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Muscle sensory neurons in the spinal ganglia in the rat determined by the retrograde transport of horseradish peroxidase
EXPERIMENTAL
NEUROLOGY
70,438-445
(1980)
Muscle Sensory Neurons in the Spinal Ganglia in the Rat Determined by the Retrograde Transport of Horseradish Peroxidase HONGCHIEN
HA,
T.
KAO,
AND
E. C.
TAN’
Department of Anatomy, National Yang-Ming Medical College, Taipei China Medical College, Taichung, Taiwan, Republic of China Received
April
29,
and
1980
The method of retrograde transport of horseradish peroxidase (HRP) was used to identify muscle sensory neurons in the spinal ganglia in the rat. Experiments were conducted on 25 albino rats. Injections of 0.06 to 0.08 ml 2 to 20% Sigma type VI HRP were made unilaterally into anterior tibia1 muscle. Cells of origin of muscle receptors and motor endings in the same area where HRP was administered were demonstrated. The labeled cells, medium to large, were found in fourth and fifth lumbar ganglia ipsilateral to the site of injection. Simultaneously, labeled neurons were also found in the ipsilateral ventral horn of the same cord segments as the labeled sensory ganglia.
INTRODUCTION Spinal ganglia in mammals consist of large populations of neurons of various sizes and types. Except for the classic morphologic studies of the neurons in the ganglia (2-4, 8, 9, 18-20), the classification of the spinal ganglia neurons based on their receptor types has not been available. The present study takes advantage of the method of retrograde axonal transport of horseradish peroxidase (10-1.5, 17, 24) to label sensory neurons in the spinal ganglia after injection of muscle, tendon, and skin. Muscle was chosen for this study because it offers the advantage of labeling both sensory and motoneurons simultaneously. Abbreviations: HRP-horseradish peroxidase, DAB-3,3’-diaminobenzidine. 1 Dr. Ha was supported by a research grant from the National Health Administration, Republic of China. Thanks are due to Professors J. M. Sprague and C. N. Liu, Department of Anatomy and Institute of Neurological Sciences, University of Pennsylvania for critically reading this manuscript. 438
0014-4886/80/l 10438-08$02.00/O Copyright All rights
0 1980 by Academic Press, Inc. of reproduction in any form reserved.
SPINAL
MATERIALS
SENSORY
AND
NEURONS
439
METHODS
Twenty-five adult Sprague-Dawley rats weighing 250 to 300 g were used. In 23 animals injections of 0.06 to 0.08 ml 2 to 20% horseradish peroxidase (HRP), Sigma type VI, in saline were made unilaterally into a locus at the upper one-third of the tibialis anterior. Prior to and during injection of HRP, electromyography was recorded through insulated, stainless-steel electrodes inserted into the muscle adjacent to the injected site. Muscle activity (Fig. 1) was evoked by an acupuncture needle inserted into the muscle; this was then withdrawn and replaced by the HRP needle. Both electromyography and injection of HRP were made in situ without anesthesia. After survival times between 20 and 36 h, the animals were anesthetized with sodium pentobarbital and perfused through an intracardiac catheter with 200 ml normal saline followed by a solution of 4% glutaraldehyde and 4% sucrose in 0.1 M phosphate buffer at pH 7.3. Immediately after perfusion the leg on the injected side was dissected to determine the nerve innervating the muscle and trace it from the site of injection to the spinal cord. The lumbar spinal cord and spinal ganglia were removed immediately after dissection and immersed in 0.1 M phosphate buffer containing 30% sucrose and 4% glutaraldehyde and refrigerated overnight. The following morning, the tissue blocks including the third to sixth lumbar segments and corresponding ganglia were cut longitudinally and transversely, respectively, at 40 pm on a freezing microtome and the serial sections were collected in the phosphate buffer. These sections were then incubated 30 min at room temperature in Tris-HCl buffer (pH 7.6) containing 1% hydrogen peroxide and 3,3’-diaminobenzidine (DAB) (7). The histochemical reaction was stopped by placing the sections in distilled water and they were then mounted on glass slides coated with celloidin and counterstained lightly with 0.01% cresyl fast violet. Sections of spinal ganglia of third through sixth cord segments from two animals, without injection of HRP into muscle, were used as a control. Measurement of the cell body size of spinal ganglia neurons was made on both control animals and neurons containing HRP-positive granules from experimental animals. RESULTS Measurement of Lumbar Spinal Ganglion Neurons. Measurement of cell body size was made on 330 neurons chosen at random from the third through sixth lumbar spinal ganglion of control and experimental rats. The size of the cell body measured was quite variable, ranging from 17 x 14 to 83 x 69 pm in diameter. Based on the size of the cell body, these neurons could be divided into three categories: large (54 x 28 to 83 x 69
FIG. 1. Electromyogram recorded (B) injection of HRP. Open arrow needle and solid arrow indicates
from anterior tibia1 muscle in rat before (A) and during indicates onset of manual manipulation of acupuncture injection of HRP. 440
SPINAL
SENSORY
441
NEURONS
2k-5 2,0-jf( 30
20
0’ 0
I 20
I 40 MICRON
80
c 100
FIG. 2. Measurements of330lumbar spinal ganglion neurons in controland experimental rats.
