Calcitonin gene-related peptide in the eye: release by sensory nerve stimulation and effects associated with neurogenic inflammation

The structure and function of the human choroid

In this manuscript, the structure of the human choroid is reviewed with emphasis of the macro- and microscopic anatomy including Bruch's membrane, choriocapillaris, Sattler's and Haller's layer, and the suprachoroid. We here discuss the development of the choroid, as well as the question of choroidal lymphatics, and further the neuronal control of this tissue, as well as the pathologic angiogenesis. Wherever possible, functional aspects of the various structures are included and reviewed.

Topical application of calcitonin gene-related peptide as a regenerative, antifibrotic, and immunomodulatory therapy for corneal injury

Calcitonin gene-related peptide (CGRP) is a multifunctional neuropeptide abundantly expressed by corneal nerves. Using a murine model of corneal mechanical injury, we found CGRP levels in the cornea significantly reduced after injury. Topical application of CGRP as an eye drop accelerates corneal epithelial wound closure, reduces corneal opacification, and prevents corneal edema after injury in vivo. CGRP promotes corneal epithelial cell migration, proliferation, and the secretion of laminin. It reduces TGF-β1 signaling and prevents TGF-β1-mediated stromal fibroblast activation and tissue fibrosis. CGRP preserves corneal endothelial cell density, morphology, and pump function, thus reducing corneal edema. Lastly, CGRP reduces neutrophil infiltration, macrophage maturation, and the production of inflammatory cytokines in the cornea. Taken together, our results show that corneal nerve-derived CGRP plays a cytoprotective, pro-regenerative, anti-fibrotic, and anti-inflammatory role in corneal wound healing. In addition, our results highlight the critical role of sensory nerves in ocular surface homeostasis and injury repair.

Dim the Lights: A Narrative Review of Photophobia in Migraine

A preference for darkness is one of the main associated features in people with migraine, the cause remaining a mystery until some decades ago. In this article, we describe the epidemiology of photophobia in migraine and explain the pathophysiological mechanisms following an anatomical structure. In addition, we review the current management of migraine and photophobia. Ongoing characterization of patients with photophobia and its different manifestations continues to increase our understanding of the intricate pathophysiology of migraine and vice versa. Detailed phenotyping of the patient with photophobia is encouraged.

The role of erenumab in the treatment of migraine

Calcitonin gene related peptide (CGRP) monoclonal antibodies (mAbs) have been the first class of specifically developed preventive treatments for migraine. Clinical trials data suggest superiority of the CGRP mAbs to placebo in terms of prevention of migraine symptoms, migraine-specific quality of life and headache related disability. Treatment-related side effects overall did not differ significantly from placebo and discontinuation rate due to side effects has been low across the clinical trials, perhaps in view of their peripheral mode of action. Along with their route and frequency of administration, these novel class of drugs may constitute an improvement compared with the established arsenal of migraine treatments. Erenumab is a fully human antibody and the only mAb acting on the CGRP pathway by blocking its receptor. It is the first of the CGRP mAb class approved by the US Food and Drug Administration (May 2018) and the European Medicines Agency (July 2018). Erenumab exists in two different doses (70 mg and 140 mg) and it is administered with monthly subcutaneous injections. This review summarises erenumab pharmacological characteristics, clinical trials data, focusing on the potential role of this treatment in clinical practice.

Morphology and neurochemistry of rabbit iris innervation

The aim of this study was to map the entire nerve architecture and sensory neuropeptide content of the rabbit iris. Irises from New Zealand rabbits were stained with antibodies against neuronal-class βIII-tubulin, calcitonin gene-related peptide (CGRP) and substance P (SP), and whole-mount images were acquired to build a two-dimensional view of the iridal nerve architecture. After taking images in time-lapse mode, we observed thick nerves running in the iris stroma close to the anterior epithelia, forming four to five stromal nerve rings from the iris periphery to the pupillary margin and sub-branches that connected with each other, constituting the stromal nerve plexus. In the anterior side, fine divisions derivated from the stromal nerves, forming a nerve network-like structure to innervate the superficial anterior border layer, with the pupillary margin having the densest innervation. In the posterior side, the nerve bundles ran along with the pupil dilator muscle in a radial pattern. The morphology of the iris nerves on both sides changed with pupil size. To obtain the relative content of the neuropeptides in the iris, the specimens were double stained with βIII-tubulin and CGRP or SP antibodies. Relative nerve fiber densities for each fiber population were assessed quantitatively by computer-assisted analysis. On the anterior side, CGRP-positive nerve fibers constituted about 61%, while SP-positive nerves constitute about 30.5%, of the total nerve content, which was expressed as βIII tubulin-positive fibers. In addition, in the anterior stroma of the collarette region, there were non-neuronal cells that were positive for SP. On the posterior side, CGRP-positive nerve fibers were about 69% of total nerve content, while SP constituted only up to 20%. Similarly, in the trigeminal ganglia (TG), the number of CGRP-positive neurons significantly outnumbered those that were positive for SP. Also, all the SP-positive neurons were labeled with CGRP. This is the first study to provide a two-dimensional whole mount and a cross-sectional view of the entire iris nerve architecture. Considering the anatomical location, the high expression of CGRP and SP suggests that these neuropeptides may play a role in the pathogenesis of anterior uveitis, glaucoma, cataracts and chronic ocular pain.

Pathophysiology of JIA-associated uveitis

Juvenile idiopathic arthritis (JIA)-associated uveitis is an intriguing manifestation of JIA and an important contributor of long-term damage. Its pathophysiology is still poorly understood. This review summarizes current concepts. JIA is both a multifactorial and polygenetic disease. In the past 2 decades, multiple studies have indicated that the genetic contribution to both JIA and JIA-associated uveitis is modest. From an ophthalmological point of view, much of the pathophysiological data is derived from studies in experimental uveitis animal models. The pathophysiology of the arthritic manifestations of JIA has been studied extensively in humans. These studies have focused on the principal cells of the adaptive immune system, in particular different subsets of regulatory and effector T cells, as well as on antigen presenting cells or dendritic cells. With advancing technology and advancing knowledge of the underlying mechanisms of JIA-associated uveitis, new targets for therapy might evolve in the coming years.

