Direct Measurement of the

One of the main neutron sources for the astrophysical s process is the reaction ^{13}C(α,n)^{16}O, taking place in thermally pulsing asymptotic giant branch stars at temperatures around 90 MK. To model the nucleosynthesis during this process the reaction cross section needs to be known in the 150-230 keV energy window (Gamow peak). At these sub-Coulomb energies, cross section direct measurements are severely affected by the low event rate, making us rely on input from indirect methods and extrapolations from higher-energy direct data. This leads to an uncertainty in the cross section at the relevant energies too high to reliably constrain the nuclear physics input to s-process calculations. We present the results from a new deep-underground measurement of ^{13}C(α,n)^{16}O, covering the energy range 230-300 keV, with drastically reduced uncertainties over previous measurements and for the first time providing data directly inside the s-process Gamow peak. Selected stellar models have been computed to estimate the impact of our revised reaction rate. For stars of nearly solar composition, we find sizeable variations of some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular, the two radioactive nuclei ^{60}Fe and ^{205}Pb, as well as ^{152}Gd.

The baryon density of the Universe from an improved rate of deuterium burning.

Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN)1,2. Among the light elements produced during BBN1,2, deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of neutrino species permeating the early Universe. Although astronomical observations of primordial deuterium abundance have reached percent accuracy3, theoretical predictions4-6 based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)3He reaction. Here we show that our improved cross-sections of this reaction lead to BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent analysis of the cosmic microwave background7. Improved cross-section data were obtained by exploiting the negligible cosmic-ray background deep underground at the Laboratory for Underground Nuclear Astrophysics (LUNA) of the Laboratori Nazionali del Gran Sasso (Italy)8,9. We bombarded a high-purity deuterium gas target10 with an intense proton beam from the LUNA 400-kilovolt accelerator11 and detected the γ-rays from the nuclear reaction under study with a high-purity germanium detector. Our experimental results settle the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances to probe the physics of the early Universe.

Direct Capture Cross Section and the E_{p}=71 and 105 keV Resonances in the

The ^{22}Ne(p,γ)^{23}Na reaction, part of the neon-sodium cycle of hydrogen burning, may explain the observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new resonances at E_{p}=156.2, 189.5, and 259.7 keV have recently been observed and confirmed. However, significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested resonances at E_{p}=71 and 105 keV. Here, new ^{22}Ne(p,γ)^{23}Na data with high statistics and low background are reported. Stringent upper limits of 6×10^{-11} and 7×10^{-11} eV (90% confidence level), respectively, are placed on the two suggested resonances. In addition, the off-resonant S factor has been measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the ^{22}Ne(p,γ)^{23}Na rate is now reduced by 3 orders of magnitude.

A new trifluorinated quinolone: Ro 23-6240 (AM 833).

Ro 23-6240 is a new fluoroquinolone displaying pronounced activity against a wide range of Gram-positive and Gram-negative pathogens. In order to obtain information about the absorption, distribution and excretion of this quinolone in man, six healthy volunteers received in cross-over an intravenous infusion of 100 mg Ro 23-6240 and an oral dose of two tablets corresponding to 400 mg Ro 23-6240. Serial plasma and urine samples were assayed for unchanged substance by HPLC with subsequent fluorescence or UV detection. Pharmacokinetics were evaluated from these data assuming a two-compartment open model. Characteristic of this new antibacterial are the high plasma levels following oral administration (Cmax: 4.5 micrograms/ml) and the long elimination half-lives (8-12 h). Both these parameters are favourable kinetic prerequisites for a once-a-day dosage regimen. In addition, the volume of distribution at steady state clearly exceeds 1 l/kg and points to good tissue penetration. Total systemic clearance was 122 ml/min and total renal clearance reached 89 ml/min. Within 96 h, 60-70% of the administered dose was recovered from urine as unchanged drug. The absolute bioavailability (extent of absorption) of the tablet amounted to 96%, indicating a complete absorption of this galenic formulation.

Uptake and subsequent retrograde axonal transport of nerve growth factor (NFG) are not influenced by neuronal activity.

NFG is taken up by adrenergic nerve terminals by a highly efficient and selective mechanism and is subsequently transported to the perikaryon by retrograde axonal transport. Neither enhanced (cold stress) nor reduced (decentralization, ganglionic blocking agents) neuronal activity affects this mechanism. In contrast, the non-specific uptake followed by retrograde axonal transport of macromolecules, which depends on excessively high concentrations of these compounds in the vicinity of the corresponding nerve terminals, is enhanced by neuronal activity.

