Neonatal Administration Of Capsaicin Research Articles

Neonatal Capsaicin Administration Impairs Postnatal Development of the Cardiac Chronotropy and Inotropy in Rats

The present study evaluated the impact of neonatal administration of capsaicin (neurotoxin from red hot pepper used for sensory denervation) on postnatal development of the heart rate and ventricular contractility. In the rats subjected to capsaicin administration (100 mg/kg) on postnatal days 2 and 3 and their vehicle-treated controls at the ages of 10 to 90 days, function of the sympathetic innervation of the developing heart was characterized by evaluation of chronotropic responses to metipranolol and atropine, norepinephrine concentrations in the heart, and norepinephrine release from the heart atria. Sensory denervation was verified by determination of calcitonin gene-related peptide levels in the heart. Direct cytotoxic effects of capsaicin were assessed on cultured neonatal cardiomyocytes. Capsaicin-treated rats displayed higher resting heart rates, lower atropine effect, but no difference in the effect of metipranolol. Norepinephrine tissue levels and release did not differ from controls. Contraction force of the right ventricular papillary muscle was lower till the age of 60 days. Significantly reduced viability of neonatal cardiomyocytes was demonstrated at capsaicin concentration 100 micromol/l. Our study suggests that neonatal capsaicin treatment leads to impaired maturation of the developing cardiomyocytes. This effect cannot be attributed exclusively to sensory denervation of the rat heart since capsaicin acts also directly on the cardiac cells.

Localization of SSeCKS in unmyelinated primary sensory neurons

BackgroundSSeCKS (Src SupprEssed C Kinase Substrate) is a proposed protein kinase C substrate/A kinase anchoring protein (AKAP) that has recently been characterized in the rat peripheral nervous system. It has been shown that approximately 40% of small primary sensory neurons contain SSeCKS-immunoreactivity in a population largely separate from substance P (95.2%), calcitonin gene related peptide (95.3%), or fluoride resistant acid phosphatase (55.0%) labeled cells. In the spinal cord, it was found that SSeCKS-immunoreactive axon collaterals terminate in the dorsal third of lamina II outer in a region similar to that of unmyelinated C-, or small diameter myelinated Aδ-, fibers. However, the precise characterization of the anatomical profile of the primary sensory neurons containing SSeCKS remains to be determined. Here, immunohistochemical labeling at the light and ultrastructural level is used to clarify the myelination status of SSeCKS-containing sensory neuron axons and to further clarify the morphometric, and provide insight into the functional, classification of SSeCKS-IR sensory neurons.MethodsColocalization studies of SSeCKS with myelination markers, ultrastructural localization of SSeCKS labeling and ablation of largely unmyelinated sensory fibers by neonatal capsaicin administration were all used to establish whether SSeCKS containing sensory neurons represent a subpopulation of unmyelinated primary sensory C-fibers.ResultsDouble labeling studies of SSeCKS with CNPase in the dorsal horn and Pzero in the periphery showed that SSeCKS immunoreactivity was observed predominantly in association with unmyelinated primary sensory fibers. At the ultrastructural level, SSeCKS immunoreactivity was most commonly associated with axonal membrane margins of unmyelinated fibers. In capsaicin treated rats, SSeCKS immunoreactivity was essentially obliterated in the dorsal horn while in dorsal root ganglia quantitative analysis revealed a 43% reduction in the number of SSeCKS-labeled cells. This attenuation is concomitant with a decrease in fluoride-resistant acid phosphatase labeled fibers in the spinal cord dorsal horn and small neuronal somata in sensory ganglia.ConclusionThese results demonstrate that SSeCKS is primarily localized within a distinct subpopulation of small diameter, largely unmyelinated C-fiber primary sensory neurons putatively involved in nociception.

Effects of neonatal administration of capsaicin on nociceptive thresholds in the mouse and rat.

Effects of neonatal administration of capsaicin on nociceptive thresholds in the mouse and rat.

Effects of neonatal capsaicin administration on the nociceptive response of the rat to mechanical and chemical stimuli.

