Lamina X of primate spinal cord: distribution of five neuropeptides and serotonin

The tracts, cytoarchitecture, and neurochemistry of the spinal cord

The human spinal cord can be described using a range of nomenclatures with each providing insight into its structure and function. Here we have comprehensively reviewed the key literature detailing the general structure, configuration of tracts, the cytoarchitecture of Rexed's laminae, and the neurochemistry at the spinal segmental level. The purpose of this review is to detail current anatomical understanding of how the spinal cord is structured and to aid researchers in identifying gaps in the literature that need to be studied to improve our knowledge of the spinal cord which in turn will improve the potential of therapeutic intervention for disorders of the spinal cord.

Neurochemistry study of spinal cord in non-human primate (Sapajus spp.)

The spinal cord is involved in local, ascending and descending neural pathways. Few studies analyzed the distribution of neuromediators in the laminae of non-human primates along all segments. The present study described the classic neuromediators in the spinal cord of the non-human primate Sapajus spp. through histochemical and immunohistochemical methods. Nicotinamide adenine dinucleotide hydrogen phosphate-diaphorase (NADPH-d) method showed neuronal somata in the intermediolateral column (IML), central cervical nucleus (CCN), laminae I, II, III, IV, V, VI, VII, VIII and X, besides dense presence of nerve fibers in laminae II and IX. Acetylcholinesterase (AChE) activity was evident in the neuronal somata in laminae V, VI, VII, VIII, IX, CCN, IML and in the Clarke’s column (CC). Immunohistochemistry data revealed neuronal nitric oxide synthase (nNOS) immunoreactivity in neuronal somata and in fibers of laminae I, II, III, VII, VIII, X and IML; choline acetyltransferase (ChAT) in neuronal somata and in fibers of laminae VII, VIII and IX; calcitonin gene-related peptide (CGRP) was noticed in neuronal somata of lamina IX and in nerve fibers of laminae I, II, III, IV, V, VI and VII; substance P (SP) in nerve fibers of laminae I, II, III, IV, V, VI, VII, VIII, IX, X, CCN, CC and IML; serotonin (5-HT) and vesicular glutamate transporter-1 (VGLUT1) was noticed in nerve fibers of all laminae; somatostatin (SOM) in neuronal somata of laminae III, IV, V, VI, VII, VIII and IX and nerve fibers in laminae I, II, V, VI, VII, X and IML; calbindin (Cb) in neuronal somata of laminae I, II, VI, VII, IX and X; parvalbumin (PV) was found in neuronal somata and in nerve fibers of laminae III, IV, V, VI, VII, VIII, IX and CC; finally, gamma-amino butyric acid (GABA) was present in neuronal somata of laminae V, VI, VII, VIII, IX and X. This study revealed interesting results concerning the chemoarchitecture of the Sapajus spp. spinal cord with a distribution pattern mostly similar to other mammals. The data corroborate the result described in literature, except for some differences in CGRP, SP, Cb, PV and GABA immunoreactivities present in neuronal somata and in nerve fibers. This could suggest certain specificity for the neurochemistry distribution in this non-human primate species, besides adding relevant data to support further studies related to processes involving spinal cord components.

Ganglioside GM3 synthase depletion reverses neuropathic pain and small fiber neuropathy in diet-induced diabetic mice

Background

Small fiber neuropathy is a well-recognized complication of type 2 diabetes and has been shown to be responsible for both neuropathic pain and impaired wound healing. In previous studies, we have demonstrated that ganglioside GM3 depletion by knockdown of GM3 synthase fully reverses impaired wound healing in diabetic mice. However, the role of GM3 in neuropathic pain and small fiber neuropathy in diabetes is unknown.

Purpose

Determine whether GM3 depletion is able to reverse neuropathic pain and small fibers neuropathy and the mechanism of the reversal.

Results

We demonstrate that GM3 synthase knockout and the resultant GM3 depletion rescues the denervation in mouse footpad skin and fully reverses the neuropathic pain in diet-induced obese diabetic mice. In cultured dorsal root ganglia from diet-induced diabetic mice, GM3 depletion protects against increased intracellular calcium influx in vitro.

Conclusions

These studies establish ganglioside GM3 as a new candidate responsible for neuropathic pain and small fiber neuropathy in diabetes. Moreover, these observations indicate that systemic or topically applied interventions aimed at depleting GM3 may improve both the painful neuropathy and the wound healing impairment in diabetes by protecting against nerve end terminal degeneration, providing a disease-modifying approach to this common, currently intractable medical issue.

CXCR4 chemokine receptor signaling mediates pain in diabetic neuropathy

Background

Painful Diabetic Neuropathy (PDN) is a debilitating syndrome present in a quarter of diabetic patients that has a substantial impact on their quality of life. Despite this significant prevalence and impact, current therapies for PDN are only partially effective. Moreover, the cellular mechanisms underlying PDN are not well understood. Neuropathic pain is caused by a variety of phenomena including sustained excitability in sensory neurons that reduces the pain threshold so that pain is produced in the absence of appropriate stimuli. Chemokine signaling has been implicated in the pathogenesis of neuropathic pain in a variety of animal models. We therefore tested the hypothesis that chemokine signaling mediates DRG neuronal hyperexcitability in association with PDN.

