Substance P Immunoreactivity Research Articles

Mimicry between neurokinin-1 and fibronectin may explain the transport and stability of increased substance P immunoreactivity in patients with bone marrow fibrosis

AbstractBone marrow (BM) fibrosis may occur in myeloproliferative diseases, lymphoma, myelodysplastic syndrome, myeloma, and infectious diseases. In this study, the role of substance P (SP), a peptide with pleiotropic functions, was examined. Some of its functions—angiogenesis, fibroblast proliferation, and stimulation of BM progenitors—are amenable to inducing BM fibrosis. Indeed, a significant increase was found in SP-immunoreactivity (SP-IR) in the sera of patients with BM fibrosis (n = 44) compared with the sera of patients with hematologic disorders and no histologic evidence of fibrosis (n = 46) (140 ±12 vs 18 ±3; P < .01). Immunoprecipitation of sera SP indicated that this peptide exists in the form of a complex with other molecule(s). It was, therefore, hypothesized that SP might be complexed with NK-1, its natural receptor, or with a molecule homologous to NK-1. To address this, 3 cDNA libraries were screened that were constructed from pooled BM stroma or mononuclear cells with an NK-1 cDNA probe. A partial clone (clone 1) was retrieved that was 97% homologous to the ED-A region of fibronectin (FN). Furthermore, sequence analyses indicated that clone 1 shared significant homology with exon 5 of NK-1. Immunoprecipitation and Western blot analysis indicated co-migration of SP and FN in 27 of 31 patients with BM fibrosis. Computer-assisted molecular modeling suggested that similar secondary structural features between FN and NK-1 and the relative electrostatic charge might explain a complex formed between FN (negative) and SP (positive). This study suggests that SP may be implicated in the pathophysiology of myelofibrosis, though its role would have to be substantiated in future research.

Production of neuropeptide substance P by synovial fibroblasts from patients with rheumatoid arthritis and osteoarthritis

We examined the production of substance P (SP) in synovial fibroblasts derived from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Immunoreactive SP was observed in non-stimulated RA fibroblasts. The expression of β-preprotachykinin-A (β-PPT-A) mRNA was confirmed by reverse transcription-polymerase chain reaction analysis. SP contents in culture medium were increased by treatment of RA fibroblasts with transforming growth factor-β (TGFβ) (10 ng/ml). Levels of SP release were elevated at 12 h after TGFβ stimulation whereas the expression of β-PPT-A mRNA was enhanced at 3 h. Furthermore, SP production in response to TGFβ was dose-dependently enhanced by basic fibroblast growth factor (bFGF). OA fibroblasts also significantly released SP in the presence of TGFβ (10 ng/ml) plus bFGF (50 ng/ml). These results suggest that SP produced by synovial fibroblasts may participate in joint diseases.

Characterization of the innervation of the gallbladder mucosa in the Australian brush-tailed possum

Intrinsic and extrinsic nerves innervate the gallbladder epithelium and modulate its functions. Some neurochemicals of this innervation are known in some species, however, the intrinsic and extrinsic origin of this innervation is unclear. Aim: To characterize the neurons projecting to the gallbladder epithelium in the Australian Brush-tailed possum using in vitro retrograde tracing, extrinsic denervation in culture and immunohistochemistry. Methods: Gallbladders were harvested from 9 anesthetized possums. In 6 gallbladders, a fluorescent neural tracer was focally applied to the epithelial surface to identify intrinsic neurons innervating the epithelium. Following organotypic culture, the preparations were dissected and an antiserum against nitric oxide synthase (NOS) was applied. Retrogradely traced and antibody labeled neurons were visualized using fluorescence microscopy and their positions recorded. A further 3 gallbladders were cut into 4 longitudinal segments. Two segments from each gallbladder were fixed immediately and the others placed in organotypic culture for 5 days to achieve extrinsic penervatlon. Multiple-labeling immunohistochemistry for substance P (SP), vasoactive intestinal polypeptide (VlP), calcitonin gene related peptide (CGRP) and tyrosine hydroxylase (TH) were used to characterize the intrinsic and extrinsic innervation of the ganglionated and non-ganglionated sub-epithelial plexus of the gallbladder. Results: Retrogradely traced neurons were found within lOmm of the tracer application site, exclusively within the subepithelial plexus, with 63 _+ 9% being immunoreactive for NOS. The majority of neurons within the sub-epithelial plexus colocalized both NOS and MIP. Some SP immunoreactive neurons were seen. Varicose nerve fibres showing immunoreactivity for NOS, VIP, SP, CGRP and TH were seen within the sub-epithelial plexuses in freshly fixed tissue. Immunoreactivity for CGRP and TH were abolished post-culture, with some reduction in the SP and MIP innervation. Summary: NOS and VlP-colocalizing and SP-immunoreactive neurons of the ganglionated sub-epithelial plexus innervate the gallbladder epithelium, with no innervation from the muscular and serosal plexuses. This is the first demonstration of the neurochemistry and spatial organisation of the intrinsic innervation of the gallbladder epithelium. Sympathetic and extrinsic afferent neurons also directly innervate the epithelium and the ganglionated subepithelial plexus.