Journal Article Effects of neonatal capsaicin administration on the nociceptive response of the rat to mechanical and chemical stimuli Get access D C Faulkner, D C Faulkner Biology Department, I.C.I. Limited, Pharmaceuticals Division, Mereside, Alderley Park, Macclesfield, Cheshire, UK Search for other works by this author on: Oxford Academic Google Scholar J W Growcott J W Growcott Biology Department, I.C.I. Limited, Pharmaceuticals Division, Mereside, Alderley Park, Macclesfield, Cheshire, UK Correspondence: Biology Department, I.C.I. Limited, Pharmaceuticals Division, Mereside, Alderley Park, Macclesfield, Cheshire, U.K. Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 32, Issue 1, September 1980, Pages 656–657, https://doi.org/10.1111/j.2042-7158.1980.tb13027.x Published: 12 April 2011 Article history Received: 28 February 1980 Published: 12 April 2011

Effect of neonatal capsaicin treatment on orthodontic tooth movement in male Sprague-Dawley rats

In this study, we examined the effect of neonatal administration of capsaicin on the magnitude of orthodontic tooth movement in rats. Twelve timed pregnant Sprague-Dawley rats were randomized between the capsaicin group and the vehicle group. The pups received treatment with either capsaicin or vehicle on day 2 of life. Capsaicin treatment has been shown to produce a selective destruction of fine myelinated and unmyelinated Aδ and C sensory nerve fibers, causing an inhibition of the effects from neurogenic inflammation. Tooth-movement experiments began at 12 weeks of age. A mesial tipping force was applied to the maxillary first molar by using a 3-mm length of Sentalloy closed-coil spring (Dentsply GAC Intl, Bohemia, NY) activated from a bonded molar cleat to the maxillary incisors; this appliance delivers a constant tipping force of 50 g. Diastema measurements between the first and second molars were made at 2 and 4 weeks after appliance placement. Measurements were made indirectly from stone models by using a charge-coupled device microscope camera and Optimas 5.2 measurement software (Media Cybernetics, Bethesda, Md). Two-way repeated-measures analysis of variance (ANOVA) was used to analyze the differences between the groups. The capsaicin-treated rats and the controls did not differ in the amount of tooth movement at the collected time points (P>0.05). Similarly, the magnitude of change of tooth movement from 2 to 4 weeks did not differ between the groups (P>0.05). An increase in average diastema size was observed between 2 and 4 weeks after appliance activation in both treatment groups (P<0.0001). These results suggest that neonatal capsaicin desensitization in the rat does not affect the rate of orthodontic tooth movement after the application of a 50-g tipping force to the maxillary first molar. This might be due in part to the development of compensatory mechanisms in the chronically desensitized rat. Further studies are necessary to determine the reproducibility and histologic characteristics of this treatment.

P4.20 On the role of adenosine (A 2A) tonus and cross talk with NK 1 and M 3 receptors regulating acetylcholine release from myenteric neurons of the rat ileum

Gastrointestinal motility relies on the release of acetylcholine (ACh), purines and tachykinins (e.g. substance P) from excitatory enteric neurons. Tachykinins acting via NK1 and NK3 receptors facilitate cholinergic neurotransmission in the enteric nervous system. Recently, we showed that muscarinic M3 receptors facilitate ACh release indirectly by increasing adenosine outflow from stimulated myenteric neurons leading to the activation of excitatory A2A receptors [1]. It is well established that adenosine A2A receptors play a widespread role in synaptic plasticity via a sophisticated interaction with receptors for other neurotransmitters/neuromodulators. In the myenteric plexus, endogenous adenosine may arise from the catabolism of released ATP through the ectonucleotidase pathway together with the release of the nucleoside per se via the equilibrative transport system [2]. Preliminary accounts from our lab, suggest that CAP-sensitive tachykinergic neurons are an important source of purines in the rat myenteric plexus. These findings prompted us to investigate the cross talk between facilitatory A2A, M3 and NK1 receptors in rat longitudinal muscle-myenteric plexus preparations, focusing our attention on the role of tachykinergic nerve fibres which can be selectively eliminated (>95%) by neonatal capsaicin administration (CAP, 50 mg/kg, SC).

