A non-peptide substance P antagonist down-regulates SP mRNA expression in human mononuclear phagocytes

Substance P (SP), a potent modulator of neuroimmunoregulation, exerts its activity by binding to the neurokinin-1 receptor (NK-1R). The SP-NK-1R interaction is important in inflammation and viral infections, including HIV infection of human immune cells. We recently demonstrated that SP modulates HIV replication and that a non-peptide SP antagonist CP-96,345 inhibits HIV replication in human monocyte-derived macrophages (MDM) by affecting the SP-NK-1R interaction. In order to examine the effect of the SP antagonist on SP mRNA expression, MDM was incubated with or without CP-96,345 in the presence or absence of HIV infection. SP mRNA expression in these cells was then determined by real-time PCR technology. The effect of CP-96,345 on chemokine gene expression was also investigated by using a cDNA array assay. CP-96,345 down-regulated SP mRNA expression and antagonized exogenous SP-enhanced SP expression at the mRNA level, suggesting that SP autocrine regulation was interrupted by CP-96,345. CP-96,345 inhibited HIV replication in MDM, associated with down-regulated SP mRNA expression in comparison to HIV infection controls. In parallel with down-regulated SP and CCR5 mRNA expression, cDNA array assays indicated that CP-96,345 treatment also inhibited IL-8 gene expression, while enhancing expression of fractalkine and monocyte chemotactic protein-3 (MCP-3). Since SP plays an important role in inflammation and viral infections, these studies may have potential applications for therapeutic intervention of inflammation and viral infection of immune cells.

Substance P receptor mediated macrophage responses

Taken together, these studies demonstrate an important role for substance P receptor expression by macrophages. The results to date suggest proinflammatory signals mediated by this receptor, and it is clear that substance P can act synergistically with other factors to stimulate macrophage activity. Antagonism of substance P/substance P receptor interactions in vivo profoundly affect immunity against Salmonella. This model provides evidence that an optimal host response against this intracellular pathogen of macrophages requires signaling through the substance P receptor. The ability of interferon gamma or IL-4 to upregulate substance P receptor mRNA expression on macrophages suggests that substance P-mediated amplification loops might involve either T helper type 1 or T helper type 2 responses. Thus, depending upon the immunologic stimulus, substance P could contribute to cell mediated as well as humoral immune responses. Several important questions remain. Since the antigen processing and presenting function is an important macrophage activity, the effect of signaling through the substance P receptor on these events has not been defined. Furthermore, since macrophages are only one type of antigen presenting cell, it will be important to determine the role of substance P receptor expression in the activity of dendritic cells. We anticipate that these ongoing investigations will further define the positive contributions that substance P/substance P receptor interactions have in the initiation of immune responses.

Co-localization of NK(1)-receptor mRNA with glutamate immunopositivity in cat hypothalamic neurons by the combination of in situ hybridization and immunohistochemistry

Previous studies had demonstrated that, in the cat, aggression is mediated by glutamatergic neurons in the anterior medial hypothalamus which project to the periaqueductal gray. Additionally, NK(1) receptor activation in the medial hypothalamus plays a role in the regulation of aggressive behavior by the medial amygdala. In the present study, in situ hybridization and immunohistochemistry were combined in order to provide neurochemical characterization of medial hypothalamic neurons containing NK(1)-receptor mRNA. In order to identify NK(1) receptors in cat brain, a 650-bp fragment of the cat NK(1) cDNA was cloned. This fragment was used to synthesize a riboprobe for in situ hybridization. Partial DNA sequence analysis of the fragment indicated a 90% homology with human cDNA. In situ hybridization revealed the presence of NK(1)-receptor mRNA in cat hypothalamic neurons. Tissue used to localize NK(1) receptors was also processed for glutamate immunopositivity. The results demonstrated that NK(1)-receptor mRNA is present in glutamate-immunopositive neurons in the anterior medial hypothalamus of cat, thus reinforcing the hypothesis that NK(1) receptors play an important role in this neural circuit.

