Regional distribution of substance P binding sites in the brainstem of the human newborn

Normative distribution of substance P and its tachykinin neurokinin-1 receptor in the medullary serotonergic network of the human infant during postnatal development

Substance P (SP) and its tachykinin NK1 receptor (NK1R) function within key medullary nuclei to regulate cardiorespiratory and autonomic control. We examined the normative distribution of SP and NK1R in the serotonergic (5-Hydroxytryptamine, [5-HT]) network of the human infant medulla during postnatal development, to provide a baseline to facilitate future analysis of the SP/NK1R system and its interaction with 5-HT within pediatric brainstem disorders in early life. [¹²⁵I] labelled Bolton Hunter SP (BH-SP) tissue receptor autoradiography (n = 15), single label immunohistochemistry (IHC) and double label immunofluorescence (IF) (n = 10) were used to characterize the normative distribution profile of SP and NK1R in the 5-HT network of the human infant medulla during postnatal development. Tissue receptor autoradiography revealed extensive distribution of SP and NK1R in nuclei intimately related to cardiorespiratory function and autonomic control, with significant co-distribution and co-localization with 5-HT in the medullary network in the normal human infant during development. A trend for NK1R binding to decrease with age was observed with significantly higher binding in premature and male infants. We provide further evidence to suggest a significant role for SP/NK1R in the early postnatal period in the modulation of medullary cardiorespiratory and autonomic control in conjunction with medullary 5-HT mediated pathways and provide a baseline for future analysis of the potential consequences of abnormalities in these brainstem neurotransmitter networks during development.

Vulnerability of fourth ventricle choroid plexus in sudden unexplained fetal and infant death syndromes related to smoking mothers

The human choroid plexuses in the ventricular system represent the main source of cerebrospinal fluid secretion and constitute a major barrier interface that controls the brain's environment. The present study focused on the choroid plexus of the fourth ventricle, the main cavity of the brainstem containing important nuclei and/or structures mediating autonomic vital functions. In serial sections of 84 brainstems of subjects aged from 17 gestational weeks to 8 postnatal months of life, the deaths due to both known and unknown causes, we examined the cytoarchitecture and the developmental steps of the fourth ventricle choroid plexus to determine whether this structure shows morphological and/or functional alterations in unexplained perinatal deaths (Sudden Infant Death Syndrome and Sudden Intrauterine Unexplained Death Syndrome). High incidence of histological and immunohistochemical alterations (prevalence of epithelial dark cells, the presence of cystic cells in the stroma, decreased number of blood capillaries, hyperexpression of Substance P and apoptosis) were prevalently observed in unexplained death victims (p<0.05 vs. controls). A significant correlation was found between maternal smoking in pregnancy and choroidal neuropathological parameters (p<0.01). This work underscores the negative effects of prenatal exposure to nicotine on the development of the autonomic nervous system, and in particular of the fourth ventricle choroid plexus that is a very vulnerable structure in the developing CSF-brain system.

Developmental alterations of the spinal trigeminal nucleus disclosed by substance P immunohistochemistry in fetal and infant sudden unexplained deaths

We investigated the immunohistochemical expression of substance P (SP) in the brainstems of 56 subjects aged from 17 gestational weeks to 10 post natal months, who died of unknown (sudden unexplained fetal deaths and SIDS) and known causes (controls). The goals of this study were: (i) to obtain basic information about the expression of SP during the first phases of human nervous system development; (ii) to evaluate whether there are alterations of this neuromodulator in victims of sudden death; and (iii) to verify any correlation with maternal cigarette smoking. Immunohistochemistry demonstrated SP immunoreactivity in the caudal trigeminal nucleus area, with a progressive increase in the density of SP-positive fibers of the corresponding tract during normal development from fetal life to the first post natal months. Delineation of the structure of the human trigeminal nucleus, little investigated so far, provided essential data on its morphologic and functional development. Instead, a negative or low SP expression was detectable in the fibers of this tract in a wide subset of SIDS victims and, conversely, a high SP-expression in a wide subset of sudden fetal deaths. We postulate, on the basis of these results, that SP has a functional importance in the early phases of central nervous system development and in the regulation of autonomic functions. In addition, the observation of a significant correlation between sudden unexplained death, altered SP staining and maternal smoking leads us to suggest a close relation between the absorption of cigarette smoke in utero and a decreased functional activity of the trigeminal nucleus, that can trigger sudden death of the fetus during pregnancy or of the infant in the first months of life.