Results

We demonstrated that intraperitoneal administration of the specific CXCR4 antagonist AMD3100 reversed PDN in two animal models of type II diabetes. Furthermore DRG sensory neurons acutely isolated from diabetic mice displayed enhanced SDF-1 induced calcium responses. Moreover, we demonstrated that CXCR4 receptors are expressed by a subset of DRG sensory neurons. Finally, we observed numerous CXCR4 expressing inflammatory cells infiltrating into the DRG of diabetic mice.

Conclusions

These data suggest that CXCR4/SDF-1 signaling mediates enhanced calcium influx and excitability in DRG neurons responsible for PDN. Simultaneously, CXCR4/SDF-1 signaling may coordinate inflammation in diabetic DRG that could contribute to the development of pain in diabetes. Therefore, targeting CXCR4 chemokine receptors may represent a novel intervention for treating PDN.

Calcitonin gene-related peptide (CGRP) and its receptor components in human and rat spinal trigeminal nucleus and spinal cord at C1-level

Background

Calcitonin gene-related peptide (CGRP) has a key role in migraine pathophysiology and is associated with activation of the trigeminovascular system. The trigeminal ganglion, storing CGRP and its receptor components, projects peripheral to the intracranial vasculature and central to regions in the brainstem with Aδ- and C-fibers; this constitutes an essential part of the pain pathways activated in migraine attacks. Therefore it is of importance to identify the regions within the brainstem that processes nociceptive information from the trigeminovascular system, such as the spinal trigeminal nucleus (STN) and the C1-level of the spinal cord. Immunohistochemistry was used to study the distribution and relation between CGRP and its receptor components - calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1 (RAMP1) - in human and rat STN and at the C1-level, using a set of newly well characterized antibodies. In addition, double-stainings with CGRP and myelin basic protein (MBP, myelin), synaptophysin (synaptic vesicles) or IB4 (C-fibers in general) were performed.

Results

In the STN, the highest density of CGRP immunoreactive fibers were found in a network around fiber bundles in the superficial laminae. CLR and RAMP1 expression were predominately found in fibers in the spinal trigeminal tract region, with some fibers spanning into the superficial laminae. Co-localization between CGRP and its receptor components was not noted. In C1, CGRP was expressed in fibers of laminae I and II. The CGRP staining was similar in rat, except for CGRP positive neurons that were found close to the central canal. In C1, the receptor components were detected in laminae I and II, however these fibers were distinct from fibers expressing CGRP as verified by confocal microscopy.

Conclusions

This study demonstrates the detailed expression of CGRP and its receptor components within STN in the brainstem and in the spinal cord at C1-level, and shows the possibility of CGRP acting postjunctionally in these areas putatively involved in primary headaches.

Spinal cord mechanisms mediating behavioral hyperalgesia induced by neurokinin-1 tachykinin receptor activation in the rostral ventromedial medulla

Hyperalgesia in animal injury models is linked to activation of descending raphespinal modulatory circuits originating in the rostral ventromedial medulla (RVM). A neurokinin-1 (NK-1) receptor antagonist microinjected into the RVM before or after inflammation produced by complete Freund's adjuvant (CFA) resulted in an attenuation of thermal hyperalgesia. A transient (acute) or a continuous infusion of Substance P (SP) microinjected into the RVM of non-inflamed animals led to similar pain hypersensitivity. Intrathecal pretreatment or post-treatment of a 5-HT3 receptor antagonist (Y-25130 or ondansetron) blocked the SP-induced hyperalgesia. The SP-induced hyperalgesia was both GABA(A) and NMDA receptor-dependent after pre- and post-treatment with selective antagonists at the spinal level. A microinjection of SP into the RVM also led to increased NMDA NR1 receptor subunit phosphorylation in spinal cord tissue. The GABA(A) receptor-mediated hyperalgesia involved a shift in the anionic gradient in dorsal horn nociceptive neurons and an increase in phosphorylated NKCC1 protein (isoform of the Na-K-Cl cotransporter). Following a low dose of SP infused into the RVM, intrathecal muscimol (GABA(A) agonist) increased SP-induced thermal hyperalgesia, phosphorylated NKCC1 protein expression, and NMDA NR1 subunit phosphorylation in the spinal cord. The thermal hyperalgesia was blocked by intrathecal gabazine, the GABA(A) receptor antagonist, and MK-801, the NMDA receptor channel blocker. These findings indicate that NK-1 receptors in the RVM are involved in SP-induced thermal hyperalgesia, this hyperalgesia is 5-HT3-receptor dependent at the spinal level, and involves the functional interaction of spinal GABA(A) and NMDA receptors.

