Effect of sensory denervation on the structure and physiologic responsiveness of rabbit lacrimal gland

Ocular surface changes in mice with streptozotocin-induced diabetes and diabetic polyneuropathy

PURPOSE

Diabetes mellitus (DM) is a leading risk factor for corneal neuropathy and dry eye disease (DED). Another common consequence of DM is diabetic peripheral polyneuropathy (DPN). Both complications affect around 50 % of the DM patients but the relationship between DM, DED and DPN remains unclear.

METHODS

In this study, we examined mice with early onset of DM and PN after streptozotocin (STZ)-induced diabetes (DPN). We compared the early morphological changes of the sciatic nerve, dorsal root and trigeminal ganglia with the changes in the ocular surface, including tear proteomic and we also investigated respective changes in the gene expressions and morphological alterations in the eye tissues involved in tear production.

RESULTS

The lacrimal gland, conjunctival goblet cells and cornea showed morphological changes along with alterations in tear proteins without any obvious signs of ocular surface inflammation. The gene expression for respectively altered tear proteins i.e., of Clusterin in cornea, Car6, Adh3a1, and Eef1a1 in eyelids, and Pigr in the lacrimal gland also showed significant changes compared to control mice. In the trigeminal ganglia like in the dorsal root ganglia neuronal cells showed swollen mitochondria and, in the latter, there was a significant increase of NADPH oxidases and MMP9 suggestive of oxidative and neuronal stress. In the dorsal root ganglia and the sciatic nerve, there was an upregulation of a number of pro-inflammatory cytokines and pain-mediating chemokines.

CONCLUSION

The early ocular changes in DM Mice only affect the lacrimal gland. Which, is reflected in the tear film composition of DPN mice. Due to the high protein concentration in tear fluid in humans, proteomic analysis in addition to noninvasive investigation of goblet cells and cornea can serve as a tools for the early diagnosis of DPN, DED in clinical practice. Early treatment could delay or even prevent the ocular complications of DM such as DED and PN.

Hyperglycemia Induces Tear Reduction and Dry Eye in Diabetic Mice through the Norepinephrine-α1 Adrenergic Receptor-Mitochondrial Impairment Axis of Lacrimal Gland

Dry eye syndrome is a common complication in diabetic patients with a prevalence of up to 54.3%. However, the pathogenic mechanisms underlying hyperglycemia-induced tear reduction and dry eye remain less understood. The present study indicated that both norepinephrine (NE) and tyrosine hydroxylase levels were elevated in the lacrimal gland of diabetic mice, accompanied by increased Fos proto-oncogene (c-FOS)+ cells in the superior cervical ganglion. However, the elimination of NE accumulation by surgical and chemical sympathectomy significantly ameliorated the reduction in tear production, suppressed abnormal inflammation of the lacrimal gland, and improved the severity of dry eye symptoms in diabetic mice. Among various adrenergic receptors (ARs), the α1 subtype played a predominant role in the regulation of tear production, as treatments of α1AR antagonists improved tear secretion in diabetic mice compared with βAR antagonist propranolol. Moreover, the α1AR antagonist alfuzosin treatment also alleviated functional impairments of the meibomian gland and goblet cells in diabetic mice. Mechanically, the α1AR antagonist rescued the mitochondrial bioenergetic deficit, increased the mitochondrial DNA copy numbers, and elevated the glutathione levels of the diabetic lacrimal gland. Overall, these results deciphered a previously unrecognized involvement of the NE-α1AR-mitochondrial bioenergetics axis in the regulation of tear production in the lacrimal gland, which may provide a potential strategy to counteract diabetic dry eye by interfering with the α1AR activity.

Nicotinic acetylcholine receptor stimulation: A new approach for stimulating tear secretion in dry eye disease

Tear secretion is regulated by the lacrimal functional unit consisting of afferent and efferent nerve innervation. The afferent arm consists of trigeminal nociceptors on the ocular surface and nasal mucosa. When stimulated by agonists, nicotinic acetylcholine receptors on nerve endings in the nose initiate a reflex arc resulting in instantaneous tear secretion. Pharmacologic nasal neural stimulation to increase endogenous tear production is a novel approach to treating dry eye disease.

