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PubMed1993

Evidence for a novel regulatory pathway for herpes simplex virus gene expression in trigeminal ganglion neurons.

Thymidine kinase (TK)-negative (TK-) mutant strains of herpes simplex virus type 1 (HSV-1) show reduced expression of alpha and beta viral genes during acute infection of trigeminal ganglion neurons following corneal infection (M. Kosz-Vnenchak, D. M. Coen, and D. M. Knipe, J. Virol. 64:5396-5402, 1990). It was surprising that a defect in a beta gene product would lead to decreased alpha and beta gene expression, given the regulatory pathways demonstrated for HSV infection of cultured cells. In this study, we have examined viral gene expression during reactivation from latent infection in explanted trigeminal ganglion tissue. In explant reactivation studies with wild-type virus, we observed viral productive gene expression over the first 48 h of explant incubation occurring in a temporal order (alpha, beta, gamma) similar to that in cultured cells. This occurred predominantly in latency-associated transcript-positive neurons but was limited to a fraction of these cells. In contrast, TK- mutant viruses showed greatly reduced alpha and beta gene expression upon explant of latently infected trigeminal ganglion tissue. An inhibitor of viral TK or an inhibitor of viral DNA polymerase greatly decreased viral lytic gene expression in trigeminal ganglion tissue latently infected with wild-type virus and explanted in culture. These results indicate that the regulatory mechanisms governing HSV gene expression are different in trigeminal ganglion neurons and cultured cells. We present a new model for viral gene expression in trigeminal ganglion neurons with implications for the nature of the decision process between latent infection and productive infection by HSV.

Animals↗
PubMed1996

Inflammatory infiltration of the trigeminal ganglion after herpes simplex virus type 1 corneal infection.

Following herpes simplex virus type 1 (HSV-1) infection of the cornea, the virus is transmitted to the trigeminal ganglion, where a brief period of virus replication is followed by establishment of a latent infection in neurons. A possible role of the immune system in regulating virus replication and maintaining latency in the sensory neurons has been suggested. We have investigated the phenotype and cytokine pattern of cells that infiltrate the A/J mouse trigeminal ganglion at various times after HSV-1 corneal infection. HSV antigen expression in the trigeminal ganglion (indicative of the viral lytic cycle) increased until day 3 postinfection (p.i.) and then diminished to undetectable levels by day 7 p.i. The period of declining HSV antigen expression. was associated with a marked increase in Mac-1+ cells. These cells did not appear to coexpress the F4/80+ (macrophage) or the CD8+ (T cell) markers, and none showed polymorphonuclear leukocyte morphology, suggesting a possible early infiltration of natural killer cells. There was also a significant increase in the trigeminal ganglion of cells expressing the gamma delta T-cell receptor, and these cells were found almost exclusively in very close association with neurons. This period was also characterized by a rapid and equivalent increase in cells expressing gamma interferon and interleukin-4. The density of the inflammatory infiltrate in the trigeminal ganglion increased until days 12 to 21 p.i., when it was predominated by CD8+, Mac-1+, and tumor necrosis factor-expressing cells, which surrounded many neurons. By day 92 p.i., the inflammatory infiltrate diminished but was heaviest in mice with active periocular skin disease. Our data are consistent with the notion that gamma interferon produced by natural killer cells and/or gamma delta T cells may play an important role in limiting HSV-1 replication in the trigeminal ganglion during the acute stage of infection. In addition, tumor necrosis factor produced by CD8+ T cells and macrophages may function to maintain the virus in a latent state.

Animals↗
PubMed2000

Retinal ganglion cell death in experimental glaucoma.