Ex vivo lumbar and post mortem ventricular cerebrospinal fluid substance P-immunoreactivity in Alzheimer's disease patients

The concentration of substance P-immunoreactivity (SPIR) in ex vivo lumbar cerebrospinal fluid (CSF) of patients with probable Alzheimer's disease (AD), non-Alzheimer dementias, neurological patients without dementia and control subjects was determined using a sensitive and specific competitive enzyme-immunoassay. There were no significant differences between AD patients and the other groups, but patients with late onset AD (>65 years) showed significantly higher levels of SPIR than patients with early onset (<65 years) and controls. In post mortem ventricular fluid, SPIR levels of all groups were lower compared with the lumbar compartment, but without significant group differences. It is concluded that CSF SPIR may not serve as a diagnostic marker for AD, but possibly could reflect immunological or neuroprotective processes modulated by substance P in late onset AD patients.

Rectal mucosal biopsy compared with laparoscopic seromuscular biopsy in the diagnosis of intestinal neuronal dysplasia in children with slow-transit constipation

Background/Purpose: Intestinal neuronal dysplasia (IND) as a cause for severe chronic constipation remains controversial. The aim of this study is to examine the correlation between a deficiency of substance P (SP) immunoreactive nerve fibers in the colon and enzyme histochemistry of rectal biopsies in children with slow-transit constipation. Methods: Fifty children with intractable constipation have been assessed by rectal biopsies examined with histochemical staining for lactate dehydrogenase, and 32 children among those 50 have been studied by laparoscopic seromuscular biopsy of the colon labelled with antibodies to SP using immunofluorescence methods. Results: Four children have evidence of IND. Fifteen children, including all 4 IND cases, showed a deficiency of SP immunoreactivity. There is a significant correlation between giant ganglia and SP deficiency (P <.01). Conclusion: This study is attempting to propose that a deficiency of SP immunoreactivity in colonic circular muscle nerves may be used as a histologic marker for slow-transit constipation and that IND may be a small subset of patients with SP deficiency. J Pediatr Surg 35:1724-1727. Copyright © 2000 by W.B. Saunders Company.

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.

Activation of silent mechanoreceptive cat C and Adelta sensory neurons and their substance P expression following peripheral inflammation.

