|Functional activation of glutamate ionotropic receptors in the human peripheral retina. |
Clairton F de Souza,Michael Kalloniatis,Philip J Polkinghorne,Charles N J McGhee,Monica L Acosta
Experimental eye research
Glutamate is the major neurotransmitter in the vertebrate retina. Neurons involved in the glutamate pathway express ?-amino-3-hydroxyl-5-methylisoxazole-4-propionic acid (AMPA), kainic acid (KA) and N-methyl-D-aspartate (NMDA) receptors. Functional characterization of these ionotropic glutamate receptors can be achieved by using a cation channel permeating probe named agmatine (1-amino-4-guanidobutane; AGB). Retinal mapping using this guanidinium analog has certain advantages including the immunocytochemical identification of a whole population of neurons expressing functional glutamate gated receptor channels. We have extended AGB studies into the functionality of ionotropic receptors in peripheral aged human retina to serve as a comparison for functional analysis of retinopathies such as retinal detachment. We probed the human retina with AGB after activation with AMPA, KA and NMDA. The results showed patterns of AGB entry into neurons consistent with those previously observed in subunit localization studies in adult mammalian retinae including primates. Application of 30 ?M AMPA activated receptors in virtually all calretinin immunoreactive AII amacrine cells in the mid-peripheral human retina. About half of the AII amacrine cells showed AGB permeation after incubation with 50 ?M KA. Some bipolar cells including DB3 OFF bipolar cells displayed functional KA receptors. Colocalization of AGB with parvalbumin labeled horizontal cells revealed functional KA and AMPA receptors with no responsiveness to NMDA activation. NMDA activation resulted in AGB labeling of ganglion cells and amacrine cells. The present study provides a description of functional ionotropic glutamate receptors in the aged mid-peripheral human retina.
|Functional units of a compound nose: aesthetasc sensilla house similar populations of olfactory receptor neurons on the crustacean antennule. |
Steullet, P, et al.
J. Comp. Neurol., 418: 270-80 (2000)
The lateral flagellum of the antennule of the spiny lobster Panulirus argus houses more than 1,000 morphologically similar olfactory sensilla, called aesthetascs. By using a high-resolution activity labeling technique that depends on entry of agmatine into olfactory receptor neurons (ORNs) through cation channels during odor stimulation, we examined the distribution of different functional types of ORNs within and across mature aesthetascs. A significant number of ORNs in mature aesthetascs are labeled with agmatine during stimulation by single odorants, including adenosine-5'-monophosphate, ammonium chloride, cysteine, glycine, proline, and taurine. The percentage of ORNs per aesthetasc that was agmatine labeled during odor stimulation averaged 0.5-1.6% for single compounds and 4.6% for a 33-component mimic of oyster tissue. For most antennules and antennular regions studied, the percentage of agmatine-labeled ORNs by stimulation with single or complex odorants was statistically homogeneous across most or all aesthetascs. The extent of heterogeneity among mature aesthetascs was correlated with their age: extensive heterogeneity was observed only in the distal part of the flagellum containing the oldest aesthetascs and their ORNs. Thus, it appears that over most of the length of the aesthetasc-bearing region of the lateral flagellum, different and distinct functional types of aesthetascs do not exist. Rather, aesthetascs appear to be repetitive morphological and functional units in olfactory coding. However, because odor sensitivity of ORNs can change with the age of an aesthetasc, some development-related functional heterogeneity exists among aesthetascs.
|Pattern recognition of amino acid signatures in retinal neurons. |
Marc, R E, et al.
J. Neurosci., 15: 5106-29 (1995)
Pattern recognition of amino acid signals partitions the cells of the goldfish retina into nine statistically unique biochemical theme classes and permits a first-order chemical mapping of virtually all cellular space. Photoreceptors, bipolar cells, and ganglion cells display a set of unique, nominally glutamatergic type E1, E1+E2, and E4 signatures, respectively. All horizontal cells are assignable to a GABAergic gamma 2 class or a non-GABAergic class with a glutamate-rich E3 signature. The amacrine cell layer is largely a mixture of (1) a taurine-dominated T1 Müller's cell signature and (2) GABAergic gamma 1, glycinergic G1, and dual glycinergic/GABAergic G gamma 1 amacrine cell signatures. Several major conclusions emerge from this work. (1) Glutamatergic, GABAergic, and glycinergic neural signatures and glial signatures account for over 99% of the cellular space in the retina. (2) All known neurons in the goldfish retina are associated with a set of conventional nonpeptide neurotransmitters. (3) Multiple forms of metabolic profiles are associated with a single nominal neurotransmitter category. (4) Glutamate and aspartate contents exhibit overlapping distributions and are not adequate univariate probes for identifying cell classes. (5) Signatures can serve as quantitative measures of cell state.
|Inhibition of nicotinic receptor mediated ion fluxes in rat sympathetic ganglia by BGT II-S1 a potent phospholipase. |
Brain Res., 325: 79-88 (1985)
The mechanism of action of the bungarotoxin fraction II-S1 (BGT II-S1), which copurifies with alpha-bungarotoxin (alpha-BGT) and inhibits nicotinic transmission, has been further characterized. BGT II-S1 (1 microM) inhibited the carbachol (100 microM) or nicotine (50 microM) stimulated uptake of [3H]agmatine into rat sympathetic ganglia by 73% and 52%, respectively. These responses were inhibited 90% by D-tubocurarine (100 microM), but unaffected by alpha-BGT (1 microM) or atropine (10 microM), suggesting that BGT II-S1 affects nicotinic function at a postsynaptic site. Binding of physiologically active [125I]BGT II-S1 could be demonstrated to intact sympathetic ganglia; however, the binding could not be displaced by nicotinic agents, suggesting that BGT II-S1 is not interacting at the receptor. Because some neurotoxins produce their effect at the synapse through a phospholytic action, the phospholipase activity of BGT II-S1 was determined. The results demonstrate that BGT II-S1 is a very potent calcium dependent phospholipase. In addition, conditions which abolished the toxin's phospholytic activity prevented its effects on nicotinic transmission and on nicotinic receptor mediated ion fluxes. These include irreversible inhibition of enzymic activity by treatment of BGT II-S1 with p-bromophenacylbromide, as well as reversible inhibition of the phospholipase by substitution of Ba2+ or Sr2+ ions for Ca2+ ions in the physiological medium. Thus, in rat sympathetic ganglia, BGT II-S1 blocks the nicotinic receptor mediated movement of ions across the membrane. This is probably not due to a direct interaction at the nicotinic acetylcholine recognition site; rather, it may be an ion channel associated effect which is mediated by alterations in the phospholipid environment of the receptor complex or of the membrane. Although BGT II-S1 also has presynaptic actions, in a cultured system of postsynaptic cells, it could prove a useful tool to study the role of phospholipids in neuronal nicotinic receptor regulation.
|Transmitter sensitivity of neurons assayed by autoradiography. |
Science, 212: 929-30 (1981)
Ionic conductance channels that are opened by activating nicotinic acetylcholine receptors at synapses of sympathetic neurons are permeable to small organic amines. Uptake of a tritium-labeled amine through these channels can be measured by autoradiography. This provides a simple and direct way to assess the sensitivity of individual neurons to acetylcholine without using microelectrodes.