Substance P-containing projections in the dorsal columns of rats and cats

Characterization of putative tachykinin peptides in Caenorhabditis elegans

Tachykinin-like peptides, such as substance P, neurokinin A, and neurokinin B, are among the earliest discovered and best-studied neuropeptide families, and research on them has contributed greatly to our understanding of the endocrine control of many physiological processes. However, there are still many orphan tachykinin receptor homologs for which cognate ligands have not yet been identified, especially in small invertebrates, such as the nematode Caenorhabditis elegans (C. elegans). We here show that the C. elegans nlp-58 gene encodes putative ligands for the orphan G protein-coupled receptor (GPCR) TKR-1, which is a worm ortholog of tachykinin receptors. We first determine, through an unbiased biochemical screen, that a peptide derived from the NLP-58 preprotein stimulates TKR-1. Three mature peptides that are predicted to be generated from NLP-58 show potent agonist activity against TKR-1. We designate these peptides as C. elegans tachykinin (CeTK)-1, -2, and -3. The CeTK peptides contain the C-terminal sequence GLR-amide, which is shared by tachykinin-like peptides in other invertebrate species. nlp-58 exhibits a strongly restricted expression pattern in several neurons, implying that CeTKs behave as neuropeptides. The discovery of CeTKs provides important information to aid our understanding of tachykinin-like peptides and their functional interaction with GPCRs.

The Effect of Cold Water on Pain Evaluation During Negative Pressure Wound Therapy Dressing Changes: A Prospective, Randomized Controlled Study

Negative pressure wound therapy (NPWT) is a technique using vacuum dressing to promote wound healing in complicated wound. However, for many patients, the application and removal of the NPWT is source of procedural pain. The authors hypothesized that administering cold sterile water into the NPWT sponge would decrease pain during dressing changes. A prospective randomized controlled study was conducted on 27 patients who were undergoing 81 NPWT wound dressing changes (n = 81) at a single institution between October 2016 and September 2017. Each patient had 3 NPWT dressing changes. Cold sterile water (5.74 °C), room temperature sterile water (26.89 °C), and nothing were randomized and administered in the NPWT tubing into the sponge 10 minutes before changing the dressing in each and every procedure. Pain scores were assessed using a 0 to 10 numeric pain scale. Patients administered with cold water reported less pain than those administered with room temperature sterile water during the dressing change (4 vs 5.67; P < .003), and much less pain than those with nothing instilled before dressing change (4 vs 6.59; P < .001). There is no statistically significant difference in pain score between using the room temperature sterile water group and the control group that instilled nothing (5.67 vs 6.59; P = .065). This study has shown that cold water administered through the suction tubing before the dressing change had a better reduction in pain score than using room temperature sterile water and the control group.

TRPV1-Like Immunoreactivity in the Human Locus K, a Distinct Subregion of the Cuneate Nucleus

The presence of transient receptor potential vanilloid type-1 receptor (TRPV1)-like immunoreactivity (LI), in the form of nerve fibres and terminals, is shown in a set of discrete gray matter subregions placed in the territory of the human cuneate nucleus. We showed previously that those subregions share neurochemical and structural features with the protopathic nuclei and, after the ancient name of our town, collectively call them Locus Karalis, and briefly Locus K. TRPV1-LI in the Locus K is codistributed, though not perfectly overlapped, with that of the neuropeptides calcitonin gene-related peptide and substance P, the topography of the elements immunoreactive to the three markers, in relation to each other, reflecting that previously described in the caudal spinal trigeminal nucleus. Myelin stainings show that myelinated fibres, abundant in the cuneate, gracile and trigeminal magnocellular nuclei, are scarce in the Locus K as in the trigeminal substantia gelatinosa. Morphometric analysis shows that cell size and density of Locus K neurons are consistent with those of the trigeminal substantia gelatinosa and significantly different from those of the magnocellular trigeminal, solitary and dorsal column nuclei. We propose that Locus K is a special component of the human dorsal column nuclei. Its functional role remains to be determined, but TRPV1 appears to play a part in it.

