Analysis of receptive fields revealed by in vivo patch-clamp recordings from dorsal horn neurons and in situ intracellular recordings from dorsal root ganglion neurons

It has been thought that spinal dorsal horn neurons receive convergent inputs from not only somatosensory but also visceral pathways. For instance, the referred pain is presumed to be due to the convergence of sensory inputs from cardiac and shoulder receptive fields. However, precise investigation has not been made from dorsal horn neurons yet, because of difficulty in studying the pathways from those regions by means of conventional electrophysiology. The purpose of this study is to clarify the convergent inputs to single dorsal horn neurons from wide receptive fields using an in vivo patch-clamp recording technique from the superficial spinal dorsal horn and an intracellular recording from dorsal root ganglion neurons that keep physiological connections with the peripheral sites. Identified dorsal root ganglion neurons received an input from a quite small area, about 1 x 1 mm in width of the skin. In contrast, substantia gelatinosa neurons in the spinal cord received inputs from an unexpectedly wide area of the skin. Previous extracellular recordings have, however, revealed that substantia gelatinosa neurons have small receptive field. This discrepancy is probably due mainly to an availability of the in vivo patch-clamp method to analyze sub-threshold synaptic responses. In contrast, the extracellular recording technique allows us to analyze predominantly the firing frequency of neurons. Thus, the in vivo patch-clamp recordings from dorsal horn neurons and the intracellular recordings from DRG neurons will be useful for well understanding the sensory processing in the spinal cord.     

Peptide- and non-peptide-containing unmyelinated primary afferents: the parallel processing of nociceptive information

Primary afferent C fibres can be subdivided into a number of subgroups on the basis of cytochemistry or receptor binding characteristics. Numerous peptides have been localized to dorsal root ganglia, yet these appear to be only found in approximately 50% of small perikarya. A large proportion of the remaining small cells do not contain peptides but are identifiable in rodents by their content of a fluoride resistant acid phosphatase. Attempts have been made to correlate particular biochemical types with particular receptive field profiles, with rather modest success. As an alternative we suggest, principally from an analysis of skin afferents, that peptide- and non-peptide-containing afferents are two distinct C fibre pathways innervating similar peripheral structures and conveying similar information, but to different areas within the dorsal horn. Morphological evidence also suggests that these two subsystems form either glomerular or simple synaptic arrangements in the dorsal horn. The significance of parallel pathways for the processing of nociceptive information is briefly discussed.     

P2X receptor-mediated purinergic sensory pathways to the spinal cord dorsal horn

P2X receptors are expressed on different functional groups of primary afferent fibers. P2X receptor-mediated sensory inputs can be either innocuous or nociceptive, depending on which dorsal horn regions receive these inputs. We provide a brief review of P2X receptor-mediated purinergic sensory pathways to different regions in the dorsal horn. These P2X purinergic pathways are identified in normal animals, which provides insights into their physiological functions. Future studies on P2X purinergic pathways in animal models of pathological conditions may provide insights on how P2X receptors play a role in pathological pain states.     

Nociceptive pathways: anatomy and physiology of nociceptive ascending pathways

In primates, the principal nociceptive pathways ascend in the anterolateral quadrant of the spinal cord. Among these, the spinothalamic tract (s.t.t.) is the best studied. Cells in Rexed's laminae I and V project to the ventro-posterolateral (v.p.l.) thalamic nucleus. Other cells in the same and deeper laminae terminate in the intralaminar complex. Spinothalamic tract cells may be nociceptive-specific or multireceptive. Those ending in v.p.l. have restricted, contralateral receptive fields, whereas those projecting to the intralaminar region often have large, bilateral receptive fields. Spinoreticular tract (s.r.t.) cells are concentrated in laminae VII and VIII and may be nociceptive. It is proposed that the s.t.t. contributes to sensory-discriminative processing of pain and that the s.t.t. and s.r.t. play a role in the motivational-affective components of pain. Alternative nociceptive pathways are the spinocervical and postsynaptic dorsal column tracts.     