Paraventricular thalamic nucleus: subcortical connections and innervation by serotonin, orexin, and corticotropin-releasing hormone in macaque monkeys

The present study examines subcortical connections of paraventricular thalamic nucleus (Pa) following small anterograde and retrograde tracer injections in cynomolgus monkeys (Macaca fascicularis). An anterograde tracer injection into the dorsal midline thalamus revealed strong projections to the accumbens nucleus, basal amygdala, lateral septum, and hypothalamus. Retrograde tracer injections into these areas labeled neurons specifically in Pa. Following a retrograde tracer injection into Pa, labeled neurons were found in the hypothalamus, dorsal raphe, and periaqueductal gray. Pa contained a remarkably high density of axons and axonal varicosities immunoreactive for serotonin (5-HT) and orexin/hypocretin (ORX), as well as a moderate density of fibers immunoreactive for corticotropin-releasing hormone (CRH). A retrograde tracer injection into Pa combined with immunohistochemistry demonstrated that ORX and 5-HT axons originate from neurons in the hypothalamus and midbrain. Pa-projecting neurons were localized in the same nuclei of the hypothalamus, amygdala, and midbrain as CRH neurons, although no double labeling was found. The connections of Pa and its innervation by 5-HT, ORX, and CRH suggest that it may relay stress signals between the midbrain and hypothalamus with the accumbens nucleus, basal amygdala, and subgenual cortex as part of a circuit that manages stress and possibly stress-related psychopathologies.

Contribution of substance P and neurokinin A to the differential injury-induced thermal and mechanical responsiveness of lamina I and V neurons

In a previous report, we compared the properties of lamina V neurons of the spinal cord dorsal horn in wild-type mice and in mice with a deletion of the preprotachykinin-A (PPT-A) gene, which encodes substance P (SP) and neurokinin A (NKA). The mutant mice had pronounced deficits in the response to thermal stimulation, both before and after mustard oil induced sensitization. Here, we extended our analysis to the properties of lamina I neurons and also examined responsiveness to mechanical stimulation. Consistent with the properties of lamina V neurons, in the PPT-A mutant mice we found significantly reduced responses of lamina I neurons to noxious thermal stimulation, and mustard oil sensitization of these neurons to heat was lost. In contrast, not only were the responses of lamina I neurons to noxious mechanical stimulation unchanged in the mutant mice, but in neither the wild-type nor the mutant mice could sensitization be induced. However, mustard oil profoundly sensitized lamina V neurons to mechanical stimulation in both wild-type and mutant mice. We conclude that SP and/or NKA are required for the transmission of noxious thermal stimulation by lamina I and V neurons, both before and after tissue injury. The persistence of mechanical sensitization of lamina V neurons in the mutant mice further shows that mustard oil induces mechanical and thermal sensitization through different mechanisms. Finally, we conclude that lamina I sensitization to mechanical stimulation is not required for this form of injury-increased responsiveness of lamina V neurons.

The caudal end of the rat spinal cord: transformation to and ultrastructure of the filum terminale

Contrary to the current belief, the spinal cord of the rat does not terminate with the conus terminalis (CT), but its basic components (central canal, gray matter, white matter) continue in the filum terminale (FT). Proceeding caudally in the conus terminalis, first the motoneuron cell column discontinues in the ventral horn. More caudally the dorsal horns separate from the intermediate zone, and discontinue. The ensuing filum terminale consists of the slit-like central canal lined by ciliated ependymal cells, the periventricular gray matter and the peripheral white matter. Uniform small size neurons and glial cells populate the gray matter. Ultrastructural analysis revealed various types of axodendritic and axosomatic synapses as well as fine unmyelinated axons. The white matter consists mainly of myelinated nerve fibers. The neuronal components of the filum terminale, if they occur also in the human spinal cord, should be involved in the diagnosis and treatment of various diseases, e.g. tethered spinal cord syndrome, vascular malformations and disraphysm.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.

Dorsal border periaqueductal gray neurons project to the area directly adjacent to the central canal ependyma of the C4-T8 spinal cord in the cat

In a previous study horseradish peroxidase (HRP) injections in the upper thoracic and cervical spinal cord revealed some faintly labeled small neurons at the dorsal border of the periaqueductal gray (PAG). The present light microscopic and electronmicroscopic tracing study describes the precise location of these dorsal border PAG-spinal neurons and their terminal organization. Wheat germ agglutinin-conjugated HRP (WGA-HRP) injections into cervical and upper thoracic spinal segments resulted in several hundreds of small retrogradely labeled neurons at the dorsal border of the ipsilateral caudal PAG. These neurons were not found after injections in more caudal segments. WGA-HRP injections in the dorsal border PAG region surprisingly resulted in anterogradely labeled fibers terminating in the area dorsally and laterally adjoining the central canal ependyma of the C4-T8 spinal cord. No anterogradely labeled fibers were found more caudal in the spinal cord. The labeled fibers found in the upper cervical cord were not located in the area immediately adjoining the ependymal layer of the central canal, but in the lateral part of laminae VI, VII and VIII and in area X bilaterally. Electronmicroscopic results of one case show that the dorsal border PAG-spinal neurons terminate in the neuropil of the subependymal area and in the vicinity of the basal membranes of capillaries located laterally to the central canal. The terminal profiles contain electron-lucent and densecored vesicles, suggesting a heterogeneity of possible transmitters. A striking observation was the lack of synaptic contacts, suggesting nonsynaptic release from the profiles. The function of the dorsal border PAG-spinal projection is unknown, but considering the termination pattern of the dorsal border PAG neurons on the capillaries the intriguing similarity between this projection system and the hypothalamohypophysial system is discussed.

