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Visceral pain is a prominent cause of morbidity in gastrointestinal (GI) diseases, like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), but many current analgesics produce GI side effects. To develop much needed, novel treatments, further understanding of the pro-inflammatory mediators and mechanisms underpinning visceral nociception in disease states is required. In GI disease, mast cell number is elevated in the gut and activation leads to synthesis and release of many pro-inflammatory mediators, which modulate afferent function and induce hypersensitivity, and contribute to persistent pain in clinical remission. Using Ca2+ imaging of cultured DRG neurons, I first examined the ability of several mast cell mediators to activate sensory neurons. I observed that mast-cell derived cytokines (TNFα & IL-4), lipids (PGD2 & LTC4) and growth factors (NGF & SCF) all increased [Ca2+]i in distinct populations of DRG neurons, the majority of which also responded to the TRPV1 agonist capsaicin, thus indicating that these neurons were nociceptors. TNFα levels correlate with pain in IBD and IBS, and TNFα is known to sensitise colonic sensory neurons. Somatic, TNFα-triggered thermal and mechanical hypersensitivity is mediated by TRPV1 signalling and p38 MAPK activity respectively, downstream of TNFR1 receptor activation. I therefore sought to investigate whether TNFR1-evoked p38 MAPK activity is also involved in TNFα sensitisation of colonic afferent responses to capsaicin and noxious distension of the bowel. In Ca2+ imaging of DRG neurons, TNFα sensitised neuronal capsaicin responses in a TNFR1-dependent manner, an effect attenuated by p38 MAPK inhibition. In ex vivo colonic afferent fibre recordings, pre-treatment with TNFα enhanced responses to both noxious ramp distention of the bowel and bath perfusion with capsaicin. TNFα-induced sensitisation was reversed by p38 MAPK inhibition and absent in TNFR1 knockout mice, thus demonstrating a role for TNFR1, p38 MAPK and TRPV1 in TNFα-induced sensitisation of colonic afferents. IL-13 is also released from mast cells during inflammation and, whilst inhibition of IL-13 signalling pathways has proven effective in treating other inflammatory conditions, little is known about its role in GI disease. I therefore aimed to determine whether IL-13 could sensitise colonic afferent responses to mechanical and chemical stimuli and whether effects were reversed by inhibition of downstream p38 MAPK and JAK signalling pathways. I observed an IL-13-dependent increase in colonic afferent activity to noxious distension, but not capsaicin, which was reversed by p38 MAPK or JAK inhibition. Overall, I have demonstrated that TNFα and IL-13-induced mechanosensitivity in colonic afferents is reversed by inhibition of p38 MAPK and/or JAK signalling pathways. This work highlights the potential utility of targeting TNFα and IL-13 signalling for treating visceral pain in GI disease.

Introduction: Cough in asthma predicts disease severity, poor prognosis, and is a common troublesome symptom, yet remarkably, little is understood about the underlying neuronal mechanisms. Current dogma suggests asthma symptoms arise as a consequence of bronchial hyper-responsiveness and airway inflammation. Yet despite effective treatments targeting these pathologies, many patients have substantial residual disease and symptoms. Symptoms such as wheeze, cough, chest tightness and breathlessness occur as a consequence of neuronal input from the airways and chest wall. However, there is a paucity of data investigating whether sensory nerve function is heightened in patients with asthma. Many symptoms are challenging to study as they can only be reported subjectively. In contrast, cough is more readily accessible to objective quantification and hence has the most potential for providing insights into the role of nerves in asthma. Methods: We performed capsaicin cough challenges to experimentally evoke the cough reflex via activation of the transient receptor potential vanilloid type-1 (TRPV1) receptor found characteristically on airway c-fibres. Evoked and spontaneous coughs were objectively quantified and verified using a semi-automated cough recorder (VitaloJAK). We first performed an observational cross-sectional study comparing full dose capsaicin cough responses in patients with mild to moderate stable asthma with healthy volunteers. We performed non-linear pharmacodynamic modelling (NONMEM) to compare differences in the maximum evoked coughs (Emax) and the dose of capsaicin that evoked at least half the responses (ED50). This was followed by two separate randomised, single-blind, placebo controlled cross-over studies investigating the effects of methacholine induced bronchoconstriction and inhaled allergen challenge on capsaicin ED50 evoked coughs. Generalised estimating equations (GEE) were used to model the effects of bronchoconstriction on cough responses. Results: i. Compared with healthy volunteers (HV), patients with asthma (A) displayed higher Emax and lower ED50 on full dose capsaicin evoked cough challenge. Emax was influenced by disease group (HV or A), gender, atopic status and objective cough rates, whilst ED50 was influenced by disease group, gender, asthma control (ACQ), and total serum IgE. ii. Methacholine induced bronchoconstriction was associated with an increase in capsaicin evoked cough response, but capsaicin evoked coughs had no influence on bronchial hyper-responsiveness to methacholine. iii. Inhaled allergen challenge induced an acute early asthmatic response (EAR) and a late asthmatic response (LAR). There was an increase in capsaicin evoked coughs in the EAR and 24 hours after the start of inhaled allergen challenge. Conclusions: Patients with asthma exhibited heightened cough responses to capsaicin at baseline, which increased further after inducing bronchoconstriction and allergen exposure. The exaggerated cough reflex observed could be due to peripheral sensitisation and/or central sensitisation. The exact mechanism of how bronchoconstriction and airway inflammation influences the cough reflex to capsaicin requires further evaluation.