Spinocervical tract-dorsal column postsynaptic neurons: a double-projection neuronal system

Evidence is presented for the existence of a newly discovered double-projection spinal neuronal system, the spinocervical tract-dorsal column postsynaptic neurons. The neurons are characterized by axonal bifurcation in the cervico-thoracic junction, by branched axons traveling in the dorsal column and the dorsolateral funiculus, and by double projection to the dorsal column nuclei and the lateral cervical nucleus. The neurons, with longitudinally distributed dendritic trees and local axon collaterals, primarily originate in laminae III-V of the dorsal horn and receive innocuous and noxious inputs transmitted along the A-beta primary afferents from the periphery. These neurons are thought to be an intersection of the spinocervical tract and the dorsal column postsynaptic neurons, and to function as a nonlemniscal system in mediation and modulation of ascending sensory information, including pain.     

Spinocervical Tract-Dorsal Column Postsynaptic Neurons: A Double-Projection Neuronal System

Evidence is presented for the existence of a newly discovered double-projection spinal neuronal system, the spinocervical tract-dorsal column postsynaptic neurons. The neurons are characterized by axonal bifurcation in the cervico-thoracic junction, by branched axons traveling in the dorsal column and the dorsolateral funiculus, and by double projection to the dorsal column nuclei and the lateral cervical nucleus. The neurons, with longitudinally distributed dendritic trees and local axon collaterals, primarily originate in laminae III-V of the dorsal horn and receive innocuous and noxious inputs transmitted along the A-beta primary afferents from the periphery. These neurons are thought to be an intersection of the spinocervical tract and the dorsal column postsynaptic neurons, and to function as a nonlemniscal system in mediation and modulation of ascending sensory information, including pain.     

Normal anatomy and physiology of the spinal cord dorsal horn

The dorsal horn of the spinal cord receives afferent input from innocuous primary afferent neurons via collaterals from the dorsal columns. This input is integrated and relayed primarily by neurons in laminae III-VI. Dorsal horn neurons which encode innocuous inputs project to the medulla and the cervical spinal cord via the dorsal columns and the dorsolateral funiculus. Nociceptive primary afferent neurons enter the spinal dorsal horn via collaterals from Lissauer's tract. Nociceptive input is integrated and relayed by neurons in laminae I, II and V which project to the reticular formation and thalamus via the anterolateral tract.     

去甲肾上腺素在脊髓背角的镇痛机制

疹髓背角浅层是传递和调制外周伤害性信息的关键部位。起源于脑干的去甲肾上腺素（NA）能纤维终止脊髓背角,它们释放的NA具有抑制初级传入末梢释放谷氨酸和P物质、增加Ⅱ层（胶状质）抑制性神经活性物质释放的作用。此外,形态学研究提示NA可能直接抑制Ⅰ/Ⅲ层向丘脑传递伤害性信息的投射神经元。NA可能通过以上途径,实现对外周伤害性信息传递的调制而发挥镇痛作用。     

Projection linkage from spinal neurons to both lateral cervical nucleus and solitary tract nucleus in the cat

Intracellular recordings from the lumbosacral dorsal horn were made to identify the axonal projection and the afferent innervation of the lateral cervical nucleus (LCN) and solitary tract nucleus (STN) on the spinal neurons of chloralose-anesthetized cats. A total of 49 neurons from laminae III-V in the spinal dorsal horn responded to stimulation of both the LCN and STN. Of these, 28 and 21 neurons responded antidromically and orthodromically to stimulation of the LCN and STN, respectively. Seven of the 28 antidromically activated neurons were followed by one or more responses synaptically driven from the LCN and/or STN. The diameter of these ascending or descending fibers was in the range of A delta fibers. The results indicate that (1) some spinal neurons, namely spinocervical tract-spinosolitary tract (SCT-SST) neurons, issue branched axons of A delta-fibers and dually project to both LCN and STN; (2) some SCT-SST neurons receive innervation from both the LCN and STN; (3) some spinal neurons and interneurons are dually innervated by descending fibers originating from both the LCN and STN, and (4) the convergence and integration between somatic and visceral sensory inputs might occur in the SCT-SST neurons.     