Peptidergic nerves in the eye, their source and potential pathophysiological relevance

Over the last five decades, several neuropeptides have been discovered which subsequently have been found to be highly conserved during evolution, to be widely distributed both in the central and peripheral nervous system and which act as neurotransmitters and/or neuromodulators. In the eye, the first peptide to be explored was substance P which was reported to be present in the retina but also in peripherally innervated tissues of the eye. Substance P is certainly the best characterized peptide which has been found in sensory neurons innervating the eye. Functionally, it has been shown to act trophically on corneal wound healing and to participate in the irritative response in lower mammals, a model for neurogenic inflammation, where it mediates the noncholinergic nonadrenergic contraction of the sphincter muscle. Over the last three decades, the interest has extended to investigate the presence and distribution of other neuropeptides including calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, pituitary adenylate cyclase-activating polypeptides, cholecystokinin, somatostatin, neuronal nitric oxide, galanin, neurokinin A or secretoneurin and important functional results have been obtained for these peptides. This review focuses on summarizing the current knowledge about neuropeptides in the eye excluding the retina and retinal pigment epithelium and to elucidate their potential functional significance.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Studies on ocular inflammation and development of a prostaglandin analogue for glaucoma treatment

This review summarizes the Ernst H. Bárány Prize Lecture given at the meeting of the International Society of Eye Research in Geneva 2002. In the paper the path from the author's early studies on neurogenic inflammation in the eye to the search for a suitable prostaglandin analogue for glaucoma treatment, and the development of latanoprost are described. In particular the solution to the nociceptive and hyperemic side-effects of naturally occurring prostaglandins in the eye, the mechanism of action of FP prostanoid receptor agonists as well as the selection of dose for glaucoma treatment are discussed. In addition, pharmacokinetical aspects of latanoprost, and the melanogenic side-effect of prostaglandins in the iris are addressed. The paper is primarily focused on studies performed by the author and complete reference to other previous, or contemporary studies is therefore not always given as the purpose is not to present a comprehensive review article.

Amylin Competes for Binding Sites of CGRP in the Chamber Angle and Uvea of Monkey, Cat, and Pig Eye

Calcitonin gene-related peptide (CGRP) binding sites have been identified previously in the eyes of monkey, cat, pig, and guinea pig. In this study, the ability of cat, human, and rat amylins to displace the binding of CGRP in the anterior part of the eye of monkey, cat, and pig was studied. The location and displacement of 125I-hCGRPalpha by amylins as concentrations of 1-1000 nM were studied in cryosections by autoradiography. In the monkey eye, cat and rat amylins were able to compete for the binding sites of CGRP in ciliary muscle and ciliary processes. In the cat eye, cat and human amylins clearly displaced CGRP binding from ciliary muscle, ciliary processes, iris, and chamber angle. Furthermore, rat amylin clearly displaced CGRP binding from ciliary muscle and ciliary processes. In the pig eye, cat, human, and rat amylins competed for the binding sites of CGRP in ciliary muscle, ciliary processes, iris, and limbal conjunctiva. Specific amylin receptors or the possible physiological role of amylin in the eye have not hitherto been reported. It seems, however, that amylin can bind to ocular CGRP receptors and thus probably plays a role in the regulation of the same functions as CGRP, (e.g., aqueous humor outflow).

Neuroimmunomodulation and immune privilege: the role of neuropeptides in ocular immunosuppression

Regional immunoregulatory mechanisms insure that the most effective immune defense mounted is in proportion with preserving unique tissue functionalities. Immune-privileged tissues, such as the eye, are tissue sites of extreme regional immunoregulation. They have evolutionarily adapted several mechanisms to prevent the induction of inflammation within their tissue microenvironment. With over half a century of experimental examinations of ocular immune privilege, only recently have we come to understand that neuropeptides constitutively present in ocular tissues are part of the mechanisms of immune privilege.

Influence of intense light stimulation on trigeminal and cervical pain perception thresholds

Thirty-three migraineurs and 23 healthy controls were submitted to pressure algometry before and after light-induced discomfort was elicited by progressive light stimulation in a monoblind fashion. Pressure algometries were performed on the emergence of the supraorbital, infraorbital, mental and greater occipital nerves, and over the temporal muscles, always throughout the same sequence and from right to left. Measurements were carried out before and immediately after light stimulation and after 10 min of the second algometry. The final result for each site measured at each time-point was the mean of the three measurements. Light stimulation was carried out progressively until light-induced discomfort was reported, to a maximum of 20,000 lux. A heat-blocking glass protected patients' eyes. Migraineurs presented significant and persistent drops in pain perception thresholds after light stimulation, at all sites tested (P = 0.002 to < 0.0001). These drops were not seen in controls, in whom, conversely, a less significant increase was seen on right infraorbital and left temporal muscle sites. Our results indicate that in migraineurs, light may have a relevant role in trigeminal and cervical pain perception thresholds.

Self-reported photophobic symptoms in migraineurs and controls are reliable and predict diagnostic category accurately

OBJECTIVES

To assess the reliability of self-reported photophobia across different patient populations and to examine how visual stress thresholds and photophobic symptoms may be predictive of diagnosis.

BACKGROUND

Relatively little is known about interictal photophobia in migraine. In particular, the variability of photophobia across different patient groups has not previously been studied, and a pathophysiological hypothesis to account for the symptoms is not agreed upon.

METHODS AND RESULTS

Study 1 compared 99 self-selected Dutch patients and 101 headache-free controls using survey methods. Patients both with and without aura were significantly more likely to report symptoms, such as the wearing of sunglasses in normal daylight, consistent with interictal photophobia. Study 2 replicated these findings in a series of consecutive referrals to a headache clinic in the United States. Study 3 used a specially designed laboratory test to examine the threshold for visual stress in those patients who had participated in study 2. Visual stress thresholds were significantly lower in patients than in controls. A discriminant function analysis of data from both studies 2 and 3 showed that diagnostic category (migraine; control) could be predicted from photophobic symptoms and visual stress thresholds at a level significantly better than chance.

CONCLUSIONS

We suggest that interictal photophobia is common in migraine and similar across different patient populations. One pathophysiological hypothesis is that interictal photophobia is associated with cortical hypersensitivity to stimulation. The predictive validity of interictal photophobic symptoms suggests that clinical diagnosis may be aided by questioning the patient about light sensitivity in the period between attacks.

Allergic and immunologic disorders of the eye. Part I: immunology of the eye

Immuno-ophthalmology evolved during the 20th century as a subspecialty linking ophthalmologists and immunologists. This emerging subspecialty has focused on the use of immunology to better understand and treat ocular disorders. To help the allergist/clinical immunologist better appreciate the growing field of immuno-ophthalmology, this 2-part review series (Part II: Ocular Allergy will appear in the December issue of the Journal) will provide an overview of the impact that immunology has had on our understanding and treatment of allergic and immunologic eye diseases. The current review will focus on mechanisms by which mast cells, T cells, eosinophils, cytokines, and other inflammatory constituents contribute to the unique features of eye disease and their link to allergic responses that occur in other organs of the body.