The human cuneate nucleus contains discrete subregions whose neurochemical features match those of the relay nuclei for nociceptive information

The present paper is aimed at defining distinctive subdivisions of the human cuneate nucleus (Cu), evident from prenatal to old life, whose occurrence has never been clearly formalized in the human brain, or described in other species so far. It extends our early observations on the presence of gray matter areas that host strong substance P (SP) immunoreactivity in the territory of the human Cu and adjacent cuneate fascicle. Here we provide a three-dimensional reconstruction of the Cu fields rich in SP and further identify those areas by means of their immunoreactivity to the neuropeptides SP, calcitonin gene-related peptide, methionine- and leucine-enkephalin, peptide histidine-isoleucine, somatostatin and galanin, to the trophins glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor, and to the neuroplasticity proteins polysialylated neural cell adhesion molecule and growth-associated protein-43. The presence, density and distribution of immunoreactivity for each of these molecules closely resemble those occurring in the superficial layers of the caudal spinal trigeminal nucleus (Sp5C). Myelin and Nissl stainings suggest that those Cu subregions and the Sp5C superficial layers share a similar histological aspect. This work establishes the existence of definite subregions, localized within the Cu territory, that bear the neurochemical and histological features of sensory nuclei committed to the neurotransmission of protopathic stimuli, including pain. These findings appear of particular interest when considering that functional, preclinical and clinical studies show that the dorsal column nuclei, classical relay station of fine somatic tactile and proprioceptive sensory stimuli, are also involved in pain neurotransmission.

Nociceptive behavior in animal models for peripheral neuropathy: spinal and supraspinal mechanisms

Since the initial description by Wall [Wall, P.D., 1967. The laminar organization of dorsal horn and effects of descending impulses. J. Neurophysiol. 188, 403-423] of tonic descending inhibitory control of dorsal horn neurons, several studies have aimed to characterize the role of various brain centers in the control of nociceptive input to the spinal cord. The role of brainstem centers in pain inhibition has been well documented over the past four decades. Lesion to peripheral nerves results in hypersensitivity to mild tactile or cold stimuli (allodynia) and exaggerated response to nociceptive stimuli (hyperalgesia), both considered as cardinal signs of neuropathic pain. The increased interest in animal models for peripheral neuropathy has raised several questions concerning the rostral conduction of the neuropathic manifestations and the role of supraspinal centers, especially brainstem, in the inhibitory control or in the abnormal contribution to the maintenance and facilitation of neuropathic-like behavior. This review aims to summarize the data on the ascending and descending modulation of neuropathic manifestations and discusses the recent experimental data on the role of supraspinal centers in the control of neuropathic pain. In particular, the review emphasizes the importance of the reciprocal interconnections between the analgesic areas of the brainstem and the pain-related areas of the forebrain. The latter includes the cerebral limbic areas, the prefrontal cortex, the intralaminar thalamus and the hypothalamus and play a critical role in the control of pain considered as part of an integrated behavior related to emotions and various homeostatic regulations. We finally speculate that neuropathic pain, like extrapyramidal motor syndromes, reflects a disorder in the processing of somatosensory information.

Analysis of the unmyelinated primary sensory neurone projection through the dorsal columns of the rat spinal cord using transganglionic transport of the plant lectin Bandeiraea simplicifolia I-isolectin B4

We have examined the projection of unmyelinated primary sensory neurones through the dorsal columns of the rat spinal cord using transganglionic transport of the plant lectin Bandeiraea simplicifolia I-isolectin B4. A small volume of the lectin was injected into the sciatic nerve of anaesthetised rats to label the central terminals of nociceptive primary sensory neurones. Following a survival period of 7 days, transverse and longitudinal sections of the superficial dorsal horn, dorsolateral funiculus and the dorsal columns from spinal segments L4 through to T13 were screened for lectin transport using light and electron microscopy. Longitudinal sections of the thoraco-lumbar region of spinal cord were also examined for lectin binding. Light and electron microscopy revealed transganglionically transported and bound lectin in the superficial dorsal horn and dorsolateral funiculus of the L3 and L4 segments of spinal cord. However, no lectin transport or binding was observed within the dorsal columns at any level of spinal cord examined. From these results, we suggest that the unmyelinated neurones within the dorsal columns do not express the binding site for BSI-B4 and, as such, may be responsible for visceral rather than cutaneous sensation. In line with the theories regarding a postsynaptic dorsal column pathway, these results suggest that nociceptors that bind BSI-B4 are not involved in a direct ascending projection through the dorsal columns.

