The role of SiGe buffer in growth and relaxation of Ge on free-standing Si(001) nano-pillars.

We study the growth and relaxation processes of Ge nano-clusters selectively grown by chemical vapor deposition on free-standing 90 nm wide Si(001) nano-pillars with a thin Si(0.23)Ge(0.77) buffer layer. We found that the dome-shaped SiGe layer with a height of about 28 nm as well as the Ge dot deposited on top of it partially relaxes, mainly by elastic lattice bending. The Si nano-pillar shows a clear compliance behavior-an elastic response of the substrate on the growing film-with the tensile strained top part of the pillar. Additional annealing at 800 °C leads to the generation of misfit dislocation and reduces the compliance effect significantly. This example demonstrates that despite the compressive strain generated due to the surrounding SiO(2) growth mask it is possible to realize an overall tensile strain in the Si nano-pillar and following a compliant substrate effect by using a SiGe buffer layer. We further show that the SiGe buffer is able to improve the structural quality of the Ge nano-dot.

Growth and relaxation processes in Ge nanocrystals on free-standing Si(001) nanopillars.

We study the growth and relaxation processes of Ge crystals selectively grown by chemical vapour deposition on free-standing 90 nm wide Si(001) nanopillars. Epi-Ge with thickness ranging from 4 to 80 nm was characterized by synchrotron based x-ray diffraction and transmission electron microscopy. We found that the strain in Ge nanostructures is plastically released by nucleation of misfit dislocations, leading to degrees of relaxation ranging from 50 to 100%. The growth of Ge nanocrystals follows the equilibrium crystal shape terminated by low surface energy (001) and {113} facets. Although the volumes of Ge nanocrystals are homogeneous, their shape is not uniform and the crystal quality is limited by volume defects on {111} planes. This is not the case for the Ge/Si nanostructures subjected to thermal treatment. Here, improved structure quality together with high levels of uniformity of the size and shape is observed.

Devices for noninvasive transcranial electrostimulation of the brain endorphinergic system: application for improvement of human psycho-physiological status.

It is well known that deficit of endorphins plays an important role in disturbances of human psycho-physiological status. Previously, we revealed that brain endorphinergic structures have quasiresonance characteristics. On the basis of these data, a method of activation of the brain endorphinergic structures by means of noninvasive and rather selective transcranial electrostimulation (TES) as a kind of functional electrical stimulation (FES) was elaborated. New models of TES devices (TRANSAIR) were developed for indoor and outdoor usage. To increase the efficacy of TES, the frequency modulation according to normal distribution in the limits of the quasiresonance characteristics was put into operation. The blind and placebo-controlled (passive and active placebo) study was produced to estimate the TES effects on stress events and accompanied psycho-physiological and autonomic disturbances of different intensities on volunteers and patients in the following groups: everyday stress and fatigue; stress in regular military service and in field conditions; stress in the relatives of those lost in mass disaster; posttraumatic stress (thermal burns); and affective disorders in a postabstinence period. Some subjective verbal and nonverbal tests and objective tests (including heart rate variability) were used for estimation of the initial level of psycho-physiological status, which changes after TES sessions. It was demonstrated that fatigue, stress, and other accompanied psycho-physiological disturbances were significantly improved or abolished after 2-5 TES sessions. The TES effects were more pronounced in cases of heavier disturbances. In conclusion, activation of the brain endorphinergic structures by TES is an effective homeostatic method of FES that sufficiently improves quality of life.

Historical bottlenecks decrease genetic diversity in natural populations of Dryopteris cristata.