AIMS: To determine whether parasol retinal ganglion cells (magnocellular pathway) are selectively lost in the primate model of glaucoma. METHODS: Ocular hypertension was induced in one eye of six Macaca fascicularis monkeys for 6-14 weeks. The retinal ganglion cells in these eyes were labelled retrogradely with the tracer horseradish peroxidase (HRP) implanted into the optic nerve and subsequently examined in retinal whole mount preparations. The degree of retinal ganglion cell loss was estimated from Nissl stained tissue by comparison with the contralateral untreated control eye. RESULTS: In the three glaucomatous retinas with the best labelling 1282 cells could be classified, of which 182 were parasol cells and 1100 were midget cells. Linear regression analysis did not demonstrate a significant reduction in the proportion of parasol to midget cells with increasing cell loss (regression slope 0.023, 95% CI -0.7 to 0.11). Compared with the control eye the cell soma of the remaining retinal ganglion cells in glaucomatous eyes were reduced in size by 20% for parasol cells (p=0.003) and by 16% for midget cells (p <0.001). CONCLUSION: The results of this study do not support the hypothesis that selective loss of parasol retinal ganglion cells occurs in experimental glaucoma. In addition, the change in cell soma size distributions following ocular hypertension suggests that both parasol and midget retinal ganglion cells undergo shrinkage before cell death.

Animals↗
PubMed2005

Functional organization of ganglion cells in the salamander retina.

Recently, we reported a novel technique for recording all of the ganglion cells in a retinal patch and showed that their receptive fields cover visual space roughly 60 times over in the tiger salamander. Here, we carry this analysis further and divide the population of ganglion cells into functional classes using quantitative clustering algorithms that combine several response characteristics. Using only the receptive field to classify ganglion cells revealed six cell types, in agreement with anatomical studies. Adding other response measures served to blur the distinctions between these cell types rather than resolve further classes. Only the biphasic off type had receptive fields that tiled the retina. Even when we attempted to split these classes more finely, ganglion cells with almost identical functional properties were found to have strongly overlapping spatial receptive fields. A territorial spatial organization, where ganglion cell receptive fields tend to avoid those of other cells of the same type, was only found for the biphasic off cell. We further studied the functional segregation of the ganglion cell population by computing the amount of visual information shared between pairs of cells under natural movie stimulation. This analysis revealed an extensive mixing of visual information among cells of different functional type. Together, our results indicate that the salamander retina uses a population code in which every point in visual space is represented by multiple neurons with subtly different visual sensitivities.

Action Potentials↗
PubMed1990

Actions of excitatory amino acids on brisk ganglion cells in the cat retina.

1. Retinal ganglion cell activity was recorded extracellularly in the intact cat eye. We examined the effects of iontophoretically applied glutamate (GLU), aspartate (ASP), and the specific agonists kainate (KA), quisqualate (QQ), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), and N-methyl-D-aspartate (NMDA) on the spontaneous and light-driven activity of ganglion cells. 2. ASP and GLU increased the spontaneous as well as the light-driven activity of all brisk cell types. The effects of the two drugs were very similar. The activity of most cells remained at a constant increased level during prolonged application of these drugs. 3. KA also excited all brisk ganglion cell classes and caused effects very similar to those of GLU and ASP but was effective at a much lower concentration. In general, brisk ganglion cells responded most vigorously to KA application. 4. QQ excited approximately 50% of all ON-X and OFF-X cells encountered, the other 50% of the X cells and all Y cells were inhibited during QQ-application. This inhibition was quite likely due to the stimulation of glycinergic and GABAergic interneurons, because it was reduced or abolished during application of the respective antagonists strychnine and bicuculline. All ganglion cells apparently received either direct or indirect excitatory input from QQ receptors, which can be revealed by blocking the inhibitory interneurons. 5. The major actions of QQ on the discharge rate of ganglion cells are mimicked by AMPA. Hence, the actions of QQ are likely to be mediated by the "classical" QQ-receptor, ion-channel complex rather than by the recently described type of QQ-receptor that is coupled to a second messenger system. 6. NMDA excited ON-X, OFF-X, and OFF-Y cells but inhibited ON-Y cells. Excitatory and inhibitory NMDA effects could be blocked by the specific NMDA-receptor antagonists D(-)-2-amino-7-phosphono-heptanoate (AP-7) or 3-((+/-)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP). If the GABAergic transmission was blocked by bicuculline, the NMDA-induced inhibition of ON-Y cells was abolished. We conclude that NMDA activates GABAergic interneurons that in turn reduce the activity of ON-Y cells.

Amino Acids↗
PubMed1992

Site of action potential initiation in amphibian retinal ganglion cells.

