Brain Research, 165 (1979) 219-233
219
© Elsevier/North-Holland Biomedical Press
RESPONSES IN S Y M P A T H E T I C NERVES OF T H E D O G EVOKED BY S T I M U L A T I O N OF SOMATIC NERVES
J. G. W H I T W A M , C. KIDD and I. V. FUSSEY
Department of Anaesthetics, Royal Postgraduate Medical School, London, I¥12 OHS, ( C.K.) Department of Cardiovascular Studies, Department of Physiology, University of Leeds, Leeds, LS2 9JT, and (L V.F.) Department of Surgery, SheffieM Royal Infirmary, SheffieM $6 3DA, ( U.K.)
(Accepted July 27th, 1978)
SUMMARY Responses in thoracic and renal sympathetic nerves evoked by electrical stimulation of cutaneous and muscle nerves in anaesthetized mongrel dogs were observed. Supramaximal stimulation of cutaneous nerves evoked two responses in both thoracic and renal nerves with latencies in the ranges 58-184 msec and 349-733 msec which are referred to as the early and late responses. It was shown that the early and late responses were evoked by group III and group IV afferent fibres respectively. Stimulation of muscle nerves of the forelimb and the hypoglossal nerve evoked smaller early responses which were considered to be due to activation of group III fibres and which had latencies in the range 92-157 msec. Supramaximal stimulation of muscle nerves in the hind limb failed to evoke any responses in approximately two-thirds of preparations and in the remainder only low level inconsistent early responses were observed. No matter how intense the stimuli applied to muscle nerves there were never any responses which could be related to the activation of group IV fibres.
INTRODUCTION The characteristics of reflex responses evoked in sympathetic efferent fibres by stimulation of somatic afferent fibres have been defined 2s. During the course of experiments on dogs, some of the characteristics of the responses evoked by stimulation of cutaneous and muscle nerves were found to be different from those previously described6,S,25,29,30,31 and this paper presents an account of these differences. Preliminary reports have already been published10,21,sL METHODS Observations were made on mongrel dogs. Three anaesthetic techniques were
220 used. In some preparations anaesthesia was induced with thiopentone sodium (BP) 30-40 mg/kg and continued with either nitrous oxide (70-80 ~ ) and oxygen (20-30 ~°/o) or chloralose in an initial dose of 100 mg/kg followed by an average maintenance dose of 18 mg/kg/h; alternatively chloralose was used as the sole agent in which case the tissues around the saphenous vein were infiltrated with 2 ml of a 5 ~ solution of amethocaine, the vein exposed and chloralose was injected through a nylon catheter placed so that the tip was lying in the inferior vena cava; the mean induction and maintenance doses were 123 mg/kg (range 100-150 mg/kg) and 18 mg/kg/h (range 12-28 mg/kg/h) respectively. The trachea was cannulated, and catheters were placed in a femoral artery and vein and in some preparations in the right carotid artery. When required, the carotid arteries and sinuses, and the vagus and hypoglossal nerves were exposed in the neck. The preparation was then placed on its left side. The preparations were paralyzed with intermittent intravenous injections of succinylcholine chloride (1-2 mg/kg/h) and artificially ventilated, with oxygen enriched air in animals anaesthetized with chloralose, using a positive pressure pump. The respiratory rate was 18/min and stroke volume was adjusted so that the PaCO2 was in the range 34-43 mm Hg. The PaO2 was maintained in the range 100-120 mm Hg by altering the inspired oxygen concentration. Blood was collected anaerobically in heparinized syringes at intervals of 2-3 h and pH, PCO2 and POz were measured in arterial samples using a model 48C blood gas analyzer (Electronic Instruments Ltd., Richmond, Surrey) 16. The pH was maintained in the range 7.3-7.4 by intermittent intravenous injection of molar NaHCOa solution. Oesophageal temperature was measured with a thermistor (Yellow Springs Instrument Co. Ltd.,) and maintained between 37 and 39 °C. The right stellate ganglion and sympathetic nerves in the thorax were exposed by removing the 2nd and 3rd ribs, and when necessary the upper lobe of the lung and part of the innominate-subclavian vein. Recordings were made from the peripheral end of desheathed branches arising from the stellate ganglion, the inferior ansate nerve or a fascicle of the inferior or caudal limb of the ansa subclavia 19,2°. The renal sympathetic nerves were exposed retroperitoneally close to the renal artery and recordings were made from desheathed fascicles of the nerves. In 20 preparations simultaneous recordings were made from the renal and thoracic nerves. The lateral branch of the superficial branch of either the right or left radial nerve was exposed for electrical stimulation: a small fascicle from the proximal part of the nerve was sometimes prepared for recording the afferent compound action potential. In some experiments the nerves to flexor carpi radialis, flexor digitorum superficialis and flexor digitorum profundus were exposed in the left foreleg close to these muscles. In the hind limb, the sciatic nerve, the nerves to biceps, semitendinosus, semimembranosus and gastrocnemius (usually three in number), the caudal cutaneous sural, deep fibula (peroneal), tibial and medial and lateral plantar nerves were exposed. All exposed nerves were covered by mineral oil and the temperature was maintained close to 38 °C (range 37-39 °C). All the nerves were desheathed for approximately 1 cm for recording and stimulation. Arterial pressures were recorded with short nylon cannulae attached to trans-
