Sensory Afferent Nerves Research Articles

Neurogenic painful inflammation

Neurogenic inflammation results from the release of neuropeptides from peripheral nerve terminals. This secretion can be induced by two mechanisms: activation of afferent sensory nerves (e.g. by disease processes or experimentally by electrical stimulation) or activation of receptors expressed on peripheral nerve terminals. While the role of these mechanisms in the regulation of inflammation is well described, its significance for the generation of pain is much less clear and will be examined in this review. Activation of two receptors on peripheral sensory neurons (i.e. transient receptor potential vanilloid-1 channel and proteinase activated receptor-2) has been shown to induce neurogenic inflammation. Interference with this activation can ameliorate pain, but it remains uncertain whether this effect is indeed mediated by blockage of neurogenic inflammation. Two human diseases (complex regional pain syndrome and migraine) are believed to result from aberrant neuronal activation. In complex regional pain syndrome, studies in human patients and in a recently established animal model do not support a role for neurogenic inflammation in pain. In migraine, antagonists to the receptor for calcitonin gene related peptide ameliorated headache and could be the first conclusive evidence for the role of neurogenic inflammation in the generation of pain. Lastly, spinal mechanisms also appear to regulate immune cell recruitment to a peripheral site and seem to interfere with antinociception. While considerable experimental and clinical evidence supports the existence of neurogenic inflammation, it is less clear whether this process plays an important role in the generation of pain.

Anatomy of efferent hepatic nerves

The role of neural elements in regulating blood flow through the hepatic sinusoids, solute exchange, and parenchymal function is incompletely understood. This is due in part to limited investigation in only a few species whose hepatic innervation may differ significantly from humans. For example, most experimental studies have used rats and mice having livers with little or no intralobular innervation. In contrast, most other mammals, including humans, have aminergic and peptidergic nerves extending from perivascular plexus in the portal space into the lobule, where they course in Disse's space in close relationship to stellate cells (fat storing cells of Ito) and hepatic parenchymal cells. While these fibers extend throughout the lobule, they predominate in the periportal region. Cholinergic innervation, however, appears to be restricted to structures in the portal space and immediately adjacent hepatic parenchymal cells. Neuropeptides have been colocalized with neurotransmitters in both adrenergic and cholinergic nerves. Neuropeptide Y (NPY) has been colocalized in aminergic nerves supplying all segments of the hepatic-portal venous and the hepatic arterial and biliary systems. Nerve fibers immunoreactive for substance P and somatostatin follow a similar distribution. Intralobular distribution of all of these nerve fibers is species-dependent and similar to that reported for aminergic fibers. Vasoactive intestinal peptide and calcitonin gene-related peptide (CGRP) are reported to coexist in cholinergic and sensory afferent nerves innervating portal veins and hepatic arteries and their branches, but not the other vascular segments or the bile ducts. Nitrergic nerves immunoreactive for neuronal nitric oxide (nNOS) are located in the portal tract where nNOS colocalizes with both NPY- and CGRP-containing fibers. In summary, the liver is innervated by aminergic, cholinergic, peptidergic, and nitrergic nerves. While innervation of structures in the portal tract is relatively similar between species, the extent and distribution of intralobular innervation are highly variable as well as species-dependent and may be inversely related to the density of gap junctions between contiguous hepatic parenchymal cells.

Expression of neurokinin a receptor mRNA in human nasal mucosa

In airway tissues, it has been suggested that tachykinins act as the transmitter for afferent sensory nerves which respond to various irritants and may be involved in airway allergic reactions. Three classes of tachykinin receptor have been recognized, denoted NK1, NK2 and NK3, which exhibit preferential affinity for substance P, neurokinin A and neurokinin B, respectively. We used molecular probes to study the gene expression and distribution of NK2 receptor in human nasal mucosa. Total RNA was isolated from human nasal mucosa and NK2 receptor mRNA was detected in these tissues using reverse transcriptase polymerase chain reaction (RT-PCR). For an in situ hybridization study of human nasal mucosa, we utilized the PCR directly to incorporate a T7 RNA polymerase promoter sequence onto the NK2 receptor cDNA, and these PCR products were used as the DNA template for producing digoxigenin-labeled antisense and sense RNA probes. These studies revealed that NK2 receptor mRNA was expressed in blood vessels. The results suggest a primary role for neurokinin A in the form of vascular responses in the upper respiratory tract.