Localization of enkephalin immunoreactivity in the spinal cord of the long-tailed ray Himantura fai

Enkephalin-like immunoreactivity (ENK-LI) was found throughout the spinal cord of the long-tailed ray Himantura fai. The densest ENK-LI was in the superficial portion of lamina A of the dorsal horn. Lamina B and the deeper parts of lamina A contained radially oriented, labelled fibres. Laminae C, D, and E contained many longitudinally oriented fascicles which were surrounded by a reticulum of transversely oriented, labelled fibres, some of which projected into the ventral and lateral funiculi. Labelled fibres were found in the dorsal commissure and around the central canal, but the later did not cross the midline. One-third of all enkephalinergic cells were found throughout laminae A and B, while two-thirds were located in the medial half of C, D, and E. Occasionally a labelled cell was located in the lateral funiculus. The ventral horn (laminae F and G) contained many enkephalinergic fibres but no labelled nuclei. A few dorsal column axons contained ENK-LI. In the lateral funiculus there were two groups of labelled axons, a superficial, dorsolateral group, and a deeper group, occupying a crescent-shaped region. The ventral funiculus also contained many labelled axons. The central projection of the dorsal root passed through the substantia gelatinosa and divided into rostrally and caudally projecting fascicles within lamina C. The root, and these fascicles, both lacked ENK-LI. In contrast, the fascicles in laminae D and E did contain enkephalinergic fibres. The origin of the various fibre systems and the role of enkephalin in the regulation of sensory processing and motor output are discussed.

Patch-clamp characterization of nicotinic receptors in a subpopulation of lamina X neurones in rat spinal cord slices

1. Nicotinic acetylcholine receptors (nAChRs) on lamina X neurones in neonate (P1-P12) rat transverse thoracolumbar spinal cord slices were studied using the whole-cell patch-clamp technique. These visually selected neurones are located dorsal to the central canal, mainly in the ventral half of the dorsal commissure. 2. Pressure application of the nicotinic agonist 1,1-dimethyl-4-phenyl-piperazinium (DMPP) (1 mM) induced a rapid depolarization on which action potentials are superimposed. 3. At -50 mV, DMPP (1 mM), pressure ejected for 100 ms, induced a fast inward current with a mean amplitude of -280 pA (n = 28) in 90% of the neurones recorded. Superfusion of tetrodotoxin (TTX), a solution containing 0 Ca(2+)-high Mg2+, CdCl2 or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) did not abolish the DMPP-induced current, which confirmed a direct postsynaptic effect of DMPP on recorded neurones. 3. The current-voltage (I-V) relationship for DMPP-induced current exhibited a reversal potential of 0 mV (NaCl outside, potassium gluconate inside) and a strong inward rectification. 4. The DMPP-induced responses were blocked by mecamylamine, hexamethonium and d-tubocurarine (dTC) but were insensitive to alpha-bungarotoxin and methyllycaconitine (MLA). 5. We conclude that lamina X neurones located dorsally to the central canal possess nicotinic acetylcholine receptors. Activation of these nicotinic receptors results in depolarization and generation of action potentials. These receptors may be involved in the modulation of the somato- and viscerosensory transmission.

5-HT1A receptor localization on the axon hillock of cervical spinal motoneurons in primates

Serotonin (5-HT) has direct and specific effects on the activity of spinal cord motoneurons. The 5-HT1A receptor has been shown to mediate motoneuron responses in spinal reflex pathways using the highly selective 5-HT1A receptor agonist 8-OH-DPAT. We have developed an antipeptide antibody that recognizes a specific region (the second external loop) of the 5-HT1A receptor. This 5-HT1A receptor antibody labels populations of neurons and glia in the primate cervical spinal cord. The highest receptor density is present in the superficial lamina of the dorsal horn, around the central canal, and on the axon hillock of large ventral horn motoneurons. The cellular labeling pattern on motoneurons shows a single, densely stained, tapering process emanating from the perikaryon. A more diffuse label is also present throughout the soma. Dendritic labeling was not apparent. These results suggest that post-synaptic 5-HT1A receptors may be involved in modulating spinal motoneuron activity at the key site of action potential initiation, the axon hillock.

Distribution of secretoneurin immunoreactivity in the spinal cord and lower brainstem in comparison with that of substance P and calcitonin gene-related peptide

Secretoneurin is a peptide of 33 amino acids generated in brain by proteolytic processing of secretogranin II. The distribution of this newly characterized peptide was investigated by means of immunocytochemistry and in situ hybridization in the spinal cord and lower brainstem of the rat. The staining pattern of secretoneurin immunoreactivity (IR) was compared to that of substance P (SP) and calcitonin gene-related peptide (CGRP) in adjacent sections. A high density of secretoneurin-IR fibers and terminals was found in lamina I and outer lamina II of the caudal trigeminal nucleus and of the spinal cord at all levels, around the central canal, and in the sympathetic and parasympathetic areas of the lateral cell columns. The ventral horn displayed a low to moderate density of secretoneurin-IR. The highest number of secretogranin II mRNA-containing cells was found in lamina II of the dorsal horn and in neurons of the dorsal root ganglia. In the white matter, secretoneurin-IR was most prominent in the dorsolateral part of the lateral funiculus and in the tract of Lissauer. The distributions of secretoneurin-IR and SP-IR were strikingly similar. CGRP-IR and secretoneurin-IR overlapped in the outer laminae of the dorsal horn, in the lateral cell column, and probably in some motoneurons. This study establishes that, like SP and CGRP, secretoneurin is a peptide highly concentrated in the terminal field of primary afferents and in sympathetic and parasympathetic areas. Thus secretoneurin might be involved in the modulation of afferent transmission.