Pre-Bötzinger neurons with preinspiratory discharges "in vivo" express NK1 receptors in the rat

Substance P stimulates respiration, in part by a direct action on the pre-Bötzinger complex (preBötC). This region of the medulla oblongata contains neurons that are strongly immunoreactive for the neurokinin-1 receptor (NK1R-ir), and a recent theory has postulated that these cells might be the adult form of excitatory interneurons that are essential for respiratory rhythmogenesis in neonates. Here we sought to determine whether preBötC respiratory neurons are indeed NK1R-ir in the adult rat. Preinspiratory (pre-I) neurons were recorded in the preBötC region of halothane-anesthetized rats. Most pre-I cells could be antidromically activated from the contralateral side of the medulla (7 of 10; latency 1.3 +/- 0.2 ms), suggesting that most of them were propriomedullary neurons rather than respiratory motoneurons or bulbospinal cells. Thirty-two pre-I neurons including seven cells with contralateral projection were labeled with biotinamide using the juxtacellular method. Eleven cells (34.4%) were NK1R-ir, including three of the seven pre-I cells that were antidromically activated from the contralateral side. In 3 control rats we labeled 20 preBötC neurons with patterns of discharge other than pre-I and found that none were detectably NK1R-ir. In conclusion, some of the intensely NK1R-ir neurons of the adult preBötC region are indeed respiratory interneurons as suggested by Gray et al. The subtype of NK1R identified by the antibody is detectable only in a small minority of preBötC respiratory cells, most notably in pre-I interneurons. Given prior anatomical evidence, these NK1R-ir pre-I interneurons are most likely glutamatergic. The data are consistent with the possibility that the NK1R-ir pre-I interneurons of the adult preBötC could be the adult form of a class of inspiratory neurons that are rhythmogenic in the neonate (either the pacemakers and/or an excitatory subtype of follower neurons).

Substance P (NK1) receptor in relation to substance P innervation in rat duodenum after irradiation

It has previously been shown that high dose of irradiation to the rat abdomen leads to an increased level of substance P (SP) in the duodenum. In the present study the pattern of distribution of NK1 receptors (NK1-R) in rat duodenum after irradiation (5-30 Gy), was examined at the same time-point (7 days) after irradiation, comparisons being made with the distribution of SP-innervation. Immunohistochemical methods were used. In controls, NK1-R-like immunoreactivity (-LI) was detected in epithelial cells, in cells in the region of the intestinal cells of Cajal within the deep muscular plexus (ICC-DMP), in neuronal cells in the myenteric plexus, and variably in granulocytes in the mucosa. Irradiation with 5-10 Gy did not lead to obvious changes in the pattern of NK1-R-LI. After irradiation with the highest doses (25-30 Gy), the mucosa was often gravely damaged, displaying granulation tissue. No epithelial NK1-R-LI was detected in this tissue, but was present in less affected mucosa after these doses. In the region of the ICC-DMP, in the myenteric plexus, and in granulocytes, NK1-R-LI was detected also after high dose irradiation. However, the degree of NK1-R-LI in the region of the ICC-DMP was somewhat lower than seen in controls and after low doses. SP-immunoreactive nerve fibers were present in the regions where NK1-R-LI was detected. These findings support a suggestion that an increased level of SP after irradiation may contribute to the dose-dependent gastrointestinal adverse effects that occur after radiotherapy.

Expression of authentic substance P receptors in murine and human dendritic cells

Recent studies from our laboratory have shown that substance P can elicit transcription factor activation in dendritic cells. In the present study, we extend these findings by demonstrating the presence of authentic substance P (NK-1) receptors on both normal murine and human dendritic cells. Specifically, we demonstrate the presence of mRNA encoding NK-1 tachykinin receptors and have utilized specific antibodies to detect the expression of NK-1 receptor protein in dendritic cells by Western blot analysis and flow cytometry. These data provide a crucial first step in determining the potential of substance P to modulate dendritic cell function.

