Corneal morphology and sensitivity in lattice dystrophy type II (familial amyloidosis, Finnish type).

PURPOSE: To describe the corneal abnormalities and to measure different modalities of corneal sensitivity in corneal lattice dystrophy type II (familial amyloidosis, Finnish type, also known as gelsolin-related amyloidosis and originally as Meretoja syndrome). METHODS: Twenty eyes of 20 patients were examined by in vivo confocal microscopy and noncontact gas esthesiometry. RESULTS: Pleomorphism of, and dense deposits between or posterior to, the basal epithelial cells were frequently observed, as well as a reduction of long nerve fiber bundles in the subbasal nerve plexus. The anterior stroma was altered in most cases, with fibrosis and abnormal extracellular matrix. In 15 corneas, thick anterior and midstromal filaments, corresponding to lattice lines, and in 11 corneas, thin undulated structures were observed. The average mechanical sensitivity threshold of 12 subjects was increased, and in the remaining 8 subjects there was no response, even to the highest intensity of stimuli used. Three patients did not respond to CO(2), 11 to heat, and 2 to cold, but those patients who responded had normal thresholds. Patients with more long nerve fiber bundles per confocal microscopic image had better mechanical and cold sensitivity than patients with fewer nerve fiber bundles. CONCLUSIONS: Lattice lines seem to be related to amyloid material and not to corneal nerves. However, the subbasal nerve density appears reduced, which results mainly in a decrease in mechanical and, to a lesser extent, thermal sensitivity. The location of stromal filaments and undulated structures changes with increasing age.

Arginine-rich peptides are blockers of VR-1 channels with analgesic activity.

Vanilloid receptors (VRs) play a fundamental role in the transduction of peripheral tissue injury and/or inflammation responses. Molecules that antagonize VR channel activity may act as selective and potent analgesics. We report that synthetic arginine-rich hexapeptides block heterologously expressed VR-1 channels with submicromolar efficacy in a weak voltage-dependent manner, consistent with a binding site located near/at the entryway of the aqueous pore. Dynorphins, natural arginine-rich peptides, also blocked VR-1 activity with micromolar affinity. Notably, synthetic and natural arginine-rich peptides attenuated the ocular irritation produced by topical capsaicin application onto the eyes of experimental animals. Taken together, our results imply that arginine-rich peptides are VR-1 channel blockers with analgesic activity. These findings may expand the development of novel analgesics by targeting receptor sites distinct from the capsaicin binding site.

Responses of nerve fibres of the rat saphenous nerve neuroma to mechanical and chemical stimulation: an in vitro study.

The response of neuroma nerve endings to different stimuli was studied in a saphenous nerve neuroma preparation in vitro. Electrical activity was recorded from 141 single fibres dissected of saphenous nerve. One-third (27 %) displayed spontaneous activity. Based on their response to mechanical and chemical stimuli, neuroma nerve fibres were classified as mechanosensory fibres (47.5 %), mechanically insensitive chemosensory fibres (17.0 %), polymodal nociceptor fibres (28.4 %) and unresponsive fibres (7.1 %). Mechanosensory and polymodal neuroma endings responded to von Frey hair stimulation either with a few impulses (phasic units) or a sustained discharge (tonic units). Polymodal units were additionally activated by at least one of the following stimuli: acidic solutions; a combination of bradykinin, prostaglandin E2, serotonin, substance P and histamine (all at 1 microM) plus 7 mM KCl (inflammatory soup); 600 mM NaCl and capsaicin. Low pH solutions increased the firing discharge of polymodal endings proportionally to the proton concentration. The 'inflammatory soup' evoked a firing response characterized by the absence of tachyphylaxis, which appeared when its components were applied separately. Both stimuli sensitized polymodal fibres to mechanical stimulation. Hypertonic NaCl (600 mM) and capsaicin (3.3 mM) induced a prolonged discharge that outlasted the stimulus duration. Mechanically insensitive chemosensory neuroma fibres exhibited responses to chemical stimuli analogous to polymodal fibres. They became mechanically sensitive after chemical stimulation. These findings show that neuroma nerve endings in the rat saphenous nerve neuroma in vitro are functionally heterogeneous and exhibit properties reminiscent of those in intact mechanosensory, polymodal and 'silent' nociceptor sensory afferents, including their sensitization by algesic chemicals.

