(Received 5 August 1970)

Transcription

1 J. Physiol. (1971), 212, pp With 5 text-ftigurem Printed in Great Britain SPINAL AND SUPRASPINAL COMPONENTS OF THE REFLEX DISCHARGES INTO LUMBAR AND THORACIC WHITE RAMI BY AKIO SATO* AND ROBERT F. SCHMIDT From II. Physiologische8 Indtitut, Universitdt Heidelberg, Germany (Received 5 August 1970) SUMMARY 1. In chloralose anaesthetized cats reflex discharges in thoracic and lumbar white rami were elicited by single shock stimulation of intercostal, spinal and hind limb nerves. 2. In animals with an intact neuraxis single stimuli of sufficient strength usually elicited a white rami mass discharge having two distinct components. Following spinal transaction only the late reflex component disappeared. 3. The early (spinal) reflex component had its largest amplitude if the afferent volley entered the spinal cord at the same or an adjacent segment of the white ramus under observation, whereas the size of the late (supraspinal) component was rather independent of the segmental level of the afferent input. 4. It was concluded that somatic afferent volleys have a twofold action on the sympathetic nervous system: a more generalized action via the supraspinal sympathetic reflex centres and a more circumscribed action on the preganglionic neurones at the segmental level. INTRODUCTION It is generally agreed that the reflex activity induced in pre- and postganglionic sympathetic nerves by somatic afferent activity is mediated via spinal as well as through supraspinal pathways. Most investigators found that the short latency, spinal reflex component usually was much smaller than the long latency, supraspinal one (see, for instance, Sato, Tsushima & Fujimori, 1965; Coote & Downman, 1966). An interesting exception has recently been reported by Coote, Downman & Weber (1969). These authors recorded sympathetic mass reflex discharges from thoracic white rami (WR) following single electrical stimulation of dorsal roots and * Gast-Dozent of the Alexander von Humboldt-Stiftung.

2 840 AKIO SATO AND ROBERT F. SCHMIDT of splanchnic and intercostal nerves. The discharges were recorded 'as compact summated waves of 8-15 msec duration' appearing after a latency of msec. The authors concluded from their results, that 'the major part of the reflex discharge evoked in a white ramus by somatic or visceral afferent volleys follows a central path which is complete at the spinal segmental level. The WR reflexes are not long-circuited through a supraspinal path.' Using lumbar WR instead of the thoracic ones Sato, Kaufman, Koizumi & Brooks (1969) after single shock stimulation of peripheral afferent nerves recorded two sympathetic reflex components, an early one (latency msec) which they associated with a spinal reflex pathway and a late one (latency msec) which they associated with a supraspinal pathway. Typically the early response was much smaller than the late one. Furthermore, low strength peripheral stimulation gave only late discharges whereas with high strength stimulation early and late responses appeared. In view of their importance for the central organization of sympathetic reflex pathways the diverse conclusions drawn by Coote et al. (1969) and Sato et al. (1969) from their respective results challenged us to solve these discrepancies by recording from thoracic and lumbar white rami the sympathetic mass discharges evoked by different types of afferent inputs. In this paper evidence is presented that depending on the experimental situation both types of responses can be obtained and that the respective sizes of the spinal and supraspinal components depend strongly on the segmental level of the afferent input. The functional significance of these findings will be outlined in the discussion. A preliminary report of part of the results has been given to the Deutsche Physiologische Gesellschaft (Sato & Schmidt, 1970). METHODS The experiments were performed on seven adult cats (weight kg) anaesthetized with chloralose (70 mg/kg) given intraperitoneally. All animals were immobilized by the i.v. injection of gallamine triethiodide (Flaxedil). The artificial respiration was usually adjusted to an end-expiratory CO2 of %. The mean blood pressure of the animals was continuously recorded and kept above 90 mm Hg, if necessary by infusion of Macrodex or Haemaccel. The rectal temperature was kept between 37 and 380 C. In order to eliminate effects from the peripheral baroreceptors the vagal and depressor nerves as well as the carotid sinus nerves were cut bilaterally. Dissection of lumbar and thoracic white rami was always done on the left side. In four experiments the lumbar white rami L 1 and L 2 were exposed retroperitoneally. The rami were cut just proximal to the sympathetic trunk and the connective sheaths were removed before recording with the aid of a binocular microscope. In the other three experiments a comparable dissection of the thoracic white rami T 3 and T 4 was performed. The corresponding and neighbouring spinal respectively intercostal nerves were dissected free and mounted for stimulation as described by Beacham & Perl (1964) and Coote et al. (1969). The length of the spinal and intercostal nerves between the proximal stimulating electrode and the spinal cord were