Deafferentation-induced changes in neuropeptides of the adult rat dorsal horn following pronase injection of the sciatic nerve

The effect of deafferentation on the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), somatostatin (SS), and cholecystokinin (CCK) in the lumbar dorsal horn of the adult rat was examined by the indirect immunohistochemical method. Deafferentation was induced by injecting the sciatic nerve of anesthetized rats with proteolytic enzymes (20 mg pronase), which cause selective death of the nerve's ganglion cells and degeneration of their terminal arborization in the spinal cord. The density of immunolabel of each peptide was determined by using a computerized densitometry analysis system in two animal groups, i.e., short-term (10-13 days after injection) and long-term (4-9 months). In both groups, the deafferentation produced a significant ipsilateral depletion of CGRP, SP, CCK, and SS immunoreactivity. This depletion was limited to the area occupied by the sciatic terminals in the dorsal horn. In the long-term group, the loss of CGRP and SP staining was significantly less than that in the short-term animals, thus indicating partial recovery. A similar, but not statistically significant, trend was observed for CCK and SS. The large decrease in CGRP and SP seen in short-term animals reflects the large contribution of the sciatic nerve to the lumbar dorsal horn. The partial recovery of peptides demonstrates the plasticity of the nervous system and may parallel sprouting of primary afferents from other nerves, such as the saphenous nerve, as we have demonstrated in previous studies.

Distribution of 5-HT1 binding sites in cat spinal cord

Quantitative analysis of high affinity [3H]5-HT binding to 5-HT1 receptors in the cervical, thoracic, lumbar, and sacral spinal cord of the cat revealed specific binding throughout the grey matter, with the highest levels of binding in laminae II and III, and the lowest levels in laminae I and VII. Relatively high levels were also observed in the thoracic intermediolateral cell column. There were no significant differences in the degree of binding between various segmental levels. Comparison of these data with published maps of 5-HT immunoreactivity reveals--with the exception of lamina I--a close correspondence between the degree of immunoreactivity and the degree of 5-HT binding. These results suggest that 5-HT plays an important role in a variety of spinal cord sensory, motor and autonomic functions.

Distribution of vasoactive intestinal peptide- and peptide histidine isoleucine amide-like immunoreactive neurons and fibers in the thoracic spinal cord of the rat

The distributions of vasoactive intestinal peptide (VIP)- and peptide histidine isoleucine amide (PHI)-immunoreactivities (IR) in the thoracic spinal cord of the rat are described. VIP- and PHI-IR were present in cells and fibers in the lateral spinal nucleus, lamina VII, nucleus proprius, substantia gelatinosa, intermediolateral cell column, and the area around the central canal. The functions of these peptides in the thoracic spinal cord are not known; however, their locations suggest that they are involved in sensory and autonomic functions, among others.

[125I]vasoactive intestinal polypeptide binding sites: quantitative autoradiographic distribution in the rat spinal cord

The quantitative autoradiographic distribution of [125I]vasoactive intestinal polypeptide (VIP) receptor binding sites was investigated in the rat spinal cord. [125I]VIP binding sites are discretely distributed, with a rostro-caudal gradient, along the longitudinal length of the cord; highest densities of sites being observed in its lumbar and sacral segments. In transverse sections, highest levels of [125I]VIP sites are present in laminae I and II, around the central canal, and in the parasympathetic lateral horn of the sacral segment. Moderate densities are seen along the medial border of the dorsal horn and the sympathetic lateral horn of the thoracic cord. Low amounts of labeling are observed in most structures of the ventral horn while white matter areas are apparently devoid of specific [125I]VIP binding. Thus, the distribution of spinal [125I]VIP receptor sites correlates well with that of VIP-like immunoreactive materials and support possible roles for this peptide in sensory neurotransmission and in the control of autonomic functions.

