Proton-Capture Rates on Carbon Isotopes and Their Impact on the Astrophysical ^{12}C/^{13}C Ratio

The ^{12}C/^{13}C ratio is a significant indicator of nucleosynthesis and mixing processes during hydrogen burning in stars. Its value mainly depends on the relative rates of the ^{12}C(p,γ)^{13}N and ^{13}C(p,γ)^{14}N reactions. Both reactions have been studied at the Laboratory for Underground Nuclear Astrophysics (LUNA) in Italy down to the lowest energies to date (E_{c.m.}=60  keV) reaching for the first time the high energy tail of hydrogen burning in the shell of giant stars. Our cross sections, obtained with both prompt γ-ray detection and activation measurements, are the most precise to date with overall systematic uncertainties of 7%-8%. Compared with most of the literature, our results are systematically lower, by 25% for the ^{12}C(p,γ)^{13}N reaction and by 30% for ^{13}C(p,γ)^{14}N. We provide the most precise value up to now of 3.6±0.4 in the 20-140 MK range for the lowest possible ^{12}C/^{13}C ratio that can be produced during H burning in giant stars.

Direct Measurement of the ^{13}C(α,n)^{16}O Cross Section into the s-Process Gamow Peak

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 BBN^1,2, 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 predictions^4-6 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.

Successful Prediction of Total α-Induced Reaction Cross Sections at Astrophysically Relevant Sub-Coulomb Energies Using a Novel Approach

The prediction of stellar (γ,α) reaction rates for heavy nuclei is based on the calculation of (α,γ) cross sections at sub-Coulomb energies. These rates are essential for modeling the nucleosynthesis of so-called p nuclei. The standard calculations in the statistical model show a dramatic sensitivity to the chosen α-nucleus potential. The present study explains the reason for this dramatic sensitivity which results from the tail of the imaginary α-nucleus potential in the underlying optical model calculation of the total reaction cross section. As an alternative to the optical model, a simple barrier transmission model is suggested. It is shown that this simple model in combination with a well-chosen α-nucleus potential is able to predict total α-induced reaction cross sections for a wide range of heavy target nuclei above A≳150 with uncertainties below a factor of 2. The new predictions from the simple model do not require any adjustment of parameters to experimental reaction cross sections whereas in previous statistical model calculations all predictions remained very uncertain because the parameters of the α-nucleus potential had to be adjusted to experimental data. The new model allows us to predict the reaction rate of the astrophysically important ^{176}W(α,γ)^{180}Os reaction with reduced uncertainties, leading to a significantly lower reaction rate at low temperatures. The new approach could also be validated for a broad range of target nuclei from A≈60 up to A≳200.

Direct Capture Cross Section and the E_{p}=71 and 105 keV Resonances in the ^{22}Ne(p,γ)^{23}Na Reaction

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.

Erratum: Three New Low-Energy Resonances in the ^{22}Ne(p,γ)^{23}Na Reaction [Phys. Rev. Lett. 115, 252501 (2015)]

This corrects the article DOI: 10.1103/PhysRevLett.115.252501.

Improved Direct Measurement of the 64.5 keV Resonance Strength in the ^{17}O(p,α)^{14}N Reaction at LUNA

The ^{17}O(p,α)^{14}N reaction plays a key role in various astrophysical scenarios, from asymptotic giant branch stars to classical novae. It affects the synthesis of rare isotopes such as ^{17}O and ^{18}F, which can provide constraints on astrophysical models. A new direct determination of the E_{R}=64.5  keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator has led to the most accurate value to date ωγ=10.0±1.4_{stat}±0.7_{syst}  neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at E_{x}=5672  keV in ^{18}F is Γ_{p}=35±5_{stat}±3_{syst}  neV. This width is about a factor of 2 higher than previously estimated, thus leading to a factor of 2 increase in the ^{17}O(p, α)^{14}N reaction rate at astrophysical temperatures relevant to shell hydrogen burning in red giant and asymptotic giant branch stars. The new rate implies lower ^{17}O/^{16}O ratios, with important implications on the interpretation of astrophysical observables from these stars.