Detection of hypoxia-evoked ATP release from chemoreceptor cells of the rat carotid body

The carotid body (CB) is a chemosensory organ that detects changes in chemical composition of arterial blood and maintains homeostasis via reflex control of ventilation. Thus, in response to a fall in arterial PO 2 (hypoxia), CB chemoreceptors (type I cells) depolarize, and release neurotransmitters onto afferent sensory nerve endings. Recent studies implicate ATP as a key excitatory neurotransmitter released during CB chemoexcitation, but direct evidence is lacking. Here we use the luciferin–luciferase bioluminescence assay to detect ATP, released from rat chemoreceptors in CB cultures, fresh tissue slices, and whole CB. Hypoxia evoked an increase in extracellular ATP, that was inhibited by L-type Ca 2+channel blockers and reduced by the nucleoside hydrolase, apyrase. Additionally, iberiotoxin (IbTX; 100 nM), a blocker of O 2-sensitive Ca 2+-dependent K + (BK) channels, stimulated ATP release and largely occluded the effect of hypoxia. These data strongly support a neurotransmitter role for ATP in carotid body function.

Muscle pressor reflex: potential role of vanilloid type 1 receptor and acid-sensing ion channel.

Reflex cardiovascular responses to muscle contraction are mediated by mechanical and metabolic stimulation of thin muscle afferent fibers. Metabolic stimulants and receptors involved in responses are uncertain. Capsaicin depolarizes thin sensory afferent nerves that have vanilloid type 1 receptors (VR1). Among potential endogenous ligands of thin fibers, H+ has been suggested as a metabolite mediating the reflex muscle response as well as a potential stimulant of VR1. It has also been suggested that acid-sensing ion channels (ASIC) mediate H+, evoking afferent nerve excitation. We have examined the roles of VR1 and ASIC in mediating cardiovascular reflex responses to acid stimulation of muscle afferents in a rat model. In anesthetized rats, injections of capsaicin into the arterial blood supply of triceps surae muscles evoked a biphasic response (n = 6). An initial fall in mean arterial pressure (from baseline of 95.8 +/- 9.5 to 70.4 +/- 4.5 mmHg, P < 0.05 vs. baseline) was followed by an increase (to 131.6 +/- 11.3 mmHg, P < 0.05 vs. baseline). Anandamide (an endogenous substance that activates VR1) induced the same change in blood pressure as did capsaicin. The pressor (but not depressor) component of the response was blocked by capsazepine (a VR1 antagonist) and section of afferent nerves. In decerebrate rats (n = 8), H+ evoked a pressor response that was not blocked by capsazepine but was attenuated by amiloride (an ASIC blocker). In rats (n = 12) pretreated with resiniferatoxin to destroy muscle afferents containing VR1, capsaicin and H+ responses were blunted. We conclude that H+ stimulates ASIC, evoking the reflex response, and that ASIC are likely to be frequently found on afferents containing VR1. The data also suggest that VR1 and ASIC may play a role in processing of muscle afferent signals, evoking the muscle pressor reflex.

Increased prevalence of semaphorin 3C, a repellent of sympathetic nerve fibers, in the synovial tissue of patients with rheumatoid arthritis.

