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

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.

Morphological, neurochemical and electrophysiological features of parvalbumin-expressing cells: a likely source of axo-axonic inputs in the mouse spinal dorsal horn

Perception of normal bodily sensations relies on the precise regulation of sensory information entering the dorsal horn of the spinal cord. Inhibitory, axoaxonic, synapses provide a mechanism for this regulation, but the source of these important inhibitory connections remains to be elucidated. This study shows that a subpopulation of spinal interneurons that expresses parvalbumin and have specific morphological, connectivity and functional characteristics are a likely source of the inhibitory inputs that selectivity regulate non-noxious tactile input in the spinal cord. Our findings suggest that a loss of normal function in parvalbumin positive dorsal horn neurons may result in the development of tactile allodynia, where non-painful stimuli gain the capacity to evoke the sensation of pain.

Mapping of CGRP in the alpaca (Lama pacos) brainstem

In this study, we demonstrate the presence of immunoreactive structures containing calcitonin gene-related peptide in the alpaca brainstem. This is the first time that a detailed mapping of the cell bodies and fibers containing this neuropeptide in the alpaca brainstem has been carried out using an immunocytochemical technique. Immunoreactive cell bodies and fibers were widely distributed throughout the alpaca brainstem. A high density of calcitonin gene-related peptide-immunoreactive perikarya was found in the superior colliculus, the dorsal nucleus of the raphe, the trochlear nucleus, the lateral division of the marginal nucleus of the brachium conjunctivum, the motor trigeminal nucleus, the facial nucleus, the pons reticular formation, the retrofacial nucleus, the rostral hypoglossal nucleus, and in the motor dorsal nucleus of the vagus, whereas a high density of fibers containing calcitonin gene-related peptide was observed in the lateral division of the marginal nucleus of the brachium conjunctivum, the parvocellular division of the alaminar spinal trigeminal nucleus, the external cuneate nucleus, the nucleus of the solitary tract, the laminar spinal trigeminal nucleus, and in the area postrema. This widespread distribution indicates that the neuropeptide studied might be involved in multiple functions in the alpaca brainstem.

Upregulation of substance P in low-threshold myelinated afferents is not required for tactile allodynia in the chronic constriction injury and spinal nerve ligation models

It has been proposed that substance P and calcitonin gene-related peptide (CGRP) are upregulated in low-threshold myelinated primary afferents after certain types of nerve injury, and that release of substance P from these afferents contributes to the resulting tactile allodynia. To test this hypothesis, we looked for neuropeptides in Abeta primary afferent terminals in the ipsilateral gracile nucleus and spinal dorsal horn in three nerve injury models: sciatic nerve transection (SNT), spinal nerve ligation (SNL), and chronic constriction injury (CCI). We also looked for evidence of neurokinin 1 (NK1) receptor internalization in the dorsal horn after electrical stimulation of Abeta afferents. We found no evidence of either substance P or CGRP expression in injured Abeta terminals in the spinal cord in any of the models. Although substance P was not detected in terminals of injured afferents in the gracile nucleus, CGRP was expressed in between 32 and 68% of these terminals, with a significantly higher proportion in the SNL and CCI models, compared with SNT. In addition, we did not detect any Abeta-evoked NK1 receptor internalization in neurons from laminas I, III, or IV of the dorsal horn in the CCI or SNL models. These results do not support the proposal that substance P is present at significant levels in the terminals of injured Abeta primary afferents in neuropathic models. They also suggest that any release of substance P from injured Abeta afferents is unlikely to activate NK1 receptors in the dorsal horn or contribute to neuropathic pain.

Effect of Brn-3a deficiency on CGRP-immunoreactivity in the dorsal root ganglion

Immunohistochemistry for calcitonin gene-related peptide (CGRP) was performed on the dorsal root ganglion (DRG) and spinal cord in wildtype and knockout mice for Brn-3a. CGRP-immunoreactive (-IR) neurons were abundant in the DRG of wildtype, heterozygous and knockout mice. Cell size analysis revealed that CGRP-IR neurons were of various sizes in wildtype and heterozygous mice. In the knockout mice, however, most of CGRP-IR neurons were small. In the spinal cord of knockout mice, the number of CGRP-IR fibers increased in the dorsal column but decreased in the deep part of the dorsal horn. The loss of Brn-3a may have different effects on CGRP-IR expression in small and large DRG neurons.

