Serotonin-containing neurones in vertebrate retinas

Abstract: It has been established by a combination of HPLC and electrochemical detection that frog, lizard, goldfish, rabbit, and bovine retinas contain both dopamine and serotonin. Immunohistological and immunoradiographical methods show that serotonin is localised in amacrine perikarya and processes situated in the inner plexiform layers of frog, lizard, and goldfish retinas. The amount of serotonin in the mammalian retina appears to be too low for detection in neurones. The serotonin in the bovine retina is located mainly in the inner nuclear and plexiform layers, suggesting that the amine is present in the same types of cells as found for frog, lizard, and goldfish retinas. Retinas incubated in [³H]serotonin showed that radioactivity is associated with processes in the inner plexiform layer and amacrine perikarya. These results suggest that the neuronal elements that contain endogenous serotonin also have the capacity to accumulate exogenous amine and are consistent with the opinion that serotonin has a neuronal function in retinas of a variety of vertebrates.     

CHLOROPHYLL-SPECIFIC PHOTOSYNTHESIS AND QUANTUM EFFICIENCY AT SUBSATURATING LIGHT INTENSITIES12

Light-limited rates of photosynthesis normalized for chlorophyll a, (α), and actual photon absorption (quantum efficiency, Ф) were determined for six eponentially growing algal species grown under identical conditions. The same parameters, α and Ф, were also monitored for a single diatom species, Thalassiosira pseudonana Hasle & Heimdal, through its growth cycle in batch culture. Statistical differences in α could be demonstrated among the six different exponentially growing species while no differences could be shown for Ф. Statistical differences among the six species were minimized when photosynthetic rates were normalized for in vivo fluorescence rather than extracted chlorophyll a. Both α and Ф were constant while T. pseudonana was in the exponential phase of growth, but both declined as the culture entered stationary phase. While cells were in exponential growth, differences in a were attributed to varying rates of in vivo light absorption per chlorophyll a, thus providing experimental evidence that the in vivo chlorophyll a extinction coefficient, k_c (m²· mg Chl a^?1), cannot be assumed constant.     

Hyperthermic modification of cyclophosphamide metabolism in rat hepatic microsomes and liver slices

The ability of rat liver microsomes and liver slices to metabolize the antineoplastic compound cyclophosphamide was studied at 37° and at elevated temperatures comparable to those used for human systemic hyperthermic antineoplastic therapy. Temperatures above 40.5° and 41.8° inhibited cyclophospamide metabolism by microsomes and liver slices respectively. Therefore, cyclophosphamide may not be a suitable drug for combination with systemic hyperthermia in cancer therapy.     

Comparative evaluation of macrophage stimulation and depression on tumor growth and macrophage content and function in mice

Summary In a syngeneic murine adenocarcinoma model, the administration of glucan, an RE stimulant, inhibited tumor growth and increased tumor macrophage populations. Conversely, the administration of methyl palmitate, an RE depressant, potentiated tumor growth and decreased the number of tumor macrophages. Glucan and methyl palmitate also produced diverse alterations in serum lysozyme levels that reflected their contrasting influences on RE functional status, thus supporting the role of serum lysozyme as an index of macrophage function. The diverse results produced by macrophage stimulation or depression in regard to tumor growth, tumor macrophage population, and serum lysozyme concentration indicate that a relationship may exist between macrophage functional activity and host resistance to neoplasia.     

Sensitivity of cultured rat hepatocytes to aflatoxin B1 and benzo(a)pyrene

Summary We have tested the sensitivity of a cloned rat hepatocyte line, RL-PR-C, to aflatoxin B₁ and benzo(a)pyrene as a function of population-doubling level. The cells were much more sensitive to the cytotoxic action of these agents subsequent to 230 population doublings. This sensitivity corresponded to the enhanced inducibility of arylhydrocarbon hydroxylase activity by 3-methylcholanthrene. Supported by Grants CA 21258 and CA 12056 from the National Cancer Institute.     

Effects of amino acids, adenine nucleotides and inorganic pyrophosphate on glutamine synthetase from Anabaena cylindrica.