Ocular effects of adrenomedullin

The purpose of this study was to determine the expression and effects of adrenomedullin (AM), a novel vasodilator peptide, in the eye. Expression of AM mRNA was examined in the rat iris-ciliary body using reverse transcription-polymerase chain reaction (RT-PCR). In rabbits, intraocular pressure (IOP) was measured periodically after intravitreal injection (20 microl) of AM (10(-7)-10(-4)m) into one eye. In separate groups of rabbits, 30 min after intravitreal injection of either AM-(22-52) (10(-3)m), a specific AM receptor antagonist, or CGRP-(8-37) (10(-3)m), a CGRP1 receptor antagonist, into one eye, AM (10(-6)m) was injected into both eyes, and IOP was measured. Using different rabbits, aqueous protein and cAMP concentrations were determined 6 hr after injection of AM. Expression of AM mRNA was detected in the rat iris-ciliary body. In rabbits, intravitreally administered AM (10(-6)-10(-4)m) profoundly lowered IOP, and the maximum effect was observed at 4-8 h. The ocular hypotensive effect of AM was dose-dependent (10(-7)-10(-4)m). Pretreatment with CGRP-(8-37) did not significantly inhibit the ocular hypotensive effect of AM (10(-6)m), whereas pretreatment with AM-(22-52) completely abolished it. AM (10(-6)m) did not significantly affect aqueous protein concentration. The higher dose of AM (10(-5)m) induced a significant increase in aqueous protein, which was not associated with an increase in the aqueous cAMP content and was significantly inhibited by AM-(22-52) and CGRP-(8-37). These results demonstrate that AM is expressed in the iris-ciliary body and decreases IOP mainly via specific AM receptors, and suggest that AM may play a role in controlling IOP.

Influence of ophthalmic nerve fibers on choroidal blood flow and myopic eye growth in chicks

Ophthalmic sensory nerve fibers containing substance P and calcitonin gene-related peptide' innervate the choroid in mammals and are known to vasodilate choroidal blood vessels. The avian choroid is also innervated by ophthalmic nerve fibers containing substance P and calcitonin gene-related peptide. The present studies were carried out to determine the influence of these sensory fibers on choroidal blood flow in birds and characterize their interaction with manipulations affecting eye growth. In these studies, ChBF was measured using laser Doppler flowmetry in both eyes in the following groups of birds: (1) normal chicks; (2) chicks with right optic nerve transected for 2 weeks; (3) chicks with right optic nerve transected and a goggle over the right eye for 2 weeks; and (4) chicks with right optic and ophthalmic nerves transected and a goggle over the right eye for 2 weeks. The eyes were refracted and various ocular dimensions measured after the blood-flow measurements. It was found that optic nerve transection reduced ChBF to 30% of normal. Placing a goggle (which increases ocular temperature by 4 degrees C) over an optic nerve transected eye nearly doubled choroidal blood flow over that in an optic nerve transected eye without a goggle. Additional transection of the ophthalmic nerve in a goggled optic nerve-transected eye, yielded choroidal blood flow that was indistinguishable from that in a nongoggled optic nerve-transected eye. Optic nerve transection had a slight stunting effect on axial growth of the eye. While myopic axial elongation was observed in goggled eyes with the optic nerve cut, the extent of myopia was less than in normal goggled eyes. Ophthalmic nerve transection further reduced the myopia induced by goggling in an optic nerve cut eye. These results suggest that ophthalmic nerve input to the choroid exerts a vasodilatory influence, which is activated in a goggled eye. This increased choroidal blood flow may be in response to elevated ocular temperatures caused by the goggling and this increase appears to be masked in goggled eyes with an intact optic nerve by the reduction in choroidal blood flow normally accompanying myopic eye growth. Our results thus show that the induction of myopic eye growth (as in our optic nerve cut eyes with a goggle) need not be accompanied by a decrease in choroidal blood flow from the baseline no-goggle condition (in this case, with the optic nerve cut).

Cellular and plasma fibronectin in the aqueous humour of primary open-angle glaucoma, exfoliative glaucoma and cataract patients

PURPOSE

To compare the concentrations of cellular fibronectin (cFN), plasma fibronectin (pFN), tenascin and calcitonin gene-related peptide (CGRP) in the aqueous humour in primary open-angle glaucoma (POAG), exfoliative glaucoma (EXFG) or cataract (control group).

METHODS

The concentrations were determined by enzyme-linked immunoassays in the aqueous humour of patients with EXFG (n = 26), POAG (n = 29) or cataract (control group, n = 13).

RESULTS

The pFN concentrations of the three patient groups differed significantly from each other (p = 0.0004 in a non-parametric analysis of variance). In multiple comparisons EXFG patients showed significantly higher pFN levels than POAG patients (p < 0.05) or cataract patients (p < 0.01). the cFN level was also significantly higher in EXGF patients than in POAG patients (p < 0.05) or cataract patients (p < 0.05). The pFN or cFN concentrations of the POAG group did not differ from those of the control group. Neither tenascin nor CGRP was detected in the aqueous humour of any of our patients.

CONCLUSIONS

The significantly higher aqueous humour pFN concentration in exfoliative glaucoma may be a consequence of disruption of the blood-aqueous barrier and may further add to an increased outflow resistance.

Binding of CGRP analogs and their effect on adenylate cyclase activity in porcine iris-ciliary body

The structure-activity relationship of the calcitonin gene-related peptide (CGRP) in the porcine iris-ciliary body was studied using different CGRP analogs. The receptor binding affinity is located mainly in the carboxyterminal end of the CGRP peptide while the ability to stimulate adenylate cyclase (AC) enzyme is mainly in the aminoterminal end of the peptide. The binding of CGRP analogs was also found to be temperature-dependent. Changes in the alpha-helical region or in the beta-turn, as well as replacements of threonine-4, asparagine-25 or asparagine-26, reduce the binding affinity already at +4 degrees C. Truncated aminoterminus, changes in the loop region between cysteines 2 and 7, and especially in threonine 6, have for their part an important role in maintaining AC-stimulating activity.

Effect of intracameral and intravitreal injection of calcitonin gene-related peptide on the intraocular pressure and outflow facility of aqueous humor in the rabbit

After intracameral injection calcitonin gene-related peptide has been demonstrated to break the blood aqueous barrier and increase intraocular pressure in rabbits. However in cats, calcitonin gene-related peptide decreases intraocular pressure by increasing the outflow facility of aqueous humor. In the present study, the effect of intracameral injection of calcitonin gene-related peptide on the outflow facility in rabbits has been investigated and the intraocular pressure and outflow facility were measured following intravitreal administration of calcitonin gene-related peptide. The results demonstrate that in spite of the apparent pseudofacility component caused by a breakdown of the blood aqueous barrier also the true trabecular outflow is probably increased in the rabbit eye after intracameral injection of calcitonin gene-related peptide. The intravitreal administration of calcitonin gene-related peptide leaves the blood aqueous barrier intact and causes an increase in the outflow facility of aqueous humor with a concomitant long-lasting decrease in intraocular pressure.

