Central nervous system mechanisms in Sjögren's syndrome

Abnormal Spontaneous Brain Activities of Limbic-Cortical Circuits in Patients With Dry Eye Disease

Whether brain function is altered in patients with dry eye disease (DED) remains unclear. Twenty patients with DED and 23 healthy controls (HCs) were scanned using resting-state functional magnetic resonance imaging. Regional homogeneity (ReHo) and support vector machine (SVM) were used to analyze the imaging data. Relative to the HCs, the patients with DED showed significantly increased ReHo values in the left inferior occipital gyrus (IOG), left superior temporal gyrus, and right superior medial prefrontal cortex, and significantly decreased ReHo values in the right superior frontal gyrus/middle frontal gyrus and bilateral middle cingulum (MC). SVM results indicated that the combination of ReHo values in the left MC and the left IOG in distinguishing patients with DED from HCs had a sensitivity of 95.00%, a specificity of 91.30%, and an accuracy of 93.02%. The present study found that the patients with DED had abnormal ReHo values in the limbic-cortical circuits. A combination of ReHo values in the left MC and the left IOG could be applied as a potential imaging biomarker to distinguish patients with DED from HCs. The dysfunction of limbic-cortical circuits may play an important role in the pathophysiology of DED.

Neurological and Inflammatory Manifestations in Sjögren's Syndrome: The Role of the Kynurenine Metabolic Pathway

For decades, neurological, psychological, and cognitive alterations, as well as other glandular manifestations (EGM), have been described and are being considered to be part of Sjögren's syndrome (SS). Dry eye and dry mouth are major findings in SS. The lacrimal glands (LG), ocular surface (OS), and salivary glands (SG) are linked to the central nervous system (CNS) at the brainstem and hippocampus. Once compromised, these CNS sites may be responsible for autonomic and functional disturbances that are related to major and EGM in SS. Recent studies have confirmed that the kynurenine metabolic pathway (KP) can be stimulated by interferon-γ (IFN-γ) and other cytokines, activating indoleamine 2,3-dioxygenase (IDO) in SS. This pathway interferes with serotonergic and glutamatergic neurotransmission, mostly in the hippocampus and other structures of the CNS. Therefore, it is plausible that KP induces neurological manifestations and contributes to the discrepancy between symptoms and signs, including manifestations of hyperalgesia and depression in SS patients with weaker signs of sicca, for example. Observations from clinical studies in acquired immune deficiency syndrome (AIDS), graft-versus-host disease, and lupus, as well as from experimental studies, support this hypothesis. However, the obtained results for SS are controversial, as discussed in this study. Therapeutic strategies have been reexamined and new options designed and tested to regulate the KP. In the future, the confirmation and application of this concept may help to elucidate the mosaic of SS manifestations.

Somatotopic Representation of Second Pain in the Primary Somatosensory Cortex of Humans and Rodents

There is now compelling evidence that selective stimulation of Aδ nociceptors eliciting first pain evokes robust responses in the primary somatosensory cortex (S1). In contrast, whether the C-fiber nociceptive input eliciting second pain has an organized projection to S1 remains an open question. Here, we recorded the electrocortical responses elicited by nociceptive-specific laser stimulation of the four limbs in 202 humans (both males and females, using EEG) and 12 freely moving rats (all males, using ECoG). Topographical analysis and source modeling revealed in both species, a clear gross somatotopy of the unmyelinated C-fiber input within the S1 contralateral to the stimulated side. In the human EEG, S1 activity could be isolated as an early-latency negative deflection (C-N1 wave peaking at 710–730 ms) after hand stimulation, but not after foot stimulation because of the spatiotemporal overlap with the subsequent large-amplitude supramodal vertex waves (C-N2/P2). In contrast, because of the across-species difference in the representation of the body surface within S1, S1 activity could be isolated in rat ECoG as a C-N1 after both forepaw and hindpaw stimulation. Finally, we observed a functional dissociation between the generators of the somatosensory-specific lateralized waves (C-N1) and those of the supramodal vertex waves (C-N2/P2), indicating that C-fiber unmyelinated input is processed in functionally distinct somatosensory and multimodal cortical areas. These findings demonstrated that C-fiber input conveys information about the spatial location of noxious stimulation across the body surface, a prerequisite for deploying an appropriate defensive motor repertoire.

