An intraocular injection of kainate induces expression of c-fos-like protein and activation of protein kinase C (alpha) in specific rabbit retinal neurones

Retinal function and PKC alpha expression after focal laser photocoagulation

PURPOSE

To examine the effects of focal laser photocoagulation on general and local retinal function and to relate electrophysiological findings with changes in protein kinase C (PKC) alpha expression.

METHODS

Twelve rabbits were treated with 70 spots of laser photocoagulation in the central cone-rich retina. The operated eyes were investigated with electroretinography (full-field ERG and multifocal electroretinography, mfERG) preoperatively and at 1, 3, and 5 weeks after surgery. The expression of PKC alpha was examined at all three time points using immunohistochemistry, and PKC alpha mRNA levels were quantified using real-time polymerase chain reaction (PCR). Immunohistochemistry for glial fibrillary acidic protein (GFAP) and hematoxylin and eosin staining was employed to monitor the extent and dynamics of the morphological response.

RESULTS

The full-field ERG revealed a significant increase in b-wave amplitudes derived from the isolated rod response (blue light) at all three time points after surgery (p < 0.05). Supernormal b-wave amplitudes were also found for the combined rod-cone response at 3 weeks (white light), and for the isolated cone response (light-adapted 30-Hz flicker) at 5 weeks after treatment. In the mfERG, amplitudes derived from the central retina did not change postoperatively, while the implicit time was significantly increased at all time points. Immunohistochemistry for PKC alpha revealed a reduced expression of the enzyme in rod bipolar cells 1 and 3 weeks after laser treatment compared with untreated controls. Five weeks postoperatively, no PKC alpha labeling in rod bipolar cells was found in any part of the retina. Real-time PCR 1 and 3 weeks after treatment displayed a decreased level of PKC alpha mRNA compared to the controls. Immunolabeled tissue sections from laser-treated eyes displayed GFAP expression in Müller cells in the treated as well as untreated retina 1 week postoperatively. At 3 and 5 weeks, GFAP labeling was less pronounced and was concentrated around the laser-treated spots.

CONCLUSIONS

Focal laser treatment in the rabbit eye induces local and wide-spread alterations in both rod- and cone-mediated retinal function in the form of supernormal b-wave amplitudes in the full-field ERG and increased latency in the mfERG. The electrophysiological abnormalities are accompanied by a progressive down-regulation of the PKC alpha isoenzyme in rod bipolar cells, reaching far beyond the treated area. PKC alpha is down-regulated directly by impaired protein synthesis, and also possibly indirectly by protein consumption related to GFAP up-regulation. The results indicate that focal laser photocoagulation interferes with PKC-alpha-mediated inhibitory regulation of inner retinal signal transmission.

Activity-dependent expression of acyl-coenzyme a-binding protein in retinal muller glial cells evoked by optokinetic stimulation

Long-term horizontal optokinetic stimulation (HOKS) decreases the gain of the horizontal optokinetic reflex and evokes the second phase of optokinetic afternystagmus (OKAN-II). We investigated the possible molecular constituents of this adaptation. We used a differential display reverse transcriptase-PCR screen for mRNAs isolated from retinas of rabbits that received HOKS. In each rabbit, we compared mRNAs from the retina stimulated in the posterior-->anterior (preferred) direction with mRNAs from the retina stimulated in the anterior-->posterior (null) direction. Acyl-CoA-binding protein (ACBP) mRNA was one of four mRNAs selected by this screen, the proteins of which interact with GABA receptors. HOKS in the preferred direction increased ACBP mRNA transcription and ACBP protein expression. ACBP was localized to Muller glial cells by hybridization histochemistry and by immunohistochemistry. ACBP interacts with the alpha1-subunit of the GABA(A) receptor, as determined by a yeast two-hybrid technique. This interaction was confirmed by coimmunoprecipitation of ACBP and the alpha1-subunit of the GABA(A) receptor using an antibody to GABA(A)alpha1. The interaction was also confirmed by a "pull-down" assay in which histidine-tagged ACBP was used to pull down the GABA(A)alpha1. ACBP does not cross the blood-brain barrier. However, smaller truncated proteolytic fragments of ACBP do, increasing the excitability of central cortical neurons. Muller cells may secrete ACBP in the inner plexiform layer, thereby decreasing the sensitivity of GABA(A) receptors expressed on the surface of ganglion cell dendrites. Because retinal directional sensitivity is linked to GABAergic transmission, HOKS-induced expression of ACBP could provide a molecular basis for adaptation to HOKS and for the genesis of OKAN-II.