The effect of inflammation on the excitability and the level of substance P (SP) in cat mechanoreceptive C and Adelta dorsal root ganglion (DRG) neurons were studied in vivo using intracellular recording and immunocytochemical techniques. Following injections of carrageenan (Carg) into the cat hindpaw, the percentage of C neurons exhibiting spontaneous activity increased from 7.2 to 20.7% and the percentage of Adelta neurons increased from 6.9 to 18.6%. In contrast to most cells from normal cats, which fired regularly below 10 Hz, many cells from Carg-treated cats fired at higher frequencies or in bursts. Inflammation (Carg treatment) also depolarized membrane potentials, increased membrane input resistance, caused the disappearance of inward rectifying currents and lowered the mean current thresholds of tibial nerve-evoked responses in DRG neurons. With inflammation, the percentage of C or Adelta neurons responding to low threshold mechanoreceptive stimuli increased (C neurons: normal, 13%; inflamed, 41%; Adelta neurons: normal, 13 %; inflamed, 39 %), while the percentage of C or Adelta neurons responding to high threshold mechanoreceptive stimuli remained unchanged. Some receptive field (RF)-responsive cells were injected with Lucifer Yellow and their SP immunoreactivity was determined. Following Carg treatment, substantially higher percentages of RF-responsive cells were SP positive (C neurons: normal, 35.7%; inflamed, 60%; Adelta neurons: normal, 18.2%; inflamed, 66.7%). These combined increases in the excitability of DRG neurons and SP-containing RF-responsive neurons could lead to sensitization of sensory neurons, thus contributing to the development of hyperalgesia.

Neonatal capsaicin treatment decreased substance P receptor immunoreactivity in lamina III neurons of the dorsal horn.

Using immunohistochemistry and in situ hybridization technique, the distribution of substance P (SP) and SP receptors was studied in the dorsal horn of the rat spinal cord after neonatal capsaicin treatment. Sprague-Dawley rats administered 100 mg/kg of capsaicin subcutaneously within 24 h after birth were examined at 8 weeks of age. In the capsaicin administered rats, slight reduction of SP immunoreactivities in lamina I, and severe decrease in lamina II were observed. In the control group, SP receptor-mRNA was observed in all laminae, and SP receptor-immunoreactivities were seen to be intense in laminae I and III. In contrast, in the capsaicin administered rats, the SP receptor-mRNA expression was low in laminae II-V, and SP receptor immunoreactivities decreased in laminae III-V. Furthermore, the density of the SP receptor immunoreactivities was considerably decreased in the nerve cells of lamina III. We concluded that elevation of the threshold to painful stimulation in rats was as a result of the decrease in SP immunoreactive afferent fibers in laminae I and II, decrease of the SP receptor-mRNA in the laminae II-V, or the decrease in SP receptor immunoreactive neurons in laminae III-V.

Localization of amino acids, neuropeptides and cholinergic markers in neurons of the septum-diagonal band complex projecting to the retrosplenial granular cortex of the rat

Retrograde labelling was combined with immunohistochemistry to localize neurons containing choline acetyltransferase, γ-aminobutyric acid (GABA), glutamate, leu-enkephalin, neurotensin, and substance P-like immunoreactivity in the projection pathways from the septum-diagonal band complex to the retrosplenial granular cortex in the rat. Injections of horseradish peroxidase conjugated to subunit B of cholera toxin (CT-HRP) into the retrosplenial granular cortex resulted in retrogradely labelled neurons in the ipsilateral nuclei of the diagonal band of Broca, especially in the horizonatal nucleus of the diagonal band, and small numbers of CT-HRP-labelled neurons were also found in the medial septal nucleus. In the horizontal and vertical nuclei of the diagonal band of Broca, 90–95% of CT-HRP-labelled neurons (35–45 per section) were immunoreactive for choline acetyltransferase and small numbers of retrogradely labelled neurons (2 to 4–5 per section) were also immunoreactive for GABA, glutamate, neurotensin, leu-enkephalin, or substance P. In the medial septal nucleus approximately 75–80% of the retrogradely labelled neurons (8–10 per section) were immunoreactive for choline acetyltransferase and up to 25% of the CT-HRP labelled neurons (1–3 per section) in the medial septal nucleus also displayed GABA-, glutamate-, neurotensin-, leu-enkephalin-, or substance P-immunoreactivity. These results suggest that the complexity of the neurotransmitter(s)/neuromodulator(s) of septum-diagonal band complex projections to the retrosplenial granular cortex should be taken into account when considering the mechanisms of cortical activation.

Regulatory effects of electro-acupuncture at Zusanli on ir-SP content in rat pituitary gland and peripheral blood and their immunity.

