Cone Bipolars Research Articles

Differential distribution of hyperpolarization‐activated and cyclic nucleotide‐gated channels in cone bipolar cells of the rat retina

The hyperpolarization-activated and cyclic nucleotide-gated (HCN) channel isoforms HCN1, HCN2, and HCN4 were localized by immunofluorescence in the rat retina. Double labeling with the vesicular glutamate transporter (VGLUT1) was used to identify bipolar cell axon terminals in the inner retina. The HCN1 channel was localized to two cell types with differing intracellular distributions, insofar as staining was seen in the dendrites of a putative OFF-type cone bipolar cell and in the axon terminals of an ON-type bipolar that ramifies in stratum 3 (s3) of the inner plexiform layer (IPL). Staining for HCN4 was seen in two sets of bipolar axon terminals located in s2 and s3 and positioned between the two bands of choline acetyltransferase (ChAT) staining. The cells that ramify in s2 were identified as type 3 cone bipolar cells and the cells that ramify in s3 cells as a subclass of type 5 cone bipolars. The latter group, designated here as type 5b, exhibit diffuse axon terminals and can be distinguished from the narrowly stratifying type 5a cells. Double labeling showed that type 5b cone bipolar cells express both HCN1 and HCN4 as well as HCN2. Superposition of HCN channel labeling with VGLUT1 staining confirmed the presence of a cone bipolar cell whose terminals ramify in the same stratum of the IPL as type 5b cells but that do not express these HCN channels.

Different Functional Types of Bipolar Cells Use Different Gap-Junctional Proteins

Rod signals are transmitted to ON retinal ganglion cells by means of gap junctions between AII amacrine cells and ON bipolars. The AII amacrine cells are known to express connexin36 (Cx36), but previous studies of Cx36 in ON cone bipolars have been ambiguous. Here, we studied bipolar cells in a transgenic mouse line that expresses high levels of green fluorescent protein (GFP) in one type of ON cone bipolar cell. We found strong Cx36 immunostaining in the axon terminals of the GFP-labeled type 357 bipolar cells in both vertical sections and whole mounts of the retina. This finding was confirmed by single-cell immunostaining and single-cell reverse transcription-PCR (RT-PCR). As reported previously (Maxeiner et al., 2005), Cx45 was found in some ON bipolar cells, but RT-PCR showed Cx36 and not Cx45 to be expressed by the type 357 bipolar cells. Some of the remaining GFP-negative bipolar cells expressed Cx45 but not Cx36. It appears that different types of ON cone bipolar cells express different connexins at their gap junctions with AII amacrine cells.

Comparative Study on Calretinin Immunoreactivity in Gerbil and Rat Retina

Expression of calretinin in retina has been ascribed to multiple biological and functional aspects in the visual system. In this study, we examined the distribution patterns of calretinin immunoreactivity in gerbil and rat retina. In the gerbil, calretinin immunoreactivity was present in bipolar and amacrine cells of the inner nuclear layer and in neurones of the ganglion cell layer. In the rat, amacrine and ganglion cells showed calretinin immunoreactivity, but bipolar cells did not contain calretinin immunoreactivity. In both species, calretinin immunoreactivity was absent in cones, cone bipolars, and horizontal cells. In conclusion, gerbil as well as rat has a rod-dominant retina. The differences in calretinin expression between rat and gerbil require further investigations under various functional and developmental conditions.

Light Signaling in Scotopic Conditions in the Rabbit, Mouse and Rat Retina: A Physiological and Anatomical Study