Ocular Autonomic Nervous System: An Update from Anatomy to Physiological Functions

The autonomic nervous system (ANS) confers neural control of the entire body, mainly through the sympathetic and parasympathetic nerves. Several studies have observed that the physiological functions of the eye (pupil size, lens accommodation, ocular circulation, and intraocular pressure regulation) are precisely regulated by the ANS. Almost all parts of the eye have autonomic innervation for the regulation of local homeostasis through synergy and antagonism. With the advent of new research methods, novel anatomical characteristics and numerous physiological processes have been elucidated. Herein, we summarize the anatomical and physiological functions of the ANS in the eye within the context of its intrinsic connections. This review provides novel insights into ocular studies.

Mechanistic investigations of diabetic ocular surface diseases

With the global prevalence of diabetes mellitus over recent decades, more patients suffered from various diabetic complications, including diabetic ocular surface diseases that may seriously affect the quality of life and even vision sight. The major diabetic ocular surface diseases include diabetic keratopathy and dry eye. Diabetic keratopathy is characterized with the delayed corneal epithelial wound healing, reduced corneal nerve density, decreased corneal sensation and feeling of burning or dryness. Diabetic dry eye is manifested as the reduction of tear secretion accompanied with the ocular discomfort. The early clinical symptoms include dry eye and corneal nerve degeneration, suggesting the early diagnosis should be focused on the examination of confocal microscopy and dry eye symptoms. The pathogenesis of diabetic keratopathy involves the accumulation of advanced glycation end-products, impaired neurotrophic innervations and limbal stem cell function, and dysregulated growth factor signaling, and inflammation alterations. Diabetic dry eye may be associated with the abnormal mitochondrial metabolism of lacrimal gland caused by the overactivation of sympathetic nervous system. Considering the important roles of the dense innervations in the homeostatic maintenance of cornea and lacrimal gland, further studies on the neuroepithelial and neuroimmune interactions will reveal the predominant pathogenic mechanisms and develop the targeting intervention strategies of diabetic ocular surface complications.

Identification of Lacrimal Gland Postganglionic Innervation and Its Regulation of Tear Secretion

Tear fluid secreted from the exocrine lacrimal gland (LG) has an essential role in maintaining a homeostatic environment for a healthy ocular surface. Tear secretion is regulated by the sympathetic and parasympathetic components of the autonomic nervous system, although the contribution of each component is not fully understood. To investigate LG innervation, we identified sympathetic and parasympathetic postganglionic nerves, specifically innervating the mouse LG, by injecting a retrograde neuronal tracer into the LG. Interruption of neural stimuli to the LG by the denervation of these postganglionic nerves immediately and chronically decreased tear secretion, leading to LG atrophy along with destruction of the lobular structure. This investigation also found that parasympathetic, but not sympathetic, innervation was involved in these alterations.

Preganglionic Parasympathetic Denervation Rabbit Model for Innervation Studies

PURPOSE

Tear secretion from the main lacrimal gland (LG) is mainly regulated by parasympathetic nerves. We performed several innervation studies to investigate lacrimation.

METHODS

In male rabbits, we performed a retrograde dye-tracing study of LG innervation, evaluated preganglionic parasympathetic denervation, and administered glial cell-derived neurotrophic factor (GDNF) in the surgical area after parasympathetic denervation.

RESULTS

Accumulation of fluorescent dye was observed in the pterygopalatine ganglion cells on the same side as the dye injection into the main LG. Fewer stained cells were observed in the cervical and trigeminal ganglia. After parasympathetic denervation surgery, tear secretion was decreased, and fluorescein and rose bengal staining scores were increased at day 1 after surgery and remained increased for 3 months on the denervated side only. Most of the effects in rabbits with parasympathetic denervation were not recovered by administration of GDNF.

CONCLUSIONS

The main LG is primarily innervated by parasympathetic nerves to stimulate tear secretion. After preganglionic parasympathetic denervation, lacrimation was decreased, resulting in dry eyes, and this was maintained for at least 3 months. Administration of GDNF only minimally altered the effects of denervation.