Cross talk between facilitatory adenosine A2A, Tachykinin NK1 and Muscarinic M3 receptors in the rat Mynteric plexus: on the role of Capsaicin-sensitive Tachykinergic neurons

Event Abstract Back to Event Cross talk between facilitatory adenosine A2A, Tachykinin NK1 and Muscarinic M3 receptors in the rat Mynteric plexus: on the role of Capsaicin-sensitive Tachykinergic neurons I. Silva1*, C. Vieira1, F. Ferreirinha1, M. Duarte-Araujo1 and P. Correia- De-Sa1 1 Instituto de Ciencias Biomedicas Abel Salazar - Universidade do Porto (ICBAS-UP), Laboratorio de Farmacologia e Neurobiologia, Unidade Multidisciplinar de Investigacao Biomedica (UMIB), Portugal Gastrointestinal motility relies on the release of acetylcholine (ACh), purines and tachykinins (e.g. substance P) from excitatory enteric neurons. Tachykinins (TK) acting via NK1 and NK3 receptors facilitate cholinergic neurotransmission in the enteric nervous system. Recently, we showed that muscarinic M3 receptors facilitate ACh release indirectly by increasing adenosine outflow from stimulated myenteric neurons leading to the activation of excitatory A2A receptors (Vieira et al., 2009, Neurogastroenterol. Motil. in press). These findings prompted us to investigate the cross talk between facilitatory A2A, M3 and NK1 receptors in the rat myenteric plexus, focusing our attention on the role of tachykinergic nerve fibres which can be selectively eliminated (>95%) by neonatal capsaicin administration (CAP, 50 mg/Kg, SC).The muscarinic agonist, oxotremorine (Oxo, 300 μM) and the selective adenosine A2A agonist, CGS21680C (CGS, 3 nM), increased evoked (5 Hz, 200 pulses) [3H]-ACh release from myenteric neurons respectively by 34±4% (n=5) and 53±10% (n=5) in controls (C) but were devoid of effects in CAP animals. Selective activation of NK1 receptors with Sar9,Met(O2)11-Substance P (s,m-SP, 300 nM) restored CGS facilitation (46±17%, n=6) to control levels in CAP rats. Cross talk between A2A and NK1 receptors was evaluated using selective antagonists of NK1 (L732128, 20 nM) and A2A (ZM241385, 50 nM) receptors. Pretreatment with s,m-SP did not restore Oxo facilitation (3±7%, n=4) in CAP animals. Incubation of C with the M3 antagonist (J104129, 6 nM) attenuated CGS (3±5%, n=5)-induced facilitation of [3H]-ACh release, but (like in CAP rats) its effect was partially recovered (23±2%, n=3) in the presence of s,m-SP.Data suggest that facilitation of [3H]-ACh release by A2A receptors requires tonic activation of NK1 receptors by endogenously released TK from CAP-sensitive myenteric neurons. Confocal microscopy studies show that A2A receptors co-localize with cholinergic nerve fibres (labelled with VAChT), but not with CAP-sensitive neurons exhibiting substance P immunoreactivity. Data also indicate that endogenous release of TK (as well as adenosine, see Vieira et al., 2009) may be tightly controlled by M3 receptors. In support of this hypothesis, we showed that CAP-sensitive tachykinergic neurons might be an important source of purines in the rat myenteric plexus (see, Marques et al., 2009, this meeting).Work supported by FCT (FEDER funding, PTDC/CVT/74462/2006) Conference: 11th Meeting of the Portuguese Society for Neuroscience, Braga, Portugal, 4 Jun - 6 Jun, 2009. Presentation Type: Poster Presentation Topic: Neuronal Communication Citation: Silva I, Vieira C, Ferreirinha F, Duarte-Araujo M and Correia- De-Sa P (2009). Cross talk between facilitatory adenosine A2A, Tachykinin NK1 and Muscarinic M3 receptors in the rat Mynteric plexus: on the role of Capsaicin-sensitive Tachykinergic neurons. Front. Neurosci. Conference Abstract: 11th Meeting of the Portuguese Society for Neuroscience. doi: 10.3389/conf.neuro.01.2009.11.149 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 12 Aug 2009; Published Online: 12 Aug 2009. * Correspondence: I. Silva, Instituto de Ciencias Biomedicas Abel Salazar - Universidade do Porto (ICBAS-UP), Laboratorio de Farmacologia e Neurobiologia, Unidade Multidisciplinar de Investigacao Biomedica (UMIB), Porto, Portugal, isabelsds@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers I. Silva C. Vieira F. Ferreirinha M. Duarte-Araujo P. Correia- De-Sa Google I. Silva C. Vieira F. Ferreirinha M. Duarte-Araujo P. Correia- De-Sa Google Scholar I. Silva C. Vieira F. Ferreirinha M. Duarte-Araujo P. Correia- De-Sa PubMed I. Silva C. Vieira F. Ferreirinha M. Duarte-Araujo P. Correia- De-Sa Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Neurotoxic catecholamine metabolite in nociceptors contributes to painful peripheral neuropathy