This thesis examined how and why TRPV1 function is being modulated in sensory neuropathy and explored the potential of its rescue in the urinary bladder of STZ-­‐induced diabetic rats. Diabetes induced a rapid decline in TRPV1 function and changes in neurogenically mediated electrically-­‐evoked responses together with a gradual decline in muscarinic function. Diabetic bladder was also deficient in muscarinic and TRPV1 organ bath temperature-­‐induced changes but not in those affecting spontaneous contractile activity. Exposure to a potential neuropathy causative agent, methylglyoxal was studied and its mechanism of action explored through the use of TRPA1 ligands. Methylglyoxal exposure mimicked some of the effects of diabetes on TRPV1, neurogenic electrically evoked responses and muscarinic function. Methylglyoxal effects were seen to be partly through TRPA1 receptor activation but other as yet undefined pathways were also involved. Use of TRPA1 ligands revealed an unexpected complexity of the interaction of the TRPA1 receptor with TRPV1. Finally the potential of reversing the diminished TRPV1 response was examined through the use of three known sensitising agents, bradykinin, NGF and insulin. Bradykinin was the only agent seen to reverse the TRPV1 diminished response back up to to control equivalent levels and through the use of bradykinin selective ligands, it was seen that the dual activation of BK-­‐1 and BK-­‐2 receptor was necessary to rescue the TRPV1 response. The likely mechanism of action of bradykinin was through prostaglandin production as indomethacin blocked TRPV1 rescue. In the acute stage of diabetes, TRPV1 function is downregulated and may be caused by exposure to a neuropathy-­‐causing metabolite such as methylglyoxal. The TRPV1 function still retains plasticity at this acute stage because function could be enhanced back to control levels by bradykinin receptor activation : a potential for early therapeutic intervention.

Successful infant feeding requires effective milk acquisition, followed by the transport of ingested material across the oral cavity and through the pharynx, ultimately culminating in esophageal peristalsis. Several elements that underlie the neural control of swallowing are underexplored, including the neurological relationships among different aspects of swallowing (oral, pharyngeal, and esophageal). The works described here aim to improve our understanding of the sensorimotor relationships that drive infant swallowing, primarily by stimulating specific areas with capsaicin. To begin, we use an animal model of superior laryngeal nerve lesion to assess the effects of oropharyngeal capsaicin administration on feeding physiology. Next, we analyze the impacts of esophageal afferents on upstream feeding behaviors using a model of simulated gastroesophageal reflux. Finally, we explore the role of mandibular afferents in infant feeding, and determine whether capsaicin administration can recover any deficits resulting from anesthetization of these afferents. All experiments were conducted using infant pigs, a validated model for the study of infant feeding. Common methodology across specific aims includes videofluoroscopy (to assess kinematics and feeding performance) and electromyography (to assess motor outputs to muscles of interest). These experiments ultimately shed light on the extent of brainstem sensorimotor integration across feeding behaviors. Additionally, the results of these studies provide insights into the mechanisms by which specific sensory signals are integrated during feeding. These insights are critical and will ultimately facilitate the design of targeted interventions for specific feeding pathophysiologies in infants.

