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S Yazulla

Publications and source records attributed to S Yazulla.

At least 73 records · Page 4Linked to original sources
PubMed1984

Non-correspondence of [3H]GABA uptake and GAD localization in goldfish amacrine cells.

Ultrastructural analysis of the inner synaptic layer of goldfish retina, using a double-label technique, showed that [3H]GABA uptake and glutamic acid decarboxylase (GAD)-immunoreactivity (IR) occurred in different neuronal processes in most cases. Many [3H]GABA-accumulating processes were found surrounding GAD-IR processes, though not necessarily in a postsynaptic relationship. Co-localization of [3H]GABA uptake and GAD-IR occurred only when one GAD-IR process was juxtaposed to another GAD-IR process. This study suggests that [3H]GABA uptake may be a poor marker for GABA releasing neurons.

Animals↗
PubMed1983

Stimulation of GABA release from retinal horizontal cells by potassium and acidic amino acid agonists.

The release of [3H]GABA from horizontal cells of goldfish retina was studied by biochemical analysis of perfused isolated retina. Retinas were incubated for 15 min in 0.72 microM [3H]GABA, rinsed for 30 min and then perfused with 1 min pulses of increasing concentrations of K+ and acidic amino acid agonists under a variety of conditions. Radioactivity in the perfusate was determined by liquid scintillation spectroscopy. The main findings are: (1) virtually all of the [3H]GABA released by L-glutamate (L-Glu) and L-aspartate (L-Asp) and 50% of the K+-evoked release, is calcium independent; (2) K+-evoked [3H]GABA release is only 10% of that released by L-Glu; (3) threshold [3H]GABA release occurs with 320 microM L-Glu, 1175 microM L-Asp, 4 microM quisqualic acid (QA), 4 microM kainic acid (KA) and 53 microM N-methyl-DL-aspartate (NMDLA); (4) the quisqualate antagonist glutamic acid diethyl ester (GDEE), has no specific inhibitory action on any of the agonists, whereas D-alpha-aminoadipic acid (D alpha AA), an NMDA antagonist, potently inhibits the action of NMDLA and L-Asp; (5) the presence of Mg2+, even at 1 mM, totally inhibits NMDLA and also inhibits the action of L-Glu and L-Asp below 1 mM; (6) D-Asp potentiates the action of L-Glu by 0.6-0.8 log units and completely inhibits the action of L-Asp; (7) L-Asp at a ratio of 3:1 potentiates the effect of L-Glu. From these and other results one concludes that: (a) [3H]GABA release from H1 cells is calcium independent and depends on factors other than passive depolarization, probably sodium; (2) the likely transmitter of red cones is L-Glu acting on quisqualate or kainate receptors, and (3) L-Asp acts predominantly on NMDA receptors and may provide a modulatory role in the outer retina by potentiating the action of L-Glu.

Amino Acids↗
PubMed1983

Carrier-mediated release of GABA from retinal horizontal cells.

H1 horizontal cells in goldfish retina are probably GABAergic and receive excitatory synaptic input from red cones. This input should affect the synaptic release of GABA from H1 cells. We studied the uptake and release of [3H]GABA from the isolated goldfish retina by use of autoradiography. When retinas were incubated in the light for 15 min in 0.72 microM [3H]GABA, heavy label was found over the somata (HS) and axon terminals (HAT) of H1 horizontal cells, and over pyriform amacrine cell bodies and their processes in sublamina b of the IPL. Postincubation of retinas, preloaded with [3H]GABA, in 0.5-10 mM L-glutamate or 0.1-10 mM L-aspartate, resulted in a dose-dependent and selective loss of [3H]GABA from HS and very little loss from HAT. This loss was not due to an efflux of metabolites of [3H]GABA or to any calcium-dependent vesicular release of [3H]GABA from HS. The glutamate-evoked release of [3H]GABA by H1 cells was sodium dependent, sensitive to substitution of lithium for sodium, and inhibited by nipecotic acid. In addition, [3H]GABA was released from HS by 0.1 mM ouabain but not by 50 mM potassium chloride. Our results suggest that the chemically evoked release of [3H]GABA from HS is mediated by a sodium-dependent transport carrier which may be responsible for the high affinity uptake of [3H]GABA by H1 cells as well. Since synaptic vesicles are not found at presumed synaptic release sites in H1 cells, we suggest that the GABA which is released synaptically from H1 cells may derive from a cytoplasmic pool of GABA and is released by means of a transport carrier. This carrier appears to depend primarily on the sodium concentration gradient across the H1 cell membrane rather than on the membrane potential of the H1 cell for its action. The relevance of the carrier-mediated release of GABA from HS in regard to the synaptic function of H1 cells is discussed.