The reconstruction of recent historical population sizes allowed us to investigate the influence of random evolutionary processes on present-day genetic diversity in populations of Dryopteris cristata. This long-lived, allotetraploid fern is rare and endangered in the study area at the southwestern border of its European distribution. Random amplified polymorphic DNA (RAPD) diversity of 280 individuals from 14 populations of D. cristata was extraordinarily low, suggesting an ancient bottleneck in the species' history. Analysis of molecular variance (AMOVA) of 25 different RAPD multiband phenotypes revealed significant genetic variation among three geographical regions (15%) and among populations within regions (34%); 51% of total variance was attributed to variation within populations. High population differentiation indicated limited gene flow among populations, and genetic divergence was not correlated with geographical distance. There was no relationship between genetic variation within population, estimated as molecular variance, and present-day population size. Populations with recent historical bottlenecks of fewer than 25 individuals showed a substantial and significant reduction in genetic variation, compared with populations without bottlenecks. Comparatively high levels of genetic variation were still maintained in small remnants (60-110 individuals) of formerly large populations. Average deviations of frequencies of widespread polymorphic markers within populations from their frequencies in the whole dataset were significantly higher in small or recently bottlenecked populations than in constantly large populations, thus providing evidence for random sampling effects during genetic bottlenecks and drift in small populations. The present investigation demonstrates the importance of population history for understanding present-day genetic diversity within natural populations, as well as for conservation biology.

Differential effects from parapyramidal region and rostral ventrolateral medulla mediated by substance P.

Rostral ventrolateral medulla (rVLM) and parapyramidal region (PPr) serve as important medullary control sites for sympathoexcitation. rVLM and PPr have direct projections to the intermediolateral cell column (IML) that are thought to be important in maintaining mean arterial blood pressure (MAP). Substance P (SP) is found in PPr neurons and in and near the subretrofacial area of the rVLM. At least some of these cells project to the IML. We investigated the involvement of SP at the IML in mediating rVLM- and PPr-evoked pressor responses in the chloralose-anesthetized cat. Pressor responses to electrical and chemical PPr and rVLM stimulation were altered after intrathecal injection, at the level of the T1-T3 spinal cord, of either SP antagonist [D-Pro(2), D-Phe(7), D-Trp(9)]-SP, SP antagonist CP 96,345, or SP antiserum. Although MAP and heart rate responses to PPr stimulation were attenuated by intrathecal SP antagonists or antiserum, MAP responses to rVLM stimulation were augmented. Previous studies have revealed differences in transmitters associated with these two areas, even though the general response of both areas is sympathoexcitatory. The present study implies that the identical substance may increase or decrease the MAP response depending on the pathway activated.

Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior.

The hypothalamus plays a central role in the integrated control of feeding and energy homeostasis. We have identified two novel neuropeptides, both derived from the same precursor by proteolytic processing, that bind and activate two closely related (previously) orphan G protein-coupled receptors. These peptides, termed orexin-A and -B, have no significant structural similarities to known families of regulatory peptides. prepro-orexin mRNA and immunoreactive orexin-A are localized in neurons within and around the lateral and posterior hypothalamus in the adult rat brain. When administered centrally to rats, these peptides stimulate food consumption. prepro-orexin mRNA level is up-regulated upon fasting, suggesting a physiological role for the peptides as mediators in the central feedback mechanism that regulates feeding behavior.

Expression of tyrosine hydroxylase gene in cultured hypothalamic cells: roles of protein kinase A and C.

In hypothalamic cells cultured in serum-free medium, the quantity of tyrosine hydroxylase mRNA increases after treatment with an activator of the protein kinase A pathway (8-bromoadenosine cyclic AMP, 3-isobutyl-1-methylxanthine, or forskolin) or an activator of protein kinase C (12-O-tetradecanoylphorbol 13-acetate or sn-1,2-diacylglycerol). The tyrosine hydroxylase mRNA level decreases in the cells after inhibition of protein kinase C with calphostin C or after depletion of protein kinase C by extended phorbol ester treatment. These data suggest that both protein kinase pathways regulate tyrosine hydroxylase gene expression in hypothalamic cells. As simultaneous activation of both pathways has less than an additive effect on the tyrosine hydroxylase mRNA level, they appear to be interrelated. Compared with the rapid and dramatic increase of the tyrosine hydroxylase mRNA level in pheochromocytoma cells, activation of the protein kinase A or protein kinase C pathway in the cultured hypothalamic cells induces slow changes of a small magnitude in the amount of tyrosine hydroxylase mRNA. The slow regulation of tyrosine hydroxylase gene expression in hypothalamic dopaminergic neurons corresponds to the relatively high stability of tyrosine hydroxylase mRNA (half-life = 14 +/- 1 h) in these cells.