1. We applied morphological, pharmacological, electrophysiological, and computer simulation techniques to analyze the origin of impulse initiation in amphibian retinal ganglion cells. 2. Morphological studies of retinal ganglion cells in the mudpuppy (Necturus maculosus) and larval tiger salamander (Ambystoma tigrinum) were carried out with the use of either retrograde or intracellular labeling with horseradish peroxidase. These studies identified a characteristic thinning of the axon that begins after the initial segment of axon emerges from the ganglion cell soma or primary dendrite. Morphometric analysis of the thin segment revealed an average length of 74 microns with a standard deviation of 22 microns. For 20 conventionally placed ganglion cells, the length of the thin segment could not be correlated with soma size, initial segment diameter, or distance from the optic disk. There was also little or no correlation for seven displaced ganglion cells. The diameter of the thin segment was below reliable estimation by light microscopy. 3. We studied the possible significance of the thin axonal segment for ganglion cell impulse generation through a combination of electrophysiological recordings (intracellular and whole-cell recordings) together with computer modeling experiments. 4. Electrophysiological experiments are consistent with the idea that the thin segment and cell soma are less excitable than the initial segment region, which appears to be the principal site of initiation of the nerve impulse. The initial segment is that portion of the axon that is bounded by the soma (or proximal dendrite) at its origin and the thin segment at its distal end. 5. Computer simulations of impulse activation were carried out with the use of two different anatomic constraints: one class of simulations did not take into account the thin segment and assumed uniform cylinder conditions, whereas the other class of simulations included a model of the thin axonal segment. These comparative simulations indicate that the thin segment must contain a relatively high density of voltage-gated Na+ channels and support impulse traffic to account for physiological observations on orthodromic and antidromic impulse propagation. In addition, to match the physiological recordings, it is necessary for both the initial segment and the soma compartments to contain moderately high levels of Na+ channels. 6. Our physiological and simulation studies are consistent with the idea that the nerve impulse is normally initiated in the initial segment of axon and then spreads to activate a somatic impulse in the retrograde direction and the axonal impulse in the anterograde direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1994

Calcium currents in turtle retinal ganglion cells. I. The properties of T- and L-type currents.

1. Voltage-activated calcium currents from single, isolated turtle retinal ganglion cells were characterized with standard whole cell patch clamp techniques. Calcium current amplitude was increased with the use of 10 mM extracellular Ca2+, whereas sodium and potassium currents were pharmacologically suppressed. 2. A transient component, expressed in approximately 39% of the cells recorded from, closely resembled the T-type calcium current described previously in other tissues. This component activated at low voltages (around -50 mV from a holding potential of -70 mV) and inactivated with a time constant 10-30 ms at -20 mV; the inactivation was strongly voltage dependent. Substitution of Ca2+ with Ba2+ reduced this current in most cases or had no effect in some instances. Surprisingly, the transient calcium current was potentiated by Bay-K 8644 and inhibited by nifedipine in some of the ganglion cells tested. 3. A sustained component, which activated at between -20 and -10 mV from a holding potential of -70 mV, was found in all ganglion cells from which we recorded. This component was substantially larger when equimolar Ba2+ replaced Ca2+ as the charge carrier, and was sensitive to the dihydropyridine agonist Bay-K 8644 and the antagonist nifedipine. Thus the sustained current in turtle retinal ganglion cells was similar to the L-type calcium current described in chick DRG neurons. However, unlike the typical L-type current, this component in turtle ganglion cells showed an inactivation that was highly dependent on the intracellular free Ca2+ concentration but not the membrane potential. 4. Synthetic omega-conotoxin MVIIC selectively blocked the sustained calcium current while sparing the transient component. It could completely block the sustained current that was resistant to nifedipine in some cells. Thus there may exist several different high voltage-activated calcium channels in turtle retinal ganglion cells.

Animals↗
PubMed1995

Direction biases of X and Y type retinal ganglion cells in the cat.