The site of origin of calcitonin gene-related peptide-like immunoreactive afferents to the inferior olivary complex of the mouse

The intent of the present study is to define the brainstem nuclei which give rise to CGRP-immunolabeled afferents to the inferior olivary complex of the mouse. A technique which combines retrograde transport of fluorescent microspheres with immunohistochemistry was used to address this question. In the present study, intensely labeled CGRP neurons were localized within several cranial nerve nuclei including the hypoglossal, facial, oculomotor, motor nucleus of the trigeminal nerve and nucleus ambiguus, as well as in the parabrachial nucleus, locus coeruleus and medullary and pontine reticular formation. In addition, lightly labeled CGRP neurons were identified within the deep cerebellar nuclei, the inferior olivary complex, lateral reticular nucleus, medial and lateral vestibular nuclei, nucleus Darkschewitsch, interstitial nucleus of Cajal, the central gray area adjacent to the third ventricle, and the zona incerta. The origin of the projection to the inferior olivary complex primarily arises from the deep cerebellar nuclei, the locus coeruleus, and the central gray matter of the mesodiencephalic area. In addition, a small CGRP input is derived from the superior and lateral vestibular nuclei as well as the zona incerta. In conclusion, we have identified several extrinsic sources of CGRP to the inferior olivary complex and have localized it within afferents that have been shown to have either excitatory (mesodiencephalic nuclei) or inhibitory (cerebellar nuclei) effects on olivary circuits. The presence of CGRP in these functionally diverse brainstem and cerebellar afferents suggests that the peptide may act as a co-transmitter to modulate the activity of olivary neurons.

Calcitonin gene-related peptide and neuropeptide Y in the raccoon cuneate nucleus

Immunocytochemical methods were used to determine the distribution of calcitonin gene-related peptide (CGRP) and neuropeptide Y (NPY) in the middle region of the adult raccoon cuneate nucleus. Extensive CGRP-immunoreactive fibers and darkly stained punctate structures, thought to be terminals, were concentrated in the dorsal cap and basal region of the middle cuneate nucleus. These regions receive input from the claws and the hairy skin of the paw and forearm. The NPY-immunoreactive fibers and terminals were also found within the dorsal cap of the cuneate nucleus, but were less abundant than CGRP. However, most of the NPY-immunostained fibers and terminals were found in the cluster region of the cuneate nucleus, which receives input from glabrous skin. No CGRP- or NPY-immunoreactive cell bodies were found in the raccoon middle cuneate nucleus. This description of the distribution of CGRP and NPY in the normal animal provides a baseline for future investigations into injury-induced neuropeptide plasticity in the raccoon middle cuneate nucleus.

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.

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.

Colocalization of GABA and glycine in the rat dorsal column nuclei

About half the neurons in the rat dorsal column nuclei were immunopositive for glycine or for GABA; these were smaller than immunonegative neurons. In double-stained material, 29% of stained neurons were immunopositive for GABA only, and 42% for both antigens. The results resemble those reported for spinal cord laminae that receive fast-conducting primary afferents, and suggest that glycine is an inhibitory neurotransmitter in the dorsal column nuclei.

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.

Distribution of calcitonin gene-related peptide-like immunoreactivity in the brain of the small-spotted dogfish, Scyliorhinus canicula L

The distribution of neuropeptides has been useful in comparing neuronal aggregates of elasmobranchs with those in other vertebrates. The distribution of calcitonin gene-related peptide (CGRP)-like immunoreactivity in the brain of the dogfish was examined with an antiserum to rat alpha-CGRP. Western blot analysis confirms that our antiserum recognizes a single peptide in the dogfish brain very similar to mammalian CGRP. CGRP-like immunoreactivity was located in discrete neuronal groups. CGRP-like-immunoreactive (CGRP-ir) neurons were found in the motor nuclei III, IV, V, VI, VII, IX, and X of the brainstem motor column and in the octavolateral efferent neurons. In the isthmal region, two groups of CGRP-ir neurons appeared in the parabrachial region and reticular substance. Three other CGRP-ir cell groups were observed in the mesencephalon: in the ventral tegmental area, in the substantia nigra, and one widely scattered but numerous population in superficial layers of the optic tectum. In the diencephalon, CGRP-ir cells were observed in the magnocellular preoptic nucleus and the organon vasculosum hypothalami. A population of CGRP-ir cells was also observed in the entopeduncular nucleus in the impar telencephalon. CGRP-ir fibers of central origin were widely distributed in the brain, but the most conspicuous areas were found in the ventral telencephalon, the hypothalamus, the mesencephalic lateral reticular area, and the dorsolateral isthmal region. The neurointermediate lobe of the hypophysis was also richly innervated by CGRP-ir fibers. CGRP-ir sensory fibers of cranial nerves IX and X and of dorsal spinal roots formed very conspicuous terminal fields in the lobus vagi and Cajal's nucleus commissuralis and in the dorsal region of the substantia gelatinosa, respectively. Comparison of the distribution of fibers and perikarya in dogfish and other vertebrates suggests that this CGRP-ir system has been well conserved during evolution.