Leucine5-enkephalin afferents to midbrain dopaminergic neurons: light and electron microscopic examination.

The relationship between leucine5-enkephalin-containing nerve terminals and midbrain dopaminergic neurons was studied in the adult rat by light and electron microscopy. For light microscopy, alternate midbrain sections were immunostained with rabbit polyclonal antibodies against leucine5-enkephalin and tyrosine hydroxylase, by means of the peroxidase antiperoxidase technique. Leucine5-enkephalin stained fibers and terminals were observed with varying density in the retrorubral field (dopaminergic nucleus A8 region), substantia nigra pars compacta (dopaminergic nucleus A9 region), and ventral tegmental area and related nuclei (dopaminergic nucleus A10 region). For electron microscopy, midbrain sections were immunostained with a mouse monoclonal antibody against leucine5-enkephalin and a rabbit polyclonal antibody against tyrosine hydroxylase, by means of the peroxidase antiperoxidase technique and silver-intensified colloidal gold reactions, respectively. The nucleus A10 area was examined at the electron microscopic level, and there were a) both symmetric (75%) and asymmetric (25%) synapses made between leucine5-enkephalin axon terminals and dopaminergic dendrites, and also synaptic contacts with unlabeled dendrites; b) leucine5-enkephalin synaptic contacts with dopaminergic dendrites that were covered with astrocytic membranes; and c) leucine5-enkephalin appositions with unlabeled nerve terminals that made synaptic contacts with dopaminergic dendrites, suggestive of axo-axonic connections. These findings provide the structural basis for both direct and indirect control of A10 dopaminergic neurons by enkephalin-containing nerve terminals.

Actions of endogenous vasopressin and oxytocin on anterior pituitary hormone secretion.

To evaluate the significance of endogenous vasopressin and oxytocin in control of anterior pituitary hormone release, antiserum against vasopressin (AB-VP) or oxytocin (AB-OT) were microinjected into the third ventricle (3V) of conscious, ovariectomized rats to immunoneutralize endogenous VP or OT, respectively. Blood samples were collected just before and at different times after the microinjections. There were no differences in the plasma LH, FSH, PRL and TSH concentrations between control groups injected into the 3V with normal rabbit serum (NRS) and groups submitted to the intraventricular injection of AB-OT or AB-VP for 24 h after the injections. Plasma growth hormone (GH) declined significantly by 4 h after NRS injection, remained low at 6 h and had rebounded to nearly initial levels at 24 h. This pattern was not changed by microinjection of AB-VP, but plasma GH increased significantly compared to initial values in the period from 1 to 24 h after intraventricular microinjection of AB-OT. The intraventricular injection of AB-VP or AB-OT significantly decreased plasma ACTH; however, the effect of AB-VP was more prolonged and persisted for 6 rather than 4 h after injection. Thus, endogenous oxytocin may play a role in the control of basal GH release probably by stimulating somatostatin secretion and/or inhibiting GH-releasing hormone secretion or by both actions. On the other hand, both endogenous vasopressin and oxytocin play a physiologically significant stimulatory role in the control of basal ACTH release.

ACTH1-39 inputs to mesocorticolimbic dopaminergic neurons: light and electron microscopic examination.

Single- and double-labeling immunocytochemical staining procedures were used to examine the relationship between adrenocorticotropin (ACTH)-containing nerve terminals and dopaminergic (DA) neurons in the rat midbrain, using both light and electron microscopy. At the light microscopic level, ACTH neuronal processes were found largely in restricted regions occupied by the mesolimbic and mesocortical DA neurons. At the electron microscopic level, in the central linear nucleus, ACTH axon terminals made symmetric and asymmetric synaptic contacts with DA dendrites, as well as appositions with unlabeled axon terminals which, in turn, synapsed upon DA dendrites. These data suggest that ACTH functions as a neurotransmitter/neuromodulator in the brain, and such ACTH-DA synapses may be important for stress-induced changes in mesocorticolimbic DA neuronal activity.

Acoustic microscopy and nonlinear effects in pressurized superfluid helium.