In the dark, light signals are conventionally routed through the following circuit: rods synapse onto rod bipolar (RB) cells, which in turn contact AII amacrine cells. AII cells segregate the light signal into the on and off pathways by making electrical synapses with on cone bipolar (CB) cells and glycinergic inhibitory chemical synapses with off CB cells. These bipolar cells synapse onto their respective ganglion cells, which transfer on and off signals to the visual centers of the brain. Two alternative pathways have recently been postulated for the signal transfer in scotopic conditions: 1) electrical coupling between rods and cones, and 2) a circuit independent of cone photoreceptors, implying direct contacts between rods and off CB cells. Anatomical evidence supports the existence of both these circuits. To investigate the contribution of these alternative pathways to scotopic vision in the mammalian retina, we have performed patch-clamp recordings from ganglion cells in the dark-adapted retina of the rabbit, mouse, and rat. Approximately one-half of the ganglion cells in the rabbit retina received off signals through a circuit that was independent of RB cells. This was shown by their persistence in the presence of the glutamate agonist 2-amino-4-phosphonobutyric acid (APB), which blocks rod-->RB cell signaling. Consistent with this result, strychnine, a glycine receptor antagonist, was unable to abolish these off responses. In addition, we were able to show that some off cone bipolar dendrites terminate at rod spherules and make potential contacts. In the mouse retina, however, there seems to be a very low proportion of off signals carried by an APB-resistant pathway. No ganglion cells in the rat retina displayed APB- and strychnine-resistant responses. Our data support signaling through flat contacts between rods and off CB cells as the alternative route, but suggest that the significance of this pathway differs between species.

Simultaneous Contribution of Two Rod Pathways to AII Amacrine and Cone Bipolar Cell Light Responses

Rod signals traverse several synapses en route to cone bipolar cells. In one pathway, rods communicate directly with cones via gap junctions. In a second pathway, signals flow rods-rod bipolars-AII amacrines-cone bipolars. The relative contribution of each pathway to retinal function is not well understood. Here we have examined this question from the perspective of the AII amacrine. AIIs form bidirectional electrical synapses with on cone bipolars. Consequently, as on cone bipolars are activated by outer plexiform inputs, they too should contribute to the AII response. Rod bipolar inputs to AIIs were blocked by AMPA receptor antagonists, revealing a smaller, non-AMPA component of the light response. This small residual response did not reverse between -70 and +70 mV and was blocked by carbenoxolone, suggesting that the current arose in on cone bipolars and was transmitted to AIIs via gap junctions. The residual component was evident for stimuli 2 log units below cone threshold and was prolonged for bright stimuli, demonstrating that it was rod driven. Because the rod bipolar-AII pathway was blocked, the rod-driven residual current likely was generated via the rod-cone pathway activation of on cone bipolars. Thus for a large range of intensities, rod signals reach the inner retina by both rod bipolar-AII and rod-cone coupling pathways.

The population of bipolar cells in the rabbit retina.

The population of bipolar cells in the rabbit retina was studied using Golgi impregnation and photocatalyzed filling of single cells with dihydrorhodamine, a quantitative sampling technique. The Golgi method revealed the morphology and stratification of cells in detail. The photofilling method allowed us to estimate the frequency of the cell types. From a sample of 243 Golgi-impregnated bipolar cells and 107 photofilled cells, we identified 1 type of rod bipolar cell and 12 types of cone bipolar cells. An analysis based on retinal coverage indicates that this number of types could be contained within the number of bipolar cells known to exist. The dendrites of most cone bipolars contacted all the cones within the individual cone bipolar cell's dendritic field. Types of bipolar cell were encountered at roughly similar frequency, without any one type predominating. The rabbit retina thus contains about a dozen parallel and roughly equipotent through-pathways.

Control of late off-center cone bipolar cell differentiation and visual signaling by the homeobox gene Vsx1.

Retinal bipolar cells are interneurons that transmit visual signals from photoreceptors to ganglion cells. Although the visual pathways mediated by bipolar cells have been well characterized, the genes that regulate their development and function are largely unknown. To determine the role in bipolar cell development of the homeobox gene Vsx1, whose retinal expression is restricted to a major subset of differentiating and mature cone bipolar (CB) cells, we targeted the gene in mice. Bipolar cell fate was not altered in the absence of Vsx1 function, because the pan-bipolar markers Chx10 and Ret-B1 continued to be expressed in inner nuclear layer neurons labeled by the Vsx1-targeting reporter gene, tauLacZ. The specification, number, and gross morphology of the subset of on-center and off-center (OFF)-CB cells defined by tauLacZ expression from the Vsx1 locus were also normal in Vsx1(tauLacZ)/Vsx1(tauLacZ) mice. However, the terminal differentiation of OFF-CB cells in the retina of Vsx1(tauLacZ)/Vsx1(tauLacZ) mice was incomplete, as demonstrated by a substantial reduction in the expression of at least four markers (recoverin, NK3R, Neto1, and CaB5) for these interneurons. These molecular abnormalities were associated with defects in retinal function and documented by electroretinography and in vitro ganglion cell recordings specific to cone visual signaling. In particular, there was a general reduction in the light-mediated activity of OFF, but not on-center, ganglion cells. Thus, Vsx1 is required for the late differentiation and function of OFF-CB cells and is associated with a heritable OFF visual pathway-specific retinal defect.