TFOS DEWS II pain and sensation report

Pain associated with mechanical, chemical, and thermal heat stimulation of the ocular surface is mediated by trigeminal ganglion neurons, while cold thermoreceptors detect wetness and reflexly maintain basal tear production and blinking rate. These neurons project into two regions of the trigeminal brain stem nuclear complex: ViVc, activated by changes in the moisture of the ocular surface and VcC1, mediating sensory-discriminative aspects of ocular pain and reflex blinking. ViVc ocular neurons project to brain regions that control lacrimation and spontaneous blinking and to the sensory thalamus. Secretion of the main lacrimal gland is regulated dominantly by autonomic parasympathetic nerves, reflexly activated by eye surface sensory nerves. These also evoke goblet cell secretion through unidentified efferent fibers. Neural pathways involved in the regulation of meibomian gland secretion or mucin release have not been identified. In dry eye disease, reduced tear secretion leads to inflammation and peripheral nerve damage. Inflammation causes sensitization of polymodal and mechano-nociceptor nerve endings and an abnormal increase in cold thermoreceptor activity, altogether evoking dryness sensations and pain. Long-term inflammation and nerve injury alter gene expression of ion channels and receptors at terminals and cell bodies of trigeminal ganglion and brainstem neurons, changing their excitability, connectivity and impulse firing. Perpetuation of molecular, structural and functional disturbances in ocular sensory pathways ultimately leads to dysestesias and neuropathic pain referred to the eye surface. Pain can be assessed with a variety of questionaires while the status of corneal nerves is evaluated with esthesiometry and with in vivo confocal microscopy.

The potential role of neuropathic mechanisms in dry eye syndromes

Dry eye syndromes can involve both nociceptive and neuropathic symptoms. Nociceptive symptoms are the normal physiological responses to noxious stimuli. Neuropathic symptoms are caused by a lesion or disease of the somatosensory nervous system and can be the result of hypersensitisation of peripheral or central corneal and conjunctival somatosensory nerves. For example, inflammation could induce neuroplastic peripheral sensitisation of the ocular surface or lid wiper and exacerbate nociceptive symptoms. Neuropathic symptoms may explain the incommensurate relation between signs and symptoms in some dry eye syndromes although absence of signs of a dry eye syndrome may also be a consequence of inappropriate methods used when examining for them. Involvement of neuropathic mechanisms may also help explain dry eye symptoms which occur in association with reduced corneal sensitivity. This review includes a discussion of the potential for ocular symptoms involving neuropathic mechanisms to contribute to psychosocial problems such as depression, stress, anxiety and sleep disorders as well as for these types of psychosocial problems to contribute to neuropathic mechanisms and dry eye syndromes. Failure to consider the possibility that neuropathic mechanisms can contribute to dry eye syndromes may reduce accuracy of diagnosis and the suitability of treatment provided. Dry eye symptoms in the absence of commensurate evidence of tear dysfunction, and unsatisfactory response to tear dysfunction therapies should prompt consideration of neuropathic mechanisms being involved. Symptoms which persist after local anaesthetic instillation are more likely to be neuropathic in origin. Reducing inflammation may help limit any associated neuroplastic hypersensitivity.

Identification of orexins and cognate receptors in the lacrimal gland of sheep

The aim of the present work was to study, by means of immunohistochemical and RT-PCR techniques, the presence and distribution of immunopositivity for orexin A and B (OXA and OXB) and orexin type 1 and 2 receptors (OX(1)R and OX(2)R) in the lacrimal gland of sheep as well as the gene expressions for prepro-orexin (PPOX) and cognate receptors. In serial sections, positive staining for OXA and OXB were localized in the same nervous fibers within the connective tissue septa. Positive staining for OX(1)R was evidenced in the wall of small arteries while that for OX(2)R was observed in the secretory portion of the acinar gland cells with a characteristic localization in the apical cytoplasm. RT-PCR analysis showed the presence of transcripts for PPOX, OX(1)R and OX(2)R in the sheep lacrimal gland; the gene expression of OX(1)R was two-fold greater (p<0.01) than that of OX(2)R. Taken together the present findings raise intriguing questions on the potential role of the orexinergic system in the regulation of lacrimal gland functions that require further investigations.

Cold-sensitive corneal afferents respond to a variety of ocular stimuli central to tear production: implications for dry eye disease

PURPOSE

To investigate the response characteristics of the corneal afferents that detect ocular conditions critical to the activation of the "afferent limb" of the lacrimation reflex.

METHODS

In isoflurane-anesthetized male rats, trigeminal ganglia were explored extracellularly in vivo to identify the corneal neurons that can be activated by ocular stimuli important to lacrimation. After verifying their receptive field loci to be restricted to the cornea, neural response properties were characterized with a variety of stimuli, such as drying and wetting of the cornea, by applying and removing artificial tears, temperature changes (35 degrees C-15 degrees C and 39 degrees C-51 degrees C), menthol (10-100 microM), and hyperosmolar solutions (NaCl, sucrose; 297-3014 mOsm), applied to the ocular surface.