1. It has been reported that in the cat only a specialized group of retinal ganglion cells constituting approximately 1% of the overall population are direction sensitive. Two major groups of retinal ganglion cells, the X and Y cells, have been reported not to be sensitive to the direction of stimulus motion. 2. We recorded action potentials of retinal ganglion cells intraocularly. We studied quantitatively the visual responses elicited by drifting sinusoidal gratings of various spatial frequencies, bars, and spots. 3. The results confirm previous reports that most cat retinal ganglion cells exhibit orientation biases when tested with gratings of relatively high spatial frequency. 4. Additionally, we find that 22% of X and 34% of Y type retinal ganglion cells exhibit direction biases. Overall, Y cells displayed significantly stronger direction biases than did X cells. 5. In general, direction biases are clearest when the test gratings are of relatively low spatial frequency. 6. The direction biases of X and Y cells subserving the central 15 degrees of retina were weaker than those of cells subserving more peripheral regions. 7. The direction-biased responses of cat ganglion cells were similar to those of X and Y type relay cells in the cat dorsal lateral geniculate nucleus (LGNd). Thus we suggest that the direction biases of LGNd cells are a reflection of their retinal inputs.

Animals↗
PubMed1996

Effect of spike blockade on the receptive-field size of amacrine and ganglion cells in the rabbit retina.

1. Intracellular recordings were obtained from 21 amacrine cells and 12 ganglion cells in the isolated, superfused retina-eyecup of the rabbit. Cells were subsequently labeled with horseradish peroxidase (HRP) or N-(2-aminoethyl)-biotinamide hydrochloride (Neurobiotin) for morphologic identification. 2. Initial experiments performed on three amacrine cells and three ganglion cells showed that 1 microM tetrodotoxin (TTX) abolished all spiking. This included both large-amplitude and small-amplitude spikes recorded in many amacrine cells, indicating that they are mediated by voltage-gated sodium channels. 3. The center-receptive-field size of 18 amacrine cells and 9 ganglion cells was measured with the use of a 50-microns-wide/6.0-mm-long rectangular slit of light that was displaced along its minor axis (parallel to the visual streak) in steps as small as 3 microns. The retina was then bathed in 1 microM TTX, or individual cells were injected with 50 mM QX-314, a quatemary lidocaine derivative, to abolish all spiking, and the center-receptive field of each cell was then remeasured. 4. Although TTX blocked spiking in all ganglion cells (dendritic diameters ranging from 302 to 969 microns), it produced no significant change in the size of their center-receptive fields. This finding argues that passive, electrotonic spread of synaptic inputs to ganglion cell dendritic arbors is adequate for efficient propagation from terminal branches to the soma; active propagation via voltage-gated sodium channels plays no apparent role. 5. In contrast, TTX and QX-314 had variable effect on the receptive fields of amacrine cells, which was related to the size of their dendritic arbors. Whereas TTX had no significant effect on the receptive-field size of amacrine cells whose dendritic arbors were < 525 microns across, the center-receptive fields of larger amacrine cells were reduced, on average, by 40%; QX-314 produced a very similar average reduction of 39%. Moreover, for these larger cells, there was a direct relationship between the magnitude of the reduction in receptive-field size produced by TTX or QX-314 and the size of a cell's dendritic arbor. This relationship was true whether the change in receptive-field size was measured in absolute terms or as percent reduction from control values. 6. Interestingly, TTX and QX-314 also significantly reduced the amplitude of slow potentials recorded in amacrine cells by an average of 22 and 24%, respectively. However, the amplitude of slow potentials recorded in ganglion cells were relatively uneffected by TTX. 7. These findings are consistent with the idea that, for amacrine cells with dendritic arbors spanning > 525 microns, active propagation of synaptic signals mediated by voltage-gated sodium channels is necessary for efficient movement of information across a cell's dendritic arbor and thus plays a major role in shaping their receptive fields. Although the TTX effects may also reflect an indirect contribution from altered synaptic input derived from presynaptic spiking neurons, the strong similarity between the effects of TTX and QX-314 argues that any such contribution was minor. For smaller amacrine cells, passive, electrotonic spread of signals appears adequate for efficient propagation within their limited dendritic arbors.

Anesthetics, Local↗
PubMed1997

Pharmacology of directionally selective ganglion cells in the rabbit retina.

