Long-range afferents in the rat spinal cord. II. Arborizations that penetrate grey matter.

1. The caudal extent of the collateral arborizations of entering sensory fibres in rat spinal cord was investigated by two methods: bulk labelling of peripheral nerves by injection of horseradish peroxidase conjugated to cholera toxin (B-HRP) and by antidromic stimulation using small currents from microelectrodes in the spinal cord while recording from single units in peripheral nerve or dorsal root. 2. The results show that injection of B-HRP into the sural or sciatic nerve labelled sural afferents in the grey matter three to four segments caudal to their root entry and sciatic nerve fibres were located in S4, the most caudal segment examined, four to six segments caudal to their root entry. 3. Detailed mapping with microelectrode stimulation showed that the parent descending fibres from filaments dissected from the L1 dorsal root coursed more than 20 mm, seven to eight segments caudal to the entry point in the dorsal columns and sent branches into the grey matter. Single units from the sural nerve were also followed caudally into the S2 and S3 spinal cord segments and also issued collateral branches into the grey matter. 4. The present results suggest that there is close agreement in the caudal penetration of long-ranging afferents by using complementary anatomical and electrophysiological methods.     

Effect of multiple dorsal rhizotomies on calcitonin gene-related peptide-like immunoreactivity in the lumbosacral dorsal spinal cord of the cat: a radioimmunoassay analysis

Calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) was measured by radioimmunoassay in the cat lumbosacral dorsal spinal cord following unilateral dorsal rhizotomy of 5 consecutive dorsal roots. The dorsal rhizotomies greatly reduced but did not eliminate the CGRP-LI from the ipsilateral rhizotomized segments. The amount of CGRP-LI remaining in the rhizotomized segments was greatest in the most caudal segment (846 +/- 311 pmoles/g tissue) and decreased below 300 pmoles/g tissue in the remaining segments. When these values were compared to the intact contralateral side, the percent CGRP remaining ranged from 65% in the sacral segments to less than 20% in the lumbar segments. Rostral to the rhizotomized segments there was a gradual return of CGRP-LI to control levels within 3 segments. Small diameter primary afferent fibers are the only known source of CGRP within the dorsal spinal cord. These results suggest that the most likely origin of the CGRP that remained in the rhizotomized lumbar segments was the rostrally and caudally projecting branches of ipsilateral primary afferents that entered the spinal cord through intact dorsal roots caudal and rostral to the transected roots. These results support the hypothesis that small diameter primary afferents project several segments in the cat spinal cord.     

Mechanism of expiratory muscle activation during lower thoracic spinal cord stimulation.

Lower thoracic spinal cord stimulation (SCS) may be a useful method to restore an effective cough mechanism. In dogs, two groups of studies were performed to evaluate the mechanism of the expiratory muscle activation during stimulation at the T(9)-T(10) level, which results in the greatest changes in airway pressure. In one group, expiratory muscle activation was monitored by evoked muscle compound action potentials (CAPs) from the internal intercostal muscles in the 10th, 11th, and 12th interspaces and from portions of the external oblique innervated by the L(1) and L(2) motor roots. SCS, applied with single shocks, resulted in short-latency CAPs at T(10) but not at more caudal levels. SCS resulted in long-latency CAPs at each of the more caudal caudal recording sites. Bilateral dorsal column sectioning, just below the T(11) spinal cord level, did not affect the short-latency CAPs but abolished the long-latency CAPs and also resulted in a fall in airway pressure generation. In the second group, sequential spinal root sectioning was performed to assess their individual mechanical contribution to pressure generation. Section of the ventral roots from T(8) through T(10) resulted in negligible changes, whereas section of more caudal roots resulted in a progressive reduction in pressure generation. We conclude that 1) SCS at the T(9)-T(10) level results in direct activation of spinal cord roots within two to three segments of the stimulating electrode and activation of more distal roots via spinal cord pathways, and 2) pathway activation of motor roots makes a substantial contribution to pressure generation.     