Peptidergic innervation of the rat cornea

Corneal nerves regulate corneal epithelial integrity, proliferation, and wound healing. The mechanisms by which the nerves mediate their effects remain poorly understood; however, the release of biologically active neuropeptides has been hypothesized. The purpose of the current investigation was to determine the relative densities, distribution patterns, and origins of rat corneal nerves containing each of eight different neuropeptides, calcitonin gene-related peptide (CGRP), substance P (SP), galanin (GAL), neuropeptide Y (NPY), methionine-enkephalin (M-ENK), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), and cholecystokinin (CCK). In the first set of experiments, immunohistochemical demonstrations of the above neuropeptides were performed on free-floating corneal sections cut tangential to the corneal surface. The results showed that six of the peptides, CGRP, SP, GAL, NPY, M-ENK, and VIP were present in rat corneal nerves. The innervation patterns of corneal nerves containing each of these six peptides were then documented by mapping all fibers in serial sections from select corneal quadrants onto a series of line drawings by using a drawing tube. In the second set of experiments, the origins of the corneal peptidergic nerve fibers were determined by selective ocular denervations. Unilateral combined sensory and sympathetic ocular denervations or unilateral sympathetic ocular denervations were performed in adult rats by transecting the ophthalmomaxillary nerve and/or removing the superior cervical ganglion. After 5-7 days, each of the ipsilateral corneas was sectioned and processed immunohistochemically for the presence of one of the six peptides found in experiment one, and the fibers that survived the ocular denervations were plotted onto line drawings. Ocular denervations revealed that corneal peptidergic nerves have sensory (CGRP, SP, and GAL), sympathetic (NPY), and parasympathetic (GAL, NPY, M-ENK, and VIP) origins. The results of this investigation have shown that the peptidergic innervation of the rat cornea is more extensive and complex than previously reported. This is the first investigation to show the presence of GAL in the rat cornea, and the first to demonstrate the presence of NPY-, VIP-, and M-ENK-IR nerve fibers in the cornea of any species.

Ocular inflammation induced by electroconvulsive treatment: contribution of nitric oxide and neuropeptides mobilized from C-fibres

1. Electroconvulsive treatment (ECT) of rabbits produced ocular inflammation consisting of conjunctival hyperaemia, miosis and protein extravasation into the aqueous humour, reflected by the so-called aqueous flare response (AFR): the maximal reduction in pupil size was 3.8 +/- 0.1 mm (s.e. of mean, n = 16) while the maximal AFR was 28.1 +/- 2.8 (arbitrary units). 2. ECT also caused release of substance P (SP), pituitary adenylate cyclase-activating peptide (PACAP)-27, -38 and calcitonin gene-related peptide (CGRP). The concentrations of SP and CGRP in the aqueous humour of normal, untreated eyes were 10.6 +/- 1.4 and 117.4 +/- 12.4 pmol l-1, respectively, while the concentrations of PACAP-27 and -38 were below the detection limit. After ECT the concentrations of SP, PACAP-27, -38 and CGRP were 65.0 +/- 9.6, 46.9 +/- 8.4, 50.2 +/- 5.4 and 1109.9 +/- 133.1 pmol l-1, respectively (s.e. of mean, n = 12). Conceivably, ECT evoked an antidromic activation of sensory neurones in the trigeminal ganglion with the consequent release of neuropeptides from C-fibres in the uvea and the development of neurogenic inflammation. 3. Rabbits received the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 200 mg kg 1, i.v.). This pretreatment inhibited the ECT-evoked conjunctival hyperaemia, miosis and AFR: under these circumstances the maximal reduction in pupil size was 1.9 +/- 0.1 mm while the maximal AFR was 2.7 +/- 0.9 (n = 16). L-NAME also inhibited the ECT-evoked release of SP, PACAP-27, -38 and CGRP into the aqueous humour; the concentrations of SP and CGRP were 13.2 +/- 1.5 and 204.8 +/- 33.5 pmol l-1, respectively, while PACAP-27 and -38 were below the detection limit (n = 12). 4. The ECT-evoked miosis was also inhibited by pretreatment with the tachykinin receptor antagonist D-Pal9 spantide 11 (90 nmol, intravitreal injection); under these circumstances the maximal reduction in pupil size was only 0.7 +/- 0.03 mm, indicating an important role for SP in the miotic response. Pretreatment of the eye with capsaicin, which is known to cause functional ablation of C-fibres, inhibited the conjunctival hyperaemia, miosis and AFR by 40-50%; the maximal reduction in pupil size being 2.2 +/- 0.2 mm and the maximal AFR 13.8 +/- 2.1 (arbitrary units) (n = 8). 5. The results suggest (1) that ECT evokes ocular inflammation through antidromic C-fibre activation; (2) that SP contributes to the ECT-evoked miosis; and (3) that NO contributes to the antidromic C-fibre activation and possibly to the vascular responses mediated by the C-fibre transmitters.

Ganglionic axons in motor roots and pia mater

In addition to motor axons and preganglionic axons, ventral roots contain unmyelinated or thin myelinated sensory axons and postganglionic sympathetic axons. It has been said that ventral roots channel sensory axons to the CNS. However, it now seems that these axons end blindly, shift to the pia or loop and return towards the periphery and that these units reach the CNS via dorsal roots. Sensory ventral root axons project from a variety of somatic or visceral receptors; some of them are third branches of dorsal root afferents and some seem to lack a CNS projection. Many ventral root afferents contain substance P (SP) and/or calcitonin gene-related peptide (CGRP). These fibres are not affected by neonatal capsaicin treatment and they cannot induce radicular or pial extravasation. Some thin ventral root axons are sympathetic and relate to blood vessels. Afferents containing SP and/or CGRP and sympathetic axons also occur in the spinal pia mater. The sensory axons mediate pain. They might also have vasomotor, tissue-regulatory and/or mechanoreceptive functions. The motor roots of cranial nerves IV, VI and XI contain unmyelinated axons arranged like in ventral roots outside the autonomic outflow. However, the motor root of cranial nerve V channels some unmyelinated axons into the CNS. The occurrence of thin axons in ventral roots and pia mater changes during development and ageing. After peripheral nerve injury, ipsilateral ventral roots and pia are invaded by new sensory and postganglionic sympathetic axons.