Transient receptor potential (TRP) channels are expressed throughout the central nervous system and have a unique ability to detect a wide range of stimuli including changes in voltage, temperature, pH, lipid environment, small molecule agonists, and mechanical stress. While it is known that TRP channels contain the same six transmembrane helix (S1-S6), tetrameric architecture as voltage-gated channels, the degree to which functional and structural analogies are relevant remains poorly understood. This thesis describes a multidisciplinary approach toward understanding the structure and function of TRP channel transmembrane domains by focusing on the S1-S4 transmembrane helices of the TRPV1. This focus is inspired by the voltage-sensor domain (VSD) of the S1-S4 helices of voltage-gated channels, for which a range of studies show functional and structural independence. While some TRP channels are voltage-sensitive, their S4 helix does not contain the positive string of amino acids of canonical VSDs. However, the S1-S4 helices are functionally significant as the binding site of small molecule ligands in both TRPV1 and TRPM8 (for capsaicin and menthol, respectively). The question of TRP channel transmembrane domain modularity is addressed in this thesis by expression and purification trials as well as radioligand-binding assays. It is demonstrated that the S1-S4 and S1-S6 helices of TRPV1 can be properly inserted, overexpressed, and show signs of stability upon detergent-extraction from Saccharomyces cerevisiae membranes. However the TRPV1 S1-S4 and S1-S6 helices do not show wildtype (WT)-like binding in [3H]-RTX binding assays. These results indicate that the TRPV1 transmembrane domains are likely structural but not functional domains. The S. cerevisiae expression system remained promising for the overexpression of TRP transmembrane domains as well as the production of functional, though not stable upon detergent-extraction, WT TRPV1. This WT TRPV1 was subsequently found to functionally bind both RTX, used in ligand binding assays, as well as the double-knot toxin (DkTx), targeted to the pore domain (the S5-S6 helices). An effect of DkTx on RTX binding affinity demonstrates an allosteric interaction indicative of a possible tighter packing between the two transmembrane domains than is seen in voltage-gated channels containing the canonical VSD. Computational approaches additionally allowed for the investigation of the intramembrane capsaicin binding site in the TRPV1 S1-S4 helices, crucial to the initial motivations of this study. While the literature locates the capsaicin binding site to the TRPV1 S1-S4 helices, a `binding pocket' has yet to be defined, with regards to the orientation of bound capsaicin and its access route to the site via the bilayer. Using molecular dynamics (MD) simulations the preferred location of capsaicin within the bilayer is defined, as well as the elucidiation of capsaicin flip-flop between bilayer leaflets as a key event prior to TRPV1 binding. A transient binding was also observed between a homology model of the TRPV1 S1-S4 helices and capsaicin, possibly encouraging the idea that the S1-S4 helices still contain a partial binding site, though of too low affinity to be observed in the binding experiments performed here.

The trigeminal ganglion (TG) is a complex sensory structure and multiple lines of evidence suggest that significant differences exist in anatomical, neurochemical and physiological properties between it and its equivalent structure in the somatosensory system, the dorsal root ganglion (DRG). This is likely to be a reflection, first on the unique areas of tissue innervation of the TG and second, on the unusual responses to injury which give rise to distinct pain symptoms such as toothache, migraine and temporomandibular joint disorders. In an attempt to address this disparity in knowledge, we have carried out an in-depth in vivo study investigating neurochemical populations and cell size distributions of sensory neurons within the rat TG. We have performed a detailed analysis of expression patterns for receptor components of important inflammatory mediators, NGF (TrkA), TNFα (p55) and IL-6 (gp130), along with the thermo-transducers TRPV1 and TRPM8. For each analysis we have compared our findings with those of the rat DRG. We have shown a significantly larger population of NF200+ neurons within the TG (51%) compared to the DRG (40%), and most interestingly, the majority of NF200+ neurons in the TG were within the small to medium cell size range, conferring a nociceptive phenotype. We have for the first time, determined expression of p55 and gp130 protein levels within neurochemically defined subpopulations of the TG. We show that a large proportion (33%) of TG neurons, in particular 27% of NF200+ neurons co-express p55, and thereby have the potential to respond directly to TNFα. Furthermore, we have observed gp130 protein expression to be ubiquitous within the TG, suggesting all neurons, including non-nociceptors, could respond to IL-6. In addition, we have utilised biochemical and electrophysiological techniques in vitro to measure the functional outcome of exposure of TG neurons to IL-6. We have demonstrated that IL-6 activates the JAK/STAT signalling pathway, preferentially within NF200+ neurons. Furthermore, we have shown that IL-6 sensitises the response of TG neurons to the TRPV1 agonist capsaicin, altering the gating properties and prolonging the opening time of the channel. Taken together, our findings support the emerging picture of a complex combinatorial pattern of co-expression of sensory neurochemicals, transducers and receptor components that help to define TG neuronal modality and function. We would advocate caution in making generalisations across sensory ganglia in particular in extrapolating data from the DRG to the trigeminal ganglion.