km), medium (37 x 17 to 57 x 43 pm), and small (17 x 14 to 36 x 31 pm). The average cell body sizes of the large, medium, and small groups were 62 x 42, 45 x 28, and 25 x 20 pm, respectively (Fig. 2). HRP Study of Spinal Ganglion Neurons. After the injection of HRP into the tibialis anterior, retrogradely labeled neurons were found in spinal ganglia at levels L3 through L5 ipsilateral to the site of injection. The majority of labeled cells was observed in the fourth and fifth lumbar spinal ganglia, and no HRP-positive cells were found in L6. A few labeled cells were found scattered in the third lumbar spinal ganglion but these cases were of the prefixed type of lumbar plexus. The HRP reaction product of spinal ganglion neurons took the form of numerous fine brown granules distributed evenly within the cytoplasm (Fig. 3A). The cytoplasm of HRP reaction cells were chromatophobic to cresyl fast violet. Measurement of labeled neurons was made in 100 cells. The range was 40 x 23 to 83 x 54 pm and the average size 57 x 37 pm which was in the category of medium to large size. Occasionally, small neurons in the spinal ganglion were also labeled (34 x 14 pm). Motor Neurons Labeled with HRP. After injection of HRP into the anterior tibia1 muscle, labeled neurons were also found in the ipsilateral ventral horn of the same cord segments as the labeled sensory ganglia. HRP granules were distributed evenly within the cytoplasm and some extended into the initial p&ion of the dendrites (Fig. 3B). Concentration of HRP granules around the nucleus was occasionally observed. In addition to the large alpha neurons labeled in the ventral horn, a much smaller number of small gamma motor neurons (less than 30 pm in diameter) (5) were also labeled. The labeled motoneurons were chiefly in the dorsolateral portion of the ventral gray at L4 and gradually shifted ventrolaterally and descended to the level of L5 and tapered away (Fig. 4). The lamination concept of the spinal cord (21, 22) was not introduced for
FIG. 3. A-large spinal ganglion cell (L4) 20 h after injection of HRP into ipsilateral anterior tibia1 muscle in rat. The HRP reaction product is seen as fine granules within the cytoplasm. x 1187.5. B-an alpha motor neuron in the ventral horn (L4) 24 h after injection of HRP into the ipsilateral anterior tibia1 muscle in rat. HRP reaction product is more distinctive, seen as coarse granules distributed throughout the cytoplasm. x 1187.5.
SPINAL
SENSORY
NEURONS
443
FIG. 4. Composite drawing from cross sections of L4 and L5 of rat spinal cord showing the sites of motor neurons after injection of HRP into the ipsilateral anterior tibia1 muscle. The drawings are compiled from 15 experimental animals.