The operation of an acoustic microscope having a resolution of 15 mm has been demonstrated. It uses as a coupling medium superfluid (4 )He colder than 0.9 K and pressurized to greater than 20 bar. The microscope has been used to image objects that show little or no contrast on a scanning electron microscope. In addition, the acoustic microscope has been used to study the properties of sound propagation in the coupling fluid. At low acoustic intensities, the coupling fluid has very low acoustic attenuation at the microscope's operating frequency (15.3 GHz), but near the focal point the acoustic intensity can be high enough that the helium behaves with extreme nonlinearity. In fact, this medium is capable of entering new regimes of nonlinear interaction. Plots of the received signal versus input power display a nearly complete source depletion at certain input power levels and a reconversion to the source frequency at higher power levels. Arguments that the process underlying this nonlinear behavior is harmonic generation are presented.

Immunocytochemical distribution of aromatase cytochrome P450 in the rat brain using peptide-generated polyclonal antibodies.

Estrogen formation is catalyzed by the aromatase cytochrome P450 (P450AROM) enzyme. Aromatase activity has been detected in several regions in the rat brain. In the present study, we used peptide-generated polyclonal antibodies raised against a 20-amino acid synthetic fragment of the rat P450AROM protein (as deduced from the nucleic acid sequence of the rat P450AROM complementary DNA), to determine the location of this enzyme in rat brain sections. Immunoreactive antisera were titered by means of an enzyme-linked immunosorbent assay and purified by diethylaminoethyl-Affigel Blue chromatography. Specific immunoreactivity was confirmed by Western blot analysis using known aromatase-containing tissue (rat ovary homogenates and microsomal fractions). Evaluation of the distribution of P450AROM immunoreactivity in brain sections of male and female rats (30 and 60 days of age) was performed using the avidin biotin peroxidase immunocytochemical technique and light microscopy. P450AROM immunoreactivity appeared to be localized to neurons, and was present in brain regions and nuclei where enzymatic activity has been reported. For example, intense immunoreactivity was observed in the amygdaloid structures and supraoptic nucleus, whereas moderate to light immunoreactivity was evident in the paraventricular and arcuate nuclei and hippocampus. Surprisingly, neurons in the bed nucleus stria terminalis, medial basal hypothalamic, and preoptic areas displayed little aromatase immunoreactivity. However, P450AROM immunoreactivity was detected in specific brain regions not previously recognized to contain the enzyme (i.e. intense staining was seen in the reticular thalamic nucleus, olfactory tract and piriform cortex, as well as other brain structures). The pattern, distribution, and intensity of P450AROM immunoreactivity was similar regardless of sex or age. In this study, microsomal preparations derived from a new brain area (i.e. the reticular thalamic nucleus; Rt) displaying P450AROM immunoreactivity were observed to contain detectable levels of aromatase enzymatic activity, as determined by the 3H2O-release assay. The activity in the Rt was inhibited by a known aromatase inhibitor, 4-hydroxyandrostenedione. These results confirm histologically the localization of P450AROM to brain regions where aromatase enzymatic activity has been detected and extend the knowledge of its location to areas previously unknown as sites of aromatase activity, which may be involved in the modulation of neuroendocrine function and reproductive behavior.

Tyrosine hydroxylase expression in hypothalamic cells: analysis of the roles of adenosine 3',5'-monophosphate- and Ca2+/calmodulin-dependent protein kinases in the action of pituitary cytotropic factor.