Animals↗
PubMed1983

Comparison of fixation and penetration enhancement techniques for use in ultrastructural immunocytochemistry.

Electron microscopic immunohistochemistry, although generally providing good localization, has often failed to produce satisfying ultrastructural preservation. Techniques that result in well-preserved tissue ultrastructure often hinder penetration of immunological reagents or render antigens non-immunoreactive. These are particularly serious limitations in studies of central nervous system and retina. We have evaluated several fixatives, including picric acid, high pH paraformaldehyde, and glutaraldehyde with subsequent sodium borohydride treatment, and penetration enhancement techniques, including buffered-ethanolic treatment and freeze--thaw, for their applicability in the retina. Our best fixation was achieved with 1 hr in 4% paraformaldehyde and 0.2% glutaraldehyde (pH 7.4) followed by overnight fixation in 4% paraformaldehyde (pH 10.4). Treatment with sodium borohydride after glutaraldehyde fixation restores much of the immunoreactivity that would otherwise be undetectable. The penetration of immunological reagents can be greatly increased by using either a buffered-ethanolic series or by freezing the tissue after careful cryoprotection. Using these methods we have been able to achieve specific immunological staining throughout the full thickness of retinal slices, up to 500 microns across, while preserving good ultrastructure. The methods should prove useful in the immunocytochemical localization of many different antigens in a variety of tissues.

Animals↗
PubMed1982

Localization of synaptic and nonsynaptic nicotinic-acetylcholine receptors in the goldfish retina.

The localization of nicotinic-cholinergic receptors in the inner plexiform layer (IPL) of goldfish retina was studied by electron microscopic analysis of the binding pattern of a conjugate or horseradish peroxidase and alpha bungarotoxin (HRP-alpha BTx). Specific HRP reaction product (blockade by 1mM curare) was found at both synaptic and nonsynaptic sites. Synaptic binding sites for HRP-alpha BTx, which accounted for only 16% of the total specific reaction product sites, always involved an amacrine process as the presynaptic element, whereas amacrine, ganglion, and bipolar cells could be post-synaptic elements at labeled synapses. Only 17.5% of the total number of amacrine synapses were labeled by HRP-alpha BTx. Labeled synapses showed the same distribution in the IPL as unlabeled synapses: bimodal for amacrine-to-bipolar synapses with peak concentrations at the 20% and 80% layers and unimodal for amacrine-to-nonbipolar synapses with a peak concentration at the 60% layer. Nonsynaptic binding sites for HRP-alpha BTx (84% of total) were seen on the dendrites of ganglion, amacrine, and bipolar cells. The distribution of the nonsynaptic sites in the IPL largely accounts for the trilaminar binding pattern of 125I-alpha BTx as observed in light microscopic autoradiographs. If, as appears likely, the distribution of synapses is the relevant variable in determining the sites of neuronal interaction for a given transmitter system, then this study further illustrates the importance of distinguishing synaptic from nonsynaptic binding when using receptor-ligand probes to localize sites of chemical synaptic transmission.

Animals↗
PubMed1981

GABAergic synapses in the goldfish retina: an autoradiographic study of 3H-muscimol and 3H-GABA binding.

