Expression of natriuretic peptide-activated guanylate cyclases by cholinergic and dopaminergic amacrine cells of the rat retina

Recently, the natriuretic peptides were detected in the cholinergic and dopaminergic amacrine cells of the retina. We performed immunofluorescence labeling of rat retinal sections to examine the immunoreactivity of natriuretic peptide-activated guanylate cyclases (NPR-A and NPR-B) in the rat retina, in particular whether they were localized to dopaminergic and cholinergic amacrine cells. NPR-A and NPR-B immunoreactivity was detected in several layers of the retina including amacrine cells. In amacrine cells, both NPR-A and NPR-B were co-localized with tyrosine hydroxylase, a marker of dopaminergic cells. NPR-B, but not NPR-A, was localized to amacrine cells expressing choline acetyltransferase (ChAT), a marker of cholinergic cells. These findings suggest that natriuretic peptides have different regulatory systems in dopaminergic and cholinergic amacrine cells in rat retina.     

Proneural bHLH neurogenin 2 differentially regulates Nurr1-induced dopamine neuron differentiation in rat and mouse neural precursor cells in vitro

Roles of Nurr1 and neurogenin 2 (Ngn2) have been shown in midbrain dopamine (DA) neuron development. We present here rat and mouse species-dependent differences of Nurr1 and Ngn2 actions in DA neuron differentiation. Nurr1 exogene expression caused an efficient generation of tyrosine hydroxylase (TH)-positive DA cells from rat neural precursor cells (NPCs). Nurr1-induced TH+ cell yields were low and highly variable depending on the origins of NPCs in mouse cultures. Coexpression of Ngn2 repressed Nurr1-induced generation of TH+ cells in rat cultures. In clear contrast, a robust enhancement in Nurr1-induced DA cell yields was observed in mouse NPCs by Ngn2. These findings imply that DA neurons may develop differently in the midbrains of these two species.     

Dopaminergic Neuronal Conversion from Adult Rat Skeletal Muscle-Derived Stem Cells In Vitro

Muscle-derived stem cells reside in the skeletal muscle tissues and are known for their multipotency to differentiate toward the mesodermal lineage. Recent studies have demonstrated their capacity of neuroectodermal differentiation, including neurons and astrocytes. In this study, we investigated the possibility of dopaminergic neuronal conversion from adult rat skeletal muscle-derived stem cells. Using a neurosphere protocol, muscle-derived stem cells form neurosphere-like cell clusters after cultivation as a suspension, displaying an obvious expression of nestin and a remarkable down-regulation of myogenic associated factors desmin, MyoD, Myf5 and myogenin. Subsequently, these neurosphere-like cell clusters were further directed to dopaminergic differentiation through two major induction steps, patterning to midbrain progenitors with sonic hedgehog and fibroblast growth factor 8, followed by the differentiation to dopaminergic neurons with neurotrophic factors (glial cell line-derived neurotrophic factor) and chemicals (ascorbic acid, forskolin). After the differentiation, these cells expressed tyrosine hydroxylase, dopamine transporter, dopamine D1 receptor and synapse-associated protein synapsin I. Several genes, Nurr1, Lmx1b, and En1, which are critically related with the development of dopaminergic neurons, were also significantly up-regulated. The present results indicate that adult skeletal muscle-derived stem cells could provide a promising cell source for autologous transplantation for neurodegenerative diseases in the future, especially the Parkinson's disease.     

Differential distribution of a second type of tyrosine hydroxylase immunoreactive amacrine cell in the chick retina

A second population of tyrosine hydroxylase-immunoreactive amacrine cells was demonstrated in embryonic and adult chicken retinas by immunohistochemistry techniques in whole flat-mount preparations. The populations were differentiated on a basis of different immunostaining intensities, levels of stratification in the inner plexiform layer, and topographical distributions. Cells of one type were similar to the previously described dopaminergic amacrine cells, denoted here as tyrosine hydroxylase type 1 cells. Immunoreactive neurons of the second type observed in the present work had relatively smaller somata size, and weaker immunostaining than type 1 cells, and were located preferentially in the ventral retina. These tyrosine hydroxylase type 2 cells could be visualized from embryonic day 14 to 21 days after hatching animals. The distribution of the second population was coincident with that of the targets of centrifugal fibres and with cells involved in long proprioretinal connections. We propose that the tyrosine hydroxylase type 2 amacrine cells found in the ventral retina could mediate an important pathway to the upper half of the visual field so as to aid in the detection of predators.     

Brain-derived neurotrophic factor modulates the dopaminergic network in the rat retina after axotomy

Dopaminergic cells in the retina express the receptor for brain-derived neurotrophic factor (BDNF), which is the neurotrophic factor that influences the plasticity of synapses in the central nervous system. We sought to determine whether BDNF influences the network of dopaminergic amacrine cells in the axotomized rat retina, by immunocytochemistry with an anti-tyrosine hydroxylase (TH) antiserum. In the control retina, we found two types of TH-immunoreactive amacrine cells, type I and type II, in the inner nuclear layer adjacent to the inner plexiform layer (IPL). The type I amacrine cell varicosities formed ring-like structures in contact with AII amacrine cell somata in stratum 1 of the IPL. In the axotomized retinas, TH-labeled processes formed loose networks of fibers, unlike the dense networks in the control retina, and the ring-like structures were disrupted. In the axotomized retinas treated with BDNF, strong TH-immunoreactive varicosities were present in stratum 1 of the IPL and formed ring-like structures. Our data suggest that BDNF affects the expression of TH immunoreactivity in the axotomized rat retina and may therefore influence the retinal dopaminergic system. E.-J. Lee and M.-C. Song contributed equally to this work. This work was supported by Korea Research Foundation (grant no. E00004, 2004).     

