Cell type and conduction velocity of rat primary sensory neurons with substance P-like immunoreactivity

Substance P- and calcitonin gene-related peptide immunoreactivity in primary afferent neurons of the cat's knee joint

The distribution of substance P and calcitonin gene-related peptide was determined in primary afferent neurons of the medial and posterior articular nerve of the cat's knee joint. Perikarya of articular afferents were visualized by retrograde labelling with the fluorescent dye Fast Blue which was applied at the transected end of the peripheral nerves. Substance P was found in about 17% of labelled medial articular afferents and in about 16% of labelled posterior articular afferents, respectively, whereas calcitonin gene-related peptide was present in about 35 and 32% of the medial and posterior articular nerve cells, respectively. Taking into account that these neuropeptides are known to be co-localized, probably not more than one-third of the joint afferents contain substance P and/or calcitonin gene-related peptide. Quantification of cell diameters revealed that substance P was found only in small- or intermediate-sized perikarya (less than 50 microns) indicating that this peptide is predominantly found in unmyelinated neurons. Calcitonin gene-related peptide was present mainly in small- and intermediate- but also in some large-sized neurons (greater than 50 microns) providing evidence that this peptide is found in unmyelinated and to a lesser extent in myelinated neurons. This is consistent with previous studies that show that substance P and calcitonin gene-related peptide are present primarily in unmyelinated and thinly myelinated primary afferents. When the portion of substance P-positive neurons of the medial articular nerve is compared to the number of articular afferents displaying a nociceptive function as determined in earlier electrophysiological studies, it can be calculated that at most 30% of the nociceptive-specific articular afferents contain this neuropeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

c-JUN-like immunoreactivity in the CNS of the adult rat: basal and transynaptically induced expression of an immediate-early gene

An immunocytochemical study of dorsal root ganglia, spinal cord and medulla oblongata was performed with antisera against the c-jun proto-oncogene encoded protein. The c-JUN-like immunoreactivity was restricted to the cell nucleus. In the CNS of untreated rats a basal c-JUN-like immunoreactivity was present in the nuclei of two types of neurons: motor and autonomic. Labelled nuclei could be seen in many motoneurons of the ventral horn of the entire length of spinal cord and the lower medulla oblongata, as well as in the area of the nucleus hypoglossus, the dorsal motor nucleus of nucleus vagus, nucleus ambiguus, nucleus facialis, nucleus abducens and motor nucleus of nucleus trigeminus. Additionally, labelled nuclei were found in the preganglionic sympathetic and preganglionic parasympathetic cells of the nucleus intermediolateralis and nucleus intercalatus in the spinal cord. In the medulla oblongata we found a cluster of cells with c-JUN-like immunoreactivity in an area between the dorsomedial part of the oral nucleus spinalis trigeminalis and the lateral border of the knee of facial nerve. Additionally, a second cluster of c-JUN-like immunoreactivity cells was visible between the ventromedial part of the oral nucleus spinalis trigeminalis and the lateral border of the rostral nucleus facialis. Examination of the characteristics of all cell groups with a basal c-JUN-like immunoreactivity in the spinal cord and lower brainstem revealed an overlapping distribution with cholinergic cell groups. Basal c-JUN-like immunoreactivity was also seen in the dorsal root ganglion cells. We examined the factors which can effect the expression of the c-JUN protein. Maximal expression of c-JUN-like immunoreactivity was observed after electrical stimulation of primary afferents. Stimulation of sciatic nerve at a strength sufficient to recruit A delta- and C-fibres produced c-JUN-like immunoreactivity in many nuclei of the ipsilateral dorsal horn of the lumbar spinal cord. c-JUN-like immunoreactivity was first detectable at 30 min following the end of stimulation, reached a maximum after 1 h, remained unchanged for another 1 h and declined to the basal level after 16 h. The distribution of c-JUN-like immunoreactivity in the lumbar cord coincided with the region of termination of sciatic nociceptive afferents. Contralateral c-JUN-like immunoreactivity appeared after 4 h. After noxious mechanical stimulation of the plantar hindpaw c-JUN-like immunoreactivity occurred in the spinal area of termination of nociceptive afferents of the tibial nerve. Noxious stimulation did not provoke additional c-JUN-like immunoreactivity in dorsal root ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of the spinal cord in four species of elasmobranch fish: cytoarchitecture and distribution of serotonin and selected neuropeptides