Alterations in growth-associated protein (GAP-43) expression in lower urinary tract pathways following chronic spinal cord injury

Alterations in the expression of growth-associated protein 43 (GAP-43) were examined in lower urinary tract micturition reflex pathways 6 or 8 weeks following complete spinal cord transection (~ T9). In control animals, expression of GAP-43 was present in specific regions of the gray matter in the rostral lumbar and caudal lumbosacral spinal cord, including: (1) the dorsal commissure; (2) the corticospinal tract; (3) the dorsal horn; and (4) the regions of the intermediolateral cell column (L1-L2) and the sacral parasympathetic nucleus (L6-S1); and (5) in the lateral collateral pathway of Lissauer in L6-S1 spinal segments. Densitometry analysis has demonstrated significant increases (p 0.001; 1.3-6.4-fold increase) in GAP-43-immunoreactivity (IR) in these regions of the rostral lumbar (L1-L2) and caudal lumbosacral (L6-S1) spinal cord 6 weeks following spinal cord injury. Changes in GAP-43-IR were restricted to the L1-L2 and L6-S1 segments that are involved in lower urinary tract reflexes. Changes in GAP-43-IR were not observed at the L5 segmental level except for an increase in GAP-43-IR in the superficial, dorsal horn at 6 weeks post-injury. In all segments examined, GAP-43-IR was decreased (2-5-fold) in the corticospinal tract (dorsal division) 6 and 8 weeks following spinal cord injury. Eight weeks following spinal cord injury, changes in GAP-43-IR had returned to control levels except for the persistence of increased GAP-43-IR in the region of the sacral parasympathetic nucleus and the lateral collateral pathway in the S1 spinal segment. Alterations in GAP-43-IR following chronic spinal cord injury may suggest a reorganization of bladder afferent projections and spinal elements involved in urinary bladder reflexes consistent with alterations in urinary bladder function (hyperreflexia) observed in animals following spinal cord injury above the lumbosacral spinal cord.     

Alterations in growth-associated protein (GAP-43) expression in lower urinary tract pathways following chronic spinal cord injury

Alterations in the expression of growth-associated protein 43 (GAP-43) were examined in lower urinary tract micturition reflex pathways 6 or 8 weeks following complete spinal cord transection (approximately T9). In control animals, expression of GAP-43 was present in specific regions of the gray matter in the rostral lumbar and caudal lumbosacral spinal cord, including: (1) the dorsal commissure; (2) the corticospinal tract; (3) the dorsal horn; and (4) the regions of the intermediolateral cell column (L1-L2) and the sacral parasympathetic nucleus (L6-S1); and (5) in the lateral collateral pathway of Lissauer in L6-S1 spinal segments. Densitometry analysis has demonstrated significant increases (p < or =0.001; 1.3-6.4-fold increase) in GAP-43-immunoreactivity (IR) in these regions of the rostral lumbar (L1-L2) and caudal lumbosacral (L6-S1) spinal cord 6 weeks following spinal cord injury. Changes in GAP-43-IR were restricted to the L1-L2 and L6-S1 segments that are involved in lower urinary tract reflexes. Changes in GAP-43-IR were not observed at the L5 segmental level except for an increase in GAP-43-IR in the superficial, dorsal horn at 6 weeks post-injury. In all segments examined, GAP-43-IR was decreased (2-5-fold) in the corticospinal tract (dorsal division) 6 and 8 weeks following spinal cord injury. Eight weeks following spinal cord injury, changes in GAP-43-IR had returned to control levels except for the persistence of increased GAP-43-IR in the region of the sacral parasympathetic nucleus and the lateral collateral pathway in the S1 spinal segment. Alterations in GAP-43-IR following chronic spinal cord injury may suggest a reorganization of bladder afferent projections and spinal elements involved in urinary bladder reflexes consistent with alterations in urinary bladder function (hyperreflexia) observed in animals following spinal cord injury above the lumbosacral spinal cord.     

