Immunohistochemical localization of guanine nucleotide-binding protein in rat retina

RET-RGS, a retina-specific regulator of G-protein signaling, is located in synaptic regions of the rat retina

RGS (regulators of G protein signaling) proteins negatively regulate the alpha subunit of G proteins by accelerating their intrinsic GTPase activity. In a previous work, we reported the cloning of a cDNA encoding for a new RGS protein, RET-RGS. We showed that it is specifically expressed in the retina, notably by photoreceptor cells and that it has an in vitro GAP activity on transducin. To understand the role of RET-RGS, and in particular to determine whether it regulates the phototransduction cascade in photoreceptor cells, RET-RGS was immunolocalized on rat retina sections. Whereas no labeling was detected in outer nor inner segments of photoreceptors cells, dense immunoreactive products were localized in the outer and inner plexiform layers which correspond to the regions of synaptic interplay between the different neurons of the retina including the photoreceptor cells. These results rule out a role of RET-RGS on the phototransduction cascade and suggest that it may participate in retina specific synaptic transductions.

Dopamine receptor localization in the mammalian retina

After a short history of dopamine receptor discovery in the retina and a survey on dopamine receptor types and subtypes, the distribution of dopamine receptors in the retinal cells is described and correlated with their possible role in cell and retinal physiology. All the retinal cells probably bear dopamine receptors. For example, the recently discovered D1B receptor has a possible role in modulating phagocytosis by the pigment epithelium and a D4 receptor is likely to be involved in the inhibition of melatonin synthesis in photoreceptors. Dopamine uncouples horizontal and amacrine cell-gap junctions through D1-like receptors. Dopamine modulates the release of other transmitters by subpopulations of amacrine cells, including that of dopamine through a D2 autoreceptor. Ganglion cells express dopamine receptors, the role of which is still uncertain. Müller cells also are affected by dopamine. A puzzling action of dopamine is observed in the ciliary retina, in which D1- and D2-like receptors are likely to be involved in the cyclic regulation of intraocular pressure. Most of the dopaminergic actions appear to be extrasynaptic and the signaling pathways remain uncertain. Further studies are needed to better understand the multiple actions of dopamine in the retina, especially those that implicate rhythmic regulations.

AMPA receptor activates a G-protein that suppresses a cGMP-gated current

The AMPA receptor, ubiquitous in brain, is termed "ionotropic" because it gates an ion channel directly. We found that an AMPA receptor can also modulate a G-protein to gate an ion channel indirectly. Glutamate applied to a retinal ganglion cell briefly suppresses the inward current through a cGMP-gated channel. AMPA and kainate also suppress the current, an effect that is blocked both by their general antagonist CNQX and also by the relatively specific AMPA receptor antagonist GYKI-52466. Neither NMDA nor agonists of metabotropic glutamate receptors are effective. The AMPA-induced suppression of the cGMP-gated current is blocked when the patch pipette includes GDP-beta-S, whereas the suppression is irreversible when the pipette contains GTP-gamma-S. This suggests a G-protein mediator, and, consistent with this, pertussis toxin blocks the current suppression. Nitric oxide (NO) donors induce the current suppressed by AMPA, and phosphodiesterase inhibitors prevent the suppression. Apparently, the AMPA receptor can exhibit a "metabotropic" activity that allows it to antagonize excitation evoked by NO.

A novel Go-mediated phototransduction cascade in scallop visual cells

Scallop retinas contain ciliary photoreceptor cells that respond to light by hyperpolarization like vertebrate rods and cones, but the response is generated by a different phototransduction cascade from those of rods and cones. To elucidate the cascade, we investigated a visual pigment and a G-protein functioning in the hyperpolarizing cell. Sequencing of cDNAs and in situ hybridization experiments showed that the hyperpolarizing cells express a novel subtype of visual pigment, which showed significant differences in amino acid sequence from other visual pigments. Cloning cDNA genes of G-protein and immunohistochemical analysis revealed the presence of an alpha subunit of a Go type G-protein, 83% identical in amino acid sequence to mammalian Go(alpha) in the nervous system, in the photoreceptive region of the cells. The results demonstrate that a novel, Go-mediated, phototransduction cascade is present in the hyperpolarizing cells. The phototransduction cascade in the scallop hyperpolarizing cell provides an alternative system to investigate Go-mediated transduction pathways in the nervous system. Molecular phylogenetic analysis strongly suggests that the Go-mediated phototransduction system emerged before the divergence of animals into vertebrate and invertebrate in the course of evolution.