Neurokinin 1 receptor distribution in cholinergic neurons and targets of substance P terminals in the rat nucleus accumbens

Substance P (SP) is the major endogenous ligand for neurokinin 1 (NK1) receptors and, together with acetylcholine, has an important role in motivated behaviors involving the limbic shell and motor core of the nucleus accumbens (NAc). To determine the functional sites for SP activation of NK-1 receptors and potential interactions with cholinergic neurons in these regions, the authors examined the electron microscopic immunocytochemical localization either of antisera against the NK1 receptor or of the NK1 receptor and either 1) SP or 2) the vesicular acetylcholine transporter (VAchT) in rat NAc. In both the NAc shell and core, NK1 receptor labeling was localized mainly to somatic and dendritic plasma membranes and nearby endosomal organelles in aspiny neurons. In sections through the ventromedial shell that were processed for NK1/SP labeling, 46% of the NK1-immunoreactive dendrites (n = 603 dendrites) showed symmetric or appositional contacts with SP-containing terminals. These terminals and several others that formed symmetric synapses also occasionally were immunoreactive for NK1 receptors. Analysis of the shell region for NK1/VAchT labeling showed that 61% of the total immunoreactive dendrites (n = 534 dendrites) contained NK1 receptors without VAchT, 29% contained both products, and 10% contained VAchT only. Many of the labeled somata and dendrites also received synaptic contact from VAchT-containing terminals. These findings suggest that, in the NAc, NK1 receptors are recycled through endosomal compartments and play a role in modulating mainly the postsynaptic responses, but also the presynaptic release, of SP and/or inhibitory neurotransmitters onto aspiny interneurons, some of which are cholinergic.

IL-4 and IFN-gamma up-regulate substance P receptor expression in murine peritoneal macrophages

While the ability of macrophages to express authentic substance P receptors (i.e., NK-1 receptors) has been inferred from radioreceptor binding assays and functional assays and, most recently, by identification of NK-1 receptor mRNA expression, we know little about NK-1 expression at the protein level or what host factors might up-regulate expression of this receptor. In the present study we demonstrate that the cytokines IL-4 and IFN-gamma can increase the expression of NK-1 receptors on murine peritoneal macrophages. Specifically, we show that IL-4 and IFN-gamma can elicit increases in the level of mRNA encoding the NK-1 receptor by up to 12- and 13-fold, respectively. Furthermore, these cytokines can significantly increase the expression of the NK-1 receptor protein as measured by Western blot and FACS analysis using specific Abs developed in our laboratory. In addition, we have demonstrated the ability of both IL-4 and IFN-gamma to enhance the ability of macrophages to bind substance P as measured by radiolabeled binding assay. The observation that the level of expression of this receptor protein can be enhanced by cytokines that promote either cell-mediated (Th1) or humoral (Th2) immune responses supports the idea that this receptor can be induced during either type of immune response. As such, these results may point to a more ubiquitous role for substance P in the generation of optimal immune responses than previously appreciated.

Immunohistochemical localization of substance P receptors in the midline glia of the developing rat medulla oblongata with special reference to the formation of raphe nuclei

Immunohistochemical localization of the substance P receptor (SPR) was examined in the developing rat medulla oblongata, with special reference to the development of substance P (SP)-immunoreactive neurons which form the medullary raphe nuclei. During development, SPR immunoreactivity was detected in cells lying lateral to the medullary midline from embryonic day 13 (E13) to postnatal day 5 (P5). The SPR-positive cell bodies were located close to the fourth ventricle, and bore long processes extending to the ventral pial surface. This SPR immunoreactivity co-localized with staining for monoclonal antibody 1D11, a specific marker of immature astrocytes. Substance P (SP)-immunoreactive neurons were first detected at E14 in the ventrolateral part of the medulla. By E16 their number had increased and they were arrayed in two rows closely parallel to the SPR-immunoreactive processes of non-neuronal cells. By P1, two separate SP-immunoreactive cell clusters could be recognized at the midline, representing dorsally the nascent raphe pallidus and ventrally the raphe obscurus. In addition, many SP-immunoreactive fibers traveled rostrocaudally in the medulla oblongata, juxtaposed to the midline sheets of SPR-immunoreactive long processes. SPR-immunoreactive processes at the midline were also immunoreactive for S-100, a glia-specific calcium-binding protein that is known to promote axonal growth of raphe neurons. These results suggest that SPR-expressing immature glial cells at the medullary midline are involved in the development of SP-immunoreactive raphe neurons, both in the formation of the medullary raphe nuclei and in axon guidance and growth.

