Cells In Tiger Salamander Retina Research Articles

Effects of Histamine on Light Responses of Amacrine Cells in Tiger Salamander Retina

Using immunofluorescence, we showed that histamine receptor 1 is expressed by horizontal cell axons and a subset of amacrine cells in the tiger salamander retina. The effects of histamine on light responses of amacrine cells were studied in slice preparations. Histamine modulated the light responses of many salamander amacrine cells, depending upon the morphological type. The most pronounced effects of histamine were decreases in the light responses of broadly stratified amacrine cells, particularly those having medium-sized dendritic field diameters. To determine whether the effects of histamine were direct, Co(++) was substituted for Ca(++) in the extracellular medium to block synaptic transmission. Histamine still affected broadly stratified amacrine cells, but not narrowly stratified amacrine cells under these conditions. Taken together, these findings suggest that inhibitory interactions between strata of the IPL and within the classical receptive fields of the ganglion cells would be particularly sensitive to histamine released from retinopetal axons.

Low-voltage activated calcium currents in ganglion cells of the tiger salamander retina: Experiment and simulation

We examined the functional properties of a low-voltage-activated (LVA) calcium current in ganglion cells of the neotenous tiger salamander (Ambystoma tigrinum) retina. Our analysis was based on whole-cell recordings from acutely dissociated ganglion cell bodies identified by retrograde dye injections. Using a continuously perfused cell preparation, the LVA current was isolated with the use of potassium channel blocking agents added to the bathing medium and the pipette solution, while tetrodotoxin was added to the bathing medium to block Na+ channels. Approximately 70% of ganglion cells had an easily identified LVA current. The LVA current activated at membrane potentials more positive than -90 mV, and inactivated rapidly. It was relatively insensitive to nickel (IC50 > 500 microM) and amiloride (IC50 > 750 microM). Voltage- and current-clamp studies allowed us to generate a model of this current using the NEURON simulation program. Studies were also carried out to measure the LVA Ca2+ current in ganglion cells with dendrites to confirm that it had a significant dendritic representation. Physiological mechanisms that may depend on LVA Ca2+ currents are discussed with an emphasis on the role that dendrites play in ganglion cell function.

Anatomical and electrophysiological evidence for GABAergic bipolar cells in tiger salamander retina

Our previous work showed that about 12% of bipolar cells in salamander retina synthesize and take up γ-aminobutyric acid (GABA), are GABA transporter (GAT)-immunoreactive, and respond with a GAT current to extracellularly applied GABA, suggesting that these bipolar cells use GABA, in addition to glutamate, as a neurotransmitter. Further support for this idea was obtained in this study by use of immunogold electron microscopy and whole-cell patch clamp electrophysiology. Ultrastructural analysis showed that amacrine cell and ganglion cell processes were postsynaptic to GABA-immunoreactive synapses made by bipolar cell axon terminals. Whole-cell recordings were obtained from amacrine and ganglion cells in response to activation of bipolar cells by puffing KCl at their dendrites in the outer plexiform layer. Inhibitory postsynaptic currents were observed in several third order neurons, even after blocking the excitatory postsynaptic responses, generated in the inner plexiform layer, with a combined application of NMDA and non-NMDA receptor antagonists, AP-5 and CNQX. These ultrastructural and electrophysiological data support our previous neurochemical results, and suggest that the retinal through-information pathway in salamander includes both inhibitory GABAergic as well as excitatory glutamatergic synaptic mechanisms.