Inner Structure of Protostellar Collapse Candidate B335 Derived from Millimeter‐Wave Interferometry

We present a study of the density structure of the protostellar collapse candidate B335 using continuum observations from the IRAM Plateau de Bure Interferometer made at wavelengths of 1.2 and 3.0 mm. We analyze these data, which probe spatial scales from 5000 to 500 AU, directly in the visibility domain by comparison with synthetic observations constructed from models that assume different physical conditions. This approach allows for much more stringent constraints to be derived from the data than from analysis of images. A single radial power law in density provides a good description of the data, with a best-fit power-law density index p = 1.65 ± 0.05. Through simulations, we quantify the sensitivity of this result to various model uncertainties, including assumptions of temperature distribution, outer boundary, dust opacity spectral index, and an unresolved central component. The largest uncertainty comes from the unknown presence of a centralized point source. The maximal point source, with 1.2 mm flux of F = 12 ± 7 mJy, reduces the power-law density index to p = 1.47 ± 0.07. The remaining sources of systematic uncertainty, of which the most important is the radial dependence of the temperature distribution, likely contribute a total uncertainty at the level of δp 0.2. Taking into account the uncertainties, we find strong evidence that the power-law index of the density distribution within 5000 AU is significantly less than the value at larger radii, close to 2.0, from previous studies of dust emission and extinction. Images made from the data show clear departures from spherical symmetry, with the globule being slightly extended perpendicular to the outflow axis. The inclusion of a crude model of the outflow as a hollow bipolar cone of constant opening angle improves the fit and leaves the resulting density power-law index unchanged. These results conform well to the generic paradigm of isolated, low-mass star formation, which predicts a power-law density index close to p = 1.5 for an inner region of gravitational free fall onto the protostar. However, the standard inside-out collapse model does not fit the data as successfully as a simple p = 1.5 power law, because of the relative shallowness of the predicted density profile just within the infall radius.

Connexin36 Is Essential for Transmission of Rod-Mediated Visual Signals in the Mammalian Retina

To examine the functions of electrical synapses in the transmission of signals from rod photoreceptors to ganglion cells, we generated connexin36 knockout mice. Reporter expression indicated that connexin36 was present in multiple retinal neurons including rod photoreceptors, cone bipolar cells, and AII amacrine cells. Disruption of electrical synapses between adjacent AIIs and between AIIs and ON cone bipolars was demonstrated by intracellular injection of Neurobiotin. In addition, extracellular recording in the knockout revealed the complete elimination of rod-mediated, on-center responses at the ganglion cell level. These data represent direct proof that electrical synapses are critical for the propagation of rod signals across the mammalian retina, and they demonstrate the existence of multiple rod pathways, each of which is dependent on electrical synapses.

Kinematics of the 12 GHz Methanol Masers toward W3(OH)