Effects of oleoresin capsicum pepper spray on human corneal morphology and sensitivity.

PURPOSE: To examine the potential harmful effects on corneal structure, innervation, and sensitivity of a spray containing the neurotoxin capsaicin (oleoresin capsicum, OC). METHODS: Ten police officers who volunteered for the study were exposed to OC. Clinical signs were assessed. Corneal sensitivity was measured using a Cochet-Bonnet or a noncontact esthesiometer that provides separate measurements of mechanical, chemical, and thermal sensitivity. Tear fluid nerve growth factor (NGF) was measured. Corneal cell layers and subbasal nerves were examined by in vivo confocal microscopy. The subjects were examined before application and 30 minutes, 1 day, 1 week, and 1 month after OC exposure. RESULTS: OC spray produced occasional areas of focal epithelial cell damage that healed within 1 day. Each eye showed conjunctival hyperemia and in two subjects, mild chemosis. All except one eye had unchanged best corrected visual acuity (BCVA). A transient decrease (day 1) of mechanical sensitivity was observed with the Cochet-Bonnet esthesiometer. With the gas esthesiometer, mechanical sensitivity remained below normal values for 7 days. Chemical sensitivity to CO2 was high for as much as 1 day and decreased below normal 1 week later, whereas sensitivity to cold was unaffected. Two subjects had measurable tear NGF that increased after exposure. Basal epithelial cell morphology suggested temporary corneal epithelial swelling, whereas keratocytes, endothelial cells, and subbasal nerves remained unchanged. CONCLUSIONS: Although OC causes immediate changes in mechanical and chemical sensitivity that may persist for a week, a single exposure to OC appears harmless to corneal tissues. The changes are possibly associated with damage of corneal nerve terminals of mainly unmyelinated polymodal nociceptor fibers.

[Corneal trophism and sensitivity changes after penetrating keratoplasty]. / Variaciones en el trofismo y la sensibilidad corneal tras la queratoplastia penetrante.

PURPOSE: To evaluate in the rabbit eye the changes in mechanical sensitivity and trophic function of the corneal epithelium after the denervation consecutive to circular trephinations of the peripheral cornea, similar to those produced by penetrating keratoplasty. METHODS: Complete trephination (8 mm diameter) with rotation of corneal button (PK) was performed in 12 eyes. Non-penetrating trephination, affecting 2/3 of the corneal depth, was made in a group of 12 eyes (NPK). A separate group of 16 nonoperated eyes served as control. Mechanical corneal sensitivity was measured with the Cochet-Bonnet esthesiometer (No. 12 filament). Trophic function of the corneal epithelium was assessed by determining the healing rate of epithelial wounds performed with n-heptanol. RESULTS: Three months after surgery, sensitivity in the center of the cornea was significantly reduced in both PK and NPK eyes (240+/-0 mg/S and 179+/-20 mg/S, respectively) when compared with control (88+/-10 mg/S, p<0.001). The ability of denervated corneas to regenerate corneal epithelial defects was similar in both, operated and non-operated eyes. Also, no differences were found between PK and NPK eyes. CONCLUSIONS: Results suggest that three months after corneal graft, throphic maintenance of the epithelium remains unaffected in spite of the significant hypoesthesia recorded at this time. Further experiments are needed to analyze the interaction between corneal epithelial cells and the trigeminal neurons innervating the cornea

Reduction by antiinflammatory drugs of the response of corneal sensory nerve fibers to chemical irritation.