Topographical localization of glial cell line-derived neurotrophic factor in the human brain stem: an immunohistochemical study of prenatal, neonatal and adult brains

As a step towards the identification of the neuronal populations responsive to glial cell line-derived neurotrophic factor (GDNF) in the human nervous system and their changes with age, this study reports on the immunohistochemical localization of the protein GDNF in the autoptic normal human brain stem of pre- and full-term newborns and adult subjects. Two different anti-GDNF polyclonal antibodies were used. Western blot analysis on homogenates of human and rat brain and recombinant human GDNF resulted in differential detection of monomeric and dimeric forms of the proteins. The ABC immunohistochemical technique on cryostat tissue sections showed an uneven distribution of GDNF-like immunoreactive nerve fibers and terminals and neuronal cell bodies. Immunoreactive elements were mainly localized to the spinal trigeminal, cuneate, solitary, vestibular, and cochlear sensory nuclei, dorsal motor nucleus of the vagus nerve, ventral grey column, hypoglossal nucleus, dorsal and ventrolateral medullary reticular formation, pontine subventricular grey and locus coeruleus, lateral regions of the rostral pontine tegmentum, tectal plate, trochlear nucleus, dorsal and median raphe nuclei, caudal and rostral linear nuclei, cuneiform nucleus, and substantia nigra. Comparison between pre- and full-term newborns and adult subjects revealed changes with age in density of positive innervation and frequency of immunoreactive perikarya. The results obtained provide detailed information on the occurrence of GDNF-like immunoreactive neurons in the human brain stem and suggest that the protein is present in a variety of neuronal systems, which subserve different functional activities, at developmental ages and in adult brains.

Inflammatory pain reduces correlated activity in the dorsal column nuclei

Persistent pain can result in sensitization of neurons in the spinal cord dorsal horn and produce physiological changes in sites such as the thalamus, that receive projections from the dorsal horn. Although the dorsal column nuclei receive both primary afferent input and projections from the dorsal horn, their participation in persistent pain states is relatively unexplored, perhaps because they play a limited role in acute, cutaneous nociception. We have used a model of inflammatory pain to examine the physiological properties of dorsal column nucleus neurons during persistent pain. We used this model in order to minimize direct damage to large myelinated primary afferents that project directly to the dorsal column nuclei. Inflammation was produced by injection of complete Freund's adjuvant into one hindpaw in rats, and neurons in the gracile nucleus were recorded 2-8 days later. Inflammation resulted in increased responsiveness to nociceptive (pinch) stimulation and increased incidence of afterdischarge firing 2-3 days after injection. Spontaneous activity was increased 6-8 days after injection. Inflammation decreased the strength of correlated firing in neuron pairs that shared common inputs, but did not affect the strength of monosynaptic interactions between neurons. These results suggest that the dorsal column nuclei can participate in persistent pain processes. Based on their anatomical connections, the dorsal column nuclei may contribute to thalamic changes during persistent pain as well as to supraspinal centers that modulate pain transmission in the spinal cord.

Unmasking of an early laser evoked potential by a point localization task

OBJECTIVES

The investigation of the CO(2) laser evoked potential (LEP) modifications following a point localization task.

METHODS

LEPs were recorded from 10 healthy subjects in two different conditions. (1) Task condition: laser stimuli were shifted among 3 different locations on the right hand dorsum, and the subjects were asked to identify the stimulated area. The mean error rate in point localization was 4.5%. (2) Non-task condition: laser pulses were delivered on the first intermetacarpal space, and the subject was asked to count the number of stimuli. The mean error rate in counting was 5.8%.

RESULTS

In the task condition, the temporal traces contralateral to the stimulation showed an early positive component (eP, mean peak latency 83 ms) preceding the N1 negativity (mean peak latency 144 ms). At the eP peak latency, topographic maps showed a positivity highly focused on the contralateral temporal region. In the non-task recordings no reliable response was identifiable before the N1 potential.

CONCLUSIONS

While no LEP component earlier than the middle-latency N1 potential can be recorded in the non-task condition, a positive response (eP) preceding the N1 component is identifiable in the contralateral temporal region during the spatial localization of painful stimuli. The eP scalp distribution is compatible with its origin from a radial source in the second somatosensory (or insular) area, thus suggesting that the opercular cortex is involved not only in the middle-latency (N1 potential), but also in early pain processing.

Neuroanatomical localisation of Substance P in the CNS and sensory neurons

The anatomical distribution of Substance P (SP) has been investigated since the development of antibodies against it in the 1970s. Although initial studies were performed with antibodies that also recognised the other endogenous neurokinins, most of the initial descriptions are surprisingly still valid today. In this review, we provide an integrated overview of the pathways containing SP in the central and peripheral nervous systems. The highest densities of SP immunoreactivity occur in the superficial dorsal horn of the spinal cord, in the substantia nigra and in the medial amygdaloid nucleus. In the peripheral nervous system, SP occurs in high concentrations in small diameter primary sensory fibres and in the enteric nervous system. SP is extensively co-localised with classical transmitters and other neuropeptides. In the spinal cord, SP immunoreactive axonal boutons are preferentially presynaptic to neurons expressing the SP receptor, suggesting that the neurokinin acts at a short distance from the release site. In contrast, in the periphery, the situation probably differs in the autonomic ganglia, where the targets are directly innervated by SP, and in other peripheral territories, where SP has to diffuse through the connective tissue to reach the structures expressing the receptor.