Ngn2 and Nurr1 act in synergy to induce midbrain dopaminergic neurons from expanded neural stem and progenitor cells

Parkinson's Disease (PD) is a debilitating motor function disorder due primarily to a loss of midbrain dopaminergic neurons and a subsequent reduction in dopaminergic innervation of the striatum. Several attempts have been made to generate dopaminergic neurons from progenitor cell populations in vitro for potential use in cell replacement therapy for PD. However, expanding cells from fetal brain with retained potential for dopaminergic differentiation has proven to be difficult. In this study, we sought to generate mesencephalic dopaminergic (mesDA) neurons from an expanded population of fetal mouse ventral midbrain (VM) progenitors through the use of retroviral gene delivery. We over-expressed Ngn2 and Nurr1, two genes present in the ventral midbrain and important for normal development of mesDA neurons, in multi-passaged neurosphere-expanded midbrain progenitors. We show that over-expression of Ngn2 in these progenitors results in increased neuronal differentiation but does not promote mesDA formation. We also show that over-expression of Nurr1 alone is sufficient to generate tyrosine hydroxylase (TH) expressing cells with an immature morphology, however the cells do not express any additional markers of mesDA neurons. Over-expression of Nurr1 and Ngn2 in combination generates morphologically mature TH-expressing neurons that also express additional mesencephalic markers.     

猫视网膜多巴胺能神经元的形态和发育

Morphology and development of dopaminergic neurons has been studied in the kitten retina, using tyrosine hydroxylase (TH) immunocytochemistry. TH immunoreactive (TH+) cells are already presented in whole amount and sectioned retina at first postnatal day (P1). According to soma size, shape, dendritic process pattern and immunoreactivity, two classes, type I or large dark staining TH+ cells and type II or small light staining TH+ cells are recognized. The TH I cells which consisting of normal placed DA amacrine cells, displaced DA amacrine cells and DA interplex-form-like cells, gradually mature during postnatal development, while TH II cells decrease quickly and through disappear at P30. After eye opening TH I amacrine cells, especially their dendrites develop quickly. The soma diameters increase from 11.8 microns (P1) to 14.2 microns (P30). The dendritic fields increase in size and complexity. At P1 the thick radiating dendrites emerge from the cell body with small or large "spines" and many growth cones. At P13 the dendritic field is markedly enlarged and only a few growth cones can be seen on some stained dendrites. In addition, the dendritic spines are no longer apparent and they are a part of rudimentary rings. By P30 the dendritic plexus of TH+ dendrites and rings in the out most part of IPL, typical of the adult cells, are complete. The influence of light on the development of DA cells after eye opening and the possibility of neurotransmitter changing are discussed.     

A distinct centro-peripheral gradient of development in dopaminergic amacrine cells of cat retina

The centro-peripheral gradient of development in dopaminergic (DA) amacrine cells of cat retina has been studied by TH immunocytochemical method. Type I of TH immunoreactive neurons is typical DA cell. They reveal a clear centro-peripheral gradient of differentiation and maturation in space and time course during postnatal development. (1) At P1 stage, the TH I cells vary in TH immunoreactivity, soma sizes and dendritic maturation. Responding to degree of development, they can be divided into I1, I2 and I3. The more differentiated I1 cells, larger and darkly immuno-stained stellate cells mostly concentrates at central retina, while the less differentiated I3 cells, smaller and lightly immunostained irregular cells concentrate at peripheral retina. I2 cells of moderate differentiation distribute over all the retina. (2) During the postnatal development, from P1 to P13, the dense area of the TH I1 cells spreads peripherally in company with the increase of the total number of TH I1 cells, comprising the central 30% of the retina at P1, 65% at P6 and almost the whole of the retina by P13. After eye opening, as the TH I cells have spread at far peripheral region, the differences in soma diameters and dendritic maturation of TH I cells between central and peripheral retina decrease gradually and the centro-peripheral gradient of maturity of TH I cells becomes less distinct. At P23, no significant difference is visible in either soma diameter or dendritic maturation in these two areas: thus, the centro-peripheral gradient is no longer apparent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunocytological localization of dopamine in the guinea pig retina

We examined dopaminergic neurons in the guinea pig retina; antisera against tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and an antiserum against gamma-aminobutyric acid (GABA) were used. In the present study, two types of amacrine cells were labeled with an anti-TH antiserum. However, no DBH and PNMT immunoreactivities were seen. The type 1 cell had a larger-sized soma located in the inner nuclear layer with processes ramifying mainly in stratum 1 of the inner plexiform layer (IPL). The type 2 cell had a smaller-sized soma and processes branching in stratum 3 of the IPL. The mean densities were 56.4 +/- 11.5/mm2 for the type 1 cell and 166.6 +/- 30.3/mm2 for the type 2 cell. Double immunocytochemistry using an antiserum against GABA revealed that while none of the type 1 cells showed GABA immunoreactivity, all of the type 2 cells displayed GABA immunoreactivity. Our results suggest that, in the guinea pig retina, the type 1 amacrine cells are pure dopaminergic and the type 2 cells are dopaminergic elements that use GABA as their second transmitter.