Quantitative Changes in Myelin Proteins in a Peripheral Neuropathy Caused by Tullidora (Karwinskia humboldtiana)

Peripheral nerve demyelination was induced in cats by oral administration of ether extracts of Tullidora (Karwinskia humboldtiana). Proteins from several hindlimb nerves, spinal roots, and dorsal columns of the spinal cord were subjected to slab gel electrophoresis and quantified by densitometry. In Tullidora-treated cats with severe motor disturbances, specific myelin proteins were reduced by at least 50% in motor nerves and less than 25% in cutaneous axons. There was a greater decrease of these proteins in the distal than in the cephalad segments of the sciatic nerve; no changes were detected either in the spinal roots or in the white matter of the spinal cord. Electron microscopy revealed intense demyelination in the motor nerves only. Both the density of the 100 A-thick neurofilaments and the relative proportion of a polypeptide with a molecular weight of 68,000 were considerably increased in the affected nerves. It is tentatively concluded that the active principles of Tullidora may enter the axons through the motor nerve terminals. The distal segments of the motor nerves would then be preferentially affected and demyelination could result from axonal damage.     

The motor nuclei of the glossopharyngeal-vagal and the accessorius nerves in the rat

Retrograde cobalt labeling was performed by incubating the rootlets of cranial nerves IX, X and XI, or the central stumps of the same nerves, in a cobaltic lysine complex solution, and the distribution of efferent neurons sending their axons into these nerves was investigated in serial sections of the medulla and the cervical spinal cord in young rats. The following neuron groups were identified. The inferior salivatory nucleus lies in the dorsal part of the tegmentum at the rostral part of facial nucleus. It consists of a group of medium-sized and a group of small neurons. Their axons make a hair-pin loop at the midline and join the glossopharyngeal nerve. The dorsal motor nucleus of the vagus situates in the dorsomedial part of the tegmentum. Its rostral tip coincides with the first appearance of sensory fibres of the glossopharyngeal nerve, the caudal end extends into the pyramidal decussation. The constituting cells have globular or fusiform perikarya and they are the smallest known efferent neurons. The ambiguous nucleus is in the ventrolateral part of the tegmentum. The rostral tip lies dorsal to the facial nucleus, and the caudal tip extends to the level of the pyramidal decussation. The rostral one third of the ambiguous nucleus is composed of tightly-packed medium sized neurons, while larger neurons are arranged more diffusely in the caudal two thirds. The long dendrites are predominantly oriented in the dorsoventral direction. The dorsally-oriented axons take a ventral bend anywhere between the ambiguous nucleus and dorsal motor nucleus of the vagus. The motoneurons of the accessorius nerve are arranged in a medial, a lateral and a weak ventral cell column. The medial column begins at the caudal aspect of the pyramidal decussation and terminates in C2 spinal cord segment. The lateral and ventral columns begin in C2 segment and extend into C6 segment. The neurons have large polygonal perikarya and characteristic cross-shaped dendritic arborizations. The axons follow a dorsally-arched pathway between the ventral and dorsal horns. The accessorius motoneurons have no positional relation to any of the vagal efferent neurons. It is concluded that the topography and neuronal morphology of accessorius motoneurons do not warrant the designation of a bulbar accessorius nucleus and a bulbar accessorius nerve.     

Electrophysiological characteristics of lumbosacral evoked potentials in patients with established spinal cord injury

Surface electrodes positioned over the S1 and T12 vertebrate and referenced to T6 were used to record spinal potentials evoked by unilateral stimulation of the posterior tibial nerve at the knee. Data were collected on 24 patients who received spinal cord injuries 2 months to 31 years previously. The recording sites were below the level of spinal injury. The lumbosacral evoked potentials (LSEPs) were compared with the results of measurements obtained from 19 neurologically healthy subject. Additional data were collected on each patient to characterize segmental reflex responses and preservation of sensory and motor functions associated with the L5 through S2 segments of the spinal cord. Assuming that the LSEP reflects demonstrate a degree of spinal cord dysfunctions caudal to the area of injury in s substantial number of the patients with spinal cord injury which we studied.     