221 ducers and the ECG (lead II) was recorded with needle electrodes. The heart rate was recorded from either the ECG or the pressure pulse by a tachometer (Model 121, Gilford Instrument Laboratories Inc. Oberlin, Ohio). The tracheal pressure was measured by a nylon catheter attached to the tracheotomy tube. Action potentials were recorded with bipolar silver-silver chloride electrodes with a pre-amplifier (Tektronix type 122) and displayed on either an ultraviolet recorder (S.E. Laboratories, type 2000) using conditioning amplifiers and galvanometers with a frequency response of 3000 Hz, or a dual beam oscilloscope (Tektronix type 565). In many experiments a storage oscilloscope (Tektronix type 564) or a Linc 8 computer (Digital Corporation) were used to display responses and their average transients respectively. More recently a Neurolog system (N.L. 750 Digitimer) has been used to record average transients of evoked responses (Fig. 6). Electrical stimuli were applied to the peripheral nerves through bipolar silversilver chloride electrodes using a Grass $8 stimulator with matching direct coupled isolation units (Grass type 478A). In all the experiments, stimuli were applied at a frequency of 0.5 or 0.33 Hz. Nerve lengths were measured by a thread placed close to the nerve between the stimulating cathode and the nearest recording electrode. The carotid sinuses were denervated bilaterally to reduce the cardiovascular modulation of the sympathetic discharge and hence to decrease the variability of the latencies of the evoked responses n. Measurement of latencies of evoked responses were made from projected images of film from the oscilloscope display magnified 12 ×. In some experiments direct current (anodal block) was used to block selectively conduction in myelinated fibres 36. Approximately 3 cm of nerve was dissected free of the surrounding tissues and the middle 7-8 mm was desheathed. Direct current was applied to this section using grooved felt pads soaked in 0.9 ~ saline and mounted on 16-gauge stainless steel needles attached to syringes filled with 0.9~ saline. This system ensured that the nerve was completely surrounded by saline, and the nerve pad contact points could be flushed with saline when necessary. In addition excess saline or accumulated serum could be aspirated from the area of the electrodes without disturbing the preparation. In 6 preparations the effect of pentobarbitone in doses up to 60 mg/kg was observed. Frequently at the end of experiments hexamethonium chloride 5 mg/kg was administered intravenously to define whether recordings of sympathetic activity were from pre- or postganglionic fibres. RESULTS Nature of the evoked responses Nerves containing cutaneous fibres A single electrical stimulus of sufficient intensity to activate all afferent fibres in the radial nerve evoked a response with two principal components which are referred
222 B.
T TibiaI
A,
R
T
Radial
T Sura[ R
~
T Flex. Dig. R Pr°fundus ~
T R i
~
Sciatic
T
Semimern. Tibia[ lOOms¢c
~
R
mwl)
T
Gastroc.
IR
200msec Fig. 1. Responses in thoracic and renal sympathetic nerves, recorded simultaneously, evoked by supramaximal electrical stimulation of somatic nerves of the dog. Stimulus intensity I> 20 V; stimulus duration, 0.5 msec. A : single responses in one preparation. B: 5 responses superimposed on a storage oscilloscope in another preparation.
to as the 'early' and 'late' responses and which are illustrated in Fig. 1. The mean latency of the early response recorded in thoracic nerves varied between 66.3 and 136 msec in different preparations and in renal nerves from 83.5 to 155 msec (Table I). The mean latencies of the late responses recorded in thoracic and renal nerves were in the ranges of 349-601 msec and 398-618 msec respectively (Table II). Early and late responses similar to those illustrated in Fig. 1 were evoked by electrical stimulation of any nerve containing cutaneous fibres (e.g. radial and sural). A summary of the responses evoked by stimulation of all the nerves in this study is presented in Table III. In one preparation only an early response and in another only a late response could be obtained by radial nerve stimulation. These may be explained by injury to the afferent nerves. M u s c l e nerves
The effect of high intensity stimulation of muscle nerves on activity in sympathetic nerves was different to that evoked by stimulation of cutaneous nerves (Table III). In the foreleg, stimulation of muscle nerves caused relatively small early responses (Fig. 1A) which had latencies comparable to those observed for early responses evoked by stimulation of the radial nerve (Table III). Although high stimulus intensities were applied to muscle nerves late responses were never evoked.