Three New Low-Energy Resonances in the ^{22}Ne(p,γ)^{23}Na Reaction

The ^{22}Ne(p,γ)^{23}Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle affects the synthesis of the elements between ^{20}Ne and ^{27}Al in asymptotic giant branch stars and novae. The ^{22}Ne(p,γ)^{23}Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window. At proton energies below 400 keV, only upper limits exist in the literature for the resonance strengths. Previous reaction rate evaluations differ by large factors. In the present work, the first direct observations of the ^{22}Ne(p,γ)^{23}Na resonances at 156.2, 189.5, and 259.7 keV are reported. Their resonance strengths are derived with 2%-7% uncertainty. In addition, upper limits for three other resonances are greatly reduced. Data are taken using a windowless ^{22}Ne gas target and high-purity germanium detectors at the Laboratory for Underground Nuclear Astrophysics in the Gran Sasso laboratory of the National Institute for Nuclear Physics, Italy, taking advantage of the ultralow background observed deep underground. The new reaction rate is a factor of 20 higher than the recent evaluation at a temperature of 0.1 GK, relevant to nucleosynthesis in asymptotic giant branch stars.

First direct measurement of the 2H(α,γ)6Li cross section at big bang energies and the primordial lithium problem

Recent observations of (6)Li in metal poor stars suggest a large production of this isotope during big bang nucleosynthesis (BBN). In standard BBN calculations, the (2)H(α,γ)(6)Li reaction dominates (6)Li production. This reaction has never been measured inside the BBN energy region because its cross section drops exponentially at low energy and because the electric dipole transition is strongly suppressed for the isoscalar particles (2)H and α at energies below the Coulomb barrier. Indirect measurements using the Coulomb dissociation of (6)Li only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the (2)H(α,γ)(6)Li cross section at big bang energies. The experiment was performed deep underground at the LUNA 400 kV accelerator in Gran Sasso, Italy. The primordial (6)Li/(7)Li isotopic abundance ratio has been determined to be (1.5 ± 0.3) × 10(-5), from our experimental data and standard BBN theory. The much higher (6)Li/(7)Li values reported for halo stars will likely require a nonstandard physics explanation, as discussed in the literature.

Constraining the astrophysical origin of the p-nuclei through nuclear physics and meteoritic data

A small number of naturally occurring, proton-rich nuclides (the p-nuclei) cannot be made in the s- and r-processes. Their origin is not well understood. Massive stars can produce p-nuclei through photodisintegration of pre-existing intermediate and heavy nuclei. This so-called γ-process requires high stellar plasma temperatures and occurs mainly in explosive O/Ne burning during a core-collapse supernova. Although the γ-process in massive stars has been successful in producing a large range of p-nuclei, significant deficiencies remain. An increasing number of processes and sites has been studied in recent years in search of viable alternatives replacing or supplementing the massive star models. A large number of unstable nuclei, however, with only theoretically predicted reaction rates are included in the reaction network and thus the nuclear input may also bear considerable uncertainties. The current status of astrophysical models, nuclear input and observational constraints is reviewed. After an overview of currently discussed models, the focus is on the possibility to better constrain those models through different means. Meteoritic data not only provide the actual isotopic abundances of the p-nuclei but can also put constraints on the possible contribution of proton-rich nucleosynthesis. The main part of the review focuses on the nuclear uncertainties involved in the determination of the astrophysical reaction rates required for the extended reaction networks used in nucleosynthesis studies. Experimental approaches are discussed together with their necessary connection to theory, which is especially pronounced for reactions with intermediate and heavy nuclei in explosive nuclear burning, even close to stability.

