Loss of sensory neurons after sciatic nerve section in the rat

In this study, the loss of sensory neurons in the rat was assessed after sciatic nerve section at birth and at 4 weeks of age. The neuronal deficit in ganglia L4-L6, 39-89 weeks after neonatal denervation, was 10,000-17,000. The nerve contains about 19,000 afferent axons, so some axotomized neurons survived. Degenerating perikarya were absent, probably because all surviving neurons had reestablished target contacts. Sectioning the nerve at age 4 weeks, in five rats, after 19-92 weeks had caused the death of 7,000-11,500 neurons. Whether the nerve regenerated or not in these rats apparently did not influence the extent of neuron death. Nevertheless, no deficit was observed in a sixth rat in which muscle reinnervation was very good. Therefore, the results are inconclusive with respect to the effect of axonal regeneration. Ganglia of rats operated at age 4 weeks regularly contained perikarya with axonal reaction; this supports the notion that some mature neurons are able to permanently survive without target contact. There was no evidence for selective loss of large or small neurons after nerve section at birth or at age 4 weeks. The extent of cell loss in individual ganglia varied, indicating varying contributions of the three ganglia to the nerve. Hence, it is not possible to quantify the effect of experimental conditions on the number of sensory neurons when only one of the several ganglia contributing to the nerve is investigated.     

Effect of chronic sciatic nerve section on saphenous nerve input to midline bulboreticular formation in the rat

The sciatic nerve was transected unilaterally 7-10 weeks before electrophysiological single unit recordings were made from somatically activated neurons in the midline bulboreticular formation of the rat. Their responses to high-intensity electrical stimulation of the saphenous nerve area were significantly stronger on the lesioned side. In control rats no such side difference was found. The result indicates that sciatic nerve transection unmasks polysynaptic somatic input to the midline bulboreticular formation.     

周围神经65KD蛋白在损伤性大鼠坐骨神经中的表达

目的：研究周围神经６５ＫＤ蛋白在损伤性大鼠坐骨神经中的分布与表达。方法：取损伤１５ｄ后的大鼠坐骨神经近侧端及远侧端,冰冻切片,与抗６５ＫＤ蛋白单克隆抗体与切片孵育后,加羊抗小鼠ＩｇＧＨＲＰ,ＤＡＢ反应成色。结果：大鼠坐骨神经远侧端及近侧端中均有６５ＫＤ蛋白阳性免疫反应产物,阳性免疫反应产物位于雪旺氏细胞。阳性免疫反应产物的密度及强度在神经的远侧端大于近侧端。结论：神经诱向因子６５ＫＤ蛋白由雪旺氏细胞产生。在损伤后神经近、远侧端都存在６５ＫＤ蛋白,远侧端的强度大于近侧端,这一浓度梯度可能是诱导再生的神经纤维定向生长过程中的一个重要因素。     

Altered metabolism of rat contralateral sciatic nerve after microinjection into the endoneurium of the ipsilateral sciatic nerve

Microinjection of substances into the endoneurium of the sciatic nerve is a technique widely used. Because the contralateral nerve is often used as control nerve, we studied the incorporation of [14C]galactose into myelin lipids in normal nerves, saline-injected nerves and their contralateral nerves. Results show that incorporation of radioactivity into contralateral nerve lipids is affected as compared with normal nerves. We conclude that the contralateral nerve of an injected nerve is not a good control.     

Altered expression of nectin-like adhesion molecules in the peripheral nerve after sciatic nerve transection

Following axotomy several processes involving cell-cell interaction occur, such as loss of synapses, axon guidance, and remyelination. Two recently discovered families of cell-cell adhesion molecules, nectins and nectin-like molecules (necls) are involved in such processes in vitro and during development, but their roles in nerve injury have been largely unknown until recently. We have previously shown that axotomized motoneurons increase their expression of nectin-1 and nectin-3 and maintain a high expression of necl-1. We here investigate the expression of potential binding partners for motoneuron nectins and necls in the injured peripheral nerve. In situ hybridization (ISH) revealed a decreased signal for necl-1 mRNA in the injured nerve, whereas no signal for necl-2 was detected before or after injury. The signals for necl-4 and necl-5 mRNA both increased in the injured nerve and necl immunoreactivity displayed a close relation to axon and Schwann cell markers. Finally, signal for mRNA encoding necl-5 increased in axotomized spinal motoneurons. We conclude that peripheral axotomy results in altered expression of several necls in motoneurons and Schwann cells, suggesting involvement of the molecules in regeneration.     

