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Electrodermal reflexes induced by activity in somatic afferent fibers
Brain Research, 87 (1975) 145-150
145
© Elsevier ScientificPublishingCompany,Amsterdam- Printed in The Netherlands
ELECTRODERMAL REFLEXES INDUCED BY ACTIVITY IN SOMATIC AFFERENT FIBERS
HERMANN KARL, AKIO SATO* ANDROBERT F. SCHMIDT Physiologisches Institut der Universitiit Kiel, Lehrstuhl I, D 2300 Kiel (G.F.R.)
During the last decade, the electrophysiological study of somatosympathetic reflexes has clearly shown that these reflexes depend on (a) the modality of the peripheral receptors and the types of afferent fibers being activated, (b) the central reflex pathways involved (spinal, medullary, supramedullary), (c) the region of the sympathetic outflow under observation, and (d) the effector organ subserved by the postganglionic neurons. Several recent reviews have summarized our present state of knowledge in this field (refs. 5, 1L and 12 and several contributions of this symposium). In the present communication observations will be reported concerning the reflex connections between the somatic nervous system and the sweat glands of the cat's foot pads. In particular it will be demonstrated that the various types of somatic afferent fibers are remarkably different in regard to their potency to induce or to modify the electrodermal potentials indicating the activity of these glands. As suggested by Wang 14, who has greatly contributed to our present understanding of the nervous control of the electrical activity of the sweat glands, the spontaneous electric activity will be called spontaneous potential waves and the evoked activity will be designated electrodermal reflex in preference to the synonymous expression 'galvanic skin reflex'. In cats anesthetized with chloralose (initial dose 30-50 mg/kg i.p.) and immobilized with Flaxedil, the electrodermal activity was recorded from the central pads of the right forelimb and hind limb paws using zinc plate electrodes connected to an AC differential preamplifier (response width usually set at 0.08-250 Hz). Indifferent zinc plate electrodes were attached to shaved skin areas of the dorsum of the same feet. A mixture of zinc sulfate solution and kaoline paste was used for optimum contact between electrodes and skin. The electrodermal reflexes were evoked by stimulating the following nerves of the left hind limb which were mounted on platinum electrodes: the flexor muscle nerve branches of the peroneal and deep peroneal nerves (PDP); the extensor muscle nerves, gastrocnemius and soleus (GS); the cutaneous nerves, sural (SU) and superficial peroneal nerve (SP). The thresholds for electrical * Present address: 2nd Department of Physiology,Tokyo MetropolitanInstitute of Gerontology, Itabashiku, Tokyo, Japan.
146 stimulation of these nerves were determined by the evoked potentials which were recorded from proximal parts of these nerves or from the main sciatic nerve trunk. The strength of stimulation of nerves will be given relative to threshold, which was expressed as 1 T. Spontaneous potential waves (Fig. 1A) and electrodermal reflexes (Fig. 1B) can only be recorded under conditions of very light anesthesia (see also ref. 14). The spontaneous waves are irregular and, in contrast to other types of sympathetic outflow, do not correspond to either circulatory or respiratory rhythms. Similarly, the latency and the amplitude of the individual electrodermal reflexes vary to a certain extent (Fig. 1B) as is well known from other types of somatosympathetic reflexes ]1. Since this type of variability has also been found when recording from pre- or post-ganglionic neuronsg, 1~, it is assumed that it is caused by central rather than by peripheral mechanisms. Averaging of 5 (Fig. 1C) to 10 individual reflexes usually gives reasonably constant results that allow quantitative measurement of the size of the response by determining the maximum amplitude or the area under the evoked response. In addition to the variation of individual reflexes the amplitudes and the latencies of electrodermal reflexes in different animals have a certain variability. Thus in 11 cats for single shocks the reflex latency varied between 1.0 and 1.5 sec, and the reflex lasted between 2 and 4 sec at normal body temperatures (36-38 °C). When stimulating the lumber sympathetic trunk Patton 7 found a reflex latency of 0.54-0.98 sec (average 0.71 sec), and he concluded that most of this period was due to neuroglandular delay, since synaptic delay and conduction velocity, assuming group IV fiber velocity, can scarcely account for more than 0.20-0.25 sec. The neuroglandular delay time as well as the duration of the electrodermal reflex itself depend very much on the local temperature ~ which has not been recorded in the present experiments.