Ultrastructural localization of substance P, met-enkephalin, and somatostatin immunoreactivity in lamina X of the primate spinal cord

The ultrastructural localization of substance P (SP), met-enkephalin (MENK), and somatostatin (SS) in the lamina X area surrounding the central canal of the macaque monkey was examined by the indirect peroxidase-antiperoxidase method. The most common synaptic terminals in lamina X were simple terminals (S) with small rounded or pleomorphic clear vesicles; one to two dense-core vesicles were occasionally also present. These were found on soma, dendrites, and dendritic spines, in all regions of lamina X. A second class of terminal with round or oval clear vesicles was glomerular (G) in shape, with scalloped edges, and contained many mitochondria. These large terminals had several synaptic contacts onto dendrites, spines, and small terminals and were found mainly in the lateral region. The third class (L) contained small clear vesicles and several vesicles with large, dense cores (100-125 nm), and also contacted dendrites, mainly lateral to the canal. The fourth class of terminal (D) contained small clear vesicles and several vesicles with small, dense cores (75-100 nm); these contacted dendrites and somata in all areas. Very few terminals with flat vesicles were identified. There was an unequal distribution of immunoreactivity among the several terminal classes identified in lamina X. Most SP terminals were S terminals, but SP L terminals were also common; few were D terminals. MENK terminals were usually either S terminals or D terminals; L terminals were rarely MENK positive. SS terminals were commonly D terminals or S terminals; L terminals were also rarely SS positive. Only SP terminals were identified as G terminals. Synaptic targets of SP, MENK, and SS terminals were most commonly dendrites. In addition to unlabelled neurons, peptidergic neurons and their processes were also synaptic targets of terminals containing the same peptide. The distributions of these peptides in primate lamina X differ from that of the same peptides in primate superficial dorsal horn. These differences are important, in consideration of some of the parallels that may be drawn between the lamina X area and the superficial dorsal horn; both areas have high concentrations of the same peptides, receive nociceptive primary afferents, and contain spinothalamic and other projection neurons. Nevertheless, comparison of the distribution of immunoreactivity among terminal classes indicates that neurochemical organization at the ultrastructural level is quite distinct in each of the two areas. This may also reflect other roles of the lamina X area, including its involvement in visceral functions, although it would be expected that this element might be less prominent at the cervical levels we investigated.

Cholecystokinin-like immunoreactivity in the rat spinal cord: effects of thoracic transection

A study of cholecystokinin-like immunoreactivity in the lumbar (L1-L5) spinal cord segments of rats was realised 24-48 hours after complete thoracic transection (T6-T8). A comparison was made with corresponding spinal cord segments from control and sham-operated animals. The immunocytochemical study with light microscopy showed cholecystokinin-like immunoreactive cell bodies in laminae VII and X at L1-L5, caudal to the transection. In addition, the immunoreactivity was greatly enhanced in bundles of the dorsolateral funiculus compared to sham-operated animals. Our results suggest that part of cholecystokinin-like cell bodies of laminae VII and X send projections to supraspinal sites. Some of these supraspinal projections would go through the dorsolateral funiculus. In the lumbar dorsal horn of operated animals, the immunoreactivity was greatly enhanced in lamina I, while it was slightly decreased in lamina II, compared to control animals. Using electron microscopy, in lamina I, the immunoreactivity localized in different neurites was generally very intense. Moreover, axon terminals showed swelling: their mean size was 0.8-1.8 microns (0.5-1.2 in control animals). This result suggests that some cholecystokinin-like neurons also project to lamina I of rostral cervical segments. In lamina II, numerous degenerating axons were observed (24 hours after thoracic spinal transection). This would suggest that part of descending cholecystokinin-like projections terminate in lamina II.

Descending adrenergic input to the primate spinal cord and its possible role in modulation of spinothalamic cells

The present study focuses on 3 different aspects of the descending adrenergic system in the primate: (1) the distribution of adrenergic fibers and terminals in the spinal cord, (2) the source of this input and (3) the possible physiological effects of this system on spinal nociceptive processing. Antibodies to the enzyme phenylethanolamine-N-methyltransferase (PNMT) were employed to map the distribution of epinephrine-containing axonal profiles in the primate spinal cord. Smooth longitudinally oriented fibers were localized to the outer edge of the lateral funiculus. PNMT-containing axonal enlargements were distributed to the superficial dorsal horn, intermediate gray matter and the region surrounding the central canal at all spinal cord levels. PNMT-immunostained profiles were also observed in the intermediolateral cell column. A double labeling study employing retrograde transport of HRP from the spinal cord and PNMT immunohistochemistry identified a small population of HRP-PNMT-labeled neurons in the 'C1' region at the levels of the medulla and ponto-medullary junction. Thus, these cells are a probable source of adrenergic input to the spinal cord. Electrophysiological studies demonstrated that iontophoresis of epinephrine onto identified primate spinothalamic tract neurons in the lumbar dorsal horn resulted in inhibition of the glutamate-induced firing of these cells. The data from these studies support the hypothesis that adrenergic (PNMT-containing) cells in the caudal brainstem project to all levels of the cord and may contribute to descending modulation of nociceptive processing at these levels.