Influence of age and anti-nerve growth factor treatment on the sympathetic and sensory innervation of the rat iris

We have investigated alterations in the nerve supply to the iris of aged rats and the role of endogenous nerve growth factor in these changes. The overall density of nerve fibres, and the density of calcitonin gene-related peptide containing sensory nerves, were decreased by over 20% on the aged iris, as measured by computerized image analysis on immunostained preparations, while the density of sympathetic innervation was maintained. Whilst the majority of nerves supplying the iris (sympathetic, sensory and parasympathetic) are known to respond to exogenous nerve growth factor during development and in adulthood, the role of endogenous, target-derived nerve growth factor in nerve maintenance in maturity and old age awaits confirmation. Our results showed that localized treatment with anti-nerve growth factor of iridial nerve terminals did not affect sympathetic or sensory neurons in young rats, but caused a dramatic reduction of sympathetic nerve density on irides of old rats. The effect of anti-nerve growth factor treatment on the sensory innervation of old irides was less obvious. We conclude that aged sympathetic nerves are more susceptible to nerve growth factor deprivation than young ones, or than young or aged sensory neurons, perhaps as a result of reduced responsiveness to nerve growth factor with age. Since sympathetic innervation is maintained, whilst sensory innervation is decreased in the aged iris, age-related changes in innervation are unlikely to be due to altered availability of endogenous nerve growth factor.

The contribution of nitric oxide to endotoxin-induced ocular inflammation: interaction with sensory nerve fibres

1. The actions of nitric oxide (NO) have been investigated in an endotoxin-evoked ocular inflammatory model in the rabbit, with particular emphasis on the relationship between NO, sensory nerves (C-fibres) and the C-fibre neuropeptides, calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase activating peptide (PACAP). 2. Endotoxin, injected intravitreally, evoked inflammatory responses, i.e. conjunctival hyperaemia, miosis and protein extravasation, reflected by the aqueous flare response (AFR). In control rabbits, the maximum AFR was 66.5 +/- 9.5 (arbitrary units). Pretreatment with the NO synthase (NOS) inhibitor, NG-nitro-L-arginine (L-NAME, 200 mg kg-1) given by intravenous injection, inhibited the endotoxin-evoked responses; the AFR was 16.5 +/- 1.9 (n = 8, P < 0.001) and the conjunctival hyperaemia was abolished. 3. Endotoxin-evoked ocular inflammation is associated with the release of CGRP and PACAP from C-fibres. In the eyes challenged with endotoxin, the concentrations of PACAP-27, -38 and CGRP in the aqueous humour were 58.2 +/- 10.9, 54.4 +/- 12.4 and 5526 +/- 519 (pmoll'), respectively. L-NAME inhibited the release of PACAP-27, -38 and CGRP; the concentrations were 14.3 +/- 2.5, 13.5 +/- 2.5 and 510 +/- 67 (pmoll-1), respectively (n = 8, P < 0.01 or 0.001). 4. Intravitreal injection of 0.3 nmol CGRP induced conjunctival hyperaemia and AFR; the maximum AFR was 140.2 +/- 11.4. L-NAME suppressed the response induced by CGRP; the AFR was 23.4 +/- 5.5 (n = 8, P < 0.001). L-NAME abolished the conjunctival hyperaemia induced by PACAP-27 and -38 (0.3 nmol) and reduced the AFR. 5. The inflammatory cells that infiltrated the uvea, cornea and aqueous humour in large numbers in response to intravitreal injection of endotoxin were found to express inducible NOS. L-NAME prevented the appearance of such cells. 6. Our findings suggest that NO plays an important role in the endotoxin-evoked ocular inflammation in the rabbit: NO activates C-fibres causing release of C-fibre neuropeptides into the aqueous humour. In addition, NO mediates scme of the ocular effects of CGRP and PACAP, since L-NAME suppressed the AFR induced by these peptides.

Release of preprotachykinin-A mRNA from rabbit iris upon C-fibre stimulation

It is usually said that axons and nerve terminals do not contain messenger RNA (mRNA) and that peptide transmitters are packaged in granules and transported towards the periphery of the neuron. However, several recent reports challenge this view by showing evidence of the existence of mRNA in axons. In the present study, we demonstrate the existence of mRNA coding for gamma-preprotachykinin-A in rabbit iris by Northern blot analysis and Southern blot analysis of the polymerase chain reaction (PCR)-amplified products. Interestingly, mRNA coding for gamma-preprotachykinin-A was detected also in aqueous humor from eyes exposed to injury (infrared irradiation of the iris or retrobulbar injection of the C-fibre excitant capsaicin), but not from contralateral eyes and normal eyes of untreated rabbits. Our results suggest that the mRNA coding for gamma-preprotachykinin-A occurs in C-fibres in the iris and that it is released into the aqueous humor together with tachykinins in response to C-fibre stimulation.

Calcitonin gene-related peptide induced relaxation of the rabbit iris dilator muscle

Calcitonin gene-related peptide (CGRP) and Substance P (SP) -immunoreactive nerves have been found in the anterior uvea of various mammalian species. Although SP is known to play a major role in control of pupil motility in rabbits, little is known about the effect of CGRP on the iris smooth muscles. We isolated iris sphincter and dilator muscles from rabbit eyes and investigated the mechanical responses and intracellular cyclic AMP (cAMP) levels in these muscles. CGRP (up to 0.1 microM) had no effect on either the resting muscle tone or the amplitude of contraction evoked by field stimulation of the sphincter. On the other hand, CGRP (0.1 microM) relaxed dilator muscle which had been pre-contracted by phenylephrine and reduced the amplitude of contraction evoked by field stimulation. These responses were antagonized by CGRP (8-37), a CGRP antagonist. The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), dose-dependently inhibited the contraction evoked by field stimulation. However, 3 microM IBMX had no effect on CGRP inhibition of twitch contraction in this preparation. CGRP had little effect on cAMP production in dilator muscle either with or without IBMX. In conclusion, the miosis which occurs during an ocular inflammatory response, when both CGRP and SP are thought to be released from terminals of sensory neurons, results from CGRP relaxation of the dilator and from the strong contractile effect of SP on the sphincter. Adenylate cyclase activation does not seem to be involved in the relaxant effect of CGRP on the dilator.

CGRP increases the rate of corneal re-epithelialization in an in vitro whole mount preparation

A number of studies have localized CGRP to nerves in the cornea and iris, and it is thought that CGRP, along with other neuropeptides, is involved in pain sensation. It is also possible that CGRP could mediate trophic influences between nerve endings and corneal epithelium. This investigation utilized an in vitro rabbit corneal whole mount preparation to study the effect of topical 2.5 microM CGRP application on epithelial wound healing rates of 5 mm diameter epithelial wounds. CGRP (2.5 microM) was applied topically to 5 mm epithelial wounds at 0, 4, 16, 20, 24, 28, 40, 44, 48, 52, 56, 64, 68, and 72 hours after wounding and healing was visualized with fluorescein. CGRP was found to increase the epithelial wound healing rate by 25%, from 51 +/- 3 microns/hr for the control corneas, to 64 +/- 2 microns/hr for CGRP-treated corneas (mean +/- standard error, n = 10). Histological examination of the corneas following healing showed that the epithelium of the CGRP-treated corneas healed in a similar manner as in the control corneas. These findings may have clinical utility for the understanding and treatment of corneal and other epithelial wounds.