3 WHITE RAMI REFLEXES usually 2*0-3*0 cm. The spinal dorsal roots were exposed by a laminectomy. In all experiments the following hind-limb nerves were dissected and mounted for stimulation on platinum electrodes: the flexor muscle nerves, posterior biceps plus semitendinosus (abbreviated PBST) and the flexor muscle nerve branches of the peroneal and deep peroneal nerve (PDP); the extensor muscle nerves, gastroonemius and soleus (GS) and the cutaneous nerves, sural (SU) and superficial peroneal (SP). Fig. 1 shows schematically the arrangement of the stimulating and recording electrodes when recording reflex discharges from lumbar white rami. The set-up used to record from thoracic white rami resembled that shown in Fig. 1 except that the intercostal instead of spinal nerves were used for stimulation. Stim. spinal nerves. IL LF L2 L3 LO R.com.albi (WR) L7 I v Stim. dorsal roots \' PBST ~~~~G PDP` SP Stim. limb nerves Fig. 1. Schematic diagram of the arrangement of the stimulation and recording electrodes when recording sympathetic reflex discharges from the lumbar white rami (WR). The stimuli were delivered to the spinal nerves L 1-L 4, the dorsal roots L 7-S1, and also to cutaneous and muscle hind limb nerves. 841 The thresholds for electrical stimulation of peripheral nerves were determined by recording the afferent volleys from the appropriate dorsal root entry zones at the cord dorsum. The strength of stimulation of nerves will be given relative to threshold, which was expressed as l1ot. Usually, with 0-2 msec square pulses, l1ot was in the range from 80 to 150 mv. The reflex potentials were made monophasic by repeatedly crushing the cut nerve ends, and they were recorded with platinum electrodes using an ac. -differential preamplifier with long time constants. The low frequency response was set at 0'02 or 0'08 Hz, the high frequency response at 250 Hz or 1 khz. Depending on the experimental conditions ten to twenty individual records were averaged in a CAT computer and plotted with an X-Y plotter. Thereafter the magnitude of the monophasic mass reflex potentials was measured with a planimeter as the area under the evoked response (cf. Schmidt & Schonfuss, 1970).

4 842 AKIO SATO AND ROBERT F. SCHMIDT RESULTS Shape and latency of the white rami discharges elicited by high strength afferent stimulation; the relation between the size of the early and late reflex components and the site of afferent stimulation The specimen records of Fig. 2 were recorded from a L 1 WR following single electrical stimulation of high strength (50T) applied to the somatic nerves L 1 through L 4 (columns A to D) and to the sural nerve (E). The reflex discharges show the variability in latency and amplitude typical for 20V Recorded from Li WR A B C D E me I. t. A go A.4X4 f A- Stim. LI(50x T) Stim. L2 Stim. L3 Stim. L4 *Stim. SU 100 msec Fig. 2. Specimen records of sympathetic reflex discharges recorded from the LI WR. Single electrical stimuli were delivered to the spinal nerves L 1-L4 (A-D) and to the SU (E) with 50 T intensity at a repetition rate of 1/4 see. The stimuli were given at the end of the 20 #sv calibration pulses (arrows). In each column 5 specimen records were selected from a series of fifty consecutive records to illustrate the most frequent appearances of the reflex. somatically evoked sympathetic reflex potentials (Schmidt & Sch6nfuss, 1970) but in most records two reflex components, an early and a late one, can be recognized. The shape of the late component appears to be rather independent of the site of afferent stimulation whereas the early component is large in A and gradually declines as the afferent volleys enter at L2 to L4 (B-C). Following sural nerve stimulation (E) the early component is either very small or absent. The grouping of the sympathetic reflex discharges into two components became more obvious if ten to twenty individual records were averaged in a computer. Such average records from three different cats are shown in