A monoclonal antibody directed against the neurokinin-1 receptor contains a peptide sequence with similar hydropathy and functional properties to substance P, the natural ligand for the receptor

Monoclonal antibody (mAb) PS12, obtained using the complementary peptide methodology, mimics the neuropeptide substance P (SP) in recognizing the SP-binding domain of the neurokinin-1 receptor (NK1R) and eliciting production of polyclonal antibodies cross-reacting with SP with a high affinity (Déry et al., 1997. J. Neuroimmunol. 76, 1-9). The aim of the present study was to investigate which structural features of mAb PS12 might account for this molecular mimicry. Cloning and sequencing of variable regions of both light (VL) and heavy (VH) chains of this 'SP-like' antibody did not indicate any primary sequence homology between SP and any antibody region. Instead, they revealed a striking similarity between the hydropathic profile of SP and that of an 11-amino-acid region in the light chain encompassing the second complementarity determining region (CDR2). When applied to CHO cells expressing the human NK1R, a synthetic extended 17-amino-acid peptide (denoted CDR2L) corresponding to this VL region inhibited the high-affinity binding of radiolabeled SP and antagonized the SP-induced inositol phosphate production. Moreover, a re-examination of the sequences of several antibodies that previously served in the design of CDR-derived bioactive peptides indicated that these antibodies also carried the hydropathic image of the respective ligands that they mimic. In agreement with previous observations on artificial synthetic peptides, our data thus suggest that the molecular mimicry between natural proteins (i.e. antibody and hormone, for example) could be understood on a structural level directly related, at least in part, to hydropathic homology. These results could then guide the search for bioactive paratope-derived peptides of potential pharmacological interest. We also observed inverse hydropathy between multiple CDRs of mAb PS12 (including CDR3H and CDR3L) and the peptide epitope, confirming the importance of hydropathic complementarity in antigen-antibody interactions.

Immunohistochemical localization of substance P and substance P receptor (NK1) in the olivary pretectal nucleus of the rat

The olivary pretectal nucleus (OPN) is the first central nucleus in the pupillary light reflex arc (PLR). Substance P (SP) is a neuropeptide present in the OPN. The present immunohistochemical study, performed at the ultrastructural level, aimed to determine the synaptic localization of SP and SP receptor in the OPN. Three types of SP-positive terminals were found. The most abundant type was of retinal origin, characterized by electron-lucent mitochondria and round vesicles, organized in glomerular structures, making asymmetric synaptic contacts with dendrites, and profiles containing pleomorphic vesicles, also making synaptic contacts with dendrites. The second type of SP-immunoreactive terminal contained electron-dense mitochondria and pleomorphic vesicles. This type made symmetric synaptic contacts and may originate from the ventral part of the lateral geniculate nucleus. The third type of SP-immunoreactive terminals contained electron-dense mitochondria, clear round vesicles, and made an asymmetric synaptic contact. This type originates from the contralateral OPN. SP receptors of the NK1 subtype were revealed to be on dendrites and were part of the glomerular-like arrangement. On account of the present observations, it can be concluded that retinal projections to the OPN use SP as a neuromodulator and synapse on NK1 receptor-containing dendrites of large neurons projecting to the Edinger-Westphal nucleus. Since SP also modulates the parasympathetic component of the PLR, we postulate that SP plays a modulating role in all components of the PLR.

Neurothekeoma palpebrae: a rare nerve sheath tumor arising in the eyelid

PURPOSE

To report a case of an eyelid neurothekeoma, a rare peripheral nerve sheath tumor.

METHODS

Case report.

RESULTS

An excisional biopsy, performed on a lesion removed from the upper eyelid of a 76-year-old woman, revealed the clinical and histopathologic features of a neurothekeoma, a tumor consisting of multiple collections of spindle cells in a myxomatous background. Immunohistochemical characterization showed positivity for NK1/C3, neuron-specific enolase, and alcian blue.