A I
5s~
SPI' 50T
15s°
C 0.5 m SP50T
Y
~ i
5s
i
Fig. 1. Spontaneous potential waves (A) and evoked electrodermal reflexes (B) recorded from a forepaw of a cat. Each sweep starts 45 sec after the preceding one. The record in C has been averaged from 5 electrodermal reflexesrecorded consecutivelyfrom the same pad. In all cases the reflexes were evoked by single stimuli of 50 T to the superficial peroneal nerve (SP). The stimulus strength was supramaximal for group II and III fibers, but subthreshold for group IV fibers in the peroneal nerve.
147
A i
B lOOr -E75~
/
t
t
'
•
f
/ f
q¢I
o
t
, 10
stim. G$ 50T 21
0
31
0
, , i 40 50 60s stimulus interval
Fig. 2. Time course of depression of electrodermal reflex by preceding afferent activity. Single conditioning and testing stimuli of 50 T were given to the combined nerve of the gastrocnemius-soleus muscle (GS). The specimen records in A are averages of 5 conditioning-testing sequences recorded at stimulus intervals of 10, 30 and 60 sec, respectively. In B amplitudes of the test reflex (ordinate) are plotted for various conditioning-testing intervals (abscissa). The amplitude of the test reflex was taken as 100~. The stimulus strength was supramaximal for group I-III fibers but subthreshold for group IV fibers.
Electrodermal reflexes evoked by single afferent volleys are followed by a period of post-excitatory depression lasting some 20-30 sec. This depression manifests itself by a reduction (Fig. 1B) or abolition of the spontaneous potential waves and by the depression of subsequent electrodermal reflexes. An example of a conditioningtesting sequence showing the time course of the post-excitatory depression following a single stimulus to a muscle nerve is given in Fig. 2. This time course of reflex recovery is similar though somewhat shorter than that found with tetanic stimulation of cutaneous nerves 15. Since in the latter case it has been demonstrated that the time course of the post-excitatory depression can be drastically shortened by spinalization it is assumed that in both cases this inhibition is exerted by descending influences from those supraspinal structures which were defined by Wang and collaborators as inhibitory sweat centers (cJ~ ref. 14). To avoid interference with activity from these centers, in the following experiments electrodermal reflexes were evoked at stimulus intervals of at least 45, usually 60 sec. The types of afferent fibers evoking electrodermal reflexes have been investigated in 8 cats. Fig. 3 illustrates the results of one of these experiments. As can be seen from the specimen records in A and the open circles in C, single afferent volleys in cutaneous nerves evoked by stimulus strength of less than 2 T were able to elicit electrodermal reflexes. Usually the threshold for eliciting a reflex was at 1.2-1.4 T, and almost maximal reflex responses could be obtained at 2-5 T, i.e., at stimulus strengths at which practically only group II afferent fibers were excited. At stimulus strengths extending into the group I I I and IV range no regular increase of the electrodermal reflex has been found. At first sight, the latter result is surprising since these fiber groups subserve the
148
SP 2T
3T
I5T
GS 5T
7T
20T
50T ~ s
2.0 mV
o
o
1.5 ~.
o o ~"''~lw ~ o
1.0
o ....
e-~
......
0.5
/
/ 2
5 10 90 stimulus strength
50T
Fig. 3. Types of cutaneous and muscle afferent fibers evoking electrodermal reflexes. The specimen records are averages of 5 consecutive reflex responses recorded after single stimuli of the indicated intensity to the SP (A) and GS (B) nerves. The stimuli were given at the beginning of each record (arrows) at a repetition rate of once every 45 sec. The complete series are plotted in C, open circles giving the results of stimulating the cutaneous nerve (SP), and filled circles those obtained when stimulating the muscle nerve (GS).