SIGNIFICANCE STATEMENT Unmyelinated C-fibers are the evolutionarily oldest peripheral afferents responding to noxious environmental stimuli. Whether C-fiber input conveys information about the spatial location of the noxious stimulation to the primary somatosensory cortex (S1) remains an open issue. In this study, C-fibers were activated by radiant heat stimuli delivered to different parts of the body in both humans and rodents while electrical brain activity was recorded. In both species, the C-fiber peripheral input projects to different parts of the contralateral S1, coherently with the representation of the body surface within this brain region. These findings demonstrate that C-fiber input conveys information about the spatial location of noxious stimulation across the body surface, a prerequisite for deploying an appropriate defensive motor repertoire.

How Many Types of Dystonia? Pathophysiological Considerations

Dystonia can be seen in a number of different phenotypes that may arise from different etiologies. The pathophysiological substrate of dystonia is related to three lines of research. The first postulate a loss of inhibition which may account for the excess of movement and for the overflow phenomena. A second abnormality is sensory dysfunction which is related to the mild sensory complaints in patients with focal dystonias and may be responsible for some of the motor dysfunction. Finally, there are strong pieces of evidence from animal and human studies suggesting that alterations of synaptic plasticity characterized by a disruption of homeostatic plasticity, with a prevailing facilitation of synaptic potentiation may play a pivotal role in primary dystonia. These working hypotheses have been generalized in all form of dystonia. On the other hand, several pieces of evidence now suggest that the pathophysiology may be slightly different in the different types of dystonia. Therefore, in the present review, we would like to discuss the neural mechanisms underlying the different forms of dystonia to disentangle the different weight and role of environmental and predisposing factors.

Association of dry eye disease with psychiatric or neurological disorders in elderly patients

Dry eye disease (DED) is a common disease that can impair quality of life significantly. Its prevalence increases with advancing age, and the economic burden of the disease on both a patient and the society is increasing with elongation of life expectancy. The diagnosis and treatment of DED are often difficult due to the discordance between symptoms and signs of the disease. Recent studies have suggested the role of neurological or psychological factors in the development of dry eye symptoms and discrepancy of the symptoms and signs, particularly in elderly patients. In this review, the authors discuss the association of DED with various psychiatric and neurological disorders. In addition to psychiatric conditions, including depression, anxiety, stress, posttraumatic stress disorder and sleep disorders, medications for the psychiatric disorders have association with DED. Neurological disorders, such as neuropathic pain, chronic pain syndrome, peripheral neuropathy and several central nervous system disorders, are related to DED. Treatment of DED, combined with psychiatric or neurological disorders, is also discussed. Attention should be paid to the DED patients with discordant symptoms and signs, and unsatisfactory response to conventional treatment for associated psychiatric or neurological disorders, as well as an integrated treatment approach, could be helpful for these patients.

The neural pathway for lacrimal gland tear secretion in New Zealand White rabbits

OBJECTIVE

We investigated the neural pathway for tear secretion from the lacrimal gland of New Zealand White rabbits.

METHODS

Nine healthy adult New Zealand White rabbits were randomly divided into three experimental groups, namely, an irritant-stimulated group, a non-stimulated group, and a saline-stimulated group. Sanitized dry cotton swabs with menthol were used to wipe both of the rabbits' eyelids in the irritant-stimulated group, and the non-stimulated group and saline- stimulated group were compared as controls. The animals in the three groups were killed 2h later and the expressions of c-Fos in the frontal cortex, hippocampus, hypothalamus, pons, and medulla oblongata of the rabbits were detected using immunofluorescence labeling. According to the distribution of c-Fos protein expression, 12 healthy adult New Zealand rabbits were similarly divided into three groups for retrograde tract tracing via pseudorabies virus (PRV) injection into the lacrimal gland. Immunofluorescence labeling was used to analyze PRV-infected neurons in the brains of rabbits after survival for 30h, 38h, and 46h.

RESULTS

The most c-Fos-positive immunolabeled cells were observed in the menthol-stimulated group, whereas fewer c-Fos-positive immunolabeled cells were observed in the saline-stimulated group.The non-treated group showed the least c-Fos-positive immunolabeled cells. At 30h after PRV injection, PRV-positive neurons were found only in the superior salivary nucleus of the pons (SSN). At 38h, PRV-infected neurons were observed in the lateral nucleus of the superior olive (LSO) and the medial nucleus of the superior olive (MSO). At 46h, PRV-infected neurons were found in the nucleus of the trapezoid body (Tz) and the hypothalamic paraventricular nucleus (PVN), and their distributions were dense in the LSO and MSO.

