Immunocytochemical identification of long ascending peptidergic neurons contributing to the spinoreticular tract in the rat

Substance P-expressing Neurons in the Superficial Dorsal Horn of the Mouse Spinal Cord: Insights into Their Functions and their Roles in Synaptic Circuits

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Substance P-expressing radial cells in lamina II receive half of their excitatory synaptic input from other interneurons.

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They are preferentially innervated by transient central cells that express eGFP in a GRP-eGFP mouse line.

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Around 40% of projection neurons in lamina I express Tac1, the gene for substance P.

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Silencing Tac1 cells in the dorsal horn reduces reflex responses to cold and radiant heat.

The tachykinin peptide substance P (SP) is expressed by many interneurons and some projection neurons in the superficial dorsal horn of the spinal cord. We have recently shown that SP-expressing excitatory interneurons in lamina II correspond largely to a morphological class known as radial cells. However, little is known about their function, or their synaptic connectivity. Here we use a modification of the Brainbow technique to define the excitatory synaptic input to SP radial cells. We show that around half of their excitatory synapses (identified by expression of Homer) are from boutons with VGLUT2, which are likely to originate mainly from local interneurons. The remaining synapses presumably include primary afferents, which generally have very low levels of VGLUT2. Our results also suggest that the SP cells are preferentially innervated by a population of excitatory interneurons defined by expression of green fluorescent protein under control of the gene for gastrin-releasing peptide, and that they receive sparser input from other types of excitatory interneuron. We show that around 40% of lamina I projection neurons express Tac1, the gene encoding substance P. Finally, we show that silencing Tac1-expressing cells in the dorsal horn results in a significant reduction in reflex responses to cold and radiant heat, but does not affect withdrawal to von Frey hairs, or chloroquine-evoked itch.

Preprotachykinin A is expressed by a distinct population of excitatory neurons in the mouse superficial spinal dorsal horn including cells that respond to noxious and pruritic stimuli

Expression of the substance P precursor preprotachykinin A defines a distinct population of superficial dorsal horn excitatory neurons, many of which respond to noxious or pruritic stimuli.

The superficial dorsal horn, which is the main target for nociceptive and pruritoceptive primary afferents, contains a high density of excitatory interneurons. Our understanding of their roles in somatosensory processing has been restricted by the difficulty of distinguishing functional populations among these cells. We recently defined 3 nonoverlapping populations among the excitatory neurons, based on the expression of neurotensin, neurokinin B, and gastrin-releasing peptide. Here we identify and characterise another population: neurons that express the tachykinin peptide substance P. We show with immunocytochemistry that its precursor protein (preprotachykinin A, PPTA) can be detected in ∼14% of lamina I-II neurons, and these are concentrated in the outer part of lamina II. Over 80% of the PPTA-positive cells lack the transcription factor Pax2 (which determines an inhibitory phenotype), and these account for ∼15% of the excitatory neurons in this region. They are different from the neurotensin, neurokinin B, or gastrin-releasing peptide neurons, although many of them contain somatostatin, which is widely expressed among superficial dorsal horn excitatory interneurons. We show that many of these cells respond to noxious thermal and mechanical stimuli and to intradermal injection of pruritogens. Finally, we demonstrate that these cells can also be identified in a knock-in Cre mouse line (Tac1^Cre), although our findings suggest that there is an additional population of neurons that transiently express PPTA. This population of substance P–expressing excitatory neurons is likely to play an important role in the transmission of signals that are perceived as pain and itch.