Increase of calcitonin gene-related peptide immunoreactivity in the axonal fibers of the gracile nuclei of adult and aged rats after complete and partial sciatic nerve injuries

Neuropeptide changes in primary sensory neurons are thought to be involved in the pathological mechanisms of neuropathic pain caused by peripheral nerve injuries. In this study, using immunocytochemistry, we observed that calcitonin gene-related peptide (CGRP) immunoreactive (IR) fibers were increased, qualitatively and quantitatively, in the injured side gracile nuclei of adult (2 months old) and aged (16 months old) rats 2 weeks following complete transection (CSNT) or chronic constriction injury (CCI) of sciatic nerves. This increase was more pronounced after CCI than after CSNT. In aged rats, the CGRP-IR fibers which appeared were dystrophic. In contrast to the increases which we saw in the gracile nucleus, after both types of injury there was a decrease in CGRP-IR in all laminae of the dorsal horn. The percentage of CGRP-IR DRG neurons was decreased after CSNT, but unchanged after CCI. We interpret our results in terms of local sprouting in the gracile nucleus and suggest that the increased response following CCI is due to the involvement of fibers from DRG neurons spared by the partial nerve injury. Increased CGRP release from spared afferents in the gracile nucleus might be important in neuropathic pain.

Control of size and excitability of mechanosensory receptive fields in dorsal column nuclei by homolateral dorsal horn neurons

Both accidental and experimental lesions of the spinal cord suggest that neuronal processes occurring in the spinal cord modify the relay of information through the dorsal column-lemniscal pathway. How such interactions might occur has not been adequately explained. To address this issue, the receptive fields of mechanosensory neurons of the dorsal column nuclei were studied before and after manipulation of the spinal dorsal horn. After either a cervical or lumbar laminectomy and exposure of the dorsal column nuclei in anesthetized cats, the representation of the hindlimb or of the forelimb was defined by multiunit recordings in both the dorsal column nuclei and in the ipsilateral spinal cord. Next, a single cell was isolated in the dorsal column nuclei, and its receptive field carefully defined. Each cell could be activated by light mechanical stimuli from a well-defined cutaneous receptive field. Generally the adequate stimulus was movement of a few hairs or rapid skin indentation. Subsequently a pipette containing either lidocaine or cobalt chloride was lowered into the ipsilateral dorsal horn at the site in the somatosensory representation in the spinal cord corresponding to the receptive field of the neuron isolated in the dorsal column nuclei. Injection of several hundred nanoliters of either lidocaine or cobalt chloride into the dorsal horn produced an enlargement of the receptive field of the neuron being studied in the dorsal column nuclei. The experiment was repeated 16 times, and receptive field enlargements of 147-563% were observed in 15 cases. These data suggest that the dorsal horn exerts a tonic inhibitory control on the mechanosensory signals relayed through the dorsal column-lemniscal pathway. Because published data from other laboratories have shown that receptive field size is controlled by signals arising from the skin, we infer that the control of neuronal excitability, receptive field size and location for lemniscal neurons is determined by tonic afferent activity that is relayed through a synapse in the dorsal horn. This influence of dorsal horn neurons on the relay of mechanosensory information through the lemniscal pathways must modify our traditional views concerning the relative independence of these two systems.

Distribution of substance P receptor binding in dorsal column nuclei of rat, cat, monkey and human

In the present study, substance P receptor binding was localized in the dorsal column nuclei (DCN) of the rat, cat, monkey, and human. Bolton-Hunter-labeled [125I]substance P binding was most concentrated in the cell nests of the core region, but was present throughout the DCN of each species. The distribution of substance P receptors may reconcile apparent mismatches between the widespread responsiveness of DCN neurons to substance P and the restricted distribution of substance P containing afferents.

Neuroanatomy of the pain system and of the pathways that modulate pain

We review many of the recent findings concerning mechanisms and pathways for pain and its modulation, emphasizing sensitization and the modulation of nociceptors and of dorsal horn nociceptive neurons. We describe the organization of several ascending nociceptive pathways, including the spinothalamic, spinomesencephalic, spinoreticular, spinolimbic, spinocervical, and postsynaptic dorsal column pathways in some detail and discuss nociceptive processing in the thalamus and cerebral cortex. Structures involved in the descending analgesia systems, including the periaqueductal gray, locus ceruleus, and parabrachial area, nucleus raphe magnus, reticular formation, anterior pretectal nucleus, thalamus and cerebral cortex, and several components of the limbic system are described and the pathways and neurotransmitters utilized are mentioned. Finally, we speculate on possible fruitful lines of research that might lead to improvements in therapy for pain.