cutaneous thermo- and nociceptors which should have access to the nervous control of the sweat glands. Presumably the large effects of the highly synchronous group II volleys occlude the action of the group I I I and IV afferent volleys. In a short communication Lloyd 6 reported to have seen remarkable increases of the electrodermal reflex by group I I I and IV volleys. As far as can be judged from his specimen records there were no signs of spontaneous potential waves at the time of the reflex recording. This points to a rather deep state of anesthesia, and it appears possible that at this state the cutaneous group II volleys were not able to elicit maximum electrodermal reflexes. Low threshold (group I) muscle afferents did not produce electrodermal reflexes (Fig. 3C). Actually the stimulus strength had to be extended well into the group II range before electrodermal reflexes were recorded (specimen in Fig. 3B and filled circles in C). Addition of group I I I fiber impulses definitely increased the reflex further but again only small increases of the electrodermal reflex were observed when group IV impulses were included in the volley. Lloyd 6 did not see any contribution of muscle group II fibers which again may point to a rather deep state of anesthesia in his experiments (see above). Brief tetanie stimulation either of cutaneous or of muscle (Fig. 4) afferents potentiated the electrodermal reflexes. For the same number of stimuli in the train short stimulus intervals (100-200 Hz, Fig. 4A) usually gave better results than longer intervals (Fig. 4B). Maximum potentiation was regularly obtained with 5-10 stimuli. In preparations without spontaneous potential waves brief tetanic stimulation often evoked an electrodermal reflex while single stimuli even at high strength remained ineffective (cf also ref. 14). The present experiments demonstrate that impulses in cutaneous group II
149 4
j,O
mq 3
0
0
B 0
3
jJ'f~
SS~ ~ 0
~2
i/ E e~
4 mV
stim.GS
s
50"l',100Hz
!
0
stim.GS 50T,2OHz
1 I
2
I
[
3 5 number of stimuli
I
Io
o
I
2
I
3
I
5 number of stimuli
I
lO
Fig. 4. Temporal facilitation of electrodermal reflexes. In A and B the amplitudes of the electrodermal reflexes (averages of 5 consecutive trials), evoked by stimulation of the GS nerve at 50 T, are plotted against the number of stimuli in the trains. A shows the results obtained at a train frequency of 100 Hz (stimulus interval 10 msec) and B those at 20 Hz (stimulus interval 50 msec). The trains were repeated once every 45 sec.
afferent fibers elicit powerful electrodermal reflexes although they do not subserve those receptors thought to increase the activity of sweat glands, namely cutaneous warm receptors and nociceptors. In contrast, group III and IV fibers are remarkably ineffective. As mentioned above, this ineffectiveness is probably an experimental artifact due to the c o m b i n e d excitation o f g r o u p I I - I V afferent fibers. Therefore these experiments s h o u l d be r e p e a t e d using a b l o c k i n g device to suppress the c o n d u c t i o n in the large afferents. W h e n r e c o r d i n g f r o m pre- o r p o s t - g a n g l i o n i c neurons4,8-10,13, it was seen t h a t g r o u p I I volleys f r o m c u t a n e o u s nerves e v o k e d powerful s o m a t o s y m p a t h e t i c reflexes p a r t i c u l a r l y in those c u t a n e o u s p o s t g a n g l i o n i c fibers p r e s u m e d to have v a s o c o n s t r i c t o r f u n c t i o n 3. N a t u r a l s t i m u l a t i o n o f those r e c e p t o r t y p e s subserved by g r o u p I I fibers revealed t h a t these reflexes can o n l y be i n d u c e d b y a c t i v a t i o n o f h a i r follicle receptors (ref. 2 a n d Janig, tbJs s y m p o s i u m ) . F r o m these results it is tentatively suggested t h a t those g r o u p I I afferent fibers inducing e l e c t r o d e r m a l reflexes subserve h a i r follicle receptors in the cat's skin. This w o r k has been s u p p o r t e d by a g r a n t f r o m the D e u t s c h e F o r s c h u n g s gemeinschaft a n d by a fellowship to A.S. f r o m the A l e x a n d e r von H u m b o l d t - S t i f t u n g .
1 FUJIMORI,B., Studies on the galvanic skin reflex using the current and potential method, Jap. 3. Physiol., 5 (1955) 394-405. 2 HOR~YSECK,G., AND J~,NIG,W., Reflexes in postganglionic fibres within skin and muscle nerves after mechanical non-noxious stimulation of skin, Exp. Brain Res., 20 (1974) 115-123. 3 J~,NIO,W., SATO,A., A~D SCHMmT, R. F., Reflexes in postganglionic cutaneous fibres by stimulation of group I to group IV somatic afferents, Pfliigers Arch. ges. PhysioL, 331 (1972) 244--256. 4 J.g.NIG, W., AND SCttMIDT, R. F., Single unit responses in the cervical sympathetic trunk upon somatic nerve stimulation, Pfliigers Arch. ges. Physiol., 314 (1970) 199-216. 5 KOIZUMI,K., AND BROOKS, C. McC., The integration of autonomic reactions: a discussion of autonomic reflexes, their control and their association with somatic reactions, Ergebn. Physiol., 67 (1972) 1-68. 6 LLOYD, D. P. C., The classification of galvanic skin reflex afferent fibers, Proc. nat. Acad. Sci. (Wash.), 48 (1962) 814-817. 7 PATTON,H. D., Secretory innervation of the cat's foot-pad, Y. NeurophysioL, 11 (1948) 211-227.