Neurotrophin-induced preprotachykinin-A gene promoter modulation in organotypic rat spinal cord culture

To study regulation of the preprotachykinin-A gene promoter, we utilised a biolistic gene transfer protocol to deliver a DNA construct that incorporates a portion of the preprotachykinin-A gene promoter and an enhanced green fluorescent protein reporter gene into neonatal rat spinal cord organotypic slices. The ability of the neurokinin-1 receptor agonist [Sar9,Met(O2)11]-substance P, nerve growth factor and brain derived neurotrophic factor to modulate positively preprotachykinin-A gene promoter construct activity, as indicated by de novo enhanced green fluorescent protein expression, was determined. Treatment of organotypic slices with [Sar9, Met(O2)11]-substance P (10 microm, P < 0.05), nerve growth factor (200 ng/mL, P < 0.001) or brain derived neurotrophic factor (200 ng/mL, P < 0.02) significantly increased the proportion of cytomegaloviral promoter-DsRed transfected cells (used to visualise total transfected cells) that co-expressed enhanced green fluorescent protein. The distribution of enhanced green fluorescent protein/DsRed-positive neurones across spinal laminae was broadly in line with the known distribution of spinal Trk and neurokinin-1 receptors. These data suggest a modulated activity of the preprotachykinin-A gene promoter in spinal neurones in vitro by substance P and/or neurotrophins. The functional consequences of such transcriptional changes within central peptidergic circuitry and their relevance to chronic pain are considered.

Effect of nor-trimebutine on neuronal activation induced by a noxious stimulus or an acute colonic inflammation in the rat

Nor-trimebutine is the main metabolite of trimebutine that is used in the treatment of patients with irritable bowel syndrome. Nor-trimebutine has a blocking activity on sodium channels and a potent local anesthetic effect. These properties were used to investigate the effect of nor-trimebutine on spinal neuronal activation induced by models of noxious somato-visceral stimulus and acute colonic inflammation. Nor-trimebutine was administered in rats either subcutaneously 30 min before intraperitoneal administration of acetic acid or intracolonically 30 min before intracolonic infusion of trinitrobenzenesulfonic acid. Abdominal contractions were counted for 1 h as a marker of abdominal pain. c-fos expression was used as a marker of neuronal activation and revealed by immunohistochemistry 1h after intraperitoneal acetic acid injection and 2 h after colonic inflammation. Nor-trimebutine decreased Fos expression in the thoraco-lumbar (peritoneal irritation) and lumbo-sacral (colonic inflammation) spinal cord in laminae I, IIo V, VII and X. This effect was also observed in the sacral parasympathetic nucleus after colonic inflammation. Nor-trimebutine induced a significant decrease of abdominal contractions following intraperitoneal acetic acid injection. These data may explain the effectiveness of trimebutine in the therapy of abdominal pain in the irritable bowel syndrome.

A model of organotypic rat spinal slice culture and biolistic transfection to elucidate factors that drive the preprotachykinin-A promoter

The tachykinin substance P (SP) is a neuropeptide that is expressed in some nociceptive primary sensory afferents and in discrete populations of spinal cord neurons. Expression of spinal SP and the preprotachykinin-A (PPT-A) gene that encodes SP exhibits plasticity in response to conditions such as peripheral inflammation but the mechanisms that regulate expression are poorly understood. We have developed a spinal cord organotypic culture system that is suitable for the analysis of PPT-A gene promoter activity following biolistic transfection of recombinant DNA constructs. Spinal cord organotypic slices showed good viability over a 7-day culture period. Immunostaining for phenotypic markers such as NeuN and beta-III tubulin demonstrated preservation of neurons and their structure, although there was evidence of axotomy-induced down-regulation of NeuN in certain neuronal populations. Neurokinin-1 receptor (NK-1R) immunostaining in laminae I and III was similar to that seen in acute slices. Biolistic transfection was used to introduce DNA constructs into neurons of these organotypic cultures. Following transfection with a construct in which expression of enhanced green fluorescent protein (EGFP) is controlled by the PPT-A promoter, we showed that induction of neuronal activity by administration of a forskolin analogue/high K(+) (10 microM/10 mM) for 24 h resulted in a fourfold increase in the number of EGFP-positive cells. Similarly, a twofold increase was obtained after treatment with the NK-1R-specific agonist [Sar(9),Met (O(2))(11)]-substance P (10 microM). These data demonstrate the usefulness of this model to study physiological and pharmacological factors relevant to nociceptive processing that can modulate PPT-A promoter activity.