5 WHITE RAMI REFLEXES , Recorded from Li WR 'SecE ~~'-' L7. SIJ G r 40.: thw GS0x Stim.50x Ttf S0xT i.0 K * ~~~~60' 10xT *, i~~~~~~i4~~ok Is ',, * i Be T?40' o *1 V A H o,- A 40 L 2- LI WR.4, Late /AM,20-I. J, g Early ,2OxT x 20- ALate *Eary '2~ k 4 4 L i 0. LI" L71 SU L2 L4 Si GS LI.13 L7 *SU L2 L4 SI GS LI L3 L7 SUU L2 L4 St GS Fig. 3. Specimen records in A-H are sympathetic reflexes recorded from the L 1 WR. Single stimuli were given at the end of the calibration pulses (indicated by arrows) to the spinal nerves L 1, 2, 3, 4, 7 and S 1 (A to F) and to the limb nerves SU (E) and GS (H) with 50 T intensity at a repetition rate of 1/4 see. Each specimen is the average of ten individual reflexes. In I, K and L the integrated sizes (ordinate) of the early (filled circles) and late (triangles) reflex components evoked at stimulus intensities of 50 T (I), 10 T (K) and 4 T (L), are plotted against a variety of afferent inputs shown in the abscissa. In M, the integrated sizes (ordinate) of the early (filled circles) and late (triangles) LI WIR reflex components are plotted against the stimulus strength (abscissa) to the L2 spinal nerve. The integrated sizes of the early and late components were measured from 7 to 40 msec, and from 50 to 130 msec after the stimulus respectively.

6 844 AKIO SATO AND ROBERT F. SCHMIDT Figs. 3A-H, 4A-C, and 5A, B, E, F. In Figs. 3I and 4H the sizes (ordinates) of the early (filled circles) and late (triangles) reflex components obtained from all afferent inputs abscissaee) are plotted. In all cases it is Early Recorded from LIWR 20pV A 50 msec E Late arly- 20V LI Su L2 L3 C SP F L4 D GS St'm.S~~~~~xT ~Stim. ~~~~~G 0xT 110' 120 S0x T IOxT 150 * Early L * A Late Early ~ L2-LIWR 80 H s80o * 4 ~~~~~~ 1~~ xT * :: o~~~~60 X I E g 40 40~~~~~ x3 11 X ~~~~~~~~~~~K S S L 3 SUG 1L UG 20 4o LO* SP L2 S4S2LOT LI L3 SU.-GS LI L3 SU GS LI L3 SU GS L2 L4 SP L2 L4 SP L2 L4 SP Fig. 4. Specimen records in A-G are sympathetic reflexes recorded from the Li WR. Different experiment but same recording and plotting procedures as in Fig. 3. Note that the gains of the amplifier in A-D and in E-G are different. H, I, K and L correspond to I, K, L and M in Fig. 3. The sizes of the early and late reflex components were measured from 7 to 64 msec and from 64 to 120 msec respectively.