CONCLUSION

Neurothekeoma palpebrae should be considered in the differential diagnosis of solitary nodules of the eyelids.

Neuropeptides and their receptors in the immune system

Neuropeptides and their receptors are produced and expressed by neuroendocrine tissues and function as neurotransmitters and/or mediators of well-defined hormonal activities in specific tissues and cells. However, neuropeptides and their receptors are also found in the immune system, and various neuropeptides are involved in both systems. In this review we discuss the role of two of these neuropeptides, somatostatin and substance P, with regard to their receptor expression in the human immune system and their role in the diagnosis and treatment of immune-mediated diseases.

Differential modulation of human immunoglobulin isotype production by the neuropeptides substance P, NKA and NKB

The modifying effects of tachykinins substance P, neurokinin A and neurokinin B on immunoglobulin production were analyzed in an in vitro culture system. Purified human T- and B-cells were stimulated with TGFbeta2 and IL-5 to induce preferential IgA production. Neuropeptides had the following effects. (1) The levels of IgA and IgG4 production were enhanced by IL-5 and TGFbeta2; IgA levels remained constant or were slightly augmented by neuropeptides, whereas IgG4 was further augmented. (2) IL-5 and TGFbeta2 did not alter IgG3 production, but neuropeptides stimulated secretion of this subclass. (3) IgG1 and IgM production were inhibited by IL-5 and TGFbeta2. This effect was prevented by neuropeptides. (4) Other isotypes including IgG2 and IgE remained unaffected. Except for IgM, these effects were blocked by specific receptor antagonists indicating specificity. The tachykinin receptor NK-1 mRNA was detected in B- and T-cells, whereas NK-3 mRNA was only present in T- and B-cell coculture following activation. Furthermore, neuropeptide effects depended on cytokine co-stimulation and the presence of T-cells. These results suggest that neuropeptides are potent modifiers of preferential IgA synthesis.

Substance P receptor (neurokinin-1)-expressing neurons in lamina I of the spinal cord encode for the intensity of noxious stimulation: a c-Fos study in rat

The substance P receptor neurokinin-1 is expressed by a subset of neurons in the rat spinal cord. We have combined immunostaining for Fos, a marker of noxious peripheral stimulation, and neurokinin-1 to examine whether nociceptive signals from particular peripheral tissues (skin, muscle or knee joint) or activity generated by nerve injury or formalin-induced inflammation are preferentially modulated by substance P. Our results indicate that superficial and deep spinal neurokinin-1-positive neurons process nociceptive information in markedly different ways. In lamina I, the number of double-labelled neurons was positively correlated with the intensity of the stimulus (defined by the total Fos count) and was not directly related to any particular peripheral target. However, in the deeper layers of the spinal cord (V-X), there was no such correlation, and stimulation of joint nociceptors and formalin-induced inflammation produced the greatest proportion of Fos/neurokinin-1 co-localization, suggesting a particular role for substance P in the mediation of joint pain and inflammatory hyperalgesia. Thus, lamina I neurokinin-1 receptor-bearing neurons appear to be involved in intensity discriminative aspects of pain, whereas the deep neurokinin-1 cells are involved in spatial localization or the detection of particular nociceptive submodalities.

Distinct subsets of CD1d-restricted T cells recognize self-antigens loaded in different cellular compartments