Origins of Spinal Ascending Pathways that Reach Central Areas Involved in Visceroception and Visceronociception in the Rat

The location of spinal cells projecting rostrally to central areas that process visceroception and visceronociception were studied in rat using the retrograde transport of a protein - gold complex. Origins of afferents to the nucleus tractus solitarius (the spinosolitary tract), the parabrachial area (the spinoparabrachial tract), the hypothalamus (the spinohypothalamic tract) and the amygdala (the spinoamygdalar tract) were studied at thoracic, lumbar and sacral levels, where spinal visceroceptive areas are concentrated. All of the afore-mentioned pathways have common origins in the lateral spinal nucleus and in the reticular formation of the neck of the dorsal horn at all the levels studied, and also in the dorsal grey commissure and adjacent areas at sacral levels. The spinosolitary and the spinoparabrachial tracts are dense pathways, both of which are also characterized by afferents from the superficial layers of the dorsal horn at all the levels studied and from cells lying in close proximity to some autonomic spinal areas. These autonomic areas are the central autonomic nucleus (dorsal commissural nucleus) of lamina X at thoracolumbar levels and the parasympathetic column at sacral levels; some projections from the intermediolateral cell column at thoracic levels were also noted. Projections from all these autonomic structures to the parabrachial area have not yet been recognized. Thus, the origin of the spinoparabrachial tract closely resembles that of the spinomesencephalic tract that reaches the periaquaductal grey and adjacent areas. The spinohypothalamic and the spinoamygdalar tracts are smaller pathways. Direct spinal connections to the amygdala have not been reported previously. Both the hypothalamus and amygdala receive projections from lamina VII cells at low thoracic and upper lumbar levels in a pattern that resembles that of the preganglionic cells of the intercalated nucleus. Hypothalamic projections from the sacral parasympathetic area were also noted. The use of c-fos as a functional marker to identify spinal neurons that are activated by noxious visceral stimulation suggests that both the spinoparabrachial and the spinosolitary tracts contribute significantly to the central transmission of visceronoceptive messages. Most of the visceronociceptive ascending projections in these pathways issued from lamina I cells. The results presented here confirm previous observations regarding the spinosolitary and the spinohypothalamic tracts and also demonstrate, for the first time, the complex origin of the spinoparabrachial tract and the existence of direct spinal afferents to the amygdala. These findings suggest that rostral transmission and central integration of visceral inputs require several parallel routes. The spinosolitary and spinoparabrachial tracts clearly play a role in conveying information regarding visceronociception.

An immunohistochemical investigation of the opioid cell column in lamina X of the male rat lumbosacral spinal cord

Tri-color immunohistochemistry was employed to examine enkephalin-like immunoreactive neurons in lamina X of the rat lumbosacral spinal cord. Serial coronal sections from levels L1 to S3 were examined. A rostral group of large (40-50 microm diameter), pyramidal-shaped enkephalin-like immunoreactive neurons were shown from levels L1 to L4-5. Essentially all of these neurons were also immunoreactive for galanin and cholecystokinin. A second enkephalin-like immunoreactive cell group, extending from L5 to approximately the S2-3 level, contained smaller (20-30 microm diameter), ovoid-shaped perikaryia. Approximately 75% of these enkephalin-like immunoreactive neurons were also immunoreactive for neuropeptide Y. Neurotensin-immunoreactivity was also present in this area, having varying amounts of co-localization with these other two peptides. These results demonstrate that the lumbosacral opioid cell column in lamina X is not a neurochemically homogenous structure.