RESULTS

A specific type of corneal afferent was identified that responded to drying of the ocular surface. These neurons were classified as innocuous "cold" thermoreceptors by their responses to steady state and dynamic temperature changes applied to the cornea. In addition to drying and slight cooling (<1 degree C) of the corneal surface, these neurons were excited by evaporation of tears from the ocular surface and hyperosmolar tears. Moreover, these neurons were activated by noxious thermal stimulation and menthol applied to the corneal surface.

CONCLUSIONS

These results demonstrate that innocuous "cold" cornea thermoreceptors are activated by drying of the ocular surface and hyperosmotic solutions, conditions that are consistent with a role in tear production. The authors hypothesize that the dysfunction of these corneal afferents and the lacrimation reflex pathway they activate lead to some forms of dry eye disease.

Neural regulation of lacrimal gland secretory processes: relevance in dry eye diseases

The lacrimal gland is the major contributor to the aqueous layer of the tear film which consists of water, electrolytes and proteins. The amount and composition of this layer is critical for the health, maintenance, and protection of the cells of the cornea and conjunctiva (the ocular surface). Small changes in the concentration of tear electrolytes have been correlated with dry eye syndrome. While the mechanisms of secretion of water, electrolytes and proteins from the lacrimal gland differ, all three are under tight neural control. This allows for a rapid response to meet the needs of the cells of the ocular surface in response to environmental conditions. The neural response consists of the activation of the afferent sensory nerves in the cornea and conjunctiva to stimulate efferent parasympathetic and sympathetic nerves that innervate the lacrimal gland. Neurotransmitters are released from the stimulated parasympathetic and sympathetic nerves that cause secretion of water, electrolytes, and proteins from the lacrimal gland and onto the ocular surface. This review focuses on the neural regulation of lacrimal gland secretion under normal and dry eye conditions.

Corneal melt in lattice corneal dystrophy type II after cataract surgery

We report a patient with lattice corneal dystrophy type II, also known as Meretoja syndrome or familial amyloidosis Finnish type, who developed a corneal melt 15 days after uneventful phacoemulsification. Despite conservative treatment, the corneal melt resulted in perforation. Uneventful penetrating keratoplasty was performed, but delayed graft epithelial healing was noticed postoperatively. Corneal button histopathological evaluation confirmed the initial clinical diagnosis. To our knowledge, this is the first reported case of corneal melt and perforation in a patient with lattice corneal dystrophy type II.

Neurologic evaluation of acute lacrimomimetic effect of cyclosporine in an experimental rabbit dry eye model

PURPOSE

To evaluate neurologically acute lacrimation caused by cyclosporine (CsA) eyedrops in rabbit.

METHODS

Normal adult male New Zealand White rabbits and those that underwent parasympathectomy each received a single instillation of 0.1% CsA or vehicle eyedrops. Schirmer tear test (STT) results, flow rate of lacrimal gland (LG) fluid from the excretory lacrimal duct of the main LG, and blink rate (over a 3-minute period) were measured before and after instillation of CsA or vehicle. Light microscopy was performed to examine the main LG in vitro. Protein release from LG fragments was assessed after incubation with CsA for 30 minutes.

RESULTS

In normal rabbits, the STT value and the flow rate of LG fluid were significantly increased after treatment with CsA compared with vehicle (P < 0.05). In contrast, no changes were found in denervated eyes. The blink rate of CsA-treated eyes was significantly higher than that of vehicle-treated eyes in normal rabbits (P < 0.005), whereas that of denervated eyes decreased significantly after CsA instillation compared with before administration (P < 0.005). Light microscopy showed that the cytoplasm of acinar cells was packed with secretory granules in denervated LG tissue 7 days after parasympathectomy. The same finding was observed 3 hours after CsA instillation. CsA had no stimulatory effect on protein release by acinar cells in LG fragments at all concentrations tested.

CONCLUSIONS

These results suggest that CsA has no direct effect on tear fluid secretion from the LG in an acute model. Instead, CsA increases reflex tear flow.