Ontogeny of GTP-binding proteins, Gi and G(o), in rat retina

The distribution and the levels of Gi1 (plus Gi3), Gi2, and G(o) in rat retina were studied immunohistochemically and immunochemically during development. At embryonic day (E) 15, Gi1 alpha/Gi3 alpha was observed in the inner layer of the neural retina, the future nerve fiber layer (NFL), while Gi2 alpha was observed both in the inner and outer layers of the neural retina. No immunoreactivity for G(o) alpha was observed. At E18, Gi1 alpha/Gi3 alpha and Gi2 alpha appeared in the inner plexiform layer (IPL), while G(o) alpha was faintly immunoreactive only in the NFL. At birth, Gi2 alpha/Gi3 alpha and G(o) alpha appeared in the ganglion cell layer. Gi2 alpha was intensely immunoreactive in the NFL and IPL. At postnatal day (P) 10, the inner portions of the retina, from the NFL to the outer plexiform layer, were immunoreactive to Gi1 alpha/Gi3 alpha, Gi2 alpha, and G(o) alpha. Gi1 alpha/Gi3 alpha and G(o) alpha were distributed characteristically in a laminated pattern in the IPL, but Gi2 alpha was present homogeneously in the IPL. At P12, Gi2 alpha appeared in the outer nuclear layer. As the postnatal days advanced, the laminated pattern of immunoreactivity to G(o) alpha in the IPL became diffuse, but immunoreactivity to Gi1 alpha/Gi3 alpha remained. The results of enzyme immunoassays showed that the concentration of G(o) alpha increased rapidly from P10 to P15 and reached almost the adult level at P20-P30, while Gi2 alpha decreased until P15 and was almost constant thereafter. These results showed that the distribution of Gi1 alpha/Gi3 alpha, Gi2 alpha, and G(o) alpha differs during development, suggesting that each G protein in the developing retina has a unique function.

Vasoactive intestinal polypeptide modulates GABAA receptor function through activation of cyclic AMP

Vasoactive intestinal polypeptide (VIP) has been shown to potentiate current responses elicited by activation of the GABAA receptor (IGABA) in freshly dissociated ganglion cells of the rat retina. Here we tested the hypothesis that this heteroreceptor cross talk is mediated by an intracellular cascade of events that includes the sequential activation of a stimulatory guanine nucleotide binding (Gs) protein and adenylate cyclase, the subsequent increase in levels of cyclic AMP and, finally, the action of the cyclic AMP-dependent protein kinase (PKA). Intracellular dialysis of freshly dissociated ganglion cells with GTP gamma s irreversibly potentiated IGABA, while GDP beta s either decreased or had no effect on IGABA. Additionally, GDP beta s blocked the potentiation of IGABA by VIP. Cholera toxin rendered VIP ineffective in potentiating IGABA, while pertussis toxin had no effect on the VIP-induced potentiation of IGABA. Extracellular application of either forskolin or 8-bromo-cyclic AMP potentiated IGABA, as did the introduction of cyclic AMP directly into the intracellular compartment through the recording pipet. Intracellular application of cyclic AMP-dependent protein kinase (PKA) potentiated IGABA, while a PKA inhibitor blocked the potentiating effect of VIP. These results lead us to conclude that activation of a cyclic AMP-dependent second-messenger system mediates the modulation of GABAA receptor function by VIP in retinal ganglion cells.

Visualization of G(o)alpha subtype guanine nucleotide-binding regulatory protein in the medulla oblongata and pons of the rat

This study reports on the visualization of G(o) protein in the medulla oblongata and pons of Sprague-Dawley rats, using a commercially available selective polyclonal antiserum against a 39-kDa protein corresponding to the alpha subunit of G(o). Specific immunofluorescent-staining was widely distributed in neuropils and neuronal cell bodies but displayed regional heterogeneity. The immunoreactive product exhibited a punctate appearance and was most pronounced in the cell membrane and cytoplasm of the perikarya and proximal dendrites whereas the nucleus remained unstained. Positive immunoreactivity of G(o)alpha was present in nucleus reticularis gigantocellularis, nucleus reticularis paramedialis, nucleus tractus solitarii, nucleus nervi hypoglossi, nucleus raphé pallidus, locus coeruleus, nucleus tractus mesencephali nervi trigemini and nucleus cuneatus. These results provided anatomic evidence to support the participation of G(o) protein in both sensory and motor functions that originate from the medulla oblongata and pons of the rat.