Phosphorylation of GluR4 AMPA-type glutamate receptor subunit by protein kinase C in cultured retina amacrine neurons

We have previously reported that the activity of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors is potentiated by protein kinase C (PKC) in cultured chick retina amacrine neurons, and that constitutive PKC activity is necessary for basal AMPA receptor activity (Carvalho et al., 1998). In this study, we evaluated the phosphorylation of the GluR4 subunit, which is very abundant in cultured amacrine neurons, to correlate it with the effects of PKC on AMPA receptor activity in these cells. 32P-labelling of GluR4 increased upon AMPA receptor stimulation or cell treatment with phorbol 12-myristate 13-acetate (PMA) before stimulating with kainate. By contrast, phosphorylation of GluR4 was not changed when PKC was inhibited by treating the cells with the selective PKC inhibitor GF 109203X before stimulation with kainate. We conclude that GluR4 is phosphorylated upon PKC activation and/or stimulation of AMPA receptors in cultured amacrine cells. Additionally, AMPA receptor activation with kainate in cultured chick amacrine cells leads to translocation of conventional and novel PKC isoforms to the cell membrane, suggesting that PKC could be activated upon AMPA receptor stimulation in these cells.

Immediate early gene expression within the visual system: light and circadian regulation in the retina and the suprachiasmatic nucleus

Immediate early genes are a family of genes that share the characteristic of having their expression rapidly and transiently induced upon stimulation of neuronal and non-neuronal cells. In this review, first a short description of the IEGs is given, then it is discussed the stimulus-induced and circadian-induced variations in the expression of IEGs in the visual system, mainly in the retina and the suprachiasmatic nucleus. The possible physiological consequences of these variations in IEG expression are also considered. Finally, we refer to two aspects of our recent studies and those of other laboratories involving light-driven IEG expression. The first is the finding that in the chick retina, the expression of c-fos is differentially modulated in the different cell types and that c-fos regulates the synthesis of the quantitatively most important lipids of all cells, the phospholipids, by a non-genomic mechanism. The second is the occurrence of differential waves of IEG expression in the mammalian suprachiasmatic nucleus regarding light induction or spontaneous oscillations.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Motion-sensitive neurons in the chick retina: a study using Fos immunohistochemistry

Fos immunohistochemistry was used to characterize neurons in the chick retina activated by optokinetic and stationary stimuli. Higher percentages of co-localization of Fos and the alpha5 subunit of the nicotinic acetylcholine receptor, and Fos and GABA were observed in retinal neurons after optokinetic compared to the stationary stimulation. These results indicate an involvement of the cholinergic and GABAergic circuitries in the motion detection by chick retinal cells.

Identification of c-fos related genes and their induction by neural activation in rainbow trout brain

A number of studies have shown that the induction of c-fos gene is an indicator of the responses of cells and tissues to the environmental stimuli. In the present study, using RT-PCR-based strategy, we isolated, from the brain of the rainbow trout, two partial cDNA clones (RT-fos1 and RT-fos2) that code proteins homologous to c-Fos proteins of higher vertebrates. Sequence analysis of the two clones indicated that the two rainbow trout clones are very similar to each other over the entire cloned region (88% amino acid identity) and showed moderate similarity to c-Fos proteins of higher vertebrates (40% amino acid identity with human c-Fos). Two functionally important domains (i.e. the leucine zipper and zinc finger) are highly conserved among all the vertebrate species analyzed, although the region between the two domains was highly variable between different species. Intraperitoneal administration of kainic acid, a stable agonist of glutamate receptors, transiently induced the mRNAs for both RT-fos1 and RT-fos2 in the rainbow trout brain. These results indicate that the expression pattern of the two clones can be utilized as a suitable anatomical marker for the increased neural activities in salmonid fish brain to investigate the higher order behavior such as the learning and imprinting of odors of the home river.