150 8 SATO,A., KAUFMANN,A., KOIZUMI,K., AND BROOKS, C. McC., Afferent nerve groups and sympathetic reflex pathways, Brain Research, 14 (1969) 575-587. 9 SATO, A., AND SCHMrOT, R. F., Ganglionic transmission of somatically induced sympathetic reflexes, Pfliigers Arch. ges. Physiol., 326 (1971) 240-253. 10 SATO,A., AND SCHMIDT,R. F., Spinal and supraspinal components of the reflex discharges into lumbar and thoracic white rami, J. Physiol. (Lond.), 212 (1971) 839-850. 11 SATO,A., AND SCHMIDT,R. F., Somatosympathetic reflexes: afferent fibers, central pathways, discharge characteristics, Physiol. Rev., 53 (1973) 916-947. 12 SCHMrOT,R. F., Pre- and postganglionic neurons as final common pathways of somato-sympathetic reflexes. In W. UMBACHANDH. P. KOEPCHEN(Eds.), Central Rhythmic and Regulation, Hippokrates, Stuttgart, 1974, pp. 178-190. 13 SCHMIOT,R. F., AND SCH6NFUSS,K., An analysis of the reflex activity in the cervical sympathetic trunk induced by myelinated somatic afferents, Pfliigers Arch. ges. PhysioL, 314 (1970) 175-198. 14 WANG,G. H., The Neural ControlofSweating, Univ. Wisconsin Press, Madison, 1964, pp. 1-130. 15 WANG,G. H., AND HIND, J. E., Supraspinal origin of a poststimulatory long-lasting inhibition of galvanic skin reflex, J. NeurophysioL, 22 (1959) 360-366.
145
© Elsevier ScientificPublishingCompany,Amsterdam- Printed in The Netherlands
ELECTRODERMAL REFLEXES INDUCED BY ACTIVITY IN SOMATIC AFFERENT FIBERS
HERMANN KARL, AKIO SATO* ANDROBERT F. SCHMIDT Physiologisches Institut der Universitiit Kiel, Lehrstuhl I, D 2300 Kiel (G.F.R.)
During the last decade, the electrophysiological study of somatosympathetic reflexes has clearly shown that these reflexes depend on (a) the modality of the peripheral receptors and the types of afferent fibers being activated, (b) the central reflex pathways involved (spinal, medullary, supramedullary), (c) the region of the sympathetic outflow under observation, and (d) the effector organ subserved by the postganglionic neurons. Several recent reviews have summarized our present state of knowledge in this field (refs. 5, 1L and 12 and several contributions of this symposium). In the present communication observations will be reported concerning the reflex connections between the somatic nervous system and the sweat glands of the cat's foot pads. In particular it will be demonstrated that the various types of somatic afferent fibers are remarkably different in regard to their potency to induce or to modify the electrodermal potentials indicating the activity of these glands. As suggested by Wang 14, who has greatly contributed to our present understanding of the nervous control of the electrical activity of the sweat glands, the spontaneous electric activity will be called spontaneous potential waves and the evoked activity will be designated electrodermal reflex in preference to the synonymous expression 'galvanic skin reflex'. In cats anesthetized with chloralose (initial dose 30-50 mg/kg i.p.) and immobilized with Flaxedil, the electrodermal activity was recorded from the central pads of the right forelimb and hind limb paws using zinc plate electrodes connected to an AC differential preamplifier (response width usually set at 0.08-250 Hz). Indifferent zinc plate electrodes were attached to shaved skin areas of the dorsum of the same feet. A mixture of zinc sulfate solution and kaoline paste was used for optimum contact between electrodes and skin. The electrodermal reflexes were evoked by stimulating the following nerves of the left hind limb which were mounted on platinum electrodes: the flexor muscle nerve branches of the peroneal and deep peroneal nerves (PDP); the extensor muscle nerves, gastrocnemius and soleus (GS); the cutaneous nerves, sural (SU) and superficial peroneal nerve (SP). The thresholds for electrical * Present address: 2nd Department of Physiology,Tokyo MetropolitanInstitute of Gerontology, Itabashiku, Tokyo, Japan.
