Determination of dopamine D1 receptors in the human uveo scleral tissue by light microscope autoradiography

Evaluation of corneal endothelial cell morphology off and on treatment by specular microscopy in children and adolescents with attention deficit hyperactivity disorder

PURPOSE

To determine the structure and properties of corneal endothelial cells in children and adolescents with ADHD who received methylphenidate treatment at least six months.

METHOD

The prospective, observational study included 33 eyes of 33 patients diagnosed with ADHD who received methylphenidate treatment for at least six months, 33 eyes of 33 patients newly diagnosed with ADHD who did not start medication treatment, and 33 eyes of 33 healthy individuals. Average cell density, coefficient of variation, maximum cell area, normal cell area, minimum cell area, average cell area, and hexagonality ratio values were evaluated by non-contact specular microscopy. The parameters recorded in all three groups were compared.

RESULTS

The average age of children in the ADHD + MPH, ADHD, and control groups is 9 ± 1.7, 8.9 ± 2.3, and 8.9 ± 1.8 years, respectively. (p > 0.05) The average MPH treatment dose is 0.94 ± 0.19 mg/kg, the average daily MPH intake is 34.12 ± 14.04 mg, and the average duration of use of MPH is 24.03 ± 12.46 months. Central corneal thickness (CCT) was measured as an average of 540.45 ± 31.23 in the ADHD + MPH group, 540.61 ± 29.69 in the ADHD group, and 546.58 ± 27.72 in the control group. (p = 0.499) The average coefficient of variation (CV) values were measured as 25.48 ± 4.22 in the ADHD + MPH group, 26.12 ± 3.48 in the ADHD group, and 26.12 ± 3.64 in the control group. (p = 0.491) The average hexagonality ratio (%) (HEX) values were measured as 69.45 ± 8.41 in the ADHD + MPH group, 68.21 ± 6.82 in the ADHD group, and 68.91 ± 7.97 in the control group. (p = 0.892) No statistically significant difference was observed between all three groups in terms of all parameters.

CONCLUSION

Methylphenidate treatment administered for at least six months with a diagnosis of ADHD did not have a toxic effect on the corneal endothelium.

Dopamine outside the brain: The eye, cardiovascular system and endocrine pancreas

Dopamine (DA) and DA receptors (DR) have been extensively studied in the central nervous system (CNS), but their role in the periphery is still poorly understood. Here we summarize data on DA and DRs in the eye, cardiovascular system and endocrine pancreas, three districts where DA and DA-related drugs have been studied and the expression of DR documented. In the eye, DA modulates ciliary blood flow and aqueous production, which impacts on intraocular pressure and glaucoma. In the cardiovascular system, DA increases blood pressure and heart activity, mostly through a stimulation of adrenoceptors, and induces vasodilatation in the renal circulation, possibly through D1R stimulation. In pancreatic islets, beta cells store DA and co-release it with insulin. D1R is mainly expressed in beta cells, where it stimulates insulin release, while D2R is expressed in both beta and delta cells (in the latter at higher level), where it inhibits, respectively, insulin and somatostatin release. The formation of D2R-somatostatin receptor 5 heteromers (documented in the CNS), might add complexity to the system. DA may exert both direct autocrine effects on beta cells, and indirect paracrine effects through delta cells and somatostatin. Bromocriptine, an FDA approved drug for diabetes, endowed with both D1R (antagonistic) and D2R (agonistic) actions, may exert complex effects, resulting from the integration of direct effects on beta cells and paracrine effects from delta cells. A full comprehension of peripheral DA signaling deserves further studies that may generate innovative therapeutic drugs to manage conditions such as glaucoma, cardiovascular diseases and diabetes.

Circadian rhythms, refractive development, and myopia

PURPOSE

Despite extensive research, mechanisms regulating postnatal eye growth and those responsible for ametropias are poorly understood. With the marked recent increases in myopia prevalence, robust and biologically-based clinical therapies to normalize refractive development in childhood are needed. Here, we review classic and contemporary literature about how circadian biology might provide clues to develop a framework to improve the understanding of myopia etiology, and possibly lead to rational approaches to ameliorate refractive errors developing in children.

