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.     

Hrp-labeled sources of descending propriospinal pathways in cats

Unilateral injections of horseradish peroxidase into the cat spinal cord at different segmental levels revealed a laminar distribution of spinal interneurons that are sources of ipsilateral and contralateral propriospinal pathways of different lengths. The majority of the long pathways connecting cervical and lumbar segments are formed by neurons located in the central quadrants (laminae VII and VIII) bilaterally; a few such neurons also are present in the marginal layer and in lateral zones at the base of the dorsal horn (ipsilaterally). The zones containing numerous propriospinal neurons forming short (extending over a few segments) connections were more extensive. In the lumbar portion neurons which were sources of short uncrossed pathways tended to be concentrated in the lateral areas of the base of the dorsal horn, intermediate zone, and ventral horn, whereas sources of crossed pathways were concentrated in the ventromedial zones of gray matter. In the cervical portion "short" propriospinal neurons forming both ipsilateral and contralateral projections were concentrated in the lateral zones of gray matter. Neurons of the marginal layer and substantia gelatinosa and neurons of intermediolateral sympathetic nuclei also were sources of descending propriospinal pathways. Some propriospinal axons were intermediate in length. The distribution of neurons with axons of this kind largely coincided with the distribution of neurons that were sources of long propriospinal pathways. The connection between the spatial distribution of different groups of propriospinal neurons and the organization of the synaptic inputs into them, and also correlation between the morphological and functional characteristics of these neurons are discussed.     

Neurokinin A, calcitonin gene-related peptide, and dynorphin A (1-8) in spinal dorsal horn contribute to descending inhibition evoked by nociceptive afferent pathways: an immunocytochemical study

Immunocytochemical technique was used to compare the contents of neurokinin A (NKA), calcitonin gene-related peptide (CGRP), and dynorphin A (1-8) (DynA) on two sides of the lumbar dorsal horn of rats in which the unilateral thoracic dorsalateral funiculus (DLF) was transected while formalin (0.2 ml, 0.5%) was injected equally into two hindpaws. The results showed that all the NKA-like, CGRP-like, and DynA (1-8)-like immunoreactivities were significantly lower in the superficial laminae of the dorsal horn on the side ipsilateral to the lesioned DLF than that on the side with intact DLF. This implies that peripheral noxious inputs activate the supraspinal descending inhibitory systems which in turn modulate the transmission of noxious message at the spinal level by changing the release of related neuropeptides.     

Quantitative autoradiographic analysis of [I]-human CGRP binding sites in the dorsal horn of rat following chronic constriction injury or dorsal rhizotomy

Quantitative receptor autoradiography was used to examine the binding of [¹²⁵I]-human CGRP in the dorsal horn of the L4 spinal segment of rats with a chronic constriction injury (CCI) of the sciatic nerve or unilateral dorsal rhizotomies of spinal segments L1–L6. At the times selected for study, we found no change in the amount of CGRP binding in any areas examined following CCI. In contrast, our results showed a temporally related increase in the amount of CGRP binding in areas within laminae I–II and in lateral lamina V of the dorsal horn ipsilateral to the rhizotomies. These results indicate that CGRP binding sites are regulated, most likely, by changes in the release of CGRP. Further, our results suggest that the release of CGRP from primary afferent neurons is unchanged in animals with a CCI.     

Topographic mapping of the axons of the femoral chordotonal organ neurons in the cricket Gryllus bimaculatus

Central projections of the femoral chordotonal organ (FCO) neurons in the cricket Gryllus bimaculatus were investigated by selectively staining small numbers of axons. The FCOs in all legs consist of partly fused ventral and dorsal scoloparia in the proximal femur. The ventral scoloparium neurons can be reliably divided into two groups: the ventral group neurons (VG), which are arranged in a sequentially smaller manner distally, and dorsal group neurons (DG), which simply aggregate in the proximal region near the dorsal scoloparium. All axons of the FCO projected to the ipsilateral half of the respective thoracic ganglion. The VG axons possessed dorso-lateral branches in the motor association neuropile and antero-ventral branches dorso-lateral to the anterior ventral association centre. However, the more proximally the somata were situated, the more medially the main neurites terminated. The DG axons showed some variations: some axons of the distally located neurons possessed dorso-lateral branches and terminated on the boundary region of the mVAC, while the other axons terminated exclusively in the medical ventral association centre (mVAC), including the ventral part, which receives auditory sensory neuron projections. All axons of the dorsal scoloparium neurons projected exclusively into the dorsal part of the mVAC; however, the ventrally located neurons projected more ventrally than did the dorsally located neurons. The above characteristics were nearly identical in the pro- and metathoracic FCOs. These results suggest that the cricket FCO axons are roughly organized in a somatotopic map and are broadly differentiated in their function.     