146 stimulation of these nerves were determined by the evoked potentials which were recorded from proximal parts of these nerves or from the main sciatic nerve trunk. The strength of stimulation of nerves will be given relative to threshold, which was expressed as 1 T. Spontaneous potential waves (Fig. 1A) and electrodermal reflexes (Fig. 1B) can only be recorded under conditions of very light anesthesia (see also ref. 14). The spontaneous waves are irregular and, in contrast to other types of sympathetic outflow, do not correspond to either circulatory or respiratory rhythms. Similarly, the latency and the amplitude of the individual electrodermal reflexes vary to a certain extent (Fig. 1B) as is well known from other types of somatosympathetic reflexes ]1. Since this type of variability has also been found when recording from pre- or post-ganglionic neuronsg, 1~, it is assumed that it is caused by central rather than by peripheral mechanisms. Averaging of 5 (Fig. 1C) to 10 individual reflexes usually gives reasonably constant results that allow quantitative measurement of the size of the response by determining the maximum amplitude or the area under the evoked response. In addition to the variation of individual reflexes the amplitudes and the latencies of electrodermal reflexes in different animals have a certain variability. Thus in 11 cats for single shocks the reflex latency varied between 1.0 and 1.5 sec, and the reflex lasted between 2 and 4 sec at normal body temperatures (36-38 °C). When stimulating the lumber sympathetic trunk Patton 7 found a reflex latency of 0.54-0.98 sec (average 0.71 sec), and he concluded that most of this period was due to neuroglandular delay, since synaptic delay and conduction velocity, assuming group IV fiber velocity, can scarcely account for more than 0.20-0.25 sec. The neuroglandular delay time as well as the duration of the electrodermal reflex itself depend very much on the local temperature ~ which has not been recorded in the present experiments.
A I
5s~
SPI' 50T
15s°
C 0.5 m SP50T
Y
~ i
5s
i
Fig. 1. Spontaneous potential waves (A) and evoked electrodermal reflexes (B) recorded from a forepaw of a cat. Each sweep starts 45 sec after the preceding one. The record in C has been averaged from 5 electrodermal reflexesrecorded consecutivelyfrom the same pad. In all cases the reflexes were evoked by single stimuli of 50 T to the superficial peroneal nerve (SP). The stimulus strength was supramaximal for group II and III fibers, but subthreshold for group IV fibers in the peroneal nerve.
147
A i
B lOOr -E75~
/
t
t
'
•
f
/ f
q¢I
o
t
, 10
stim. G$ 50T 21
0
31
0
, , i 40 50 60s stimulus interval
Fig. 2. Time course of depression of electrodermal reflex by preceding afferent activity. Single conditioning and testing stimuli of 50 T were given to the combined nerve of the gastrocnemius-soleus muscle (GS). The specimen records in A are averages of 5 conditioning-testing sequences recorded at stimulus intervals of 10, 30 and 60 sec, respectively. In B amplitudes of the test reflex (ordinate) are plotted for various conditioning-testing intervals (abscissa). The amplitude of the test reflex was taken as 100~. The stimulus strength was supramaximal for group I-III fibers but subthreshold for group IV fibers.