Chapter 1 gives an overview of the fluorine chemistry field, from its early developments to recent applications in medicinal chemistry. The development of asymmetric electrophilic or nucleophilic installation of fluorine in organic molecules is highlighten. Chapter 2 of this thesis discusses the enantioselective synthesis of α-fluoroamides. The study is applied to the synthesis of fluoroenantiomers of the bioactive molecule capsaicin and short-chain analogues. The biological activity of these compounds is assayed with the TRPV1 receptor. Results show that enantioselective α-fluoroamides (R)-97, (R)-99 and (S)-99 can generate differentiated biological responses, from TRPV1 agonists to TRPV1 antagonists. Chapter 3 focuses on the optimisation and development of 2-(aminomethyl)piperidine (R)-251 dihydrochloride. The development of 2-(aminomethyl)piperidine (R)-251 as its ditetrafluoroborate salt proved to offer excellent reactivity and solubility for the preparation of derivatives. This tetrafluoroborate salt was used to improve the syntheses of organocatalysts 2,2,2-trifluoro-N-(piperidin-2-ylmethyl)acetamide 363 and 4-methyl-N-(piperidin-2-ylmethyl)benzenesulfonamide 364.The catalytic properties of these latter two molecules for asymmetric Mannich reaction is demonstrated. Both (R)-363 and (R)-364 show up to 86% ee, in a typical 20 mol% loading, but loading of (R)-363 as low as 5 mol% still induces the catalysis.

Early pharmacological studies (Szolcsanyi and Jancso-Gabor, 1975, Wood, 1988) showed that capsaicin, the pungent ingredient of chilli peppers and other vanilloids, can specifically stimulate the C unmyelinated fibres which transmit nociceptive information i.e. information about noxious thermal, chemical and mechanical stimuli. The specific action of capsaicin on this subset of sensory neurons led researchers to postulate the existence of a capsaicin receptor. Caterina et al (1997) cloned Vanilloid Receptor 1 (VR1) from dorsal root ganglia, where the somata of C fibres reside. VR1 responds to capsaicin, heat, protons and to the cannabinoid ligand, anandamide (Zygmunt et al., 1999). Discrepancies between the pharmacological profile of VR1 and native vanilloid responses fuelled research for the identification of other vanilloid receptors. In this thesis, the cloning of a new member of the vanilloid receptor family is described using bioinformatics tools. The novel receptor was named Vanilloid Receptor-like (VR-L) and was found to share 49% identity with VR1 and 20% with members of the Transient Receptor Potential (TRP) family. VR-L transcripts were identified in a wide range of tissues including the capsaicin insensitive dorsal root ganglia neurons. The expression of the channel in these neurons can be upregulated by Nerve Growth Factor, as it was established with semi-quantitative RT- PCR. Co-immunoprecipitation studies were carried out to investigate the possibility that VR-L interacts with VR1 and other members of the TRP family to regulate indirectly vanilloid and other responses. VR1 and VR-L were found to form homomultimers and also to interact with each other and with members of the TRP family. A VR-L stable cell line was generated to study the functional significance of the interactions identified.