Is there a pathway in the posterior funiculus that signals visceral pain?

The present report provides evidence that axons in the medial part of the posterior column at T10 convey ascending nociceptive signals from pelvic visceral organs. This evidence was obtained from human surgical case studies and histological verification of the lesion in one of these cases, along with neuroanatomical and neurophysiological findings in animal experiments. A restricted lesion in this area can virtually eliminate pelvic pain due to cancer. The results remain excellent even in cases in which somatic structures of the pelvic body wall are involved. Following this procedure, neurological testing reveals no additional neurological deficit. There is no analgesia to pinprick stimuli applied to the body surface, despite the relief of the visceral pain. Since it is reasonable to attribute the favorable results of limited midline myelotomies to the interruption of axons of visceral nociceptive projection neurons in the posterior column, we have performed experiments in rats to test this hypothesis. The results in rats indicate that the dorsal column does indeed include a nociceptive component that signals pelvic visceral pain. The pathway includes neurons of the postsynaptic dorsal column pathway at the L6-S1 segmental level, axons of these neurons in the fasciculus gracilis, and neurons of the nucleus gracilis and the ventral posterolateral nucleus of the thalamus.

Anuran dorsal column nucleus: organization, immunohistochemical characterization, and fiber connections in Rana perezi and Xenopus laevis

As part of a research program on the evolution of somatosensory systems in vertebrates, the dorsal column nucleus (DCN) was studied with (immuno)histochemical and tract-tracing techniques in anurans (the large green frog, Rana perezi, and the clawed toad, Xenopus laevis). The anuran DCN contains some nicotinamide adenine dinucleotide phosphate diaphorase-positive neurons, very little calbindin D-28k, and a distinct parvalbumin-positive cell population. The anuran DCN is innervated by primary and non-primary spinal afferents, by primary afferents from cranial nerves V, VII, IX, and X, by serotonin-immunoreactive fibers, and by peptidergic fibers. Non-primary DCN afferents from the spinal cord appear to arise throughout the spinal cord, but particularly from the ipsilateral dorsal gray. The present study focused on the efferent connections of the DCN, in particular the targets of the medial lemniscus. The medial lemniscus could be traced throughout the brainstem and into the diencephalon. Along its course, the medial lemniscus gives off collaterals to various parts of the reticular formation, to the octavolateral area, and to the granular layer of the cerebellum. At mesencephalic levels, the medial lemniscus innervates the lateral part of the torus semicircularis as well as various tegmental nuclei. A striking difference between the two species studied is that while in R. perezi medial lemniscal fibers do not reach the tectum mesencephali, in X. laevis, intermediate and deep tectal layers are innervated. Beyond the midbrain, both dorsal and ventral thalamic areas are innervated by the medial lemniscus. The present study shows that the anuran "lemniscal pathway" is basically similar to that of amniotes.

Calcitonin gene-related peptide- and substance P-immunoreactive axons in the nucleus gracilis of the rat with special reference to axonal dystrophy: light and electron microscopic observations

Calcitonin gene-related peptide (CGRP) and substance P (SP)-immunoreactive (IR) axons in the nucleus gracilis of normal rats (1-15 months of age) were studied by light and electron microscopy. Besides many CGRP-IR and SP-IR varicosities with normal appearance, we found a few swollen (nearly round or oval) varicosities with either CGRP or SP immunoreactivity. Swollen CGRP-IR varicosities were more frequently seen than SP-IR ones, appearing from 3 months of age and increasing in number and size (up to approximately 25 microns in diameter) with advancing age. At the electron microscopic (EM) level, CGRP-IR and SP-IR swollen varicosities showed dystrophic changes, i.e., many membranous dense bodies, and proliferation of microtubules and neurofilaments. CGRP-IR or SP-IR dystrophic axons also contained many mitochondria and sometimes made synaptic contacts with nonreactive dendrites (occasionally with non-IR axons). These findings suggest that the dystrophic CGRP and SP axonal profiles represent a functionally distinct subpopulation of axonal dystrophy in the nucleus gracilis and use CGRP or SP as a neuroactive substance. Using a double-immunostaining method, many of normal CGRP-IR axons were identified to be SP-IR. However, no single dystrophic varicosity was found to contain both CGRP and SP immunoreactivities. These findings suggest that CGRP and SP afferents are independently affected and progress to dystrophic changes.