The localization of synaptic receptor sites for gamma-amino butyric acid (GABA) in the goldfish retina was studied by light microscopic (LM) and electron microscopic autoradiography (EM-ARG) of 3H-muscimol and 3H-GABA binding. Sodium-independent binding of both 3H-muscimol and 3H-GABA was localized to a uniform band throughout the inner plexiform layer (IPL) by LM-ARG of cryostat sections incubated in these compounds. No binding was observed over the outer plexiform layer. This binding pattern differs from the uptake pattern of 3H-GABA in the IPL, which shows very heavy labeling in the most proximal IPL and little labeling throughout the rest of the IPL. Statistical analysis of EM-ARGs of 3H-muscimol labeling in the IPL suggests that only amacrine synapses bind 3H-muscimol (i.e., make GABAergic synapses). Labeled amacrine-to-amacrine synapses are mostly concentrated in the 20-80% levels of the IPL, whereas amacrine-to-bipolar synapses are concentrated at about the 70-90% depth. Maximal 3H-GABA uptake, however, occurs at the 90-100% depth. This difference in the location of GABAergic synaptic binding and GABAergic uptake leads to the conclusion that the density of uptake label provides little information about the density of synaptic contacts. Thus, in order to localize GABAergic interactions, synaptic binding rather than neuronal uptake appears to provide the more appropriate description.

Animals↗
PubMed1981

Localized binding of [3H]muscimol to synapses in chicken retina.

Binding sites for [3H]muscimol, an analogue of gamma-aminobutyric acid (GABA) were localized in the synaptic layers of chicken retina by light microscopic and electron microscopic autoradiography. Light microscopic autoradiography of cryostat sections incubated in [3H]muscimol or [3H]GABA revealed identical binding patterns: a band over the inner plexiform layer (IPL) and a band over the outer plexiform layer (OPL). This binding pattern differed from the uptake pattern for [3H]GABA: labeling over horizontal, amacrine, and ganglion cell bodies as well as very intense labeling over lamina 5 in the proximal IPL. Statistical analysis of electron microscopic autoradiography data from the IPL indicated that only amacrine synapses bind [3H]muscimol (i.e., make GABAergic synapses). Processes of amacrine, bipolar, or ganglion cells can be postsynaptic to these amacrine synapses. The highest concentration of synapses binding [3H]muscimol occurred in laminae 2 and 4 of the IPL and not in lamina 5 as might be expected from the density of [3H]GABA uptake. In the OPL, [3H]muscimol binding occurred over specialized junctions proximal to photoreceptor terminals. In cone receptor terminals, [3H]muscimol binding was suspected near horizontal cell dendrite/receptor terminal membranes lateral to the synaptic ribbon, supporting the hypothesis that horizontal cells are involved in a GABAergic feedback loop with cone terminals. We conclude that the synaptic binding pattern provides a more accurate concept of GABAergic synaptic interaction than does the uptake pattern for [3H]GABA because the two patterns in the IPL are not related.

Animals↗
PubMed1980

The effects of intraocular injection of kainic acid on the synaptic organization of the goldfish retina.

Kainic acid (KA), an extended analog of L-glutamate, was injected into the eyes of living goldfish. After survival times ranging from 15 min to 6 days, retinae were inspected for KA-induced degeneration at both the LM and EM levels. KA had little effect on photoreceptors, mixed rod-cone bipolar cells, Müller cells, at least two types of amacrine cells and the optic nerve. Reversible edema was seen in both rod and cone horizontal cells. Pure cone bipolar cells and the majority of amacrine cells appeared to be destroyed by KA. The effect of KA is selective not only on the cell types involved, but also in the location of KA-induced edema on the affected cells, i.e., soma and proximal portions of dendrites of cone horizontal cells as opposed to the distal ends of dendrites of rod horizontal cells. Implications of these data are discussed in regard to the use of KA as a probe for glutamatergic pathways in the retina. One hypothesis suggested by our results is that rods use glutamate whereas cones use aspartate as their neurotransmitter.