Hand-feel touch cues have been shown to influence the perception of other sensory modalities and can be used as means to create expectations toward food or beverage products presented concurrently with such cues. However, to date, there has been limited research on how these hand-feel touch cues could impact oral irritation elicited by capsaicin-containing products. Because oral irritation sensation is a dynamic perception lasting a period of time, temporal methodologies, such as Time-Intensity (TI) and Temporal-Check-All-That-Apply (TCATA), must be used when evaluating capsaicin-containing products. The use of temporal methodologies when examining the cross-modal effects of other cues on capsaicin irritation has been limited. To fill these knowledge gaps, this dissertation aimed to determine 1) temporal sensory characteristics of capsaicin solution as a model irritant stimulus using TI and TCATA; 2) cross-modal associations between hand-feel touch cues (9 material tiles) and capsaicin-induced oral irritation; 3) crossmodal influences of hand-feel touch cues (2 cup materials) on oral irritation attributes in capsaicin solution; and 4) cross-modal influences of hand-feel touch cues (2 cup materials) on “tingling” sensation, as a subquality of overall oral irritation perception, in spicy beverages. Capsaicin solution (0.002 mg/mL) could be mostly described using four irritation subqualities – “burning”, “stinging/pricking”, “tingling”, and “warm/hot”, with moderate overall oral irritation maximum intensity that lasted 448 s on average. At this capsaicin concentration, the oral irritation sensation was best paired with rough sandpaper and least paired with stainless steel, which could be due to underlying similarities in the emotional responses evoked by both touch cues and capsaicin solution (high arousal, negative valence), as well as material pleasantness and instrumentallymeasured surface texture characteristics. Out of the four irritation subqualities, “tingling” was influenced the most by the differences in hand-feel touch cues (rough sandpaper & stainless steel materials). When presented with rough sandpaper cups, “tingling” sensation in capsaicin solutions and spicy beverages were felt to a greater degree and lasted longer than when presented with stainless steel cups. Meanwhile, when presented with stainless steel cups, “burning” sensation in capsaicin solution was felt to a greater degree than when presented with rough sandpaper cups. The findings of this dissertation highlighted the importance of considering hand-feel touch cues in product evaluation involving capsaicin. Noting the continued popularity of spicy food and beverage products, food and beverage professionals and researchers should consider incorporating more hand-feel textural features on product packaging and container design to elevate consumer consumption experience and create expectations that would match the oral irritation characteristics of their products.

Feed additives such as capsaicin, prebiotics, and microbiota feed additives can increase postweaning growth performance of pigs while decreasing antibiotic use. Therefore, we conducted two experiments to evaluate the growth performance of newly weaned pigs fed capsaicin, prebiotics, and microbiota feed additives. On the first experiment, we observed that feeding Capsaicin to sows during lactation and the corresponding offspring during weaning was more effective at increasing feed efficiency of weaning pigs than feeding Capsaicin only in lactation or only to nursery pigs. Likewise, there was a greater number of genes differentially expressed when sows and their offspring consumed Capsaicin than feeding to sows or nursery pigs alone. On the second experiment, we observed that the offspring of multiparous sows had greater post-weaning growth performance than those of primiparous sows and that feeding four different microbial feed additives did not increase the growth performance of the offspring of either group of sows.

The effective use of land for maximal food production is a forever-increasing worry to islands in the Pacific, which have experienced rapid population growth. To address this we examine linked fish and vegetable production using a recirculating water system. This system is designed to achieve a high degree of efficiency of water use for food production without soil. Twenty-four identical systems were used, in which each system contained a biomass of 1.5-kg tilapia species (Oreochromis spp.) grown in 400-L freshwater tanks associated with two ebb-and-flow 25-L bio-filters (cinder rocks). Capsicum frutescens (Hawaiian chili) was cultivated in these experimental aquaponic systems and analyzed for capsaicin content. The purpose of this investigation was to: 1) obtain baseline water quality criteria 2) remediate pH for ammonia bio-filtration and pepper yield in recirculating aquaponic system in order to compare buffering capacity and understand treatment effect, and 3) quantify and compare capsaicinoid concentration between treatments using Rapid-High Performance Liquid Chromatography (r-HPLC) for quality analysis. This work helps address the need for combined approaches to complex agricultural research questions and food sustainability.