The presence of selective sympathetic nerve repellents, i.e., semaphorins, may be responsible for the observed reduction of sympathetic innervation in the synovial tissue of patients with rheumatoid arthritis (RA). This study was undertaken to investigate the presence of different semaphorins in synovial tissue of patients with RA, patients with osteoarthritis (OA), and control subjects without inflammation. In situ hybridizations with digoxigenin-labeled RNA probes directed against different semaphorins were performed. The presence of semaphorin 3C (S3C) in the synovial tissue of 10 RA, 10 OA, and 5 control subjects was investigated using a polyclonal antiserum directed against S3C. All in situ hybridizations revealed the presence of S3C messenger RNA, but no other investigated semaphorin (i.e., against primary afferent sensory nerve fibers), in the synovial tissue of RA and OA patients. Immunohistologic double staining demonstrated that macrophages and fibroblasts were positive for S3C protein. Quantitative analysis of S3C protein staining showed an increased density of S3C-positive cells in the synovial tissue of RA patients (mean +/- SEM 339 +/- 65 cells/mm(2)) in comparison with OA patients (168 +/- 27/mm(2); P = 0.031 versus RA) and controls (126 +/- 26/mm(2); P = 0.027 versus RA). Studies of the relationship between sympathetic nerve fiber density and S3C-positive cell density in the tissue of all patients showed that RA patients generally had lower densities of sympathetic nerve fibers and higher densities of S3C-positive cells than OA patients and control subjects. These findings suggest that S3C from macrophages and fibroblasts, which is selectively directed against sympathetic nerve fibers, could be one element responsible for reduced sympathetic innervation in RA tissue. The inability of sympathetic nerve fibers to reinnervate synovial tissue could contribute to the chronic nature of RA.

Induced Sputum Inflammatory Mediator Concentrations in Chronic Cough

Previous studies have shown evidence of airway inflammation in patients with chronic cough and have suggested that the cough may be due to release of tussive mediators and activation of afferent sensory nerve endings. We measured the concentration of various proinflammatory and tussive mediators in induced sputum supernatants from 20 patients with cough variant asthma or eosinophilic bronchitis, 20 patients with nonasthmatic chronic cough, 22 patients with idiopathic chronic cough, and 18 healthy control subjects. We measured histamine, cysteinyl-leukotrienes, prostanoids (prostaglandin D2 and prostaglandin E2), and interleukin-8 by enzyme immunoassay. The median sputum histamine concentrations were significantly higher in patients with idiopathic chronic cough (8.0 ng/ml) and cough variant asthma/eosinophilic bronchitis (10.2 ng/ml) than in normal subjects (2.6 ng/ml; 95% confidence interval of difference from idiopathic chronic cough, 0.8 to 25.8 [p = 0.009] and 95% confidence interval of difference from cough variant asthma/eosinophilic bronchitis, 1.1 to 20.1 [p = 0.01]). Median sputum prostaglandin D2 and prostaglandin E2 concentrations were significantly higher in all categories of chronic cough. Our findings support the view that there is release of inflammatory and tussive mediators in patients with chronic cough and suggest that there might be similarities in the mechanism of cough in a diverse range of conditions.

Interaction of EGF family growth factors and neurotransmitters in regulating lacrimal gland secretion

The lacrimal gland is the primary source for the aqueous portion of the tear film. This portion contains water, electrolytes and proteins, which are necessary for the health and maintenance of the cells of the ocular surface. Afferent sensory nerves in the cornea and conjunctiva stimulate efferent parasympathetic and sympathetic nerves in the lacrimal gland. Cholinergic agonists, released from parasympathetic nerves, and norepinephrine, released from sympathetic nerves, are major stimuli of lacrimal gland secretion. These neurotransmitters activate distinct, but overlapping signal transduction pathways leading to lacrimal gland secretion. Other stimuli of lacrimal gland secretion are the EGF family of growth factors. In addition to stimulation of secretion, these growth factors can interact with the cells of the lacrimal gland themselves or with the cells of the ocular surface depending upon the location from which these growth factors are released. This review will focus on the effects of the EGF family of growth factors on the lacrimal gland and their interactions with the pathways stimulated by the neurotransmitters released from nerves.

Expression of substance P and vanilloid receptor (VR1) in trigeminal sensory neurons projecting to the mouse nasal mucosa