L‐Glutamic acid decarboxylase‐ and γ‐aminobutyric acid‐immunoreactive bipolar cells in tiger salamander retina are of ON‐ and OFF‐response types as inferred from Lucifer Yellow injection

The bipolar cells in vertebrate retinas are considered to be excitatory in nature and use L-glutamate as their neurotransmitter. Our earlier studies have provided evidence demonstrating that a small but significant population of orthotopic bipolar cells in salamander retina may be γ-aminobutyric acid (GABA)ergic. In this work, the stratification levels of axon terminals in the inner plexiform layer (IPL) of single L-glutamic acid decarboxylase-immunoreactive (GAD-IR) and GABA-immunoreactive (GABA-IR) bipolar cells in the salamander retinal slices were studied. GAD-IR and GABA-IR bipolar cells marked by a fluorescent probe, Texas Red, were injected with Lucifer Yellow (LY) through a patch pipette under visual control. A total number of 42 GAD-IR bipolar cells in 24 slices and 84 GABA-IR bipolar cells in 56 slices were injected. Among these, terminals of nine GAD-IR bipolar cells and 22 GABA-IR bipolar cells were sufficiently filled with LY for determination of the stratification levels in the IPL. The stratification patterns and levels of GAD-IR and GABA-IR bipolar cells were very similar. GAD-IR and GABA-IR orthotopic type I and type II bipolar cells (soma located in the most distal or middle of the inner nuclear layer [INL], respectively), had their axon terminals stratified in sublamina a and sublamina b of the IPL with comparable frequency. Axonal processes were restricted largely to either the distal or the proximal region within sublaminae a and b. In addition, three of the bipolar cells had their terminals located in the middle region of the IPL. The similarities of stratification patterns and levels between GAD-IR and GABA-IR type I and type II bipolar cells indicate that they represent the same population of presumed GABAergic bipolar cells. Based on comparative stratifications of GABA bipolar cells reported here and those derived from electrophysiological studies (Hensley et al. [1993] J. Neurophysiol. 69:2086–2098), it is suggested that putative GABAergic bipolar cells represent cone-dominated and rod-dominated ON- and OFF-bipolar cells and that they subserve a broad role in the ON- and OFF-visual pathways in the retina. J. Comp. Neurol. 385:651–660, 1997. © 1997 Wiley-Liss, Inc.

L-Glutamic acid decarboxylase- and ?-aminobutyric acid-immunoreactive bipolar cells in tiger salamander retina are of ON- and OFF-response types as inferred from Lucifer Yellow injection

The bipolar cells in vertebrate retinas are considered to be excitatory in nature and use L-glutamate as their neurotransmitter. Our earlier studies have provided evidence demonstrating that a small but significant population of orthotopic bipolar cells in salamander retina may be gamma-aminobutyric acid (GABA)ergic. In this work, the stratification levels of axon terminals in the inner plexiform layer (IPL) of single L-glutamic acid decarboxylase-immunoreactive (GAD-IR) and GABA-immunoreactive (GABA-IR) bipolar cells in the salamander retinal slices were studied. GAD-IR and GABA-IR bipolar cells marked by a fluorescent probe, Texas Red, were injected with Lucifer Yellow (LY) through a patch pipette under visual control. A total number of 42 GAD-IR bipolar cells in 24 slices and 84 GABA-IR bipolar cells in 56 slices were injected. Among these, terminals of nine GAD-IR bipolar cells and 22 GABA-IR bipolar cells were sufficiently filled with LY for determination of the stratification levels in the IPL. The stratification patterns and levels of GAD-IR and GABA-IR bipolar cells were very similar. GAD-IR and GABA-IR orthotopic type I and type II bipolar cells (soma located in the most distal or middle of the inner nuclear layer [INL], respectively), had their axon terminals stratified in sublamina a and sublamina b of the IPL with comparable frequency. Axonal processes were restricted largely to either the distal or the proximal region within sublaminae a and b. In addition, three of the bipolar cells had their terminals located in the middle region of the IPL. The similarities of stratification patterns and levels between GAD-IR and GABA-IR type I and type II bipolar cells indicate that they represent the same population of presumed GABAergic bipolar cells. Based on comparative stratifications of GABA bipolar cells reported here and those derived from electrophysiological studies (Hensley et al. [1993] J. Neurophysiol. 69:2086-2098), it is suggested that putative GABAergic bipolar cells represent cone-dominated and rod-dominated ON- and OFF-bipolar cells and that they subserve a broad role in the ON- and OFF-visual pathways in the retina.