Spinal Cord Transection Significantly Influences nNOS-IR in Neuronal Circuitry that Underlies the Tail-Flick Reflex Activity

Aim Spinal cord transection interrupts supraspinal input and leads to the development of prominent spasticity. In this study, we investigated the effect of rat spinal cord transection performed at low thoracic level on changes in (i) neuronal nitric oxide synthase immunoreactivity (nNOS-IR), and (ii) the level of neuronal nitric oxide synthase (nNOS) protein in the neuronal circuitry that underlies tail-flick reflex. Methods nNOS-IR was detected by immunohistochemistry and the level of nNOS protein was determined by the Western blot analysis. The tail-flick reflex was tested by a noxious thermal stimulus delivered to the tail of experimental animals. After surgery, experimental animals survived for 7 days. Results A significant increase in the level of nNOS protein was found 1 week after thoracic transection in the L2–L6 segments. Immunohistochemical analysis discovered that this increase may be a result of (1) a high nNOS-IR in a large number of axons, located predominantly in the dorsal columns (DCs) of lower lumbosacral segments, and (2) a slight increase of density in nNOS-IR in motoneurons. On the other hand the number of nNOS-IR neurons in the superficial dorsal horn and in area surrounded the central canal (CC) was greatly reduced. The tail-flick response was immediate in animals after spinal transection, while control rats responded to thermal stimulus with a slight delay. However, the tail-flick latency in experimental animals was significantly higher than in control. Conclusion These data indicate that transection of the spinal cord significantly influences nNOS-IR in neuronal circuitry that underlies the tail-flick reflex activity.     

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.     

Chemical activation of C(1)-C(2) spinal neurons modulates activity of thoracic respiratory interneurons in rats

Discharge patterns of thoracic dorsal horn neurons are influenced by chemical activation of cell bodies in cervical spinal segments C(1)-C(2). The present aim was to examine whether such activation would specifically affect thoracic respiratory interneurons (TRINs) of the deep dorsal horn and intermediate zone in pentobarbital sodium-anesthetized, paralyzed, artificially ventilated rats. We also characterized discharge patterns and pathways of TRIN activation in rats. A total of 77 cells were classified as TRINs by location, continued burst activity related to phrenic discharge when the respirator was stopped, and lack of antidromic response from selected pathways. A variety of respiration-phased discharge patterns was documented whose pathways were interrupted by ipsilateral C(1) transection. Glutamate pledgets (1 M, 1 min) on the dorsal surface of the spinal cord inhibited 22/49, excited 15/49, or excited/inhibited 3/49 tested cells. Incidence of responses did not depend on whether the phase of TRIN discharge was inspiratory, expiratory, or biphasic. Phrenic nerve activity was unaffected by chemical activation of C(1)-C(2) in this preparation. Besides supraspinal input, TRIN activity may be influenced by upper cervical modulatory pathways.     

异丙酚对正常大鼠脊髓背角感觉神经元反应性的抑制作用

脊髓背角感觉神经元不仅在感觉信息的传递和调节中起到重要作用,也是各种内源性和外源性药物的作用靶位.为了解静脉麻醉剂异丙酚是否对背角感觉神经元的反应性具有调节作用,本实验采用在体单细胞胞外记录技术,观察了脊髓背表面直接滴注0.5 μmol异丙酚对戊巴比妥钠麻醉大鼠脊髓背角广动力域(WDR)神经元和低阈值机械感受型(LTM)神经元反应性的影响.实验发现,异丙酚能抑制背角WDR神经元由施加于外周感受野伤害性热刺激(45、47、49和53℃,15 s)和夹捏机械刺激(10 s)诱发的反应性,与DMSO对照组比较具有显著性统计学差异(P＜0.05);同样,异丙酚对非伤害性机械刺激诱发的WDR或LTM神经元的反应性也具有显著的抑制作用(P＜0.05).本结果提示,异丙酚可直接作用于正常大鼠脊髓背角神经元,对由非伤害性和伤害性纤维介导的神经元反应性均产生抑制作用,因此异丙酚的脊髓抗伤害作用可能不是特异性的.     