The neurotoxic effects of catecholamine metabolites have been implicated in neurodegenerative diseases. As some sensory neurons express tyrosine hydroxylase and monoamine oxidase (MAO), we investigated the potential contribution of catecholamine metabolites to neuropathic pain in a model of alcoholic neuropathy. The presence of catecholamines in sensory neurons is supported by capsaicin-stimulated epinephrine release, an effect enhanced in ethanol-fed rats. mRNA for enzymes in dorsal root ganglia involved in catecholamine uptake and metabolism, dopamine beta-hydroxylase and MAO-A, were decreased by neonatal administration of capsaicin. Ethanol-induced hyperalgesia was attenuated by systemic and local peripheral administration of inhibitors of MAO-A, reduction of norepinephrine transporter (NET) in sensory neurons and a NET inhibitor. Finally, intradermal injection of 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), a neurotoxic MAO-A catecholamine metabolite, produced robust mechanical hyperalgesia. These observations suggest that catecholamines in nociceptors are metabolized to neurotoxic products by MAO-A, which can cause neuronal dysfunction underlying neuropathic pain.

The effect of neonatal capsaicin treatment on the CGRP-immunoreaction in the trigeminal subnucleus caudalis of mice

The calcitonin-gene related peptide (CGRP) is a primary afferent neurotransmitter in the trigeminal system. Although a neonatal administration of capsaicin eliminates substance P (SP)-mediated nociceptive responses to induce a permanent functional reduction in C-fibers, little information is available regarding changes in CGRP-immunoreaction in mice undergoing neonatal capsaicin treatment (CP mice). This study examined postnatal changes in the distribution of CGRP-immunoreaction in the trigeminal subnucleus caudalis and trigeminal ganglion of CP mice by immunohistochemical technique and a quantitative analysis. Immunohistochemistry for CGRP in the subnucleus caudalis (Vc) demonstrated two dense distributions of neurons in the CP mice as well as naïve mice: in the marginal layer and the region 400-600 mum deep. The quantitative analysis revealed no significant difference in the density of CGRP immunoreaction between naïve and CP mice 1-8 weeks of age. In the trigeminal ganglion of both groups, the size distribution of CGRPpositive neurons displayed a distribution pattern with one peak in 200-300 mum(2) at week 1 and with two peaks in 200-300 mum(2) and 600-700 mum(2) at week 8 but no significant difference in neural density existed between these regions. When double staining in the naïve mice with CGRP or SP and VR1, a capsaicin receptor, was done, many trigeminal ganglion neurons co-expressed SP- and VR1-immunoreactions, but rarely exhibited CGRP/VR1-co-localization. Taken together with previous data, these current observations suggest that CGRP containing afferent neurons possibly performs differing roles in nociceptive afferent input transmission within the Vc from SP-containing neurons in mice.

Effects of sensory denervation by neonatal capsaicin administration on experimental pancreatitis induced by dibutyltin dichloride

Increase in the number of intrapancreatic sensory nerve fibers has been implicated in the generation of pain in chronic pancreatitis. Because some sensory neurotransmitters (e.g., substance P) are known to have proinflammatory effects, we hypothesized that denervation of intrapancreatic nerves might influence not only pain generation but also inflammation. Neonatal Lewis rats were injected with capsaicin (50 mg/kg or 0 mg/kg), a neurotoxin, to induce denervation of primary sensory neurons. When rats reached 170-190 g body weight, experimental pancreatitis was induced by a single administration of dibutyltin dichloride (7 mg/mg). The severity of pancreatitis was evaluated in both groups in the acute phase (at 3 and 7 days) and chronic phase (at 28 days). At day 7, the sensory denervation induced by neonatal capsaicin administration inhibited pancreatic inflammation on both histological (determination of interstitial edema, expansion of interlobular septa and intercellular spaces, and inflammatory cell infiltration) and biochemical (intrapancreatic myeloperoxidase activity) evaluation. Furthermore, at day 28, glandular atrophy, pseudotubular complexes, and rate of fibrosis were each significantly lower in the capsaicin-pretreated group than in the vehicle-pretreated group. Our findings provide in vivo evidence that primary sensory neurons play important roles in both acute pancreatitis and chronic pancreatic inflammation with fibrosis.