C2 spinal cord stimulation induces dynorphin release from rat T4 spinal cord: potential modulation of myocardial ischemia-sensitive neurons

During myocardial ischemia, the cranial cervical spinal cord (C1-C2) modulates the central processing of the cardiac nociceptive signal. This study was done to determine 1) whether C2 SCS-induced release of an analgesic neuropeptide in the dorsal horn of the thoracic (T4) spinal cord; 2) if one of the sources of this analgesic peptide was cervical propriospinal neurons, and 3) if chemical inactivation of C2 neurons altered local T4 substance P (SP) release during concurrent C2 SCS and cardiac ischemia. Ischemia was induced by intermittent occlusion of the left anterior descending coronary artery (CoAO) in urethane-anesthetized Sprague-Dawley rats. Release of dynorphin A (1-13), (DYN) and SP was determined using antibody-coated microprobes inserted into T4. SCS alone induced DYN release from laminae I-V in T4, and this release was maintained during CoAO. C2 injection of the excitotoxin, ibotenic acid, prior to SCS, inhibited T4 DYN release during SCS and ischemia; it also reversed the inhibition of SP release from T4 dorsal laminae during C2 SCS and CoAO. Injection of the kappa-opioid antagonist, nor-binaltorphimine, into T4 also allowed an increased SP release during SCS and CoAO. CoAO increased the number of Fos-positive neurons in T4 dorsal horns but not in the intermediolateral columns (IML), while SCS (either alone or during CoAO) minimized this dorsal horn response to CoAO alone, while inducing T4 IML neuronal recruitment. These results suggest that activation of cervical propriospinal pathways induces DYN release in the thoracic spinal cord, thereby modulating nociceptive signals from the ischemic heart.     

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.     

Experimental morphological study of primary afferent terminals at the base of the dorsal horn of the cat spinal cord

The distribution and ultrastructure of primary afferent terminals in the gray matter of the cervical and lumbar regions of the cat spinal cord were studied by the experimental degeneration method of Fink and Heimer. Most preterminals of primary afferents were shown to be concentrated in the region of the intermediate nucleus of Cajal (central part of Rexed's laminae VI–VII), in the substantial gelatinosa (laminae II–III), and in the nucleus proprius of the dorsal horn (central and medial parts of lamina IV). Fewer are found in the region of the motor nuclei. The number of degenerating axon terminals in the lateral parts of laminae IV and V differed: 31.5 and 0.4% respectively of all axon terminals. Many terminals of primary afferents in lamina IV contribute to the formation of glomerular structures in which they exist as terminals of S-type forming axo-axonal connections with other terminals. These results are in agreement with electrophysiological data to show that interneurons in different parts of the base of the dorsal horn differ significantly in the relative numbers of synaptic inputs formed by peripheral afferents and descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 406–414, July–August, 1973.     

Transganglionic transport of the lectin Soybean agglutinin (Glycine max) following injection into the sciatic nerve of the adult rat

The lectin soybean agglutinin (SBA) from Glycine max binds to small-sized dorsal root ganglion cells and their central terminals in the superficial dorsal horn of the spinal cord. Here we investigated the ability of SBA and SBA conjugated to horseradish peroxidase(SBA-HRP) to trace thin calibre afferents into the spinal cord from a peripheral nerve. Following injection into the sciatic nerve, labelled cells in the dorsal root ganglion were predominantly small-sized but some medium-sized cells were also labelled. Colocalisation studies of transported SBA with various neuronal markers showed that all neurons that transported SBA-HRP showed SBA binding, indicating high uptake specificity for the conjugate. 15% were immunoreactive for RT97 indicating that some axons were myelinated, and 54% also expressed binding sites for isolectin B4 from Griffonia simplicifolia, a selective marker for a subpopulation of unmyelinated afferents. With regard to neurotransmitter content, 43% of the SBA cells contained calcitonin gene-related peptide, 33% contained substance P and 2.5% somatostatin. In addition, 3% contained carbonic anhydrase. Centrally, injection of SBA in the sciatic nerve resulted in labelled terminals in somatotopically appropriate regions of laminae I–II of the dorsal horn, and in the gracile nucleus. A few neurons in the dorsal horn were labelled indicating that some transneuronal transport of SBA had occurred. The results show that SBA can be used as a transganglionic tracer to label fine calibre primary afferents that project to laminae I–II of the spinal cord and the gracile nucleus. It appears to label more afferents than isolectin B4, including also a subpopulation of myelinated afferents.     