Role of nitric oxide (NO) in ocular inflammation

1. The actions of nitric oxide (NO) have been investigated in the rabbit eye, with particular emphasis on the relationship between NO and C-fibres and on those effects of NO that may be of importance in the inflammatory response to C-fibre stimulation. 2. The NO synthase inhibitor, NG-nitro-L-arginine (L-NAME; 10-200 mg kg-1), but not the inactive analogue D-NAME (200 mg kg-1), was found to block the inflammatory response induced by infrared irradiation of the iris in a dose-dependent manner. The inhibitory effects of L-NAME (200 mg kg-1) were partially reversed by L-arginine (500 mg kg-1), but not by D-arginine (500 mg kg-1). 3. L-NAME (200 mg kg-1) virtually abolished the ocular effects of intravitreal injection of calcitonin gene-related peptide (CGRP) (0.3 nmol). 4. The concentration of CGRP in aqueous humour from untreated rabbit eyes was 0.1 +/- 0.001 nmol l-1. Irradiation of the iris raised the CGRP concentration to 8.9 +/- 1.5 nmol l-1. L-NAME (200 mg kg-1) greatly suppressed the irradiation-evoked release of CGRP, the concentration in the aqueous humour being 1.2 +/- 0.2 nmol l-1 (P < 0.001). L-Arginine reversed the L-NAME-induced inhibition of release of CGRP, the concentration of CGRP in the aqueous humour being 9.7 +/- 0.6 nmol l-1. 5. In addition, a NO donor, sodium nitroprusside (0.9 mumol), was found to raise the concentration of CGRP in the aqueous humour (14.8 +/- 0.8 nmol l-1) and to induce symptoms of ocular inflammation. The elevation in concentration of CGRP induced by sodium nitroprusside was not affected by L-NAME (200 mg kg-1) (14.5 +/- 1.2 nmol l-1). Ocular responses were not inhibited by L-NAME. 6. Our findings suggest that NO plays an important role in ocular inflammation by activating C-fibres (directly or indirectly) and by mediating CGRP-induced responses.

Distribution and effects of pituitary adenylate cyclase-activating peptide in the rabbit eye

Pituitary adenylate cyclase-activating peptide (PACAP)-like immunoreactivity was demonstrated by immunocytochemistry together with calcitonin gene-related peptide (CGRP)-like immunoreactivity in small to medium-sized neurons in the trigeminal ganglion and in nerve fibers in the iris, ciliary body, cornea, choroid and sclera of the rabbit eye. The regional distribution of PACAP-27- and PACAP-38-like immunoreactivity in the eye was studied by radioimmunoassay: the highest concentrations were found in the iris sphincter and ciliary body. The distribution pattern resembled that of CGRP-like immunoreactivity, which is a well-known constituent of sensory C-fibre neurons. Intravitreal injection of PACAP-27 or PACAP-38 induced conjunctival hyperemia, swelling of the anterior segment of the eye, miosis and breakdown of the blood-aqueous barrier, manifested as a marked aqueous flare response. Tetrodotoxin pretreatment inhibited the conjunctival hyperemia, the swelling of the anterior segment of the eye, and the miosis but not the aqueous flare response. The concentration of PACAP-like immunoreactivity in the aqueous humor was increased greatly following infrared irradiation of the iris, topical application of formaldehyde to the cornea, or intravitreal injection of endotoxin or bovine serum albumin. Also the concentration of CGRP-like immunoreactivity in the aqueous humor was increased greatly. Both in vivo and in vitro studies showed that capsaicin caused a parallel release of PACAP-like immunoreactivity and CGRP-like immunoreactivity from the uvea. Injection of PACAP-27 and PACAP-38 resulted in the release of CGRP-like immunoreactivity (and PACAP-like immunoreactivity) into the aqueous humor and PACAP-27 and PACAP-38 were also found to evoke tachykinin-mediated contractions of the isolated iris sphincter muscle, indicating that PACAP induces positive feedback on C-fibres. Thus, PACAP is a sensory neuropeptide in the eye. Since the PACAP-induced ocular responses mimicked the symptoms of inflammation, and since the PACAP-like immunoreactivity concentration in the aqueous humor was greatly increased following noxious stimulation, we suggest that it takes part in the inflammatory responses of the rabbit eye.

Local anesthetic effects in the presence of chronic osteomyelitis (necrosis) of the mandible: implications for localizing the etiologic sites of referred trigeminal pain

The aims of this study were: (1) to demonstrate how reproducible variations in incomplete anesthesia of the inferior alveolar nerve can be used as a guide to locate the etiologic sites of referred trigeminal pain emanating from the mandible; (2) to describe the salient histopathologic features of a lowgrade, nonsuppurative osteomyelitis seen in this patient population. Forty-six patients with idiopathic facial pain were subjected to a specific protocol of local anesthetic injections to sequentially block branches of the mandibular nerve to determine the effects on his/her pain. If this significantly reduced or altered the pain on three separate appointments, then exploratory surgery was conducted near identified zones of unanesthetized gingiva. Blocking (92%), bridging (4%), and divergence (4%) were observed patterns of anesthetic resistance of the mucogingival tissues used to categorize the incomplete anesthesia. A 100% correlation was found between the identified zones of unanesthetized gingiva and the discovery of intramedullary pathology. Medullary fibrosis with ischemic and degenerative changes in the cancellous bone were common findings, along with chronic inflammatory cell infiltrates and clusters of lymphocytes. It is concluded that Ratner's method of diagnostic anesthesia be implemented when searching for occult pain producing pathology of the jaws.

Substance P gene expression in acute experimental colitis

We have previously shown (Gastroenterology, 101 (1991) 1211-1219), that substance P (SP) decreases early in the colon muscle layer after induction of colitis in rabbits. Since the SP content in the colonic muscle layer was unchanged by sensory denervation with capsaicin, we assume that SP is located predominantly in intrinsic neurons of the colon, and that the decrease of SP during inflammation reflects changes in intrinsic SP content. However, damage of SP neurons by inflammation would be another likely explanation for the decrease in SP content. The aim of this study was to determine SP gene expression in intrinsic (colonic muscle layer) and extrinsic (dorsal root ganglia, DRG) neurons to prove that SP transcription is preserved during colitis as an indicator of neuronal integrity. Colitis was induced in adult white New Zealand rabbits by formalin enemas (4 ml of 0.4% formalin) followed by 0.85 ml immune complex i.v. 2 h later. The animals were sacrificed 48 h after induction of colitis, and SP content and gene expression were determined by radioimmunoassay (RIA) and Northern blot analysis, respectively. Immunoreactive SP was reduced by 40% in the colon muscle layer and by 60% in the dorsal root ganglia (L4-S4) in the animals with colitis compared to controls without colitis. In contrast to the protein data, SP gene expression was not significantly altered in the colon muscle layer and the dorsal root ganglia 48 h after induction of inflammation compared to the control tissue. The preserved SP gene expression suggests that the intrinsic and extrinsic SP neurons are viable in this inflammatory model. The decreases of immunoreactive SP in the colonic extracts and the DRG after induction of colitis suggest that SP is released from extrinsic and intrinsic neurons during inflammation.

