Ultrastructural localization of the calcium-binding protein parvalbumin in neurons of the song system of the zebra finch,Poephila guttata

Summary The distribution of parvalbumin (PV) within neurons of the vocal motor nucleus hyperstriatum ventralepars caudalis (HVc) was investigated in the forebrain of adult male zebra finches by means of light and electron microscopy using the indirect immunoperoxidase technique. Parvalbumin-reaction product was located in the amorphous material of perikarya, dendrites and nuclei, and associated to microtubuli, postsynaptic densities and intracellular membranes; it was found in some axons and Gray type-2 boutons, but rarely in type-1 boutons and never in the Golgi apparatus. These observations suggest that parvalbumin may regulate calcium-dependent processes at the postsynaptic membrane and in the cytosol. Furthermore, the partial association of parvalbumin to microtubuli points to an involvement in calcium-dependent tubular functions. Calcium currents and microtubular assembly or transport may be relevant for the known functions of HVc in song learning.     

Effects of irradiance and temperature on photosynthesis in C3, C4 and C3/C4 Panicum species

Species in the Laxa and Grandia groups of the genus Panicum are adapted to low, wet areas of tropical and subtropical America. Panicum milioides is a species with C₃ photosynthesis and low apparent photorespiration and has been classified as a C₃/C₄ intermediate. Other species in the Laxa group are C₃ with normal photorespiration. Panicum prionitis is a C₄ species in the Grandia group. Since P. milioides has some leaf characteristics intermediate to C₃ and C₄ species, its photosynthetic response to irradiance and temperature was compared to the closely related C₃ species, P. laxum and P. boliviense and to P. prionitis. The response of apparent photosynthesis to irradiance and temperature was similar to that of P. laxum and P. boliviense, with saturation at a photosynthetic photo flux density of about 1 mmol m^-2 s^-1 at 30°C and temperature optimum near 30°C. In contrast, P. prionitis showed no light saturation up to 2 mmol m^-2 s^-1 and an optimum temperature near 40°C. P. milioides exhibited low CO₂ loss into CO₂-free air in the light and this loss was nearly insensitive to temperature. Loss of CO₂ in the light in the C₃ species, P. laxum and P. boliviense, was several-fold higher than in P. milioides and increased 2- to 5-fold with increases in temperature from 10 to 40°C. The level of dark respiration and its response to temperature were similar in all four Panicum species examined. It is concluded that the low apparent photorespiration in P. milioides does not influence its response of apparent photosynthesis to irradiance and temperature in comparison to closely related C₃ Panicum species.Abbreviations AP apparent photosynthesis - I CO₂ compensation point - gl leaf conductance; gm, mesophyll conductance - PPFD photosynthetic photon flux density - PR apparent photorespiration rate - RuBPC sibulose bisphosphate carboxylase     

1H nmr studies of complexes of ferric leghemoglobin with substituted pyridines and nicotinic acids

The ¹H nuclear magnetic resonance (nmr) spectra of complexes of soybean ferric leghemoglobin with 3-substituted pyridines and 5-substituted nicotinic acids have been recorded in order to determine the influence of axial ligands on heme electronic structure. The hyperfine shifted resonances of the heme group were assigned by analogy to previous assignments for the pyridine and nicotinic acid complexes of leghemoglobin. The spectra are characteristic of predominantly low-spin ferric heme complexes. For the pyridine complexes, the rate of ligand exchange was found to increase with decreasing ligand pK_A. For many of the complexes, optical and nmr spectra reveal the presence of an equilibrium mixture of high- and low-spin states of the iron atom. The percentage of high-spin component increases with decreasing ligand pK_A Smaller hyperfine shifts are noted for leghemoglobin complexes with ligands capable of weak ligand → metal π bonding. The pattern of hyperfine shifted resonances is similar for all complexes studied and indicates that the overall heme electronic structure is dominated by the bonding to the proximal histidine.     

Morphometrisch-ultrastrukturelle Untersuchungen am Nucleus supraopticus der Ratte nach Dehydratation

Zusammenfassung Der Nucleus supraopticus der Ratte, die einer Dehydratation ausgesetzt war, wurde ultrastrukturell-morphometrisch analysiert. Dabei zeigte sich, daß die relativen Volumenanteile der einzelnen Zellkompartimente während der fünftägigen Durstperiode eine auffallende Konstanz aufweisen. Hingegen läßt sich eine absolute Zunahme der Einzelzellvolumina und somit auch der an der Synthese und Sekretion der Neurohormone beteiligten Zellkompartimente feststellen. Die vorliegenden Befunde sprechen für einen beschleunigten Abtransport des neurosekretorischen Materials bei gesteigerter Synthese. Auf eine optimale Standardisierung der Perfusionsmethode bei Untersuchungen am neurosekretorischen Zwischenhirnsystem wird hingewiesen.

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Morphometric-ultrastructural investigations on the supraoptic nucleus of dehydrated rats

Summary The supraoptic nucleus of the dehydrated rat has been analysed by electron microscopy and morphometry. With that it appears, that the relative volumes of the different cell compartments are striking constant. Otherwise one can see an absolute increase of the cell volume together with the cell compartments which take part at the synthesis and secretion of the neurohormones. These results are expression of an accelerated move of the neurosecretory material during increased synthesis. The importance of an optimal standardization of the perfusion-method in investigations of the neurosecretory system is demonstrated.

Wesentliche Teile der vorliegenden Arbeit werden von H. F. Reinhardt der Medizinischen Fakultät der Universität Basel als Dissertation vorgelegt.     

Relative contribution of promoter and intragenic sequences in the hormonal regulation of rat beta-casein transgenes

In order to identify DNA sequences responsible for the regulation beta-casein gene expression, lines of transgenic mice bearing the entire rat beta-casein gene and two rat beta-casein promoter chloramphenicol acetyltransferase (CAT) fusion genes have been established. All three transgenes have been shown previously to be regulated in a tissue- and stage specific manner. To investigate the relative contribution of promoter and intragenic sequences in the hormonal regulation of the beta-casein gene, mammary explant cultures derived from these lines of mice have now been performed, and the effects of PRL and glucocorticoids on transgene as compared with endogenous beta-casein gene expression have been quantified. After the addition of PRL to cultures performed in the presence of insulin and glucocorticoids, a 25- to 40-fold induction of endogenous mouse beta-casein mRNA was observed after 48 hr. A comparable greater than 25-fold induction of transgene expression after PRL addition was observed in explant cultures derived from a line of mice expressing the entire rat beta-casein gene. In contrast, PRL addition elicited only a 1- to 4.5-fold increase in CAT activity in cultures derived from two lines of mice bearing casein-CAT fusion genes with either 524 or 2300 base pairs of 5'-flanking DNA. In the presence of insulin, glucocorticoid or PRL addition alone increased endogenous beta-casein gene expression 2- to 2.5-fold and 5- to 10-fold, respectively, but only a 1.2- to 2.5-fold induction of CAT activity was observed for each hormone.(ABSTRACT TRUNCATED AT 250 WORDS)