Interaction of excitatory and depressant amino acids in the frog retina

(1) Application of excitatory or depressant amino acids (concentrations from 10(-4) to 10(-2) M) could modify response patterns of the retinal ganglion cells to photic stimulus. Excitatory amino acids gave rise to spontaneous discharge while depressant amino acids inhibited spike discharge in response to test flashes. (2) Application of excitatory amino acids of more than 10(-3) M resulted in irreversible termination of spike discharges while recovery was always observed in the case of depressant amino acids even when the concentration of the applied solution was as high as 10(-2) M. No effect was observed when one exciting and one depressant amino acid were properly combined. (3) There is a mixture of four amino acids (two excitatory and two depressant) which could enhance the spike discharge in response to test flashes without giving rise to spontaneous firing. (4) It is implied that proper balance of excitatory and depressant amino acids is important in regulating the excitability of a number of neurons.     

Free amino acids in spider hemolymph

We examined the free amino acid composition of hemolymph from representatives of five spider families with an interest in knowing if the amino acid profile in the hemolymph of orb-web-building spiders reflects the high demands for small organic compounds in the sticky droplets of their webs. In nearly all analyses, on both orb and non-orb builders, glutamine was the most abundant free amino acid. Glycine, taurine, proline, histidine, and alanine also tended to be well-represented in orb and non-orb builders. While indications of taxon-specific differences in amino acid composition were observed, it was not apparent that two presumptive precursors (glutamine, taurine) of orb web sticky droplet compounds were uniquely enriched in araneids (orb builders). However, total amino acid concentrations were invariably highest in the araneids and especially so in overwintering juveniles, even as several of the essential amino acids declined during this winter diapause. Comparing the data from this study with those from earlier studies revealed a number of discrepancies. The possible origins of these differences are discussed.     

Free amino acids in some sponges

Most invertebrates, particularly those of marine origin, have relatively high concentrations of free amino acids which are considered an important constituent of their osmoregulatory mechanisms [1]. Very little information is available on the free amino acid distribution in Porifera [2,3]. Common amino acids in some sponges were recognised by paper chromatography by Inskip and Cassidy [4] and Ackermann et al. [5,6] included a few sponges in their survey of the occurence of nitrogen compounds in marine invertebrates. More recently Bergquist and Hartman [7] surveyed semiquantitatively the distribution of free amino acids in several sponges. In the present paper we report on the amino acid composition of 12 species of sponges belonging to the class Demospongiae as a part of a study on the metabolites of Porifera [8]. Fresh sponges were extracted with aqueous ethanol. The organic solvent was removed and the aqueous solution, after removal of the ether soluble compounds, was separated into cationic, anionic and neutral fractions by ion-exchange chromatography. The cation fraction was analysed for amino acids using an automatic amino acid analyser. The results, which are presented in Table 1, show that all species of sponges examined have a similar composition in common amino acids. Glycine almost always appears as the dominant protein amino acid, followed by high concentrations of alanine and glutamic acid, whereas relatively lower concentrations of basic amino acids are present. In Axinella cannabina, Chondrosia reniformis, Chondrilla nucula, Cliona viridis and Hymeniacidon sanguinea, glycine represents more than 77% of the total amino acids. The high percentage of free glycine (90.4%) in Chondrosia reniformis is noteworthy. The anionic and the neutral fractions were examined for sulfur-containing amino acids using PC. Taurine (Table 2) was detected in all the Porifera examined; this is in agreement with previous observations [5–7]. N-Methyltaurine was identified in some of the species examined, whereas neither N,N-dimethyltaurine nor N,N,N-trimethyltaurine were found.     

Free amino acids in calf embryos

In this work have been reported the research results tending to establish the free amino acidis concentration, existing in the calf embryos. The free embryonal amino acidis composition has been determined through an analysis effected with "Amino Acid Analyzer". Such studies, which conern the researches under execution in our Institute on the chemical composition of the calf embryos furnish the biochemical determination of a biological material, used in some Nations like a commercial product.     

Free amino acids from pollens

Pollens from Pinus canariensis, P. nigra, P. pinaster, P. pinea, Castanea sativa, Magnolia grandiflora, Olea sativa cv frantoio, cv itrana, cv pisciottana were examined for their free amino acid composition. A large amount of proline was found in all species; pollens of Olea also contain a large amount of serine.     

On the stability of DNA in photoreceptor cells of rat retina

Summary DNA turnover in post-mitotic photoreceptor cells of F344 rat retina was investigated. Developing retinas of newborn rats were labelled by multiple injections of (methyl-³H)thymidine. One eye was removed on day 60 and embedded in paraffin. The groups of rats were killed 180, 365, 540 or 730 days later and the second eye was removed. Autoradiographic studies on pairs of eyes showed no detectable DNA turnover in photoreceptor cells up to the end of the experiment (near median life-span, 50% survival age). The DNA of these photoreceptor cells is not replaced through the life span of the animals; the results thus suggest that it is very stable and possibly protected in a specific manner.     

Potassium conductivity of the plasma membrane of frog photoreceptor cells

Potassium channels, uniformly distributed over the cell surface (0.5 channel/micron2) have been found in isolated fragments of plasma membranes of frog photoreceptor cells. Their conductance under symmetrical conditions (0.1 M KCl at both the membrane surfaces) is 72 +/- 6 pS for rods and 88 +/- 8 pS for cones. The channels are reversibly blocked by tetraethylammonium (TEA), Cs+, Rb+ at intra- and extracellular membrane surfaces. Half-inactivation of a channel occurs at concentrations of TEA, Cs+ and Rb+ at the intracellular surface 0.12, 2.2 and 3.9 mM, correspondingly.     

Light-stimulated protein movement in rod photoreceptor cells of the rat retina

We examined the intracellular distribution of three proteins involved in the cyclic GMP cascade of visual transduction; cGMP phosphodiesterase, the alpha-subunit of G-protein and arrestin. In adult rats, light-induced changes in the amounts of G and arrestin in the photoreceptor cell outer segments were observed both by polyacrylamide gel analysis of purified ROS and by immunocytochemical localization on retinal sections. In dark conditions, G was concentrated in the outer segments of photoreceptor cells while in the light G alpha was seen in the inner segments and the outer nuclear layer. Arrestin had the opposite distribution, appearing in the inner segments and outer nuclear layer under dark conditions and in the ROS under light conditions. In contrast, PDE, the enzyme which is activated by G and inhibited by arrestin showed no light-stimulated movement. In both light- and dark-adapted retinas, PDE was localized primarily in the outer segments of the photoreceptor cells.     

Free amino acids of maize seedlings

The free amino acids were determined in different parts of maize seedlings (seeds, roots and shoots), 0, 2, 4 and 6 days after sowing.     

Dopaminergic interplexiform cells contact photoreceptor terminals in catfish retina

Summary Dopaminergic interplexiform cells in retinae of glass catfish were investigated using an antiserum against tyrosine hydroxylase and peroxidase-anti-peroxidase (PAP) visualization. In whole-mount preparations, we observed a homogeneous distribution of cell bodies throughout the retina without any indication of regional specializations. At the ultrastructural level, we studied the morphology of labelled telodendria within the outer plexiform layer. Apart from contacts with horizontal cells and bipolar cell dendrites, we report for the first time direct contacts with cone pepdicles and rod spherules. Quantitative evaluation of short series of sections showed that all cone pedicles, and a major part of the rod terminals, were approached in this way. The dopaminergic pathway terminating on photoreceptors is discussed in the context of pharmacological effects of this transmitter in the distal retina during light adaptation, i.e., cone contraction, spinule formation and horizontal cell coupling.