It has been reported in many studies that electro-acupuncture (EA) can positive ly regulate erythrocytic immunityandT-lymphocyticsubgroups[1-8]. Nevertheless, its mechanism remains to be explored. In the present study, a multi -group, multi-stepped and multi-indexed observation was conducted on the effe cts of EA on erythyrocytic immunity and T-lymphocytic subgroups. A simultaneous assay of the changes in immunoreactive substance-P (ir-SP) content in the pit uitary gland and peripheral blood was also carried out. The objective of the study was to investigate the regulatory effects of the immune system and their poss ible mechanism in the treatment of relevant diseases with EA.

Anabolic-androgenic steroids affect the content of substance P and substance P 1–7 in the rat brain

The effects of intramuscular (i.m.) injections of nandrolone decanoate (15 mg/kg/day), an anabolic-androgenic steroid, on the levels of substance P (SP) and on its N-terminal fragment SP 1–7 were examined in the male rat brain by radioimmunoassay. The results demonstrated that the SP immunoreactivity in amygdala, hypothalamus, striatum, and periaqueductal gray was significantly enhanced, whereas the concentration of the N-terminal fragment SP 1–7 was enhanced in the nucleus accumbens and in periaqueductal gray. In the striatum the steroid induced a decrease in the content of SP 1–7. The relevance of these peptides in connection with anabolic-androgenic steroid-induced aggression is discussed.

Co-distribution of NK2 tachykinin receptors and Substance P in nerve endings of guinea-pig ileum

The distribution of NK2 tachykinin receptors-immunoreactivity (NK2r-IR) in the guinea-pig ileum and the co-distribution of NK2r-IR with substance P-immunoreactivity (SP)-IR were investigated. NK2r-IR was detected in varicose fibers of myenteric and submucous ganglia and nerve strands, in the longitudinal and circular muscle layers and at the deep muscular plexus (DMP). Except for the submucous plexus, some of the NK2r-IR varicose fibers were co-distributed with SP-IR ones and quantitative analysis showed significant regional differences in the percentages of these fibers. These results demonstrate that presynaptic NK2 receptors are located at varicose fibers likely originating from motor neurons projecting to muscle layers and DMP, and from interneurons. Furthermore, the NK2r/SP-IR co-distribution suggests that some of these receptors are autoreceptors on SP nerve endings.

Immunohistochemical localization of neuropeptides in bovine pancreas.

The occurrence and density of distribution of nerves and endocrine cells that are immunoreactive for neuropeptides in the bovine pancreas were studied by immunohistochemistry. The six neuropeptides localized were galanin (GAL), substance P (SP), methionine-enkephalin (MENK), neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP). The exocrine pancreas was shown to have an appreciable number of GAL- and SP-immunoreactive nerve fibres but few fibres showing immunoreactivity for VIP and CGRP. Numerous MENK-, GAL-, SP-, and NPY-immunoreactive nerve fibres were seen in the endocrine portion of the pancreas. Nerve cell bodies in the intrapancreatic ganglia showed immunoreactivity for all of the neuropeptides except CGRP. Endocrine cells showing immunoreactivity for GAL and SP were observed in the large islets and islets of Langerhans, respectively. The present results indicate a characteristic distribution of neuropeptides in the bovine pancreas, which may regulate both exocrine and endocrine secretions of pancreas.

Nerve growth factor-induced phenotypic switch in guinea pig airway sensory neurons.

Immunohistochemistry was combined with retrograde tracing techniques to characterize the effect of nerve growth factor (NGF) on substance P (SP) producing vagal neurons innervating the guinea pig trachea. Fast blue dye instilled into the trachea retrogradely labeled nerve cell bodies located in the nodose and jugular ganglia. In untreated guinea pigs > 99% of the SP-containing neurons labeled with fast blue were located in the jugular ganglia. The SP-positive neurons were small in diameter (23 +/- 1 microm) and were negative for neurofilament immunoreactivity. The fast-blue-positive neurons in the nodose ganglia, by contrast, were large in diameter (40 +/- 3 microm) and were negative for SP immunoreactivity and positive for neurofilament immunoreactivity. After NGF-beta injections into the tracheal wall, approximately 10% of the large-diameter nodose neurofilament-positive neurons projecting fibers to the trachea became SP-positive (p < 0.05). We previously demonstrated that nodose nerve endings supplying the trachea are exquisitely mechanically sensitive, but capsaicin- and bradykinin-insensitive. These results suggest that NGF not only increases SP expression in airway neurons, but changes the neuronal phenotype such that large, capsaicin-insensitive nodose neurons with fast-conducting "Adelta" fibers provide a component of the tachykinergic innervation.