Electrodermal reflexes evoked by single afferent volleys are followed by a period of post-excitatory depression lasting some 20-30 sec. This depression manifests itself by a reduction (Fig. 1B) or abolition of the spontaneous potential waves and by the depression of subsequent electrodermal reflexes. An example of a conditioningtesting sequence showing the time course of the post-excitatory depression following a single stimulus to a muscle nerve is given in Fig. 2. This time course of reflex recovery is similar though somewhat shorter than that found with tetanic stimulation of cutaneous nerves 15. Since in the latter case it has been demonstrated that the time course of the post-excitatory depression can be drastically shortened by spinalization it is assumed that in both cases this inhibition is exerted by descending influences from those supraspinal structures which were defined by Wang and collaborators as inhibitory sweat centers (cJ~ ref. 14). To avoid interference with activity from these centers, in the following experiments electrodermal reflexes were evoked at stimulus intervals of at least 45, usually 60 sec. The types of afferent fibers evoking electrodermal reflexes have been investigated in 8 cats. Fig. 3 illustrates the results of one of these experiments. As can be seen from the specimen records in A and the open circles in C, single afferent volleys in cutaneous nerves evoked by stimulus strength of less than 2 T were able to elicit electrodermal reflexes. Usually the threshold for eliciting a reflex was at 1.2-1.4 T, and almost maximal reflex responses could be obtained at 2-5 T, i.e., at stimulus strengths at which practically only group II afferent fibers were excited. At stimulus strengths extending into the group I I I and IV range no regular increase of the electrodermal reflex has been found. At first sight, the latter result is surprising since these fiber groups subserve the
148
SP 2T
3T
I5T
GS 5T
7T
20T
50T ~ s
2.0 mV
o
o
1.5 ~.
o o ~"''~lw ~ o
1.0
o ....
e-~
......
0.5
/
/ 2
5 10 90 stimulus strength
50T
Fig. 3. Types of cutaneous and muscle afferent fibers evoking electrodermal reflexes. The specimen records are averages of 5 consecutive reflex responses recorded after single stimuli of the indicated intensity to the SP (A) and GS (B) nerves. The stimuli were given at the beginning of each record (arrows) at a repetition rate of once every 45 sec. The complete series are plotted in C, open circles giving the results of stimulating the cutaneous nerve (SP), and filled circles those obtained when stimulating the muscle nerve (GS).
cutaneous thermo- and nociceptors which should have access to the nervous control of the sweat glands. Presumably the large effects of the highly synchronous group II volleys occlude the action of the group I I I and IV afferent volleys. In a short communication Lloyd 6 reported to have seen remarkable increases of the electrodermal reflex by group I I I and IV volleys. As far as can be judged from his specimen records there were no signs of spontaneous potential waves at the time of the reflex recording. This points to a rather deep state of anesthesia, and it appears possible that at this state the cutaneous group II volleys were not able to elicit maximum electrodermal reflexes. Low threshold (group I) muscle afferents did not produce electrodermal reflexes (Fig. 3C). Actually the stimulus strength had to be extended well into the group II range before electrodermal reflexes were recorded (specimen in Fig. 3B and filled circles in C). Addition of group I I I fiber impulses definitely increased the reflex further but again only small increases of the electrodermal reflex were observed when group IV impulses were included in the volley. Lloyd 6 did not see any contribution of muscle group II fibers which again may point to a rather deep state of anesthesia in his experiments (see above). Brief tetanie stimulation either of cutaneous or of muscle (Fig. 4) afferents potentiated the electrodermal reflexes. For the same number of stimuli in the train short stimulus intervals (100-200 Hz, Fig. 4A) usually gave better results than longer intervals (Fig. 4B). Maximum potentiation was regularly obtained with 5-10 stimuli. In preparations without spontaneous potential waves brief tetanic stimulation often evoked an electrodermal reflex while single stimuli even at high strength remained ineffective (cf also ref. 14). The present experiments demonstrate that impulses in cutaneous group II
149 4
j,O
mq 3
0
0
B 0
3
jJ'f~
SS~ ~ 0
~2
i/ E e~
4 mV
stim.GS
s
50"l',100Hz
!
0
stim.GS 50T,2OHz
1 I
2
I
[
3 5 number of stimuli
I
Io
o
I
2
I
3
I
5 number of stimuli
I
lO
Fig. 4. Temporal facilitation of electrodermal reflexes. In A and B the amplitudes of the electrodermal reflexes (averages of 5 consecutive trials), evoked by stimulation of the GS nerve at 50 T, are plotted against the number of stimuli in the trains. A shows the results obtained at a train frequency of 100 Hz (stimulus interval 10 msec) and B those at 20 Hz (stimulus interval 50 msec). The trains were repeated once every 45 sec.