Evaluation of novel dry eye model: preganglionic parasympathetic denervation in rabbit

PURPOSE

To evaluate ocular surface status after interruption of preganglionic, parasympathetic neural control after surgical removal of the greater superficial petrosal nerve (GSPN).

METHODS

New Zealand White rabbits underwent unilateral section and removal of a 5-mm portion of the GSPN by a route through the inner ear; no ocular or orbital tissue was involved. Before and 7 days after surgery, all animals underwent preliminary examination, including fluorescein staining, rose bengal instillation, blink rate, tear breakup time (BUT), tear flow, and impression cytology. Total tarsorrhaphy was carried out in four additional rabbits, and another four animals underwent unilateral sham procedures. The GSPN, pterygopalatine ganglion, lacrimal gland, and conjunctiva were evaluated by light and transmission electron microscopy (TEM).

RESULTS

GSPN sectioning resulted in significant changes of the ocular surface after 7 days: intense rose bengal staining of the conjunctiva, fluorescein staining of the cornea, increased blink rate (P < 0.05), decreased BUT (P < 0.005), decreased tear flow by 26% (P < 0.005), and decreased goblet cell density (P < 0.01). TEM revealed massive accumulation of secretory granules in lacrimal acinar cells. The changes were also seen after tarsorrhaphy. Neither the contralateral control nor the sham eyes were affected.

CONCLUSIONS

The effects of GSPN nerve section led to the rapid onset of a dry eye condition in the rabbits that continued for at least 1 week. The authors suggest that continuous neural drive of the pterygopalatine ganglion is necessary to maintain adequate tear flow and mucin secretion. It is likely the trigeminal system is the afferent origin of this continuous neural tone.

Eye Dryness Sensations After Refractive Surgery: Impaired Tear Secretion or "Phantom" Cornea?

The cornea is richly innervated by various functional types of sensory nerve fibers. When stimulated, these fibers evoke conscious sensations of different quality including ocular dryness, discomfort, and pain. Refractive surgery involves a variable degree of damage to corneal nerves. This leads to an altered expression of membrane ion channels at the injured and regenerating nerve fibers, giving rise to aberrant spontaneous and stimulus-evoked nerve impulse firing. It is speculated that these abnormal sensory discharges are read by the brain as ocular surface dryness. This would explain the high incidence of eye dryness sensations after photorefractive surgery, which are experienced by a large number of patients despite the often modest disturbance of tear secretion. Therefore, drugs that reduce abnormal activity in injured nerves may represent a therapeutic alternative for eye dryness sensations after refractive surgery.

Sensory denervation modulates eIF-2 alpha kinase expression in the rabbit lacrimal gland

PURPOSE

To investigate the hypothesis that sensory denervation of the rabbit lacrimal gland results in dysregulation of protein synthesis. We used differential display of mRNA to identify genes associated with protein synthesis and secretion that may be altered in this situation.

METHODS

New Zealand white rabbits underwent unilateral sensory denervation by the ablation of the trigeminal ganglion. After 7 days, the denervated and contralateral control lacrimal glands were removed. The effects of denervation on gene expression were carried out using differential mRNA display. Northern and Western blot analyses were used to verify differential gene expression.

RESULTS

Differential mRNA display identified the gene heme-regulated inhibitor eukaryotic initiation factor-2 alpha kinase (HRI eIF-2a kinase) in the lacrimal gland, the expression of which was reduced in the denervated lacrimal gland. The sequenced fragment from differential display showed 94% identity to rabbit HRI eIF-2a kinase. The decreased expression of HRI eIF-2a kinase was confirmed by Northern and Western blots, and measurement of HRI eIF-2a kinase phosphorylation activity in the lacrimal gland after ablation of sensory neurons showed that it was significantly decreased compared with that of normal and control lacrimal glands.

CONCLUSIONS

The results suggest that loss of sensory innervation has a role in the lacrimal gland, contributing to the expression of HRI eIF-2a kinase, a pivotal negative regulator of protein synthesis. A reduction in control of protein synthesis may lead to the translation of repressed messages associated with cell stress responses.

