nerve. Paired silver wire stimulating electrodes were placed along the thoracic sympathetic trunk. Compound nerve action potentials were recorded from the greater splanchnic nerve. Upper trace is from a control cat, lower trace is from an acrylamide poisoned cat.
cats were enlarged ( × 5) and the areas under the action potentials measured. The results were expressed as millivolt seconds (mVs). The compound nerve action potential of the cat greater splanchnic nerve has four component waves, each with a characteristic conduction velocity. The Aft fibres and the A),t~ fibres conduct at 70-75 m/see and 30-35 m/see respectively. The B fibres conduct at about 10-12 m/see and the unmyelinated C fibres conduct at 1-2 m/see (Amassian 1951; Widdn 1955; McLeod 1958). Only the A/3 and B waves were analysed routinely since it was difficult to measure accurately the point at which the A76 wave left the base line, and the C wave was not recorded consistently.
357
Histological techniques The animals were killed with an overdose of halothane or pentobarbitone. Segments of at least 10 mm in length were removed from the nerve to the medial head of the left gastrocnemius muscle ( N M G ) j u s t before it entered the muscle; from the left greater splanchnic nerve (Spl) 20 m m above the coeliac ganglion; and from the left cervical vagus (Vag) 20 mm below the nodose ganglion.
Light microscopy The tissues were fixed for a minimum of 2 hr in 2 . 5 ~ glutaraldehyde in 0.1 M cacodylate buffer, post-fixed for 1½ hr in Dalton's solution (Dalton 1955), followed by 1~-2 hr in aqueous 2.5 ~ uranyl acetate. After dehydration, the tissues were blocked in araldite. Transverse thick sections of 0.5-2 #m were cut on a LKB ultramicrotome, stained with toluidine blue, photographed and printed at an enlargement of x 1,000. The splanchnic and vagus nerves always consisted of only one large fascicle whilst the N M G , at the level sampled, was composed of between 1 and 3 fascicles. Always the largest fascicle, and often all fascicles were selected and the size and number of all myelinated fibres were measured to the nearest 1 # m using a Zeiss T G Z 3 particle size analyser. All fibres less than 2 #m in diameter were grouped with the 2 #m fibres. The fascicular area was measured using an Ott planimeter Type 30139 and the fibre density was calculated as the number of myelinated fibres per intraperineural area (Swallow 1966).
Electron microscopy Thin sections (6-9 #m) from araldite blocks were cut on an LKB ultramicrotome, double-stained on copper grids with lead citrate and uranyl acetate, and examined with a Phillips EM 200 or 300 electron microscope. The tissues examined ultrastructurally were N M G and Spl from control and acrylamide-poisoned cats.
Statistical methods Mean values are given with the standard deviation. The significance of the difference between the groups was measured by the Student t-test, corrected for small numbers, and significance was accepted at P ~< 0.05. RESULTS
Neurophysiological studies Somatic nervous system Motor conduction velocity. In control cats, the mean maximal CV in the posterior tibial nerve ranged from 55 to 71 m/sec (mean 62.6 ~- 5.4 m/sec); in the mildly poisoned cats it ranged from 53 to 70 m/sec (mean 60.0 ± 7.4 m/sec), which did not differ significantly from the control values (P /> 0.05). In the severely poisoned cats the maximal CV ranged from 45 to 59 m/sec (mean 49.3 ~_ 4.1 m/sec), which was signif-
358 TABLE 1 NEUROPHYSIOLOGICAL STUDIES IN THE PERIPHERAL NERVOUS SYSTEM
Control Mild acrylamide intoxication Severe acrylamide intoxication
>I---
I~-
0 ._i w >
Amplitude of compound muscle action potential from flexor digitorum brevis and lumbrical muscles of the foot (mV)
mean range
SD n
P
mean range
SD n
P
62.6 60.0
55-71 53-70
5.4 17 7.4 7
t>0.05
24.4 12.5
15.1-39.9 10.0-16.0
7.0 17 1.9 7
~
50
Z
0
:i:i:i:!:
(9
.°,°o°o%1 ~%°o°°°ol
,OoOo%Ool
Z
© (9
A
B
100 °/o
100 % _1
w
n~ (,9 W
~_q
e_z
50
50.
