Activation of muscarinic acetylcholine receptors elicits pigment granule dispersion in retinal pigment epithelium isolated from bluegill

Circadian Rhythms of Retinomotor Movement in a Marine Megapredator, the Atlantic Tarpon, Megalops atlanticus

Many ecologically and economically important marine fish species worldwide spend portions of their lives in coastal regions that are increasingly inundated by artificial light at night. However, while extensive research illustrates the harmful effects of inappropriate light exposure on biological timing in humans, rodents and birds, comparable studies on marine fish are virtually nonexistent. This study aimed to assess the effects of light on biological clock function in the marine fish retina using the Atlantic tarpon (Megalops atlanticus) as a model. Using anti-opsin immunofluorescence, we observed robust rhythms of photoreceptor outer segment position (retinomotor movement) over the course of the daily light-dark cycle: cone outer segments were contracted toward the inner retina and rods were elongated during the day; the opposite occurred at night. Phase shifting the daily light-dark cycle caused a corresponding shift of retinomotor movement timing, and cone retinomotor movement persisted in constant darkness, indicating control by a circadian clock. Constant light abolished retinomotor movements of both photoreceptor types. Thus, abnormally-timed light exposure may disrupt normal M. atlanticus clock function and harm vision, which in turn may affect prey capture and predator avoidance. These results should help inform efforts to mitigate the effects of coastal light pollution on organisms in marine ecosystems.

Near-infrared fundus autofluorescence in subclinical best vitelliform macular dystrophy

PURPOSE

To describe fundus autofluorescence (FAF) on short-wavelength FAF and near-infrared FAF in the subclinical form of Best vitelliform macular dystrophy.

DESIGN

Cross-sectional prospective study.

METHODS

Patients affected by the subclinical form of Best vitelliform macular dystrophy (positive testing for BEST1 gene mutation, fully preserved best-corrected visual acuity, normal fundus appearance) were recruited. Each patient underwent a complete ophthalmologic examination, including electro-oculogram (EOG), short-wavelength FAF, near-infrared FAF, spectral-domain OCT (SD OCT), and microperimetry. Main outcome measure was the identification of abnormal FAF patterns.

RESULTS

Forty-six patients showing mutations in the BEST1 gene were examined. Forty patients presented a bilateral Best vitelliform macular dystrophy, 2 patients showed a unilateral Best vitelliform macular dystrophy, and 4 patients had a bilateral subclinical form. Patients with the unilateral form (2 eyes) and patients with the subclinical form (8 eyes) were analyzed. Three BEST1 sequence variants were identified: c.73C>T (p.Arg25Trp), c.28G>A (p.Ala10Thr), and c.652C>G (p.Arg218Gly). Short-wavelength FAF was normal in all eyes. Near-infrared FAF detected a pattern consisting of a central hypo-autofluorescence surrounded by a round area of hyper-autofluorescence. A bilateral reduced EOG response was detected in 1 patient. SD OCT revealed a thicker, well-defined, and more reflective interdigitation zone in 2 patients (4 eyes, 40%). Microperimetry of the central 10 degrees revealed a slight, diffuse reduction of retinal sensitivity. Mean retinal sensitivity within the central 2 and 4 degrees was lower and matched the hypo-autofluorescent area detected on near-infrared FAF. Additional relative scotomata were detected within the 10-degree area. No change in clinical, functional, or FAF pattern was found over the follow-up.

CONCLUSIONS

Subclinical Best vitelliform macular dystrophy is characterized by the absence of biomicroscopic fundus abnormality and fully preserved visual acuity, but shows an abnormal near-infrared FAF pattern, with central hypo-autofluorescence.

Fundus autofluorescence patterns in Best vitelliform macular dystrophy

PURPOSE

To provide a systematic classification of fundus autofluorescence (FAF) patterns in patients affected by Best vitelliform macular dystrophy.

DESIGN

Cross-sectional prospective study.