determining the location of labeled motor neurons because it is not established in the rat. DISCUSSION The morphologic distinction of sensory neurons in the spinal ganglia has not been possible until the recent application of the retrograde axon transport of horseradish peroxidase to the peripheral nerves (5, 6). After immersion of the sciatic nerve in HRP, labeled neurons were found throughout the extent of the ipsilateral dorsal root ganglia after 24 and 48 h (6). The present study demonstrated that injection of HRP into the anterior tibia1 muscle in the rat was sufficient to label the cell bodies of a number of spinal ganglia neurons. The labeled neurons were characterized by fine brown granules within the cytoplasm and by their size. Measurements indicated they belong to the medium to large categories. It is reasonable to assume that they supply muscle spindles which provide origins to the large-caliber, afferent fibers of groups I and II. Occasional small HRP-
444
HA, KAO,
AND TAN
labeled neurons were also found in the spinal ganglion. They are possibly related to the small-caliber neurons of groups III and IV which subserve muscular pain (16). The cells of origin of motor endings in the same region of the anterior tibia1 muscle were simultaneously labeled. Our results showed that labeled motor neurons formed a rather distinct cell column with the highest density at the level of the fourth lumbar segment. It differed from the segmental distribution of the same motor nucleus in the cat which occupies L6 and L7 (23). The differentiation of alpha and gamma motor neurons is based primarily on their size (1); they are intermingled in the motor nuclei. No marked difference was found in the appearance of HRP reaction product within the cytoplasm of alpha and gamma motor neurons. This finding is in contrast to that of Strick et al. (25) who stated that the HRPlabeled granules are both larger in diameter and more numerous in the gamma than in the alpha motor neurons. Finally, simultaneous labeling of medium to large size spinal ganglia neurons and both alpha and gamma motor neurons in the ventral horn of the same segment of the spinal cord after a relatively small injection of HRP into the anterior tibia1 muscle, indicates that muscle spindles and motor endings share a very close proximity in the muscle. REFERENCES 1. BRYAN, R. N., D. L. TREVINO, AND W. D. WILLIS. 1972. Evidence for a common location of alpha and gamma motoneurons. Brain Res. 38: 193-l%. 2. DAWSON, I. M., J. HOSSACK, AND G. M. WYBURN. 1955. Observation on the Nissl’s substance, cytoplasmic filaments and the nuclear membrane of spinal ganglion cells. Proc. R. Sot. London Ser.B 144: 132-142. 3. DOGIEL, A. S. 1898. Zur Frage iiber den Bau der Spinalganglien beim Menschen und bei den SBugetieren. Interant, Monatsschr. Anat. Physiol. 15: 343. 4. DOWEL, A. S. 1908. Der Bau der Spinalganglien des Menschen and der SBugetiere. Gusta; Fisher, Jena. 5. ELFVIN, L.-G., AND C. J. DALSGAARD. 1977. Retrograde axonal transport ofhorseradish peroxidase in afferent fibers of the inferior mensenteric ganglion of the guinea pig. Identification of the cells of origin in dorsal root ganglia. Brain Res. 126: 149- 153. 6. FURSTMAN, L., S. SAPORTA, AND L. KRUGER. 1975. Retrograde axonal transport of horseradish peroxidase in sensory nerves and ganglion cells of the rat. Brain Res. 84: 320-324.
f. GRAHAM, R. C., JR., AND M. J. KARNOVSKY. 1966. The early stages of absorption of injected horseradish peroxidase in the proximal tubules of mouse kidney: ultrastructural cytochemistry by a new technique. .I. Histochem. Cytochem. 14: 291-302. 8. HATAI, S. 1902 The finer structure of the spinal ganglion cells in the white rat. J.
Comp.
Neural.
11: l-24.
9. HESS, A. 1955. The fine structure of young and old spinal ganglia. Anat.
Rec.
123:
399-424.
10. KRISTENSSON, K., AND Y. OLSSON. 1971. Retrograde axonal transport of protein. Brain
Res.
20: 363-365.
SPINAL
SENSORY
NEURONS
445
11. KRISTENSSON, K. 1973. Uptake and retrograde axonal transport of protein tracers in hypoglossal neurons. Fate of a tracer and reaction of the nerve cell bodies. Acta
Neuropathol.
(Berlin)
23: 43-47.