PURPOSE: Nonsteroidal antiinflammatory drugs (NSAIDs) have been applied topically to reduce ocular pain caused by corneal injury or anterior segment surgery. The authors investigated whether the analgesic effects of the NSAIDs diclofenac, indomethacin, and flurbiprofen and of the calcium channel antagonist diltiazem on corneal pain are mediated by a reduction of nerve activity in corneal polymodal nociceptive fibers. METHODS: Impulse activity of single A-delta and C corneal nerve fibers was recorded from the ciliary nerves of anesthetized cats. Polymodal units were identified by their response to both touching with the Cochet-Bonnet esthesiometer and to acidic stimulation with 30-second pulses of 80% or 98.5% CO2 or 60 microl of 10 mM acetic acid, applied to the corneal receptive area. Ongoing impulse activity, firing responses to CO2 or acetic acid, and mechanical threshold of single fibers were recorded before and at various times (5 to 90 minutes) after topical application of 0.1% sodium diclofenac, 0.03% sodium flurbiprofen, 0.1% indomethacin, and 0.045% diltiazem hydrochloride or of their vehicles. RESULTS: Indomethacin, diclofenac, and flurbiprofen, in decreasing order of potency, gradually reduced the mean frequency of the impulse response of corneal polymodal nerve fibers evoked by CO2 stimuli. The progressive increase of ongoing activity, observed in vehicle-treated eyes after repeated CO2 stimulation was also prevented by NSAIDs. Diltiazem also attenuated the response to CO2 for a shorter period of time and with a faster time course. The mechanical threshold of corneal polymodal fibers was not affected by treatment with any of these drugs. CONCLUSIONS: Indomethacin, diclofenac, and flurbiprofen, as well as the calcium antagonist diltiazem, diminish the responsiveness of corneal polymodal nociceptors to chemical stimuli. This appears to be caused, in part, by a direct effect of these drugs on the excitability of polymodal nerve endings, but also by an inhibition by NSAIDs of the formation of cyclooxygenase products such as prostaglandins, thus reducing the enhanced responsiveness of nociceptors caused by local release of arachidonic acid metabolites from injured cells.

In vivo cAMP level in rabbit iris-ciliary body after topical epinephrine treatment.

PURPOSE: The present study estimates the in vivo cyclic AMP (cAMP) level in the rabbit iris-ciliary body after topical treatment with epinephrine. METHODS: Epinephrine 1% was applied unilaterally to pigmented rabbits. At selected time points between 10 min and 6 hr, a 2.5-mm diameter iris-ciliary body, in the treated eye, was irradiated with 2 J diode laser (2 W for 1 sec). Instant heat generated by the irradiation deactivated the cellular enzymes used in the synthesis and degradation of cAMP. Rabbits were sacrificed immediately, and samples of the iris-ciliary body were isolated from the irradiated area, the non-irradiated area, and from the contralateral, untreated eye. Levels of cAMP in these samples and in the aqueous humor were determined by radioimmunoassay. Further experiments were performed in rabbits pretreated with an alpha 2-adrenergic antagonist, yohimbine, and a beta-adrenergic antagonist, timolol, 30 min before the epinephrine treatment. Unilateral laser photocoagulation of the iris-ciliary body was performed at 10 min and 1 hr after the epinephrine treatment. RESULTS: The cAMP level in the photocoagulated iris-ciliary body did not change in parallel to the change in the aqueous humor. An increase of aqueous humor cAMP was observed for 6 hr. However, a reduction of cAMP level in the photocoagulated iris-ciliary body was observed at 1 hr after the epinephrine treatment. In yohimbine-pretreated rabbits, the reduction of cAMP level in the photocoagulated iris-ciliary body was absent. Pretreatment with timolol had no effect. CONCLUSIONS: These observations suggest that, at 1 hr after the epinephrine treatment, the cellular signal via the alpha 2-adrenergic receptors in the iris-ciliary body, which reduces the intracellular cAMP level, is stronger than that via the beta-adrenergic receptors.

Irritation of the anterior segment of the eye by ultraviolet radiation: influence of nerve blockade and calcium antagonists.