In this paper, two epochs (1994 February and 1998 December) of Very Long Baseline Array observations of the 12 GHz CH3OH masers toward the ultracompact (UC) H II region W3(OH) are compared. The 12 GHz maser emission is observed in three separated clumps (<500 AU in size), located north, south, and at the center of the UC H II region. The general of the 12 GHz maser emission has remained remarkably constant, with the maser spots identified in the 1994 epoch maps having similar relative positions (within a few milliarcseconds), shapes, and line-of-sight velocities (within a few tenths of a kilometer per second) as in the 1998 epoch maps. Cross-correlating the intensity distribution of the corresponding spots between the two epochs, we measure relative proper motions of amplitude in the range 1-7 km s-1. The spots of the southern clump move relative to the reference feature (located in the northern clump) with high velocities (≈4 km s-1) and have similar directions of motion. This suggests that the whole southern clump moves relative to the northern clump. The amplitude of the proper motions of the 12 GHz masers agrees well with the values measured for the 1.665 GHz OH masers in W3(OH). The different spatial distribution of the 1.665 and 12 GHz maser spots prevents one from performing a detailed comparison of the gas motion traced by the two maser transitions. The 12 GHz CH3OH masers of the northern clump are clearly associated with both the 6.035 GHz OH and 6.7 GHz CH3OH masers. In particular, the same linear structure (≈200 mas in size at P.A. = 141°) is traced by the most intense spots of the three maser species, and they all show a common regular variation of the line-of-sight velocities along it. We fit the measured three-dimensional velocities and the sky-projected positions of the 12 GHz maser spots of the northern clump with an expanding conical model, in which the spots lie on the surface of a bipolar cone and are accelerated radially outward, spiraling with a constant angular velocity around the cone axis. The model suggests that geometrical conditions may play an important selective role in the observation of the strong 12 GHz masers since the strongest spots are predicted at positions on the conical surface where the cone generators are approximately parallel (within a few degrees) to the line of sight.

Two‐dimensional Kinematical and Ionization Structure of the Warm Gas in the Nuclear Regions of Arp 220

Integral field optical spectroscopy using the INTEGRAL system has been used to characterize the kinematic and ionization properties of the warm gas within 2 kpc of the dust-enshrouded nucleus of Arp 220. Owing to the large internal extinction toward the nuclei, the brightest stellar and line-emitting regions observed at optical wavelengths do not coincide with the dust-enshrouded near-infrared and radio nuclei of Arp 220 but are located northwest of the nucleus at a distance of about 750 pc. Moreover, although the continuum and the line-emitting gas share similar distributions, their emission peaks are displaced, with the Hα emission peak located at about 300 pc southwest of the optical stellar continuum emission peak. A line decomposition analysis has been performed in the complex and high spatially variable emission-line profiles. Three different kinematically distinct and extended gaseous components have been identified in the ionized gas. One narrow component (R) indicates rotation, while the other two components (O and B) are well interpreted by the presence of a biconical outflow. Specifically, the rotational component R traces quiescent gas located in a nuclear disk with the spin axis along the southeast-northwest direction (P.A. 135°). This component of ionized gas seems to be coupled with the 100 kpc disklike H I gas and the 1 kpc molecular disk detected in CO (Scoville et al.). The inclination-corrected rotational velocities imply a dynamical mass (Mdyn) of 2 × 1010 M☉ within a radius of 1.5 kpc. This relatively high value indicates a large mass concentration in the nuclear region of Arp 220, as Scoville et al. already inferred by the presence of 5 × 109 M☉ of molecular gas in a nuclear, 0.5 kpc disk. One of the outflow components, O, has peak-to-peak velocities of 1000 km s-1. The broad component B, with an average width of 815 km s-1, is detected at about 600 pc northwest of the dust-enshrouded nucleus and is blueshifted by 300 km s-1 with respect to the system velocity. The two-dimensional distribution and kinematics of the components are consistent with a bipolar cone geometry with an opening angle of about 90° and are perpendicular to the nuclear disk of gas, as expected in the starburst-driven galactic wind scenario proposed by Heckman, Armus, & Miley. In most of the observed regions, the ionization status of the different gas components is consistent with a shock-heated LINER-like or Seyfert 2 nebula as judged by the [N II]/Hα and [S II]/Hα emission-line ratios. Although the [O III] and Hβ lines are undetected in most of the regions, the brightest zone located northwest of the nucleus could be classified as a Seyfert 2 nebula based on the additional constraint given by the measured lower limit (≥5) for the [O III]/Hβ ratio. There is no evidence of excitation gradients along the symmetry axis of the outflow nor of a biconical ionization structure, which suggests that the ionizing field is homogeneous and less collimated than the gas outflow. However, there are four clearly identified extranuclear regions where the [N II]/Hα ratio decreases by a factor of 5 and is close to the typical values of H II regions. None of these regions are in spatial agreement with the star clusters found in the infrared by Scoville et al., confirming that they must be relatively old globular clusters.