Participation of CGRP and prostanoids in the sex-linked differences of vascular anandamide effects in mesenteric beds of Sprague-Dawley rats

The in vitro exposure to anandamide elicits greater relaxations in mesenteric beds isolated from female compared to male rats. The present work shows that in mesenteric beds precontracted with noradrenaline the removal of endothelium increased the relaxation caused by anandamide in male and ovariectomized female but not in sham-operated female rats. The nitric oxide synthase inhibition with 100 μM N ω-nitro- l-arginine methyl ester hydrochloride ( l-NAME) and the sensory in vivo denervation through neonatal administration of capsaicin also reduced anandamide-induced relaxations but these effects had the same extent in male and in female mesenteries. The content of calcitonin gene related peptide (CGRP) in mesenteric beds, that was higher in intact female than in male rats, was reduced by ovariectomy and restored to control values 21 days after a 3 weekly i.m. administration of 450 μg/kg 17β-oestradiol. This latter treatment also increased CGRP content in mesenteries from males up to the same levels observed in females. The basal release of CGRP in mesenteric beds was equivalent in either sex, but the exposure to anandamide increased CGRP release solely in female mesenteries. The ratio prostacyclin/thromboxane A 2 was selectively reduced in mesenteries from male rats after exposure to anandamide, due to the decrease of the tissue levels of prostacyclin. Moreover, the cyclooxygenase-2 inhibitor 0.1 μM N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulphonamide (NS-398) diminished the relaxations caused by anandamide solely in female rats. It is proposed that relaxing factors such as CGRP and prostacyclin contribute to the higher relaxations caused by anandamide in the vasculature of female rats.

Activation of the caspase cascade underlies the rat trigeminal primary neuronal apoptosis induced by neonatal capsaicin administration

The systemic administration of capsaicin is known to cause a massive loss of sensory primary neurons in newborn rats. Here we examined the trigeminal ganglion neurons immunohistochemically for the possible induction of activated forms of caspases-9 and -3 following a subcutaneous injection of capsaicin in newborn rats. The DNA fragmentation signal was labeled by a TUNEL method. TUNEL-positive neurons were rare (< 0.5%) at 24 h after injection of the vehicle without capsaicin. After the capsaicin injection, TUNEL-positive neurons began to increase by 12 h, reached a peak at 24 h (11.4%), and returned to the control level by 120 h. Vehicle control levels of caspase- 9-immunoreactive (ir) and caspase-3-ir neurons were low (< 0.5%). Neonatal capsaicin administration induced caspase-9-immunoreactivity (ir) and -3-ir. The temporal distributions of caspase-9-ir and caspase-3-ir neurons were similar to those of TUNEL-positive neurons with peak expressions at 24 h of 13.2 and 11.1%, respectively. A double-stain analysis at 24 h post-injection indicated 72% of TUNEL-positive neurons were caspase-9-ir, and 70% caspase-3-ir. Conversely, 78 and 68% of caspase-9-ir and caspase-3-ir neurons, respectively, were TUNEL-positive. Comparison of two adjacent sections immunostained for the two different antigens revealed the co-expression of the two caspases. These results suggest that neonatal capsaicin triggers the caspase cascade and, thereby, induces trigeminal primary neuronal apoptosis.

Sensory nerves contribute to insulin secretion by glucagon-like peptide-1 in mice.