Transneuronal labeling of neurons in the adult rat central nervous system following inoculation of pseudorabies virus into the colon

Transneuronal tracing with pseudorabies virus (PRV) was used to identify sites in the central nervous system involved in the neural control of colon function. PRV-immunoreactive (IR) cells were primarily localized to the caudal lumbosacral (L6-S1) and caudal thoracic-rostral lumbar (T13-L1) spinal segments with the distribution varying according to survival time (72-96 h). In the lumbosacral spinal cord at all time points examined, significantly (PА.005) greater numbers of PRV-IR cells were present in the region of the sacral parasympathetic nucleus (SPN) of the S1 spinal segment compared to that of the L6 segment. These studies also revealed morphologically distinct cell types with a differential distribution (probably interneurons and preganglionic parasympathetic neurons) in the region of the SPN in the L6-S1 spinal segments following colon inoculation. PRV-labeled neurons were located at various levels of the neuraxis and at many sites had a distribution similar to that following injection of virus to other urogenital organs. However, some unique sites in the dorsal motor nucleus of the vagus, nucleus of the solitary tract, nucleus ambiguus and area postrema were also identified. To determine if labeling in these caudal medullary sites was mediated by spinal or vagal pathways, the colon was inoculated with PRV in animals with a complete spinal cord (T8) transection (5-7 days prior). Following spinal transection, PRV-infected cells were detected in the same caudal medullary regions; however, labeling in other regions (e.g., Barrington's nucleus) was eliminated or significantly reduced. These studies have yielded several novel observations concerning the central neural control of colonic function: (1) the preganglionic efferent and primary afferent innervation of the colon arises primarily from the S1 spinal segment; (2) the distribution of PRV-infected neurons in the central nervous system following colon inoculation was similar to that following PRV inoculation of other urogenital organs; (3) Barrington's nucleus, which has been identified previously as the pontine micturition center, may have a role in colonic function; and (4) PRV infection in Barrington's nucleus following colon inoculation is mediated by bulbospinal pathways whereas labeling in caudal medullary regions is mediated, at least in part, by vagal pathways.     

Terrapin muscle afferents studied by cord dorsum potential analyses

Rostro-caudal ramification of terrapin hindlimb afferent nerves have been studied by cord dorsum potential analyses. Stimulation of muscle and cutaneous nerves evoke different waveforms, related to the difference in fibre diameter spectra. Afferents of small muscles enter the cord through one spinal nerve, while afferents of large muscles are connected to the cord by up to four spinal roots. In their entrance segment muscle afferents bifurcate into branches extending in rostral and caudal direction over at least three segments.     

Stimulating regeneration in the damaged spinal cord.

Great progress has been made in recent years in experimental strategies for spinal cord repair. In this review we describe two of these strategies, namely the use of neurotrophic factors to promote functional regeneration across the dorsal root entry zone (DREZ), and the use of synthetic fibronectin conduits to support directed axonal growth. The junction between the peripheral nervous system (PNS) and central nervous system (CNS) is marked by a specialized region, the DREZ, where sensory axons enter the spinal cord from the dorsal roots. After injury to dorsal roots, axons will regenerate as far as the DREZ but no further. However, recent studies have shown that this barrier can be overcome and function restored. In animals treated with neurotrophic factors, regenerating axons cross the DREZ and establish functional connections with dorsal horn cells. For example, intrathecal delivery of neurotrophin 3 (NT3) supports ingrowth of A fibres into the dorsal horn. This ingrowth is revealed using a transganglionic anatomical tracer (cholera toxin subunit B) and analysis at light and electron microscopic level. In addition to promoting axonal growth, spinal cord repair is likely to require strategies for supporting long-distance regeneration. Synthetic fibronectin conduits may be useful for this purpose. Experimental studies indicate that fibronectin mats implanted into the spinal cord will integrate with the host tissue and support extensive and directional axonal growth. Growth of both PNS and CNS axons is supported by the fibronectin, and axons become myelinated by Schwann cells. Ongoing studies are aimed at developing composite conduits and promoting axonal growth from the fibronectin back into the spinal cord.     