In this report we describe extracellular recordings made from ON and ON-OFF directionally selective (DS) ganglion cells in the rabbit retina during perfusion with agonists and antagonists to acetylcholine (ACh), glutamate, and gamma-aminobutyric acid (GABA). Nicotinic ACh agonists strongly excited DS ganglion cell in a dose-dependent manner. Dose-response curves showed a wide range of potencies, with (+/-)-exo-2-(6-chloro-3pyridinyl)-7-azabicyclo[2.2.1] heptane dihydrochloride (epibatidine) > > > nicotine > 1,1-dimethyl-4-phenylpiperazinium iodide = carbachol. In addition, the mixed cholinergic agonist carbachol produced a small excitation, mediated by muscarinic receptors, that could be blocked by atropine. The specific nicotinic antagonists hexamethonium bromide (100 microM), dihydro-beta-erythroidine (50 microM), mecamylamine (50 microM), and tubocurarine (50 microM) blocked the responses to nicotinic agonists. In addition, nicotinic antagonists reduced the light-driven input to DS ganglion cells by approximately 50%. However, attenuated responses were still DS. We deduce that cholinergic input is not required for directional selectivity. These experiments reveal the importance of bipolar cell input mediated by glutamate. N-methyl-D-aspartic acid (NMDA) excited DS ganglion cells, but NMDA antagonists did not abolish directional selectivity. However, a combined cholinergic and NMDA blockade reduced the responses of DS ganglion cells by > 90%. This indicates that most of the noncholinergic excitatory input appears to be mediated by NMDA receptors, with a small residual made up by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate (KA) receptors. Responses to AMPA and KA were highly variable and often evoked a mixture of excitation and inhibition due to the release of ACh and GABA. Under cholinergic blockade AMPA/KA elicited a strong GABA-mediated inhibition in DS ganglion cells. AMPA/KA antagonists, such as 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo (F)quinoxaline dione and GYKI-53655, promoted null responses and abolished directional selectivity due to the blockade of GABA release. We conclude that GABA release, mediated by non-NMDA glutamate receptors, is an essential part of the mechanism of directional selectivity. The source of the GABA is unknown, but may arise from starburst amacrine cells.

Acetylcholine↗
PubMed1997

Functional development of intrinsic properties in ganglion cells of the mammalian retina.

Senosory neurons manifest pronounced changes in excitability during maturation, but the factors contributing to this ubiquitous developmental phenomenon are not well understood. To assess the contribution of intrinsic membrane properties to such changes in excitability, in the present study whole cell patch-clamp recordings were made from developing ganglion cells in the intact retina of postnatal rats. During a relatively brief developmental period (postnatal days P7-P27) ganglion cells exhibited pronounced changes in the discharge patterns generated by depolarizing current injections. The youngest cells (P7-P17) typically responded to maintained depolarizations with only a single spike or a rapidly adapting discharge pattern. In contrast, the predominant response mode of more mature cells (P21-P27) was a series of repetitive discharges that lasted for the duration of the depolarization period, and by P25 all cells responded in this manner. These functional changes characterized all three morphologically defined cell classes identified by intracellular labeling with Lucifer yellow. To determine if expression of the potassium current (Ia) and the kinetics of the Na-channel related to the increased excitability of developing ganglion cells described above, current- and voltage-clamp recordings were made from individual neurons. The different firing patterns manifested by developing retinal ganglion cells did not reflect the presence or absence of the Ia conductance, although cells expressing Ia tended to generate spikes of shorter duration. With maturation the speed of recovery from inactivation of the Na current increased markedly and this related to the increased excitability of developing ganglion cells. Neurons yielding only a single spike to maintained depolarization were characterized by the slowest speed of recovery; cells with rapidly adapting discharges showed a faster recovery and those capable of repetitive firing recovered fastest from Na-channel inactivation. It is suggested that these changes in intrinsic membrane properties may relate to the different functional roles subserved by ganglion cells during development.

Action Potentials↗
PubMed1998

Characterization of spontaneous inhibitory synaptic currents in salamander retinal ganglion cells.