It has been hypothesized that the potent insulinotropic action of the gut incretin hormone glucagon-like peptide-1 (GLP-1) is exerted not only through a direct action on the beta cells but may be partially dependent on sensory nerves. We therefore examined the influence of GLP-1 in mice rendered sensory denervated by neonatal administration of capsaicin performed at days 2 and 5 (50 mg/kg). Control mice were given vehicle. Results show that at 10-16 wk of age in control mice, intravenous GLP-1 at 0.1 or 10 nmol/kg augmented the insulin response to intravenous glucose (1 g/kg) in association with improved glucose elimination. In contrast, in capsaicin-pretreated mice, GLP-1 at 0.1 nmol/kg could not augment the insulin response to intravenous glucose and no effect on glucose elimination was observed. Nevertheless, at the high dose of 10 nmol/kg, GLP-1 augmented the insulin response to glucose in capsaicin-pretreated mice as efficiently as in control mice. The insulin response to GLP-1 from isolated islets was not affected by neonatal capsaicin, and, furthermore, the in vivo insulin response to glucose was augmented whereas that to arginine was not affected by capsaicin. It is concluded that GLP-1-induced insulin secretion at a low dose in mice is dependent on intact sensory nerves and therefore indirectly mediated and that this distinguishes GLP-1 from other examined insulin secretagogues.

Tachykinin receptor (NK 1, NK 2, NK 3) binding sites in the rat caudal brainstem following neonatal capsaicin administration

Binding of [ 125I]-Bolton–Hunter substance P ([ 125I]-BHSP), [ 125I]-neurokinin A and [ 3H]-senktide to tachykinin NK 1, NK 2 and NK 3 receptors, respectively, was examined in caudal brainstem sections of 10-week-old rats pretreated as neonates (P2) with capsaicin (50 mg/kg, s.c.) or vehicle. [ 125I]-BHSP binding was localised to the nucleus of the solitary tract (NTS), hypoglossal nucleus and inferior olivary complex, whereas [ 125I]-neurokinin A and [ 3H]-senktide binding were confined to the NTS. The distribution and density of binding sites were similar in vehicle- and capsaicin-pretreated rats, suggesting that sensory neuron ablation by neonatal capsaicin does not affect tachykinin receptor numbers in the rat caudal brainstem.

Primary sensory neurons: a common final pathway for inflammation in experimental pancreatitis in rats.

We hypothesized that neurogenic inflammation is a common final pathway for parenchymal inflammation in pancreatitis and evaluated the role of primary sensory neurons in secretagogue-induced and obstructive pancreatitis. Neonatal rats received either the primary sensory neuron-denervating agent capsaicin (50 mg/kg s.c.) or vehicle. At 8 wk of age, pancreatitis was produced by six hourly injections of caerulein (50 microg/kg i.p.) or by common pancreaticobiliary duct ligation (CPBDL). The severity of pancreatitis was assessed by serum amylase, pancreatic myeloperoxidase (MPO) activity, histological grading, pancreatic plasma extravasation, and wet-to-dry weight ratio. Caerulein significantly increased MPO activity and wet-to-dry weight ratio, produced histological evidence of edematous pancreatitis, induced plasma extravasation, and caused hyperamylasemia. CPBDL increased MPO activity and produced histological evidence of pancreatitis. Neonatal capsaicin administration significantly reduced tissue MPO levels, histological severity scores, and wet-to-dry weight ratio and abolished plasma extravasation. These results demonstrate that primary sensory neurons play a significant role in the inflammatory cascade in experimental pancreatitis and appear to constitute a common final pathway for pancreatic parenchymal inflammation.

Characterization and regulation of tachykinin receptors in the nucleus tractus solitarius.

1. The characteristics, localization and regulation of tachykinin receptors in the rat nucleus tractus solitarius (NTS) involved in respiratory control were investigated using a combination of in vivo microinjection and in vitro autoradiographic techniques. 2. Microinjection of receptor-selective tachykinin agonists and antagonists into the NTS of urethane-anaesthetized rats suggests that stimulation of NK1 and NK3 receptors increases tidal volume, whereas NK2 and NK3 receptor activation produces a bradypnoea. 3. Depletion of NK1 receptors in the NTS due to either ageing or acute hypoxia correlates with a markedly reduced respiratory response to substance P. In contrast, chemical ablation of sensory neurons by neonatal capsaicin administration dramatically increases the respiratory response to a variety of NK1, NK2 and NK3 agonists. 4. These studies suggest that all three tachykinin receptors are present in the rat NTS and that these receptors are subject to both acute and chronic regulation.