Specific projections of sympathetic preganglionic neurons are not intrinsically determined by segmental origins of their cell bodies

Sympathetic preganglionic projections of the chick are segmentally specific. Neurons from the 16th cervical (C16) and the first thoracic (T1) spinal cord segments project almost exclusively in the rostral direction, while those from the fifth thoracic (T5) to the first lumbar (L1) spinal segments project almost exclusively in the caudal direction. Neurons from the intervening spinal cord segments (T2–4) project in rostral and caudal directions. There is also a tendency for rostrally located neurons in each segment to project rostrally and caudally located neurons to project caudally. To investigate whether specific projections of preganglionic neurons are intrinsically determined by segmental origins of their cell bodies, neural tube segments were transplanted or rotated in embryos at stages 19–26; these stages include times during and after preganglionic cell birth and just prior to axon outgrowth. When the T1 neural tube segment was replaced with the T5 or T7 neural tube segment, the transplanted T5 or T7 preganglionic neurons, now in the T1 position, projected rostrally. Conversely, when the T5 or T7 neural tube segment was replaced with the T1 neural tube, the transplanted T1 preganglionic neurons projected caudally. In addition, when individual T3 spinal cord segments were rotated 180° along the A-P axis, neurons which were originally in the caudal part of the segment projected rostrally, whereas neurons originally from the rostral part of the segment projected caudally. These results show that specific projections of preganglionic neurons are not intrinsically determined by segmental origins of their cell bodies. © 1998 John Wiley & Sons, Inc. J Neurobiol 35: 371–378, 1998     

Dorsal horn administration of muscimol abolishes the muscle pressor reflex.

The purpose of this study was to determine the effect of blocking synaptic transmission in the dorsal horn on the cardiovascular responses produced by activation of muscle afferent neurons. Synaptic transmission was blocked by applying the GABA(A) agonist muscimol to the dorsal surface of the spinal cord. Cats were anesthetized with alpha-chloralose and urethane, and a laminectomy was performed. With the exception of the L(7) dorsal root, the dorsal and ventral roots from L(5) to S(2) were sectioned on one side, and static contraction of the ipsilateral triceps surae muscle was evoked by electrically stimulating the peripheral ends of the L(7) and S(1) ventral roots. The dorsal surface of the L(4)--S(3) segments of the spinal cord were enclosed within a "well" created by applying layers of vinyl polysiloxane. Administration of a 1 mM solution of muscimol (based on dose-response data) into this well abolished the reflex pressor response to contraction (change in mean arterial blood pressure before was 47 +/- 7 mmHg and after muscimol was 3 +/- 2 mmHg). Muscle stretch increased mean arterial blood pressure by 30 +/- 8 mmHg before muscimol, but after drug application stretch increased MAP by only 3 +/- 2 mmHg. Limiting muscimol to the L(7) segment attenuated the pressor responses to contraction (37 +/- 7 to 24 +/- 11 mmHg) and stretch (28 +/- 2 to 16 +/- 8 mmHg). These data suggest that the dorsal horn of the spinal cord contains an obligatory synapse for the pressor reflex. Furthermore, these data support the hypothesis that branches of primary afferent neurons, not intraspinal pathways, are responsible for the multisegmental integration of the pressor reflex.     

正常小儿胫神经诱发脊髓电位特征和脑瘫小儿该电位的变化

采取刺激后胫神经(PTN)诱发叠加技术,利用体表无创伤性双极记录方法观察了16例正常小儿和43例脑瘫小儿的脊髓诱发电位(SCEP)。正常小儿的SCEP自下而上潜伏时逐渐延长、电压减小。从椎体C6到T10表现为Pa-Na-Pb三相波,T10～T12为Pa-Na1-Na2-Pb波,T12～L4为多相复合波。左右侧SCEP波形相似,潜伏时、电压相同,它们之间无统计学显著差别;但不同节段之间SCEP差异显著;脊髓传导速度为57.14m/s。脑瘫小儿SCEP正常者占14％;全髓反应低下者占20％;左右侧反应不对称者占46％;节段性反应低下者占15％;其它异常约占5％。不但节段间存在显著差异,而且全脊髓左右侧电压间以及颈、腰骶髓的潜伏时间出现显著差异。脊髓传导速度减低(患侧46.22m/s,对侧53.48m/s)。结果提示:(1)正常小儿脊髓活动左右对称,不同脊髓节段对PTN刺激反应不同。(2)脑瘫小儿脊髓活动左右不对称,一侧功能下降时对侧有一定代偿力,脊髓传导速度减慢。     