RECENT FINDINGS

Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Systemically, such rhythms are primarily generated by the 'master clock' in the surpachiasmatic nucleus, which receives input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) through the activation of the photopigment melanopsin. The retina also has an endogenous circadian clock. In laboratory animals developing experimental myopia, oscillations of ocular parameters are perturbed. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light:dark cycle, but it also modulates refractive development. Circadian clocks comprise a transcription/translation feedback control mechanism utilizing so-called clock genes that have now been associated with experimental ametropias. Contemporary clinical research is also reviving ideas first proposed in the nineteenth century that light exposures might impact refraction in children. As a result, properties of ambient lighting are being investigated in refractive development. In other areas of medical science, circadian dysregulation is now thought to impact many non-ocular disorders, likely because the patterns of modern artificial lighting exert adverse physiological effects on circadian pacemakers. How, or if, such modern light exposures and circadian dysregulation contribute to refractive development is not known.

SUMMARY

The premise of this review is that circadian biology could be a productive area worthy of increased investigation, which might lead to the improved understanding of refractive development and improved therapeutic interventions.

Role of dopaminergic receptors in glaucomatous disease modulation

Both studies on animals and humans suggest the presence of dopamine (DA) receptors in the anterior segment of the eye. Their role in the dynamics of intraocular pressure (IOP) is not yet clear. DA₂ and DA₃ receptors are mainly located on postganglionic sympathetic nerve endings. Their stimulation reduces the release of norepinephrine and suppresses the production of aqueous humor. DA₁ receptors seem to be more expressed by the ciliary body and the outflow pathway of aqueous humor. The administration of DA₁-selective agonists stimulates the production of aqueous humor, increasing IOP, whereas DA₂- and DA₃-selective agonists could reduce IOP and, therefore, the risk to develop a glaucoma (GL). GL is a broad spectrum of eye diseases which have in common the damage to the optic nerve and the progressive loss of the visual field. Further studies are desirable to clarify the role of the dopaminergic system and the usefulness of DA₂ and DA₃ agonists in reducing IOP.

Dose-dependent immunohistochemical changes in rat cornea and retina after oral methylphenidate administration

Methylphenidate hydrochloride (MPH), more commonly known as Ritalin, is a piperidine derivative and is the drug most often used to treat attention deficit/hyperactivity disorder, one of the most common behavioural disorders of children and young adults. The aim of this study was to investigate dose-dependent immunohistochemical Dopamine 2 receptor (D2) expression and apoptosis in the rat cornea and cornea. In this study, 27 female pre-pubertal Wistar albino rats, divided into three different dose groups (5, 10 and 20 mg/kg) and their control groups, were used. They were treated orally with methylphenidate dissolved in saline solution for 5 days per week during 3 months. At the end of the third month, after perfusion fixation, eye tissue was removed. Paraffin sections were collected for immunohistochemical and terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick end labelling assay studies. In our study, we observed that the cornea D2 receptor reactivity showed a dose-related increase after MPH treatment, especially in basal cells of the epithelium and a dose-dependent decrease in the retinal ganglion cell which was statistically meaningful. Analysis of the cornea thickness results showed no meaningful difference between groups. Apoptotic cell number showed a meaningful increase in the high dose treated group compared to the other groups of the study. The data suggest that Ritalin has degenerative effect on the important functional part of the eye, such as cornea and retina and its activating dopaminergic mechanism via similar neuronal paths, functionally and structurally, to induce morphological changes. As a result, we believe that this morphological changes negatively effecting functional organization of the affected cornea and retina.

Dopamine receptors in the human dura mater

Dopamine receptors (Dar) were studied as a component of the nervous dopaminergic system in the human dura mater. Dar were stained in several dural zones (vascular, perivascular, intervascular) in different regions (basal, calvarial, tentorial, occipital, frontal, parietal, temporal) of the cranial meninges. Specimens of human dura mater were harvested from autopsies of 10 elderly male subjects (age range, 60-75 years). Dar were labeled with specific (H3) markers, studied with radiobinding techniques (including liquid scintillation), stained for light microscope autoradiography, and measured by means of quantitative analysis of images. All results were evaluated with statistical analysis to identify significant results. More dural Dar were found in the basal region than in the calvarial one. Moreover, Dar are more abundant in the vascular and perivascular dural zone than in the intervascular one. The vascular distribution of Dar seemed to indicate that Dar play a role in the control of meningeal blood vessels. The location and distribution of D1 and D2 receptors in the human cranial dura mater confirmed the presence of a dopaminergic system, which could play an important role in controlling blood flow and/or other functions of meningeal membranes.