METHODS

Patients affected by Best vitelliform macular dystrophy at different stages of the disease were prospectively enrolled from January 2012 to July 2013. Eighty eyes of 40 patients were included in the study. All patients underwent a complete ophthalmologic examination, including genetic characterization, short-wavelength FAF, and near-infrared FAF. Main outcome measures were the recognition of the FAF patterns in the different stages and the identification of a relationship between FAF patterns and best-corrected visual acuity (BCVA).

RESULTS

Six FAF patterns for both short-wavelength and near-infrared FAF were identified, including normal, hyper-autofluorescent, hypo-autofluorescent, patchy, multifocal, and spoke-like patterns. Applying Gass's classification for defining consecutive stages of Best vitelliform macular dystrophy (namely vitelliform, pseudohypopyon, vitelliruptive, atrophic, and cicatricial) identified no pattern as stage-specific. Patchy patterns had the highest prevalence. A statistically significant difference (Kruskal-Wallis ANOVA) was found among hyper-autofluorescent, patchy, and hypo-autofluorescent patterns, both in short-wavelength (P = .001) and near-infrared FAF (P = .001). Hyper-autofluorescent and hypo-autofluorescent patterns were associated with better and worse BCVA, respectively.

CONCLUSIONS

Six main patterns on both short-wavelength and near-infrared FAF were identified in Best vitelliform macular dystrophy. No FAF pattern can be considered stage-specific. Although a difference in the BCVA among the FAF patterns was registered, only a longitudinal study designed to evaluate the clinical and FAF modifications over the follow-up will help clarify the prognostic implications of each FAF pattern.

Muscarinic receptor agonists and antagonists: effects on ocular function

Muscarinic agonists act mainly via muscarinic M₃ cholinoceptors to cause contraction of the iris sphincter, ciliary muscle and trabecular meshwork as well as increase outflow facility of aqueous humour. In the iris dilator, the effect of muscarinic agonists is species dependent but is predominantly relaxation via muscarinic M₃ receptors. In the conjunctiva, muscarinic agonists stimulate goblet cell secretion which contributes to the protective tear film. Muscarinic M₂ and M₃ receptors appear mainly involved. In the lens muscarinic agonists act via muscarinic M₁ receptors to produce depolarization and increase [Ca(2+)](i). All five subtypes of muscarinic receptor are present in the retina. In the developing retina, acetylcholine appears to limit purinergic stimulation of retinal development and decrease cell proliferation. In the adult retina acetylcholine and other muscarinic agonists may have complex effects, for example, enhancing light-evoked neuronal firing in transient ON retinal ganglion cells and inhibiting firing in OFF retinal ganglion cells. In the lacrimal gland, muscarinic agonists activate M₃ receptors on secretory globular acinar cells to stimulate tear secretion and also cause contraction of myoepithelial cells. In Sjögren's syndrome, antibodies to the muscarinic M₃ receptor disrupt normal gland function leading to xerophthalmia although the mechanism of action of the antibody is still not clear. Atropine and pirenzepine are useful in limiting the development of myopia in children probably by an action on muscarinic receptors in the sclera, although many other muscarinic receptor antagonists are not effective.

On the action and mechanism of withaferin-A from Withania somnifera, a novel and potent melanin dispersing agent in frog melanophores

The present work was carried out to determine the effects of lyophilized root extracts of Withania somnifera along with pure withaferin-A, on the isolated skin melanophores of frog, Rana tigerina which are disguised type of smooth muscle cells and offer excellent in vitro opportunities for studying the effects of pharmacological and pharmaceutical agents. The lyophilized extract of W. somnifera and its active ingredient withaferin-A induced powerful dose-dependent physiologically significant melanin dispersal effects in the isolated skin melanophores of R. tigerina, which were completely blocked by atropine as well as hyoscine. The per se melanin dispersal effects of lyophilized extracts of W. somnifera and its active ingredient withaferin-A got highly potentiated by neostigmine. It appears that the melanin dispersal effects of the extracts of W. somnifera and withaferin-A is mediated by cholino-muscarinic like receptors having similar properties.