Although recent studies have indicated that the major histocompatibility complex-like, beta2-microglobulin-associated CD1 molecules might function to present a novel chemical class of antigens, lipids and glycolipids, to alpha/beta T cells, little is known about the T cell subsets that interact with CD1. A subset of CD1d-autoreactive, natural killer (NK)1.1 receptor-expressing alpha/beta T cells has recently been identified. These cells, which include both CD4(-)CD8(-) and CD4(+) T cells, preferentially use an invariant Valpha14-Jalpha281 T cell receptor (TCR) alpha chain paired with a Vbeta8 TCR beta chain in mice, or the homologous Valpha24-JalphaQ/Vbeta11 in humans. This cell subset can explosively release key cytokines such as interleukin (IL)-4 and interferon (IFN)-gamma upon TCR engagement and may regulate a variety of infectious and autoimmune conditions. Here, we report the existence of a second subset of CD1d-restricted CD4(+) T cells that do not express the NK1.1 receptor or the Valpha14 TCR. Like the Valpha14(+) NK1.1(+) T cells, these T cells exhibit a high frequency of autoreactivity to CD1d, use a restricted albeit distinct set of TCR gene families, and contribute to the early burst of IL-4 and IFN-gamma induced by intravenous injection of anti-CD3. However, the Valpha14(+) NK1.1(+) and Valpha14(-) NK1.1(-) T cells differ markedly in their requirements for self-antigen presentation. Antigen presentation to the Valpha14(+) NK1.1(+) cells requires endosomal targeting of CD1d through a tail-encoded tyrosine-based motif, whereas antigen presentation to the Valpha14(-) NK1.1(-) cells does not. These experiments suggest the existence of two phenotypically different subsets of CD1d-restricted T cells that survey self-antigens loaded in distinct cellular compartments.

Stress and mind-body impact on the course of inflammatory bowel diseases

At present, the medical management of inflammatory bowel diseases (IBD) including Crohn's disease and ulcerative colitis, are focused on topical, locally active antiinflammatories and systemic immunosuppressives, which are thought to exert their targeted effects in the gastrointestinal mucosa. There is a paucity of controlled trials assessing the impact of mind, central nervous system (CNS), and neuromodulation on the overly active immune response in the intestinal mucosa. Patients and their physicians have long been aware of a strong association between attitude, stress, and flares of their IBD. Although reports to date remain mostly anecdotal, the degree to which mind-body influences and stress impact levels of local inflammation deserves closer attention with the aim of identifying contributing mechanisms, which may highlight new therapeutic interventions, as well as assist in identifying particular subsets of patients that may respond to novel forms of adjunctive treatments for IBD, including hypnosis, meditation, neuropeptide receptor modulation, and cortisol-releasing factor (CRF) modulation.

Neurokinin type-1 receptor antagonist inhibits enhancement of T cell functions by substance P in normal and neuromanipulated capsaicin-treated rats

Substance P (SP) plays a major role in the regulation of the interaction between immune and nervous systems. SP administration stimulates Con A-induced proliferation of spleen and peripheral blood lymphocytes from normal and neonatally capsaicin treated rats, which correlated with enhanced IL-2 production and expression of activation antigens such as IL-2 receptor alpha chain (CD25) and RT1B MHC class II molecule. Moreover, SP markedly increased the percentage of CD5+ and CD4+ T lymphocytes in the peripheral blood of capsaicin-treated rats. Concomitant administration of SP with the non-peptide Neurokinin-1 receptor (NK1R) antagonist SR140333 completely inhibited the SP-mediated augmentation of Con A-induced PBL proliferation and IL-2 production as well as of CD4+ CD25+ and CD4+ RT1B+ T cell numbers in normal and capsaicin-treated rats. SR 140333 also blocked the increased percentage of peripheral blood CD4+ T cells induced by SP in capsaicin-treated rats.

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

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

A monoclonal antibody to the ligand-binding domain of the neurokinin 1 receptor (NK1-R) for the neuropeptide substance P

Monoclonal antibodies to the binding site of the NK1 receptor for the neuropeptide substance P were produced in mice using the complementary or antisense peptide methodology. Among several anti-peptide monoclonal antibodies, we selected the mAb12 antibody which specifically crossreacted, through its paratope, with a binding site present on membranes from rat parotid gland cells, with an affinity close to 2 x 10(-7) M and with membranes from CHO cells expressing human brain NK1 receptors. Immunocytochemical investigations using mAb12 revealed immunostaining whose distribution in the dorsal horns of rat spinal cord fits well with the known location of NK1 receptors. In both biochemical and immunocytochemical experiments, the competition occurring between the antibody and substance P, or a substance P-protein conjugate, indicates that mAb12 recognizes a membrane epitope located at or near the substance P binding domain on the NK1 receptor. Immunization of mice with mAb12 led to the production of specific anti-substance P antibodies, again suggesting that mAb12 shares common structural features with the neuropeptide. This monoclonal antibody can now be used in further biochemical or cytochemical characterizations of NK1 receptors. Owing to its fine specificity, mAb12 could also serve as a molecular model for designing peptides, possibly displaying pharmacological properties in the various processes in which substance P is involved, e.g. immunomodulation, inflammation or chronic pain.