Ultrastructural and immunocytochemical characterization of terminals of postsynaptic ascending dorsal column fibers in the rat cuneate nucleus

The morphology, synaptic contacts, and neurotransmitter enrichment of postsynaptic dorsal column terminals in the cuneate nucleus of rats were investigated and compared with those of identified primary afferents. For this purpose, anterograde transport of horseradish peroxidase-based tracers injected in the spinal cord was combined with postembedding immunogold labeling for glutamate and gamma-aminobutyric acid (GABA). Anterogradely labeled postsynaptic dorsal column terminals were morphologically homogeneous: they were small (mean area = 1.37 microns 2) and dome-shaped, contacted single dendritic shafts or cell bodies, and were not involved in axoaxonic synapses. The majority of them were not enriched in glutamate or GABA immunoreactivity compared with other tissue components. Their morphology, size, and neurotransmitter content thus differed from that of primary afferents. These differences are consistent with distinct functional roles for the two main afferent systems ascending to the cuneate nucleus.

A comparative study of the calcium-binding proteins calbindin-D28K, calretinin, calmodulin and parvalbumin in the rat spinal cord

Comparison of the immunocytochemical localizations revealed distinct patterns of differential distribution and overlapping of calbindin-D28K (CB-D28K), calretinin (CR), calmodulin (CM) and parvalbumin (PV) in the rat spinal cord. In some areas, one of the four calcium-binding proteins (CBPs) appears to be predominant, for example, CB-D28K in lamina I and ependymal cells, PV at the inner part of laminae II, CR in laminae V and VI and CM in motoneurons of lamina IX. In other regions of the spinal cord, more than one CBPs was abundant. CB-D28K and CR were similarly distributed in lamina II and the lateral spinal and cervical nucleus; CM and PV were similarly abundant in the ventromedial dorsal horn, internal basilar and central cervical nucleus; CR and PV were similarly abundant in the ventromedial dorsal horn, internal basilar and central cervical nucleus; CR and PV were similarly heterogeneous in the gracile fasciculus from caudal to rostral spinal cord. In the sacral dorsal gray commissure, the distribution patterns of CR and PV were clearly complementary. The unilateral ganglionectomies resulted in a substantial reduction of CBP-like immunoreactivity (CBP-LI) in the dorsal columns and a reduction of CM- and PV-LI in the ventromedial dorsal horn. In the motor system, only CM labeled large motoneurons in lamina IX and CB-D28K lightly stained pyramidal tract. The apparent absence of CM-LI in the superficial dorsal horn is contradictory to the presence of a CM-dependent nitric oxide synthase in the region. These data indicate that most CBP-LI in the dorsal column pathway had primary afferent origin, while the superficial dorsal horn exhibited intrinsic CBP immunoreactivity. The differential and selective localizations of CBPs in the spinal cord suggest a role for these proteins in spinal nociceptive processing, visceral regulation and dorsal column sensory pathways.

Lesion-induced changes in the central terminal distribution of galanin-immunoreactive axons in the dorsal column nuclei

Rats that sustained forelimb removal on either embryonic day (E) 16, on the day of birth (P-0), or transection of the brachial plexus in adulthood had brainstem sections stained for galanin, calcitonin gene-related peptide (CGRP), or substance P (SP) at various intervals after these lesions were made. In normal adult rats, only a few galanin-immunoreactive fibers are present in the cuneate nucleus and most are located in its caudal portion. CGRP-positive axons are also sparse in the cuneate and are distributed mainly in the periphery of the nucleus. SP-positive axons are seen throughout the cuneate nucleus. In rats that sustained forelimb removals at birth or transection of the brachial plexus in adulthood, dense galanin immunoreactivity was present throughout the cuneate nucleus at all rostrocaudal levels on the side of the brainstem ipsilateral to the lesion. The changes after lesions that were made in the adult animals were apparent within 1 week, the earliest time analyzed. Increases in galanin immunoreactivity in the cuneate of animals that sustained forelimb removals on P-0 were first visible on P-2. Neither forelimb removal at birth nor brachial plexus lesions in adulthood had any qualitative effect upon the distribution or density of CGRP- or SP-immunoreactivity in the cuneate nucleus. Removal of a forelimb on E-16 did not increase the density of galanin-immunoreactive fibers in the cuneate nucleus. Such lesions also failed to produce any appreciable change in the density of either CGRP- or SP-positive fibers in the cuneate nucleus. The present data raise the possibility that large caliber, non-peptidergic primary afferent axons which innervate the cuneate nucleus may express galanin after damage at birth or in adulthood.