Respiratory actions of tachykinins in the nucleus of the solitary tract: effect of neonatal capsaicin pretreatment

1. The respiratory response to microinjection of capsaicin and tachykinin receptor agonists into the commissural nucleus of the solitary tract (cNTS) was investigated in adult, urethane-anaesthetized rats which had been pretreated with capsaicin (50 mg kg(-1) s.c.) or vehicle (10% Tween 80, 10% ethanol in saline) as day 2 neonates. 2. Microinjection of capsaicin (1 nmol) into the cNTS of vehicle-pretreated rats, significantly reduced respiratory frequency (59 breaths min(-1), preinjection control, 106 breaths min(-1)) without affecting tidal volume (VT). In capsaicin-pretreated rats, the capsaicin-induced bradypnoea was markedly attenuated (minimum frequency, 88 breaths min(-1); control, 106 breaths min(-1)). 3. In vehicle-pretreated rats, microinjection of substance P (SP, 33 pmol), neurokinin A (NKA, 33 pmol) and NKB (330 pmol), and the selective NK(1) tachykinin receptor agonists, [Sar(9), Met(O(2))(11)]-SP (33 pmol) and septide (10 pmol), increased VT (maxima, 3.60 - 3.93 ml kg(-1)) compared with preinjection control (2.82 ml kg(-1)), without affecting frequency. The selective NK(3) agonist senktide (10 pmol) also increased VT (3.93 ml kg(-1)) which was accompanied by a bradypnoea (-25 breaths min(-1)). The selective NK(2) agonist, [Nle(10)]-NKA(4-10) (330 pmol) increased VT slightly but significantly decreased frequency (-12 breaths min(-1)). In capsaicin-pretreated rats, VT responses to SP and [Sar(9), Met(O(2))(11)]-SP were increased whereas the response to septide was abolished. Both the VT and bradypnoeic responses to senktide and [Nle(10)]-NKA(4-10) were significantly enhanced. 4. These results show that neonatal capsaicin administration markedly reduces the respiratory response to microinjection of capsaicin into the cNTS. The destruction of capsaicin-sensitive afferents appears to sensitize the NTS to SP, NKB, [Sar(9),Met(O(2))(11)]-SP, senktide and [Nle(10)]-NKA(4-10). Moreover, the loss of septide responsiveness in capsaicin-pretreated rats, suggests that 'septide-sensitive' NK(1) receptors may be located on the central terminals of afferent neurons.

Effects of neonatal capsaicin administration on the numbers and volumes of neurons in left and right T10 dorsal root ganglia in the rat.

The long-term effects of neonatal capsaicin were studied in left and right dorsal root ganglia (T10) from control and capsaicin-treated groups of Wistar rats. At 12 hours post partum, 5 females per group were injected subcutaneously with capsaicin or vehicle solution and killed at 6 months of age. Tissues were perfusion-fixed, embedded in resin and serially sectioned. A Nissl stain was used to distinguish between A and B neurons and systematic random sampling schemes were employed to obtain stereological estimates of numbers of neurons and mean volumes of their perikarya. Numbers were calculated from ganglion volumes (estimated via the Cavalieri principle) and neuron packing densities (estimated using physical disectors). Mean perikaryal volumes were calculated from packing densities and volume densities (estimated by point counting). Data were analysed to isolate main and interaction effects of neuron subtype, laterality and treatment. There was no evidence of lateral asymmetry or interaction effects. Control ganglia contained 3320 (coefficient of variation, CV, 8%) neurons. Most (73%) were B cells with a mean volume of 13,100 microm(3) (CV 17%) of which the nucleus accounted for 1,800 microm(3) (CV 18%). About 22% were A cells with a mean volume of 79,800 microm(3) (CV 24%) and a nucleus of 6,100 microm(3) (CV 26%). After capsaicin, over half the original population of cells was destroyed and B cell loss was significantly greater than that of A cells (about 80% of all cells lost were B cells). The mean size of A cells was greater after capsaicin due to selective loss of smaller cells and a greater volume of cytoplasm. B cell perikaryal volume was not affected but nuclear volume declined. The findings show that capsaicin destruction of peripheral sensory neurons is bilaterally symmetrical. In general, smaller neurons are selectively destroyed but this operates differently in A and B cells. It is size-dependent in A cells but size-independent (possibly random) in B cells.