Activity of foot skin mechanoreceptors and afferent nerve fibres in the adult rat sciatic nerve are altered after central axotomy of sensory neurons

The functional properties of skin mechanoreceptors were examined in the hind foot of normal rats in comparison with animals subjected to dorsal rhizotomy. Evoked nerve impulses were recorded from afferent nerve fibres of the tibial nerve. The decentralized mechanoreceptors displayed evidence of autonomous functioning, but with several abnormalities as compared to normal animals. There was a decreased sensitivity to mechanical stimulation and a lower adaptive capacity as a consequence of rhizotomy. The underlying mechanism is suggested to be a loss of central trophic support because of the interrupted link between the central nervous system and the sensory ganglion cell periphery.The findings indicate that mechanical receptors continue functioning under conditions when sensory impulses flow cannot reach postsynaptic target neurons in the central nervous system, but stop at the level of the primary sensory neuron.     

The effect of intrathecal galanin on the flexor reflex in rat: increased depression after sciatic nerve section

The effect of intrathecal galanin (GAL) on the hamstring flexor reflex to sural nerve stimulation was compared in rats with intact and unilaterally sectioned sciatic nerves. GAL had a biphasic effect on the flexor reflex in rats with intact nerves, including facilitation, facilitation followed by depression and pure depression, in a dose-dependent manner. In axotomized rats, the depressive effect of GAL was significantly increased, occurring at lower drug concentrations. Furthermore, the degree of depression was significantly stronger with a more rapid onset after nerve section. It is concluded that along with an increase in GAL-like immunoreactivity in primary afferents, the inhibitory function of this neuropeptide is enhanced following axotomy. This functional change may be due to both pre- and postsynaptic mechanisms.     

Plasticity of the peptidergic mediation of spinal reflex facilitation after peripheral nerve section in the rat.

The effects of the tachykinin antagonist Spantide II (D-Nic-Lys1,3-Pal3,D-Cl2Phe5,Asn6,D-Trp7,9,Nl e11)-substance P (SP) and the vasoactive intestinal peptide (VIP) antagonist (Ac-Tyr1,D-Phe2)-GRF(1-29)-NH2 on the excitability of the spinal nociceptive flexor reflex to intrathecally (i.t.) applied SP and VIP, respectively, as well as the facilitation evoked by activation of cutaneous C-afferent was examined. Both antagonists blocked the effects of the respective neuropeptides in rats with both intact and sectioned sciatic nerves. Spantide II antagonised C-afferent induced reflex facilitation in rats with intact nerves, but the degree of antagonism declined after axotomy. In contrast, the VIP antagonist did not block C-afferent induced facilitation in rats with intact nerves, but did so after axotomy. The results indicate that the role of tachykinins in mediating C-afferent-induced reflex facilitation is taken over by VIP after axotomy.     

Expansion of afferent vestibular signals after the section of one of the vestibular nerve branches

The anterior branch of N. VIII was sectioned in adult frogs. Two months later the brain was isolated to record in vitro responses in the vestibular nuclei and from the abducens nerves following electric stimulation of the anterior branch of N. VIII or of the posterior canal nerve. Extra- and intracellularly recorded responses from the intact and operated side were compared with responses from controls. Major changes were detected on the operated side: the amplitudes of posterior canal nerve evoked field potentials were enlarged, the number of vestibular neurons with a monosynaptic input from the posterior canal nerve had increased, and posterior canal nerve stimulation recruited stronger abducens nerve responses on the intact side than vice versa. Changes in the convergence pattern of vestibular nerve afferent inputs on the operated side strongly suggest the expansion of posterior canal-related afferent inputs onto part of those vestibular neurons that were deprived of their afferent vestibular input. As a mechanism we suggest reactive synaptogenesis between intact posterior canal afferent fibers and vestibularly deprived second-order vestibular neurons.     