CONCLUSIONS

Menthol-induced c-Fos protein expression and PRV-mediated tract tracing suggest that in New Zealand White rabbits, the neural pathway that regulates tear secretion from the lacrimal gland proceeds from the PVN to the superior olivary complex of the pons to the SSN and finally to the lacrimal gland.

Corneal sensitivity following lacrimal gland excision in the rat

PURPOSE

Dry eye disease (DED) produces ocular pain and irritation, yet a detailed characterization of ocular sensitivity in a preclinical model of DED is lacking. The aim of the present study was to assess nociceptive behaviors in an aqueous tear deficiency model of DED in the rat.

METHODS

Spontaneous blinking, corneal mechanical thresholds, and eye wipe behaviors elicited by hypertonic saline (5.0 M) were examined over a period of 8 weeks following the unilateral excision of either the exorbital lacrimal gland or of the exorbital and infraorbital lacrimal glands, and in sham surgery controls. The effect of topical proparacaine on spontaneous blinking and of systemic morphine (0.5-3.0 mg/kg, subcutaneous [SC]) on spontaneous blinking and eye wipe responses were also examined.

RESULTS

Lacrimal gland excision resulted in mechanical hypersensitivity and an increase in spontaneous blinking in the ipsilateral eye over an 8-week period that was more pronounced after infra- and exorbital gland excision. The time spent eye wiping was also enhanced in response to hypertonic saline (5.0 M) at both 1- and 8-week time-points, but only in infra- and exorbital gland excised animals. Morphine attenuated spontaneous blinking, and the response to hypertonic saline in dry eye animals and topical proparacaine application reduced spontaneous blinking down to control levels.

CONCLUSIONS

These results indicate that aqueous tear deficiency produces hypersensitivity in the rat cornea. In addition, the increase in spontaneous blinks and their reduction by morphine and topical anesthesia indicate the presence of persistent irritation elicited by the activation of corneal nociceptors.

A review of salivary gland histopathology in primary Sjögren's syndrome with a focus on its potential as a clinical trials biomarker

Salivary gland changes, characterised by a focal lymphocytic sialadenitits, play an important role in the diagnosis of primary Sjögren's syndrome (PSS) and were first described over 40 years ago. Recent evidence suggests that minor salivary gland biopsy may also provide information useful for prognostication and stratification, yet difficulties may arise in the histopathological interpretation and scoring, and evidence exists that reporting is variable. With the increasing number of actual and proposed clinical trials in PSS, we review the evidence that might support the role of histopathology as a biomarker for stratification and response to therapy and highlight areas where further validation work is required.

Ocular neuropathic pain

As the biological alarm of impending or actual tissue damage, pain is essential for our survival. However, when it is initiated and/or sustained by dysfunctional elements in the nociceptive system, it is itself a disease known as neuropathic pain. While the critical nociceptive system provides a number of protective functions, it is unique in its central role of monitoring, preserving and restoring the optical tear film in the face of evaporative attrition without which our vision would be non-functional. Meeting this existential need resulted in the evolution of the highly complex, powerful and sensitive dry eye alarm system integrated in the peripheral and central trigeminal sensory network. The clinical consequences of corneal damage to these nociceptive pathways are determined by the type and location of its pathological elements and can range from the spectrum known as dry eye disease to the centalised oculofacial neuropathic pain syndrome characterised by a striking disparity between the high intensity of symptoms and paucity of external signs. These changes parallel those observed in somatic neuropathic pain. When seen through the neuroscience lens, diseases responsible for inadequately explained chronic eye pain (including those described as dry eye) can take on new meanings that may clarify long-standing enigmas and point to new approaches for developing preventive, symptomatic and disease-modifying interventions for these currently refractory disorders.

The role of corneal afferent neurons in regulating tears under normal and dry eye conditions

The cornea is one of several orofacial structures requiring glandular secretion for proper lubrication. Glandular secretion is regulated through a neural reflex initiated by trigeminal primary afferent neurons innervating the corneal epithelium. Corneal sensory afferents must respond to irritating and potentially damaging stimuli, as well as drying that occurs with evaporation of the tear film, and the physiological properties of corneal afferents are consistent with these requirements. Polymodal neurons are sensitive to noxious mechanical, thermal and chemical stimuli, mechanoreceptive neurons are selectively activated by mechanical stimuli, and cool cells respond to innocuous cooling. The central terminations of corneal primary afferents are located within two regions of the spinal trigeminal nucleus. The more rostral region, located at the transition between the trigeminal subnucleus caudalis and interpolaris, represents a critical relay for the regulation of the lacrimation reflex. From this region, major control of lacrimation is carried through projections to preganglionic parasympathetic neurons located in or around the superior salivatory nucleus. Dry eye syndrome may be caused by a dysfunction in the tear secreting glands themselves or in the neuronal circuit regulating these glands. Furthermore, the dry eye condition itself may modify the properties of corneal afferents and affect their ability to regulate secretion, a possibility just now being explored.