Animals↗
PubMed1980

Binding and uptake of the GABA analogue, 3H-muscimol, in the retinas of goldfish and chicken.

Gamma-aminobutyric acid (GABA) is a candidate as a neurotransmitter in the vertebrate retina. The GABA analogue muscimol has been used to probe the properties of GABA receptors in other parts of the vertebrate central nervous system (CNS). We thus used 3H-muscimol to investigate potential GABA receptors in the retinas of goldfish and chick by means of biochemical assay techniques and light microscopic autoradiography. In both animals 3H-muscimol shows specific and saturable binding with a dissociation constant (KD) of about 10 nM. GABA effectively inhibits 3H-muscimol binding at 50% inhibitory concentration (IC50) of 10(-6) M. The labeling pattern of 7 x 10(-7) M 3H-muscimol shows common features for both species in that amacrine cell bodies are intensely labeled, horizontal cells are much less so, and there is a laminar pattern throughout the inner plexiform layer (IPL). A 1 mM concentration of GABA abolishes 3H-muscimol labeling in the chick retina and throughout much of the goldfish retina except for some label over amacrine cells and the distal two thirds of the IPL. The intense somatic labeling suggests neuronal uptake of 3H-muscimol, and indeed, virtually all 3H-muscimol labeling is abolished with the addition of 0.4 mM ouabain. The uptake pattern of 3H-GABA differs from that of 3H-muscimol and is largely unaffected by the addition of 1 mM muscimol. We conclude that 3H-muscimol binding in retinas can be adequately demonstrated biochemically but that only 3H-muscimol uptake is observed with autoradiography from tissue conventionally processed through Epon. The fact that GABA can inhibit 3H-muscimol uptake whereas the reverse is not the case shows that the transport carriers for muscimol and GABA are different. Finally, the strong degree of 3H-muscimol uptake by retinal neurons raises serious questions about the use of 3H-muscimol as a probe for GABA synaptic receptors in the retina with autoradiography.

Animals↗
PubMed1977

Two types of receptors for alpha-bungarotoxin in the synaptic layers of the pigeon retina.

Pigeon retinae were analyzed for binding [125I]alpha-bungarotoxin (alphaBgt) by radioautographic and biochemical methods. Toxin binding, localized to the outer and inner plexiform layers (OPL and IPL), was inhibited by micromolar concentrations of native alphaBgt and D-tubocurarine and by 1 mM acetyl- and butyrylcholine in both synaptic layers. Nicotine, at comparable concentrations affected only the IPL. In vitro drug competition experiments showed that the pigeon retina contains two types of receptors for alphaBgt which differ in sensitivity to inhibition by nicotine by 4 orders of magnitued. The results suggest that: (1) the receptor for alphaBgt in the IPL is a nicotinic receptor, (2) the receptor for alphaBgt in the OPL may be involved in an unusual cholinergic system, and (3) ability to bind alphaBgt is not a sufficient criterion for identifying nicotinic-cholinergic receptors.

Animals↗
PubMed1971

The spectral sensitivity of single units in the nucleus rotundus of pigeon, Columba livia.

Responses to diffuse monochromatic light were recorded from single units in the diencephalon of pigeon. Units were both excited and inhibited by light stimulation. Intensity-response functions based on latency measures to the first spike after stimulation were used to generate action spectra. One class of spectral sensitivity functions presumably from rods, showed peak sensitivities near 500 nm: these functions were unaffected by changing criterion values used to generate the functions. A second class of cone functions showed multiple peak sensitivities at 540 nm and 600-620 nm. These units shifted their peak sensitivities with a change in criterion values. Unit response types tended to be localized differentially in the nucleus rotundus. Excitatory units were located in the dorsal half of the nucleus, while inhibitory units were located in the ventral half, with a few exceptions. An attempt was made to integrate the present findings with previous behavioral, electrophysiological, photochemical, and anatomical data in the pigeon.

Action Potentials↗