Neurokinin-1 receptor-immunoreactive sympathetic preganglionic neurons: target specificity and ultrastructure

Substance P is involved in cardiovascular control at the spinal cord level, where it acts through neurokinin-1 receptors. In this study we used immunocytochemistry and retrograde tracing to investigate the presence of the neurokinin-1 receptor and its ultrastructural localization in rat sympathetic preganglionic neurons that project to the superior cervical ganglion or the adrenal medulla. Immunofluorescence for the neurokinin-1 receptor outlined the somatic and dendritic surfaces of neurons in autonomic subnuclei of spinal cord segments T1-T12, whereas immunofluorescence for the tracer, cholera toxin B subunit, filled retrogradely labelled cells. There was a significant difference in the proportion of neurokinin-1 receptor-immunoreactive sympathetic preganglionic neurons supplying the superior cervical ganglion and the adrenal medulla. Thirty-eight percent of the neurons that projected to the superior cervical ganglion were immunoreactive for the neurokinin-1 receptor compared to 70% of neurons innervating the adrenal medulla. Of neurons projecting to the superior cervical ganglion, significantly different proportions showed neurokinin-1 receptor immunoreactivity in spinal cord segment T1 (15%) versus segments T2 T6 (45%). At the ultrastructural level, neurokinin-1 receptor staining occurred predominantly on the inner leaflets of the plasma membranes of retrogradely labelled sympathetic preganglionic neurons. Deposits of intracellular label were often observed in dendrites and in the rough endoplasmic reticulum and Golgi apparatus of cell bodies. Neurokinin-1 receptor immunoreactivity was present at many, but not all, synapses as well as at non-synaptic sites, and occurred at synapses with substance P-positive as well as substance P-negative nerve fibres. Only 37% of the substance P synapses occurred on neurokinin-1-immunoreactive neurons in the intermediolateral cell column. These results show that presence of the neurokinin-1 receptor in sympathetic preganglionic neurons is related to their target. The ultrastructural localization of the receptor suggests that sympathetic preganglionic neurons may be affected (i) by substance P released at neurokinin-1 receptor-immunoreactive synapses, (ii) by other tachykinins (e.g., neurokinin A), which co-localize in substance P fibres in the intermediolateral cell column, acting through other neurokinin receptors, and (iii) by substance P that diffuses to neurokinin-1 receptors from distant sites.

The neostriatal mosaic: basis for the changing distribution of neurokinin-1 receptor immunoreactivity during development

The pattern of neurokinin-1 receptor-like immunoreactivity (NK-1Rir) was mapped in perinatal and adult mouse striatum by using a new polyclonal antiserum. NK-1Rir was detected in the differentiating regions of the ganglionic eminences on embryonic day 12.5 (E12.5). NK-1Rir structures were enriched in the striatal patch compartment between E16.5 and approximately postnatal day 3 (P3); distributed more uniformly, within portions of both the patch and matrix compartments on P7; and enriched in the matrix compartment in the adult. Analysis of the phenotype of NK-1Rir cells on P2, P7, and in the adult suggested that cholinergic cells accounted for the majority of NK-1Rir cells early postnatally, with increasing contributions from somatostatinergic cells later postnatally. In the adult, approximately half of NK-1Rir cells were cholinergic and half were somatostatinergic. The transient enrichment of NK-1R-bearing cells and processes in the patch compartment which contains cells that express substance P (SP), a putative ligand for the NK-1R, may be a consequence of compartment formation or may be functionally important for compartment development.