Dry eye modifies the thermal and menthol responses in rat corneal primary afferent cool cells

Dry eye syndrome is a painful condition caused by inadequate or altered tear film on the ocular surface. Primary afferent cool cells innervating the cornea regulate the ocular fluid status by increasing reflex tearing in response to evaporative cooling and hyperosmicity. It has been proposed that activation of corneal cool cells via a transient receptor potential melastatin 8 (TRPM8) channel agonist may represent a potential therapeutic intervention to treat dry eye. This study examined the effect of dry eye on the response properties of corneal cool cells and the ability of the TRPM8 agonist menthol to modify these properties. A unilateral dry eye condition was created in rats by removing the left lacrimal gland. Lacrimal gland removal reduced tears in the dry eye to 35% compared with the contralateral eye and increased the number of spontaneous blinks in the dry eye by over 300%. Extracellular single-unit recordings were performed 8-10 wk following surgery in the trigeminal ganglion of dry eye animals and age-matched controls. Responses of corneal cool cells to cooling were examined after the application of menthol (10 μM-1.0 mM) to the ocular surface. The peak frequency of discharge to cooling was higher and the cooling threshold was warmer in dry eye animals compared with controls. The dry condition also altered the neuronal sensitivity to menthol, causing desensitization to cold-evoked responses at concentrations that produced facilitation in control animals. The menthol-induced desensitization of corneal cool cells would likely result in reduced tearing, a deleterious effect in individuals with dry eye.

Menthol activation of corneal cool cells induces TRPM8-mediated lacrimation but not nociceptive responses in rodents

PURPOSE

Stimulation to the cornea via noxious chemical and mechanical means evokes tearing, blinking, and pain. In contrast, mild cooling of the ocular surface has been reported to increase lacrimation via activation of corneal cool primary afferent neurons. The purpose of our study was to determine whether menthol induces corneal cool cell activity and lacrimation via the transient receptor potential melastatin-8 (TRPM8) channel without evoking nociceptive responses.

METHODS

Tear measurements were made using a cotton thread in TRPM8 wild type and knockout mice after application of menthol (0.05-50 mM) to the cornea. In additional studies, nocifensive responses (eye swiping and lid closure) were quantified following cornea menthol application. Trigeminal ganglion electrophysiologic single unit recordings were performed in rats to determine the effect of low and high concentrations of menthol on corneal cool cells.

RESULTS

At low concentrations, menthol increased tear production in TRPM8 wild type and heterozygous animals, but had no effect in TRPM8 knockout mice, while nocifensive responses remained unaffected. At the highest concentration, menthol (50 mM) increased tearing and nocifensive responses in TRPM8 wild type and knockout animals. A low concentration of menthol (0.1 mM) increased cool cell activity, yet a high concentration of menthol (50 mM) had no effect.

CONCLUSIONS

These studies indicated that low concentrations of menthol can increase lacrimation via TRPM8 channels without evoking nocifensive behaviors. At high concentrations, menthol can induce lacrimation and nocifensive behaviors in a TRPM8 independent mechanism. The increase in lacrimation is likely due to an increase in cool cell activity.

The role of ectopic germinal centers in the immunopathology of primary Sjögren's syndrome: a systematic review

OBJECTIVES

To determine whether the presence of germinal centers (GCs) in salivary glands of patients with primary Sjögren's syndrome (pSS) is related to the severity of disease course and distinct immunopathology features.

METHODS

A systematic search was performed in September 2011 for terms and synonyms of Sjögren's syndrome and germinal centers. A total of 80 articles were retrieved, of which 16 were included for (meta-) analysis.

RESULTS

GC morphology was present in a mean ± SD 25.1 ± 5.0% of pSS patients. Mean lymphocyte focus scores were 1.25 points higher in patients with GCs as compared to those without GCs. Saliva production was reduced in patients with GCs, although this did not reach statistical significance. Percentages of patients positive for rheumatoid factor, anti-Sjögren's syndrome A (SSA), and anti-Sjögren's syndrome B (SSB) antibodies were significantly higher in patients with GCs (mean increase, 15%, 18%, and 18%, respectively). Additionally, patients with GCs were characterized by enhanced levels of local and systemic proinflammatory mediators. Importantly, these patients have a higher risk of lymphoma development (14% versus 1%).