First direct measurement of the 17O(p,γ)18F reaction cross section at Gamow energies for classical novae

Classical novae are important contributors to the abundances of key isotopes, such as the radioactive (18)F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The (17)O(p,γ)(18)F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes, but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range E(c.m.)~/= 200-370 keV appropriate to hydrogen burning in classical novae. In addition, the E(c.m.)=183 keV resonance strength, ωγ=1.67±0.12 μeV, has been measured with the highest precision to date. The uncertainty on the (17)O(p,γ)(18)F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

Stellar and primordial nucleosynthesis of 7Be: measurement of 3He(alpha,gamma)7Be

The 3He(alpha,gamma)7Be reaction presently represents the largest nuclear uncertainty in the predicted solar neutrino flux and has important implications on the big bang nucleosynthesis, i.e., the production of primordial 7Li. We present here the results of an experiment using the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the 7Be ejectiles. In addition, off-beam activation and coincidence gamma-ray measurements were performed at selected energies. At energies above 1 MeV a large discrepancy compared to previous results is observed both in the absolute value and in the energy dependence of the cross section. Based on the available data and models, a robust estimate of the cross section at the astrophysical relevant energies is proposed.

Coulomb suppression of the stellar enhancement factor

It is commonly assumed that reaction measurements for astrophysics should be preferably performed in the direction of a positive Q value to minimize the impact of the stellar enhancement factor, i.e., the difference between the laboratory rate and the actual stellar rate. We show that the stellar effects can be minimized in the charged particle channel, even when the reaction Q value is negative. As a demonstration, the cross section of the astrophysically relevant 85Rb(p,n)85Sr reaction has been measured by activation between 2.16 < or = Ec.m. < or = 3.96 MeV and the astrophysical reaction rate for (p, n) as well as (n, p) is directly inferred from the data. The presented arguments are also relevant for other alpha- and proton-induced reactions in the p and rp processes. Additionally, our results confirm a previously derived modification of a global optical proton potential.

Suppression of the Coulomb interaction in the off-energy-shell p - p scattering from the p + d --> p + p + n reaction

Off-energy-shell effects in p - p scattering have been investigated at p - p relative energies from 600 down to 80 keV applying the Trojan horse method (THM) to the p + d --> p + p + n reaction at 5 MeV. In contrast with the on-energy-shell case, no Coulomb-nuclear interference minimum has been found in the extracted THM p - p cross section, due to the suppression of the Coulomb amplitude as predicted by the half-off-energy shell calculations. This hypothesis is strengthened by the agreement between THM p - p data and calculated on-energy-shell n + n, n + p and nuclear p + p cross sections.

Spectroscopic study of neutron shell closures via nucleon transfer in the near-dripline nucleus 23O

Neutron single particle energies have been measured in 23O using the 22O(d,p)23O*-->22O+n process. The energies of the resonant states have been deduced to be 4.00(2) MeV and 5.30(4) MeV. The first excited state can be assigned to the nu d3/2 single particle state from a comparison with shell model calculations. The measured 4.0 MeV energy difference between the nu s1/2 and nu d3/2 states gives the size of the N=16 shell gap which is in agreement with the recent USD05 ("universal" sd from 2005) shell model calculation, and is large enough to explain the unbound nature of the oxygen isotopes heavier than A=24. The resonance detected at 5.3 MeV can be assigned to a state out of the sd shell model space. Its energy corresponds to a approximately 1.3 MeV sized N=20 shell gap, therefore, the N=20 shell closure disappears at Z=8 in agreement with Monte Carlo shell model calculations using SDPF-M interaction.

Activation measurement of the 3He(alpha,gamma)7Be cross section at low energy

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-gamma technique and with inferior precision. Using a windowless gas target, high beam intensity, and low background gamma-counting facilities, the 3He(alpha,gamma)7Be cross section has been determined at 127, 148, and 169 keV center-of-mass energy with a total uncertainty of 4%. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3He(alpha,gamma)7Be astrophysical S factor to solar energies.