We investigated the involvement of second messenger systems in the control by pituitary cytotropic factor (CTF) of tyrosine hydroxylase (TH) expression in primary cultures of hypothalamic cells. Forskolin, an activator of adenylyl cyclase, as well as Sp-cAMP[S] [(Sp)-cyclic adenosine 3',5'-monophosphothioate], a cAMP agonist, and theophylline, an inhibitor of phosphodiesterase activity, stimulate the secretion of dihydroxyphenylalanine (DOPA) and dopamine (DA), suggesting a role for cAMP-dependent protein kinase in the secretion of catecholamines by hypothalamic dopaminergic cells. When cells were cultured with either CTF or forskolin for 14 days, a progressive increase in the secretion of DOPA and DA was observed throughout the period of incubation. At the end of the 2-week culture period, the amount of TH in the cells, determined by immunoblot analysis, was appreciably increased compared to controls. When the cells were analyzed immunocytochemically for TH, the TH-positive cells that had been incubated with CTF or forskolin for 2 weeks were found to have neurites that appeared larger than those of TH-positive cells in the controls. The diameters of the perikarya of TH-positive cells in cultures incubated with CTF also appeared larger than the controls. After incubation of hypothalamic cells with CTF for 96 h, the amount of TH mRNA in the cultures was significantly increased. When membranes isolated from PC12 cells were incubated for 10 min with 50 microM forskolin, the specific activity of adenylyl cyclase was increased 20-fold; CTF had no effect on adenylyl cyclase activity of PC12 cell membranes. Yet, CTF significantly (P less than 0.001) stimulated the secretion of DOPA and DA by PC12 cells. When hypothalamic cells were incubated with both forskolin and CTF, using doses of each that stimulated maximal secretion, the secretion of DOPA and DA was equal to sum of the secretions with each stimulant alone. These additive actions of forskolin and CTF and the failure of CTF to activate adenylyl cyclase in membranes of PC12 cells suggest that forskolin and CTF stimulate catecholamine secretion by hypothalamic dopaminergic cells through different mechanisms, perhaps through different protein kinases. When hypothalamic cells were incubated with CTF and W-7 [N-(6-aminohexyl)5-chloro-1-naphthalenesulfonamide], an inhibitor of calmodulin, the secretion of DOPA was significantly (P less than 0.001) less than that in cultures that were not incubated with W-7. The findings of this study suggest that TH expression in hypothalamic dopaminergic cells is controlled by redundant protein kinases, including cAMP-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase.

Localization of tyrosine hydroxylase and phenylethanolamine N-methyltransferase immunoreactive cells in the medulla of the dog.

The tyrosine hydroxylase (TH)- and phenylethanolamine N-methyltransferase (PNMT)-immunoreactive cells of the medulla are closely associated with cardiovascular control in both the cat and rat. Although it is often the species of choice for cardiovascular studies, no previous study had characterized these cell groups in the dog. The TH- and PNMT-immunoreactive cells of the dog were distributed much as they are in both cat and rat but with some species variations, which may be indicative of their functional role.

Neocortical transplants grafted into the newborn rat brain demonstrate a blood-brain barrier to macromolecules.

Vascular permeability was examined in fetal neocortical transplants grafted into the cerebral cortex of newborn rats. Methods based on the histochemical labeling of intravenously administered horseradish peroxidase or on the immunocytochemical demonstration of endogenous immunoglobulin showed the presence of a blood barrier within the transplants.

Water intake in rats subjected to hypothalamic immunoneutralization of angiotensin II, atrial natriuretic peptide, vasopressin, or oxytocin.

To investigate the influence of various peptides on control of dehydration-induced drinking, water intake elicited by overnight water deprivation was analyzed in groups of male rats after intracerebroventricular (third ventricle, icv) injection of 2 microliters of normal rabbit serum or an equal volume of antiserum directed against angiotensin II (Ab-AII), atrial natriuretic peptide, vasopressin, or oxytocin. There was no difference in water intake after normal rabbit serum and antiserum injections when water was offered immediately after icv injections. Water intake was greatly reduced by Ab-AII when water was offered 1 hr and 3 hr after icv injection. The other antisera were partially effective only when water was offered 3 hr after icv injection. The dipsogenic effect of icv injection of AII in normally hydrated rats was reduced only by icv injection of Ab-AII 3 hr before and not by the other antisera. Ab-AII injected icv had no effect on the drinking that occurred just before and after the onset of darkness and that was associated with eating (prandial drinking). The results indicate that AII is primarily responsible for dehydration-induced drinking, and the other peptides may play a permissive role since their antisera were partially effective, with longer latencies after antiserum injection, which is perhaps the result of gradual diffusion to effective sites within the hypothalamus. In contrast, endogenous AII appears to play little, if any, role in prandial drinking.