Structure of Protostellar Collapse Candidate B335 Derived from Near‐Infrared Extinction Maps

We present a near-infrared extinction study of the dark globule B335, a protostellar collapse candidate, using data from HST/NICMOS and the W.M. Keck Observatory. These data allow a new quantitative test of the collapse model previously proposed to explain molecular line profiles observed toward this region. We find that the shape of the density profile is well matched by the collapse model, but that the amount of extinction corresponds to larger column densities than predicted. An unstable Bonnor-Ebert sphere with dimensionless outer radius xi_max=12.5+/-2.6 provides an equally good description of the density profile, and is indistinguishable from the collapse model over the range in radius sampled by the data. The bipolar outflow driven by the embedded YSO has an important effect on the extinction through the core, and modeling the outflow as a hollowed-out bipolar cone of constant opening angle provides a good match to theobservations. The complete exinction map is well reproduced by a model that includes both infall and outflow, and an extra 20% dispersion that likely results from residual turbulent motions. This fitted model has an infall radius of R_inf=26+/-3(0.031pc for 250pc distance), and an outflow cone semi-opening angle of alpha=41+/-2 degrees. The fitted infall radius is consistent with those derived from molecular line observations and supports the inside-out collapse interpretation of the density structure. The fitted opening angle of the outflow is slightly larger than observed in CO emission, perhaps because the full extent of the outflow cone in CO becomes confused with ambient core emission at low velocities.

Hyper-Fine Features of the Dust Distribution in the Central Region of the Seyfert Galaxy NGC 4151

Fine features of the dust distribution in the central region of NGC 4151 have been studied from high resolution images obtained by the Subaru Telescope. The two dust lanes lying along a circum-nuclear ellipse of 40“ ×20” have been recognized to consist of a number of fine filaments and knots. In the inner region, there has been found dust distributed in a bipolar cone region extending to 5” from the nucleus. This cone is exactly complementary to the well-known bipolar ionized gaseous region. A dense knot is seen at 2” SE from the nucleus, but no torus-like feature is recognized. The masses of neutral gas in the outer lanes and in the inner region are estimated as 106M⊙ and 105M⊙ respectively. These observational results are compared with results of numerical simulations of gas dynamics.

Distinct Ionotropic GABA Receptors Mediate Presynaptic and Postsynaptic Inhibition in Retinal Bipolar Cells

Ionotropic GABA receptors can mediate presynaptic and postsynaptic inhibition. We assessed the contributions of GABA(A) and GABA(C) receptors to inhibition at the dendrites and axon terminals of ferret retinal bipolar cells by recording currents evoked by focal application of GABA in the retinal slice. Currents elicited at the dendrites were mediated predominantly by GABA(A) receptors, whereas responses evoked at the terminals had GABA(A) and GABA(C) components. The ratio of GABA(C) to GABA(A) (GABA(C):GABA(A)) was highest in rod bipolar cell terminals and variable among cone bipolars, but generally was lower in OFF than in ON classes. Our results also suggest that the GABA(C):GABA(A) could influence the time course of responses. Currents evoked at the terminals decayed slowly in cell types for which the GABA(C):GABA(A) was high, but decayed relatively rapidly in cells for which this ratio was low. Immunohistochemical studies corroborated our physiological results. GABA(A) beta2/3 subunit immunoreactivity was intense in the outer and inner plexiform layers (OPL and IPL, respectively). GABA(C) rho subunit labeling was weak in the OPL but strong in the IPL in which puncta colocalized with terminals of rod bipolars immunoreactive for protein kinase C and of cone bipolars immunoreactive for calbindin or recoverin. These data demonstrate that GABA(A) receptors mediate GABAergic inhibition on bipolar cell dendrites in the OPL, that GABA(A) and GABA(C) receptors mediate inhibition on axon terminals in the IPL, and that the GABA(C):GABA(A) on the terminals may tune the response characteristics of the bipolar cell.