Vanishing N = 20 shell gap: study of excited states in (27,28)Ne

This Letter reports on the (1)H((28)Ne, (28)Ne) and (1)H((28)Ne, (27)Ne) reactions studied at intermediate energy using a liquid hydrogen target. From the cross section populating the first 2(+) excited state of (28)Ne, and using the previously determined BE(2) value, the neutron quadrupole transition matrix element has been calculated to be M(n)=13.8 +/- 3.7 fm(2). In the neutron knockout reaction, two low-lying excited states were populated in (27)Ne. Only one of them can be interpreted by the sd shell model while the additional state may intrude from the fp shell. These experimental observations are consistent with the presence of fp shell configurations at low excitation energy in (27,28)Ne nuclei caused by a vanishing N=20 shell gap at Z=10.

Anomalously hindered E2 strength B(E2;2+(1)-->0+) in 16C

The electric quadrupole transition from the first 2(+) state to the ground 0(+) state in 16C is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive 16C nuclei. The measured mean lifetime is 77+/-14(stat)+/-19(syst) ps. The central value of mean lifetime corresponds to a B(E2;2+(1)-->0(+)) value of 0.63e(2) fm(4), or 0.26 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.

Relationship between the mutational status of VH genes and pathogenesis of diffuse large B-cell lymphoma in Richter's syndrome

Patients with chronic lymphocytic leukemia (CLL) may develop diffuse large B-cell lymphoma (DLBL), also known as Richter's syndrome. Mutational status of immunoglobulin (Ig) heavy-chain variable region (VH) genes have prognostic impact in CLL. Patients with mutated VH genes have a stable disease, whereas patients with unmutated VH gene have more aggressive disease. The mutational status of CLLs that transform to DLBL is unknown. To reveal whether Richter's syndrome occurs in CLLs with mutated or unmutated VH genes, we have performed mutational analysis on serial specimens from eight patients. CLL and DLBL tumorclones were identical in five cases and they were different in three cases. Six CLLs expressed unmutated and two cases expressed mutated VH genes. In five of the six unmutated CLLs, the DLBL clones evolved from CLL tumorclones and the VH genes expressed by DLBLs were also unmutated. In one unmutated and two mutated CLLs, the DLBLs expressed mutated VH genes, but in these three cases the DLBL tumorclones developed as independent secondary neoplasm. These results suggest that Richter's syndrome may develop in both mutated or unmutated CLLs, but clonal transformation of CLL to DLBL occur only in the unmutated subgroup of CLL.

Microsatellite instability and hMLH1 promoter hypermethylation in Richter's transformation of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is an indolent B cell non-Hodgkin lymphoma (NHL) that may transform into diffuse large B cell lymphoma (DLBL). This transformation is referred to as Richter's syndrome or transformation. To analyze whether microsatellite instability (MSI) and DNA mismatch repair defects are associated with Richter's transformation, we have performed microsatellite analysis, mutational analysis of hMLH1 and hMSH2 genes and methylation status analysis of CpG island of the hMLH1 promoter on serial biopsy specimens from 19 patients with CLL. Ten cases of CLL showed no histologic alteration in the second biopsy, and nine cases of CLL underwent morphologic transformation to DLBL in the second biopsy. Using eight microsatellite loci, high level of MSI was associated with Richter's transformation in four cases of CLL, but none of the CLLs displayed this level of MSI without transformation. Mutations of the hMLH1 or hMSH2 genes were not detected in any of the lymphoma samples. In five cases of Richter's transformation the hMLH1 promoter was hypermethylated in both CLL and DLBL samples. Hypermethylation of the hMLH1 promoter associated with high-level of MSI in four cases, and low-level of MSI in one case. These results suggest that in certain cases of Richter's transformation the DNA mismatch-repair defect-initiated genetic instability may play a role in tumor progression.