Spontaneous and light-evoked postsynaptic currents (sPSCs and lePSCs, respectively) in retinal ganglion cells of the larval tiger salamander were recorded under voltage-clamp conditions from living retinal slices. The focus of this study is to characterize the spontaneous inhibitory PSCs (sIPSCs) and their contribution to the light-evoked inhibitory PSCs (leIPSCs) in ON-OFF ganglion cells. sIPSCs were isolated from spontaneous excitatory PSCs (sEPSCs) by application of 10 microM 6,7-dinitroquinoxaline-2,3-dione (DNQX) + 50 microM 2-amino-5-phosphonopentanoic acid (AP5). In approximately 70% of ON-OFF ganglion cells, bicuculline (or picrotoxin) completely blocks sIPSCs, suggesting all sIPSCs in these cells are mediated by GABAergic synaptic vesicles and gamma-aminobutyric acid-A (GABAA) receptors (GABAergic sIPSCs, or GABAsIPSCs). In the remaining 30% of - ganglion cells, bicuculline (or picrotoxin) blocks 70-98% of the sIPSCs, and the remaining 2-30% are blocked by strychnine (glycinergic sIPSCs, or GLYsIPSCs). GABAsIPSCs occur randomly with an exponentially distributed interval probability density function, and they persist without noticeable rundown over time. The GABAsIPSC frequency is greatly reduced by cobalt, consistent with the idea that they are largely mediated by calcium-dependent vesicular release. GABAsIPSCs in DNQX + AP5 are tetrodotoxin (TTX) insensitive, suggesting that amacrine cells that release GABA under these conditions do not generate spontaneous action potentials. The average GABAsIPSCs exhibited linear current-voltage relation with a reversal potential near the chloride equilibrium potential, and an average peak conductance of 319.67 +/- 252.83 (SD) pS. For GLYsIPSCs, the average peak conductance increase is 301.68 +/- 94.34 pS. These parameters are of the same order of magnitude as those measured in inhibitory miniature postsynaptic currents (mIPSCs) associated with single synaptic vesicles in the CNS. The amplitude histograms of GABAsIPSCs did not exhibit multiple peaks, suggesting that the larger events are not discrete multiples of elementary events (or quanta). We propose that each GABAsIPSC or GLYsIPSC in retinal ganglion cells is mediated by a single or synchronized multiple of synaptic vesicles with variable neurotransmitter contents. In a sample of 16 ON-OFF ganglion cells, the average peak leIPSC (held at 0 mV) at the light onset is 509.0 +/- 233.85 pA and that at the light offset is 529.0 +/- 339.88 pA. The approximate number of GABAsIPSCs and GLYsIPSCs required to generate the average light responses, calculated by the ratio of the charge (area under current traces) of the leIPSCs to that of the average single sIPSCs, is 118 +/- 52 for the light onset, and 132 +/- 76 for the light offset.

Ambystoma↗
PubMed2000

Variability in the location of the retinal ganglion cell area centralis is correlated with ontogenetic changes in feeding behavior in the black bream, Acanthopagrus butcheri (Sparidae, teleostei).

The development of neural cell topography in the retinal ganglion cell layer was examined in a teleost, the black bream (Acanthopagrus butcheri). From Nissl-stained wholemounts, it was established that fish between 10 and 15 mm standard body length (SL) possess high cell densities throughout the dorso-temporal retinal quadrant, with peak cell densities located in temporal regions of the retina. However, in fish between 15 and 80 mm SL, a wide variation in the position of the peak cell density is revealed with the locations of the areae centrales (AC) ranging from exclusively temporal to periphero-dorsal retina. Fish larger than 80 mm SL always possess an AC located in the dorsal region of the dorso-temporal retinal quadrant. The topography of ganglion cells within the ganglion cell layer was determined by comparing the numbers of ganglion cells retrogradely-labeled from the optic nerve with the total population of Nissl-stained neurons (ganglion plus displaced amacrine cells) in a range of different-sized individuals. Ganglion cell topography was the same as that recorded for all Nissl-stained neurons. The feeding behavior of juveniles from metamorphosis to 80 mm SL was observed, where fish were given the choice of feeding on live food in mid-water (until 15 mm SL) or obtaining pellets from the surface or the bottom. A range of feeding patterns was recorded, with the smallest fish taking food from mid-water but individuals between 15 and 80 mm SL taking food either from the surface or the bottom or both. A correlation between the preferred mode of feeding and the position of the AC was found, such that those individuals feeding in mid-water or at the surface possess a temporal or intermediate (dorso- temporal) AC, whereas those predominantly feeding from the bottom possess a dorsal AC.

Animals↗
PubMed2000

Retinal ganglion cell topography in elasmobranchs.

