Influence of the hypothalamic arcuate nucleus on intraocular pressure and the role of opioid peptides

Paraventricular Hypothalamic Nucleus Upregulates Intraocular Pressure Via Glutamatergic Neurons

Purpose

The neuroregulatory center of intraocular pressure (IOP) is located in the hypothalamus. An efferent neural pathway exists between the hypothalamic nuclei and the autonomic nerve endings in the anterior chamber of the eye. This study was designed to investigate whether the paraventricular hypothalamic nucleus (PVH) regulates IOP as the other nuclei do.

Methods

Optogenetic manipulation of PVH neurons was used in this study. Light stimulation was applied via an optical fiber embedded over the PVH to activate projection neurons after AAV2/9-CaMKIIα-hChR2-mCherry was injected into the right PVH of C57BL/6J mice. The same methods were used to inhibit projection neurons after AAV2/9-CaMKIIα-eNpHR3.0-mCherry was injected into the bilateral PVH of C57BL/6J mice. AAV2/9-EF1α-DIO-hChR2-mCherry was injected into the right PVH of Vglut2-Cre mice to elucidate the effect of glutamatergic neuron-specific activation. IOP was measured before and after light manipulation. Associated nuclei activation was clarified by c-Fos immunohistochemical staining. Only mice with accurate viral expression and fiber embedding were included in the statistical analysis.

Results

Activation of projection neurons in the right PVH induced significant bilateral IOP elevation (n = 11, P < 0.001); the ipsilateral IOP increased more noticeably (n = 11, P < 0.05); Bilateral inhibition of PVH projection neurons did not significantly influence IOP (n = 5, P > 0.05). Specific activation of glutamatergic neurons among PVH projection neurons also induced IOP elevation in both eyes (n = 5, P < 0.001). The dorsomedial hypothalamic nucleus, ventromedial hypothalamic nucleus, locus coeruleus and basolateral amygdaloid nucleus responded to light stimulation of PVH in AAV-ChR2 mice.

Conclusions

The PVH may play a role in IOP upregulation via glutamatergic neurons.

Effect of alternate nostril breathing exercise on autonomic functions, ocular hypertension, and quality of life in elderly with systemic hypertension and high-tension primary open-angle glaucoma

Investigating the response of ocular hypertension and quality of life to a 4-week alternate-nostril breathing exercise (ANBE) in older adults with systemic hypertension (SH) and high-tension form of primary open-angle glaucoma (HTF-POAG) was our aim. Sixty older adults with SH and HTF-POAG were randomly assigned to the ANBE group (n=30, received morning and evening 30 min sessions of daily ANBE) or the control (waitlist) group (n=30). Right-eye intraocular pressure (IOP), left-eye IOP, blood pressure, short-form-36 survey (SF36S), rates of respiration and radial-artery pulsation, hospital anxiety and depression scale (depression subscale abbreviated as HADS-D and anxiety subscale abbreviated as HADS-A), and glaucoma quality-of-life 15-item questionnaire (GQoL-15) were assessed. All measurements were improved in the ANBE group only. In conclusion, a 4-week ANBE could be an adjunctive modality to improve HADS-D, rates of respiration and radial-artery pulsation, HADS-A, blood pressure, IOP, GQol-15, and SF36S in older adults SH and HTF-POAG.

Anatomical Evidence for the Neural Connection from the Emotional Brain to Autonomic Innervation in the Anterior Chamber Structures of the Eye

OBJECTIVE

Previous studies have shown that the autonomic nervous system (ANS), which can be affected by emotions, is important in the occurrence or progression of glaucoma. The autonomic innervation distributed in the anterior chamber (AC) structures might play an efferent role in the neural regulation of intraocular pressure (IOP). This study aimed to investigate the anatomic neural connection from the emotional brain to autonomic innervation in the AC.

METHODS

A retrograde trans-multisynaptic pseudorabies virus encoded with an enhanced green fluorescent protein (PRV531) and non-trans-synaptic tracer FAST Dil were injected into the right eye of mice, respectively. Fluorescent localization in the emotional brain and preganglionic nuclei was studied. Five and a half days after PRV531 injection into the right AC, fluorescent signals were observed in several emotional brain regions, including the amygdala, agranular insular cortex, lateral septal nuclei, periaqueductal gray, and hypothalamus. Autonomic preganglionic nuclei, including Edinger-Westphal nucleus, superior salivatory nucleus, and intermediolateral nucleus, were labeled using PRV531.