Substance P released from sensory nerve endings influences tear secretion and goblet cell function in the rat

The aim of this study was to present morphological and functional evidence to evaluate whether tear secretion is influenced by neuropeptides released from sensory nerve endings of the conjunctiva. Following unilateral electrical stimulation of the trigeminal ganglion, tears were collected at both sides and assessed for volume and protein concentration; as well as gel electrophoresis and luminol chemiluminescence with immunostaining to immunoglobulin A and lysozyme measurements. Goblet cell density (goblet cells/100 basal cells) was recorded during histopathological examination of removed lids. Rats were pretreated with atropine to block parasympathetic; guanethidine to block sympathetic neuronal pathways; or hexamethonium to block synaptic transmission in ganglia. Capsaicin was used to deplete neurotransmitters from sensory nerve endings or SR140333 to block substance P tachykinin NK1 receptor mediated responses. Effects of inadequate electrode position or incidental lesion of trigeminal ganglion were examined by placing the electrode in false position, or no stimulation at a correct position. Electrical stimulation resulted in 380% increase of tear secretion (p < 0.001) and 30% decrease of goblet cell density (p < 0.001) on the the stimulated side compared to the unstimulated side. Atropine, guanethidine and hexamethonium pretreatments had no effect (p > 0.05), but capsaicin and SR140333 inhibited the effect of stimulation (by 96% and 72%, respectively, p < 0.001). Inadequate stimulation did not increase the tear secretion (p < 0.05). Protein concentration decreased, whilst tear volume and total secreted protein increased (p < 0.005) after stimulation. Electrophoresis showed no difference in protein pattern between stimulated and control side and analysis of equivalent amount of tear protein with luminol chemiluminescence indicated no difference in immunoglobulin A and lysozyme ratio following stimulation (p>0.05). We conclude that antidromic electrical activation of conjunctival sensory nerve endings significantly increases water, mucus and protein phases of tear. It is suggested that the sensory neuropeptide substance P plays a pivotal role in this neurogenic regulatory mechanism.

Connections between the lacrimal gland and sensory trigeminal neurons: a WGA/HRP study in the cynomolgous monkey

The sensory innervation of the lacrimal gland (LG) in the cynomolgous monkey was studied using the retrograde wheat germ agglutinin/horsereadish peroxidase (WGA/HRP) tracer technique. A small solidified piece of WGA/HRP was implanted in the LG. Labelled sensory first-order neurons were found in the ipsilateral trigeminal ganglion (TG) and in the ipsilateral mesencephalic trigeminal nucleus (MTN). The distribution of labelled TG neurons was restricted to ophthalmic and maxillary ganglionic parts. Sensory innervation of LG by primary afferents is not only restricted to TG; an MTN involvement has also been found. This may imply that there is a central sensory role in the production and release of tears.

Changes in the tear film and ocular surface from dry eye syndrome

Dry eye syndrome (DES) refers to a spectrum of ocular surface diseases with diverse and frequently multiple aetiologies. The common feature of the various manifestations of DES is an abnormal tear film. Tear film abnormalities associated with DES are tear deficiency, owing to insufficient supply or excessive loss, and anomalous tear composition. These categorizations are artificial, as in reality both often coexist. DES disrupts the homeostasis of the tear film with its adjacent structures, and adversely affects its ability to perform essential functions such as supporting the ocular surface epithelium and preventing microbial invasion. In addition, whatever the initial trigger, moderate and severe DES is characterized by ocular surface inflammation, which in turn becomes the cause and consequence of cell damage, creating a self-perpetuating cycle of deterioration. Progress has been made in our understanding of the aetiology and pathogenesis of DES, and these advances have encouraged a proliferation of therapeutic options. This article aims to amalgamate prevailing ideas of DES development, and to assist in that, relevant aspects of the structure, function, and production of the tear film are reviewed. Additionally, a synopsis of therapeutic strategies for DES is presented, detailing treatments currently available, and those in development.

Microarray analysis of the rat lacrimal gland following the loss of parasympathetic control of secretion