7 WHITE RAMI REFLEXES 845 evident that the early component had its largest amplitude if the afferent volley entered the spinal cord at the same or a nearby segmental level of the preganglionic neurones under observation, and that it declined markedly, as the afferent volley entered at more distant segments. In contrast, the late component had a rather constant size whether spinal C.N.S. intact Spinal cat 20#V 20p A Early Recorded from L2WR Early B L2 L 3 /L 3 Late C 0msec L2 E Recorded from T3WR G 5Omsec T 3 T 3 F T4. T4 TStimrn: x T tstim. 50x T Fig. 5. Effect of spinal transection on white ramus discharges. Each record is the average of ten individual reflexes. A-D were recorded from the L 2 WVR before (A, B) and after (C, D) spinal transaction at the ClI level. E-H were recorded from the T3WR of another cat,, before (E, F) and after spinal transaction at C1. The single stimuli were given at the end of the calibration pulses (arrows) to the spinal nerve L2 (A, C) and L3 (B, D), and also to the intercostal nerves T 3 (E, G) and T 4 (F, H) with 50 T intensity at a repetition rate of 1/4 sec. Time scale in C applies to A-D, that in G to E-H. nerves, dorsal roots or cutaneous nerves of the hind limb were stimulated. Afferent volleys from muscle (GS) usually evoked no early and only small late WR reflex discharges. The relative sizes of the early versus the late reflex components elicited by a given afferent input differed from experiment to experiment. This variability can be seen by comparing the specimen records A to D of Figs. H

8 846 AKIO SATO AND ROBERT F. SCHMIDT 2, 3 and 4 which were recorded from the L 1 WR of three different cats following 50 T stimulation of L 1 to L 4 somatic nerves. In Fig. 2A the two reflex components appear to be of about equal size. In Fig. 3A the area of the late component exceeds that of the early one, and in Fig. 4A the early component is dominant. Similar differences can be seen if the other corresponding specimen records of these Figures are compared with each other. We do not know why these differences occur. We did observe, however, that in the course of many hours of recording the late reflex component tended to become smaller, thus giving the impression of a relative increase of the early reflex component. If this decrease of the late component is taken as indicating a decline of the general condition of the animal, the prevalence of the early component right from the beginning of the experiment (as in Fig. 4) may signal that in such an experiment the general condition of the animal was not as good as in the experiments of Figs. 2 and 3 (throughout the period of recording in all experiments the mean blood pressure was above 90 mm Hg, the end-expiratory CO2 between 2-5 and 3 % and the body temperature between 36 and 380 C). The latencies of the early component of the VWR discharge were within the range reported by previous observers (see the Introduction). Thus in the experiment partly shown in Fig. 2 the latencies of the early L I WR discharges induced by LI spinal nerve stimulation ranged in fifty trials from 7 to 12 msec with an average of *2 msee (mean + S.D.). When stimulating neighbouring segments the latencies increased and with fifty stimuli to L4 spinal nerve they ranged from 10 to 20 msec, with a mean of msec. A further increase was noted when hind-limb nerves were stimulated. For instance, the early discharges following sural nerve stimulation ranged from 12 to 30 msec, the mean being msec. Similar values were obtained when the latencies of the early components of thoracic white rami were measured. Latency measurements on averaged X-Y plots (see specimen in Figs. 3, 4, 5) resulted in values corresponding to those seen on individual records. The latencies of the late reflex discharges did not change appreciably when moving the afferent input away from the segmental level of recording. Thus in the experiment of Fig. 2 fifty trials of L 1 spinal nerve stimulation yielded reflex latencies from 54 to 80 msec with a mean of msec and L4 spinal nerve stimulation gave late component latencies of msec (fifty trials) with a mean of ms Slightly longer values were obtained with sural nerve stimulation (range msec, mean 70X1 ± 9.5 S.D.). Again, these values are practically identicalwiththosereported earlier (65-80 msec, Sato et al. 1969). The latencies of the thoracic late reflex discharges were somewhat shorter than those of the lumbar late discharges because the distance from the medullary sympathetic centres to the thoracic preganglionic neurones is shorter than that to the lumbar ones. On averaged X-Y plots the latencies of thoracic late discharges ranged from msec when stimulating intercostal nerves and from 47 to 51 msec when stimulating hind-limb nerves.