0-
I--
0
A
B
0
A
B
Fig. 4. Effect of acrylamide on conduction velocity, amplitude and time integral of the compound action potential of the B fibres. The values for the severely poisoned animals (B) are expressed as a
percentage of the mean control value (A). Vertical bars represent ~ 1 SD. was 68.9 zL 6.2 m/sec and 60.2 ~ 3.4 m/sec (87 % of mean control value) respectively. The difference is significant (P ~< 0.05). The mean amplitude of the A/3 wave in control and severely poisoned cats was 2.7 ± 0.9 mV and 0.5 ~z 0.2 mV (19% of mean control value) respectively. The difference is significant (P ~< 0.01). The mean time integral of the Aft wave in control and severely poisoned cats was 7.0 -L 3.4 mVs and 2.7 zL 1.1 mVs (39 % of mean control value) respectively. The difference is significant (P ~< 0.01). The decrease of both the amplitude and time integral, together with the slowing of the conduction velocity, indicate that the large myelinated fibres of the splanchnic nerve were damaged by acrylamide. The results are summarised in Table 2 and Fig. 3. B-fibres. The mean CV of the B wave in control and severely poisoned cats was
362
Fig. 5. The effect of acrylamide on the splanchnic nerve. Toluidine blue stain. A : control splanchnic with normal distribution of myelinated fibres. \: 250. B: segment of control splanchnic. Note the large numbers of small (4/~m) myelinated fibres. ~,, 400. C: segment of a severely acrylamide damaged splanchnic nerve. Some of the large fibres are degenerating (arrowedL , 400.
Control Mild acrylamide poisoning Severe acrylamide poisoning
68.4 27.3 15.7 53.4-86.5 23.2-32.6 6.4~23.5
7.4 3.4 6.5
9 6 5 ~0.01 ~0.01
P
n
140.9 138.9-144.5 6.1 3 --81.0 65.1 100.2 17.8 3
SD
mean range
n
mean range
SD
Vagus ( × 10 2 fibres/ram 2)
N M G ( × 10 2 fibres/ram 2)
~
353
A C R Y L A M I D E A U T O N O M I C N E U R O P A T H Y 1N T H E CAT Part I. Neurophysiological and Histological Studies
ELIZABETH J. POST and J. G. McLEOD Department of Medicine, University of Sydney, N.S.W. 2006 (Australia)
(Received 1 March, 1977)
SUMMARY Neurophysiological and histological studies have been performed on the sympathetic nervous system of cats poisoned with acrylamide. The neurophysiological studies indicate that the large and small diameter myelinated fibres are damaged in the sympathetic nervous system in association with damage to the fibres of the peripheral nervous system. Quantative histological studies confirmed and extended the neurophysiological findings; there was a loss of myelinated fibres of all diameters from the sympathetic, parasympathetic and peripheral nervous system.
INTRODUCTION Disturbances of autonomic function occur in association with peripheral neuropathy, and are most commonly recognised clinically in diabetic neuropathy, (Rundles 1945; Sharpey-Schafer and Taylor 1960; Low, Walsh, Huang and McLeod 1975) and in the Guillain-Barr6 syndrome (Parker and Adams 1947; Matsuyama and H a y m a k e r 1967). However, the relationship between the disturbances of physiological function and the pathological changes in the autonomic nervous system has been largely overlooked. Since the physiological studies which may be performed in man in these conditions are of necessity limited, and often the conclusions to be drawn from them about the nature and sites of the abnormalities in the autonomic nervous system are imprecise, an autonomic disorder associated with a peripheral neuropathy has been produced experimentally in cats in order to investigate the mechanism of the physiological abnormalities which result.
Elizabeth J. Post was supported by a Commonwealth Post-Graduate Student Award. The work was also supported by grants from the Postgraduate Medical Foundation, University of Sydney, the National Heart Foundation and the National Health and Medical Research Council of Australia.