Electrophysiological Study of Supraspinal Input and Spinal Output of Cat's Subnucleus Reticularis Dorsalis (SRD) Neurons

This work addressed the study of subnucleus reticularis dorsalis (SRD) neurons in relation to their supraspinal input and the spinal terminating sites of their descending axons. SRD extracellular unitary recordings from anesthetized cats aimed to specifically test, 1) the rostrocaudal segmental level reached by axons of spinally projecting (SPr) neurons collateralizing or not to or through the ipsilateral nucleus reticularis gigantocellularis (NRGc), 2) whether SPr fibers bifurcate to the thalamus, and 3) the effects exerted on SRD cells by electrically stimulating the locus coeruleus, the periaqueductal grey, the nucleus raphe magnus, and the mesencephalic locomotor region. From a total of 191 SPr fibers tested to cervical 2 (Ce2), thoracic 5 (Th5) and lumbar5 (Lu5) stimulation, 81 ended between Ce2 and Th5 with 39 of them branching to or through the NRGc; 21/49 terminating between Th5 and Lu5 collateralized to or through the same nucleus, as did 34/61 reaching Lu5. The mean antidromic conduction velocity of SPr fibers slowed in the more proximal segments and increased with terminating distance along the cord. None of the 110 axons tested sent collaterals to the thalamus; instead thalamic stimulation induced long-latency polysynaptic responses in most cells but also short-latency, presumed monosynaptic, in 7.9% of the tested neurons (18/227). Antidromic and orthodromic spikes were elicited from the locus coeruleus and nucleus raphe magnus, but exclusively orthodromic responses were observed following stimulation of the periaqueductal gray or mesencephalic locomotor region. The results suggest that information from pain-and-motor-related supraspinal structures converge on SRD cells that through SPr axons having conduction velocities tuned to their length may affect rostral and caudal spinal cord neurons at fixed delays, both directly and in parallel through different descending systems. The SRD will thus play a dual functional role by simultaneously regulating dorsal horn ascending noxious information and pain-related motor responses.     

Contribution of the dorsal branch of the accessory nerve to the innervation of the trapezius muscle in the pig – a retrograde tracing study

The study was aimed to establish the contribution of the dorsal branch of the accessory nerve (DBXI) to the innervation of the porcine trapezius muscle (TRAP). Combined retrograde tracing using fluorescent tracer Fast blue (FB) and surgical denervation procedure (excision of DBXI segment) were applied . FB+ neurons supplying the cervical (c‐TRAP) and thoracic part (th‐TRAP) of TRAP were localized in following nerve centres: the ipsilateral ventral horn of the grey matter of cervical neuromers, ipsilateral spinal ganglia and bilateral sympathetic chain ganglia. After the excision of DBXI segment, no FB+ motoneurons supplying c‐TRAP were found while the mean number of those supplying th‐TRAP was significantly decreased. A slight decrease in average numbers of sensory and autonomic neurons implemented in the innervation of both parts of TRAP was also observed. This study has revealed that in the pig DBXI is the only motor pathway to c‐TRAP while the vast majority of motoneurons supplying porcine th‐TRAP send their axons via DBXI.     

Afferent connections in the ventromedial hypothalamus of rats demonstrated by retrograde transport of horseradish peroxidase

Projections into rat ventromedial hypothalamus were studied with retrograde transport of horseradish peroxidase (HRP). Following injection of HRP into ventromedial hypothalamus, labeled neurons were found in cortical and medial amygdaloid nuclei, ipsilateral mediodorsalis thalamus (MD), dorsal raphe nucleus, and contralateral sensorimotor cortex. Futhermore, labeled axons that connect directly amygdala with hypothalamus (DAH) also were found.     