9 WHITE RAMI REFLEXES 847 White rams reflex discharges elicited by different types of afferent nerve fibres The results described so far have all been obtained using a strength of stimulation of 50T. This situation probably corresponds to that of Coote et al. (1969) who adjusted their stimulus strength so that the stimulus 'elicited the largest response under investigation'. We shall now briefly consider the results obtained after reducing the stimulus strength from 50 T down to 1 T. In the experiment illustrated in Fig. 3 stimulation of the spinal nerve L2 resulted in the appearance of the late reflex component as soon as the stimulus strength was increased to more than 1-5T. The size of the late reflex component reached its maximum around 10-20T, i.e. as soon as most of the Group III fibres were included in the afferent volley. An early reflex component only appeared after increasing the stimulus strength to more than 5T. Again the maximum reflex size was reached at about 20T. These findings correspond closely to those observed by Sato et al. (1969) following stimulation of cutaneous nerves of the hind limb. The higher threshold of the early reflex component has not been found in all experiments of this series. For instance, in the experiment partly displayed in Fig. 4 the graph in L shows that the early reflex discharge (which was very prominent in this experiment) started before the late one appeared. If it is assumed that the early and late reflex components reflect the activity in spinal and supraspinal reflex pathways respectively, the different thresholds of the two components in Figs. 3 M and 4L may be considered to indicate different general states of excitability of the sympathetic nervous system. Similar results were obtained when the effect of varying stimulus strength was tested with other afferent inputs. As can be seen from Figs. 3K, L and 4I, K the sizes of both reflex components declined when the strength of stimulation was reduced to 10T (Figs. 3K, 41) or 4-5T (3L, 4K). However, the basic pattern observed with 50T stimulation did not change; dominant early reflexes could only be evoked from spinal nerves of the same or of neighbouring segments, whereas late components could be evoked from practically all afferent inputs. Effect of spinal transaction If the pathway of the late white rami reflex discharges includes supraspinal structures no trace of this discharge should be left over after an acute spinal transaction. On the other hand a spinal reflex should either remain or recover after spinal transaction provided care is taken to prevent or shorten the spinal shock occurring after the transaction. To test these

10 848 AKIO SATO AND ROBERT F. SCHMIDT predictions acute spinal transactions at the C 1 level were performed at the end of three experiments of this series. Spinal shock was minimized by adjusting the artificial respiration to an end-expiratory CO2 of %, and by preventing the fall of blood pressure below 90 mm Hg by the i.v. infusion of a mixture of Macrodex and glucose solution to which varying amounts of noradrenaline were given. The results of two of these three experiments are displayed in Fig. 5. The reflex discharges recorded in a cat with an intact neuraxis from the L2 WR following stimulation (50T) of the L2 and L3 spinal nerves are shown in Fig. 5A and B respectively. Immediately after spinal transaction both components disappeared completely but after about 10 min the early component started to recover. Fig. 5C and D shows the situation about 1 hr later. Still no trace of the late discharge could be detected,. The recordings were continued for another 2 hr without any further change in the appearance of the reflexes. Corresponding results were obtained in the experiment represented in Fig. 5 E-H where the recordings were made from T 3 WR and the stimuli were given to the T 3 (E, G) and T 4 (F, H) intercostal nerves. In the third experiment the C 1 segment was infiltrated by a 2% Novocaine solution before transaction. The Novocaine administration resulted in the disappearance of the late T 3 WR discharges whereas the early discharges remained unaltered except for a slight reduction in amplitude. The transaction, which was performed 10 min later, produced no further change of the reflex recordings. DISCUSSION The present results show that the reflex discharges evoked in thoracic and lumbar white rami by somatic nerve stimulation usually consist of two components, one having a spinal, the other a supraspinal reflex pathway. This is in agreement with previous work of Sato et al. (1969) on lumbar white ramus discharges, and corresponds to the results obtained when recording from the lumbar sympathetic trunk (Sato et at. 1965) or from the renal nerve (Coote & Downman, 1966). Our results are in contrast to the work of Coote et al. (1969) who concluded that somatic (and visceral) afferent stimulation activated only spinal pathways to thoracic and lumbar preganglionic neurones. This discrepancy is probably due to the experimental conditions of Coote et al. (1969): they used only high strength stimulation and recorded mainly the reflex discharges obtained in the segment of the afferent input. Both factors favour the appearance of spinal reflex discharges. In our experiments the size of the spinal and supraspinal reflex components depended mainly on the segmental level of the afferent input