CONCLUSIONS

Patients with GCs are characterized by more severe disease, although the small number of studies and their design hamper generalizability of results. The precise mechanisms that contribute to the development and persistence of germinal centers in pSS are largely unknown. This and the strongly increased risk of lymphoma development warrant intensive studies for the role of germinal centers in the immunopathology of pSS.

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.

Update on blepharospasm: report from the BEBRF International Workshop

This review updates understanding and research on blepharospasm, a subtype of focal dystonia. Topics covered include clinical aspects, pathology, pathophysiology, animal models, dry eye, photophobia, epidemiology, genetics, and treatment. Blepharospasm should be differentiated from apraxia of eyelid opening. New insights into pathology and pathophysiology are derived from different types of imaging, including magnetic resonance studies. Physiologic studies indicate increased plasticity and trigeminal sensitization. While botulinum neurotoxin injections are the mainstay of therapy, other therapies are on the horizon.

Lacrimal punctum occlusion in the treatment of severe keratoconjunctivitis Sicca caused by Sjögren syndrome: a uniocular evaluation

PURPOSE

A controlled uniocular study to evaluate the short-term efficacy of lacrimal punctum occlusion in the treatment of severe dry eye caused by Sjögren syndrome.

METHODS

Uniocular punctum occlusion by punctum plug in the upper and lower puncta in 1 eye was performed in 20 patients with severe keratoconjunctivitis Sicca caused by Sjögren syndrome. To overcome possible interindividual variability between patients, the other eye, in the same patient, was not occluded and served as a control eye. The eye to be occluded was randomly selected. The patients were instructed to continue using their dry eye medications. Tear function tests (Schirmer test, rose Bengal test, and debris in de cul-de-sac) were performed in both eyes. Subjective complaints (discomfort) were registered for both eyes. All the above-mentioned data were collected before starting the treatment and at least 6 weeks later. The above-mentioned parameters were compared and statistically analyzed in both eyes.

RESULTS

Of the 20 patients, 7 patients dropped out. The remaining 13 patients completed the final analysis. In the occluded eye, we found a significant improvement in both the subjective complaints and the rose Bengal score, but the Schirmer test and the tear mucus score did not change.

CONCLUSION

Punctum occlusion therapy in a short-term study improved the rose Bengal score and discomfort score in our patients and thus may be helpful in the treatment of severe dry eye caused by Sjögren syndrome.

Is it safe to use topical NSAIDs for corneal sensitivity in Sjögren’s syndrome patients?

Sjögren's syndrome dry eye is an inflammatory disease accompanied by an impairment of the autonomous nervous system of the ocular surface. The therapy for this condition is shifting from the mere tear replacement to a more complex approach including an anti-inflammatory treatment. Clinical trials have evidenced that the use of NSAIDs is followed by a reduction of the ocular discomfort symptoms in dry-eye patients. However, sporadic case reports of corneal melting in dry-eye subjects who underwent surgical procedures has brought attention to the possible effect that NSAIDs may have on corneal sensitivity. Therefore, the effect of NSAID treatment on corneal sensitivity in normal subjects and in patients with dry eye was studied. The results of these trials seem to demonstrate that some NSAIDs, diclofenac in particular, have the effect of reducing corneal sensitivity both in normal subjects and in patients with dry eye. Therefore, NSAIDs should be used with caution in Sjögren's syndrome patients.

Endotoxin-Induced Uveitis Causes Long-Term Changes in Trigeminal Subnucleus Caudalis Neurons

Endotoxin-induced uveitis (EIU) is commonly used in animals to mimic ocular inflammation in humans. Although the peripheral aspects of EIU have been well studied, little is known of the central neural effects of anterior eye inflammation. EIU was induced in male rats by endotoxin or lipopolysaccharide (LPS, 1 mg/kg ip) given 2 or 7 days earlier. Neurons responsive to mechanical stimulation of the ocular surface were recorded under barbiturate anesthesia at the trigeminal subnucleus interpolaris/caudalis (Vi/Vc) transition and subnucleus caudalis/cervical cord (Vc/C1) junction, the main terminal regions for corneal nociceptors. Two days after LPS, Vc/C1 units had reduced responses to histamine, nicotine, and CO2 gas applied to the ocular surface, whereas unit responses were increased 7 days after LPS. Those units with convergent cutaneous receptive fields at Vc/C1 were enlarged 7 days after LPS. Units at the Vi/Vc transition also had reduced responses to histamine and CO2 2 days after LPS but no enhancement was seen at 7 days. Tear volume evoked by CO2 was reduced 2 days after LPS and returned toward control values by 7 days, whereas CO2-evoked eye blinks were normal at 2 days and increased 7 days after LPS. These results indicate that a single exposure to endotoxin causes long-term changes in the excitability of second-order neurons responsive to noxious ocular stimulation. The differential effects of EIU on tear volume and eye blink lend further support for the hypothesis that ocular-sensitive neurons at the Vi/Vc transition and Vc/C1 junction regions mediate different aspects of pain during intraocular inflammation.