Retinal wholemounts are used to examine the topographic distribution of retinal cells within the ganglion cell layer in a range of elasmobranchs from different depths. The retina is examined for regional specializations for acute vision in six species of selachians, Galeocerdo cuvieri, Hemiscyllium ocellatum, Scyliorhinus canicula, Galeus melastomus, Etmopterus spinax, Isistius brasiliensis, one species of batoid, Raja bigelowi and one species of chimaera, Hydrolagus mirabilis. These species represent a range of lifestyles including pelagic, mesopelagic and benthic habitats, living from shallow water to the sea bottom at a depth of more than 3000 m. The topography of cells within the ganglion cell layer is non-uniform and changes markedly across the retina. Most species possess an increased density of cells across the horizontal (dorsal) meridian or visual streak, with a density range of 500 to 2,500 cells per mm(2) with one or more regional increases in density lying within this specialized horizontal area. It is proposed that the higher spatial resolving power provided by the horizontal streak in these species mediates panoramic vision in the lower frontal visual field. Only I. brasiliensis possesses a concentric arrangement of retinal iso-density contours in temporal retina or an area centralis, thereby increasing spatial resolving power in a more specialized part of the visual field, an adaptation for its unusual feeding behavior. In Nissl-stained material, amacrine and ganglion cell populations could be distinguished on the criteria of soma size, soma shape and nuclear staining. Quantitative analyses show that the proportion of amacrine cells lying within the ganglion cell layer is non-uniform and ranges between 0.4 and 12.3% in specialized retinal areas and between 8.2 and 48.1% in the peripheral non-specialized regions. Analyses of soma area of the total population of cells in the ganglion cell layer also show that the pelagic species possess significantly smaller soma (9-186 micrometer(2)) than benthic and/or deep-sea species (16-338 micrometer(2)), and that a number of different morphological classes of cells are present including a small population of giant ganglion cells.

Animals↗
PubMed1994

The retinal ganglion cell layer and optic nerve in a marsupial, the honey possum (Tarsipes rostratus).

We examined the retina and optic nerve of one of the smallest mammals, the honey possum (Tarsipes rostratus), a marsupial. Ganglion and displaced amacrine cells were distinguished by morphological criteria in retinal wholemounts stained with cresyl violet. There was a mean of 90,000 ganglion cells which were distributed as an area centralis in the mid-temporal retina with a peak density of 9,000/1 mm2 falling in a concentric shallow gradient to 2,000/1 mm2 at the periphery. The unimodal and positively skewed spectra of soma diameters gave no indication of ganglion cell classes. Displaced amacrine cells numbered only 15,000, being outnumbered 6:1 by ganglion cells. This value represents by far the lowest percentage of displaced amacrine cells yet reported for a mammalian retina. The displaced amacrine population was evenly distributed. Counts of optic axons from electron micrographs were within 1-5% of the ganglion cell estimates. In the retrobulbar portion of the nerve, a substantial proportion of axons (26-43%) were unmyelinated, and many of these were concentrated within the lateral quadrant. This specialisation may represent the outflow of the area centralis. At the level of the foramen, the percentage of unmyelinated axons fell to 4-6%, and axons were more uniform in their distribution. Axon diameters were lower for the unmyelinated than the myelinated populations at both levels. As for ganglion cells, however, the spectra of axon diameters were unimodal and positively skewed for both unmyelinated and myelinated axons.

Animals↗
PubMed2003

Ganglionic action of angiotensin contributes to sympathetic activity in renin-angiotensinogen transgenic mice.

In addition to central nervous system actions, angiotensin (Ang) II may increase sympathetic nerve activity (SNA) via a direct action on sympathetic ganglia. We hypothesized that sympathetic ganglionic actions of endogenous Ang II contribute to SNA in transgenic mice that overexpress renin and angiotensinogen (R+A+ mice). Renal SNA and arterial pressure were recorded in anesthetized R+A+ and littermate control mice before and after ganglionic blockade, and after additional blockade of angiotensin type 1 (AT1) receptors with losartan. Ganglionic blockade essentially abolished SNA in control mice, but only reduced SNA to 47+/-18% of baseline in R+A+ mice. The residual SNA remaining after ganglionic blockade in R+A+ mice was reduced from 47+/-18% to 8+/-6% of baseline by losartan (P<0.05). The sympathoinhibitory response to losartan was accompanied by an enhanced decrease in arterial pressure in R+A+ mice compared with that observed in control mice. AT1 receptor expression in sympathetic ganglia, as measured by real-time reverse transcription-polymerase chain reaction, was increased approximately 3-fold in R+A+ versus control mice. The results demonstrate that, as anticipated, essentially all of the renal postganglionic SNA in control mice is driven by preganglionic input. The major new finding is that Ang II-evoked ganglionic activity accounts for approximately 40% of total SNA in R+A+ mice. The significant contribution of the direct ganglionic action of Ang II in R+A+ mice likely reflects both increased levels of Ang II and upregulation of AT1 receptors in sympathetic ganglia.