RESULTS

The sensory trigeminal nuclei were not labeled using PRV531. The fluorescence signals in the nuclei mentioned above showed bilateral distribution, primarily on the ipsilateral side. Seven days after injecting FAST Dil into the AC, we observed no FAST Dil-labeled neurons in the central nervous system.

CONCLUSION

Our results indicate a neural connection from the emotional brain to autonomic innervation in the AC, which provides anatomical support for the emotional influence of IOP via the ANS.

Glymphatic imaging and modulation of the optic nerve

Optic nerve health is essential for proper function of the visual system. However, the pathophysiology of certain neurodegenerative disease processes affecting the optic nerve, such as glaucoma, is not fully understood. Recently, it was hypothesized that a lack of proper clearance of neurotoxins contributes to neurodegenerative diseases. The ability to clear metabolic waste is essential for tissue homeostasis in mammals, including humans. While the brain lacks the traditional lymphatic drainage system identified in other anatomical regions, there is growing evidence of a glymphatic system in the central nervous system, which structurally includes the optic nerve. Named to acknowledge the supportive role of astroglial cells, this perivascular fluid drainage system is essential to remove toxic metabolites from the central nervous system. Herein, we review existing literature describing the physiology and dysfunction of the glymphatic system specifically as it relates to the optic nerve. We summarize key imaging studies demonstrating the existence of a glymphatic system in the optic nerves of wild-type rodents, aquaporin 4-null rodents, and humans; glymphatic imaging studies in diseases where the optic nerve is impaired; and current evidence regarding pharmacological and lifestyle interventions that may help promote glymphatic function to improve optic nerve health. We conclude by highlighting future research directions that could be applied to improve imaging detection and guide therapeutic interventions for diseases affecting the optic nerve.

Effect of Mindfulness Meditation on Intraocular Pressure and Trabecular Meshwork Gene Expression: A Randomized Controlled Trial

PURPOSE

To evaluate the effect of mindfulness meditation (MM) on intraocular pressure (IOP) and trabecular meshwork (TM) gene expression in patients with medically uncontrolled primary open angle glaucoma (POAG).

DESIGN

Parallel arm, single-masked, randomized controlled trial.

METHODS

Sixty POAG patients with IOP ≥21 mm Hg taking maximal topical medication and scheduled for trabeculectomy were included in this study at a tertiary eye care center in India. Thirty patients (Group 1) underwent 3 weeks of 45-minute daily MM sessions in addition to medical therapy while Group 2 continued medical therapy only. Primary outcome was change in IOP (ΔIOP) after 3 weeks of MM. Secondary outcomes were probability of success, percentage of reduction in IOP, effect on diurnal variations of IOP, changes in quality of life (QoL), and changes in gene expression patterns in TM.

RESULTS

At 3 weeks, a significant decrease in IOP was seen in Group 1 (20.16 ± 3.3 to 15.05 ± 2.4mm Hg; P = .001), compared to Group 2 (21.2 ± 5.6 to 20.0 ± 5.8mm Hg; P = .38). ΔIOP was significantly higher in Group 1 than in Group 2 (5.0 ± 1.80 vs. 0.20 ± 3.03mm Hg; P = .001). Analysis of gene expression revealed significant upregulation of nitric oxide synthetase (NOS1 and NOS3) and neuroprotective genes with downregulation of proinflammatory genes in Group 1 in comparison to Group 2 (P = .001).

CONCLUSIONS

MM was associated with significant decrease in IOP and changes in TM gene expression, indicating its direct impact on ocular tissues.