Developmental expression of muscarinic receptors in the eyes of zebrafish

In previous work, we have shown that light-adaptive pigment granule dispersion can be induced in vitro by treating retinal pigment epithelium (RPE) isolated from bluegill retina with acetylcholine or its analog carbachol and that these agents act through muscarinic receptors to induce pigment granule dispersion. RPE is a monolayer of tissue found between the neural retina and the choroid. In fish, RPE has long apical projections enmeshed with the distal part of photoreceptors, reaching down to the level of their nuclei. The RPE disperses melanin pigment granules into the apical projections to shield light-sensitive photoreceptor outer segments from photobleaching when fish are under bright-light conditions. During development, RPE begin to respond to light at 5days post-fertilization, raising the question of whether responsiveness is correlated to receptor expression. Here, we isolate, clone and sequence chrm-odd receptor genes in zebrafish, characterize them phylogenetically and observe their expression in the eyes of the zebrafish at different developmental stages using RT-PCR and immunofluorescence microscopy. We find that zebrafish express six unique chrm-odd receptor subtypes: chrm1a, chrm1b, chrm3a, chrm3b, chrm5a and chrm5b - and these receptors are differentially expressed during development. Our phylogenetic analysis confirms the assignments of chrm1b and chrm5b, isolated here, as well as other muscarinic receptor genes and their duplicates and suggests previously described muscarinic receptors may need to be reclassified. Differences between the expression patterns of ostensibly duplicated genes raise the possibility that subtle differences between the duplicates may enable refined regulation of specific developmental events.

Nigella sativa seed extract and its bioactive compound thymoquinone: the new melanogens causing hyperpigmentation in the wall lizard melanophores

OBJECTIVE

The effects of the lyophilized seed extract of Nigella sativa and its active ingredient, thymoquinone, were studied on the isolated melanophores of the wall lizard to find the mechanism of skin darkening at the cellular level.

METHODS

The integumental melanophores of the wall lizard, Hemidactylus flaviviridis, were assayed using the mean melanophore size index and their responses were recorded in the presence of various concentrations of the plant extract, thymoquinone, specific antagonists and potentiator.

KEY FINDINGS

Significant skin darkening activity of the extract of N. sativa and thymoquinone was observed on the isolated melanophores of the wall lizard. The pigment cells responded by distinct dispersion leading to skin darkening. The effect was physiologically significant as re-immersion in physiological saline made the melanophores return to their normal intermediate state. These melanin dispersal effects were antagonized by atropine as well as hyoscine and were also found to be highly potentiated by neostigmine, an anticholinesterase agent.

CONCLUSIONS

These findings suggest that the extract of N. sativa, as well as its active principle, mimic the action of acetylcholine in melanin dispersion leading to skin darkening via stimulation of cholinergic receptors of muscarinic nature within the melanophores of wall lizard. This study opens new vistas for the use of N. sativa active ingredient, thymoquinone, as a novel melanogen for its clinical application in skin disorders such as hypopigmentation or vitiligo.

Carbachol-mediated pigment granule dispersion in retinal pigment epithelium requires Ca2+ and calcineurin

Background

Inside bluegill (Lepomis macrochirus) retinal pigment epithelial cells, pigment granules move in response to extracellular signals. During the process of aggregation, pigment motility is directed toward the cell nucleus; in dispersion, pigment is directed away from the nucleus and into long apical processes. A number of different chemicals have been found to initiate dispersion, and carbachol (an acetylcholine analog) is one example. Previous research indicates that the carbachol-receptor interaction activates a G_q-mediated pathway which is commonly linked to Ca²⁺ mobilization. The purpose of the present study was to test for involvement of calcium and to probe calcium-dependent mediators to reveal their role in carbachol-mediated dispersion.

Results

Carbachol-induced pigment granule dispersion was blocked by the calcium chelator BAPTA. In contrast, the calcium channel antagonist verapamil, and incubation in Ca²⁺-free medium failed to block carbachol-induced dispersion. The calcineurin inhibitor cypermethrin blocked carbachol-induced dispersion; whereas, two protein kinase C inhibitors (staurosporine and bisindolylmaleimide II) failed to block carbachol-induced dispersion, and the protein kinase C activator phorbol 12-myristate 13-acetate failed to elicit dispersion.