Angiotensin II↗
PubMed2003

Thresholds for activation of rabbit retinal ganglion cells with an ultrafine, extracellular microelectrode.

PURPOSE: To determine electrical thresholds required for extracellular activation of retinal ganglion cells as part of a project to develop an epiretinal prosthesis. METHODS: Retinal ganglion cells were recorded extracellularly in retinas isolated from adult New Zealand White rabbits. Electrical current pulses of 100- micro s duration were delivered to the inner surface of the retina from a 5- micro m long electrode. In about half of the cells, the point of lowest threshold was found by searching with anodal current pulses; in the other cells, cathodal current pulses were used. RESULTS: Threshold measurements were obtained near the cell bodies of 20 ganglion cells and near the axons of 19 ganglion cells. Both cathodal and anodal stimuli evoked a neural response in the ganglion cells that consisted of a single action potential of near-constant latency that persisted when retinal synaptic transmission was blocked with cadmium chloride. For cell bodies, but not axons, thresholds for both cathodal and anodal stimulation were dependent on the search method used to find the point of lowest threshold. With search and stimulation of matching polarity, cathodal stimuli evoked a ganglion cell response at lower currents (approximately one seventh to one tenth axonal threshold) than did anodal stimuli for both cell bodies and axons. With cathodal search and stimulation, cell body median thresholds were somewhat lower (approximately one half) than the axonal median thresholds. With anodal search and stimulation, cell body median thresholds were approximately the same as axonal median thresholds. CONCLUSIONS: The results suggest that cathodal stimulation should produce lower thresholds, more localized stimulation, and somewhat better selectivity for cell bodies over axons than would anodal stimulation.

Action Potentials↗
PubMed2005

Stimulation of P2X7 receptors elevates Ca2+ and kills retinal ganglion cells.

PURPOSE: Retinal ganglion cells are known to express ionotropic P2X(7) receptors for ATP. Stimulation of these receptors in other cells can elevate Ca(2+) and sometimes lead to cell death. This study asked whether P2X(7) receptor stimulation alters the Ca(2+) levels and viability of retinal ganglion cells. METHODS: P2X(7) agonists were applied to retinal ganglion cells from neonatal rats loaded with fura-2 to examine their effect on intracellular Ca(2+) levels. The effect of P2X(7) receptor stimulation on cell viability was examined in rat retinal ganglion cells back-labeled with aminostilbamidine. RESULTS: The P2X(7) agonist benzoylbenzoyl adenosine triphosphate (BzATP) led to a large, sustained increase in Ca(2+). BzATP was >100-fold more effective than ATP at raising intracellular Ca(2+), when both agonists were applied at 10 microM. The response to BzATP was enhanced threefold by removal of extracellular Mg(2+), was dependent on extracellular Ca(2+), and was prevented by brilliant blue G (BBG). BzATP led to a concentration-dependent reduction in the number of cells with a median lethal dose (LD(50)) of 35 muM. Cell death was prevented by the P2X(7) antagonists BBG and oxidized ATP, but not by 30 microM suramin, consistent with the actions of the P2X(7) receptor. BzATP activated caspases in ganglion cells, but did not lead to membrane blebbing or increased permeability to Yo-Pro-1. The L-type Ca(2+) channel blocker nifedipine attenuated cell death, suggesting excessive Ca(2+) influx contributes to the lethal effects of BzATP. CONCLUSION: Short-term stimulation of the P2X(7) receptor can raise Ca(2+) in rat retinal ganglion cells, whereas sustained stimulation of the receptor can kill them.

Adenosine Triphosphate↗