人工组织神经移植物桥接修复缺损一月的大鼠坐骨神经

目的:用人工组织神经移植物桥接缺损1个月的大鼠坐骨神经,观察神经再生以及靶肌肉神经再支配的相关情况。方法:切除成年SD大鼠坐骨神经一段,造成1个月的神经缺损模型,用人工组织神经移植物进行桥接修复,3个月后进行神经及靶肌肉的观察。结果:术后3个月人工组织神经移植物组的复合肌动作电位、再生神经及腓肠肌的形态等和自体神经组接近,两组均明显优于缺损组。结论:人工组织神经移植物能在一定程度上修复缺损1个月的大鼠坐骨神经。     

The brief and the prolonged facilitatory effects of unmyelinated afferent input on the rat spinal cord are independently influenced by peripheral nerve section

Single C-fibre strength stimuli applied to the sciatic nerve in the decerebrate spinal rat evoke three separate bursts of activity in posterior biceps/semitendinosus flexor alpha motorneurones which are associated with the arrival in the spinal cord of volleys in the A-beta, A-delta and C-afferent fibres. Repetitive stimulation of the sciatic nerve at 1 Hz for 20 s generates a progressive wind-up of response and an after-discharge lasting up to 10 s. Twelve to fourteen days after section of the sciatic nerve, stimuli applied central to the section evoke a larger than normal response in the posterior biceps/semitendinosus flexor motorneurones and repetitive stimulation (1 Hz, 20 s) produces an after-discharge which is four times longer than that produced by stimulation of the intact nerve. In addition to the direct excitatory effects of sciatic nerve stimulation on the flexor motorneurones which lasts for seconds, conditioning stimuli to the sciatic nerve at C-fibre strength (1 Hz, 20 s) produce a facilitation of the flexor reflex evoked by a standard pressure stimulus to the ipsilateral and contralateral toes which lasts for 70 min. However, although the direct excitatory effects of stimulating a sectioned sciatic nerve on the posterior biceps/semitendinosus flexor motorneurones are exaggerated, the facilitation of the cutaneous flexion reflex evoked by stimulating sectioned sciatic nerves (1 Hz, 20 s) only lasts for 17 min. These results show that the mechanism which produces the rapid effects of sciatic nerve stimulation on the flexor reflex circuit can be separated from the mechanism which produces the prolonged facilitation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fiber composition of the rat sciatic nerve

The rat sciatic nerve originates from the spinal segments L4-L6. It is unifascicular at the trochanter; 5-7 mm distally, the nerve splits into two and then into four fascicles. The tibial portion gives rise to the tibial and the sural nerves, and the peroneal portion gives rise to the peroneal nerve and a cutaneous branch that perforates the lateral hamstring muscles to innervate the proximolateral face of the calf. The number and type of the axons in these branches were determined in light and electron micrographs of normal nerves, and after de-efferentation or sympathectomy. Deafferentation was technically not feasible because spinal ganglia and ventral roots were supplied by the same vascular plexus. The tibial nerve contained 1,000 motor and 3,500 myelinated afferent axons, 3,700 sympathetic axons, and 5,400 unmyelinated afferent axons. The peroneal nerve contained 600 motor and 1,300 myelinated afferent axons, 1,100 sympathetic axons and 3,000 unmyelinated afferent axons. The sural nerve contained 1,100 myelinated and 2,800 unmyelinated afferent axons; in addition, there were 1,500 unmyelinated sympathetic axons. The cutaneous branch consisted of 400 myelinated and 1,800 unmyelinated afferent axons. Thus, the entire sciatic nerve at midthigh is composed of about 27,000 axons; 6% are myelinated motor axons, 23% and 48% are myelinated and unmyelinated sensory axons, respectively, and 23% are unmyelinated sympathetic axons. The techniques used did not demonstrate sympathetic axons in the cutaneous branch and did not reveal the few motor axons contained in the sural nerve.     

Upregulation of the T-type calcium current in small rat sensory neurons after chronic constrictive injury of the sciatic nerve

Recent data indicate that peripheral T-type Ca2+ channels are instrumental in supporting acute pain transmission. However, the function of these channels in chronic pain processing is less clear. To address this issue, we studied the expression of T-type Ca2+ currents in small nociceptive dorsal root ganglion (DRG) cells from L4-5 spinal ganglia of adult rats with neuropathic pain due to chronic constrictive injury (CCI) of the sciatic nerve. In control rats, whole cell recordings revealed that T-type currents, measured in 10 mM Ba2+ as a charge carrier, were present in moderate density (20 +/- 2 pA/pF). In rats with CCI, T-type current density (30 +/- 3 pA/pF) was significantly increased, but voltage- and time-dependent activation and inactivation kinetics were not significantly different from those in controls. CCI-induced neuropathy did not significantly change the pharmacological sensitivity of T-type current in these cells to nickel. Collectively, our results indicate that CCI-induced neuropathy significantly increases T-type current expression in small DRG neurons. Our finding that T-type currents are upregulated in a CCI model of peripheral neuropathy and earlier pharmacological and molecular studies suggest that T-type channels may be potentially useful therapeutic targets for the treatment of neuropathic pain associated with partial mechanical injury to the sciatic nerve.     