The occurrence of protein kinase C theta and lambda isoforms in retina of different species

The localization and immunochemical identification of the novel protein kinase C theta (nPKC theta) and the atypical protein kinase C lambda (aPKC lambda) isoforms in retinas of different species were analyzed by immunohistochemistry and SDS-PAGE/Western blotting. nPKC theta immunoreactivity is associated with bipolar cells of mammalian (rabbit, rat and guinea pig) retinas but not the non-mammalian goldfish retina which has a lower concentration of nPKC theta. However, SDS-PAGE and Western blotting data indicate the antigen recognized by the nPKC theta monoclonal antibody in the retina is of a lower molecular weight than that expected for nPKC theta. This would suggest nPKC theta is more susceptible to degradation/breakdown than other PKC isoforms found in the retina or that the nPKC theta antibody may be recognizing an unknown retinal antigen. A comparison of nPKC theta and cPKC alpha immunoreactivities in bipolar cells shows unique distributions exist for the two isoforms. nPKC theta is present in the developing retina at an earlier stage than cPKC alpha. The typical 'transport' of cPKC alpha toward axonal terminals by phorbol-12,13-dibutyrate does not occur for nPKC theta yet both are translocated from the cytosolic to membrane compartments. The inner plexiform layer and the inner nuclear layer (putative horizontal cells) of all species examined (rabbit, rat, guinea pig and goldfish) exhibited positive immunoreactivity for aPKC lambda as confirmed by SDS-PAGE/Western blotting.

Prolonged bilateral carotid artery occlusion induces electrophysiological and immunohistochemical changes to the rat retina without causing histological damage

Reduction of the retinal blood flow by occlusion of both common carotid arteries suppressed the b-wave of the rat's electroretinogram. Transient occlusion of the carotids for 45 min reduced the b-wave by 46% without affecting the amplitude of the a-wave. The normal ERG activity returned 30 min after restoration of blood flow. Prolonged carotid occlusion for 7 days totally abolished the b-wave but enhanced the a-wave amplitude. Although b-wave amplitude suppression has been considered as an indicator of retinal ischaemia, no histological changes were seen in retinas of rats subjected to 45 min or 7 days of two-vessel occlusion, when observed by light microscopy. Moreover, GABA, GABAA receptor, calretinin and PKC-alpha immunoreactivities were unaltered. Carotid artery occlusion did, however, induce the expression of the cytoskeletal protein, glial fibrillary acidic protein (GFAP), in retinal Müller cells. The increase in the Müller cell GFAP immunoreactivity was related to how long the carotids were occluded as well as the reperfusion time. Prolonged occlusion for 7 days resulted in a 356% increase in retinal GFAP. These findings show that a reduction of retinal blood flow by occlusion of the carotids causes a metabolic stress to the retina and elicits events associated with gliosis without resulting in 'ischaemic-like' morphological changes.

The effect of kainate on protein kinase C, GABA, and the uptake of serotonin in the rabbit retina in vivo

The purpose of this study was to investigate the effect of kainate on protein kinase C (PKC), gamma-aminobutyrate (GABA) and serotonin uptake in the rabbit retina. Kainate when injected into the vitreous humour produces a change in the GABA immunoreactivity within 6 hours. After 3 days, remnants of the normal GABA immunoreactivity still persist and additionally astrocyte and microglia-like elements "stain" positively for GABA. After 7 days exposure to kainate none of the normal GABA immunoreactivity is apparent, instead a number of round-shaped elements which may be reactive astrocytes and/or microglia stain positively for GABA. During these stages kainate does not affect the alpha PKC immunoreactivity associated with the on-bipolar cells. Six hours following kainate treatment the ability of certain GABA amacrine cells to take up exogenous serotonin is unaffected. After three days only a few of these cells can still take up exogenous serotonin and then not avidly. After seven days the GABA/serotonin amacrine cells cannot take up exogenous serotonin suggesting that all of these neurons are irreversibly damaged. One hour after treatment with kainate both calcium-dependent and -independent PKC species are translocated from the cytosolic to membrane compartments. After 5 hours and 7 days there was also evidence from the enzyme assay experiments that kainate caused the calcium-dependent and -independent PKC enzymes to be translocated but because the total enzyme activity was reduced due perhaps to down-regulation of the enzyme this was difficult to assess precisely.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotransmitter modulation of Fos- and Jun-like proteins in the turtle retina