Substance P receptor immunodetection in the spinal cord: comparative use of direct anti-receptor antibody and anti-complementary peptide antibody

The immunolocalization of substance P (SP) receptors was compared in the rat spinal cord using either a direct anti-substance P NK1-receptor antibody (anti-SPR) or an anti-complementary peptide antibody (anti-CP). The first antibody recognizes an intracellular epitope, the C-terminal tail of the NK1-receptor. The second antibody recognizes an extracellular epitope located at or near the ligand-binding domain because anti-CP antibody and SP were previously shown to compete for binding to the receptor. At the light microscope level, it was observed that anti-CP antibody labels both laminae I and II of the dorsal horn, while anti-SPR antibody labels exclusively lamina I, except at the lumbar level. This could suggest that spinal NK1 receptors are heterogeneous. Anti-SPR antibodies may recognize an NK1 receptor subclass confined to lamina I. Conversely, anti-CP antibody may recognize either another receptor subclass or two different subclasses present in laminae I and II. At the electron microscope level, labeling was localized either on the intracellular or the extracellular face of the plasma membrane depending on the location of the epitope recognized by both antibodies on the transmembrane receptor. However, using either antibody, the ultrastructural labeling was found at non-junctional sites, suggesting that SP may act in a non-synaptic manner on all putative receptor subclasses.

Evidence for roles of vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) receptors in modulating the responses of rat dorsal horn neurons to sensory inputs

The extracellularly recorded electrophysiological activity of single multireceptive dorsal horn neurons was markedly increased by ionophoretic administration of vasoactive intestinal polypeptide (VIP) or pituitary adenylate cyclase activating polypeptide (PACAP)-38. Some cells responded selectively to PACAP-38 (suggesting mediation by a PACAP receptor), whereas others responded to both VIP and PACAP-38 (suggesting a VIP1 and/or VIP2 receptor). Most non-nociceptive cells were unaffected by PACAP-38 and all were unaffected by VIP. The selectivity of VIP/PACAP receptor antagonists was established on cloned rat VIP1, VIP2 and PACAP receptors in vitro before their utilization to indicate the likely involvement of VIP1, and possibly PACAP receptors, in VIP- and PACAP-38-mediated responses of dorsal horn neurons. The VIP/PACAP receptor antagonists inhibited responses of multireceptive cells to sustained innocuous (brush) and noxious (mustard oil) stimuli, with a selectivity suggesting the involvement of VIP1 and PACAP receptors, although the participation by VIP2 receptors cannot be excluded. These data implicate both VIP and PACAP in regulating the basal responsiveness of multireceptive dorsal horn neurons to sensory stimuli.

Spinal release of immunoreactive dynorphin A(1-8) with the development of peripheral inflammation in the rat

Microprobes bearing immobilised antibodies to dynorphin A(1-8) were used to study the basal and evoked release of this prodynorphin derived peptide in the spinal cord of urethane anaesthetised normal rats and those with a peripheral inflammation. In the absence of any active peripheral stimulus the antibody microprobes detected immunoreactive (ir)-dynorphin A(1-8) in two areas (lamina I and laminae IV-V) in the dorsal horn of the spinal cord of normal rats. With the development of unilateral ankle inflammation over 3 to 5 days following subcutaneous injections of Freund's complete adjuvant, a basal presence of ir-dynorphin A(1-8) was found in both the dorsal and ventral horn regions of both sides of the spinal cord. Lateral compression of the ankles of the normal animals did not release ir-dynorphin A(1-8) during the period of stimulation, but this neuropeptide was detected in increased amounts in the ventral horn following the stimulus. By contrast, compression of inflamed ankles produced elevated levels of ir-dynorphin A(1-8) during the period of stimulus application at three major sites in the ipsilateral spinal grey matter. The largest peak was in the deep dorsal horn/upper ventral horn (laminae VI-VII), with further sites of significant release in the mid dorsal horn (laminae II-V) and the lower ventral horn. The observation that ir-dynorphin A(1-8) is physiologically released in the ventral and deep dorsal in addition to the superficial dorsal horn of the rat suggests an involvement of dynorphins in several aspects of spinal function.