Neurotransmitters in subcortical somatosensory pathways

Investigations during recent years indicate that many different neuroactive substances are involved in the transmission and modulation of somesthetic information in the central nervous system. This review surveys recent developments within the field of somatosensory neurotransmission, emphasizing immunocytochemical findings. Increasing evidence indicates a widespread role for glutamate as a fast-acting excitatory neurotransmitter at different levels in somatosensory pathways. Several studies have substantiated a role for glutamate as a neurotransmitter in primary afferent neurons and in corticofugal projections, and also indicate a neurotransmitter role for glutamate in ascending somatosensory pathways. Other substances likely to be involved in somatosensory neurotransmission include the neuropeptides. Many different peptides have been detected in primary afferent neurons with unmyelinated or thinly myelinated axons, and are thus likely to be directly involved in primary afferent neurotransmission. Some neurons giving rise to ascending somatosensory pathways, primarily those with cell bodies in the dorsal horn, are also immunoreactive for peptides. Recent investigations have shown that the expression of neuropeptides, both in primary afferent and ascending tract neurons, may change as a result of various kinds of peripheral manipulation. The occurrence of neurotransmitters in intrinsic neurons and neurons providing modulating inputs to somatosensory relay nuclei (the dorsal horn, the lateral cervical nucleus, the dorsal column nuclei and the ventrobasal thalamus) is also reviewed. Neurotransmitters and modulators in such neurons include acetylcholine, monoamines, GABA, glycine, glutamate, and various neuropeptides.

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.

Time course of dorsal root axon regeneration into transplants of fetal spinal cord: I. A light microscopic study

Cut dorsal root axons regenerate into intraspinal transplants of fetal spinal cord and establish synaptic connections there. The aims of the present study were to describe the progression of dorsal root growth within the transplants and the maturation of transplant morphology and to determine whether the regenerated dorsal root axons persist within the transplants or eventually withdraw. Embryonic (E) day 14 spinal cord was grafted into the lumbar enlargement of adult Sprague-Dawley rats, and the L4 or L5 dorsal root was cut and juxtaposed to the transplants. The morphology of the transplants was examined from 1 day to over 1 year after surgery, and the regenerated dorsal roots were labeled with immunohistochemical methods to study the subset that contains calcitonin gene-related peptide (CGRP). Embryonic spinal cord transplants survived and grew within the host spinal cord in over 90% of the animals. Transplant volume increased and the morphology of the transplants matured over the first 12 weeks and then did not change for 48-60 weeks. During the first week the transplants were composed of dissociated neurons, glia, and hematogenous cells with considerable extracellular space between them. Subsequently, the grafted neurons became densely aggregated, and non-neuronal elements such as inflammatory cells and myelin debris disappeared. CGRP-immunoreactive dorsal roots began to regenerate into the transplants within 24 hours, formed dense bundles by 4 days, and were still present at 60 weeks, the longest survival period examined. Myelination of axons within transplants began at 2 weeks. Quantitative analysis showed that the area of the transplants occupied by CGRP-labeled axons and the distribution area of the labeled axons within the transplants increased until 12 weeks and persisted unchanged for over 48 weeks. These results indicate that regenerated dorsal root axons are permanently maintained within transplants of embryonic spinal cord and suggest that the transplants can contribute to the permanent restoration of damaged intraspinal neural circuits.

Substance P-containing pyramidal neurons in the cat somatic sensory cortex

Light and electron microscopic immunocytochemical methods were used to verify the possibility that neocortical pyramidal neurons in the first somatic sensory cortex of cats contain substance P. At the light microscopic level, substance P-positive neurons accounted for about 3% of all cortical neurons, and the vast majority were nonpyramidal cells. However, 10% of substance P-positive neurons had a large conical cell body, a prominent apical dendrite directed toward the pia, and basal dendrites, thus suggesting they are pyramidal neurons. These neurons were in layers III and V. At the electron microscopic level, the majority of immunoreactive axon terminals formed symmetric synapses, but some substance P-positive axon terminals made asymmetric synapses. Labelled dendritic spines were also present. Combined retrograde transport-immunocytochemical experiments were also carried out to study whether substance P-positive neurons are projection neurons. Colloidal gold-labelled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase was injected either in the first somatic sensory cortex or in the dorsal column nuclei. In the somatic sensory cortex contralateral to the injection sites, a few substance P-positive neurons in layers III and V also contained black granules, indicative of retrograde transport. This indicates that some substance P-positive neurons project to cortical and subcortical targets. We have therefore identified a subpopulation of substance P-positive neurons that have most of the features of pyramidal neurons, are the probable source of immunoreactive axon terminals forming asymmetric synapses on dendritic spines, and project to the contralateral somatic sensory cortex and dorsal column nuclei. These characteristics fulfill the criteria required for classifying a cortical neuron as pyramidal.

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.