Neuropeptide Denervation Alters Both the Elicitation and Induction Phases of Contact Hypersensitivity in Mice

The effects of permanent disruption of neuropeptide transmission on the induction (i.e., sensitization) and elicitation (i.e., challenge) phases of contact hypersensitivity (CHS) are described. BALB/c mice were chemically denervated of neuropeptide (i.e., tachykinin) containing sensory C fibers by an acute injection of capsaicin (50 mg/kg) on postnatal day (PND) 2 to 3. As young adults (PND 45–60), these mice and their control littermates were sensitized by topical application of 0.1% 2,4-dinitrofluorobenzene (DNFB) or vehicle. Treatment groups generated from this exposure regimen consisted of untreated, controls (O/O), denervated, controls (CAP/O), untreated, sensitized (O/DNFB), and denervated, sensitized (CAP/DNFB). The elicitation phase of CHS was evaluated in these animals by measuring ear thickness in response to a DNFB challenge. In DNFB-sensitized groups, ear thickness was significantly increased over controls but was additionally increased 2.4-fold in CAP/DNFB compared to O/DNFB mice. The induction phase of CHS was next assessed in young adult mice by measuring lymph node cell (LNC) proliferation. For this, mice were sensitized for 3 consecutive days before their draining, auricular nodes were removed. The LNC were dissociated and cultured for 24 h with tritiated thymidine to assess LNC proliferation. As expected, significantly higher numbers of LNC occurred in both DNFB-sensitized groups (CAP/DNFB, O/DNFB) compared to the unsensitized, controls (CAP/O, O/O). However, LNC proliferation in CAP/DNFB was significantly higher than O/DNFB animals. Flow cytometry on similarly exposed mice failed to demonstrate any significant difference in the population of CD4CD8 or CD3CD45R LNC cells from neuropeptide-denervated (CAP/O, CAP/DNFB) mice or their respective treatment mates (O/O, O/DNFB), suggesting that alterations in T or B cell populations did not underlie these changes. Finally, cytokine release from the LNC from these treatment groups was examined. For this, the auricular lymph nodes were removed from animals, 2 to 4 h after the animals were administered a single application of a sensitizing concentration (0.1%) of DNFB or acetone vehicle. LNC, dissociated from these nodes, were cultured for 24 h. The nutrient media was removed from these cultured cells and examined for the release of proinflammatory cytokines, interleukin (IL)-1β, IL-2 and tumor necrosis factor (TNF)α, by ELISA. There were no significant increases in IL-2. However, IL-1β release was significantly increased in CAP/DNFB mice over O/DNFB by 18-fold and by over 30-fold compare to O/O controls. Levels of TNFα were significantly increased in both O/DNFB and CAP/DNFB mice over the nonsensitized controls (O/O, CAP/O). CAP/DNFB values were approximately double that of O/DNFB. There was no significant difference in IL-1β or TNFα release between the nonsensitized controls (O/O, CAP/O). Collectively, these data indicate that neuropeptide denervation by neonatal administration of capsaicin alters both the induction and elicitation phases CHS and may modify sensitivity to chemically induced CHS.

Cutaneous wounds produced by capsaicin treatment of newborn rats are due to trophic disturbances.

The purpose of this study was to show that the occurrence of skin ulcers observed in animals neonatally treated with the neurotoxin capsaicin coincide with trophic disturbances. In addition, cutaneous lesions increased when self-grooming and scratching behaviors reached maturity. The temporal course of cephalic cutaneous wounds in neonatally capsaicin-treated rats was evaluated in animals wearing and not wearing plastic collars from postnatal day (P) 21 until P45. The collars were used to prevent self-grooming and scratching. Beginning on P21, capsaicin-treated rats under both conditions showed transient skin ulcers distributed throughout the head and neck regions. In the capsaicin-treated group without collars, lesions reached their greatest severity by P40, when self-grooming and scratching behaviors obtained adult characteristics. Furthermore, no lesions were detected after 25 days. In the capsaicin-treated rats that wore plastic collars, the widest distribution of skin lesions occurred on P55, after which time lesions vanished detection by 25 days. In this latter group, the cutaneous lesions were exacerbated when collars were removed. Data suggest that transient cutaneous wounds associated with neonatal capsaicin administration may be mediated via capsaicin-sensitive sensory neurons that are involved in trophic and regenerating neural mechanisms.