Cobalt accumulation in neurons expressing ionotropic excitatory amino acid receptors in young rat spinal cord: morphology and distribution

Excitatory amino acids (EAA) acting on N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate receptors play an important role in synaptic transmission in the spinal cord. Quantitative autoradiography and physiological experiments suggest that NMDA receptors are localized mainly in lamina II while kainate and AMPA receptors are found on both dorsal and ventral horn neurons. However the cell types expressing EAA receptors and their laminar distribution is not known. We have used a cobalt uptake method to study the morphology and distribution of spinal cord neurons expressing AMPA, kainate, or NMDA excitatory amino acid receptors in the lumbar enlargement of the rat spinal cord. The technique involved superfusion of hemisected spinal cords of 14 day-old rat pups in vitro with excitatory amino acid receptor ligands in the presence of CoCl2. Cobalt has been shown to enter cells through ligand-gated ion channels in place of Ca2+. Cells which accumulated cobalt ions following activation by ionotropic excitatory amino acid receptors were visualized histochemically. The cobalt uptake generated receptor-specific labeling of cells, as the NMDA receptor antagonist D-(-)-2-amino-(5)-phosphonovaleric acid (D-AP-5) (20 microM) blocked the NMDA, but not kainate-induced cobalt uptake. The kainate-induced cobalt labeling was reduced by the non-selective excitatory amino acid receptor antagonist kynurenic acid (4 mM). Passive opening of the voltage-gated Ca(2+)-channels by KCl (50 mM) did not result in cobalt uptake, indicating that cobalt enters the cells through ligand-gated Ca(2+)-channels. AMPA (500 microM), kainate (500 microM), or NMDA (500 microM) each induced cobalt uptake with characteristic patterns and distributions of neuronal staining. Overall, kainate induced cobalt uptake in the greatest number of neuronal staining. Overall, kainate induced cobalt uptake in the greatest number of neuronal perikarya while NMDA-induced uptake was the lowest. AMPA and kainate, but not NMDA superfusion, resulted in cobalt labeling of glial cells. Our results show that the cobalt uptake technique is a useful way to study the morphology and distribution of cells expressing receptors with ligand-gated Ca2+ channels.

Morphological and electrophysiological analysis of the peripheral and central afferent pathways from the clitoris of the cat

Afferent neurons projecting to the clitoris of the cat were identified by WGA-HRP tracing in the S1 and S2 dorsal root ganglia. An average of 433 cells were identified on each side of the animal. 85% and 15% of the labeled cells were located in the S1 and S2 dorsal root ganglia, respectively. The average cross sectional area of clitoral afferent neuron profiles was 1,479 +/- 627 micron2. Unilateral transection of the pudendal nerve reduced the number of labeled cells to 1% of that on the control side. Central projections of clitoral afferents were identified in the lumbo-sacral segments (L7-S3) of the spinal cord. HRP labeled fibers were located in the marginal zone on the medial side of dorsal horn and extended into the dorsal half of the dorsal gray commissure. Electrophysiological recordings detected axonal volleys in the pudendal nerve and S1 dorsal root in response to electrical stimulation (threshold, 1-4 V) of the clitoral surface. Estimated axonal conduction velocities at the two sites ranged from 7-27 m/s and 0.6-30 m/s, respectively. Multi-unit recordings from dorsal roots in the lumbo-sacral segments revealed that non-noxious pressure stimulation of the clitoris evoked discharges in the S1 dorsal root. Small increases were also detected in the S2 and L7 roots. Single unit discharges recorded from S1 dorsal roots were activated by electrical stimulation of the clitoral surface at thresholds of 0.6-1.2 V and latencies of 1.5-1.8 ms (estimated conduction velocities of 24-30 m/s.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutaminase-like immunoreactivity in rat spinomesencephalic tract cells

Retrograde transport of the fluorescent tracer Fluorogold was used in combination with immunohistochemical staining for the enzyme glutaminase to identify putative glutamatergic neurons belonging to the rat spinomesencephalic tract. Glutaminase-like staining in spinal projection neurons suggests that the relay of nociceptive information from the spinal cord to midbrain may involve the excitatory amino acid glutamate.

