Epinephrine regulates cholinergic transmission mediated by rat retinal neurons in culture

Effects of Constant Flickering Light on Refractive Status, 5-HT and 5-HT2A Receptor in Guinea Pigs

Purpose

To investigate the effects of constant flickering light on refractive development, the role of serotonin (i.e.5-hydroxytryptamine, 5-HT)and 5-HT2A receptor in myopia induced by flickering light in guinea pigs.

Methods

Forty-five guinea pigs were randomly divided into three groups: control, form deprivation myopia (FDM) and flickering light induced myopia (FLM) groups(n = 15 for each group). The right eyes of the FDM group were covered with semitransparent hemispherical plastic shells serving as eye diffusers. Guinea pigs in FLM group were raised with illumination of a duty cycle of 50% at a flash frequency of 0.5Hz. The refractive status, axial length (AL), corneal radius of curvature(CRC) were measured by streak retinoscope, A-scan ultrasonography and keratometer, respectively. Ultramicroscopy images were taken by electron microscopy. The concentrations of 5-HTin the retina, vitreous body and retinal pigment epithelium (RPE) were assessed by high performance liquid chromatography, the retinal 5-HT2A receptor expression was evaluated by immunohistofluorescence and western blot.

Results

The refraction of FDM and FLM eyes became myopic from some time point (the 4th week and the 6th week, respectively) in the course of the experiment, which was indicated by significantly decreased refraction and longer AL when compared with the controls (p<0.05). The concentrations of 5-HT in the retina, vitreous body and RPE of FDM and FLM eyes were significantly increased in comparison with those of control eyes (both p<0.05). Similar to FDM eyes, the expression of retinal 5-HT2A receptor in FLM eyes was significantly up-regulated compared to that of control eyes (both p<0.05). Western blot analysis showed that retinal 5-HT2A receptor level elevated less in the FLM eyes than that in the FDM eyes. Moreover, the levels of norepinephrine and epinephrine in FDM and FLM groups generally decreased when compared with control groups (all p<0.05).

Conclusions

Constant flickering light could cause progressive myopia in guinea pigs. 5-HT and 5-HT2A receptor increased both in form deprivation myopia and flickering light induced myopia, indicating that 5-HT possibly involved in myopic development via binding to5-HT2A receptor.

Analysis of fine structure and biochemical changes of retina during aging of Wistar albino rats

BACKGROUND

Aging is a biological phenomenon that involves an increase of oxidative stress associated with gradual degradation of the structure and function of the retina. Gender differences and subsequent deterioration of retinal cell layers is an interesting topic, especially because there is no published work concerning it.

METHODS

One hundred and twenty male and female Wistar albino rats ages 1, 6, 18, 30 and 42 months (n = 20 equal for male and female) were used. At the time interval, retinae were investigated by light and transmission electron microscopy, assessments of neurotransmitters, anti-oxidant enzymes (catalase, superoxide dismustase and glutathione S transferase), caspase-3 and -7, malonadialdhyde, and DNA fragmentation.

RESULTS

Light and transmission electron microscopy observations of the older specimens (30 and 42 months) revealed apparent deterioration of retinal cell layers, especially ganglion and nerve fibres, nuclear, pigmented epithelium and stacked membranes of the photoreceptor's outer segments. Males were highly susceptible to aging processes. Retinal DNA fragmentation was remarked parallel with increase of apoptic markers caspase 3 and 7. Concomitantly, there was a marked reduction of neurotransmitters and anti-oxidant enzymes, and an increase of lipid peroxidation.

CONCLUSIONS

Aging contributed to an increase of oxidative stress resulting from damage of mitochondria in retinal cells, a decrease of the anti-oxidant enzyme system and an increase of markers of retinal cell death.

Adenylyl cyclase/cAMP system involvement in the antiangiogenic effect of somatostatin in the retina. Results from transgenic mice

Neoangiogenesis is a response to retinal hypoxia that is inhibited by somatostatin (SRIF) through its subtype 2 receptor (sst2). Using a mouse model of hypoxia-induced retinopathy, we investigated whether inhibition of adenylyl cyclase (AC) is involved in SRIF anti-angiogenic actions. Hypoxia increased AC responsiveness in wild type (WT) retinas and in retinas lacking sst2, but not in sst2-overexpressing retinas. Hypoxia also altered AC isoform expression with different patterns depending on sst2 expression level. The AC VII isoform mRNA and protein resulted the most affected. Indeed, in hypoxia AC VII expression was enhanced in WT retinas and it was further increased in sst2-lacking retinas, whereas in sst2 overexpressing retinas the increase of AC VII was lower than in WT retinas. These data suggest an involvement of AC/cAMP in mediating both hypoxia-evoked retinal neoangiogenesis and SRIF protective actions. The AC VII isoform is a candidate to a main role in these mechanisms.

Co-localization of adrenergic receptors and vitamin-D-dependent calcium-binding protein (calbindin) in the dopaminergic amacrine cells of the rat retina

Using antisera against tyrosine hydroxylase (TH) and purified beta 2-adrenergic receptors (beta 2-AdR), we found that TH- and AdR-like immunoreactivities coexisted in large amacrine cells. These findings indicated an association between dopamine-containing amacrine cells and adrenergic amacrine cells. The present study also showed that amacrine cells with TH-like immunoreactivity have vitamin-D-dependent calcium-binding protein (calbindin, 27,000 kDa)-like immunoreactivity as well, suggesting that calbindin plays an important postsynaptic role in dopaminergic amacrine cells.

Participation of cyclic adenosine monophosphate and beta-adrenergic receptors in the facilitatory effect of noradrenaline on the response of cultured cerebellar neurons to glutamate

For the purpose of examining possible involvement of the cyclic adenosine monophosphate (cAMP) system and adrenergic receptors in the modulatory effect of noradrenaline (NA) on the glutamate-induced depolarizing response, the effects of dibutyryl cAMP (DBcAMP), forskolin, theophylline, clonidine, isoproterenol and propranolol were intracellularly investigated in the cerebellar neurons cultured from chick embryos. Not only NA-induced hyperpolarization and increase in input resistance but also the facilitatory effect of NA on the glutamate response were mimicked by DBcAMP and isoproterenol. This facilitatory effect of DBcAMP was enhanced by theophylline or forskolin, while that of isoproterenol was antagonized by propranolol. Clonidine suppressed glutamate-induced depolarization. These results that the enhancing action of NA on the responsiveness of cultured cerebellar neurons to excitatory amino acids is mediated by beta-adrenergic receptors and the intracellular cAMP system.

A vasoactive intestinal polypeptide system in retinal cell cultures: immunocytochemistry and physiology

The purpose of this study was to search for vasoactive intestinal polypeptide (VIP)-like immunoreactivity and VIP-mediated effects in cultures containing cells from the mammalian retina. VIP-like immunoreactivity was detected by indirect immunocytochemistry within 6 days after plating dissociated retinal cells from embryonic day-19 rats. In electrophysiological experiments, VIP was found to facilitate evoked transmission at cholinergic synapses formed by retinal neurons in culture.