NMDA and strychnine diversely modulate spinal dorsal horn noxious responsiveness in normal rats: potential significance to sensory disorders in neuropathic pain

Changes in neuronal excitability due to increase in excitatory transmitters and/or removal of local inhibition underlie central neuron sensitization and altered responsiveness related to painful sensory disorders. To distinguish the contribution of each of the two mechanisms, they have been mimicked separately in intact rats, by iontophoretically applying excitatory (NMDA) and disinhibitory (the glycine antagonist strychnine) substances during dorsal horn neuron recording. Wide dynamic range (WDR) neurons were extracellularly recorded at the L5-L6 lumbar level in anesthetized and paralyzed rats and an analysis was made, before and during the substance application, of the characteristics of the response to noxious stimuli applied to areas supplied by the ipsilateral sciatic nerve and the contralateral sciatic and saphenous nerves ("inappropriate" areas). The results show that the neuronal response properties were modified differently during the NMDA-induced hyperexcitability and strychnine-induced release of inhibition. Both manipulations brought about the unmasking of responses to previously ineffective, noxious stimuli applied to the contralateral sciatic and saphenous nerve areas, and the enhancement of the responses to noxious stimulation of the ipsilateral sciatic nerve area. However, it was only during the increased excitation induced by NMDA that the neurons exhibited hyperresponsiveness, with long-lasting afterdischarge, to noxious stimulation of the ipsi- and contralateral areas. Such response features resemble those described in sensitized neurons in neuropathic rats and associated with behavioral signs of hyperalgesia. This suggests, by inference, a crucial contribution of the NMDA-induced increased excitability to the expression of neuronal sensitization related to this painful sensory disorder.     

NMDA and strychnine diversely modulate spinal dorsal horn noxious responsiveness in normal rats: potential significance to sensory disorders in neuropathic pain

Changes in neuronal excitability due to increase in excitatory transmitters and/or removal of local inhibition underlie central neuron sensitization and altered responsiveness related to painful sensory disorders. To distinguish the contribution of each of the two mechanisms, they have been mimicked separately in intact rats, by iontophoretically applying excitatory (NMDA) and disinhibitory (the glycine antagonist strychnine) substances during dorsal horn neuron recording. Wide dynamic range (WDR) neurons were extracellularly recorded at the L5-L6 lumbar level in anesthetized and paralyzed rats and an analysis was made, before and during the substance application, of the characteristics of the response to noxious stimuli applied to areas supplied by the ipsilateral sciatic nerve and the contralateral sciatic and saphenous nerves ("inappropriate" areas). The results show that the neuronal response properties were modified differently during the NMDA-induced hyperexcitability and strychnine-induced release of inhibition. Both manipulations brought about the unmasking of responses to previously ineffective, noxious stimuli applied to the contralateral sciatic and saphenous nerve areas, and the enhancement of the responses to noxious stimulation of the ipsilateral sciatic nerve area. However, it was only during the increased excitation induced by NMDA that the neurons exhibited hyperresponsiveness, with long-lasting afterdischarge, to noxious stimulation of the ipsi- and contralateral areas. Such response features resemble those described in sensitized neurons in neuropathic rats and associated with behavioral signs of hyperalgesia. This suggests, by inference, a crucial contribution of the NMDA-induced increased excitability to the expression of neuronal sensitization related to this painful sensory disorder.     

吗啡耐受增加福尔马林致痛大鼠脊髓Fos和NADPH-d阳性神经元的表达

运用Ｆｏｓ免疫组织化学、ＮＡＤＰＨ－ｄ组织化学及Ｆｏｓ／ＮＡＤＰＨ－ｄ双标技术,研究了吗啡耐受对福尔马林致痛大鼠脊髓Ｆｏｓ、ＮＡＤＰＨ－ｄ阳性及Ｆｏｓ／ＮＡＤＰＨ－ｄ双标神经元表达的影响。结果观察到：在非吗啡耐受大鼠,福尔马林诱发的Ｆｏｓ－ｌｉｋｅ ｉｍｍｕｎｏｒｅａｃｔｉｖｉｔｙ（Ｆｏｓ－ＬＩ）主要分布在同侧脊髓背角浅层和颈部,急性静注吗啡可减少Ｆｏｓ－ＬＩ表达;长时间应用吗啡导致福尔马林诱发的     