Neck muscle and trigeminal input to the upper cervical cord and lower medulla of the cat.

Experiments on chloralose-anaesthetized cats have shown that low-threshold neck muscle afferents project to laminae IV and V in the dorsal horn of the upper cervical cord, to lamina VI including the region which encompasses the central cervical nucleus, as well as to extensive regions of the ventral horn. At posterior medullary levels projections also exist to laminae IV, V, and VI of the spinal nucleus of V (although those to lamina IV are circumscribed), to the deep layers and lateral margin of the cuneate nucleus, and to the inferior olive. These projections are both from low- and high-threshold afferents. Evidence of a functional relationship between the trigeminal and neck muscle afferent system was found both in the upper cervical cord and lower medulla. About 40% of units in both regions receive a convergent input and when convergence could not be demonstrated, prior stimulation of one modality in some instances affected the responsiveness of the unit to the other modality. A motor role was found for some trigeminal afferent projections to the upper cervical cord. Trigeminal afferents consistently activated antidromically identified motoneurons of splenius, biventer cervicis, and complexus.     

Immunocytochemical identification of axons containing coexistent serotonin and substance P in the cat lumbar spinal cord

Axons containing both serotonin-like (5-HT)-LI and substance P-like (SP)-LI immunoreactivity were identified in all laminae of the cat spinal cord at the level of the lumbar enlargement. Using an immunologically-specific, double immunofluorescence method, coexistent 5-HT-LI and SP-LI immunoreactivity could be visualized in the same tissue section with appropriate FITC and rhodamine fluorescent filter sets. The fewest number of coexistent axons were observed in the superficial laminae of the dorsal horn, while their number increased in the more ventral dorsal horn laminae. Numerous coexistent axons were observed in the area adjacent to the central canal. The greatest number of coexistent axons was found in the ventral horn, especially in the motoneuronal cell groups. This study demonstrates that axons containing coexistent 5-HT-LI and SP-LI immunoreactivity are found in all laminae of the cat lumbar spinal cord and are thus involved in both sensory and motor functions. Their more frequent occurrence in the ventral horn suggests a greater role for coexistent 5-HT and SP in motor function. Since axons containing coexistent 5-HT and SP, and those containing only 5-HT, likely originate from different populations of neurons, our observations provide evidence for a diverse origin of descending 5-HT afferents to the different spinal laminae.     

刺激大鼠大脑脚影响脊髓伤害感受性传递的下行途径

在麻醉大鼠用部分切割脊髓的方法分析了刺激大脑脚影响脊髓背角伤害感受性神经元的下委途径。刺激ＣＰ对背角神经元伤害感受性反应（Ｃ－反应）的影响以抑制为,部分（３０．７％）神经元在抑制作用产生之前先被兴历,抑制作用主要是通过背索或背外侧索实现的,然而在多数神经元是两者共同作用的结果,其中ＤＬＦ的作用似乎更为重要。兴历作用则是通过ＤＦ实现的。由于大鼠的皮质脊髓束位于ＤＦ中,以上结果提示大脑皮层不仅可直接通     

Mechanisms of pain arising from articular tissues

This paper reviews the peripheral and central neural mechanisms underlying pain from articular tissues innervated by spinal and trigeminal afferents. The paper especially addresses trigeminal mechanisms related to pain from the temporomandibular joint and its associated craniofacial musculature. Recent studies have shown the existence of articular nociceptive primary afferents that project to the spinal cord dorsal horn and trigeminal brainstem complex. A particular feature of most neurones receiving these deep nociceptive afferent inputs is their responsivity also to cutaneous nociceptive afferent inputs. This suggests the involvement of these neurones not only in the detection of acute articular pain, but also in the hyperalgesia and poor localization, spread, and referral of pain that characterize many painful conditions of joints and other deep structures. While only limited information is available on related higher brain centre mechanisms, convergence and interaction between cutaneous and deep afferent inputs also seem to be a characteristic of somatosensory neurones in the thalamus and somatosensory cerebral cortex. Muscle and autonomic reflexes may be induced by such deep noxious stimuli, but the functional significance of some of these effects (e.g., in relation to clinical concepts of myofascial dysfunction) requires further study in more appropriate functional settings.     