Previous studies showed that loss of muscarinic parasympathetic input to the lacrimal gland (LG) leads to a dramatic reduction in tear secretion and profound changes to LG structure. In this study, we used DNA microarrays to examine the regulation of the gene expression of the genes for secretory function and organization of the LG. Long-Evans rats anesthetized with a mixture of ketamine/xylazine (80:10 mg/kg) underwent unilateral sectioning of the greater superficial petrosal nerve, the input to the pterygopalatine ganglion. After 7 days, tear secretion was measured, the animals were killed, and structural changes in the LG were examined by light microscopy. Total RNA from control and experimental LGs (n = 5) was used for DNA microarray analysis employing the U34A GeneChip. Three statistical algorithms (detection, change call, and signal log ratio) were used to determine differential gene expression using the Microarray Suite (5.0) and Data Mining Tools (3.0). Tear secretion was significantly reduced and corneal ulcers developed in all experimental eyes. Light microscopy showed breakdown of the acinar structure of the LG. DNA microarray analysis showed downregulation of genes associated with the endoplasmic reticulum and Golgi, including genes involved in protein folding and processing. Conversely, transcripts for cytoskeleton and extracellular matrix components, inflammation, and apoptosis were upregulated. The number of significantly upregulated genes (116) was substantially greater than the number of downregulated genes (49). Removal of the main secretory input to the rat LG resulted in clinical symptoms associated with severe dry eye. Components of the secretory pathway were negatively affected, and the increase in cell proliferation and inflammation may lead to loss of organization in the parasympathectomized lacrimal gland.

Corneal innervation, corneal mechanical sensitivity, and tear fluid secretion after transscleral contact 670-nm diode laser cyclophotocoagulation

PURPOSE

To examine the effect of 670-nm diode laser cyclophotocoagulation on corneal morphology, density of corneal subbasal nerves, corneal mechanical sensitivity, and the rate of tear fluid secretion in human eyes.

PATIENTS AND METHODS

Transscleral contact cyclophotocoagulation was performed in 10 eyes of 10 consecutive patients on 180 degrees of the pars plicata of the ciliary body, using a 670-nm diode laser (power = 430 mW, application time = 10 seconds). In vivo confocal microscopy, with special attention to corneal morphology and the density of the subbasal nerves in the central and inferior perilimbal cornea, was performed preoperatively, and at 3 days and 1 month postoperatively. Corneal mechanical sensitivity was tested preoperatively, and at 3 days and 1 month postoperatively, using a Cochet-Bonnet esthesiometer. The rate of tear fluid secretion was measured preoperatively and 1 month postoperatively, using the Schirmer basic secretion tear test with topical anesthesia.

RESULTS

After cyclophotocoagulation, in vivo confocal microscopy did not reveal any changes in any of the corneal layers or in the corneal subbasal nerves. After treatment, as compared with baseline (paired samples test, > 0.05), there was no statistically significant change in the mechanical sensitivity values in any part of the cornea or in the Schirmer basic secretion tear test result.

CONCLUSION

The results of this preliminary study suggest that cyclophotocoagulation with the 670-nm diode laser does not impair corneal innervation.

Effects of diadenosine polyphosphates on tear secretion in New Zealand white rabbits

Extracellular diadenosine polyphosphates play important signaling functions in a number of physiological responses. Here we show that diadenosine polyphosphates are normal constituents of tear fluid and are potent stimulators of tear secretion through their interaction with P2Y receptors. Diadenosine tetraphosphate (Ap(4)A) and Ap(5)A were found in rabbit tears under basal conditions at concentrations of 2.92 and 0.58 microM, respectively. Single applications of UTP, ATP, and Ap(4)A increased tear secretion to 160 +/- 8% (n = 16) (P < 0.001), 131 +/- 6% (P < 0.05), and 162 +/- 11% (P < 0.05) of placebo values, respectively. Ap(4)A, Ap(5)A, and Ap(6)A, but not Ap(2)A and Ap(3)A, were able to stimulate tear secretion in a dose-dependent manner. Concentration-response studies produced pD(2) values of 5.56 +/- 0.03, 5.75 +/- 0.12, and 5.50 +/- 0.09 for Ap(4)A, Ap(5)A, and Ap(6)A, respectively, with Ap(4)A showing the greatest efficacy. Diadenosine polyphosphates also stimulated P2Y(1) and P2Y(2) receptors expressed in 1321N1 cells with no apparent effect on the other P2Y receptors tested. Nonselective P2 antagonists did not modify the tear secretion induced by UTP or Ap(4)A in rabbit eyes in vivo or in cloned receptors, except for a weak but significant reduction in stimulated tear secretion by reactive blue 2. These results suggest that diadenosine polyphosphates stimulate tear secretion via a P2Y receptor-mediated mechanism. Comparing the effects of diadenosine polyphosphates applied to the rabbit eye and to cloned P2Y receptors, it appears that the P2Y(2) receptor subtype is responsible for the prosecretory effects of these compounds.