Conclusion

A rise in intracellular calcium is necessary for carbachol-induced dispersion; however, the Ca²⁺ requirement is not dependent on extracellular sources, implying that intracellular stores are sufficient to enable pigment granule dispersion to occur. Calcineurin is a likely Ca²⁺-dependent mediator involved in the signal cascade. Although the pathway leads to the generation of diacylglycerol and calcium (both required for the activation of certain PKC isoforms), our evidence does not support a significant role for PKC.

Molecular and pharmacological characterization of muscarinic receptors in retinal pigment epithelium: role in light-adaptive pigment movements

Muscarinic receptors are the predominant cholinergic receptors in the central and peripheral nervous systems. Recently, activation of muscarinic receptors was found to elicit pigment granule dispersion in retinal pigment epithelium isolated from bluegill fish. Pigment granule movement in retinal pigment epithelium is a light-adaptive mechanism in fish. In the present study, we used pharmacological and molecular approaches to identify the muscarinic receptor subtype and the intracellular signaling pathway involved in the pigment granule dispersion in retinal pigment epithelium. Of the muscarinic receptor subtype-specific antagonists used, only antagonists specific for M1 and M3 muscarinic receptors were found to block carbamyl choline (carbachol)-induced pigment granule dispersion. A phospholipase C inhibitor also blocked carbachol-induced pigment granule dispersion, and a similar result was obtained when retinal pigment epithelium was incubated with an inositol trisphosphate receptor inhibitor. We isolated M2 and M5 receptor genes from bluegill and studied their expression. Only M5 was found to be expressed in retinal pigment epithelium. Taken together, pharmacological and molecular evidence suggest that activation of an odd subtype of muscarinic receptor, possibly M5, on fish retinal pigment epithelium induces pigment granule dispersion.

Muscarinic receptors participation in angiogenic response induced by macrophages from mammary adenocarcinoma-bearing mice

Introduction

The role of macrophages in tumor progression has generated contradictory evidence. We had previously demonstrated the ability of peritoneal macrophages from LMM3 murine mammary adenocarcinoma-bearing mice (TMps) to increase the angiogenicity of LMM3 tumor cells, mainly through polyamine synthesis. Here we investigate the ability of the parasympathetic nervous system to modulate angiogenesis induced by TMps through the activation of the muscarinic acetylcholine receptor (mAchR).

Methods

Peritoneal macrophages from female BALB/c mice bearing a 7-day LMM3 tumor were inoculated intradermally (3 × 10⁵ cells per site) into syngeneic mice. Before inoculation, TMps were stimulated with the muscarinic agonist carbachol in the absence or presence of different muscarinic antagonists or enzyme inhibitors. Angiogenesis was evaluated by counting vessels per square millimeter of skin. The expression of mAchR, arginase and cyclo-oxygenase (COX) isoforms was analyzed by Western blotting. Arginase and COX activities were evaluated by urea and prostaglandin E₂ (PGE₂) production, respectively.

Results

TMps, which stimulate neovascularization, express functional mAchR, because carbachol-treated TMps potently increased new blood vessels formation. This response was completely blocked by preincubating TMps with pirenzepine and 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), M₁ and M₃ receptor antagonists, and partly by the M₂ receptor antagonist methoctramine. M₁ receptor activation by carbachol in TMps triggers neovascularization through arginase products because N^ω-hydroxy-L-arginine reversed the agonist action. Preincubation of TMps with methoctramine partly prevented carbachol-stimulated urea formation. In addition, COX-derived liberation of PGE₂ is responsible for the promotion of TMps angiogenic activity by M₃ receptor. We also detected a higher expression of vascular endothelial growth factor (VEGF) in TMps than in macrophages from normal mice. Carbachol significantly increased VEGF expression in TMps, and this effect was totally reversed by methoctramine and pirenzepine. Arginase and COX inhibitors partly decreased VEGF derived from TMps.

Conclusion

TMps themselves induce a potent angiogenic response that is augmented by carbachol action. mAchR activation triggers arginine metabolism, PGE₂ synthesis and VEGF production, promoting neovascularization.