Substance P Modulation of Hypoglossal Motoneuron Excitability During Development: Changing Balance Between Conductances

Although Substance P (SP) acts primarily through neurokinin 1 (NK1) receptors to increase the excitability of virtually all motoneurons (MNs) tested, the ontogeny of this transmitter system is not known for any MN pool. Hypoglossal (XII) MNs innervate tongue protruder muscles and participate in several behaviors that must be functional from birth including swallowing, suckling and breathing. We used immunohistochemistry, Western immunoblotting, and whole cell recording of XII MNs in brain stem slices from rats ranging in age from postnatal day zero (P0) to P23 to explore developmental changes in: NK1 receptor expression; currents evoked by SPNK1 (an NK1-selective SP receptor agonist) and; the efficacy of transduction pathways transforming ligand binding into channel modulation. Despite developmental reductions in XII MN NK1 receptor expression, SPNK1 current density remained constant at 6.1 ± 1.0 (SE) pA/pF. SPNK1 activated at least two conductances. Activation of a pH-insensitive Na+ conductance dominated in neonates (P0–P5), but its contribution fell from ∼80 to ∼55% in juveniles (P14–P23). SPNK1 also inhibited a pH-sensitive, two-pore domain K+ (TASK)-like K+ current. Its contribution increased developmentally. First, the density of this pH-sensitive K+ current doubled between P0 and P23. Second, SPNK1 did not affect this current in neonates, but reduced it by 20% at P7–P10 and 80% in juveniles. In addition, potentiation of repetitive firing was greatest in juveniles. These data establish that despite apparent reductions in NK1 receptor density, SP remains an important modulator of XII MN excitability throughout postnatal development due, in part, to increased expression of a pH-sensitive, TASK-like conductance.

Substance P receptor antagonists in psychiatry: rationale for development and therapeutic potential

Increasing evidence suggests that substance P (SP) and its receptor (neurokinin [NK]-1 receptor [NK1R]) might play an important role in the modulation of stress-related, affective and/or anxious behaviour. First, SP and NK1R are expressed in brain regions that are involved in stress, fear and affective response (e.g. amygdala, hippocampus, hypothalamus and frontal cortex). Second, the SP content in these areas changes upon application of stressful stimuli. Third, the central administration of SP produces a range of fear-related behaviours. In addition, the SP/NK1R system shows significant spatial overlap with neurotransmitters such as serotonin and noradrenaline (norepinephrine), which are known to be involved in the regulation of stress, mood and anxiety. Therefore, it was hypothesised that blockade of the NK1R might have anxiolytic as well as antidepressant effects. Preclinical studies investigating the effects of genetic or pharmacological NK1R inactivation on animal behaviour in assays relevant to depression and anxiety revealed that the behavioural changes resemble those seen with reference antidepressant or anxiolytic drugs. Furthermore, antagonism or genetic inactivation of the NK1R causes alterations in serotonin and norepinephrine neuronal transmission that are likely to contribute to the antidepressant/anxiolytic activity of NK1R antagonists but that are--at least partially--distinct from those produced by established antidepressant drugs. This underlines the conceivable unique mechanism of action of this new class of compounds. In three independent clinical trials with three different compounds (aprepitant [MK-869], L-759274 and CP-122721), an antidepressant effect of NK1R antagonists could be demonstrated. These results, however, have been challenged by recent failed studies with aprepitant. There are numerous indications from preclinical studies that, in addition to SP and NK1R, other neurokinins and/or neurokinin receptors might also be involved in the modulation of stress-related behaviour and that exclusive blockade of the NK1R might not be sufficient to produce consistent anxiolytic and antidepressant effects. One such candidate is the neurokinin-2 receptor (NK2R), and clinical trials to assess the antidepressant effects of NK2R antagonists are currently underway. Of special interest might also be substances that block more than one receptor type such as NK1/2R antagonists or NK1/2/3R antagonists. These compounds may be more efficacious in antagonising the effects of SP than compounds that only block the NK1R.

Central neuropeptide systems and respiratory control during development

The substance P/neurotachykinin-1 (NK-1) and the mu-opioid G protein-coupled receptor systems endow brainstem respiratory regions and display discrete developmental patterns. Hypoxia-induced neuropeptide release may increase receptor endocytosis, reducing receptor accessibility to ligands. We wondered whether the attenuated respiratory response to hypoxia of developing piglets after single (Respir. Physiol. 92 (1993a) 115) or repeated daily hypoxic exposure (J. Appl. Physiol. 83 (1997) 522) is influenced by differential endocytosis of NK-1 vs mu-opioid receptors. Whereas the long-term (24 h) response of both receptors to recurrent hypoxia in piglet brainstem is similar, i.e. upregulation, the short-term (5 min) response to single or recurrent hypoxia, albeit in rats, is different: radiolabelled NK-1 receptors are greatly reduced, suggesting enhanced endocytosis, but mu-opioid receptors remain unchanged, implying unaltered endocytosis. If confirmed in piglet brainstem, this difference would produce relatively more available mu-opioid receptors to opioid peptides in hypoxia that might contribute to the attenuated respiratory responses to single and repeated hypoxia during development.