The aim of this investigation was to determine the influence on anterior segment inflammation elicited by UV radiation, of ocular denervation and pharmacological blockade of sensory nerve fibers with capsaicin, tetrodotoxin and calcium antagonists. Both eyes of pigmented rabbits were exposed for 5 min to UV radiation (254 nm); 24 h later, inflammatory signs were evaluated by biomicroscopy of the corneal epithelium, the stroma and the endothelium and scored from 0 to 4. Conjunctival vasodilation and miosis were also assessed. Two weeks before UV exposure, a group of rabbits received a retrobulbar injection of ethanol or of 1% capsaicin. Intact, capsaicin-treated and alcohol-denervated animals were treated topically, prior to UV exposure, with tetrodotoxin (0.78 mM) and the calcium antagonists diltiazem (1-28 mM) and nifedipine (10 mM). UV radiation produced at 24 h signs of corneal irritation, conjunctival hyperemia, miosis and elevated protein content of the aqueous humor. Retrobulbar injection of 99% alcohol or 1% capsaicin did not diminish significantly the inflammation of tissues directly exposed to UV radiation, although extension of inflammatory signs to unaffected areas was prevented. Pre-treatment of normal and denervated eyes with diltiazem attenuated UV-induced eye irritation signs at concentrations of 10 mM or over. The effect was less pronounced with tetrodotoxin and was not obtained with nifedipine. These findings suggest that the contribution of a neurogenic mechanism to anterior segment inflammation induced by UV exposure is modest. They also show that high concentrations of diltiazem, but not of nifedipine, effectively reduced inflammation of the anterior segment of the eye evoked by UV radiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of the cervical sympathetic nerves increases intraocular pressure.

PURPOSE: To test the hypothesis that a moderate electrical stimulation of the cervical sympathetic nerves in rabbits can increase intraocular pressure (IOP). METHODS: Electrical stimulations of the cervical sympathetic nerves were performed in anesthetized and conscious rabbits. Intraocular pressure, pupil size, and concentrations of aqueous humor components were monitored. RESULTS: In urethane-anesthetized rabbits, stimulations of 5 V and 1 ms at 2.5 Hz for 1 hr and then at 20 Hz for 2 hr caused a short inhibition of IOP decrease and a prolonged mydriasis. Concentrations of norepinephrine (NE), neuropeptide Y (NPY), and cyclic AMP (cAMP) in aqueous humor were elevated. Aqueous humor protein concentration was not changed. In rabbits anesthetized with ketamine, chlorpromazine, and pentobarbital, electrical stimulations with the same parameters caused prolonged increases in IOP and pupil size. Aqueous humor NE and cAMP concentrations increased, while NPY and protein concentrations did not change. When the stimulations were set at 5 Hz for 3 hr under this anesthesia, the increase of IOP and mydriasis persisted. However, only the NE concentration increased. In conscious rabbits, stimulations of 5 V and 1 ms at either 5 Hz or 20 Hz were delivered from a portable stimulator for 4 hr, starting 2 hr before the onset of the dark. Stimulations at 5 Hz caused an increase in IOP in the light phase. The circadian IOP elevation in the dark phase persisted. When 20 Hz was used, a transient fall in IOP was observed, and the circadian IOP elevation was eliminated. Aqueous humor NE concentration doubled in conscious rabbits receiving electrical stimulations at 5 Hz for 1 hr. CONCLUSIONS: A moderate electrical stimulation of the cervical sympathetic nerves can increase IOP in anesthetized rabbits and in conscious rabbits in the light phase.

Chronic stimulation of ocular sympathetic fibers in unanesthetized rabbits.

The goal of this study was to devise a technique to implant permanent electrodes in the cervical sympathetic trunk, to stimulate the ocular adrenergic fibers for periods of hours or days in awake, unrestrained rabbits. Electrodes were made of a silver wire soldered to a multistranded wire and enclosed in silicone. Two of these electrodes were wrapped around the preganglionic sympathetic nerve, their leads emerging through a hole in the back of the neck. Success of the procedure was confirmed by the mydriasis elicited by electrical stimulation of the nerve following surgery; threshold voltages for the pupillary response varied between 5-10 volts. In eight rabbits, suprathreshold sympathetic stimulation was performed on the following days by means of a portable stimulator using increasing frequencies (1, 3, 5, 8, and 10 Hz) during a 20-hr period. Dilation of the ipsilateral pupil and vasoconstriction in the ear, measured by the fall in temperature of the ear's surface, was observed as long as stimulation was maintained. Both effects were proportional to the frequency of stimulation. Maximal mydriasis was obtained at 8 Hz, whereas full vasoconstriction was elicited with 5 Hz. Intraocular pressure, measured in 10 rabbits with a Perkins tonometer at the end of a 24-hr stimulation period, did not differ from pre-stimulation values. It was concluded that chronic stimulation of the sympathetic nerve allows to maintain known levels of adrenergic activity in the eye, and may be a useful method to study the actions of the adrenergic system on various ocular functions in unanesthetized animals.