A hypothalamic channel-system in the inferior lobes of a trigger-fish (Rhinecanthus aculeatus, Balistidae)

In the course of a general investigation of the optic system in some trigger-fishes, a hypothalamic, ventricular channel-system with pores, leading to the outside of the brain, has been discovered in the inferior lobes ofRhinecanthus aculeatus (Balistidae). A description of the morphological relations of the channel-system to the blood-vessel-supply and the cranium suggests that the organ-systems involved form a functional unit. The possibility of a hormone-producing system is discussed in the light of physiological and ecological aspects

Convenient Labelling Technique for Mass Spectrometry - Acid Catalyzed Deuterium and Oxygen-18 Exchange via Gas-liquid Chromatography

Mass spectrometry labelling technique - acid catalyzed deuterium and oxygen 18 exchange by gas-liquid chromatograph

Phase-locking in the multidimensional Frenkel-Kontorova model

We consider the multidimensional Frenkel-Kontorova model with one degree of freedom which is a variational problem for real functions on the lattice Zn

Structures and Evaluation of Biologically Active Constituents of "Cussonia Zimmermannii" Harms

For the present thesis 22 samples of seven African medicinal plants, the extracts of which had previously proved to possess an in vitro activity against T. b. rhodesiense and/or P. falciparum and 13 samples of six randomly selected plant species based on availability were collected in Tanzania. Of these 35 samples, 140 crude extracts were produced with four solvents of different polarity, and the extracts were tested for in vitro antitrypanosomal and antiplasmodial activity and for cytotoxicity. In addition the extracts were tested for the affinity to the GABAA receptor performed by radioligand binding experiments. Based on the considerable antitrypanosomal and antiplasmodial activity and the affinity to the GABAA receptor, two extracts were selected for bioassay-guided fractionation : the petroleum ether extract of the stembark of Commiphora fulvotomentosa Engl. because of its promising IC50 value of 2.1 mg/ml against T. b. rhodesiense and the high selectivity index of 21.4, and the petroleum ether extract of the rootbark of Cussonia zimmermannii Harms because of its IC50 value of 4.8 mg/ml against T. b. rhodesiense, its IC50 value of 3.3 mg/ml against P. falciparum, and the potent modulatory effect at the GABAA receptor of 151 %. After three fractionation steps the fractions of the petroleum ether extract of the stembark of Commiphora fulvotomentosa Engl. did not show any inhibitory activity against T. b. rhodesiense and were therefore not investigated further. Bioassay-guided fractionation of the petroleum ether extract of the rootbark of Cussonia zimmermannii Harms lead to the isolation of four polyacetylenes. By the application of MS, HR-MS, UV/VIS and IR methods and NMR experiments (1H-NMR, 13C-NMR, DEPT135, 1H-1H COSY, HMQC and HMBC) the structures of the four novel diynes were established : 8-Hydroxyheptadeca-4,6-diyn-3-yl acetate (MS-1 (25)), 8-Hydroxyheptadeca-1-ene-4,6-diyn-3-yl acetate (MS-2 (26)), 16-Acetoxy-11- hydroxyoctadeca-17-ene-12,14-diynyl acetate (MS-4 (27)), and 11,16-Diacetoxyoctadeca- 17-ene-12,14-diynyl acetate (MS-5 (28)). Additionally, stigmasterol (42) was isolated and identified by comparison of its spectroscopic data with those of an authentic sample. For the determination of the absolute configuration of MS-4 (27) at C(11) the Mosher method was used. The negative d values for the neighbouring protons suggested the S-configuration. But this result could not be confirmed by the 13C-NMR data since both positive and negative d values were obtained for the neighbouring carbons. Due to the fact, that the results for the protons and the carbons were not consistent the S-configuration for C(11) of MS-4 (27) could not be assigned with certainty. The isolated compounds MS-1 (25), MS-2 (26), and MS-4 (27) were tested for in vitro inhibitory activity against additional parasites like T. cruzi and L. donovani (axenic and in infected macrophages). 42 was not tested because it was a well known phytosterol which is ubiquitous in plants. Neither was MS-5 (28) tested, since the isolated amount was not sufficient. It was found that MS-1 (25) showed in all antiparasitic in vitro assays no higher inhibitory activity than the crude extract. MS-2 (26) showed promising activities in the T. cruzi and L. donovani (axenic and in infected macrophages) assay with IC50 values of 0.2, 0.039, and 0.098 mg/ml, respectively. The respective IC50 values of the standard drugs were 0.62, 0.18, and 0.29. The cytotoxicity was relatively high; therefore the selectivity with SI values of 18.0 and 36.7, respectively (T. cruzi, L. donovani in inf. mac.), was in a moderate range. MS-4 (27) showed also interesting activities in the T. cruzi and L. donovani (axenic) assays with IC50 values of 0.15 and 0.054 mg/ml. The SI value of 145.3 (T. cruzi) was high. Compared with the standard drugs the activities of MS-2 (26) and MS-4 (27) against T. b. rhodesiense and P. falciparum were in a moderate range. MS-1 (25), MS-2 (26), and MS-4 (27) were also tested in the GABAA receptor binding assay. Here MS-4 (27) showed the highest relative specific binding of 158 % at a concentration of 20 mg/ml, followed by MS-2 (26) with 152 % and MS-1 (25) with 138 %. In order to investigate whether the modulatory effect at the GABAA receptor leads to a chanel opening, the isolated compounds were investigated electrophysiologically. It was found that MS-1 (25), MS-2 (26), and MS-4 (27) act as potent positive allosteric modulators at GABAA receptors with a half maximal stimulation at a concentration of 0.6-3.5 mM and a maximal stimulation of 110-450 %. The compounds also showed unique subunit selectivity profiles, the stimulation was independend from the presence of the g subunit and resistant to the benzodiazepine antagonist Ro15-1788. These in vitro data suggested that MS-1 (25), MS-2 (26), and MS-4 (27) may be used to treat diseases of the central nervous system, specifically they may be used to treat states of anxiety, as sedatives/hypnotics, as muscle relaxants and as anticonvulsives (e.g. in epilepsy), and in the treatment of drug addiction. Therefore it was decided to patent the compounds for these indications [174]. All data are on the in vitro level. For a pharmaceutical application in vivo data are needed. Therefore MS-1 (25), MS-2 (26), and MS-4 (27) need to be synthesized in order to get more material for subsequent in vivo experiments