Neurokinin(1) receptor antagonists as potential antidepressants

Selective, nonpeptide antagonists for tachykinin receptors first became available ten years ago. Of the three known tachykinin receptors, drug development has focused most intensively on the substance P-preferring receptor, neurokinin(1) (NK(1)). Although originally studied as potential analgesic compounds, recent evidence suggests that NK(1) receptor antagonists may possess antidepressant and anxiolytic properties. If confirmed by further controlled clinical studies, this will represent a mechanism of action distinct from all existing antidepressant agents. As reviewed in this chapter, the existing preclinical and clinical literature is suggestive of, but not conclusive, concerning a role of substance P and NK(1) receptors in the pathophysiology of depression and/or anxiety disorders. The ongoing clinical trials with NK(1) receptor antagonists have served as an impetus for much needed, basic research in this field.

Effects of age and clustered hypoxia on [(125)I] substance P binding to neurotachykinin-1 receptors in brainstem of developing swine

This work focused on the postnatal development of substance P-bound neurotachykinin-1 (NK-1) receptors in the porcine brainstem using 2-3-, 6-11-, 16-18-, and 21-28-day-old piglets versus adult, and on alterations in these receptors after single and six-daily repeated clustered hypoxia using 6-11- and 21-28-day-old piglets. NK-1 receptor localization and densities were determined by quantitative autoradiography using mono-iodinated Bolton-Hunter substance P ([(125)I]BHSP). Slide-mounted brainstem sections, incubated in [(125)I]BHSP and then exposed to film, have shown [(125)I]BHSP binding throughout many brainstem nuclei and tracts, including the ambigual/periambigual (nAmb), dorsal motor vagal (dmnv), gigantocellular (nGC), hypoglossal (nHyp), medial parabrachial (nPBM), lateral reticular (nRL), raphe magnus (nRMg), raphe obscurus (nROb) and solitary tract (nTS) nuclei. NK-1 receptor densities decreased with age. As compared to normoxia, NK-1 receptor densities increased significantly after the six-daily hypoxia protocol in nAmb, dmnv, nHyp, nRL, nRMg, nROb, and nTS of both the young and older age groups. This increase may represent receptor upregulation as an adaptation to repeated hypoxia.

Neuropeptide localization in the "migraine generator" region of the human brainstem

Evidence from animals and humans suggests that brainstem nuclei such as the raphe nuclei, the locus coeruleus (LC) and the periaqueductal grey matter (PAG), are involved in the pathophysiology of migraine. In order to understand possible neurotransmitters involved we have, by means of indirect immunocytochemistry, analysed these regions for the occurrence and distribution of calcitonin gene-related peptide (CGRP), substance P (SP), pituitary adenylate-cyclase activating peptide (PACAP) and vasoactive intestinal polypeptide (VIP). CGRP-immunoreactive (-ir) cell bodies, but no fibres, were found to occur in high numbers, constituting 80% of all nerve cell bodies in the LC. A smaller number of these nerve cell bodies (40%) in the LC proved to be PACAP-ir. The LC neurones also stored the vesicular monoamine transporter (VMAT)- and the C-terminal flanking peptide of neuropeptide Y (C-PON)-ir, illustrating their adrenergic nature. Double immunostaining revealed that all VMAT-and C-PON-containing neurones, in addition, stored CGRP. Immunoreactive cell bodies were not seen in the nucleus raphe magnus (NRM) or PAG. Numerous SP-ir nerve fibres were observed in the NRM, the LC and the PAG. Few PACAP-ir nerve fibres were detected in the PAG and few VIP-ir nerve fibres were seen in the NRM and the PAG.