Substance P-evoked release of acetylcholine from isolated spinal cord of the newborn rat

Isolated spinal cords of newborn rats were perfused with artificial cerebrospinal fluid and the release of endogenous acetylcholine was measured using high-performance liquid chromatography with an electrochemical detection system. Application of high-K+ (90 mM) medium evoked about an eight-fold increase in the acetylcholine release, and the K(+)-evoked release was Ca2+ dependent. Veratridine (20 microM) also evoked about a four-fold increase in the acetylcholine release, and this increase was suppressed by 0.2 microM tetrodotoxin. Application of substance P at 0.3-3 microM evoked a concentration-dependent release of acetylcholine. The substance P-evoked acetylcholine release was Ca2+ dependent and abolished by tetrodotoxin. Neurokinin A, neurokinin B, acetyl-Arg6-septide and senktide (3 microM each) also evoked a release of acetylcholine. Electrophysiological experiments using isolated spinal cords of newborn rats showed that bath application of substance P induced a depolarization of motoneurons, which was enhanced by edrophonium. This enhancement of substance P-induced depolarization by edrophonium disappeared in a low-Ca2+ medium or in the presence of atropine and dihydro-beta-erythroidine. In the presence of edrophonium and dihydro-beta-erythroidine, substance P induced an inhibition of monosynaptic reflex, and this inhibition was abolished by atropine. These results suggest that substance P and other tachykinins induce a release of acetylcholine from the newborn rat spinal cord by exciting cholinergic neurons.

Receptor changes in the spinal cord of sheep associated with exposure to chronic pain

There is evidence that post-injury hypersensitivity is partly due to changes in the central nervous system. Sheep with foot rot were used to investigate the effect of chronic pain on some receptors thought to be involved in spinal nociceptive processing systems (alpha 2 adrenoceptor and mu and delta opioid receptors). Saturation binding studies showed a variable distribution of [3H] clonidine (alpha 2 adrenoceptor agonist) in the spinal cord of normal sheep. The number of receptors (Bmax) present in areas thought to be involved in nociceptive processing, laminae I and II and lamina X, increased to 131% and 169% of control sheep values respectively in animals exposed to chronic pain. The affinity of the receptors (KD), however, remained unchanged at approximately 2 nM. There was less [3H]DAGO (mu opioid agonist) and [3H]DPDPE (delta opioid agonist) binding in the sheep spinal cord. Both opioid receptor types being mainly located in the superficial dorsal horn. The [3H]DPDPE binding was unchanged in the sheep with foot rot, whilst the number (Bmax), but not the affinity, of the [3H]DAGO binding sites increased in laminae I and II in lame animals to 130% of the control sheep values. Hence, in animals in chronic pain, the number of alpha 2 adrenoceptors and mu opioid receptors increased mainly in areas of the sheep spinal cord associated with nociception.

Calcium-binding proteins, parvalbumin- and calbindin-D 28k-immunoreactive neurons in the rat spinal cord and dorsal root ganglia: a light and electron microscopic study

The distribution of two calcium-binding proteins, parvalbumin (PV) and calbindin-D 28K (CaBP), was studied by the peroxidase-anti-peroxidase immunohistochemical method at the light and electron microscopic level in the rat spinal cord and dorsal root ganglia. The possible coexistence of these two proteins was also investigated. PV-positive neurons were revealed in all layers of the spinal cord, except lamina I, which was devoid of labelling. Most of the PV-positive cells were found in the inner layer of lamina II, lamina III, internal basilar nucleus, central gray region, and at the dorsomedial and ventromedial aspects of the lateral motor column in the ventral horn. Neuronal processes intensely stained for PV sharply delineated inner lamina II. With the electron microscope most of them appeared to be dendrites, but vesicle containing profiles were also found in a smaller number. CaBP-positive neurons appeared to be dispersed all over the spinal gray matter. The great majority of them were found in laminae I, II, IV; the central gray region; the intermediolateral nucleus; and in the ventral horn just medial to the lateral motor column. Laminae I and II were densely packed with CaBP-positive punctate profiles that proved to be dendrites and axons in the electron microscope. A portion of labelled neurons in lamina IV and on the ventromedial aspect of the lateral motor column in the ventral horn disclosed both PV- and CaBP-immunoreactivity. All of the funiculi of the spinal white matter contained a large number of fibres immunopositive for both PV and CaBP. The highest density of CaBP-positive fibres was found in the dorsolateral funiculus, which was also densely packed with PV-positive fibres. PV-positive fibres were even more numerous in the dorsal part of the dorsal funiculus. The territory of the gracile funiculus in the brachial cord and that of the pyramidal tract in its whole extent were devoid of labelled fibres. In the thoracic cord, the dorsal nucleus of Clarke received a large number of PV-positive fibres. Dorsal root ganglia displayed both PV- and CaBP-immunopositivity. The cell diameter distribution histogram of PV-positive neurons disclosed two peaks--one at 35 microns and the other at 50 microns. CaBP-positive cells in the dorsal root ganglia corresponded to subgroups of small and large neurons with mean diameters of 25 microns and 45 microns, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Cutaneous nerve-evoked cholinergic inhibition of monosynaptic reflex in the neonatal rat spinal cord: involvement on M2 receptors and tachykininergic primary afferents