TABLE I
Mean latencies of the early response in thoracic (T) andrenal ( R) sympathettc nerves evokedby stimulation of the lateral branch of the superficial branch of the radial nerve No. Record- Latency of response (msec) ing site Distal Proximal
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
T T T T T T T T T T T T T R T R T R T R
P Diff.
n
~Vlean ± S.E.M. n
Mean ± S.E.M.
39 70 15 98 27 38 20 39 42 82 91 51 68 53 49 51 51 52 62 61
122.8 105.6 109.5 110.6 116.9 112.3 116.8 120.0 107.5 108.8 97.2 136.2 99.0 101.8 108.2 155.3 95.1 137.2 71.6 91.1
112.9 93.4 95.0 100.6 104.9 98.0 107.7 108.0 102.6 103.2 90.1 126.0 92.3 95.1 93.2 136.7 79.5 122.5 66.3 83.5
± 3.7 ± 2.2 ± 5.8 ± 1.3 ± 1.9 ± 1.9 -4- 2.8 ± 2.6 ± 1.4 ± 1.4 ± 1.4 ± 2.2 ± 1.9 ± 2.1 d_ 2.4 ± 2.8 ± 2.6 ± 1.9 ± 0.69 ± 0.93
30 59 9 93 41 38 53 58 73 85 105 63 47 33 44 46 63 66 56 53
Nerve length (cm)
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
2.6 2.2 4.3 1.1 1.4 3.5 1.9 1.5 1.1 1.2 1.2 3.2 2.1 2.3 2.04 2.3 2.4 1.7 0.86 0.78
Conduction velocity afferent pathway (msec 1)
9.9 12.2 14.5 10.0 12.0 14.3 9.1 12.0 4.9 5.6 7.1 10.2 2.51 2.1 4.78 5.1 4.41 8.7 4.87 6.12
< < < < < < < < < < < < < < < < < < <
219
© Elsevier/North-Holland Biomedical Press
RESPONSES IN S Y M P A T H E T I C NERVES OF T H E D O G EVOKED BY S T I M U L A T I O N OF SOMATIC NERVES
J. G. W H I T W A M , C. KIDD and I. V. FUSSEY
Department of Anaesthetics, Royal Postgraduate Medical School, London, I¥12 OHS, ( C.K.) Department of Cardiovascular Studies, Department of Physiology, University of Leeds, Leeds, LS2 9JT, and (L V.F.) Department of Surgery, SheffieM Royal Infirmary, SheffieM $6 3DA, ( U.K.)
(Accepted July 27th, 1978)
SUMMARY Responses in thoracic and renal sympathetic nerves evoked by electrical stimulation of cutaneous and muscle nerves in anaesthetized mongrel dogs were observed. Supramaximal stimulation of cutaneous nerves evoked two responses in both thoracic and renal nerves with latencies in the ranges 58-184 msec and 349-733 msec which are referred to as the early and late responses. It was shown that the early and late responses were evoked by group III and group IV afferent fibres respectively. Stimulation of muscle nerves of the forelimb and the hypoglossal nerve evoked smaller early responses which were considered to be due to activation of group III fibres and which had latencies in the range 92-157 msec. Supramaximal stimulation of muscle nerves in the hind limb failed to evoke any responses in approximately two-thirds of preparations and in the remainder only low level inconsistent early responses were observed. No matter how intense the stimuli applied to muscle nerves there were never any responses which could be related to the activation of group IV fibres.