Substance P immunoreactivity in Rett syndrome

Severe autonomic dysfunction occurs in Rett syndrome (RS). Substance P, a tachykinin peptide that localizes to several brain regions, including the autonomic nervous system, is reduced in the cerebrospinal fluid of patients with RS. The anatomic localization and intensity of substance P immunoreactivity and glial fibrillary acidic protein-positive astrocytes in the brains of 14 patients with RS were compared with those in the brains of 10 age-matched normal patients. Substance P immunoreactivity expression was significantly decreased in RS tissue compared with control tissue in the following regions: dorsal horns, intermediolateral column of the spinal cord, spinal trigeminal tract, solitary tract and nucleus, parvocellular and pontine reticular nuclei, and locus ceruleus. A less significant decrease of substance P immunoreactivity occurred in the substantia nigra, central gray of the midbrain, frontal cortex, caudate, putamen, globus pallidus, and thalamus. Antiglial fibrillary acidic protein-positive astrocytes were increased in the areas in which substance P immunoreactivity was decreased and in other brain regions. Because many of the brain regions with the greatest decrease in substance P immunoreactivity are involved in the control of the autonomic nervous system, especially the solitary tracts and reticular formation, reduced substance P may contribute to the autonomic dysfunction in RS.

Ontogeny of neurokinin-1 receptors in the porcine respiratory system

We characterized the ontogeny of NK-1 receptor agonist affinity (Kd) and density (Bmax) in membranes from tracheal epithelium, smooth muscle, and lung of pigs aged 1-7 days, 8-21 days, and adult in comparison to contractile responses in vitro. Affinity of [125I] Bolton-Hunter substance P ([125I]BH-SP) in epithelium and smooth muscle was three- to fourfold lower in young piglets than in adults. The Bmax of NK-1 sites in epithelium was elevated by more than twofold at 8-21 days relative to 1-7 days piglets and adults. In the lung, NK-1 density as well as affinity was lower than in trachea, regardless of age. In all three groups, [125I]BH-SP binding was potently inhibited by Gpp(NH)p, in both trachea and lung, implying coupling to G-proteins. Inhibition by Gpp(NH)p was most potent in the adult relative to younger animals, in both tracheal epithelium and smooth muscle. Functional sensitivity to the NK-1 agonists substance P and septide was reduced in neonates, as shown by the higher concentration of agonist required to elicit contractile responses. We conclude that the reduced sensitivity of newborn piglet airways to substance P reflects immaturity of G-protein coupling to NK-1, independent of receptor density.

Autoradiographic distribution of brainstem substance P binding sites in humans: ontogenic study and relation to sudden infant death syndrome (SIDS)

The precise distribution of substance P (SP) binding sites in the human brainstem was investigated in normal cases (3 fetuses and 24 new-borns) and in 9 cases of Sudden Infant Death Syndrome (SIDS) by in vitro quantitative autoradiography. We discussed the widely but uneven distribution of SP binding sites as regards to the role of SP in brainstem cardio-respiratory ontogenic control and its possible involvement in SIDS.

The neuropeptide/mast cell secretagogue substance P is expressed in cutaneous melanocytic lesions

Substance P (SP) is a neuropeptide found in both the central and peripheral nervous system. In the skin, SP-containing neurons stimulate the release of histamine from connective tissue mast cells (MC). SP also can potentiate neoangiogenesis and induce dermal fibrosis. MC-derived histamine has potent vasoactive effects, is angiogenic, and promotes tissue fibroplasia. In addition to histamine, MC contain many other angiogenic factors and a variety of cytokines, growth factors, and proteolytic enzymes implicated in tissue remodeling, and normal as well as tumor-associated neoangiogenesis. Many MC-derived factors, including histamine, can enhance melanoma cell growth directly. MC often concentrate around cutaneous melanomas which also frequently are associated with angiogenesis and peritumoral fibrosis. The precise mediators of these responses have not been well defined. We evaluated by immunohistochemistry cutaneous lesions representing stages of progression of malignant melanoma and its precursor lesions for the expression of SP. SP was expressed in 17/25 (68%) primary invasive malignant melanomas, 2/5 (40%) metastatic melanomas, 6/10 (60%) melanomas in situ, 7/12 (58%) atypical (dysplastic) nevi, and 4/10 (40%) spindle and epithelioid cell (Spitz) nevi, but was not detected in any (0/11, 0%) acquired benign melanocytic nevi (p<0.05). Invasive melanomas were immunolabeled in both the intraepidermal and the dermal components of the lesions. For those atypical and Spitz nevi which expressed SP, most of the immunoreactive melanocytes were located at the dermal-epidermal junction overlying areas of papillary dermal fibrosis. The results show differential expression of SP among cutaneous melanocytic lesions and suggest that the expression of this neuropeptide together with other factors may contribute to some of the host responses associated with these lesions.