Substance P and neurokinin A (NKA) have potent pro-inflammatory effects in the airways. The release of these neuropeptides from primary afferent (sensory) nerve endings to various stimuli is considered to be induced by activation of the capsaicin (vanilloid) receptor (VR1). In this study, retrograde neuronal tracing studies were combined with immunohistochemistry for VR1 and substance P to investigate the occurrence and distribution of substance P and VR1 receptor expression in mouse trigeminal neurons that were identified by retrograde labeling with Fast blue dye from the nasal mucosa. Fast blue signaling was observed in mucosa layers of the right nasal cavity and in sensory trigeminal neurons close to the division of the ophthalmic and maxillary nerve. Expression patterns of VR1 and substance P were found with different frequencies: 11.3 ± 1.2% (mean ± SEM) were immunoreactive for VR1, 4.9 ± 1.1% for VR1 and SP, and 6.4 ± 1.3% only for VR1 but not for SP. These VR1-positive neurons were partly binding to lectin I-B4, indicating VR1-expression in non-peptidergic upper airway C-fibers. In conclusion, based on the extent of SP and VR1 co-localization in nasal afferent neurons, the present study suggests that, following a peripheral activation of the VR1 receptor on SP afferents, there could be a triggering of SP-mediated phenomena, including those related to inflammation, such as plasma extravasation.

Glucose acts in the CNS to regulate gastric motility during hypoglycemia.

Our purposes were to 1) develop an animal model where intravenously (iv) administered d-glucose consistently inhibited antral motility, and 2) use this model to assess whether iv glucose acts to inhibit motility from a peripheral or a central nervous system site and to elucidate the factor(s) that determine(s) whether stomach motor function is sensitive to changes in blood glucose. Rats were anesthetized with alpha-chloralose-urethane, and antral motility was measured by a strain-gauge force transducer sutured to the antrum. In some cases, antral motility and gastric tone were measured by monitoring intragastric balloon pressure. Increases in blood glucose were produced by continuous iv infusion of 25% d-glucose at 2 ml/h. Inhibition of antral motility and gastric tone was observed when gastric contractions were induced by hypoglycemia (subcutaneously administered insulin, 2.5 IU/animal). In contrast, no inhibition of gastric motor function was observed when glucose infusion was tested on gastric contractions that were 1) spontaneously occurring, 2) evoked by iv administered bethanechol in vagotomized animals, and 3) evoked by the TRH analog RX77368, microinjected into the dorsal motor nucleus of the vagus. Using the model of insulin-induced hypoglycemia to increase gastric motor activity, we found that neither sectioning the hepatic branch of the vagus (n = 5), nor treating animals with capsaicin to destroy sensory vagal afferent nerves (n = 5) affected the ability of iv d-glucose to inhibit gastric motor function. Our results indicate that an important factor determining whether stomach motor function will be sensitive to changes in blood glucose is the method used to stimulate gastric contractions, and that the primary site of the inhibitory action of iv glucose on gastric motility is the central nervous system rather than the periphery.

Capsaicin-sensitive nerves regulate the metabolic response to abdominal sepsis

Background. Both the systemic release of inflammatory mediators and activation of the neuroendocrine axis by sensory afferent nerves (SANs) have been implicated as initiators of the metabolic response to infection. In this study, we investigate the role of SANs as mediators of protein catabolism and the insulin-like growth factor (IGF) axis during abdominal sepsis using capsaicin (Cap) to selectively destroy nociceptive sensory axons. Methods. Four groups of male Sprague-Dawley rats were studied: Control, Control+Cap, Sepsis, and Sepsis+Cap. Rats were injected with Cap (75 mg/kg) on day 1 and (50 mg/kg) on day 2 to destroy SANs. Time-matched control and septic rats were pair-fed and injected with vehicle on the same schedule. Controls underwent sham laparotomy, while septic rats had a fecal-agar pellet inoculated with Escherichia coli and Bacteroides fragilis implanted in the peritoneal cavity. Blood and tissues were harvested 5 days after the induction of sepsis. Plasma IGF-I, IGFBP-1, and -3 were measured by radioimmunoassay and Western blot analysis. IGF-I, acid-labile subunit (ALS), IGFBP-1 and -3 mRNA levels were determined by Northern blot analysis. Results. Mortality was 40% in septic rats vs 0% in the sepsis+Cap group. Capsaicin had no effect on muscle mass, protein content, or the IGF system in control rats. However, sepsis-induced reductions in gastrocnemius mass (25%) and protein content (35%) were ameliorated by capsaicin. The sepsis-induced decrease in hepatic IGF-I mRNA and circulating IGF-I (26%), as well as the 4-fold increase in plasma IGFBP-1 and hepatic IGFBP-1 mRNA were prevented by capsaicin. Conclusions. Capsaicin-sensitive nerves mediate mortality, the catabolism of skeletal muscle, and selected elements of the IGF system during abdominal sepsis. The results suggest an important role for nociceptive SANs and the neuroendocrine system in mediating the host response to abdominal infection.