The expression of the Fos and Jun families of nuclear phosphoproteins can be induced by a variety of extracellular stimuli and is known to participate in the transcriptional regulation of target genes. To examine the role of these transcription factors in retinal function, we used polyclonal antisera to localize these protein families in the turtle retina. Fos-like immunoreactivity was in many somata in the inner nuclear and ganglion cell layers. In contrast, Jun-like immunoreactivity was in a smaller number of amacrine cells and many somata in the ganglion cell layer. The monostratified dendritic arbors of one prominent amacrine cell type with Jun-like immunoreactivity were also labeled. There were no dramatic differences in the levels of Fos-like immunoreactivity or Jun-like immunoreactivity between light- or dark-adapted retinas. We examined the effects of excitatory amino acids and gamma-aminobutyric acid (GABA) on the expression of these proteins in vitro. In some experiments, cobalt was used to block synaptic transmission. The excitatory amino acids increased both Fos- and Jun-like immunoreactivity, while GABA generally showed no such stimulatory effect. In cobalt-treated retinas, the same cell types had Jun-like immunoreactivity as seen in the controls, but overall levels of immunoreactivity were increased. In cobalt-treated dark-adapted retinas, some excitatory amino acids increased cytoplasmic Fos-like immunoreactivity in the somata and processes of large cells in the ganglion cell layer. Our results suggest that Fos- and Jun-related proteins may play an important role in the postsynaptic responses to amino acid transmitters in a wide variety of amacrine and ganglion cells.

Differential role of two Ca(2+)-permeable non-NMDA glutamate channels in rat retinal ganglion cells: kainate-induced cytoplasmic and nuclear Ca2+ signals

1. The permeability of non-N-methyl-D-aspartate (non-NMDA) glutamate channels to divalent cations and specifically the entry of Ca2+ and subsequent elevations in cytoplasmic and nuclear Ca2+ signals were investigated in cultured neonatal rat retinal ganglion cells using the whole cell patch-clamp technique and Ca2+ imaging with confocal microscopy. In addition, divalent-permeable non-NMDA receptor channels were studied in retinal slices using a Co2+ staining technique. 2. Using Ca2+ (2.5 mM) as the only permeable cation in the external solution, stimulation with 100 microM kainate produced nondesensitizing, nonselective cation currents with either low or high Ca2+ permeability. Both currents were reversibly blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Neurons with the low divalent-permeable currents (type 1) had reversal potentials of -41.5 +/- 4.4 mV (mean +/- SD), and neurons with the high divalent-permeable currents (type 2) had reversal potentials of -22.6 +/- 5.5 mV. The permeability ratio PCa/PCs was 3.3 for the type 1 currents and 8.5 for the type 2 currents, indicating a 2.5-fold greater permeability to Ca2+ for the type 2 non-NMDA glutamate channels. 3. Both types of non-NMDA glutamate channels showed relatively little selectivity between Ca2+ and Co2+. The type 1 neurons had a slightly higher permeability to Co2+ than to Ca2+, whereas the type 2 neurons were equally permeable to both divalent cations. The type 2 neurons had a much higher permeability for both divalent cations compared with the type 1 neurons. 4. Staining for Co2+ uptake through kainate-stimulated non-NMDA glutamate channels in retinal slices provided additional evidence for the presence of the two ganglion cell populations. Activation of the neurons by kainate in conditions isolating the non-NMDA glutamate channel caused differential uptake of Co2+. In contrast, depolarization in the presence of the non-NMDA antagonist CNQX failed to cause Co2+ influx. 5. Imaging experiments using confocal microscopy showed that kainate stimulation induced an increase in intracellular Ca2+ in both types of retinal ganglion cells, but only the type 2 neurons showed a substantial increase in cytoplasmic and nuclear Ca2+ signals. Kainate-induced Ca2+ signals in the type 2 neurons were almost nine times greater than those of the type 1 neurons. 6. When intracellular Ca2+ stores were depleted by brief treatment with thapsigargin, kainate-induced Ca2+ signals in the type 1 neurons were unchanged. However, in the type 2 neurons kainate no longer induced large Ca2+ signals in the cytoplasm and nucleus, despite normal influx of Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

The occurrence of three calcium-independent protein kinase C subspecies (delta, epsilon and zeta) in retina of different species