Glutamine synthetase (L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2) from Anabaena cylindrica was inhibited by alanine, glycine, serine and aspartate. The effects of alanine and serine were uncompetitive with respect to glutamate, while those of glycine and asparatate were uncompetitive with respect to glutamate, while those of glycine and aspartate were non-competitive and mixed type respectively. Different pairs of amino acids and their various combinations caused a cumulative inhibition of the enzyme activity. Glutamine synthetase was also inhibited by ADP and AMP and both nucleotides affected the enzyme competitively with respect to ATP and non-competitively for glutamate. Inorganic pyrophosphate, between 2 and 3 mM, produced a very pronounced inhibiton of enzyme activity. The inhibition by PPi was uncompetitive for ATP. Various combinations of the adenine nucleotides, PPi and Pi exerted a cumulative inhibitory effect on the enzyme activity, as did the amino acids, in different combinations with either adenine nucleotides, PPi or Pi. The effects of the adenine nucleotides and the amino acids were more pronounced at higher concentrations of ammonia. Except for serine similar responses of these effectors were obtained with increasing concentrations of Mg2+. It is proposed that changes in the free concentrations of Mg2+ are important in energy-dependent regulation of the enzyme activity in this alga.     

Water impermeable seed dormancy

Viable seeds that do not imbibe water and thus fail to germinate in an apparently favorable environment are commonly termed impermeable or hard seed. This physical, exogenous dormancy is especially common in species of the Fabaceae. The ecological significance of hard seed includes the ability to rapidly recolonize burnt areas after fire and to withstand ingestion by animals and birds. Advantages and problems that hard seed cause in agriculture are discussed. Species from different families with impermeable seeds appear to have in common a layer of macrosclerid cells that form a palisade layer in the testa. The term strophiole and its contradictory use in botanical literature are discussed. Genetic factors and environmental conditions both affect the proportion of impermeable seeds produced. Methods of artificially softening impermeable seeds include acid and solvent, soaking, mechanical scarification, pressure, percussion, freezing, heating, and radiation treatments that can result in a change in germination from less than 20% in some untreated species up to 90% or more in treated species. Natural softening involves high temperatures and temperature fluctuations and the degree of desiccation of the seed. The mechanism of water impermeability is related to the testa and is thought to involve waterproofing substances including wax, lignin, tannin, suberin, pectin, and quinone derivatives. The hilum acts as a hygroscopic valve that prevents water uptake but allows water loss to occur at low relative humidities in some species. The strophiole is an area of weakness in the testa of some Papilionoideae while the chalaza region has been determined as an area of weakness inPisum andGossypium. The water impermeable status of some species is reversible at a seed moisture content greater than 10%. The hard seed of a species can be described both in terms of the amount and the degree of impermeability.     

Activation of sulphate in Anabaena cylindrica

Summary Crude cell-free extracts of Anabaena cylindrica synthesized adenosine-5-phosphosulphate (AP³⁵S) and 3-phosphoadenosine-5-phosphosulphate (PAP³⁵S) from ³⁵SO₄ ^2- in the presence of Mg²⁺, ATP and inorganic pyrophosphatase. Maximum AP³⁵S and PAP³⁵S were produced at pH 7.15 and 8.05, respectively. APS kinase was detected in the supernatant of crude cell-free extracts by a spectrophotometric procedure. ATP-Sulphurylase had an absolute requirement for Mg²⁺ and less than 30% AP³⁵S was formed when Mg²⁺ was replaced by either Mn²⁺ or Co²⁺. Nucleotide triphosphates other than ATP and 2-deoxyATP were ineffective in this reaction. Maximum enzyme activity was observed at equimolar concentrations of Mg²⁺ and ATP and excess of either of these was inhibitory. Other nucleotide triphosphates, like GTP, UTP, CTP, TTP, ITP, or 2-deoxyATP also inhibited the enzyme activity. Inhibition by GTP was competitive with respect to ATP. ATP-sulphurylase activity was not affected by cysteine, methionine or glutathione.Abbreviations APS adenosine-5-phosphosulphate - PAPS 3-phosphoadenosine-5-phosphosulphate