Central nervous system manifestations of rheumatologic diseases

PURPOSE OF REVIEW

To summarize the current literature on central nervous system manifestations of vasculitides and connective tissue diseases.

RECENT FINDINGS

There have been advances in understanding the mechanisms behind the initiation and perpetuation of inflammatory processes in vasculitic neuropathy. Clinically relevant data have been obtained on the predictive criteria for a positive biopsy result in giant cell arteritis, the imaging characteristics of primary angiitis of the central nervous system, and Behçet disease, and the clinical and radiologic features of neuro-Behçet disease. There is more clarity about the central nervous system syndromes attributable to systemic lupus erythematosus and new insights into the central mechanisms involved in the manifestations of Sjögren syndrome and rheumatoid arthritis. Novel immunomodulatory agents, such as infliximab, have shown some benefit in rheumatoid vasculitis and Sjögren syndrome.

SUMMARY

A better understanding of the clinical, radiographic, and serologic characteristics of various central nervous system complications of rheumatologic diseases has been gained in the past year. Recent advances in understanding the pathophysiology of peripheral nervous system complications and their treatment may affect the management of the central nervous system complications.

A novel class of neurons at the trigeminal subnucleus interpolaris/caudalis transition region monitors ocular surface fluid status and modulates tear production

Reflex tears are produced by many conditions, one of which is drying of the ocular surface. Although peripheral neural control of the lacrimal gland is well established, the afferent pathways and properties of central premotor neurons necessary for this reflex are not known. Male rats under barbiturate anesthesia were used to determine whether neurons at the ventral trigeminal subnucleus interpolaris- caudalis (Vi/Vc) transition or the trigeminal subnucleus caudalis-cervical cord (Vc/C1) junction region in the lower brainstem were necessary for tears evoked by noxious chemical stimulation (CO2 pulses) or drying of the ocular surface. Both the Vi/Vc transition and Vc/C1 junction regions receive a dense direct projection from corneal nociceptors. Synaptic blockade of the Vi/Vc transition, but not the Vc/C1 junction, by the GABA(A) receptor agonist muscimol inhibited CO2-evoked tears. Glutamate excitation of the Vi/Vc transition, but not the Vc/C1 junction, increased tear volume. Single units recorded at the Vi/Vc transition, but not at the Vc/C1 junction, were inhibited by wetting and excited by drying the ocular surface. Nearly all moisture-sensitive Vi/Vc units displayed an initial inhibitory phase to noxious concentrations of CO2 followed by delayed excitation and displayed an inhibitory surround receptive field from periorbital facial skin. Drying of the ocular surface produced many Fos-positive neurons at the Vi/Vc transition, but not at the Vc/C1 junction. This is the first report of a unique class of moisture-sensitive neurons that exist only at the ventral Vi/Vc transition, and not at more caudal portions of Vc, that may underlie fluid homeostasis of the ocular surface.

New Insights into the Diagnosis and Treatment of Dry Eye

Over the past decade, numerous advances have been made in relation to dry eye diagnostic markers, technologies, and treatment options. The mainstay of treatment of dry eye is the use of artificial tear solutions and punctum plugs. A goal is the development of agents that provide symptomatic treatment and, at the same time, improve ocular surface keratinization. It is the authors' opinion that the functional visual acuity tester and the new tear stability analysis system will be widely used to improve diagnosis and evaluate treatment outcomes in KCS. Advances in treatment will utilize anti-inflammatory agents, immune suppressants such as Cyclosporin A and FK-506, growth hormones, androgens, topical mucins and ocular surface stimulating drugs, like INS365. Although aqueous-deficient dry eye is most commonly not associated with Sjogren syndrome (SS), aqueous-deficient dry eye is often most severe in patients with SS; thus, this article focuses mainly on SS-associated dry eye.