Highly polysialylated NCAM expression in the developing and adult rat spinal cord

The expression of a highly polysialylated neural cell adhesion molecule (NCAM-H) appeared in motor neurons, presumptive commissural neurons and floor plate at embryonic day 12, and then spread throughout the spinal cord during late embryonic and early postnatal stages. In the adult stage, the expression almost disappeared, but remained in the superficial laminae of the dorsal horn, the lateral spinal nucleus and the area around the central canal. These results suggest that the NCAM-H expression of the spinal cord is involved in the developmental events and possibly in the processing system of somatic and/or visceral information during the adult stage.

Demonstration of dynorphin A 1–8 immunoreactive axons contacting spinal cord projection neurons in a rat model of peripheral inflammation and hyperalgesia

Using a double-labeling technique, we evaluated the input of afferents immunoreactive for dynorphin peptide onto a population of lumbar spinal neurons contributing to the spinoparabrachial tract in rats with 1 inflamed hind paw. We found that the frequency and distribution with which dynorphin immunoreactive varicosities were in apposition to projection neurons varied according to neuron location. In particular, neurons in the superficial dorsal horn and neck of the dorsal horn receive a high degree of dynorphin input. We also determine that unilateral peripheral inflammation is associated with both an increase in the number of projection neurons receiving detectable DYN input and in the frequency of this input onto a given neuron, with the largest increase seen in the superficial dorsal horn. Since almost all superficial dorsal horn neurons contributing to the spinoparabrachial tract respond either exclusively or maximally to noxious stimulation, our data supports dynorphin's involvement in nociception.

Substance P innervation of the rat and cat thalamus. II. Cells of origin in the spinal cord

Evidence in the preceding paper suggests that fibers and terminals immunopositive for substance P (SP) in somatosensory thalamic nuclei are part of the spinothalamic tract (STT). In this paper, more direct evidence on this point is provided by immunocytochemistry for SP on the cervical spinal cord, alone or combined with the retrograde transport of colloidal gold-labeled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase (WGAapoHRP-Au). In cats and rats pretreated with colchicine and/or anterolateral chordotomy (to increase SP content in cell bodies), many small to large cell bodies are SP-immunopositive especially in laminae I and V, but also in more ventral laminae of the upper cervical cord. SP neurons are also present in the dorsolateral funiculus (in the lateral spinal nucleus, LSN, in rats) but not in the lateral cervical nucleus or in the internal basilar nucleus. In both species there is a considerable degree of overlap in the distribution of SP-positive neurons and that of STT neurons. SP immunocytochemistry in rats after WGAapoHRP-Au injection in the somatosensory thalamus reveals SP-positive STT neurons in LSN, in lamina I and in lamina V, and, to a lesser extent, in more ventral laminae. These results demonstrate that SP is a marker and/or neuromediator for some STT neurons. Together with the evidence discussed in the preceding paper, the results also suggest that SP-positive neurons may be involved in the transmission of nociceptive input.

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.

Ultrastructural demonstration of synaptic connections between calcitonin gene-related peptide immunoreactive axons and dynorphin A(1-8) immunoreactive dorsal horn neurons in a rat model of peripheral inflammation and hyperalgesia

Synaptic contact between dynorphin A(1-8)-like immunoreactive lamina V spinal neurons and calcitonin gene-related peptide-like immunoreactive axon terminals was demonstrated using the immuno-electron microscopic mirror technique in a rat model of peripheral inflammation and hyperalgesia. Adjacent tissue sections were immunocytochemically labeled for either dynorphin A(1-8) or calcitonin gene-related peptide and examined at the electron microscopic level for the presence of synaptic contacts. The results suggest that some opioid neurons which exhibit a dynamic increase in dynorphin peptide associated with peripheral inflammation and hyperalgesia receive direct monosynaptic input from presumptive nociceptive primary afferents.