An analysis of Nissl stained sections of the spinal cord taken from four species of elasmobranch showed that seven distinct cytoarchitectonic laminae are present. These laminae are compared with laminae described previously in the spinal cord of other vertebrates. The distribution of immunoreactivity to serotonin, substance P, somatostatin, calcitonin gene-related peptide, neuropeptide Y, and bombesin was determined in the brown stringray (Dasyatis fluviorum), the eagle ray (Aetobatis narinari), the shovelnose ray (Rhinobatis battilum), and the black-tip shark (Carcharhinus melanopterus). In all species, dense immunoreactivity to most substances tested was found in the outer part of the substantia gelatinosa. Many fibres and varicosities immunoreactive to substance P, calcitonin gene-related peptide, and bombesin were found in this region and smaller numbers of fibres were found in the nucleus proprius. Immunoreactivity to somatostatin consisted of coarse fibre bundles that entered the dorsal horn at the nucleus proprius and radiated dorsally to the substantia gelatinosa. Axons and varicosities immunoreactive to serotonin and neuropeptide Y were found in all regions of the dorsal horn but were concentrated in the outer part of the substantia gelatinosa. The distribution of immunoreactivity to met-enkephalin in the shovelnose ray was concentrated in the lateral third of the substantia gelatinosa and to a lesser extent in the nucleus proprius. The distribution of these substances is compared with that described in other vertebrates. Although the sensory information reaching the elasmobranch spinal cord is limited, compared with that of mammalian species, the distribution of these neuroactive factors in the dorsal horn of the two groups is strikingly similar.

Cell types and axonal sizes of calcitonin gene-related peptide-containing primary sensory neurons of the rat

Neurons with immunoreactivity (IR) for calcitonin gene-related peptide (CGRP) in the rat dorsal root ganglia were examined by immunoelectron microscopy. About one-half of the neurons of the L5 dorsal root ganglia of animals treated with colchicine had CGRP-IR, and 40% of these were large neurons of type A. The proximal parts of their peripheral axons were, however, unmyelinated (91%) or thinly myelinated (9%). Thickly myelinated axons observed in the same sections were always devoid of CGRP-IR. The CGRP-IR neurons were various subtypes of type A and B neurons. No specific morphological characteristics were associated with CGRP-IR.

Expression of sensory neuron antigens by a dorsal root ganglion cell line, F-11

The F-11 cell line is a fusion product of embryonic rat dorsal root ganglion (DRG) cells with mouse neuroblastoma cell line N18TG-2 (Platika, D., Boulos, M.H., Baizer, L. and Fishman, M.C., Proc. Natl. Acad. Sci. U.S.A., 82 (1985) 3499-3503). F-11 cells were uniformly labelled using a monoclonal antibody (RT-97) to the 200 kDa subunit of neurofilament protein, which labels a subpopulation of adult rat DRG neurons. F-11 cells did not stain for antigenic markers of fibroblasts or Schwann/satellite cells which are also present in DRG. Monoclonal antibodies that recognize cell surface carbohydrates have been shown to label subpopulations of DRG neurons. The stage-specific embryonic antigens SSEA-3 and SSEA-4, and the antigen recognized by B23D8, were expressed by some F-11 cells but not by the neuroblastoma parent of the hybrid cells. SSEA-3 was expressed by about 20% of the F-11 cells, whereas 40-60% expressed SSEA-4 or the antigen recognized by B23D8. The stability of F-11 cell subpopulations for sensory antigen expression was demonstrated by isolating single cells and growing the progeny as clonal lines. In some subclones, nearly 100% of the cells stably expressed SSEA-4 and/or B23D8, or failed to stain with anti-SSEA-4, anti-SSEA-3, or B23D8 over 12 passages. Other subclones were unstable for the expression of these antigens. This study demonstrates the derivation of the F-11 cell line from sensory neurons but also indicates that multiple phenotypes of varying stability are present in this line. This information is important for the use of this line as a model for DRG neurons.

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

Light and electron microscopic immunocytochemical methods were used to study the distribution and the morphology of substance P-positive fibers and axon terminals in the dorsal column nuclei of rats and cats, and to determine whether they are part of an ascending input to these nuclei. In rats, substance P-positive fibers and axon terminals are present throughout the rostrocaudal extent of the dorsal column nuclei. In cats, immunostained fibers and terminals are mostly confined to the ventral region of the caudal and middle portions of these nuclei but they are more homogeneously distributed at rostral levels. In both species, substance P-positive neurons are not present in the same nuclear complex. At the electron microscope level, substance P-positive terminals are small- to medium-sized and dome-shaped; they form asymmetric contacts on dendrites and contain many round, agranular vesicles and sparse dense core vesicles. In double-labeling experiments, visualization of substance P-immunoreactivity in the dorsal root ganglia and dorsal horn of the spinal cord was combined with the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase or of colloidal gold-labeled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase. These experiments show that substance P-positive axon terminals may originate from both small dorsal root ganglion neurons and from spinodorsal column nuclei neurons in lamina IV. Although quantitative evaluation of the contribution of these two pathways to the substance P innervation of the dorsal column nuclei has not been performed and other sources cannot be discarded on the basis of the present evidence, it is proposed that non-primary afferents to the dorsal column nuclei account for most of the substance P-positive fibers and terminals in the dorsal column nuclei. The experiments support previous findings suggesting that nociceptive input may access the dorsal column nuclei and that this may be mediated, though to a very limited extent, directly by way of small dorsal root ganglion neurons.