Cauda equina syndrome and nitric oxide synthase immunoreactivity in the spinal cord of the dog

The development of the cauda equina syndrome in the dog and the involvement of spinal nitric oxide synthase immunoreactivity (NOS-IR) and catalytic nitric oxide synthase (cNOS) activity were studied in a pain model caused by multiple cauda equina constrictions. Increased NOS-IR was found two days post-constriction in neurons of the deep dorsal horn and in large, mostly bipolar neurons located in the internal basal nucleus of Cajal seen along the medial border of the dorsal horn. Concomitantly, NOS-IR was detected in small neurons close to the medioventral border of the ventral horn. High NOS-IR appeared in a dense sacral vascular body close to the Lissauer tract in S1-S3 segments. Somatic and fiber-like NOS-IR appeared at five days post-constriction in the Lissauer tract and in the lateral and medial collateral pathways arising from the Lissauer tract. Both pathways were accompanied by a dense punctate NOS immunopositive staining. Simultaneously, the internal basal nucleus of Cajal and neuropil of this nucleus exhibited high NOS-IR. A significant decrease in the number of small NOS immunoreactive somata was noted in laminae I-II of L6-S2 segments at five days post-constriction while, at the same time, the number of NOS immunoreactive neurons located in laminae VIII and IX was significantly increased. Moreover, high immunopositivity in the sacral vascular body persisted along with a highly expressed NOS-IR staining of vessels supplying the dorsal sacral gray commissure and dorsal horn in S1-S3 segments. cNOS activity, based on a radioassay of compartmentalized gray and white matter regions of lower lumbar segments and non-compartmentalized gray and white matter of S1-S3 segments, proved to be highly variable for both post-constriction periods.     

Neurobiology of trigeminal pain

The brainstem trigeminal complex integrates somatosensory inputs from orofacial areas and meninges. Recent studies have shown the existence of a double representation of pain within the brainstem, at the level of both caudalis and oralis subnuclei. Noxious messages are mainly conveyed by C-fibers that activate the subnucleus caudalis neurons. These neurons in turn activate the subnucleus oralis whose neurons share similar features with the deep spinal dorsal horn neurons. In contrast with the nearness of the laminar organization of the dorsal horn, the vertical organization of the trigeminal complex offers an easier access for the study of segmental mechanisms of nociceptive processing. This model allowed us to show the existence of subtle NMDA-related mechanisms of segmental nocious processing. The trigeminal complex conveys nociceptive messages to several brainstem and thalamic relays that activate a number of cortical areas responsible for pain sensations and reactions. Cortical processing is sustained by reciprocal interactions with thalamic areas and also by a direct modulation of their pre-thalamic relays. The dysfunction of these multiple modulatory mechanisms probably plays a key role in the pathophysiology of chronic trigeminal pain.     

Synaptic activation of thoracic interneurons by reticulospinal fibers of the lateral funiculus

Synaptic responses of different functional groups of interneurons in segments T10 and T11 to stimulation of the ipsilateral and contralateral medullary reticular formation were investigated in anesthetized cats with only the ipsilateral lateral funiculus remaining intact. Activation of reticulospinal fibers of the lateral funiculus with conduction velocities of 30–100 m/sec was shown to induce short-latency and, in particular, monosynptic EPSPs in all types of cells tested: in interneurons excited by group Ia muscle afferents, in cells activated only by high-threshold cutaneous and muscle afferents (afferents of the flexor reflex), in cells activated mainly by descending systems, and, to a lesser degree, in neurons connected with low-threshold cutaneous afferents. These cell populations are located mainly in the central and lateral parts of Rexed's lamina VII. Most neurons in laminae I–V of the dorsal horn, except six cells located in the superficial layers of the dorsal horn, received no reticulofugal influences. The functional organization of connections of the lateral reticulospinal tract with spinal neurons is discussed and compared with the analogous organization of the medial reticulospinal tract, and also of the "lateral" (cortico- and rubrospinal) descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 150–161, March–April, 1978.