On the degeneration of rat neuromuscular junctions after nerve section

1. A study was made of functional and structural changes during degeneration of end-plates in the rat diaphragm after phrenic nerve section at two levels.2. For 8-10 hr after cutting the nerve in the neck, all end-plates retain the ability to transmit impulses. During the following 8-10 hr, an increasing number of end-plates lose this ability so that after a total of about 20 hr, no end-plates can transmit.3. Transmission failure occurs abruptly at most end-plates. This failure is usually accompanied by cessation of spontaneous miniature end-plate potentials (min.e.p.p.s), though in a few cases min.e.p.p.s persist after junctional transmission has failed. Several degenerating junctions were observed where the frequency of min.e.p.p.s was very low, suggesting an intermediate stage in min.e.p.p. failure.4. The time of junctional failure depends on the length of the degenerating nerve stump. For each additional centimetre of nerve, failure is delayed about 45 min.5. Changes in ultrastructure of nerve endings closely parallel those of function. For about 8-12 hr after cutting the nerve, nearly all end-plates appear normal. During the period when transmission is failing, some end-plates are clearly undergoing structural break-down. By the time functional failure is complete, all end-plates appear grossly abnormal.6. During degeneration, the contents of the axoplasm undergo disruption and the nerve terminal breaks up into small fragments. In contrast, the Schwann cell appears to become very active and its processes extend into the synaptic cleft to surround fragments of the nerve terminal. Ultimately, the Schwann cell completely replaces the axon at the end-plate.7. Increasing the length of the peripheral nerve stump delays the onset of structural break-down. Disruption of end-plates near the site of nerve entry into the muscle occurs before those farther away.8. It is suggested that end-plate degeneration is triggered by a signal which passes from the site of injury to the nerve terminal. The duration of the period after transection when end-plates appear to be normal would then reflect the time required for this signal to travel the length of the isolated nerve stump.     

Ultrastructural changes in the gracile nucleus of the rat after sciatic nerve transection

Summary Ultrastructural changes in the gracile nucleus of the rat have been examined after peripheral nerve injury. The sciatic nerve of adult rats was transected at mid-thigh level, and after survival times ranging from 1 day to 32 weeks sections from the gracile nucleus were prepared for electron microscopic examination. Unoperated animals served as controls. Atypical profiles were regularly observed in the experimental cases at post-operative survival times from 3 days up to 32 weeks. It was sometimes not possible to classify these as pre-terminal axons or terminals, because synaptic contacts could not be identified. The two most common changes throughout the entire post-operative period were greatly expanded myelinated axons, or unmyelinated profiles containing numerous mitochondria, osmiophilic dense bodies and vacuoles. Atypical profiles were occasionally observed in unoperated control animals. The results clearly show that various types of degenerative changes occur in the gracile nucleus after peripheral nerve injury. These changes differ markedly from previously described transganglionic changes in other systems. It cannot be excluded that some of the changes reflect growth-related reactions, although the typical features of axon regeneration could not be found.     

Injection of the sciatic nerve with TMEV: a new model for peripheral nerve demyelination

Demyelination of the human peripheral nervous system (PNS) can be caused by diverse mechanisms including viral infection. Despite association of several viruses with the development of peripheral demyelination, animal models of the condition have been limited to disease that is either autoimmune or genetic in origin. We describe here a model of PNS demyelination based on direct injection of sciatic nerves of mice with the cardiovirus, Theiler's murine encephalomyelitis virus (TMEV). Sciatic nerves of FVB mice develop inflammatory cell infiltration following TMEV injection. Schwann cells and macrophages are infected with TMEV. Viral replication is observed initially in the sciatic nerves and subsequently the spinal cord. Sciatic nerves are demyelinated by day 5 post-inoculation (p.i.). Injecting sciatic nerves of scid mice resulted in increased levels of virus recovered from the sciatic nerve and spinal cord relative to FVB mice. Demyelination also occurred in scid mice and by 12 days p.i., hindlimbs were paralyzed. This new model of virus-induced peripheral demyelination may be used to dissect processes involved in protection of the PNS from viral insult and to study the early phases of lesion development.     