Substance P-immunoreactive neurons in the rostromedian area of the midbrain send axons to the lower spinal cord in the chicken

Substance P-immunoreactivity in neurons projecting to the spinal cord was examined using retrograde tract-tracing method combined with immunohistochemical techniques in chickens. Many small substance P-immunoreactive neurons were densely clustered in the midline area in the rostral midbrain, the rostromedian area (80% of the neurons in the rostromedian area). Some of these substance P-immunoreactive neurons in the rostromedian area (about 20% of substance P-immunoreactive neurons) were retrogradely labeled by small injections of wheat germ agglutinin conjugated horseradish peroxidase into the central part of the lumber segments including the intermediomedial nucleus, suggesting the projections from the rostromedian area to the lower spinal preganglionic regions. From the present data and mammalian previous studies, it was suggested that the midline area in the midbrain has fiber connections with the regions related autonomic functions, and all of which exhibit substance P-immunoreactivity.

The relationship between neurokinin-1 receptor and substance P in the medullary dorsal horn: a light and electron microscopic immunohistochemical study in the rat.

The synaptic relationship between substance P (SP) and its receptor, i.e. neurokinin-1 receptor (NK1R), was examined in the superficial laminae of the caudal subnucleus of the spinal trigeminal nucleus (medullary dorsal horn; MDH) of the rat. For confocal laser-scanning microscopy, double-immunofluorescence histochemistry for NK1 and SP was performed. In electron microscopic double-immunolabeling study, immunoreactivity for NK1R was detected with the silver-intensified gold method, while immunoreactivity for SP was detected with peroxidase immunohistochemistry. SP-immunoreactive axon terminals were observed to be in synaptic (mostly asymmetric) contact with NK1R-immunoreactive neuronal profiles in lamina I and lamina IIo. Although some SP-immunoreactive axon terminals were in synaptic contact with NK1R-immunoreactive sites of plasma membranes, NK1R-immunoreactivity was observed at both synaptic and non-synaptic sites of plasma membrane. Thus, SP released from axon terminals might not only act on NK1Rs facing the SP-containing axon terminals, but also diffuse in the extracellular fluid for distances larger than the synaptic cleft to act on NK1Rs at some distances from the synaptic sites.

Relationship between neurokinin-1 receptor and substance P in the striatum: Light and electron microscopic immunohistochemical study in the rat

The synaptic relationship between substance P (SP) and its receptor, i.e., neurokinin-1 receptor (NK1R), was examined in the striatum of the rat by confocal laser-scanning microscopy and electron microscopy. For confocal laser-scanning microscopy, triple-immunofluorescence histochemistry was performed to label NK1R, SP, and vesicular acetylcholine transporter (a specific marker for cholinergic neurons). In electron microscopic double-immunolabeling study, immunoreactivity for NK1R was detected with the silver-intensified gold method, while immunoreactivity for SP was detected with peroxidase immunohistochemistry. Simultaneous immunolabeling of NK1R and SP revealed significant mismatch at the synaptic level: although some SP-immunopositive axon terminals were in synaptic contact with NK1R-immunopositive sites of plasma membrane, NK1R-immunoreactivity was observed at both synaptic and non-synaptic sites of plasma membrane. Thus, SP released from the sites remote from NK1Rs might diffuse in the extracellular fluid to act, as a paracrine neurotransmitter, on NK1Rs distant from its releasing site. SP neurotransmission in the striatum might occur not only synaptically but also extrasynaptically. The SP-NK1R system might constitute an association system within the striatum.