354 Acrylamide, a plastic monomer, is known to damage peripheral myelinated nerve fibres and to cause a dying-back type of degeneration (Fullerton and Barnes 1966: Prineas 1969; Hopkins 1970; Hopkins and Gilliatt 1971 ; Schaumburg, Wi~niewski and Spencer 1974). There is an extensive literature on the generalised acrylamide peripheral neuropathy and although brief mention of autonomic dysfunction has been made in some publications (Fullerton and Barnes 1966; Auld and Bedwell 1967; Leswing and Ribelin 1969; Prineas 1969; Hopkins 1970), little attention has been focused on the autonomic disturbances accompanying acrylamide peripheral neuropathy. In a previous study, Hopkins and Lambert (1972) investigated conduction in the unmyelinated fibres of the cervical sympathetic trunk of rats poisoned with acrylamide. In the present paper, the results of electrophysiological and histological studies on the sympathetic nervous system of cats poisoned with acrylamide are presented, and in the subsequent paper the effects of acrylamide on vasomotor control are reported (Post and McLeod 1977). METHODS
Animals Experiments were carried out on adult cats of weight 2-3 kg. Seventeen animals were given, with their food, 15 mg/kg acrylamide ( > 98 % pure) dissolved in 0.9% sodium chloride daily for periods of up to 16 weeks. The animals in the present study were described as mildly poisoned when they displayed weakness of the hind limbs only and severely poisoned where they were unable to walk because of severe paralysis of the fore- and hind-limbs. The severely poisoned cats also suffered from weight loss and occasionally mild diarrhoea in the final days of intoxication. The duration of poisoning was 4-6 weeks in mildly poisoned animals, and 12-16 weeks in the severely poisoned. Motor conduction studies were performed in 7 mildly acrylamide poisoned cats, and histological studies were subsequently carried out on 6 of them. Motor conduction studies were carried out in 10 severely acrylamide poisoned cats; 5 of these animals were also used for neurophysiological studies on the sympathetic nervous system and the remaining 5 were used for histological studies. Twenty-three control cats fed on a normal diet and housed in the same conditions as the poisoned animals were also studied. Neurophysiological studies of the peripheral nervous system were performed in 17 cats, and of these, neurophysiological studies of the sympathetic nervous system were performed in 9 animals. Six control cats were used for histological studies only.
Neurophysiological techniques Anaesthesia was induced and subsequently maintained after intubation, with 1% halothane/oxygen gas mixture. The body temperature, which was monitored with a rectal thermometer, was maintained at 37.5 4- 0.5 °C and an intramuscular thermistor measured limb temperature which was maintained at 33.4 4- 1.9 °C by means of a heated stage and radiant heat.
355 Peripheral nervous system Ten severely poisoned, 7 mildly poisoned and 17 control cats were studied. The motor conduction velocity (CV) of the fastest conducting fibres in the posterior tibial nerve was measured using a technique similar to that described by Kaeser and Lambert (1962) for the guinea pig. The compound muscle action potential was recorded from the flexor digitorum brevis and lumbrical muscles of the foot with a pair of stainless steel needle electrodes. The supramaximal stimulus was a square wave of 0.1 msec derived from a Devices stimulator and delivered at a rate of 1 pulse per second (pps). The nerve was stimulated at two sites through stainless steel electrodes inserted at the knee and at the ankle respectively. The preparation was earthed through another stainless steel needle inserted between the stimulating and recording electrodes. The paired recording electrodes were connected to a Tektronix FM 122 preamplifier with a 10 kilocycle high frequency response and time constant 0.02 msec. Compound muscle action potentials were displayed on the upper beam of a Tektronix 502A dual beam oscilloscope; a time scale derived from a Devices Digitimer was displayed on the lower beam. Photographic records were made on 35 m m film using a Grass oscilloscope camera. The distance between the cathodes at the two sites of stimulation was measured on the skin to the nearest 1 ram. Before measurement, the leg was straightened to ensure that the linear distance along the skin between the two points approximated