Immunocytochemical localization of nerve growth factor (NGF) in the submandibular gland of adult mice by light and electron microscopy.

Nerve growth factor (NGF) was localized in the submandibular gland of adult male mice by a direct immunocytochemical method using highly purified antibodies against NGF coupled to horseradish peroxidase. In light microscopic sections the reaction product was entirely confined to the cells of the secretory tubules. The acinar part of the gland was free of reaction product. This finding was confirmed by electron microscopy. Within the cells NGF was localized exclusively in the apical secretory granules. No reaction was observed in the rough endoplasmic reticulum, the Golgi region or in the granules of the basal part of the cells. This observation favours the assumption that NGF is derived from a precursor molecule and that the precursor is transformed into immunologically active NGF within the secretory granules during their transport from the basal to the apical part of the tubular cells. Stimulation of the submandibular gland with carbachol (2 mg/kg) led to a massive release of the content of the secretory granules, including NGF, into the salivary duct.

Comparison between the retrograde axonal transport of nerve growth factor and tetanus toxin in motor, sensory and adrenergic neurons.

In previous studies it has been shown that nerve growth factor (NGF) is taken up with high selectivity by adrenergic and sensory nerve terminals and is transported retrogradely to the corresponding cell bodies by a colchicine sensitive mechanism 10,11,23. The present study was designed to investigate whether this retrograde transport of NGF depends on properties of the nerve terminals which are common to all the neurons or restricted to those which respond to NGF either during the whole life cycle (adrenergic neurons) or during a restricted period of embryonic development (sensory neurons). In order to investigate the retrograde transport of NGF in motor neurons we injected [125I]NGF into the musculus deltoideus and measured the side differences of accumulation of radioactivity in the spinal cord (C6-C8) from 4-48 h. At no time was there a preferential accumulation of radioactivity on the injected side. In contrast, tetanus toxin was accumulated preferentially on the injected side and an approximate rate of transport of 7.5 mm/h was calculated. Astonishingly there was also a retrograde transport of tetanus toxin in sensory and adrenergic neurons. The rate of transport was identical to that of NGF and the transport could be blocked by transection of the corresponding nerve fibers and local administration of colchicine. After unilateral injection of [125I]tetanus toxin into the forepaw or the musculus deltoideus light microscopic autoradiographs revealed heavily labeled neuronal cell bodies in the dorsal root ganglia or the ventrolateral spinal cord of the injected side. It is concluded that the retrograde transport of [125I]NGF depends on properties of the neuronal membrane which are specific for adrenergic and sensory neurons, whereas that of tetanus toxin is determined by features which are common to all, or at least to all peripheral, neurons. The fact that the rate of transport for both NGF and tetanus toxin is identical in all examined neurons, supports the hypothesis that the specificity of retrograde transport is determined by specific uptake sites in the neuronal membrane whereas the retrograde transport system is non-specific.

The retrograde axonal transport of nerve growth factor.

A retrograde axonal transport of nerve growth factor (NGF) from the adrenergic nerve terminals in the mouse iris to the cell bodies of postganglionic sympathetic neurones in the superior cervical ganglion has been demonstrated. After injection of iodinated nerve growth factor (125I-NGF) into the anterior eye-chamber there was a relatively rapid accumulation of radioactivity in the superior cervical ganglia on both injected and non-injected sides, as was the case after subcutaneous injection. However, 4 h after intraocular injection a preferential accumulation of radioactivity became apparent in the superior cervical ganglion on the injected side, and this difference between the ganglia on injected and non-injected sides gradually increased to a maximum at 16 h. Transection of the postganglionic adrenergic fibres as well as the prior intraocular injection of colchicine abolished the preferential accumulation of 125I-NGF in the superior cervical ganglion of the injected side, whereas the destruction of adrenergic nerve terminals by 6-hydroxydopamine did not impair the preferential accumulation. It is concluded that the retrograde axonal transport of NGF, which was estimated to take place at a rate of about 2.5 mm/h, depends on a colchicine-sensitive mechanism as does the orthograde rapid axonal transport. However, the uptake of NGF may not only take place from the nerve terminals but also from the preterminal parts, as has been shown in other studies with horseradish peroxidase. Autoradiographic studies strongly supported the existence of a retrograde transport by showing a clear localization of radioactivity in a small number of neurones in the superior cervical ganglion on the injected side, whereas on the non-injected side there was only a diffuse distribution of radioactivity throughout the ganglion.