Serotoninergic innervation of the dorsal column nuclei and its relation to cytoarchitectonic subdivisions: an immunohistochemical study in cats and monkeys (Aotus trivirgatus)

The serotoninergic innervation of the dorsal column nuclei (DCN) was investigated in cats and owl monkeys (Aotus trivirgatus) with immunohistochemical methods. A dense network of serotonin-immunoreactive fibers was present in the reticular regions of DCN in cats, and in the pars triangularis of the cuneate nucleus and the peripheral and caudal regions of the gracile nucleus in owl monkeys. The cat's cluster regions and the monkey's rotund regions were more sparsely innervated. Electron microscopic examination showed that the labeled fibers were thin and unmyelinated. Vesicle-containing, terminal-like structures were small. They were in contact with dendrites, other terminals and cell bodies, but synapses were rare. The results demonstrate that the serotoninergic projection to the DCN in both cats and owl monkeys is heterogeneously distributed in a pattern that is faithfully related to the cytoarchitectonic subdivisions of the DCN. The densely innervated reticular regions in the DCN of cats and the corresponding regions in monkeys are predominantly involved in the processing of sensory information to the cerebellum, either directly, or indirectly through projections to the inferior olive, pontine gray, tectum, pretectum, red nucleus, or zona incerta. Thus, the present findings suggest that the serotoninergic innervation of the DCN is primarily related to the DCN's involvement in motor functions.

Further evidence for the existence of long ascending unmyelinated primary afferent fibers within the dorsal funiculus: effects of capsaicin

The present study provides further evidence in support of the hypothesis that there is a fine primary afferent system in the dorsal funiculi by determining the effects of capsaicin (8-methyl-N-vanillyl-6-noneamide) on unmyelinated fibers in the cervical fasciculus gracilis of the rat. The neurolytic effect of this procedure was demonstrated by showing an 89% decrease in the number of unmyelinated fibers in the S2 dorsal roots of the experimental animals. Consequently, we feel that unmyelinated primary afferent fibers are largely removed from these animals. Neonatal administration of capsaicin (50 mg/kg) caused a 54% decrease in the number of unmyelinated fibers in the C3 fasciculus gracilis but no significant change in myelinated fiber numbers. The data provide further evidence for the existence of a significant primary afferent unmyelinated fiber system in the dorsal funiculus and suggest a role for the dorsal funiculi in the transmission of noxious information.

Numbers and proportions of unmyelinated axons at cervical levels in the fasciculus gracilis of monkey and cat

The present study is a quantitative analysis of the unmyelinated fiber population in the fasciculus gracilis of the second cervical segment of cat and monkey. We find that unmyelinated fibers represent 13.7% of the total fiber population in this pathway in the cat and 18.9% in the monkey (Macaca fascicularis). The existence of such large numbers of these axons suggests that there may be a sizeable ascending fine primary afferent pathway in the fasciculus gracilis in cat and monkey whose destination is presumably the dorsal column nuclei. These findings are of interest in regard to classic ideas that the afferent fibers in the dorsal columns are large myelinated fibers that convey fine discriminative information to the dorsal column nuclei.

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.

Development of projections of primary afferent fibers from the hindlimb to the gracile nucleus: a WGA-HRP study in the rat

The projection of primary afferent fibers to the gracile nucleus was studied during development. Injections of wheat germ agglutinin-horseradish peroxidase were made into the hindlimb of fetal, postnatal and adult rats. In most cases the sections were alternately stained for wheat germ agglutinin-horseradish peroxidase including counter stain with Neutral red and for acetylcholinesterase. At embryonic day 17 labelled fibers could be traced to the mid-cervical spinal cord but not further rostrally. At embryonic days E18 and E19 labelled fibers penetrate the rostral pole of the nucleus, which does not happen more caudally. At embryonic day E21 the caudal-most pole of the gracile nucleus still is not penetrated by labelled fibers. From postnatal day 1 onwards labelled fibers are found throughout the entire rostrocaudal extent of the gracile nucleus. These results suggest that primary afferent fibers from the hindlimb first grow to the rostral pole of the gracile nucleus and penetrate the rostral pole immediately upon their arrival. During further development more caudal parts of the gracile nucleus are gradually penetrated in a rostrocaudal fashion by primary afferent fibers of the hindlimb.