Glutamate-, GABA-, and GAD-immunoreactivities co-localize in bipolar cells of tiger salamander retina.

The presence of inhibitory bipolar cells in salamander retina was investigated by a comparative analysis of the distribution of glutamate- and GABA-immunoreactivities (GLU-IR; GABA-IR) using a postembedding immunocytochemical method. GLU-IR was found in virtually all photoreceptors, bipolar cells and ganglion cells, neuronal elements that transfer information vertically through the retina. GLU-IR also was found in numerous amacrine cells in the mid and proximal inner nuclear layer as well as in the cytoplasm of horizontal cells, while the nucleus of horizontal cells was either lightly labeled or not labeled at all. GLU-IR was found in the outer plexiform layer and intensely in the inner plexiform layer, in which there was no apparent sublamination. Forty-seven percent of Type IB bipolar cells in the distal inner nuclear layer and 13% of the displaced bipolar cells were GABA-IR. All bipolar cells were also GLU-IR, indicating that GABA-IR bipolar cells were a subset of GLU-IR bipolar cells rather than a separate population. About 12% of the Type IB bipolar cells were moderately GABA-IR and likely comprised a GABAergic subtype. GLU-IR levels in the presumed GABAergic bipolar cells were higher than in other purely GLU-IR bipolar cells suggesting that these GABA-IR bipolar cells are glutamatergic as well. All of the displaced bipolar cells were only lightly GABA-IR, indicating that displaced bipolar cells comprise a more homogeneous class of glutamatergic cell than orthotopic bipolar cells. GAD-IR co-localized with GABA-IR in orthotopic but not displaced bipolar cells, further supporting the idea that some orthotopic bipolar cells are GABAergic. A small proportion of bipolar cells in salamander retina contain relatively high levels of both GABA and glutamate. Co-release of these substances by bipolar cells could contribute to the "push-pull" modulation of ganglion cell responses.

Localization of tyrosine-hydroxylase-like-immunoreactive amacrine cells in the larval tiger salamander retina.

Immunocytochemistry was used to localize the populations of tyrosine-hydroxylase-like (TH)-immunoreactive cells in the tiger salamander retina. Ninety percent of these cells possessed somas that were situated in the innermost cell row of the inner nuclear layer and were classified as amacrine cells. Ten percent of TH-immunoreactive somas were located in the ganglion cell layer and were tentatively designated as those of displaced amacrine cells. The processes of TH-immunoreactive cells ramified most heavily in sublayer 1 of the inner plexiform layer, while a relatively small number of TH-labelled processes distributed in sublayers 3 and 5. Less than 1% of TH-immunoreactive cells in the amacrine cell layer exhibited a short process of somal origin that extended distally toward the outer plexiform layer. However, these processes did not cross the whole of the inner nuclear layer, and no immunolabelling was observed in the outer plexiform layer. An examination of retinal whole-mounts revealed that TH-immunoreactive amacrine and displaced amacrine cells were distributed throughout the center and periphery of the retina. The density of TH-immunolabelled amacrine cells was calculated to be 49 +/- 13 (mean +/- standard error) cells per mm2. The vast majority of TH-immunoreactive amacrine and displaced amacrine cells exhibited a stellate appearance and gave rise to three or more primary dendrites. A few TH-amacrine and displaced amacrine cells possessed two primary dendrites that emerged from opposite sides of their somas. The processes of TH-immunoreactive cells were generally poorly branched and varicose with terminal branches sometimes appearing thin and beaded. Because some TH-immunolabelled processes were very long, there was considerable overlap between the dendritic fields of neighboring TH-cells. Lastly, individual TH-immunoreactive amacrine and displaced amacrine cells were often observed in whole-mounts to provide processes that ramified at more than one level of the inner plexiform layer.