The localisation and immunochemical identification of three different forms of calcium-independent protein kinase C (PKC-epsilon, PKC-delta and PKC-zeta) in retinas of different species were analysed by immunohistochemistry and SDS-PAGE/Western blotting, respectively. More than one component of different molecular weights reacted with the polyclonal antibodies in all retinal samples though in all instances a component of molecular weight corresponding to the individual PKCs was recognised and could be eliminated or reduced by preincubating the primary antibodies with the peptides used to generate the antibodies. PKC-zeta immunoreactivity was exclusively associated with the inner segments of the photoreceptors in both mammalian (guinea-pig, rabbit, rat) and non-mammalian (goldfish, chick) retinas. PKC-epsilon immunoreactivity is present in bipolar cells, particularly in their terminals of mammalian and goldfish retinas. In the chick retina immunoreactivity for this enzyme and for PKC-delta was with the inner segments of the photoreceptors. The Müller cells in mammalian retinas and a sub-population of ganglion cells in the goldfish retina exhibited positive immunoreactivity for PKC-delta. The immunoreactivities for all the PKC isoenzymes were eliminated or drastically reduced when the primary antibodies were first preincubated with the peptides used to generate the antibodies.

c-fos and NGFI-A mRNA of rat retina: evidence for light-induced augmentation and a role for cholinergic and glutamate receptors

When rats are exposed to room light from the dark, there is a transient increase of mRNA for the immediate-early genes c-fos and NGFI-A in the retina. Augmentation of c-fos and NGFI-A mRNA by light is apparently associated with activation of cholinergic nicotinic and muscarinic receptors as it can be suppressed by the nicotinic antagonist mecamylamine and the muscarinic antagonist atropine. Moreover, the light-induced increase of c-fos mRNA in retina appears to be associated with activation of glutamate receptors also as the noncompetitive inhibitor of N-methyl-D-aspartate receptors dizocilpine (MK-801) partially suppressed the increase of the c-fos message. Light-induced NGFI-A mRNA augmentation is apparently modulated by the same receptors. We were unable to detect light-induced changes of c-jun mRNA.

Transient presence of GABA in astrocytes of the developing optic nerve

Immunostaining and high-pressure liquid chromatography (HPLC) were used to study the developmental time course of astrocytic gamma-aminobutyric acid (GABA) expression in rat optic nerve. GABA immunostaining was carried out on cultured astrocytes, and on whole optic nerve. Confocal scanning laser microscopy was used to obtain optical sections in excised whole tissue in order to localize the cellular origins of GABA within the relatively intact optic nerve. GABA immunoreactivity was localized in astrocytes identified by GFAP staining; GABA staining was most intense in early neonatal optic nerve and attenuated over 3 weeks of postnatal development. The staining was pronounced in the astrocyte cell bodies and processes but not in the nucleus. There was a paucity of GABA immunoreactivity by postnatal day 20, both in culture and in whole optic nerve. A biochemical assay for optic nerve GABA using HPLC indicated a relatively high concentration of GABA in the neonate, which rapidly attenuated over the first 3 postnatal weeks. Immunoreactivity for the GABA synthesis enzyme glutamic acid decarboxylase (GAD) was pronounced in neonates but also attenuated with development. These results indicate that GABA and the GABA synthesis enzyme GAD are localized in astrocytes of optic nerve, and that their expression is transient during postnatal development.

Kainate elicits elevated nuclear calcium signals in retinal neurons via calcium-induced calcium release

Intracellular Ca2+ was imaged in cultured neonatal rat retinal neurons using the Ca(2+)-sensitive dye fluo-3 and confocal scanning laser microscopy. Depolarization via elevation of bath K+ concentration resulted in large cytoplasmic and nuclear Ca2+ signals; responses in the nucleus exceeded those of the cytoplasm. Glutamate or kainate application elicited the same intracellular pattern of elevated Ca2+ signals. Kainate stimulation was blocked by the non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and greatly reduced by removing Ca2+ from the bath and adding ethylene glycol-bis (beta-amino-ethyl ether) N,N,N',N'-tetraacetic acid (EGTA). Kainate was equally effective in eliciting Ca2+ signals when bath Na+ was replaced with equimolar concentrations of choline, or in the presence of the NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid (APV). Caffeine treatment significantly reduced the kainate-induced intracellular Ca2+ response. These results suggest that Ca2+ can enter through the kainate receptor of retinal neurons and amplify the Ca2+ signals in the cytoplasm and nucleus by releasing Ca2+ from intracellular stores.