12. KRISTENSSON, K., Y. OLSSON, AND J. SJ~STRAND. 1971. Axonal uptake and retrograde transport of exogenous proteins in the hypoglossal nerve. Brain Res. 32: 399-406. 13. LAVAIL, J. H., K. R. WINSTON, AND A. TISH. 1973. A method based on retrograde intraaxonal transport of protein for identification of cell bodies of origin of axons terminating within the CNS. Brain Res. 58: 470-477. 14. LAVAIL, J. H., AND M. M. LAVAIL. 1972. Retrograde axonal transport in the central nervous system. Science 176: 1416-1417. IS. LAVAIL, J. H. 1978. A review of the retrograde transport technique. Pages 355-384 in R. T. ROBERTSON, Ed., Methods in Physiological Psychology, Vol. II. Academic Press, New York. 16. MOUNTCASTLE, V. B. 1974. Medical Physiology, Vol. I, page 638. Mosley, St. Louis. 17. NAUTA, H. J. W., M. B. PRITZ, AND R. J. LASEK. 1974. Afferents to the rat caudoputamen studied with horseradish peroxidase. An evaluation of a retrograde neuroanatomical research method. Brain Res. 67: 219-238. 18. RAM~N, Y CAJAL, S. 1907. Die Struktur der sensiblen Ganglien des Menschen und der Tiere. Anat. Heft Abt. 2. 16: 177. 19. RAM~N, Y CAJAL, S. 1959. Summary of the normal structure of sensory ganglia. Pages 397-413 in R. M. May, Ed., Degeneration and Regeneration ofthe Nervous System, Vol. II. Hafner, New York. 20. RANSON, S. W. 1912. The structure of the spinal ganglia and of the spinal nerves. J. Comp. Neurol. 22: 159-175. 21. REXED, B. 1952. The cytoarchitectonic organization of the spinal cord in the cat. J.
Comp.
Neurol.
96: 415-495.
22. REXED, B. 1954. A cytoarchitectonic
atlas ofthe spinal cord in the cat. J. Comp.
Neural.
100: 297-380.
23. ROMANES, G. J. 1951. The motor cell columns of the lumbo-sacal cord of the cat. J. Comp.
Neural.
94: 313-363.
24. SPENCER, H. J., G. LYNCH, AND R. K. JONES. 1978. The use of somatofugal transport of horseradish peroxidase for tract tracing and cell labelling. Pages 291-316 in R. T. Robertson, Ed., Methods in Physiological Psychology, Vol. N. Academic Press, New York. 25. STRICK, P. L., R. E. BURKE, K. KANDA, C. C. KIM, AND B. WALMSLEY. 1976. Differences between alpha and gamma motoneurons labelled with horseradish peroxidase by retrograde transport. Brain Res. 113: 582-588.
NEUROLOGY
70,438-445
(1980)
Muscle Sensory Neurons in the Spinal Ganglia in the Rat Determined by the Retrograde Transport of Horseradish Peroxidase HONGCHIEN
HA,
T.
KAO,
AND
E. C.
TAN’
Department of Anatomy, National Yang-Ming Medical College, Taipei China Medical College, Taichung, Taiwan, Republic of China Received
April
29,
and
1980
The method of retrograde transport of horseradish peroxidase (HRP) was used to identify muscle sensory neurons in the spinal ganglia in the rat. Experiments were conducted on 25 albino rats. Injections of 0.06 to 0.08 ml 2 to 20% Sigma type VI HRP were made unilaterally into anterior tibia1 muscle. Cells of origin of muscle receptors and motor endings in the same area where HRP was administered were demonstrated. The labeled cells, medium to large, were found in fourth and fifth lumbar ganglia ipsilateral to the site of injection. Simultaneously, labeled neurons were also found in the ipsilateral ventral horn of the same cord segments as the labeled sensory ganglia.
INTRODUCTION Spinal ganglia in mammals consist of large populations of neurons of various sizes and types. Except for the classic morphologic studies of the neurons in the ganglia (2-4, 8, 9, 18-20), the classification of the spinal ganglia neurons based on their receptor types has not been available. The present study takes advantage of the method of retrograde axonal transport of horseradish peroxidase (10-1.5, 17, 24) to label sensory neurons in the spinal ganglia after injection of muscle, tendon, and skin. Muscle was chosen for this study because it offers the advantage of labeling both sensory and motoneurons simultaneously. Abbreviations: HRP-horseradish peroxidase, DAB-3,3’-diaminobenzidine. 1 Dr. Ha was supported by a research grant from the National Health Administration, Republic of China. Thanks are due to Professors J. M. Sprague and C. N. Liu, Department of Anatomy and Institute of Neurological Sciences, University of Pennsylvania for critically reading this manuscript. 438
0014-4886/80/l 10438-08$02.00/O Copyright All rights
0 1980 by Academic Press, Inc. of reproduction in any form reserved.