closely to that along the nerve. The latency of the action potential was always measured from the stimulus artefact to the first negative deflection of the wave. Sympathetic nervous system Five severely poisoned and 9 control cats were used in this part of the study. The compound action potential was recorded and the conduction velocity of each of its component waves was measured in the greater splanchnic nerve and thoracic sympathetic nerve trunk. The left greater splanchnic nerve was exposed retro-peritoneally through an incision in the flank of anaesthetised animals. The four or five lowermost ribs were removed to expose the thoracic sympathetic trunk. The cat was maintained with an open thorax by a Palmer respiratory pressure pump with a tidal volume of 20-50 ml and a rate of 15/rain. The nerve trunk was bathed in warm paraffin oil and the temperature, which was monitored by means of a thermistor, was maintained at 34-37 °C. The experimental technique employed was a modification of that used by McLeod (1958) in the cat and baboon (Fig. 1). The compound nerve action potential was recorded from the greater splanchnic nerve l0 m m from the coeliac ganglion. The overlying connective tissue and pleura were removed from at least 3 regions of the thoracic sympathetic trunk and paired silver wire stimulating electrodes were placed in position. The distance between the cathode and the proximal recording electrode was measured to the nearest 0.5 ram. The nerve was stimulated supramaximally at a rate of 0.5 pps for several minutes and the resulting nerve action potentials were recorded on an F.M. analogue data tape recorder. To determine the amount, if any, by which the compound action potential was dispersed, photographs of the action potential from 4 control and 5 severely poisoned
356
, i 13
B lO00~V IIII
.
-"
-
-
4m$
AI3
B 2OOMV
toms
......
.
.
.
.
.
GREATER SPLANCHNIC NERVE
.
.
~/.A~ ~COELIAC
GANGLION
Fig. 1. Experimental arrangement for the measurement of conduction velocity in the greater splanchnic nerve. Paired silver wire stimulating electrodes were placed along the thoracic sympathetic trunk. Compound nerve action potentials were recorded from the greater splanchnic nerve. Upper trace is from a control cat, lower trace is from an acrylamide poisoned cat.
cats were enlarged ( × 5) and the areas under the action potentials measured. The results were expressed as millivolt seconds (mVs). The compound nerve action potential of the cat greater splanchnic nerve has four component waves, each with a characteristic conduction velocity. The Aft fibres and the A),t~ fibres conduct at 70-75 m/see and 30-35 m/see respectively. The B fibres conduct at about 10-12 m/see and the unmyelinated C fibres conduct at 1-2 m/see (Amassian 1951; Widdn 1955; McLeod 1958). Only the A/3 and B waves were analysed routinely since it was difficult to measure accurately the point at which the A76 wave left the base line, and the C wave was not recorded consistently.
357
Histological techniques The animals were killed with an overdose of halothane or pentobarbitone. Segments of at least 10 mm in length were removed from the nerve to the medial head of the left gastrocnemius muscle ( N M G ) j u s t before it entered the muscle; from the left greater splanchnic nerve (Spl) 20 m m above the coeliac ganglion; and from the left cervical vagus (Vag) 20 mm below the nodose ganglion.
Light microscopy The tissues were fixed for a minimum of 2 hr in 2 . 5 ~ glutaraldehyde in 0.1 M cacodylate buffer, post-fixed for 1½ hr in Dalton's solution (Dalton 1955), followed by 1~-2 hr in aqueous 2.5 ~ uranyl acetate. After dehydration, the tissues were blocked in araldite. Transverse thick sections of 0.5-2 #m were cut on a LKB ultramicrotome, stained with toluidine blue, photographed and printed at an enlargement of x 1,000. The splanchnic and vagus nerves always consisted of only one large fascicle whilst the N M G , at the level sampled, was composed of between 1 and 3 fascicles. Always the largest fascicle, and often all fascicles were selected and the size and number of all myelinated fibres were measured to the nearest 1 # m using a Zeiss T G Z 3 particle size analyser. All fibres less than 2 #m in diameter were grouped with the 2 #m fibres. The fascicular area was measured using an Ott planimeter Type 30139 and the fibre density was calculated as the number of myelinated fibres per intraperineural area (Swallow 1966).