蛋白激酶C部分参与伤害性刺激在脊髓背角神经元中引起的c-fos蛋白的表达而可能不参与阿片受体对脊髓痛感受的调制

实验用免疫细胞化学技术观察了大鼠鞘内分别注入蛋白激酶(PKC)抑制剂Chelerythrine(Chel)、纳洛酮(Nal)、或二者同时注入后,由后脚掌注射福尔马林引起的脊髓腰膨大背角中c-fos蛋白样免疫活性(Fos-LI)神经元数目的改变。结果发现:(1)鞘内注入Chel可显著降低福尔马林注射侧脊髓背角中Fos-LI神经元的数目,同空白对照组(鞘内注入生理盐水或10％的DMSO)相比,降低60.3％(P<0.001):(2)鞘内注入Nal后,福尔马林注射侧背角中Fos-LI神经元显著增加,同对照组相比,增加46.0％(P<0.01),而以背角深层增加最为明显;(3)在鞘内同时注入Chel和Nal后,与单独注入Nal组相比,脊髓背角中Fos-LI神经元的数目显著降低(降低53.2％),此数值与上述单独注入Chel时引起Fos-LI神经元降低的百分率近似。结果提示:(1)PKC只参与脊髓背角中部分Fos-LI神经元中c-fos蛋白的表达;(2)PKC可能不参与背角中同时激活的μ-(以及部分δ-)阿片受体对脊髓伤害性感受的调制。     

氯胺酮对单足致炎大鼠脊髓背角神经元活动的影响

在大鼠脊髓背角用细胞外记录技术共记录到３２个单位。角叉菜胶一侧足底注射致炎后,电刺激该侧足底内外侧神经激动其中Ａ、Ｃ纤维时,脊髓背角神经元诱发放电数均显著增加;静脉注射ＮＭＤＡ受体拮抗剂氯胺酮后,Ａ、Ｃ纤维刺激诱发的放电反应均显著下降甚至消失。致炎后脊髓背角深层单位出现Ｗｉｎｄｕｐ现象,静脉注射氯胺酮后该现象减轻消失。结果提示：角叉菜胶致炎导致脊髓背角神经元兴奋性升高和Ｗｉｎｄｕｐ;ＮＭＤＡ受体参     

Sustained neurochemical plasticity in central terminals of mouse DRG neurons following colitis

Sensitization of dorsal root ganglia (DRG) neurons is an important mechanism underlying the expression of chronic abdominal pain caused by intestinal inflammation. Most studies have focused on changes in the peripheral terminals of DRG neurons in the inflamed intestine but recent evidence suggests that the sprouting of central nerve terminals in the dorsal horn is also important. Therefore, we examine the time course and reversibility of changes in the distribution of immunoreactivity for substance P (SP), a marker of the central terminals of DRG neurons, in the spinal cord during and following dextran sulphate sodium (DSS)-induced colitis in mice. Acute and chronic treatment with DSS significantly increased SP immunoreactivity in thoracic and lumbosacral spinal cord segments. This increase developed over several weeks and was evident in both the superficial laminae of the dorsal horn and in lamina X. These increases persisted for 5 weeks following cessation of both the acute and chronic models. The increase in SP immunoreactivity was not observed in segments of the cervical spinal cord, which were not innervated by the axons of colonic afferent neurons. DRG neurons dissociated following acute DSS-colitis exhibited increased neurite sprouting compared with neurons dissociated from control mice. These data suggest significant colitis-induced enhancements in neuropeptide expression in DRG neuron central terminals. Such neurotransmitter plasticity persists beyond the period of active inflammation and might contribute to a sustained increase in nociceptive signaling following the resolution of inflammation.     

Inflammation enhances reflex and spinal neuron responses to noxious visceral stimulation in rats

To improve understanding of sensory processes related to visceral inflammation, the effect of turpentine-induced inflammation on reflex (cardiovascular/visceromotor) and extracellularly recorded lumbosacral dorsal horn neuron responses to colorectal distension (CRD) was investigated. A 25% solution of turpentine, applied to the colorectal mucosa, produced inflammation, decreased compliance of the colonic wall, and enhanced reflex responses in unanesthetized rats within 2-6 h. At 24 h posttreatment, pressor responses to CRD (80 mmHg, 20 s) were 20% greater, and intraluminal pressures needed to evoke visceromotor reflexes were 30% lower than controls. Parallel electrophysiological experiments in spinal cord-transected, decerebrate rats demonstrated that two neuronal subgroups excited by CRD were differentially affected by turpentine administered 24 h before testing. During CRD, abrupt neurons were 70% less active and sustained neurons were 25% more active than similar neurons in controls. In summary, reflex and neuronal subgroup (sustained neurons) responses to CRD were both potentiated by chemical inflammation. This suggests that the neurophysiological basis for inflammation-induced increases in reflex responses to CRD is increased activity of this neuronal subgroup.