Identification of a G-protein in depolarizing rod bipolar cells

Synaptic transmission from photoreceptors to depolarizing bipolar cells is mediated by the APB glutamate receptor. This receptor apparently is coupled to a G-protein which activates cGMP-phosphodiesterase to modulate cGMP levels and thus a cGMP-gated cation channel. We attempted to localize this system immunocytochemically using antibodies to various components of the rod phototransduction cascade, including Gt (transducin), phosphodiesterase, the cGMP-gated channel, and arrestin. All of these antibodies reacted strongly with rods, but none reacted with bipolar cells. Antibodies to a different G-protein, G(o), reacted strongly with rod bipolar cells of three mammalian species (which are depolarizing and APB-sensitive). Also stained were subpopulations of cone bipolar cells but not the major depolarizing type in cat (b1). G(o) antibody also stained certain salamander bipolar cells. Thus, across a wide range of species, G(o) is present in retinal bipolar cells, and at least some of these are depolarizing and APB-sensitive.

Distribution of guanine nucleotide-binding protein in the brain of the reeler mutant mouse

The localization of a GTP-binding protein (G(o)) in the cerebellar and cerebral cortex and hippocampus of the normal and reeler mutant mouse was immunohistochemically examined using affinity-purified antibody raised against the alpha subunit of G(o). Although the general distribution pattern of G(o)-immunoreactive products in the brain of the normal mouse, i.e., abundant in the neuropil but absent from neuronal cell bodies, is also seen in the reeler brain, some differences are present, as described below. Strong G(o)-immunoreactive products are found in the molecular layer of the cerebellar cortex of the normal mouse. In the reeler cerebellum, in addition to the strong G(o)-immunoreactivity of the thin molecular layer, moderate G(o)-immunoreactivities are also found in the granular cell layer and the central cerebellar mass. G(o)-immunoreactive products are distributed throughout all layers of the cerebral cortex of the normal and reeler mouse. However, layer I of the normal cerebral cortex is more strongly stained with this antibody than the underlying layers, whereas the upper third of the reeler cerebral cortex is more strongly stained than the lower two-thirds. In the hippocampus of the normal mouse, G(o)-immunoreactive products are localized in the neuropil of the stratum oriens, stratum radiatum and stratum lacunosum-moleculare, but absent from the cell bodies of the pyramidal cells and their apical dendritic shafts. Such a distribution pattern of G(o)-immunoreactive products is also seen in the hippocampus of the reeler mouse, except that G(o)-immunonegative pyramidal cells split into 2 or 3 laminae.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural localization of the GTP-binding protein Go in neurons

The ultrastructural localization of Go, a GTP-binding protein (G protein) highly expressed in nervous tissues, was performed in cultured fetal and adult murine neurons, using affinity-purified polyclonal antibodies against the alpha subunit of the Go protein (Go alpha). These antibodies recognized denatured Go alpha and both the native Go alpha-subunit and the Go alpha beta gamma heterotrimer. At the ultrastructural level, the positive immunoreactivity detected in cultured cells as well as in thin frozen sections, showed that Go was largely distributed in cell bodies and neuritic cytoplasm. Labelling was principally noted on the cytoplasmic face of the plasma membrane lining the cell body and the neurites, especially in 'cell-cell' contacts, but also in the cytoplasmic matrix, between endoplasmic reticulum and Golgi cisternae. No immunoreactivity was observed on the inner face of the pre- or postsynaptic membranes in both adult brain and in cultured neurons. This last finding strongly suggests that the Go protein is not involved in transducing chemical signals at the level of synapses, but more probably modulates the synaptic functions by controlling the activity of effectors localized outside of the synaptic densities.

Antiserum raised against residues 159-168 of the guanine nucleotide-binding protein Gi3-alpha reacts with ependymal cells and some neurons in the rat brain containing cholecystokinin- or cholecystokinin- and tyrosine 3-hydroxylase-like immunoreactivities

Antibodies raised against a synthetic deca-peptide corresponding to a specific sequence of Gi3-alpha protein (an inhibitory guanine nucleotide-binding protein) were used to analyze Gi3-alpha-like immunoreactivity in brain sections from colchicine-treated rats by indirect immunofluorescence histochemistry. Gi3-alpha-peptide-positive cell bodies were found in the ventral tegmental area and substantia nigra, and these cells were also cholecystokinin (CCK)- and tyrosine 3-hydroxylase-positive. Gi3-alpha-peptide staining was observed in perikarya in the hippocampus and in fibers in the nucleus accumbens, tuberculum olfactorium, bed nucleus of stria terminalis, and a spino-thalamic tract, where it coexisted with CCK-like immunoreactivity as well. No coexistence with CCK occurred in Gi3-alpha-peptide-positive ependymal cells outlining the aqueduct and ventricles. Preadsorption of Gi3-alpha antibodies with CCK-8 or CCK-33 did not alter Gi3-alpha-peptide staining. The occurrence of Gi3-alpha-peptide-like immunoreactivity in CCK-containing neurons may indicate the presence of Gi3-alpha protein and in CCK/dopamine neurons may indicate an association of this Gi protein with dopamine autoreceptors.