Corneal Sensitivity and Some Properties of the Tear Film After Laser in situ Keratomileusis

PURPOSE

To investigate central corneal sensitivity, lipid layer structure of the precorneal tear film, and tear volume after laser in situ keratomileusis (LASIK).

METHODS

Central corneal sensitivity was measured using the Non-Contact Corneal Aesthesiometer. The aesthesiometer was mounted on a slit lamp and an airpulse of controlled pressure was directed onto the cornea. When central corneal sensitivity was reduced, a higher air pulse pressure was required to stimulate the cornea. The final central corneal sensitivity threshold measured was recorded in millibars. Tear lipid layer structure was assessed by optical interferometry and classified according to appearance using the Keeler Tearscope. Tear volume was measured using the phenol red cotton thread test. Subjects were recruited from a group of patients after LASIK who had experienced no complications (n=22). The average postoperative time was 14 weeks and measurements were taken on one eye. In bilateral cases, measurements were recorded from the right eye only. Average attempted correction was -6.30 D (range, -2 to -11 D). Age-matched controls were later recruited for central corneal sensitivity threshold (n=24). A second group of age-matched controls were recruited for tear volume and lipid layer structure (n=24).

RESULTS

The median (range) was 1.1 mbars (0.2 to 4.3 mbars) after LASIK and 0.58 mbars (0.20 to 1.3 mbars) in the controls; the difference was statistically significant (P = .043). The lipid layer of the tear film tended to be thinner in eyes after LASIK compared with controls (P = .032). The mean (+/- SD) tear volume was 16.9 +/- 8.3 mm after LASIK and 19.8 +/- 7.1 mm in controls. This difference was not statistically significant (P = .492).

CONCLUSION

At 14 weeks postoperatively, central corneal sensitivity was below normal levels and the tear lipid layer was thinner. The poorer quality lipid layer may predispose to symptoms of dry eye after LASIK.

Comparison of tear secretion and tear film instability after photorefractive keratectomy and laser in situ keratomileusis

PURPOSE

To evaluate and compare tear secretion and tear film instability following photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).

SETTING

Department of Ophthalmology, Yonsei University School of Medicine, Seoul, Korea.

METHODS

In a prospective study, 36 eyes (21 patients) had PRK and 39 eyes (25 patients) had LASIK to correct myopia. Tear secretion and tear film instability were tested preoperatively and 3 and 6 months postoperatively using Schirmer test values, tear breakup time (BUT) scores, and tear osmolarity.

RESULTS

Six months after surgery, the change in Schirmer test values from preoperative levels was -14.57% +/- 6.39% (SD) in the PRK eyes and -23.40% +/- 5.94% in the LASIK eyes and the change in BUT scores, -12.54% +/- 8.28% and -18.79% +/- 13.01%, respectively. The change in tear osmolarity was 14.95% +/- 6.46% and 35.63% +/- 8.51%, respectively.

CONCLUSIONS

The decrease in tear secretion was greater after LASIK than after PRK at 6 months. Proper treatment of dry eye is required after LASIK and PRK, particularly in the LASIK postoperative period.

Characterization of immortalized rabbit lacrimal gland epithelial cells

To establish an immortalized lacrimal gland epithelial cell line, the orbital lacrimal glands of normal New Zealand White rabbits were multiply injected with an immortalizing amphotropic retroviral vector (LXSN16E6E7) containing the E6 and E7 genes of human papillomavirus type 16. Lacrimal glands were removed after 2 d and acinar epithelial cells were isolated and cultured on Matrigel-coated 60 mm2 plates containing DMEM-F12 supplemented with 5% Nu-serum V. Transformed cells were selected in G418 sulfate for 7 d and passaged. Morphology of the immortalized cells was similar to that described for normal acinar cells both in vivo and in vitro, with rough endoplasmic reticulum and secretory granules. These characteristics remained unchanged and the cells continued to exhibit typical polygonal epithelioid structure. The cells have been maintained in culture for 14 mo. and have gone through 58 passages without loss of proliferation or epithelial cell characteristics. Immunohistochemistry and Western blots showed positive reactivity to secretory component, transferrin, and transferrin receptor, which are typical proteins found in the lacrimal gland. Functional analysis by stimulation with a cholinergic agonist, carbachol (100 microM), resulted in a significant release of protein. This is the first report of an immortalized rabbit lacrimal epithelial cell. These cells will provide a valuable tool for the molecular analysis of lacrimal gland epithelial cell functions.