Long-lasting neurochemical and functional changes in rats induced by neonatal administration of substance P antiserum

Substance P (SP) antiserum was administered to rats on the second day of life. Three months later, the content of SP was significantly decreased in the dorsal part of the spinal cord and in the periaqueductal gray matter of these animals, as compared to control rats receiving a neonatal treatment of non-specific immunoglobulins. Further, the levels of Met-enkephalin and 5-hydroxyindole acetic acid (5-HIAA) were concomitantly increased in the same regions. SP receptor binding sites and opioid receptors, which appear earlier in development, were not modified in the two regions studied. On the other hand, the antinociceptive response to intracerebroventricular (i.c.v.) injection of SP or of the synthetic enkephalin analog D-Ala2,D-Leu5-enkephalin, as well as the hypertensive response to i.c.v. SP were blocked. The results suggest that, after administration to newborn rats, the antiserum is able to penetrate into SP neurons, producing a long-lasting SP suppression and a subsensitivity to the pharmacological effects of the neuropeptide. The modifications in the content of Met-enkephalin and 5-HIAA are possibly compensatory changes which subserve the functionality of central cardiovascular and pain regulatory systems after the immunolesion.

Ultrastructural analysis of dynorphin B-immunoreactive cells and terminals in the superficial dorsal horn of the deafferented spinal cord of the rat

Light microscopic studies have demonstrated important differences in the distribution of enkephalin and dynorphin cells and terminals in the dorsal horn. Most importantly, dynorphin neurons are located in regions almost exclusively associated with the transmission and/or control of nociceptive messages (laminae I, IIo, and V); enkephalin neurons, although located in the same regions, are also found in areas involved in the transmission of nonnociceptive messages, e.g., laminae IIi and III. To determine whether there are also differences in the synaptic organization of the two opioid peptides, we have examined the distribution of dynorphin B immunoreactivity at the ultrastructural level. The studies were performed in colchicine-treated rats that underwent dorsal rhizotomy so that the relationship of dynorphin terminals and cells to primary afferent terminals could be established. Dynorphin B-immunoreactive cell bodies and dendrites in laminae I and IIo receive convergent primary and nonprimary afferent input, which suggests that dynorphin neurons receive a small-diameter, nociceptive input. Dynorphin terminals predominantly contain round, agranular vesicles; some terminals also contain a few dense core vesicles. Most dynorphin terminals are presynaptic to unlabelled dendrites; both asymmetric and symmetrical axonal contacts were noted. Dynorphin-immunoreactive boutons are also presynaptic to unlabelled cell bodies and spines. Twenty-nine percent of dynorphin terminals were associated with axonal profiles, including degenerating primary afferent terminals; only rarely could a synaptic density be detected. Although some degenerating primary afferent terminals were clearly presynaptic to dynorphin-immunoreactive terminals, in most cases, the polarity of the relationship between primary afferents and dynorphin terminals could not be established. These data indicate that synaptic interactions made by and with dynorphin-immunoreactive cells and terminals in the superficial dorsal horn are not very different from those that were previously reported for enkephalin cells and terminals. Thus, it is unlikely that dynorphin terminals provide a significant presynaptic input to primary afferent fibers. On the other hand, the presence of a primary afferent input to dynorphin cell bodies and dendrites in the superficial dorsal horn suggests that dynorphin cells receive a direct input from small-diameter, nociceptive primary afferents. That connection might contribute to the increased levels of dynorphin message and peptide that have been reported in rats experiencing a chronic inflammatory condition.(ABSTRACT TRUNCATED AT 400 WORDS)