Branching-pattern analysis of the dendritic arborization in the thalamic nuclei of the rat brain

We investigated the dendritic patterns of rapid Golgi-impregnated, highly similar multipolar neurons from two functionally different thalamic regions of the rat brain: two dorsal nuclei (the nucleus laterodorsalis thalami, pars dorsomedialis and the nucleus laterodorsalis thalami, pars ventrolateralis), and two ventral nuclei (the nucleus ventrolateralis thalami and the nucleus ventromedialis thalami). The analysis involved conventional morphometric parameters (height and size) and a new parameter derived from graph theory, the relative imbalance (RI), derived from the branching patterns of the dendrites, which permits quantitative characterization of the dendritic arborization of a neuron. On this basis, neurons can be grouped into three fundamentally different types: type A, or highly-polarized (imbalanced) neurons (RI values close to 1); type B, or medium-polarized neurons (RI values around 0.5); and type C, or balanced neurons with low polarization (RI values close to 0). The orientations of the dendritic arbor, and thus the receptive fields, of the dorsal and ventral thalamic neurons, were mutually perpendicular. The H and S values indicated that the neurons in the dorsal and ventral thalamic nuclei differed significantly. However, their RI values demonstrated that they were similar neurons of type B. Our data reveal that 1 ) the dendritic arbor cannot be reliably characterized purely on the basis of height and size, and 2) RI is a valuable morphometric parameter that identifies the true nature of the dendritic arborization.

Fluorescein-ERG, a sensitive method for the detection of vascular damage in diabetic patients

The purpose of this paper was to provide evidence for the reintroduction of simultaneously performed fluorescein angiography and electroretinography in the detection of diabetic retinopathy. ERG observations were made in conjunction with fluorescein angiography of 13 patients suffering from type I diabetes mellitus for five to 13 years. Only patients without any fluorescein leakage during angiography and without any morphologic changes in the fundus were involved in the study. Gold foil electrodes were used for recording. A stroboscopic lamp provided flashing light stimulation through a monochromatic blue filter. Intravenous fluorescein administration caused an immediate reduction in the ERG response. This reduction was seen both in the control subjects and in diabetes patients. In the control group, the reduction was over in 30-45 min, while in the diabetes group a considerable amplitude elevation was seen in all recordings between 15 and 60 min post-fluorescein. In the adaptation control group, where only repeated ERG recordings were employed every 15 min, a slight decrease in the a wave and a slight elevation of the b wave were observed during the whole recording period. No complaints or side-effects were detected during the observations. As all the patients displayed a normal fluorescein angiography besides elevated b wave after fluorescein administration, and this elevation was seen exclusively in the diabetic group, our study raises the possibility that this diagnostic method can be used in the detection of diabetic retinopathy.

Synaptic remodeling and free radical formation after brain contusion injury in the rat

The purpose of this study was to explore whether bilateral frontal cortex contusion in rats would demonstrate changes relevant for understanding the pathology of frontal lobe injury in humans. Rats were allowed to survive for 3, 7, or 18 days postinjury (dpi). In the contused rats, albumin was trapped in frontal cortices, as well as in other brain areas, showing that neurons were exposed to plasma components. In the sham-operated rats, which had only craniotomy but no penetration of dura, the level of trapped albumin was also increased compared to intact controls, suggesting a partial lesion-like condition. Choline acetyltransferase activity was severely decreased in the frontal cortices of contused rats, compared to the sham-operated controls. The decrease was most pronounced at 3 dpi and less pronounced 18 dpi, suggesting that after the initial damage, regeneration of the cholinergic terminals occurred. The concentration of the mature presynaptic membrane protein D3(SNAP-25) was also decreased in the frontal cortices of contused rats at 3 and 7 dpi, whereas it was normalized at 18 dpi. Previously, we have evaluated changes in the rate of synaptic remodeling in brain injury by calculating the ratio of the neural cell adhesion molecule (NCAM) to D3(SNAP-25). The NCAM/D3(SNAP-25) ratio at 3 dpi was elevated by more than 60% in the frontal cortices of contused rats, suggesting a high initial rate of synaptic remodeling. The ratios were smaller at 7 and 18 dpi, suggesting that after the initial burst, the rate of remodeling leveled off. In contrast, astrocyte activation was less pronounced at 3 dpi than at 7 and 18 dpi, as measured by the levels of glial fibrillary acidic protein and glutamine synthetase immunoactivities. The immunoreactivity of glutamine synthetase more than doubled in the contused brains but its enzymatic activity increased less than 50%, suggesting that many enzymatic centers had been inactivated by free radicals. Calculated as the difference between the relative immunoreactivity and the relative enzymatic activity the "lost glutamine synthetase activity" increased continuously in frontal cortex and striatum from 3 to 18 dpi, indicating the production of free radicals long after the initial contusion event. In conclusion, following frontal cortical contusions the early synaptic damage was partly compensated by synaptic remodeling. We suggest that the continuous production of free radicals may have contributed to the declining remodeling rate and impair functional recovery.