Peptide coexistence in axon terminals within the superficial dorsal horn of the rat spinal cord

The somata of primary sensory neurons have been shown to contain up to four (and possibly more) neuroactive peptides. Although each of these peptides has been separately located in axon terminals within the superficial dorsal horn of the spinal cord, it is not clear whether multiple peptide coexistence is also a feature of terminal varicosities. The aim of this study was to determine whether the peptides substance P (SP) and calcitonin gene-related peptide (CGRP), which are colocalized in the somata of a large number of primary sensory neurons, coexist in the central terminals of these neurons in the spinal cord. The protein A-gold technique of antigen localization was used to screen single boutons in laminae I and II of the rats spinal cord for SP- and CGRP-like immunoreactivity at the ultrastructural level. The results show that SP and CGRP are colocalized within a large number of synaptic boutons in the superficial dorsal horn. Furthermore, evidence was obtained to suggest that both SP and CGRP may be found in the same synaptic vesicle within these boutons. These findings indicate that both SP and CGRP may be coreleased from single terminals in the superficial dorsal horn. This is of considerable interest in view of the reported interaction between SP and CGRP in nociceptive behavioral responses in the rat.

Cell type and conduction velocity of rat primary sensory neurons with calcitonin gene-related peptide-like immunoreactivity

An immunocytochemical double labelling study of L4 dorsal root ganglia from rats aged seven to 10 weeks was made with an antibody to calcitonin gene-related peptide and with RT97, an anti-neurofilament antibody which specifically labels the light neuron population. Peptide immunoreactivity was found in an average of 46.5% of all neurons. Sixty-two per cent of the small dark (RT97-negative) and 30% of the light (RT97-positive) neuron populations contained the peptide. About one-third (32%) of the cells with peptide immunoreactivity were light cells and about two-thirds (68%) were small dark cells. Intracellular electrophysiological recordings were made in vitro from neurons in lumbar (L4, L5 and L6) dorsal root ganglia from six- to eight-week-old rats, followed by dye-injection and immunocytochemistry. This showed that conduction velocities of neurons with calcitonin gene-related peptide-like immunoreactivity ranged from 0.5 to 28.6 m/s. Seventy-three neurons were successfully processed. Of these, calcitonin gene-related peptide-like immunoreactivity was found in 46% of C-fibre neurons, 33% of A delta-fibre neurons and in 17% of the A alpha/beta-fibre neurons. The peptide-like immunoreactivity was found in approximately 25% of all A-fibre neurons sampled.

Differences in the chemical expression of rat primary afferent neurons which innervate skin, muscle or joint

The fluorescent dye Fast Blue was injected in anaesthetized rats into either skin, muscle or knee joint of the hindlimb. Following retrograde transport of the dye to lumbar dorsal root ganglia, the cell bodies of primary afferent neurons innervating these different target tissues were identified in ganglion sections by fluorescence microscopy. The sections were processed to demonstrate activity of the enzyme thiamine monophosphatase, or immunoreactivity to calcitonin gene-related peptide, substance P, or somatostatin, in Fast Blue labelled neurons. In all cases immunoreactivity to the antineurofilament antibody RT97 was used to classify dorsal root ganglion cells as being either small dark (RT97 negative, unmyelinated axons) or large light (RT97 positive, myelinated axons). The proportion of small dark cells labelled from each target decreased in the order: skin, muscle, joint. Thiamine monophosphatase and somatostatin were present only in small dark cells, while calcitonin gene-related peptide and substance P were found in both small dark and large light cells. In large light cells of all three targets, more contained calcitonin gene-related peptide than substance P. Among small dark cells, thiamine monophosphatase and somatostatin were found predominantly in skin afferents, while calcitonin gene-related peptide and substance P were more common in muscle and joint afferents. The chemical expression of primary afferents is therefore characteristic of the peripheral target they innervate. This could reflect either a maintained influence of the target on the afferents, or the factors which operate only during development.