INTRODUCTION The characteristics of reflex responses evoked in sympathetic efferent fibres by stimulation of somatic afferent fibres have been defined 2s. During the course of experiments on dogs, some of the characteristics of the responses evoked by stimulation of cutaneous and muscle nerves were found to be different from those previously described6,S,25,29,30,31 and this paper presents an account of these differences. Preliminary reports have already been published10,21,sL METHODS Observations were made on mongrel dogs. Three anaesthetic techniques were
220 used. In some preparations anaesthesia was induced with thiopentone sodium (BP) 30-40 mg/kg and continued with either nitrous oxide (70-80 ~ ) and oxygen (20-30 ~°/o) or chloralose in an initial dose of 100 mg/kg followed by an average maintenance dose of 18 mg/kg/h; alternatively chloralose was used as the sole agent in which case the tissues around the saphenous vein were infiltrated with 2 ml of a 5 ~ solution of amethocaine, the vein exposed and chloralose was injected through a nylon catheter placed so that the tip was lying in the inferior vena cava; the mean induction and maintenance doses were 123 mg/kg (range 100-150 mg/kg) and 18 mg/kg/h (range 12-28 mg/kg/h) respectively. The trachea was cannulated, and catheters were placed in a femoral artery and vein and in some preparations in the right carotid artery. When required, the carotid arteries and sinuses, and the vagus and hypoglossal nerves were exposed in the neck. The preparation was then placed on its left side. The preparations were paralyzed with intermittent intravenous injections of succinylcholine chloride (1-2 mg/kg/h) and artificially ventilated, with oxygen enriched air in animals anaesthetized with chloralose, using a positive pressure pump. The respiratory rate was 18/min and stroke volume was adjusted so that the PaCO2 was in the range 34-43 mm Hg. The PaO2 was maintained in the range 100-120 mm Hg by altering the inspired oxygen concentration. Blood was collected anaerobically in heparinized syringes at intervals of 2-3 h and pH, PCO2 and POz were measured in arterial samples using a model 48C blood gas analyzer (Electronic Instruments Ltd., Richmond, Surrey) 16. The pH was maintained in the range 7.3-7.4 by intermittent intravenous injection of molar NaHCOa solution. Oesophageal temperature was measured with a thermistor (Yellow Springs Instrument Co. Ltd.,) and maintained between 37 and 39 °C. The right stellate ganglion and sympathetic nerves in the thorax were exposed by removing the 2nd and 3rd ribs, and when necessary the upper lobe of the lung and part of the innominate-subclavian vein. Recordings were made from the peripheral end of desheathed branches arising from the stellate ganglion, the inferior ansate nerve or a fascicle of the inferior or caudal limb of the ansa subclavia 19,2°. The renal sympathetic nerves were exposed retroperitoneally close to the renal artery and recordings were made from desheathed fascicles of the nerves. In 20 preparations simultaneous recordings were made from the renal and thoracic nerves. The lateral branch of the superficial branch of either the right or left radial nerve was exposed for electrical stimulation: a small fascicle from the proximal part of the nerve was sometimes prepared for recording the afferent compound action potential. In some experiments the nerves to flexor carpi radialis, flexor digitorum superficialis and flexor digitorum profundus were exposed in the left foreleg close to these muscles. In the hind limb, the sciatic nerve, the nerves to biceps, semitendinosus, semimembranosus and gastrocnemius (usually three in number), the caudal cutaneous sural, deep fibula (peroneal), tibial and medial and lateral plantar nerves were exposed. All exposed nerves were covered by mineral oil and the temperature was maintained close to 38 °C (range 37-39 °C). All the nerves were desheathed for approximately 1 cm for recording and stimulation. Arterial pressures were recorded with short nylon cannulae attached to trans-
221 ducers and the ECG (lead II) was recorded with needle electrodes. The heart rate was recorded from either the ECG or the pressure pulse by a tachometer (Model 121, Gilford Instrument Laboratories Inc. Oberlin, Ohio). The tracheal pressure was measured by a nylon catheter attached to the tracheotomy tube. Action potentials were recorded with bipolar silver-silver chloride electrodes with a pre-amplifier (Tektronix type 122) and displayed on either an ultraviolet recorder (S.E. Laboratories, type 2000) using conditioning amplifiers and galvanometers with a frequency response of 3000 Hz, or a dual beam oscilloscope (Tektronix type 565). In many experiments a storage oscilloscope (Tektronix type 564) or a Linc 8 computer (Digital Corporation) were used to display responses and their average transients respectively. More recently a Neurolog system (N.L. 750 Digitimer) has been used to record average transients of evoked responses (Fig. 6). Electrical stimuli were applied to the peripheral nerves through bipolar silversilver chloride electrodes using a Grass $8 stimulator with matching direct coupled isolation units (Grass type 478A). In all the experiments, stimuli were applied at a frequency of 0.5 or 0.33 Hz. Nerve lengths were measured by a thread placed close to the nerve between the stimulating cathode and the nearest recording electrode. The carotid sinuses were denervated bilaterally to reduce the cardiovascular modulation of the sympathetic discharge and hence to decrease the variability of the latencies of the evoked responses n. Measurement of latencies of evoked responses were made from projected images of film from the oscilloscope display magnified 12 ×. In some experiments direct current (anodal block) was used to block selectively conduction in myelinated fibres 36. Approximately 3 cm of nerve was dissected free of the surrounding tissues and the middle 7-8 mm was desheathed. Direct current was applied to this section using grooved felt pads soaked in 0.9 ~ saline and mounted on 16-gauge stainless steel needles attached to syringes filled with 0.9~ saline. This system ensured that the nerve was completely surrounded by saline, and the nerve pad contact points could be flushed with saline when necessary. In addition excess saline or accumulated serum could be aspirated from the area of the electrodes without disturbing the preparation. In 6 preparations the effect of pentobarbitone in doses up to 60 mg/kg was observed. Frequently at the end of experiments hexamethonium chloride 5 mg/kg was administered intravenously to define whether recordings of sympathetic activity were from pre- or postganglionic fibres. RESULTS Nature of the evoked responses Nerves containing cutaneous fibres A single electrical stimulus of sufficient intensity to activate all afferent fibres in the radial nerve evoked a response with two principal components which are referred