Effects of isoeugenol on in vitro neuromuscular blockade of rat phrenic nerve-diaphragm preparations.

To investigate in vitro effects of isoeugenol on neuromuscular transmission in tissues obtained from rats. Tissues (phrenic nerve and diaphragm) obtained from 15 male Sprague-Dawley rats. Rats were euthanatized, and tissues (phrenic nerves and diaphragm) were obtained. Phrenic nerve-diaphragm preparations were examined in vitro. The phrenic nerve was stimulated with weak electrical impulses. Muscle-twitch responses were recorded before and after the addition of drugs (pancuronium, neostigmine, isoeugenol, and benzocaine). Pancuronium and isoeugenol in low concentrations (10 to 206 microM) caused a distinct decrease in twitch response, which could be reversed by the addition of neostigmine. The decrease in twitch response caused by benzocaine or high concentrations of isoeugenol could not be reversed by the addition of neostigmine. Isoeugenol caused a competitive blockade of neuromuscular transmission. Neostigmine restored this transmission by inhibiting acetylcholinesterase, which led to increased concentrations of acetylcholine. Because isoeugenol is used as an anesthetic in fish, further investigations are necessary to determine whether fish exposed to isoeugenol are sedated and unconscious or whether they are only paralyzed but have intact perception in afferent sensory nerves.

Dual dopamine D 2 receptor and β 2-adrenoceptor agonists for the treatment of chronic obstructive pulmonary disease: the pre-clinical rationale

This paper describes the rationale for the development of dual dopamine D 2-receptor and β 2-adrenoceptor agonists as potential treatments for the symptoms of chronic obstructive pulmonary disease (COPD). The putative involvement of pulmonary sensory afferent nerves in mediating the key COPD symptoms of breathlessness, cough and excess sputum production is outlined and the hypothesis that activation of D 2-receptors on such nerves would modulate their activity is developed. This premise was tested, in a range of animal models, using the first of a novel class of dual dopamine D 2-receptor and β 2-adrenoceptor agonists, sibenadet HCI (Viozan™, AR-C68397AA). In the course of these studies it was demonstrated that sibenadet, through activation of D 2-receptors, inhibited discharge of rapidly adapting receptors and was effective in reducing reflex-induced tachypnoea, mucus production and cough in the dog. Sibenadet, through its activation of β 2-adrenoceptors, was also shown to be an effective bronchodilator with a prolonged duration of action following topical administration to the lungs. These studies also indicated that sibenadet had a wide therapeutic ratio with respect to expected undesirable side-effects such as emesis and cardiovascular disturbances. These results provided a compelling rationale for the initiation of a clinical development programme with sibenadet for the treatment of COPD.

A-317491, a novel potent and selective non-nucleotide antagonist of P2X3 and P2X2/3 receptors, reduces chronic inflammatory and neuropathic pain in the rat.

P2X3 and P2X2/3 receptors are highly localized on peripheral and central processes of sensory afferent nerves, and activation of these channels contributes to the pronociceptive effects of ATP. A-317491 is a novel non-nucleotide antagonist of P2X3 and P2X2/3 receptor activation. A-317491 potently blocked recombinant human and rat P2X3 and P2X2/3 receptor-mediated calcium flux (Ki = 22-92 nM) and was highly selective (IC50 >10 microM) over other P2 receptors and other neurotransmitter receptors, ion channels, and enzymes. A-317491 also blocked native P2X3 and P2X2/3 receptors in rat dorsal root ganglion neurons. Blockade of P2X3 containing channels was stereospecific because the R-enantiomer (A-317344) of A-317491 was significantly less active at P2X3 and P2X2/3 receptors. A-317491 dose-dependently (ED50 = 30 micromolkg s.c.) reduced complete Freund's adjuvant-induced thermal hyperalgesia in the rat. A-317491 was most potent (ED50 = 10-15 micromolkg s.c.) in attenuating both thermal hyperalgesia and mechanical allodynia after chronic nerve constriction injury. The R-enantiomer, A-317344, was inactive in these chronic pain models. Although active in chronic pain models, A-317491 was ineffective (ED50 >100 micromolkg s.c.) in reducing nociception in animal models of acute pain, postoperative pain, and visceral pain. The present data indicate that a potent and selective antagonist of P2X3 and P2X2/3 receptors effectively reduces both nerve injury and chronic inflammatory nociception, but P2X3 and P2X2/3 receptor activation may not be a major mediator of acute, acute inflammatory, or visceral pain.