afferent fibers elicit powerful electrodermal reflexes although they do not subserve those receptors thought to increase the activity of sweat glands, namely cutaneous warm receptors and nociceptors. In contrast, group III and IV fibers are remarkably ineffective. As mentioned above, this ineffectiveness is probably an experimental artifact due to the c o m b i n e d excitation o f g r o u p I I - I V afferent fibers. Therefore these experiments s h o u l d be r e p e a t e d using a b l o c k i n g device to suppress the c o n d u c t i o n in the large afferents. W h e n r e c o r d i n g f r o m pre- o r p o s t - g a n g l i o n i c neurons4,8-10,13, it was seen t h a t g r o u p I I volleys f r o m c u t a n e o u s nerves e v o k e d powerful s o m a t o s y m p a t h e t i c reflexes p a r t i c u l a r l y in those c u t a n e o u s p o s t g a n g l i o n i c fibers p r e s u m e d to have v a s o c o n s t r i c t o r f u n c t i o n 3. N a t u r a l s t i m u l a t i o n o f those r e c e p t o r t y p e s subserved by g r o u p I I fibers revealed t h a t these reflexes can o n l y be i n d u c e d b y a c t i v a t i o n o f h a i r follicle receptors (ref. 2 a n d Janig, tbJs s y m p o s i u m ) . F r o m these results it is tentatively suggested t h a t those g r o u p I I afferent fibers inducing e l e c t r o d e r m a l reflexes subserve h a i r follicle receptors in the cat's skin. This w o r k has been s u p p o r t e d by a g r a n t f r o m the D e u t s c h e F o r s c h u n g s gemeinschaft a n d by a fellowship to A.S. f r o m the A l e x a n d e r von H u m b o l d t - S t i f t u n g .
1 FUJIMORI,B., Studies on the galvanic skin reflex using the current and potential method, Jap. 3. Physiol., 5 (1955) 394-405. 2 HOR~YSECK,G., AND J~,NIG,W., Reflexes in postganglionic fibres within skin and muscle nerves after mechanical non-noxious stimulation of skin, Exp. Brain Res., 20 (1974) 115-123. 3 J~,NIO,W., SATO,A., A~D SCHMmT, R. F., Reflexes in postganglionic cutaneous fibres by stimulation of group I to group IV somatic afferents, Pfliigers Arch. ges. PhysioL, 331 (1972) 244--256. 4 J.g.NIG, W., AND SCttMIDT, R. F., Single unit responses in the cervical sympathetic trunk upon somatic nerve stimulation, Pfliigers Arch. ges. Physiol., 314 (1970) 199-216. 5 KOIZUMI,K., AND BROOKS, C. McC., The integration of autonomic reactions: a discussion of autonomic reflexes, their control and their association with somatic reactions, Ergebn. Physiol., 67 (1972) 1-68. 6 LLOYD, D. P. C., The classification of galvanic skin reflex afferent fibers, Proc. nat. Acad. Sci. (Wash.), 48 (1962) 814-817. 7 PATTON,H. D., Secretory innervation of the cat's foot-pad, Y. NeurophysioL, 11 (1948) 211-227.
150 8 SATO,A., KAUFMANN,A., KOIZUMI,K., AND BROOKS, C. McC., Afferent nerve groups and sympathetic reflex pathways, Brain Research, 14 (1969) 575-587. 9 SATO, A., AND SCHMrOT, R. F., Ganglionic transmission of somatically induced sympathetic reflexes, Pfliigers Arch. ges. Physiol., 326 (1971) 240-253. 10 SATO,A., AND SCHMIDT,R. F., Spinal and supraspinal components of the reflex discharges into lumbar and thoracic white rami, J. Physiol. (Lond.), 212 (1971) 839-850. 11 SATO,A., AND SCHMIDT,R. F., Somatosympathetic reflexes: afferent fibers, central pathways, discharge characteristics, Physiol. Rev., 53 (1973) 916-947. 12 SCHMrOT,R. F., Pre- and postganglionic neurons as final common pathways of somato-sympathetic reflexes. In W. UMBACHANDH. P. KOEPCHEN(Eds.), Central Rhythmic and Regulation, Hippokrates, Stuttgart, 1974, pp. 178-190. 13 SCHMIOT,R. F., AND SCH6NFUSS,K., An analysis of the reflex activity in the cervical sympathetic trunk induced by myelinated somatic afferents, Pfliigers Arch. ges. PhysioL, 314 (1970) 175-198. 14 WANG,G. H., The Neural ControlofSweating, Univ. Wisconsin Press, Madison, 1964, pp. 1-130. 15 WANG,G. H., AND HIND, J. E., Supraspinal origin of a poststimulatory long-lasting inhibition of galvanic skin reflex, J. NeurophysioL, 22 (1959) 360-366.