SPINAL
MATERIALS
SENSORY
AND
NEURONS
439
METHODS
Twenty-five adult Sprague-Dawley rats weighing 250 to 300 g were used. In 23 animals injections of 0.06 to 0.08 ml 2 to 20% horseradish peroxidase (HRP), Sigma type VI, in saline were made unilaterally into a locus at the upper one-third of the tibialis anterior. Prior to and during injection of HRP, electromyography was recorded through insulated, stainless-steel electrodes inserted into the muscle adjacent to the injected site. Muscle activity (Fig. 1) was evoked by an acupuncture needle inserted into the muscle; this was then withdrawn and replaced by the HRP needle. Both electromyography and injection of HRP were made in situ without anesthesia. After survival times between 20 and 36 h, the animals were anesthetized with sodium pentobarbital and perfused through an intracardiac catheter with 200 ml normal saline followed by a solution of 4% glutaraldehyde and 4% sucrose in 0.1 M phosphate buffer at pH 7.3. Immediately after perfusion the leg on the injected side was dissected to determine the nerve innervating the muscle and trace it from the site of injection to the spinal cord. The lumbar spinal cord and spinal ganglia were removed immediately after dissection and immersed in 0.1 M phosphate buffer containing 30% sucrose and 4% glutaraldehyde and refrigerated overnight. The following morning, the tissue blocks including the third to sixth lumbar segments and corresponding ganglia were cut longitudinally and transversely, respectively, at 40 pm on a freezing microtome and the serial sections were collected in the phosphate buffer. These sections were then incubated 30 min at room temperature in Tris-HCl buffer (pH 7.6) containing 1% hydrogen peroxide and 3,3’-diaminobenzidine (DAB) (7). The histochemical reaction was stopped by placing the sections in distilled water and they were then mounted on glass slides coated with celloidin and counterstained lightly with 0.01% cresyl fast violet. Sections of spinal ganglia of third through sixth cord segments from two animals, without injection of HRP into muscle, were used as a control. Measurement of the cell body size of spinal ganglia neurons was made on both control animals and neurons containing HRP-positive granules from experimental animals. RESULTS Measurement of Lumbar Spinal Ganglion Neurons. Measurement of cell body size was made on 330 neurons chosen at random from the third through sixth lumbar spinal ganglion of control and experimental rats. The size of the cell body measured was quite variable, ranging from 17 x 14 to 83 x 69 pm in diameter. Based on the size of the cell body, these neurons could be divided into three categories: large (54 x 28 to 83 x 69
FIG. 1. Electromyogram recorded (B) injection of HRP. Open arrow needle and solid arrow indicates
from anterior tibia1 muscle in rat before (A) and during indicates onset of manual manipulation of acupuncture injection of HRP. 440
SPINAL
SENSORY
441
NEURONS
2k-5 2,0-jf( 30
20
0’ 0
I 20
I 40 MICRON
80
c 100
FIG. 2. Measurements of330lumbar spinal ganglion neurons in controland experimental rats.
km), medium (37 x 17 to 57 x 43 pm), and small (17 x 14 to 36 x 31 pm). The average cell body sizes of the large, medium, and small groups were 62 x 42, 45 x 28, and 25 x 20 pm, respectively (Fig. 2). HRP Study of Spinal Ganglion Neurons. After the injection of HRP into the tibialis anterior, retrogradely labeled neurons were found in spinal ganglia at levels L3 through L5 ipsilateral to the site of injection. The majority of labeled cells was observed in the fourth and fifth lumbar spinal ganglia, and no HRP-positive cells were found in L6. A few labeled cells were found scattered in the third lumbar spinal ganglion but these cases were of the prefixed type of lumbar plexus. The HRP reaction product of spinal ganglion neurons took the form of numerous fine brown granules distributed evenly within the cytoplasm (Fig. 3A). The cytoplasm of HRP reaction cells were chromatophobic to cresyl fast violet. Measurement of labeled neurons was made in 100 cells. The range was 40 x 23 to 83 x 54 pm and the average size 57 x 37 pm which was in the category of medium to large size. Occasionally, small neurons in the spinal ganglion were also labeled (34 x 14 pm). Motor Neurons Labeled with HRP. After injection of HRP into the anterior tibia1 muscle, labeled neurons were also found in the ipsilateral ventral horn of the same cord segments as the labeled sensory ganglia. HRP granules were distributed evenly within the cytoplasm and some extended into the initial p&ion of the dendrites (Fig. 3B). Concentration of HRP granules around the nucleus was occasionally observed. In addition to the large alpha neurons labeled in the ventral horn, a much smaller number of small gamma motor neurons (less than 30 pm in diameter) (5) were also labeled. The labeled motoneurons were chiefly in the dorsolateral portion of the ventral gray at L4 and gradually shifted ventrolaterally and descended to the level of L5 and tapered away (Fig. 4). The lamination concept of the spinal cord (21, 22) was not introduced for
FIG. 3. A-large spinal ganglion cell (L4) 20 h after injection of HRP into ipsilateral anterior tibia1 muscle in rat. The HRP reaction product is seen as fine granules within the cytoplasm. x 1187.5. B-an alpha motor neuron in the ventral horn (L4) 24 h after injection of HRP into the ipsilateral anterior tibia1 muscle in rat. HRP reaction product is more distinctive, seen as coarse granules distributed throughout the cytoplasm. x 1187.5.