Enhanced release of adenosine in rat hind paw following spinal nerve ligation: involvement of capsaicin-sensitive sensory afferents

Modulation of endogenous adenosine levels by inhibition of adenosine metabolism produces a peripheral antinociceptive effect in a neuropathic pain model. The present study used microdialysis to investigate the neuronal mechanisms modulating extracellular adenosine levels in the rat hind paw following tight ligation of the L5 and L6 spinal nerves. Subcutaneous injection of 50 μl saline into the nerve-injured paw induced a rapid and short-lasting increase in extracellular adenosine levels in the subcutaneous tissues of the rat hind paw ipsilateral to the nerve injury. Saline injection did not increase adenosine levels in sham-operated rats or non-treated rats. The adenosine kinase inhibitor 5′-amino-5′-deoxyadenosine and the adenosine deaminase inhibitor 2′-deoxycoformycin, at doses producing a peripheral antinociceptive effect, did not further enhance subcutaneous adenosine levels in the nerve-injured paw. Systemic pretreatment with capsaicin, a neurotoxin selective for small-diameter sensory afferents, markedly reduced the saline-evoked release of adenosine in rat hind paw following spinal nerve ligation. Systemic pretreatment with 6-hydroxydopamine, a neurotoxin selective for sympathetic afferent nerves, did not affect release. These results suggest that following nerve injury, peripheral capsaicin-sensitive primary sensory afferent nerve terminals are hypersensitive, and are able to release adenosine following a stimulus that does not normally evoke release in sham-operated or intact rats. Sympathetic postganglionic afferents do not appear to be involved in such release. The lack of effect on such release by the inhibitors of adenosine metabolism suggests an altered peripheral adenosine system following spinal nerve ligation.

Airway nerves: in vivo electrophysiology.

Information about the activity of airway sensory afferent nerves in vivo can be obtained electrophysiologically by extracellular recording of action potentials. Apart from data capture, the basic techniques used for recording sensory nerve activity have not advanced greatly in 50 years. However, clearly they continue to contribute vastly to our understanding of the role of these nerves in the control and functions of the airways in disease. This is particularly noticeable with the insight gained into exactly which physiological, biochemical and pharmacological events in the control of lung function rely upon the airway sensory afferent nerves and the subsequent airway vagal reflex arcs.

Cardiovascular responses to sciatic nerve stimulation are blocked by paratrigeminal nucleus lesion

The paratrigeminal nucleus (Pa5) receives primary sensory inputs from the vagus, glossopharyngeal, and trigeminal nerves and has efferent projections to the nucleus of the solitary tract (NTS), rostroventrolateral reticular nucleus (RVL), as well as to the nucleus ambiguus (Amb), lateral reticular (LRt), parabrachial (PB) and ventral posteromedial thalamic (VPM) nuclei, suggesting that it may play a significant role in cardiovascular responses to nociceptive stimuli. The aim of the present study was to evaluate the effects of unilateral lesions of the Pa5 on cardiovascular alterations induced by afferent somatic sensory nerve stimulation (SNS), also known as the somatosympathetic reflex (SSR). Cardiovascular responses were recorded in rats following either sham operation or unilateral lesions of the Pa5 with ibotenic acid. Mean arterial blood pressure (MAP) increased after SNS, which in sham-lesioned animals raised from 95±4 to 115±2 mmHg. Ipsilateral Pa5 lesion did not significantly reduce the pressor response to SNS (from 91±7 to 107±4 mmHg increase of baseline MAP). On the other hand, contralateral Pa5 lesion significantly reduced the response to SNS (from 99±5 to 104±2 mmHg). Sciatic nerve stimulation did not alter heart rate (HR) neither did ipsi- or contralateral Pa5 lesion HR baseline response level. These findings support a crucial role for the Pa5 in cardiovascular regulation, by relaying SSR input evoked by peripheral nerve stimulation.