Electron microscopy Thin sections (6-9 #m) from araldite blocks were cut on an LKB ultramicrotome, double-stained on copper grids with lead citrate and uranyl acetate, and examined with a Phillips EM 200 or 300 electron microscope. The tissues examined ultrastructurally were N M G and Spl from control and acrylamide-poisoned cats.
Statistical methods Mean values are given with the standard deviation. The significance of the difference between the groups was measured by the Student t-test, corrected for small numbers, and significance was accepted at P ~< 0.05. RESULTS
Neurophysiological studies Somatic nervous system Motor conduction velocity. In control cats, the mean maximal CV in the posterior tibial nerve ranged from 55 to 71 m/sec (mean 62.6 ~- 5.4 m/sec); in the mildly poisoned cats it ranged from 53 to 70 m/sec (mean 60.0 ± 7.4 m/sec), which did not differ significantly from the control values (P /> 0.05). In the severely poisoned cats the maximal CV ranged from 45 to 59 m/sec (mean 49.3 ~_ 4.1 m/sec), which was signif-
358 TABLE 1 NEUROPHYSIOLOGICAL STUDIES IN THE PERIPHERAL NERVOUS SYSTEM
Control Mild acrylamide intoxication Severe acrylamide intoxication
>I---
I~-
0 ._i w >
Amplitude of compound muscle action potential from flexor digitorum brevis and lumbrical muscles of the foot (mV)
mean range
SD n
P
mean range
SD n
P
62.6 60.0
55-71 53-70
5.4 17 7.4 7
t>0.05
24.4 12.5
15.1-39.9 10.0-16.0
7.0 17 1.9 7
~
50
Z
0
:i:i:i:!:
(9
.°,°o°o%1 ~%°o°°°ol
,OoOo%Ool
Z
© (9
A
B
100 °/o
100 % _1
w
n~ (,9 W
~_q
e_z
50
50.
0-
I--
0
A
B
0
A
B
Fig. 4. Effect of acrylamide on conduction velocity, amplitude and time integral of the compound action potential of the B fibres. The values for the severely poisoned animals (B) are expressed as a
percentage of the mean control value (A). Vertical bars represent ~ 1 SD. was 68.9 zL 6.2 m/sec and 60.2 ~ 3.4 m/sec (87 % of mean control value) respectively. The difference is significant (P ~< 0.05). The mean amplitude of the A/3 wave in control and severely poisoned cats was 2.7 ± 0.9 mV and 0.5 ~z 0.2 mV (19% of mean control value) respectively. The difference is significant (P ~< 0.01). The mean time integral of the Aft wave in control and severely poisoned cats was 7.0 -L 3.4 mVs and 2.7 zL 1.1 mVs (39 % of mean control value) respectively. The difference is significant (P ~< 0.01). The decrease of both the amplitude and time integral, together with the slowing of the conduction velocity, indicate that the large myelinated fibres of the splanchnic nerve were damaged by acrylamide. The results are summarised in Table 2 and Fig. 3. B-fibres. The mean CV of the B wave in control and severely poisoned cats was
362
Fig. 5. The effect of acrylamide on the splanchnic nerve. Toluidine blue stain. A : control splanchnic with normal distribution of myelinated fibres. \: 250. B: segment of control splanchnic. Note the large numbers of small (4/~m) myelinated fibres. ~,, 400. C: segment of a severely acrylamide damaged splanchnic nerve. Some of the large fibres are degenerating (arrowedL , 400.
Control Mild acrylamide poisoning Severe acrylamide poisoning
68.4 27.3 15.7 53.4-86.5 23.2-32.6 6.4~23.5
7.4 3.4 6.5
9 6 5 ~0.01 ~0.01
P
n
140.9 138.9-144.5 6.1 3 --81.0 65.1 100.2 17.8 3
SD
mean range
n
mean range
SD
Vagus ( × 10 2 fibres/ram 2)
N M G ( × 10 2 fibres/ram 2)
~