Mature but not fetal or neonatal rat superior cervical ganglion transplants survive in the cortex of adult rats

The transplantation of catecholaminergic tissues is a possible therapy for parkinsonism. Central nervous tissue is suitable for transplantation only in the immature stage, whereas peripheral nervous tissue can also be transplanted when mature. The present study compares the development of fetal (17-20 embryonic day, E17-20), neonatal (1-3 postnatal day, P1-3) and mature (5-6-week-old) rat superior cervical ganglia after transplantation into the cerebral cortex of adult rats. The mature transplants survived in greater proportion and preserved their structural characteristics, although a considerable proportion of the neurons died. The perinatal transplants only survived sporadically, decreased in size and the surviving remnants failed to display a structure comparable to the adult ganglion in situ. Thus, the use of adult donors is not only a possibility but a necessity when superior cervical ganglion (probably any ganglion) is transplanted. This principle is radically different from that seen in the case of central nervous tissues, and can be understood by the analysis of the time curves of cell proliferation and programmed cell death (apoptosis) observed during the perinatal development of sympathetic ganglia.

Blood-brain barrier breakdown and edema formation following frontal cortical contusion: does hormonal status play a role?

The present experiment was designed to evaluate and correlate the time course of blood-brain barrier (BBB) integrity and cerebral edema in adult male rats given medial frontal cortex contusions. The effect of sex hormones on BBB integrity in the same injury model was also examined, because previous work has shown that progesterone can reduce cerebral edema (Roof et al., 1993). BBB breakdown was assessed by Evans blue extravasation and albumin immunostaining while edema formation was measured by the wet weight dry weight technique. These processes were examined beginning 2 h and continuing up to 10 days after injury. Our findings show that medial frontal contusion in rats produces changes in cerebral water content and opening of the BBB that endures at least 7 days postinjury. Although pseudopregnancy has been shown to reduce cerebral edema at day 1 postinjury, we did not find any evidence that this hormonal state is associated with BBB repair.

Low extracellular magnesium unmasks N-methyl-D-aspartate-mediated graft-host connections in rat neocortex slice preparation

The main purpose of this study was to investigate the role of N-methyl-D-aspartate receptors in host-graft synaptic transmission in the neocortex. The effects of low extracellular magnesium, the glutamate agonist N-methyl-D-aspartate and N-methyl-D-aspartate antagonists on the synaptic activation of connections between embryonic neocortical graft tissue and the surrounding host tissue were studied in 17 perfused slices of rat neocortex. In standard artificial cerebrospinal fluid, stimulation of the host white matter evoked field potentials in four of 17 grafts. However, in Mg(2+)-free medium, the same stimulation evoked field potentials in an additional six grafts, with significant increases in the mean duration of the evoked responses in the 10 responsive grafts. In five of these slices stimulation of the graft also evoked field potentials in the host tissue, suggesting reciprocal interaction between graft and host. Simultaneous extracellular recordings from graft and host tissues in Mg(2+)-free medium showed that spontaneous epileptiform discharges developed in the graft and host tissue synchronously. In Mg(2+)-free medium, application of N-methyl-D-aspartate induced a shift of the baseline with superimposed epileptiform discharges in both graft and host. Application of the non-competitive N-methyl-D-aspartate antagonist ketamine and the competitive antagonist D,L-2-amino-5-phosphonovaleric acid attenuated or reversibly blocked both the spontaneous epileptiform discharges and the evoked field potentials. Our data provides evidence that N-methyl-D-aspartate receptors are present at synapses created between fetal graft and host neocortex, and that the N-methyl-D-aspartate-activated receptor-channel complex plays an active role in mediating excitatory synaptic transmission in host-graft circuitry.