High blood pressure (hypertension; HTN) is the leading risk factor for death, yet the precise causes are unclear. The nervous system is known to play a role in some forms of HTN and research has pointed to the kidneys as a likely neural target in HTN. This possibility has been strengthened by recent clinical trials showing that ablation of the renal nerves (renal denervation; RDNX) has a significant antihypertensive effect in drug resistant patients. However, failure of the most recent sham-controlled trial has raised many questions regarding this treatment. Chief among them is whether the antihypertensive effect of RDNX is due to changes in kidney function secondary to ablation of sympathetic (efferent) renal nerves, or due to a reduction in non-renal sympathetic nerve activity secondary to ablation of sensory (afferent) renal nerves. In order to address this question, I first identified an animal model of HTN in which RDNX had an antihypertensive effect. Importantly, I showed that RDNX had roughly the same effect on blood pressure in hypertensive Dahl salt-sensitive (S) rats as has been reported in clinical trials. I then developed and validated a novel method for selective ablation of afferent renal nerves (renal-CAP treatment). Using this method, I showed that afferent renal nerves are not necessary to maintain cardiovascular or sodium/water homeostasis in normotensive rats subjected to dietary sodium loading. We also showed that renal-CAP treatment and complete RDNX caused the same attenuation of deoxycorticosterone-salt HTN, suggesting that the antihypertensive effect of RDNX in this model is due to ablation of afferent renal nerves. Lastly, we showed that RDNX has the same antihypertensive effect in Dahl S rats with mild HTN (after three weeks of high salt feeding) and in those with severe HTN (after nine weeks of high salt feeding). These results suggest that the antihypertensive effect of RDNX in the Dahl S rat is not dependent on duration of high salt feeding or pretreatment blood pressure and that the antihypertensive effect of RDNX in this model is not due to ablation of afferent renal nerves.

Airway hyperresponsivness (AHR) is one of most prominent pathophysiological features of asthma. Increasing evidence suggests that vagal bronchopulmonary afferents may be involved in the development of AHR. However, the underlying mechanisms are not clear. Therefore, the purpose of this dissertation was to investigate the effect of chronic airway inflammation induced by allergen sensitization on vagal bronchopulmonary afferents. The study was carried out in an animal model of allergic asthma. Brown-Norway rats were sensitized by intraperitoneal Ovalbumin (Ova) and exposed to aerosolized Ova 3 times/week for three weeks. Control rats received the vehicle. In vivo single-fiber recording technique was applied in this study. Our results showed that chronic Ova exposure caused an elevated baseline activity of pulmonary Cfibers, and a distinctly higher sensitivity of these afferents to chemical stimulants and lung inflation. After an acute Ova inhalation challenge, the increase in baseline activity and the excitability of pulmonary C-fibers were further augmented in sensitized rats, but not in control rats. In addition, sensitivity of pulmonary myelinated afferents to capsaicin was significantly elevated after chronic airway inflammation was induced by allergen. Furthermore, immunohistochemsitry data showed that, in nodose ganglia the proportion of transient receptor potential vanilloids type 1 channels (TRPV1)-expressing bronchopulmonary neurons was significantly higher in sensitized rats than in controls. This increase of TRPV1 expression was found mainly in neurofilament-positive neurons (myelinated neurons), but this effect was absent in jugular ganglia. In conclusion, allergen-induced airway inflammation caused a pronounced sensitizing effect on vagal pulmonary non-myelinated (C-fiber) afferents and elevated the sensitivity of vagal pulmonary myelinated afferents to capsaicin. The latter was accompanied by the upregulation of TRPV1 expression in these myelinated neurons.

Anyone who has eaten spicy foods has experienced the adverse effects of capsaicin, the pungent chemical found in hot chili that causes a burning sensation. The specific action of capsaicin occurs by the activation of receptors in sensory neurons. This thesis investigates the interaction of capsaicin with model cell membranes representing the structure of neurons. In particular, we are interested in the changes induced by capsaicin to the structure and dynamics of membranes. Molecular dynamics simulations are used to study the molecular interactions. The first part of this study evaluates different molecular representations for capsaicin in an 1-octanol/water system. This inhomogeneous system is commonly used to determine the partition of compounds between hydrophilic and hydrophobic environments, as that found in biological membranes. The results of these simulations validate the OPLS united-atom force field as a reasonable molecular representation of capsaicin, as it describes the behavior of capsaicin both quantitatively and qualitatively in 1-octanol/water mixtures. In the second part, simulations are performed for capsaicin and model cell membranes consisting of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine, two of the most commonly found lipids. Simulations investigated capsaicin in the aqueous and lipid phases. The results provide insight into the changes to the bilayers caused by capsaicin. Bilayers containing dipalmitoylphosphatidylethanolamine showed lower permeabilities to capsaicin than those composed of pure dipalmitoylphosphatidylcholine. Temperature is found to be an important factor in the permeability of capsaicin in the bilayer. Capsaicin in the bilayer concentrated in a region beneath the lipid/water interface, in which favorable hydrophilic and lipophilic interactions occur. The structure of the bilayer is not significantly changed at the concentrations of capsaicin considered. One important result from the simulations indicates that the interfacial density decreases with increasing capsaicin concentration in the bilayer, supporting the experimental observations of increased permeability in bilayers exposed to capsaicin.