The role of nerves in asthma.

Asthma is a syndrome characterized by reversible episodes of wheezing, cough, and sensations of chest tightness and breathlessness. These symptoms are secondary to changes in the activity of the nervous system. The mechanisms by which the nervous system is altered such that the symptoms of asthma occur have not yet been elucidated. Airway inflammation associated with asthma may affect neuronal activity at several points along the neural reflex pathway, including the function of the primary afferent (sensory) nerves, integration within the central nervous system, synaptic transmission within autonomic ganglia, and transmission at the level of the postganglionic neuroeffector junction. We provide a brief overview of these interactions and the relevance they may have to asthma.

Ultrastructural evaluation of calcitonin gene-related peptide immunoreactivity in the human cochlea and vestibular endorgans.

Calcitonin gene-related peptide (CGRP) is a neuropeptide widely distributed in the peripheral and central nervous system. Demonstrated in the efferent systems of the mammalian cochlea and vestibule, immunoreactive patterns of CGRP may vary by species. There is, however, no information in the literature investigating CGRP localization in the human cochlea. In the present study, the ultrastructural localization of CGRP immunoreactivity was evaluated in the human inner ear with immunoelectron microscopy. It was found that, in human cochlea, CGRP immunoreactivity was located in unmyelinated nerve fibres of the spiral lamina, inner spiral fibres beneath inner hair cells, tunnel spiral fibres, tunnel crossing fibres and outer radial fibres. In endorgans of human vestibule, CGRP immunoreactivity was located in vesiculated nerve fibres and bouton-type nerve terminals which were seen to contact afferent nerve chalices surrounding type I sensory cells and afferent nerve fibres, or to form an en passant contact with afferent dendrites. CGRP immunoreactivity appeared to be confined to efferent systems in all cases. This study presents evidence that CGRP could serve a role in neurotransmission or neuroregulation in both cochlear and vestibular efferent systems of human.

Role of mitogen-activated protein kinase in cholinergic stimulation of conjunctival goblet cell secretion.

Conjunctival goblet cells are a primary source for the mucous layer of the tear film. We showed previously that conjunctival goblet cell mucin secretion is under neural control as activation of afferent sensory nerves in the cornea stimulates mucin secretion.1 This neural reflex is mediated either by the parasympathetic and sympathetic nerves that surround the goblet cells, or by antidromic stimulation of the sensory nerves in the conjunctiva and collateral sensory nerves from the cornea. Exogenous addition of the parasympathetic agonist carbachol or the parasympathetic neuropeptide VIP stimulated conjunctival goblet cell secretion.2,3 Cholinergic agonists released from parasympathetic nerves bind to and activate G protein linked- M2 and M3 muscarinic receptors. In most tissues, activation of these receptors stimulates phospholipase C to hydrolyze phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG). IP3 binds to specific receptors on the endoplasmic reticulum to increase intracellular Ca2+. The increased intracellular Ca2+ either directly, or in combination with Ca2+/calmodulin-dependent protein kinases, activates mucin secretion. DAG in turn stimulates protein kinase C (PKC). In many tissues, cholinergic agonists also activate the mitogen-activated protein kinase (MAPK) signaling pathway used by growth factor receptors, which usually regulate cell growth and proliferation. Activation of the MAPK pathway by cholinergic agonists can occur through several mechanisms. One such mechanism is through transactivation of the EGF receptor in an EGF-independent manner.4 The activated recepter then serves as a scaffold for recruitment of Grb2-SoS complex via tyrosine phosphorylation of Shc. KeywordsHormone Replacement TherapyLacrimal GlandMeibomian GlandCorneal DystrophyKeratoconjunctivitis SiccaThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.