SPINAL
SENSORY
NEURONS
443
FIG. 4. Composite drawing from cross sections of L4 and L5 of rat spinal cord showing the sites of motor neurons after injection of HRP into the ipsilateral anterior tibia1 muscle. The drawings are compiled from 15 experimental animals.
determining the location of labeled motor neurons because it is not established in the rat. DISCUSSION The morphologic distinction of sensory neurons in the spinal ganglia has not been possible until the recent application of the retrograde axon transport of horseradish peroxidase to the peripheral nerves (5, 6). After immersion of the sciatic nerve in HRP, labeled neurons were found throughout the extent of the ipsilateral dorsal root ganglia after 24 and 48 h (6). The present study demonstrated that injection of HRP into the anterior tibia1 muscle in the rat was sufficient to label the cell bodies of a number of spinal ganglia neurons. The labeled neurons were characterized by fine brown granules within the cytoplasm and by their size. Measurements indicated they belong to the medium to large categories. It is reasonable to assume that they supply muscle spindles which provide origins to the large-caliber, afferent fibers of groups I and II. Occasional small HRP-
444
HA, KAO,
AND TAN
labeled neurons were also found in the spinal ganglion. They are possibly related to the small-caliber neurons of groups III and IV which subserve muscular pain (16). The cells of origin of motor endings in the same region of the anterior tibia1 muscle were simultaneously labeled. Our results showed that labeled motor neurons formed a rather distinct cell column with the highest density at the level of the fourth lumbar segment. It differed from the segmental distribution of the same motor nucleus in the cat which occupies L6 and L7 (23). The differentiation of alpha and gamma motor neurons is based primarily on their size (1); they are intermingled in the motor nuclei. No marked difference was found in the appearance of HRP reaction product within the cytoplasm of alpha and gamma motor neurons. This finding is in contrast to that of Strick et al. (25) who stated that the HRPlabeled granules are both larger in diameter and more numerous in the gamma than in the alpha motor neurons. Finally, simultaneous labeling of medium to large size spinal ganglia neurons and both alpha and gamma motor neurons in the ventral horn of the same segment of the spinal cord after a relatively small injection of HRP into the anterior tibia1 muscle, indicates that muscle spindles and motor endings share a very close proximity in the muscle. REFERENCES 1. BRYAN, R. N., D. L. TREVINO, AND W. D. WILLIS. 1972. Evidence for a common location of alpha and gamma motoneurons. Brain Res. 38: 193-l%. 2. DAWSON, I. M., J. HOSSACK, AND G. M. WYBURN. 1955. Observation on the Nissl’s substance, cytoplasmic filaments and the nuclear membrane of spinal ganglion cells. Proc. R. Sot. London Ser.B 144: 132-142. 3. DOGIEL, A. S. 1898. Zur Frage iiber den Bau der Spinalganglien beim Menschen und bei den SBugetieren. Interant, Monatsschr. Anat. Physiol. 15: 343. 4. DOWEL, A. S. 1908. Der Bau der Spinalganglien des Menschen and der SBugetiere. Gusta; Fisher, Jena. 5. ELFVIN, L.-G., AND C. J. DALSGAARD. 1977. Retrograde axonal transport ofhorseradish peroxidase in afferent fibers of the inferior mensenteric ganglion of the guinea pig. Identification of the cells of origin in dorsal root ganglia. Brain Res. 126: 149- 153. 6. FURSTMAN, L., S. SAPORTA, AND L. KRUGER. 1975. Retrograde axonal transport of horseradish peroxidase in sensory nerves and ganglion cells of the rat. Brain Res. 84: 320-324.