Equilibrium form of crystals and stable norm

The equilibrium form of a crystal is the shape which minimizes the total surface tension for a given volume. The surface tension itself is considered to be a function of the orientation of the crystal face within the crystal lattice. This function of orientation is identified with the stable norm on the second homology classes of a Riemannian 3-torus. Minimizing the total surface tension of the crystal leads to an equilibrium form which corresponds to the dual unit ball of the stable norm. We outline the connection between surface tension and stable norm and interpret the differentiability properties of the stable norm in terms of the crystal shape. The differentiability properties, in particular, prove Sohnke's reciprocity law estimating the size of crystal faces

Spike-Based Synaptic Plasticity and the Emergence of Direction Selective Simple Cells: Mathematical Analysis

In the companion paper we presented extended simulations showing that the recently observed spike-timing dependent synaptic plasticity can explain the development of simple cell direction selectivity (DS) when simultaneously modifying the synaptic strength and the degree of synaptic depression. Here we estimate the spatial shift of the simple cell receptive field (RF) induced by the long-term synaptic plasticity, and the temporal phase advance caused by the short-term synaptic depression in response to drifting grating stimuli. The analytical expressions for this spatial shift and temporal phase advance lead to a qualitative reproduction of the frequency tuning curves of non-directional and directional simple cells. In agreement with in vivo recordings, the acquired DS is strongest for test gratings with a temporal frequency around 1–4 Hz. In our model this best frequency is determined by the width of the learning function and the time course of depression, but not by the temporal frequency of the ‘training’ stimuli. The analysis further reveals the instability of the initially symmetric RF, and formally explains why direction selectivity develops from a non-directional cell in a natural, directionally unbiased stimulation scenario

Understanding Variation in Sets of N-of-1 Trials.

A recent paper in this journal by Chen and Chen has used computer simulations to examine a number of approaches to analysing sets of n-of-1 trials. We have examined such designs using a more theoretical approach based on considering the purpose of analysis and the structure as regards randomisation that the design uses. We show that different purposes require different analyses and that these in turn may produce quite different results. Our approach to incorporating the randomisation employed when the purpose is to test a null hypothesis of strict equality of the treatment makes use of Nelder's theory of general balance. However, where the purpose is to make inferences about the effects for individual patients, we show that a mixed model is needed. There are strong parallels to the difference between fixed and random effects meta-analyses and these are discussed

An evaluation of praise as a reinforcer for preschoolers\u27 behavior

Behavior analysts and educators often recommend using praise, particularly descriptive praise, despite mixed empirical findings to support this recommendation. We evaluated the effectiveness of praise as a reinforcer during a reinforcer assessment using known tasks with preschoolers in Study 1. Praise functioned as a reinforcer for 2 of 6 participants; the remaining 4 participants required additional reinforcers (edibles) to show a reinforcement effect. We then compared the effectiveness of descriptive versus general praise for acquisition of unknown tacts and assessed participants’ preference for the different types of praise for 4 participants from Study 1. Results showed the efficacy of and preference for general and descriptive praise was idiosyncratic

Response of Spiking Neurons to Correlated Inputs

The effect of a temporally correlated afferent current on the firing rate of a leaky integrate-and-fire (LIF) neuron is studied. This current is characterized in terms of rates, auto and cross-correlations, and correlation time scale $\tau_c$ of excitatory and inhibitory inputs. The output rate $\nu_{out}$ is calculated in the Fokker-Planck (FP) formalism in the limit of both small and large $\tau_c$ compared to the membrane time constant $\tau$ of the neuron. By simulations we check the analytical results, provide an interpolation valid for all $\tau_c$ and study the neuron's response to rapid changes in the correlation magnitude.Comment: 4 pages, 3 figure