Peripheral inflammation is associated with increased dynorphin immunoreactivity in both projection and local circuit neurons in the superficial dorsal horn of the rat lumbar spinal cord

The present study combined the retrograde transport of fluorescent tracers with the immunocytochemical identification of dynorphin A(1-8) in superficial dorsal horn neurons to examine whether peripheral inflammation-induced dynorphin increases are found in local circuit neurons only or also in neurons projecting at least to the caudal mesencephalon. Evidence is presented that complete Freund's adjuvant-induced inflammation produces a large increase in the number of lamina I dynorphin-containing projection and non-projection neurons, and in the number of lamina II dynorphin local circuit neurons.

Demonstration of calcitonin gene-related peptide immunoreactive axons contacting dynorphin A(1-8) immunoreactive spinal neurons in a rat model of peripheral inflammation and hyperalgesia

In a rat model of peripheral inflammation and hyperalgesia, dynorphin A(1-8)-like immunoreactive (DYN-LIr) spinal neurons were examined for contacts from calcitonin gene-related peptide-like immunoreactive (CGRP-LIr) varicosities using a double-label PAP method. Ipsilateral to the inflammation, CGRP-LIr varicosities contacted both dendrites and somata of DYN-LIr neurons in lumbar laminae I, II and V. Few such contacts were found on the contralateral side. The results suggest that opioid neurons which exhibit a dynamic change in dynorphin associated with inflammation, represent a subpopulation of neurons that receive contacts from presumptive nociceptive primary afferents.

Studies of peptidergic input to the lateral spinal nucleus

Lesions were made to interrupt potential sources of peptidergic input to the lateral spinal nucleus (LSn) in rats. Rhizotomies and spinal transections, as well as lesions of the lateral funiculus, failed to reduce immunohistochemical staining for substance P, dynorphin, Met-enkephalin, somatostatin and FMRF-amide in the LSn at lumbar levels. Thus, all examined peptidergic afferent input to the LSn appears to originate locally within the spinal cord.

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

The distribution of substance P, somatostatin, cholecystokinin, vasoactive intestinal polypeptide, enkephalin and serotonin in axons, terminals and neurons was compared in the area surrounding the central canal (lamina X) at five representative levels of the monkey spinal cord, using peroxidase-antiperoxidase immunocytochemistry. Immunoreactive neurons containing each of the neurochemicals were identified. At the cervical, thoracic and lumbar levels the area lateral to the canal had dense terminal fields immunoreactive for each neurochemical. The dorsal commissural region, the pericanal area, and the ventral commissural area were supplied by some but not all of the substances. In the lower thoracic cord innervation extended into the dorsal midline area and into the ventromedial commissural region. In contrast, in the sacral cord, the dorsal commissural region could be subdivided on the basis of innervation, and the lateral region was densely supplied by only cholecystokinin and serotonin, while the sacral ventral commissure and the pericanal area were supplied by all six neurochemicals. The immunocytochemical mappings were compared with published maps of functional classes of neurons and with the distribution of primary afferents and descending fibers in lamina X. The dense peptidergic and serotonergic innervation in the lateral area and the dorsal commissural area corresponded particularly with the location of projection neurons and primary afferents described in other studies.

Immunocytochemical identification of long ascending, peptidergic lumbar spinal neurons terminating in either the medial or lateral thalamus in the rat

The peptidergic content of rat spinothalamic tract neurons was investigated by combining the retrograde transport of the fluorescent dye Fluoro-gold with immunocytochemistry for enkephalin, dynorphin or vasoactive intestinal polypeptide. Evidence is presented for the existence of enkephalin and dynorphin in a subpopulation of spinothalamic neurons terminating in the medial thalamus and vasoactive intestinal polypeptide in a subpopulation terminating primarily in the lateral thalamus.