Origin of pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive fibers innervating guinea pig parasympathetic cardiac ganglia

The present study investigated the origin of pituitary adenylate cyclase-activating polypeptide (PACAP) -immunoreactive (IR) fibers innervating guinea pig cardiac ganglia. Immunohistochemistry was performed on whole-mounts containing cardiac ganglia, and sections of stellate, nodose, and dorsal root ganglia (DRG, thoracic levels 1-4), and caudal medulla. In control preparations, only 4% of the cardiac neurons were PACAP-IR, although most cardiac ganglion cells were surrounded by a network of PACAP-IR fibers. After 3-7 days in explant culture, the number of PACAP-IR cardiac neurons increased approximately eightfold. However, virtually all PACAP-IR fibers surrounding the cardiac neurons had degenerated, demonstrating that the major source of the PACAP-IR fibers was extrinsic to the cardiac ganglia preparation. PACAP- and choline acetyltransferase (ChAT) immunoreactivity were colocalized in fibers within the stellate ganglia but not within neuropeptide Y (NPY) -IR cell bodies and fibers. PACAP-IR cells and fibers were present in the nodose ganglia. PACAP immunoreactivity also was present in fibers and primarily small neurons in thoracic DRGs. In situ hybridization demonstrated the presence of proPACAP mRNA within neurons in the region of the dorsal motor nucleus of the vagus and nucleus ambiguus. PACAP immunoreactivity was colocalized with ChAT immunoreactivity, but not with NPY immunoreactivity or SP immunoreactivity, in fibers surrounding neurons within cardiac ganglia. We conclude that PACAP-containing fibers innervating the postganglionic parasympathetic neurons in guinea pig cardiac ganglia are primarily preganglionic parasympathetic axons.

The fountain amacrine cells of the rabbit retina.

We have characterized a distinctive type of bistratified amacrine cell in the rabbit retina at both the single cell and population levels. These cells correspond to the "fountain" amacrine cells recently identified by MacNeil and Masland (1998). The fountain cells can be distinguished in superfused retinal wholemounts labeled with nuclear dyes, thus enabling them to be targeted for intracellular injection with Neurobiotin. This revealed that the primary dendrites ascend steeply to sublamina b of the inner plexiform layer, where they form an irregular arbor at the border of strata 4 and 5. These dendrites then give rise to multiple varicose processes that descend obliquely to sublamina a, where they form a more extensive arbor in stratum 1. The fountain amacrine cells show strong homologous tracer coupling when injected with Neurobiotin, and this has enabled us to map their density distribution across the retina and to examine the dendritic relationships between neighboring cells. The fountain amacrine cells range in density from 90 to 360 cells/mm2 and they account for 1.5% of the amacrine cells in the rabbit retina. The thick tapering dendrites in sublamina b form highly territorial arbors that tile the retina with minimal overlap, whereas the thin varicose processes intermingle in sublamina a. The fountain cells are immunopositive for y-aminobutyric acid and immunonegative for glycine. We further propose that these cells are homologous to the substance P-immunoreactive (SP-IR) amacrine cells in the cat retina and that they may account for a subset of the SP-IR amacrine cells in the rabbit retina.

Pulpal exposure alters neuropeptide levels in inflamed dental pulp and trigeminal ganglia: Evaluation of axonal transport

Dental pulp is richly innervated with neurons containing calcitonin gene-related peptide (CGRP) or substance P (SP). Prior studies have demonstrated that inflammation alters these pulpal neuropeptides. In this study, we used a radioimmunoassay to evaluate the specificity of this response and the contribution of axonal transport. Rat mandibular molars were exposed and immunoreactive CGRP (iCGRP) and immunoreactive SP were measured. At 7 to 14 days after exposure, both pulpal iCGRP (73%) and immunoreactive SP (135%) displayed peak increases above control levels. This response was somatotopically restricted, with no changes observed in contralateral (intact) molars, or in ipsilateral mandibular molars after exposure of maxillary molars. Transection of the inferior alveolar nerve on day 13 significantly reduced pulpal levels of iCGRP on day 14. Collectively, these studies indicate that pulpal inflammation evokes a selective alteration in neuropeptide levels, due at least in part to alterations in transport or synthesis of neuropeptides in the trigeminal ganglion.