Localization of calcitonin gene-related peptide binding sites in the eye of different species

The localization of calcitonin gene-related peptide (CGRP) binding sites in the eye of monkey, pig, cat and guinea pig was studied by autoradiography. Specific binding of CGRP was found in ciliary muscle, ciliary processes and limbal conjunctiva in all tested species. Furthermore, specific binding sites of CGRP was found in the choroidea of monkey, pig and guinea pig, in the iris of pig, cat and guinea pig, in the retina of pig and in the anterior chamber angle of cat. The number of specific binding sites varied depending on the tissue and species. The present study shows that there are specific binding sites of CGRP in the eye of monkey, pig, cat and guinea pig. CGRP binding sites found in vascular system of ciliary body, choroidea and iris further demonstrates the role of CGRP as a vasoregulatory peptide. Binding sites in the ciliary muscle, in the limbal conjunctiva and in the chamber angle area may indicate a role in the regulation of ciliary muscle tone, epithelial cell regeneration and aqueous humour outflow.

Vasodilation in porcine ophthalmic artery: peptide interaction with acetylcholine and endothelial dependence

Co-activation of cranial perivascular sensory and parasympathetic fibres in vivo induces simultaneous release of several vasodilatory substances with neurotransmitter or neuromodulatory roles. The role of the endothelium and possible interactions between such substances are poorly understood. The objective of this study was therefore to investigate these aspects with the sensory dilator calcitonin gene-related peptide (CGRP) and the parasympathetic dilators acetylcholine (ACh) and vasoactive intestinal peptide (VIP) in isolated porcine ophthalmic artery. Whilst ACh induced relatively rapid, endothelium-dependent dilation, CGRP and VIP induced slower dilations. Both CGRP and VIP were found to have partial endothelium-dependence in this artery. The simultaneous addition of ACh with CGRP potentiated the relaxation induced by CGRP, as has already been shown for substance P. ACh did not potentiate VIP relaxation, but the results generally indicate a potential role for ACh in initiating rapid dilation prior to strong, sustained relaxation by CGRP or VIP. The potential role of the endothelium and of substances like ACh or substance P in enhancing the rate of dilation of neuropeptides inducing strong and sustained relaxation is discussed.

Increased release of immunoreactive calcitonin gene-related peptide (CGRP) in tears after excimer laser keratectomy

The purpose of the study was to quantify the neuropeptide calcitonin gene-related peptide (CGRP) in normal human tear fluid and to determine the effect of photorefractive excimer laser keratectomy (PRK) on its release in tears. CGRP was assayed in tear fluid samples using an enzyme immunoassay (detection limit 0.2 micrograms ml-1). Tear-fluid samples were collected preoperatively, 1, 2 and 7 days after PRK and analysed for CGRP. The changes in tear-fluid secretion were also monitored. The intra-assay variation was 3.0-7.0%. Despite the marked hypersecretion of tears, the concentration of CGRP did not decrease following PRK indicating a concomitant increase in CGRP release by sensory nerves and/or lacrimal gland(s). Consequently, the release of CGRP in tears increased from 197.9 +/- 36.6 ng min-1 (mean +/- S.E.M.) to 1723.0 +/- 402.4 ng min-1 (P < 0.01) on day 1, and to 2304.2 +/- 561.1 ng min-1 (P < 0.01) on day 2. On day 7, only minor elevation (377.02 +/- 83.24 ng min-1) was observed. It is concluded that CGRP is a component of normal human tear fluid. The ocular irritation response related to the photoablation induces an enhanced release of CGRP in tears. As a compound present in corneal sensory nerves CGRP may have a role in wound-healing.

Autoimmunity in the eye and its regulation

Recent studies have provided new information concerning the development of autoimmune-mediated intraocular inflammation (uveitis) and the mechanisms that suppress this sight-robbing process. Newly collected data have led to several interesting advances: the discovery of additional uveitogenic antigens and novel uveitogenic reactions; dissection of the early steps of the pathogenic process; identification of the subsets of lymphocytes that selectively accumulate in the inflamed eye; analysis of the development of tolerance against sequestered antigens in the eye; elucidation of the cellular and molecular events of the anterior chamber-associated immune deviation, the major immunoregulatory mechanism in the eye; the capacity of this mechanism to inhibit and even treat uveitis; and examination of the mechanisms whereby oral tolerance inhibits ocular inflammation.

Peripheral neural circuits regulating IOP? A review of its anatomical backbone

The peripheral nervous system is classically separated into a somatic division containing both afferent and efferent pathways and an autonomic division composed of efferents only. The somatic afferent division is divided in A- and B-neurons. The B-neurons are supposed to be autonomic afferents as part of a reflex system involved in homeostasis. Recent data obtained by neuronal tracing and immunohistochemical experiments concerning the eye related peripheral nervous system endorse the existence of these peripheral reflex systems. Somatic afferents of trigeminal origin synaptically innervate parasympathetic neurons in the pterygopalatine ganglion. This probably represents a pathway mediating autonomically regulated ocular activity in response to sensory stimulation. In addition, it has been hypothesized that trigeminal sensory nerve fibres have an efferent function in response to noxious stimuli e.g. the ocular injury response. Sympathetic nerve fibres originating in the superior cervical ganglion course through the trigeminal and pterygopalatine ganglion without forming direct synaptic contacts. These fibres, however, contain clusters of vesicles suggesting some kind of interneural communication. Parasympathetic nerve fibres of pterygopalatine origin course through the ciliary ganglion. These nerve fibre terminals also contain clusters of vesicles without direct synaptic contacts. Experimental data concerning the distribution of neuropeptides revealed a more detailed knowledge of the anterior eye segment innervation. These experimental data are subject to some debate. The pros and cons of different techniques are discussed. Neural circuits regulating IOP have long been postulated. The possible role of peripheral reflex systems in the regulation of IOP is discussed.