Characterisation of substance P-induced endocytosis of NK1 receptors on enteric neurons

Immunoreactivity for NK1 receptors is confined to specific nerve cell bodies in the guinea-pigileum, including inhibitory motor neurons and secretomotor neurons. In the present work, endocytosis of NK1 receptors in these enteric neurons was studied following addition of substance P (SP) to isolated ileum. NK1 receptors were localised with antibodies against the C-terminus of this receptor. Some preparations were incubated with SP tagged with the fluorescent label, Cy3.18, so that the fate of SP bound to receptors could be followed. Preparations were analysed by confocal microscopy. In tissue that was incubated at 4 degrees C in the absence of SP, most NK1 receptor immunoreactivity (IR) was confined to surface membranes of nerve cells. At 37 degrees C in the presence of 10(-7) M SP (plus 3 x 10(-7)M tetrodotoxin to prevent indirect activation via other neurons) the neuronal NK1 receptor was rapidly internalised. After 5 min, NK1 receptor IR was partially internalised, at 20 min NK1 receptor IR was throughout the cytoplasm and in perinuclear aggregates and at 30 min it was again at the cell surface. SP-induced NK1 receptor endocytosis was inhibited by the specific NK1 receptor antagonist, SR140333. Cy3-SP was colocalised with NK1 receptor IR and was internalised with the NK1 receptor. These results show that enteric neurons exhibit authentic NK1 receptors that are rapidly internalised when exposed to their preferred ligand.

Characterization of antisera specific to NK1, NK2, and NK3 neurokinin receptors and their utilization to localize receptors in the rat gastrointestinal tract

Understanding the physiological role of tachykinins requires precise cellular and subcellular localization of their receptors. We raised antisera by immunizing rabbits with peptides corresponding to portions of the intracellular tails of the rat neurokinin 1, 2, and 3 receptors (NK1-R, NK2-R, NK3-R). Receptors were localized by immunofluorescence and confocal microscopy. NK1-R, NK2-R, and NK3-R were detected at the plasma membrane of transfected cells with minimal intracellular stores. Staining was abolished by preabsorption of the antisera with the peptides used for immunization. Nontransfected cells were unstained. Each antiserum only stained cells transfected with the appropriate receptor and did not stain cells transfected with the other receptors. Therefore, the antisera are specific and do not cross-react with other neurokinin receptors. We examined the distribution of the neurokinin receptors in the gastrointestinal tract of the rat. NK1-R was detected in myenteric and submucosal neurons and in interstitial cells of Cajal. NK2-R was localized to circular and longitudinal muscle cells and to nerve endings in the plexuses. NK3-R was detected in numerous myenteric and submucosal neurons. Some neurons expressed both NK1-R and NK3-R. Receptors were detected at the plasma membrane and in endosomes. Cells expressing the receptors were closely associated with tachykinin-containing nerve fibers. Thus, NK1-R and NK3-R mediate neurotransmission by tachykinins within enteric nerve plexuses, and NK1-R and NK2-R mediate the effects of tachykinins on interstitial and smooth muscle cells, respectively.

Substance P activation of enteric neurons in response to intraluminal Clostridium difficile toxin A in the rat ileum

BACKGROUND & AIMS

Nerves have been suggested to mediate the effects of bacterial toxins in intestinal diseases. However, the mechanisms involved are unknown. This study examined endogenous substance P (SP) activation of the substance P receptor (SPR) on enteric neurons in the rat ileum after exposure to intraluminal Clostridium difficile toxin A.

METHODS

After intraluminal injection of toxin A in ileal loops, tissue was examined for pathological changes by histology and for SPR activation by immunocytochemical analysis of SP-induced SPR endocytosis.

RESULTS

After toxin A administration, > 70% of enteric neurons showed SPR endocytosis and became swollen with thickened dendrites. In contrast, SPRs in control rats were largely confined to the plasma membrane. Rats denervated of primary afferent fibers with neonatal capsaicin injection and animals pretreated with a nonpeptide SPR antagonist showed few endosomal SPRs, and the pathological inflammatory effects of toxin A were ablated.

CONCLUSIONS

Intraluminal toxin A causes the release of SP from primary afferent neurons: this endogenous SP then acts on enteric neurons in the submucosal and myenteric plexuses. SP is the primary mediator of an axon reflex mediating neurogenic inflammation in the intestine. SPR blockade may prove to be a novel therapy used to prevent intestinal inflammation.