Delta Opioids: Neuroprotective Roles in Preclinical Studies

Since ancient times, opioids have been used clinically and abused recreationally. In the early stages (about 1,000 AD) of opium history, an Arab physician, Avicenna, administered opioids to control diarrhea and eye diseases. ¹ Opioids have very strong pain relieving properties and they also regulate numerous cellular responses. Opioid receptors are expressed throughout the body, including the nervous system, heart, lungs, liver, gastrointestinal tract, and retina. ^2-6 Delta opioid receptors (DORs) are a very attractive target from the perspective of both receptor function and their therapeutic potential. Due to a rapid progress in mouse mutagenesis and development of small molecules as DOR agonist, novel functions and roles of DORs have emerged in recent years. This review article focuses on the recent advances in the neuroprotective roles of DOR agonists in general and retina neuroprotection in particular. Rather than being exhaustive, this review highlights the selected studies of DOR function in neuroprotection. We also highlight our preclinical studies using rodent models to demonstrate the potentials of DOR agonists for retinal neuroprotection. Based on existing literature and our recently published data on the eye, DOR agonists possess therapeutic abilities that protect the retina and optic nerve injury against glaucoma and perhaps other retinopathies as well. This review also highlights the signaling events associated with DOR for neuroprotection in the eye. There is a need for translational research on DORs to recognize their potential for clinical application such as in glaucoma.

Meditation enhances brain oxygenation, upregulates BDNF and improves quality of life in patients with primary open angle glaucoma: A randomized controlled trial

BACKGROUND

Glaucoma (POAG) is a kind of neurodegenerative disease known to be closely associated with stress and adverse quality of life (QOL). Stress has also been shown to be involved in etiopathogenesis of primary open angle glaucoma (POAG). Complementary treatment in form of Meditation has been reported to improve QOL, brain oxygenation and decrease markers of stress. With this premise, a randomized controlled trial was carried out to assess the effect of Meditation on intraocular pressure, subjective QOL and objective markers of stress and brain oxygenation in patients with POAG.

METHODS

Sixty patients were randomized into intervention and control groups. Intervention group underwent 45 minutes of Meditation daily for 6 weeks in addition to standard medical treatment while controls received only standard medical treatment. Inclusion criteria were patients with POAG, age >45 years, best corrected visual acuity >6/60. Patients with other ocular co-morbid conditions contributing to vision loss, systemic diseases, patients already practicing meditation in any form were excluded. An assessment of IOP, brain oxygenation using functional near infrared spectroscopy (fNIRS), QOL (WHO-BREF QOL) and stress markers in serum (cortisol, β-endorphins, interleukin-6, brain derived neurotrophic factor (BDNF), reactive oxygen species) was made at baseline and at 6 weeks.

RESULTS

21 female and 39 male patients were enrolled with a mean age of 57.28±9.37 years. All parameters were comparable between two groups at baseline. At 6 weeks mean level of IOP decreased significantly in intervention group (15.9±1.8 mmHg to 14.4±1.21 mm Hg, p-value 0.0001) as compared to control group (15.7±1.4 mmHg to 15.65±1.41, p-value 0.41). fNIRS showed significant improvement in oxygenated hemoglobin change (ΔHbO) in intervention group in the prefrontal cortex (p-value <  0.0001) as compared to control group (p-value 0.52). WHO-BREF QOL score increased significantly in intervention group (86.6±6.16 to 93.3±5.66, p-value 0.0001) as compared to control (89±7.25 to 89.07±3.24, p-value 0.74).Mean serum cortisol decreased significantly in intervention group (497±46.37 ng/ml to 447±53.78 ng/ml, p-value 0.01) as compared to control group (519.75±24.5 to 522.58±26.63 ng/ml, p-value 0.64). Mean β-endorphin levels increased significantly (33±5.52pg/ml to 43.27pg/ml, p-value <  0.0001) as compared to control group (34.78±4.1pg/ml to 36.33pg±4.07pg/ml p-value 0.27). Interleukin-6 decreased significantly in intervention group (2.2±0.5 ng/ml to 1.35±0.32 ng/ml, p-value <  0.0001) as compared to control group (2.03±0.37 to 2.17±0.34 ng/ml p-value 0.25). BDNF increased significantly in intervention group (52.24±6.71 to 63.25±13.48 ng/ml p-value 0.004) as compared to control group (53.23±5.82 to 54.42±5.66 ng/ml p-value 0.54). ROS decreased significantly in intervention group (1596.19±179.14 to 1261±244.31 RLU/min/104 neutrophils p-value 0.0001) as compared to control group (1577.5±172.02 to 1662.5±84.75 RLU/min/104 neutrophils p-value 0.16).

CONCLUSIONS

A short term course of Meditation was associated with significant improvement in brain oxygenation and QOL along with a reduction in IOP and stress markers. Meditation may be a useful as an adjunct to standard treatment in patients with POAG and potentially decrease the risk of glaucoma progression.