Expt. 1 evaluated effects of 0 or 10 ppm CAP in the starter phase (d 1-16) on chicks challenged with SE on d of age. Therapeutic inclusion of 10ppm CAP increased (P < 0.05) L/S and ceca positives. In Expt. 2, capsaicin oleoresin (CO) was included in finisher diets (d 30-37) at 0, 5, or 20 ppm with SE challenge on day 31. Inclusion of 5 ppm CO increased (P < 0.05) ceca SE positives and demonstrated 1.05 and 1.39-log fewer SE cfu at CO concentration of 5 or 20 ppm, respectively. A linear decrease (P < 0.05) in lamina propria thickness of SE challenged birds was observed with increased CO. Expt. 3 evaluated prophylactic CO treatment at 0, 5, or 20 ppm in starter, grower, and finisher diets for resistance to SE or ST challenge on d 14 or 29. With challenge on d 14, 5 ppm CO reduced ceca (P

Rapid receptive field (RF) reorganization of somatosensory neurons in the rat dorsal horn was examined using extracellular single unit recording. Subcutaneous injection of lidocaine into RFs of dorsal horn neurons results in expansion of their RFs within minutes. The expanded RFs appear adjacent to or/and proximal to original RFs. Out of 63 neurons tested, 36 (58%) show RF reorganization. The data suggest that dorsal horn of spinal cord is one of the initial sites for RF reorganization. The neural mechanisms of this effect are not well understood. We propose that changes in biophysical properties (membrane conductance, length constant) of the neurons resulting from lidocaine injection contribute to RF reorganization. Iontophoretic application of glutamate onto dorsal horn neurons that show lidocaine induced RF's expansion were used to test the model. Application of glutamate produced reduction of reorganized RFs in 9 of 20 (45%) tested cells. Application of NBQX produced no effect on either original or expanded RFs indicate that RF shrinkage effects of glutamate involve NMDA receptors. The results are consistent with the prediction of the proposed model. Subcutaneous injection of capsaicin into tactile RFs of low threshold mechanoreceptive dorsal horn neurons produced no effect on the RF sizes that are consistent with other studies. Following the injection, the original RFs were completely silenced (46%) or remained responsive (54%).

Capsaicinoids are spicy substance found in capsicum fruits, the best known component of capsaicinoids being capsaicin. The objective of this study is to develop the extraction method of capsaicinoids from fruits of Capsicum frutescens L. found in Thailand and to study the cardiovascular actions of the extract on rat aorta, platelet aggregation, skin blood flow as well as skin irritation in comparison with capsaicin. Formulation of a capsaicinoid cream and test for its effect on skin blood flow in healthy volunteers were also performed. It was found that the extraction of capsaicinoids using dichloromethane, followed by column chromatography eluted with dichloromethane and methanol (98:2) yielded 2.6% capsaicinoids. Cardiovascular studies on blood vessels showed that both capsaicinoids and capsaicin could inhibit vasconstriction induced by norepinephrine and the vasocilatation effect of capsaicinoids might be due to the action of capsaicin. Both capsaicinoids and capsaicin caused significant decrease in platelet aggregation induced by ADP and collagen. Comparison of capsaicin with capsaicinoid extract having the same amount of capsaicin revealed that capsaicin had higher anti-platelet aggregating activity than capsaicinoids. This indicated that there might be other substances in the mixture which could decrease the anti-platelet aggregating effect. As for the irritation effects, capsaicinoids and capsaicin caused the same degree of irritation on rabbit skin. Both capsaicinoid and capsaicin significantly increased skin blood flow in healthy volunteers.