Techniques used in the identification and analysis of function of pertussis toxin-sensitive guanine nucleotide binding proteins

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Immunohistochemical detection of GTP-binding regulatory protein (Go) in the autonomic nervous system including the enteric nervous system, superior cervical ganglion and adrenal medulla

The localization of a GTP-binding regulatory protein, Go, in the autonomic nervous system including the enteric nervous system, superior cervical ganglion, and adrenal medulla, has been immunohistochemically examined by use of affinity-purified antibody against the alpha-subunit of Go. In the small intestine, dense Go-immunoreactive products were localized on the enteric nervous system, i.e. the myenteric plexus of Auerbach and the submucosal plexus of Meissner. In the superior cervical ganglion, presynaptic terminals were strongly immunoreactive to the Go antibody. The adrenal medulla was stained with this antibody, but the adrenal cortex was not immunoreactive to this antibody. Thus, the present study strongly suggests that Go is localized in the autonomic nervous system and plays its role in transmembrane signal transmission in this system.

Immunohistochemical analysis of the localization of guanine nucleotide-binding protein in the mouse brain

A guanine nucleotide-binding protein, G0, is a heterotrimer with the alpha- and beta gamma-subunits (referred to here as alpha 0 and beta gamma, respectively). We examined the distribution pattern of the anti-alpha 0 and anti-beta gamma immunoreactive products in the hippocampus, and cerebral and cerebellar cortices of the mouse brain. In the hippocampus, alpha 0- and beta gamma-immunoreactivities were localized in the neuropil of the stratum oriens, stratum radiatum and stratum lacunosum-moleculare, but were absent from the cell bodies of the pyramidal cells and their apical dendritic shafts. In the cerebral cortex, alpha 0- and beta gamma-immunoreactivities were seen in the neuropil of all 6 layers of the cerebral cortex, especially in the uppermost molecular layer (layer I), and were absent from cell bodies of neurons and their apical dendritic shafts. In the cerebellar cortex, the molecular layer was heavily stained with anti-alpha 0 and beta gamma-antibodies. The present study revealed that the distribution pattern of beta gamma-immunoreactivities in these structures of the mouse brain was strikingly similar to that of the alpha 0-immunoreactivities.

Light microscopy of GTP-binding protein (Go) immunoreactivity within the retina of different vertebrates

To examine species differences in the distribution pattern of guanosine triphosphate (GTP)-binding protein (Go) within the vertebrate retina, paraffin-embedded retinae from a number of vertebrate species, including the goldfish, frog, turtle, chicken, monkey, and human, were immunohistochemically stained with affinity-purified antibody against the alpha-subunit of Go. Go-immunoreactive products were found to be located in the neuropil, but not in the cell bodies of neurons, in the retina of all these species. However, some species differences were observed. In the frog, monkey and human, the inner plexiform layer (IPL) was homogeneously stained with this antibody, but in the goldfish, turtle and chicken, the IPL was heterogeneously stained. In the frog, chicken, turtle and human, the outer plexiform layer (OPL) was densely stained with this antibody, but in the goldfish and monkey, the OPL was rather faintly immunoreactive to the antibody. In the goldfish, monkey and human, the outer nuclear layer (ONL) was not immunoreactive to the Go-antibody, whereas in the frog, turtle and chicken, the ONL was immunoreactive to it. The implications of these species differences in Go localization in the vertebrate retina are discussed.

Endocrine cells in pancreatic islets of Langerhans are immunoreactive to antibody against guanine nucleotide-binding protein (Go) purified from rat brain

Guanine nucleotide-binding proteins (G proteins) are usually classified into four subclasses (Gs, Gi, Go and Gt or transducin). We localized the anti-Go immunoreactivities in islets of Langerhans of the rat pancreas by using affinity-purified antibody against the alpha-subunit of Go purified from rat brain. Endocrine cells of the islets of Langerhans were stained with this Go antibody, but the acinar cells in the exocrine portion of the pancreas were immunonegative to this antibody. These findings strongly suggest that Go protein functions as intermediaries in the transmembrane signalling pathway in the endocrine cells of the islets of Langerhans.