Convergence in a thermal afferent pathway in the rat.

1. In anaesthetized rats, unit activity was recorded in the afferent somatosensory pathway leading from the scrotum. Recording sites were in the dorsal horn near the entry zone of the scrotal nerve, in the ventrobasal complex of the thalamus and in the somatosensory (SI) cortex. During recording, the temperatures of the left and right sides of the scrotum were varied independently. 2. Almost all (64/67) the units in dorsal horn, thalamus and cortex responding specifically to scrotal temperature were equally affected by temperature changes on either side of the scrotum. The receptive fields of these units were bilateral and large, implying a massive convergence of fibres from thermoreceptors on to each central unit. In contrast, mechanosensitive units responded only to unilateral stimulation. 3. As a consequence of the convergence in the thermal pathway, the firing rate of each central unit was a function of an additive combination, often simply the sum, of the temperatures of the two sides of the scrotum. 4. The relationship between firing rate and the temperature of one side of the scrotum was sigmoid, the position, but not the shape, of the curve depending on the temperature at which the opposite side was maintained. An increase in the maintained temperature shifted the sigmoid response curve towards lower temperatures and vice versa. 5. The convergence which this pathway exhibits would be well suited to integration of the temperature of the scrotal skin, but not to spatial discrimination.     

Morphofunctional changes in the rat spleen after capsaicin blockade of peripheral afferent neurons

Certain parameters of spleen morphological state 2 wks following the administration of neurotoxic (150 and 200 mg/kg) doses of capsaicine were studied in male Wistar rats. Widening of veins, rise of splenorenal index, increase in neutrophilic granulocyte number in red pulp, appearance of pyroninophilic elements in it, intensification of plasmocytic reaction in germinal centres and phagocytic siderophages activity, growth of number of megakaryocytes and megakaryoblasts and formation of colonies of these cells were noted. Comparison of the results obtained with the effects of surgical spleen deafferentation suggest that sensory neuropeptide mediated neurons, possess bilateral connections with central nervous system and may provide its control over peripheral homeostatic functions.     

坐骨神经慢性卡压损伤模型大鼠背根神经节纤维化改变

文题释义：组织纤维化：是结缔组织过度增生和细胞外基质沉积的结果,纤维化过程是一个异常的、不受控制的组织修复过程,其中组织损伤和自身免疫疾病是导致组织纤维化的主要因素,过度的组织纤维化最终导致组织结构和功能改变。 慢性神经卡压损伤：指周围神经在特定部位受到慢性卡压引起的相应神经功能障碍。 背景：既往的研究主要集中于周围神经慢性卡压损伤所导致的靶器官——骨骼肌萎缩及其纤维化发生的机制研究,关于周围神经慢性卡压损伤信号向上引起背根神经节功能改变的研究较少。 目的：观察大鼠坐骨神经慢性卡压损伤对背根神经节纤维化的影响。方法：按照Mackinnon设计的方法制备大鼠坐骨神经慢性卡压模型,术后3周,分别取大鼠坐骨神经卡压侧和对侧L_4-6背根神经节,采用RT-PCR、Western blot及免疫荧光检测大鼠卡压侧和对照侧背根神经节内转化生长因子β1、结缔组织生长因子及胶原蛋白Ⅰ的表达变化。结果与结论：①损伤3周后,相比于对照侧,背根神经节内转化生长因子β1、结缔组织生长因子及胶原蛋白Ⅰ的mRNA及蛋白表达均具有相同的升高趋势(P < 0.05);②损伤3周后,大鼠卡压侧和对照侧背根神经节内转化生长因子β1和结缔组织生长因子主要表达在背根神经元内和轴突内,而胶原蛋白Ⅰ主要表达在背根神经元和轴突的周围,形成包绕背根神经元和轴突的网状结构;③上述数据证实,大鼠坐骨神经慢性卡压损伤可以导致背根神经节纤维化的改变,并且背根神经节纤维化的改变可能与背根神经元内转化生长因子β1及结缔组织生长因子表达升高有关。ORCID: 0000-0003-1632-0837(黎琴文) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程