The increased expression of GABA receptors within the arcuate nucleus is associated with high intraocular pressure

PURPOSE

To investigate the relationship between intraocular pressure (IOP) and GABA receptors within the arcuate nucleus (ARC).

METHODS

In the chronic high IOP rat model, ibotenic acid (IBO) was injected to induce impairment of the ARC, and IOP was measured at the 0, 1, 2, 3, and 4 week time points with a Tono-Pen. To assess the expression of GABA-A/B receptors within the ARC under persistent high IOP, we performed immunofluorescence (IF) and immunohistochemical (IHC) staining at 2 weeks and 4 weeks. Furthermore, we treated the ARC with GABA-A/B receptor antagonists separately, and IOP was evaluated, as well as retinal ganglion cell apoptosis in the chronic high IOP rat model. In the following induced high IOP animal model, the expression of GABA-A/B receptors within the ARC was evaluated in DBA/2J mice which developed progressive eye abnormalities spontaneously that closely mimic human hereditary glaucoma.

RESULTS

Compared with the control group, statistically significant downregulation of IOP was noted due to the IBO injection into the ARC at the 2, 3, and 4 week time points (p<0.05). Persistent high IOP elicited increased expression of the GABA-A/B receptors in the ARC compared with the control group (p<0.01). In addition, treatment with GABA-A/B receptor antagonists separately caused a decrease in the IOP, along with reduced retinal ganglion cell apoptosis (p<0.01). In the DBA/2J mice, the expression of the GABA receptors was statistically significantly increased (p<0.01).

CONCLUSIONS

GABA-A/B receptors in the ARC may be involved in regulation of IOP, and pathologically high IOP affects the expression of GABA-A/B receptors in the ARC.

Mental stress as consequence and cause of vision loss: the dawn of psychosomatic ophthalmology for preventive and personalized medicine

The loss of vision after damage to the retina, optic nerve, or brain has often grave consequences in everyday life such as problems with recognizing faces, reading, or mobility. Because vision loss is considered to be irreversible and often progressive, patients experience continuous mental stress due to worries, anxiety, or fear with secondary consequences such as depression and social isolation. While prolonged mental stress is clearly a consequence of vision loss, it may also aggravate the situation. In fact, continuous stress and elevated cortisol levels negatively impact the eye and brain due to autonomous nervous system (sympathetic) imbalance and vascular dysregulation; hence stress may also be one of the major causes of visual system diseases such as glaucoma and optic neuropathy. Although stress is a known risk factor, its causal role in the development or progression of certain visual system disorders is not widely appreciated. This review of the literature discusses the relationship of stress and ophthalmological diseases. We conclude that stress is both consequence and cause of vision loss. This creates a vicious cycle of a downward spiral, in which initial vision loss creates stress which further accelerates vision loss, creating even more stress and so forth. This new psychosomatic perspective has several implications for clinical practice. Firstly, stress reduction and relaxation techniques (e.g., meditation, autogenic training, stress management training, and psychotherapy to learn to cope) should be recommended not only as complementary to traditional treatments of vision loss but possibly as preventive means to reduce progression of vision loss. Secondly, doctors should try their best to inculcate positivity and optimism in their patients while giving them the information the patients are entitled to, especially regarding the important value of stress reduction. In this way, the vicious cycle could be interrupted. More clinical studies are now needed to confirm the causal role of stress in different low vision diseases to evaluate the efficacy of different anti-stress therapies for preventing progression and improving vision recovery and restoration in randomized trials as a foundation of psychosomatic ophthalmology.

Non-continuous measurement of intraocular pressure in laboratory animals

Glaucoma is a leading cause of blindness, which is treatable but currently incurable. Numerous animal models therefore have both been and continue to be utilized in the study of numerous aspects of this condition. One important facet associated with the use of such models is the ability to accurately and reproducibly measure (by cannulation) or estimate (by tonometry) intraocular pressure (IOP). At this juncture there are several different approaches to IOP measurement in different experimental animal species, and the list continues to grow. We feel therefore that a review of this subject matter is timely and should prove useful to others who wish to perform similar measurements. The general principles underlying various types of tonometric and non-tonometric techniques for non-continuous determination of IOP are considered. There follows discussion of specific details as to how these techniques are applied to experimental animal species involved in the research of this disease. Specific comments regarding anesthesia, circadian rhythm, and animal handling are also included, especially in the case of rodents. Brief consideration is also given to possible future developments.