Bilateral frontal cortical contusion in rats: behavioral and anatomic consequences

The purpose of this study was to develop a bilateral model of frontal cortical contusion in the rat that would demonstrate reproducible deficits typically found after frontal lobe injury in humans. We used a pneumatically controlled cortical impactor to create bilateral contusions of the medial prefrontal cortex (PFC) in adult male Sprague-Dawley rats. Cognitive, neurologic, physiologic, and histopathologic measures were used to evaluate changes caused by the injury. The cognitive task employed the Morris water maze (MWM). Contused rats performed worse than sham-operated controls on measures of time taken to find a submerged platform, distance to the platform, and swim strategy. Neurologic measures revealed impairments of tongue mobility and transient deficits of forelimb placing. Body weights of the contused rats were chronically reduced with respect to controls, indicating that cortical contusion produces disruption in homeostasis. All rats given bilateral PFC contusions developed marked necrotic cavities at the site of impact. The borders surrounding the cavities were heavily lined with astrocytes and ameboid microglia. There was subcortical gliosis in the medial caudate that extended throughout the rostral-caudal length of the caudate-putamen and into the mediodorsal (MD) and ventrolateral (VL) nuclei of the thalamus. The thalamus was also the site of distal transneuronal degeneration. In both the MD and the VL, there was significant neuronal loss in the contused rats as compared with sham-operated controls. This method of bilateral cortical contusion demonstrates clear, reproducible results that would be required for the development of future pharmacologic therapies designed to promote functional recovery.

Electrophysiological and morphological properties of embryonic neocortical grafts developing in different regions of the host rat brain

Parallel morphological and electrophysiological studies of embryonic neocortical tissue (primordia of anterior parietal--presumptive sensorimotor--cortex) grafted into different regions of the host adult brain (sensori-motor cortex, caudate-putamen, septum or thalamus) were carried out to investigate to what extent the properties of transplanted embryonic neocortex--an advanced organizational form of neuronal tissue--are affected by homotopic or heterotopic surroundings. The results point to the importance of the host tissue environment as it influences both the size, the morphological and functional properties of the implanted embryonic cortical plate tissue. The cortical grafts were smaller in size when developed homo-topically in sensorimotor cortex and grew larger in heterotopic environment (caudate-putamen, septum, thalamus). The orientation of neuronal dendrites in the grafts tends to follow that seen in the surroundings. The homotopic grafts showed a better structural integration into the host brain. Differences were seen between intracortical and subcortical transplants in the spontaneous firing rate of neurons and in the ratio of units with various types of spontaneous discharge.

Histological alterations in the fetal mouse cerebellum after neutron irradiation: a light and electron microscopic study

Histological effects of in utero neutron irradiation (0.5 Gy) were investigated in fetal mouse cerebellum. Irradiation was performed on the 18th embryonic day. Histological alterations were examined at 2, 6 and 12 h after irradiation. The effect was most pronounced in the EGL, 6 h after irradiation. In some cells (about 24%) karyopycnosis, destruction of cytoplasmic organelles and shrinkage were observed. Remnants of destroyed cells--the pycnotic nuclei with some cytoplasmic debris around them--were rapidly phagocytized by the surrounding cells. In addition to glial elements, the EGL germinal cells also showed phagocytic activity. Dense particles appearing light-microscopically as pycnotic nuclei, proved to be mostly remnants of destroyed, phagocytized cells under electron microscope.