A near-infrared polarized bipolar cone in the Circinus galaxy

We present near-infrared broad-band polarization images of the nuclear regions of the Circinus galaxy in the J, H and K bands. For the first time the south-eastern reflection cone is detected in polarized light, which is obscured at optical wavelengths behind the galactic disk. This biconical structure is clearly observed in J and H band polarized flux whilst in the K band a more compact structure is detected. Total flux J-K and H-K colour maps reveal a complex colour gradient toward the south-east direction (where the Circinus galactic disk is nearer to us). We find enhanced extinction in an arc shaped structure, at about 200pc from the nucleus, probably part of the star-formation ring. We model the polarized flux images with the scattering and torus model of Young etal, with the same basic input parameters as used by Alexander etal in the spectropolarimetry modelling of Circinus. The best fit to the polarized flux is achieved with a torus radius of ~16pc, and a visual extinction Av, through the torus, to the near-infrared emission regions of >66 mags.

Self‐consistent Model of the Dusty Torus around HL Tauri

We present the first comprehensive two-dimensional radiative transfer modeling of the circumstellar dusty environment of HL Tau, a remarkable embedded young stellar object often considered a prototype low-mass star, with a circumstellar disk that resembles the solar nebula at the early stages of planet formation. To recover its general structure and physical parameters, we used the entire beam-matched spectral energy distribution from optical to millimeter wavelengths, high-resolution intensity and linear polarization maps at 0.7, 1.25, 1.65, and 2.2 ?m (the R, J, H, and K bands), aperture synthesis maps at 1.36, 2.7, 3.06, and 7 mm, visibilities at 650 ?m, 870 ?m, and 1.36 mm, and large-aperture linear polarization measurements in the optical and near-infrared bands as observational constraints. Our detailed model of HL Tau explains all these observations well, making the overall picture much more certain. The central radiation source, with a bolometric luminosity of 11 L?, is embedded in a compact, dense torus having a ? r-1.25 density distribution and containing predominantly very large dust particles (radii a 0.1 mm). With two wide bipolar cones excavated by the outflow along the symmetry axis, the model torus has an opening angle of 90?, a radius of ~100 AU, maximum molecular hydrogen density of 1.6 ? 1012 cm-3, and a mass of 0.03 M? (assuming a dust-to-gas mass ratio of 0.01). A relatively large reservoir of circumstellar material, containing dust grains of submicron sizes, resides in an extended toroidal envelope of a similar mass, having a ? r-2 density profile to the adopted outer radius of 104 AU. The model of HL Tau strongly suggests that only the bright parts of the dense compact torus inclined toward us by ~43? can be seen by observers at any relevant wavelength. Direct light from the central source is heavily diluted even in the highest resolution 02 images. The dusty torus is optically thick up to millimeter wavelengths, with the total optical depth of ?V ? 33 toward the invisible central object. The optical depth is partly due to the gray extinction by very large particles in the dense torus (?V ? 10) and to the wavelength-dependent extinction by submicron-sized grains in the extended envelope (?V ? 20). If the very broad size distribution of solid particles indeed exists in the dense torus, this might indicate that in HL Tau we are observing initial phases of the accumulation of larger bodies, which may eventually lead to planet formation.

Connections of two types of flat cone bipolars in the rabbit retina.

The synaptic connections of two types of cone bipolar cells in the rabbit retina were studied with the electron microscope after labeling in vitro with 4',6-diamidino-2-phenylindole (DAPI), intracellular injection with Lucifer Yellow, and photooxidation (Mills and Massey [1992] J. Comp. Neurol. 321:133). Both types of bipolars belong to the flat variety, because they make basal junctions with a group of four to ten neighboring cone pedicles. One cell type has an axonal arborization that occupies strata 1 through 3 of the inner plexiform layer (IPL). At ribbon synaptic junctions, it is presynaptic to ganglion cell dendrites and to reciprocal dendrites belonging to narrow-field bistratified (AII) amacrine cells. In addition, it contacts and is contacted by other amacrine cell processes of unknown origin. The other cell type has an axonal arborization entirely confined to stratum 2 of the IPL; it is pre- or postsynaptic to a pleomorphic population of amacrine cell processes, and, in particular, it receives input from the lobular appendages of AII. Thus, these two bipolar types probably belong to the off-variety because they make basal junctions with cone photoreceptors and send their axon to sublamina a of the IPL, which is occupied by the dendrites of off-ganglion cells. They are also part of the rod pathway because they receive input from AII amacrine cells.