The mechanisms of a cutaneous nerve-evoked inhibition of monosynaptic reflex were investigated in an isolated spinal cord-peripheral nerve preparation of the neonatal rat. Conditioning stimulation of the saphenous nerve, with five pulses at 50 Hz and a strength sufficient to activate C fibers, evoked an inhibition lasting about 20 s of the monosynaptic reflex that was elicited by stimulation of the nerve branch to quadriceps femoris muscle and recorded from the L3 ventral root. This inhibition of monosynaptic reflex was potentiated by an anticholinesterase, edrophonium, and mostly blocked by atropine. Application of acetylcholine, muscarine, bethanechol, carbachol, arecoline and oxotremorine induced an inhibition of monosynaptic reflex. From the effects of muscarinic antagonists, pirenzepine, AF-DX 116, and 4-diphenylacetoxy-N-methylpiperidine on the agonist-evoked and primary afferent-evoked inhibition of monosynaptic reflex it was concluded that the muscarinic receptors involved in the cutaneous nerve-evoked inhibition of monosynaptic reflex are of M2 type. When monosynaptic reflexes were evoked by two successive stimuli with intervals of 15 ms to 1 s, the second response was smaller than the first. This depression of monosynaptic reflex became less pronounced when the reflex was reduced by application of oxotremorine or arecoline or by conditioning stimulation of primary afferents, suggesting that the inhibition of monosynaptic reflex is presynaptic in nature. The late phase of the cutaneous nerve-evoked inhibition of monosynaptic reflex (5-20 s after conditioning stimulation) was markedly depressed by a tachykinin antagonist, spantide. Perfusion of the spinal cord with capsaicin (1 microM) for 1 h also abolished the late phase of the inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

VIP: molecular biology and neurobiological function

In the mammalian brain, a major regulatory peptide is vasoactive intestinal peptide (VIP). This 28 amino acid peptide, originally isolated from the porcine duodenum, was later found in the central and peripheral nervous systems and in endocrine cells, where it exhibits neurotransmitter and hormonal roles. Increasing evidence points to VIP's importance as a mediator or a modulator of several basic functions. Thus, VIP is a major factor in brain activity, neuroendocrine functions, cardiac activity, respiration, digestion, and sexual potency. In view of this peptide's importance, the mechanisms controlling its production and the pathways regulating its functions have been reviewed. VIP is a member of a peptide family, including peptides such as glucagon, secretin, and growth hormone releasing hormone. These peptides may have evolved by exon duplication coupled with gene duplication. The human VIP gene contains seven exons, each encoding a distinct functional domain on the protein precursor or the mRNA. VIP gene transcripts are mainly found in neurons or neuron-related cells. VIP gene expression is regulated by neuronal and endocrine signals that contribute to its developmental control. VIP exerts its function via receptor-mediated systems, activating signal transduction pathways, including cAMP. It can act as a neurotransmitter, neuromodulator, and a secretagog. As a growth and developmental regulator, VIP may have a crucial effect as a neuronal survival factor. We shall proceed from the gene to its multiple functions.

Immunohistochemical distribution of serotonin in spinal autonomic nuclei: I. Fiber patterns in the adult rat

The differential distribution of serotonin (5HT) fibers in spinal laminae VII and X is described for the adult rat. The results indicate that descending 5HT fibers preferentially innervate those regions of lamina VII that contain sympathetic and parasympathetic neurons. In lamina X, especially the dorsal commissural nucleus, large numbers of 5HT fibers are observed throughout the spinal cord. Moreover, sympathetic nuclei are more richly innervated with 5HT than the spinal parasympathetic nuclei. Spinal cord hemisections reveal that spinal autonomic nuclei are differentially innervated: ipsilateral serotoninergic projections to the intermediolateral cell column are preferentially interrupted. In addition, a large crossed 5HT projection exists throughout the length of the spinal cord that decussates five to six spinal segments rostral to its termination. Both crossed and uncrossed 5HT fibers span many spinal segments and have large numbers of collaterals. Spinal cord transections show that the vast majority of spinal 5HT descends from the brainstem but that some 5HT fibers are of intrinsic origin.

Immunohistochemical distribution of serotonin in spinal autonomic nuclei: II. Early and late postnatal ontogeny in the rat

These studies reveal that the postnatal ontogeny of serotonin (5HT) in the sympathetic nuclei of the rat spinal cord is protracted; the adult complement of 5HT-immunoreactive fibers is not achieved until at least 60 days of age. As descending serotonin fibers innervate and demarcate the distribution of preganglionic sympathetic nuclei, rostral-caudal and temporal gradients exist. Additionally, a heterogeneous segmental 5HT ontogenetic pattern is observed in sympathetic nuclei. Most serotonin fibers in laminae VII and X are unorganized at birth except for some sympathetic nuclei in high thoracic regions where the 5HT sympathetic pattern is being initiated. By postnatal day 6 the framework of the 5HT pattern is established in all sympathetic nuclei, and by postnatal day 16 a pattern is formed, which develops into the compact adult state by postnatal day 60. The protracted period of sympathetic 5HT development corresponds with the length of time it takes for the autonomic nervous system to mature. In addition, 5HT intraspinal cell bodies are observed at all time points examined, except for the day of birth, and are found in the same regions as adult 5HT neurons, i.e., dorsal or lateral to the central canal in laminae VII and X and in all spinal segments except cervical levels. Many of the 5HT neurons are pericanalicular and bipolar in appearance. Multipolar 5HT neurons are first observed on postnatal day 45.