Adjuvant-induced inflammation of rat paw is associated with altered calcitonin gene-related peptide immunoreactivity within cell bodies and peripheral endings of primary afferent neurons

Local inflammation is associated with profound changes in the biochemistry and physiology of primary afferent nerve fibers and the central neurons responding to their signals. In some tissues, the neural changes accompanying inflammation include sprouting and cytochemical changes that are delayed several days after the initial injury. In the present study, we have analyzed the effect of complete Freund's adjuvant (CFA)-induced inflammation in the rat paw on calcitonin gene-related peptide (CGRP) immunoreactivity (IR) in dorsal root ganglia and within tissue of the inflamed paw. We quantified the CGRP-IR within the L1, L4, and L6 ganglia, and in ankle, midpaw, joint and toe tissues. Analysis of the processed tissue revealed a significant increase in the percentage of CGRP-positive cells within L4 dorsal root ganglia ipsilateral to an inflamed hindpaw six days after administration of CFA. There was a parallel increase in the number and staining density of detectable CGRP-immunoreactive fibers in periarticular and perivascular tissues of the inflamed digits and inflamed ankle. The other tissues of the paw, including epidermis and the regions surrounding the abcesses, did not have detectable changes in CGRP-immunoreactive fibers, despite tissue swelling and dystrophic changes in the foot that included loss of mast cell staining. These data demonstrate that local inflammation of the rat paw has delayed influences on the peripheral nervous system, in addition to a number of previously characterized acute effects. The alterations of CGRP-IR were focused around specific tissue types, such as joints and subdermal blood vessels, and absent from others, such as epidermis or in the areas surrounding abscesses. This suggests production of local factors within reactive tissues that selectively interact with nerve fibers to induce changes in CGRP-IR within the fibers.

Central nervous system control of intraocular pressure

Normal intraocular pressure (IOP) is the result of an equilibrium between aqueous humor (AH) production, AH outflow and episcleral venous pressure. Most available antiglaucoma agents produce their effects by interacting with autonomic mechanisms (beta-blockers, epinephrine or parasympathomimetics). In contrast, the role of the central nervous system (brain and nerves) in the regulation of IOP remains unclear in view of the complex haemodynamic, metabolic or hormonal changes which occur under experimental conditions. In this paper, we discuss a basic understanding of the anatomic and physiological relationships between central nervous system and IOP and describe how the brain can affect functions in ciliary body and trabeculum meshwork.

Protective function of extrinsic sensory neurons in acute rabbit experimental colitis

BACKGROUND/AIMS

Sensory nerves appear to have a protective effect against acute injury in the gastric mucosa. Their function in the intestine is unclear.

METHODS

In this study an immune-complex model of colitis was used to induce inflammation in the distal colon with and without functional ablation of sensory neurons by capsaicin pretreatment.

RESULTS

Colitis was more severe in the capsaicin-pretreated group than in the vehicle group 48 and 96 hours after induction of colitis. Neutrophil infiltration, expressed as inflammatory index, was significantly increased to 4.25 +/- 0.4 vs. 1.83 +/- 0.5 at 48 hours and to 2.66 +/- 0.6 vs. 1.65 +/- 0.3 at 96 hours in the capsaicin group and the vehicle group, respectively. The microscopic ulcer index also was significantly increased in the capsaicin-pretreated group compared with the vehicle group (63.3 +/- 10.6 vs. 3.3 +/- 2.4 at 48 hours, 20.0 +/- 8.4 vs. 1.5 +/- 1.1 at 96 hours). Immunoreactive substance P (SP) and calcitonin gene-related peptide (CGRP) contents were decreased in extracts of inflamed compared with uninflamed colon.

CONCLUSIONS

These data suggest that sensory neurons have a protective role in an acute rabbit model of experimental colitis by release of sensory neuropeptides (SP, CGRP), which may modulate vascular tone and mucosal blood flow.

Substance P-, calcitonin gene-related peptide, growth-associated protein-43, and neurotrophin receptor-like immunoreactivity associated with unmyelinated axons in feline ventral roots and pia mater

The spinal pia mater receives a rich innervation of small sensory axons via the ventral roots. Other sensory axons enter the ventral roots but end blindly or turn abruptly in hairpin loop-like formations and continue in a distal direction. In the present study, the content of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, growth-associated protein (GAP-43)-, and low-affinity neurotrophin receptor protein (p75NGFr)-like immunoreactivity (-LI) associated with these different types of sensory axons was assessed with light and electron microscopic immunohistochemical techniques. In addition, the binding of antibodies against synthetic peptides representing unique sequences of residues in the products of the trk and trkB protooncogenes was analyzed. These genes encode membrane spanning proteins, which have been shown to constitute specific high affinity binding sites for several members of the nerve growth factor family of neurotrophic factors. The results of the present study imply that the ventral root afferents comprise several different types of sensory axons, which all contain SP-, CGRP-, GAP-43-, and p75NGFr-like immunoreactivities. In addition, at least some of the presumed sensory fiber bundles in ventral roots and the pia mater were immunoreactive for the trkB gene product. Moreover, leptomeningeal cells and nonneuronal cells of the ventral roots were shown to bind antibodies to both the trk and trkB gene products. The ventral root afferents seem to share their immunohistochemical pattern with pain-transducing axons at some other locations, such as the tooth pulp. The contents of SP- and CGRP-LI in sensory axons that reach the central nervous system (CNS) through the ventral root indicate that ventral root afferents may be involved in sensory mechanisms, such as the ventral root pain reaction, as well as in the control of the pial blood vessels. The demonstration of GAP-43 and neurotrophin receptor-immunoreactivities associated with unmyelinated fibers in ventral roots and the pia mater is discussed in relation to previous reports on postnatal plasticity in these axonal populations.

C-terminal calcitonin gene-related peptide fragments and vasopressin but not somatostatin-28 induce miosis in monkeys

The miotic effects of C-terminal calcitonin gene-related peptide (CGRP) fragments, somatostatin-28 and vasopressin have been evaluated with special attention being paid to possible interactions with cholecystokinin (CCK)A receptors. The peptides were injected intracamerally to anesthetized monkeys pretreated with indomethacin and atropine. CGRP-(32-37) induced a miosis with a potency 1000 times lower than that previously found with sulphated CCK-8. Two other fragments, CGRP-(30-37) and CGRP-(31-37), also had miotic properties. The CGRP-(32-37)-induced miosis was antagonized by the CCKA receptor antagonist loxiglumide. No contractile effect was elicited by 67 pmol-7.4 nmol somatostatin-28. Vasopressin (360 pmol) caused a small reduction in pupil size. Loxiglumide pretreatment did not affect the reduction in pupil size but a vasopressin receptor antagonist partly inhibited the response. The results indicate that CGRP-(32-37) is a miotic with low potency but high efficacy in the monkey eye, probably interacting with CCKA receptors, and that vasopressin is a mitotic with low potency and efficacy, probably acting via vasopressin receptors.