Glutamate Responses of Bipolar Cells in a Slice Preparation of the Rat Retina

Whole-cell currents from >70 voltage-clamped bipolar cells were recorded in a slice preparation of the rat retina. The recorded cells were identified and classified by intracellular staining with Lucifer yellow. Glutamate, the specific agonists (+/-)-2-amino-4-phosphonobutyric acid (AP-4) and kainate (KA), and the antagonist 6-cyanoquinoxaline-2,3-dione (CNQX) were applied. The cells could be isolated from presynaptic influences by the co-application of bicuculline, strychnine, and cobalt ions. Responses to AP-4 were elicited only from bipolar cells with axons stratifying in the inner part of the inner plexiform layer (IPL). AP-4 caused an outward current in these cells attributable to the closure of nonspecific cation channels. Responses to kainate representing a direct action of the drug on the recorded cells were observed only in bipolar cells with axons stratifying in the outer part of the IPL. KA caused a CNQX-sensitive inward current in these cells, associated with openings of nonspecific cation channels. The results predict that cone bipolar (CB) cells with axons terminating in the outer IPL are OFF-bipolars, whereas those with axons terminating in the inner IPL are ON-bipolars. Most of the cells expressed GABA-gated Cl- conductances. In rod bipolar and in some CB cells, only part of the GABA-induced currents could be blocked by the application of bicuculline, suggesting the presence of GABAc receptors in addition to GABAA receptors.

Light responses from one type of ON-OFF amacrine cells in the rabbit retina.

1. The light responses from one type of ON-OFF amacrine cell were recorded intracellularly in the superfused rabbit retina under various conditions of light adaptation. These recordings were obtained from cells located in a central area. 5-7 mm inferior and directly below the optic nerve head. 2. ON-OFF amacrine cells responded to the initiation and termination of light stimuli with transient depolarizations. Their receptive fields were approximately 0.8-1 mm diam and did not exhibit antagonistic center-and-surround organization. 3. The cells received rod input because they responded to very dim scotopic stimuli. With prolonged dark adaptation, the cells became more sensitive to the initiation than termination of the stimulus, because the ON component of the light response had a lower threshold than the OFF component. 4. The cells continued to respond to test flashes when the retina was adapted to a background illumination of rod-saturating intensity. Thus ON-OFF amacrine cells also receive cone input. Under these photopic conditions, a secondary afterpotential was observed following the OFF component. Its characteristics were different from those of the rod aftereffect reported in other retinal cells of the rabbit because its latency and amplitude changed with increasing stimulus intensity. 5. Intracellular injections of horseradish peroxidase showed that the recordings were obtained from a class of ON-OFF amacrine cells whose wide-field, unistratified dendrites were rigorously confined to the middle of the inner plexiform layer or stratum 3. 6. The conspicuous rod and cone inputs into a class of amacrine cells that are connected neither to rod bipolars nor to All amacrine cells strongly support the idea that in the rabbit the rod pathway uses cone bipolars as interneurons to distribute scotopic signals to ganglion and cone-driven amacrine cells.

Smoke rings around supernova 1987a

Detailed observations of the [Oiii]5007 A emission from the elliptical rings around SN 1987A suggest a model wherein the two faint, outer rings are due to emission from two circular toroids moving outwards (at ≤ 25 km s−1) along a bipolar cone centred on the site of the supernova. The brighter, central ring is expanding radially outward at 8.3 km s−1. The rings must have been created ∼ 2-3 × 104 years before the supernova explosion and are thought to be a consequence of the interaction of stellar winds emanating from the progenitor system during the final stages of its evolution to a supernova.