222 B.
T TibiaI
A,
R
T
Radial
T Sura[ R
~
T Flex. Dig. R Pr°fundus ~
T R i
~
Sciatic
T
Semimern. Tibia[ lOOms¢c
~
R
mwl)
T
Gastroc.
IR
200msec Fig. 1. Responses in thoracic and renal sympathetic nerves, recorded simultaneously, evoked by supramaximal electrical stimulation of somatic nerves of the dog. Stimulus intensity I> 20 V; stimulus duration, 0.5 msec. A : single responses in one preparation. B: 5 responses superimposed on a storage oscilloscope in another preparation.
to as the 'early' and 'late' responses and which are illustrated in Fig. 1. The mean latency of the early response recorded in thoracic nerves varied between 66.3 and 136 msec in different preparations and in renal nerves from 83.5 to 155 msec (Table I). The mean latencies of the late responses recorded in thoracic and renal nerves were in the ranges of 349-601 msec and 398-618 msec respectively (Table II). Early and late responses similar to those illustrated in Fig. 1 were evoked by electrical stimulation of any nerve containing cutaneous fibres (e.g. radial and sural). A summary of the responses evoked by stimulation of all the nerves in this study is presented in Table III. In one preparation only an early response and in another only a late response could be obtained by radial nerve stimulation. These may be explained by injury to the afferent nerves. M u s c l e nerves
The effect of high intensity stimulation of muscle nerves on activity in sympathetic nerves was different to that evoked by stimulation of cutaneous nerves (Table III). In the foreleg, stimulation of muscle nerves caused relatively small early responses (Fig. 1A) which had latencies comparable to those observed for early responses evoked by stimulation of the radial nerve (Table III). Although high stimulus intensities were applied to muscle nerves late responses were never evoked.
TABLE I
Mean latencies of the early response in thoracic (T) andrenal ( R) sympathettc nerves evokedby stimulation of the lateral branch of the superficial branch of the radial nerve No. Record- Latency of response (msec) ing site Distal Proximal
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
T T T T T T T T T T T T T R T R T R T R
P Diff.
n
~Vlean ± S.E.M. n
Mean ± S.E.M.
39 70 15 98 27 38 20 39 42 82 91 51 68 53 49 51 51 52 62 61
122.8 105.6 109.5 110.6 116.9 112.3 116.8 120.0 107.5 108.8 97.2 136.2 99.0 101.8 108.2 155.3 95.1 137.2 71.6 91.1
112.9 93.4 95.0 100.6 104.9 98.0 107.7 108.0 102.6 103.2 90.1 126.0 92.3 95.1 93.2 136.7 79.5 122.5 66.3 83.5
± 3.7 ± 2.2 ± 5.8 ± 1.3 ± 1.9 ± 1.9 -4- 2.8 ± 2.6 ± 1.4 ± 1.4 ± 1.4 ± 2.2 ± 1.9 ± 2.1 d_ 2.4 ± 2.8 ± 2.6 ± 1.9 ± 0.69 ± 0.93
30 59 9 93 41 38 53 58 73 85 105 63 47 33 44 46 63 66 56 53
Nerve length (cm)
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
2.6 2.2 4.3 1.1 1.4 3.5 1.9 1.5 1.1 1.2 1.2 3.2 2.1 2.3 2.04 2.3 2.4 1.7 0.86 0.78
Conduction velocity afferent pathway (msec 1)
9.9 12.2 14.5 10.0 12.0 14.3 9.1 12.0 4.9 5.6 7.1 10.2 2.51 2.1 4.78 5.1 4.41 8.7 4.87 6.12
< < < < < < < < < < < < < < < < < < <