11 WHITE RAMI REFLEXES 849 relative to the white ramus from which the reflex discharges were recorded. Generally speaking, all afferent inputs evoked aupra8pinal reflexes of similar size and configuration in all of the white rami, whereas appreciable spinal reflexes could only be recorded in the white rami of the same or the adjacent spinal segments. Thus any afferent input has a twofold action on the sympathetic nervous system: it evokes local sympathetic reflexes at the segmental level, and, at the same time, it induces a general reaction of the supraspinal sympathetic reflex centres. From Cannon's work (Cannon, 1929) the concept was derived that the sympathetic outflow usually responds in a massive and general fashion. This concept was supported by the work of Schaefer and his associates (see for instance Sell, Erdelyi & Schaefer, 1958) who demonstrated that the simultaneously recorded discharges in the renal and cardiac sympathetic nerves were of about equal configuration following stimulation of a peripheral nerve, and that stimulation of various afferent nerves gave about equal responses in a given sympathetic nerve. Beacham & Perl (1964) questioned the concept that the sympathetic nervous system is only able to react in a general fashion because they found in spinalized animals that dorsal root volleys evoked reflex discharges in white rami of the same or adjacent segment dominantly. They concluded from their results that many portions of the sympathetic nervous system can be individually brought into action. It now seems likely that under the experimental conditions used by Sell et al. (1958) and Beacham & Perl (1964) respectively the general (supraspinal) and local (segmental) actions of somatic afferent volleys were observed in isolation from each other. The present results demonstrate that somatic afferents from all parts of the body converge onto the neurones of the supraspinal sympathetic reflex centres. This convergence gives rise to the generalized sympathetic reflex actions observed after somatic nerve volleys. In addition the somatic afferents have more specific spinal connexions with the preganglionic neurones of their own or nearby segments. These latter connexions are responsible for the circumscribed somato-sympathetic reflexes. The authors wish to thank Miss Marianne Seigis for her invaluable technical assistance. This work was supported by grants from the Deutsche Forschungsgemeinschaft. REFERENCES BEACHAM, W. S. & PERL, E. R. (1964). Background and reflex discharge of sympathetic preganglionic neurones in the spinal cat. J. Phy8iol. 173, CANNON, W. B. (1929). Bodily ChangeB in Pain, Hunger, Fear and Rage, 2nd edn. New York: D. Appleton and Co. COOTE, J. H. & DOWNMAN, C. B. B. (1966). Central pathways of some autonomic reflex discharges. J. Phyaiol. 183,

12 850 AKIO SATO AND kobert F. SCHMIDT CooTs, J. H., DowNxm"., C. B. B. & WEBER, W. V. (1969). Reflex discharges into thoracic white rami elicited by somatic and visceral afferent excitation. J. Physiol. 202, SATO, A., KAuIJF1w, A., KoIZum, K. & BROOKS, C. MCC. (1969). Afferent nerve groups and sympathetic reflex pathways. Brain Rae. 14, SATO, A. & SCHMIDT, R. F. (1970). Sympathetic activity upon stimulation of spinal nerves: a segmental or a supraspinal reflex? Pfluger8 Arch. gem. Phy8iol. 316, R-81. SATO, A., TsusIJ A, N. & FUIJJmoRI, B. (1965). Reflex potentials of lumbar sympathetic trunk with sciatic nerve stimulation in cats. Jap. J. Phy8iol. 15, SCHMIDT, R. F. & SCHmNFUSS, K. (1970). An analysis of the reflex activity in the cervical sympathetic trunk induced by myelinated somatic afferents. Pfliuger8 Arch. gee. Phy8iol. 314, SELL, R., ERDELYI, A. & SCHAEFER, H. (1958). Untersuchungen uber den Einfluss peripherer Nervenreizung auf die sympathische Aktivitat. Pfluger8 Arch. ge8. Phy8iol. 267,