Functional organization of locomotor interneurons in the ventral lumbar spinal cord of the newborn rat

Although the mammalian locomotor CPG has been localized to the lumbar spinal cord, the functional-anatomical organization of flexor and extensor interneurons has not been characterized. Here, we tested the hypothesis that flexor and extensor interneuronal networks for walking are physically segregated in the lumbar spinal cord. For this purpose, we performed optical recordings and lesion experiments from a horizontally sectioned lumbar spinal cord isolated from neonate rats. This ventral hemi spinal cord preparation produces well-organized fictive locomotion when superfused with 5-HT/NMDA. The dorsal surface of the preparation was visualized using the Ca(2+) indicator fluo-4 AM, while simultaneously monitoring motor output at ventral roots L2 and L5. Using calcium imaging, we provided a general mapping view of the interneurons that maintained a stable phase relationship with motor output. We showed that the dorsal surface of L1 segment contains a higher density of locomotor rhythmic cells than the other segments. Moreover, L1 segment lesioning induced the most important changes in the locomotor activity in comparison with lesions at the T13 or L2 segments. However, no lesions led to selective disruption of either flexor or extensor output. In addition, this study found no evidence of functional parcellation of locomotor interneurons into flexor and extensor pools at the dorsal-ventral midline of the lumbar spinal cord of the rat.     

电刺激大鼠皮神经外周端对相邻脊髓节段皮神经内Aβ纤维的机械感受特性的影响

为观察Aβ类初级传入纤维是否参与相邻脊髓节段外周末梢之间的信息传递及其相关机制 ,实验自近中端切断一侧T8～T12 脊髓节段背侧皮神经 ,将一支被切断的皮神经的外周端分离成数支细束 ,以单个Aβ纤维放电为指征 ,检测单位的传导速度、适应特性、机械感受阈值、感受野的形状和面积 ;在相邻脊髓节段、也与中枢断离的皮神经干上施加逆向电刺激 ( 0 45mA ,0 1ms,2 0Hz,10s) ,以观察该刺激对Aβ纤维的上述机械感受特性的影响。在 42只大鼠上共记录了 5 0个Aβ类单位。逆向电刺激相邻节段皮神经后 ,60 6% (n =3 3 )的单位感受野增大 ,全部单位的感受野平均面积从 8 94± 6 5 1mm2 显著增加到 2 0 3 4± 16 17mm2 (P <0 0 1)。 81 8% (n =2 0 )的单位感受野形状从点状、圆或与身体长轴垂直的椭圆变成与身体长轴斜行或平行的椭圆。 68 0 % (n =5 0 )的单位机械感受阈值下降 ,全部单位的平均阈值从 2 3 7± 1 2 4mN降至 2 2 9± 1 2 4mN (P <0 0 5 )。上述机械感受特性的改变可持续 5 2 2 3± 9 2 7至 5 6 93± 15 76min。跨节段电刺激后 ,有 5 0 0 % (n =5 0 )的单位同时出现放电的增加 ,但该增加仅持续 1 5 2± 0 46min ,显著短于机械感受特性改变的时程 (P <0 0 1)。有机械感受特性改变的单位也     

Regeneration of ventral root axons into dorsal roots as shown by increased acetylcholinesterase activity

Regeneration of ventral root axons of the lumbar seventh (L7) segment into the dorsal L7 roots on the opposite side of cat spinal cord was shown by changes in the levels of acetylcholinesterase (AChE) and pseudocholinesterase (PsChE). Low levels of AChE and PsChE were found in control dorsal roots, but when regenerating ventral root fibers entered the dorsal roots, there was a doubling of AChE activity within 2 weeks. Growth appears to start some time after the first week; this is in accord with earlier evidence based on axoplasmic flow of isotope labeled protein in this experimental preparation. The level of AChE activity in the reinnervated dorsal roots increased continually for about 100 days before reaching a plateau at approximately 20 × control levels. The gradual increase and the plateau of AChE activity is in accord with a maturation of the ventral root fibers which had regenerated into the dorsal roots. PsChE in the dorsal roots changes in parallel with AChE in a ratio of 1:10, suggesting that PsChE may in part be localized in the regenerating axons.     