Decreased weight, DNA, RNA and protein content of the brain after neutron irradiation of the 18-day mouse embryo

Pregnant mice were irradiated with 0.5 Gy fission neutrons on the eighteenth day of their gestation. The average litter size at birth was unchanged but mortality increased 5-6 fold in the first 3 days. The irradiated mice were the same weight as control mice at birth but showed a progressively increasing weight deficiency up to at least 36 days as compared to controls. Brain weight was 37, 45 and 25 per cent less in 2-, 3- and 52-week old irradiated animals, respectively, and the ratio of brain weight to body weight was 25, 27 and 13 per cent less. The concentrations of DNA, RNA and protein (mg/g wet tissue) were the same in irradiated and control mice in both brain and liver at all three ages. Total DNA, RNA and protein contents of whole brain after irradiation were 56-75 per cent of the control levels. No definite decrease was observed in liver. Histological study at 6 hours after irradiation showed nuclear pyknosis in the central nervous system from definite to very severe according to the part examined. It is concluded that damage to the central nervous system of the 18-day mouse foetus after neutron irradiation is mainly due to killing and/or inhibition of the differentiation of neuroblasts.

Mosaicism of the ventricular layer as the developmental basis of neocortical columnar organization. A 3H-thymidine autoradiographic study in newborn mice

The ratio and local distribution of intensely and weakly labelled neurons as compared with unlabelled neurons were studied in newborn mice by means of autoradiography using 3H-thymidine injected at various embryonic ages. The distribution and migrational properties of intensely labelled neurons suggest that cells contributing to any given cortical layer are not generated simultaneously but in smaller units that correspond to cortical microcolumns. This implies a mosaicity in the genetic potential of the ventricular germinative layer.

Transneuronal degeneration in different inbred strains of mice: a preliminary study of olfactory bulb events after olfactory nerve lesion

Cytological analysis of the olfactory bulb was performed in two inbred strains of mice SEC/1 ReJ and C57/B16J after the lesion of the olfactory nerve. The data show an enhanced transneural degeneration in C57 mice as compared to the controls, while in the SEC mice this phenomenon did not exceed the level of spontaneous degeneration previously described by other authors. On the basis of our findings two different genetically adaptive systems are hypothesized and correlated with onto-genetical data.

Constancy and variability in the content of DNA in cerebellar Purkinje cell nuclei. A cytophotometric study

A cytophotometric study of DNA content in Purkinje cells of the cerebellum of rats, cats, chicken and humans (Feulgen staining) revealed that in a certain number of cells the amount of NDA ranged between the diploid and tetraploid level (H2C cells). The incidence of H2C Purkinje cells varied among the species studied. In rats, which were studied most thoroughly, these cells amounted on average to 3%. In some rats, as well as in some cats and chickens H2C Purkinje cells were entirely absent. In the group of animals possesing H2C Purkinje cells, great interindividual differences were observed. In rats for instance, the incidence of these cells varied from 1 to 23 per cent. Topographic analyses carried out in rat and human cerebellum revealed that H2C Purkinje cells occurred more frequently in the hemispheres than in the vermis. No significant differences were found in the number of H2C Purkinje cells in healthy and Kilham-DNA-virus infected rats. Densitometric analysis of the distribution of nuclear chromatin showed that H2C Purkinje cells were richer in condensed chromatin, especially in the region of the nucleolus, which apparently contains the hyperploid surplus of DNA. It is proposed that the phenomenon of DNA hyperdiploidy arises as a result of either incomplete S-phase in some immature Purkinje cell precursors or the amplification of some DNA sequences particularly those localized in the nucleolar region.

Proliferation of Bergmann-glia in the developing rat cerebellum

Mitotic cells in the ganglionic layer of the infant rat cerebellum were studied between 3 to 12 postnatal days. The connection of these cells with the radial glial fibers of the primitive molecular layer could be established. On this basis it was assumed that the mitotic cells studied were immature Bergmann-glial cells whose proliferative activity seemed to continue even after the formation of their characteristic radial fibers. This phenomenon might offer an explanation for the divergent views on the generation time of Bergmann-glia.