f. GRAHAM, R. C., JR., AND M. J. KARNOVSKY. 1966. The early stages of absorption of injected horseradish peroxidase in the proximal tubules of mouse kidney: ultrastructural cytochemistry by a new technique. .I. Histochem. Cytochem. 14: 291-302. 8. HATAI, S. 1902 The finer structure of the spinal ganglion cells in the white rat. J.
Comp.
Neural.
11: l-24.
9. HESS, A. 1955. The fine structure of young and old spinal ganglia. Anat.
Rec.
123:
399-424.
10. KRISTENSSON, K., AND Y. OLSSON. 1971. Retrograde axonal transport of protein. Brain
Res.
20: 363-365.
SPINAL
SENSORY
NEURONS
445
11. KRISTENSSON, K. 1973. Uptake and retrograde axonal transport of protein tracers in hypoglossal neurons. Fate of a tracer and reaction of the nerve cell bodies. Acta
Neuropathol.
(Berlin)
23: 43-47.
12. KRISTENSSON, K., Y. OLSSON, AND J. SJ~STRAND. 1971. Axonal uptake and retrograde transport of exogenous proteins in the hypoglossal nerve. Brain Res. 32: 399-406. 13. LAVAIL, J. H., K. R. WINSTON, AND A. TISH. 1973. A method based on retrograde intraaxonal transport of protein for identification of cell bodies of origin of axons terminating within the CNS. Brain Res. 58: 470-477. 14. LAVAIL, J. H., AND M. M. LAVAIL. 1972. Retrograde axonal transport in the central nervous system. Science 176: 1416-1417. IS. LAVAIL, J. H. 1978. A review of the retrograde transport technique. Pages 355-384 in R. T. ROBERTSON, Ed., Methods in Physiological Psychology, Vol. II. Academic Press, New York. 16. MOUNTCASTLE, V. B. 1974. Medical Physiology, Vol. I, page 638. Mosley, St. Louis. 17. NAUTA, H. J. W., M. B. PRITZ, AND R. J. LASEK. 1974. Afferents to the rat caudoputamen studied with horseradish peroxidase. An evaluation of a retrograde neuroanatomical research method. Brain Res. 67: 219-238. 18. RAM~N, Y CAJAL, S. 1907. Die Struktur der sensiblen Ganglien des Menschen und der Tiere. Anat. Heft Abt. 2. 16: 177. 19. RAM~N, Y CAJAL, S. 1959. Summary of the normal structure of sensory ganglia. Pages 397-413 in R. M. May, Ed., Degeneration and Regeneration ofthe Nervous System, Vol. II. Hafner, New York. 20. RANSON, S. W. 1912. The structure of the spinal ganglia and of the spinal nerves. J. Comp. Neurol. 22: 159-175. 21. REXED, B. 1952. The cytoarchitectonic organization of the spinal cord in the cat. J.
Comp.
Neurol.
96: 415-495.
22. REXED, B. 1954. A cytoarchitectonic
atlas ofthe spinal cord in the cat. J. Comp.
Neural.
100: 297-380.
23. ROMANES, G. J. 1951. The motor cell columns of the lumbo-sacal cord of the cat. J. Comp.
Neural.
94: 313-363.
24. SPENCER, H. J., G. LYNCH, AND R. K. JONES. 1978. The use of somatofugal transport of horseradish peroxidase for tract tracing and cell labelling. Pages 291-316 in R. T. Robertson, Ed., Methods in Physiological Psychology, Vol. N. Academic Press, New York. 25. STRICK, P. L., R. E. BURKE, K. KANDA, C. C. KIM, AND B. WALMSLEY. 1976. Differences between alpha and gamma motoneurons labelled with horseradish peroxidase by retrograde transport. Brain Res. 113: 582-588.