Differential immunodetection of l ‐DOPA decarboxylase and tyrosine hydroxylase in the vertebrate retina

Cannabinoid Receptor Type 1 Expression in the Developing Avian Retina: Morphological and Functional Correlation With the Dopaminergic System

The avian retina has been used as a model to study signaling by different neuro- and gliotransmitters. It is unclear how dopaminergic and cannabinoid systems are related in the retina. Here we studied the expression of type 1 and 2 cannabinoid receptors (CB₁ and CB₂), as well as monoacylglycerol lipase (MAGL), the enzyme that degrades 2-arachidonoylglycerol (2-AG), during retina development. Our data show that CB₁ receptor is highly expressed from embryonic day 5 (E5) until post hatched day 7 (PE7), decreasing its levels throughout development. CB₁ is densely found in the ganglion cell layer (GCL) and inner plexiform layer (IPL). CB₂ receptor was also found from E5 until PE7 with a decrease in its contents from E9 afterwards. CB₂ was mainly present in the lamination of the IPL at PE7. MAGL is expressed in all retinal layers, mainly in the IPL and OPL from E9 to PE7 retina. CB₁ and CB₂ were found both in neurons and glia cells, but MAGL was only expressed in Müller glia. Older retinas (PE7) show CB₁ positive cells mainly in the INL and co-expression of CB₁ and tyrosine hydroxylase (TH) are shown in a few cells when both systems are mature. CB₁ co-localized with TH and was heavily associated to D₁ receptor labeling in primary cell cultures. Finally, cyclic AMP (cAMP) was activated by the selective D₁ agonist SKF38393, and inhibited when cultures were treated with WIN55, 212–2 (WIN) in a CB₁ dependent manner. The results suggest a correlation between the endocannabinoid and dopaminergic systems (DSs) during the avian retina development. Activation of CB₁ limits cAMP accumulation via D₁ receptor activation and may influence embryological parameters during avian retina differentiation.

The melatonin analog 5-MCA-NAT increases endogenous dopamine levels by binding NRH:quinone reductase enzyme in the developing chick retina

NRH:quinone reductase (QR2) is present in the retinas of embryonic and post-hatched (PH) chicks. 5-Methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT) is a QR2 ligand that increases cAMP levels in developing retinas, but it does not affect cAMP levels in CHO-QR2 cells. The dopamine quinone reductase activity of QR2 retrieves dopamine, which increases cAMP levels in developing retinas. The objective of the present study was to investigate whether 5-MCA-NAT increases endogenous dopamine levels in retinas from chick embryos and post-hatched chicks. Endogenous dopamine was measured by enzyme-linked immunosorbent assay (ELISA). 5-MCA-NAT increased retinal endogenous dopamine levels at all developmental stages studied and in PH chicks (-logEC50=11.62±0.34 M). This effect was inhibited by non-selective antagonists of receptors and melatonin binding sites N-acetyl-2-benzyltryptamine (luzindole, 5 μM), but it was not inhibited by the Mel1b melatonin receptor antagonist 4-phenyl-2-propionamidotetralin (4-P-PDOT, 10 nM). The QR2 cosubstrate, N-methyl-dihydronicotinamide (NMH) (-logEC50=6.74±0.26 M), increased endogenous dopamine levels in controls and in retinas stimulated with 5-MCA-NAT (3 nM). The QR2 inhibitor benzo[e]pyrene inhibited endogenous dopamine levels in both control (-logIC50=7.4±0.28 M) and NMH-stimulated (at 100 nM and 1 μM benzo[e]pyrene concentrations) retinas. Theoretical studies using Molegro Virtual Docking software corroborated these experimental results. We conclude that 5-MCA-NAT increases the level of endogenous dopamine via QR2. We suggest that this enzyme triggers double reduction of the dopamine quinone, recovering dopamine in retinal development.

Methods of dopamine research in retina cells

Dopamine is the main catecholamine found in the retina of most species, being synthesized from the L-amino acid tyrosine. Its effects are mediated by G protein coupled receptors subfamilies that are commonly coupled to adenylyl cyclase in opposite manners. There is evidence that this amine works as a developmental signal in the embryonic retina and several distinct roles have been attributed to dopamine in the retina such as proliferation, synaptogenesis, neuroprotection, increased signal transmission in cone, gap junction modulation, neuronal-pigmented epithelium-glial communication, and neuron-glia interaction. Here we describe methods that have been used in the study of the dopaminergic function in the retina in the last 40 years. We emphasize the approaches used in the studies on the development of the avian and rodent retina. The dopaminergic system is one of the first phenotypes to appear in the developing vertebrate retina.

Modulation of TGFβ(2) and dopamine by PKC in retinal Müller cells of guinea pig myopic eye

AIM

To investigate the effect of protein kinase C (PKC) on transforming growth factor-β(2) (TGFβ(2)) and dopamine in retinal Müller cells of guinea pig myopic eye.

METHODS

Myopia was induced by translucent goggles in guinea pig, whose retinal Müller cells were cultured using the enzyme-digesting method. Retinal Müller cells were divided into 5 groups: normal control, myopia, myopia plus GF109203X, myopia plus PMA, myopia plus DMSO. PKC activities were detected by the non-radioactive methods. TGFβ(2) and tyrosine hydroxylase (TH) proteins were analyzed by Western Blotting in retinal Müller cells. Dopamine was determined by the high-performance liquid chromatography-electrochemical detection in suspensions.

RESULTS

After 14 days deprived, the occluded eyes became myopic with ocular axle elongating. Müller cells of guinea pigs were obtained using enzyme digestion. Compared with normal control group, the increase in PKC activity and the up-regulation in TGFβ(2) expression were found in retinal Müller cells of myopic eyes, with the decrease of TH and dopamine content (P<0.05). After PKC activated by PMA, TGFβ(2) and TH content were up-regulated with the increase of dopamine content (P<0.05). While the PKC activities was inhibited by GF109203X, proteins of TGFβ(2) and TH were down-regulated in the myopic eyes, with the decrease of dopamine content (P<0.05).

CONCLUSION

TGFβ(2) and dopamine are modulated by PKC in Müller cells of the myopic eyes in guinea pig.

Increased A-to-I RNA editing of the transcript for GABAA receptor subunit α3 during chick retinal development

Adenosine-to-inosine (A-to-I) RNA editing is a cotranscriptional or posttranscriptional gene regulatory mechanism that increases the diversity of the proteome in the nervous system. Recently, the transcript for GABA type A receptor subunit α3 was found to be subjected to RNA editing. The aim of this study was to determine if editing of the chicken α3 subunit transcript occurs in the retina and if the editing is temporally regulated during development. We also raised the question if editing of the α3 transcript was temporally associated with the suggested developmental shift from excitation to inhibition in the GABA system. The editing frequency was studied by using Sanger and Pyrosequencing, and to monitor the temporal aspects, we studied the messenger RNA expression of the GABAA receptor subunits and chloride pumps, known to be involved in the switch. The results showed that the chick α3 subunit was subjected to RNA editing, and its expression was restricted to cells in the inner nuclear and ganglion cell layer in the retina. The extent of editing increased during development (after embryonic days 8-9) concomitantly with an increase of expression of the chloride pump KCC2. Expression of several GABAA receptor subunits known to mediate synaptic GABA actions was upregulated at this time. We conclude that editing of the chick GABAA subunit α3 transcript in chick retina gives rise to an amino acid change that may be of importance in the switch from excitatory to inhibitory receptors.