Distribution of myelinated and nonmyelinated nerve fibers of a cat cutaneous nerve in the spinal roots

The distribution of myelinated and nonmyelinated nerve fibers of the saphenous nerve of cats in the ventral and dorsal roots of the spinal cord was investigated by methods improving the signal—noise ratio in records of evoked responses from the nerve. The fibers of this nerve enter the spinal cord through roots of segments L_4–6. Nerve fibers with conduction velocities of between 80 and 0.38 m/sec were distributed in the dorsal roots of these segments. Four groups of nerve fibers with conduction velocities of 80–60, 40–30, 12.0–3.0, and 1.1–0.51 m/sec, possibly afferent in nature, were found in the ventral roots. The conditions of origin and detection of low-amplitude potentials in the roots of the spinal cord and the probable functional role of the nerve fibers in the ventral roots are discussed.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 647–654, November–December, 1975.     

Long-term acrylamide intoxication induces atrophy of dorsal root ganglion A-cells and of myelinated sensory axons

We have examined the effects of acrylamide on primary sensory nerve cell bodies and their myelinated axons in chronic acrylamide intoxication. The numbers and sizes of dorsal root ganglion cell bodies (L5) and myelinated nerve fibers were estimated with sterelogical techniques in severely disabled rats which had been treated with 33.3 mg/kg acrylamide twice a week for 7.5 weeks. There was no loss of dorsal root ganglion cells or myelinated nerve fibers in the roots, the sciatic nerve, sural nerve, and a tibial nerve branch. The mean perikaryal volume of A-cells was reduced by 20% (2P < 0.001) from 50000 μm³ in controls (CV = 0.13) to 40000 μm³ (0.12), whereas B-cell volume was unchanged. All size-frequency distribution curves of myelinated axon area of peripheral nerves and sensory roots were shifted to the left towards smaller values in rats exposed to acrylamide. In the L5 sensory root 3 mm from the ganglion, there was a significant reduction of mean cross sectional area of myelinated axons by 14% (2P < 0.05) from 7.6 μm² (0.11) in controls to 6.5 μm² (0.13) in intoxicated rats. The mean cross sectional area of myelinated sural nerve axons was reduced by 22% (2P < 0.001) from 8.6 μm² (0.08) in controls to 6.7 μm² (0.17) in intoxicated rats. We conclude that chronic intoxication with acrylamide leads to selective atrophy of type A dorsal root ganglion cell bodies and simultaneous atrophy along their peripheral axons, whereas neuronal B-cell bodies and motor axons are spared. It is suggested that the neuronal atrophy might well represent a defect of neurofilament synthesis and transport.     

Comparative dimensions of propriospinal neurons of different structural and functional groups in cats

A statistical comparison was made of geometric characteristics (area of cross section of the soma and proximal dendrites and d_con, the diameter of the circle of equivalent area to it) of propriospinal neurons of the cat spinal cord labeled with horseradish peroxidase. The linear dimensions of these cells differed by a factor of about seven. The mean d_con of propriospinal neurons in the cervical, thoracic, and lumbar divisions, whose axons reach level L6-7, was 39.9, 30.8, and 36.9 µm, respectively; direct correlation between the size of the neurons and the length of their axons was thus not observed. Characteristics of distribution of sizes of units in the cervical and thoracic divisions indicate the presence of two cell populations forming long propriospinal tracts; one consisting of a few, large neurons, concentrated in the cervical segments, the other consisting of small neurons, distributed among the cervical and thoracic segments. The mean d_con of neurons in the cervical division whose axons reach more caudal segments of the same cervical division was 44.2 µm (on account of a considerable number of large units in the ventral horn), evidence of the large relative size of the short-axon propriospinal neurons in this division of the spinal cord. Neurons located in the dorsal parts of the dorsal horn were the smallest in size, those located in the ventral horn were the largest. No significant differences were found in the dimensions of propriospinal neurons with uncrossed and crossed axons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 238–247, March–April, 1984.