Immunocytochemical localization of neuromedin K (neurokinin B) in rat spinal ganglia and cord

Specific antisera directed against substance P and neuromedin K (neurokinin B) have been used in double-label immunofluorescence studies to unambiguously localize these two neuropeptides of the tachykinin family in single tissue sections of rat spinal cord and dorsal root ganglia. Substance P-like immunoreactivity (SPLI) is present but neuromedin K-like immunoreactivity (NMKLI) is undetectable in dorsal root ganglia. Both peptides are present in the spinal cord, but NMKLI is largely restricted to the dorsal gray while SPLI shows a broader distribution. In the spinal gray, NMKLI coexists with SPLI in some, but not all, fibers. While substance P in the dorsal spinal cord is largely of primary afferent origin, neuromedin K appears to originate largely from intrinsic spinal neurons.

The expression of different cytochemical markers in normal and axotomised dorsal root ganglion cells projecting to the nucleus gracilis in the adult rat

Rat lumbar dorsal root ganglion neurones projecting to the nucleus gracilis in the brainstem were retrogradely labelled with Fluoro-Gold and analysed immunocytochemically for their expression of substance P-, calcitonin gene-related peptide-, galanin-, galanin message-associated peptide-, neuropeptide Y-, nitric oxide synthase- and carbonic anhydrase-like immunoreactivity as well as affinity to Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4, RT97 and to choleragenoid. The analysis was made both in uninjured rats and in rats which had been subjected to unilateral sciatic nerve transection and partial resection 3 weeks earlier. The data showed that 6% of the L4 and L5 lumbar dorsal root ganglion cells that projected to the nucleus gracilis showed substance P-like immunoreactivity. Following nerve injury, none of the nucleus gracilis-projecting dorsal root ganglion cells showed substance P-like immunoreactivity. Nineteen per cent of the investigated cell population showed calcitonin gene-related peptide-like immunoreactivity in uninjured rats, but no nucleus gracilis-projecting calcitonin gene-related peptide-positive cells were found after nerve injury. Galanin- and galanin message-associated peptide-like immunoreactivity were found in 2% and 3%, respectively, of the Fluoro-Gold-labelled cell population normally and in 22% and 14%, respectively, after injury. No neuropeptide Y-positive cells were found in the Fluoro-Gold-labelled cell population normally, but after nerve injury, 96% of this population became neuropeptide Y-positive. Nitric oxide synthase-like immunoreactivity was found in 2% of the Fluoro-Gold-labelled cells normally and in 10% after injury. Two per cent of the Fluoro-Gold-labelled cells in the normal cases were stained by Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4. After injury, however, no such double labelling was found. Thirty-four per cent of the Fluoro-Gold-labelled cell population was carbonic anhydrase positive normally, and 42% after injury. Seventy-five per cent of the Fluoro-Gold-labelled cells showed RT97 immunoreactivity normally and 12% after injury. Choleragenoid-like immunoreactivity was found in 99% of the Fluoro-Gold-labelled dorsal root ganglion cells normally and 81% after injury. Immunohistochemical visualisation of choleragenoid transganglionically transported from the injured sciatic nerve combined with neuropeptide Y immunocytochemistry showed that primary afferent fibres and terminals in the nucleus gracilis contain neuropeptide Y following peripheral nerve transection. Taken together, the results indicate that peripherally axotomised nucleus gracilis-projecting neurones undergo marked alterations in their cytochemical characteristics, which may be significant for the structural and functional plasticity of this system after injury.

Calcitonin gene-related peptide-positive neurons and fibers in the cat dorsal column nuclei

An antiserum raised against the C-terminal region of rat alpha-calcitonin gene-related peptide has been used to investigate the morphology and topographical distribution of neurons and terminals containing calcitonin gene-related peptide in the cat dorsal column nuclear complex. Calcitonin gene-related peptide-positive fibers and axon terminals were denser in the cuneate nucleus than in the other dorsal column nuclei subdivisions and were observed throughout all rostrocaudal levels. They were densest in the dorsal and ventrolateral portions of the middle cuneate. Immunoreactive neurons were observed only in animals pre-treated with colchicine. In these cases, some calcitonin gene-related peptide-positive neurons were present in the cuneate and in the external cuneate. In double-labeling experiments, visualization of calcitonin gene-related peptide immunoreactivity in dorsal root ganglia neurons was combined with the retrograde transport of colloidal gold-labeled wheat germ agglutinin conjugated to inactive horseradish peroxidase injected in the cuneate nucleus. These experiments show that calcitonin gene-related peptide-positive fibers in the cuneate nucleus originate mostly from C3-C6 medium sized dorsal root ganglia neurons but also from some small and large neurons. These results suggest that calcitonin gene-related peptide-positive fibers may convey sensory information from a wide range of peripheral receptors.