Serotonin Inhibits Acetylcholine Release from Rat Striatum Slices: Evidence for a Presynaptic Receptor-Mediated Effect

Rat brain striatum slices were incubated with [3H]choline, perfused with a physiological buffer, and stimulated by perfusion with a K+-enriched buffer for 2 min. The tritium overflow evoked by K+ was decreased by 5-hydroxytryptamine (serotonin, 5-HT) (maximal inhibition 10(-6) M). This effect of 5-HT was mimicked by several agonists (5-methoxytryptamine, N,N-dimethyl-tryptamine, bufotenin) and blocked by serotonergic antagonists (methiothepin, methysergide, cinanserin) but not by haloperidol; methiothepin and methysergide alone slightly increased the K+-evoked overflow of tritium (3H). Inhibition of the tritium release by 5-HT was not suppressed in the presence of tetrodotoxin (TTX) (10(-6) M). These results suggest that 5-HT tonically inhibits acetylcholine (ACh) release from striatal cholinergic neurons by acting on a presynaptic receptor localized on cholinergic terminals.     

A new, transportable ergometer for the measurement of musculotendinous stiffness during wrist flexion.

We present here a new, dedicated mechanical device for monitoring quick-release movements of the wrist. The ergometer was designed to easily assess musculotendinous properties during wrist flexion. Maximal voluntary contractions (MVC) and quick-release (QR) movements during wrist flexion were performed on 14 subjects. A validation of the ergometer, using a test-retest methodology, was performed to assess its reliability and sensitivity. The device has been technically and biomechanically validated in a range of situations, including inertia measurement (mean inertia was found 0.0119+/-0.0012 N m s(2) rad(-1)) and appearance of the unloading reflex. Our results indicate that the device provides highly reliable, sensitive evaluation of wrist muscle stiffness (intraclass correlation coefficient for inertia, maximal voluntary contraction and stiffness index were 0.873, 0.994 and 0.930, respectively). Its portability facilitates measurement of the influence of repetitive, occupational activity on the musculotendinous complex of the wrist flexors.     

Molecular Reclassification of Crohn’s Disease: A Cautionary Note on Population Stratification

Complex human diseases commonly differ in their phenotypic characteristics, e.g., Crohn’s disease (CD) patients are heterogeneous with regard to disease location and disease extent. The genetic susceptibility to Crohn’s disease is widely acknowledged and has been demonstrated by identification of over 100 CD associated genetic loci. However, relating CD subphenotypes to disease susceptible loci has proven to be a difficult task. In this paper we discuss the use of cluster analysis on genetic markers to identify genetic-based subgroups while taking into account possible confounding by population stratification. We show that it is highly relevant to consider the confounding nature of population stratification in order to avoid that detected clusters are strongly related to population groups instead of disease-specific groups. Therefore, we explain the use of principal components to correct for population stratification while clustering affected individuals into genetic-based subgroups. The principal components are obtained using 30 ancestry informative markers (AIM), and the first two PCs are determined to discriminate between continental origins of the affected individuals. Genotypes on 51 CD associated single nucleotide polymorphisms (SNPs) are used to perform latent class analysis, hierarchical and Partitioning Around Medoids (PAM) cluster analysis within a sample of affected individuals with and without the use of principal components to adjust for population stratification. It is seen that without correction for population stratification clusters seem to be influenced by population stratification while with correction clusters are unrelated to continental origin of individuals.     

Multiphasic On/Off Pheromone Signalling in Moths as Neural Correlates of a Search Strategy

Insects and robots searching for odour sources in turbulent plumes face the same problem: the random nature of mixing causes fluctuations and intermittency in perception. Pheromone-tracking male moths appear to deal with discontinuous flows of information by surging upwind, upon sensing a pheromone patch, and casting crosswind, upon losing the plume. Using a combination of neurophysiological recordings, computational modelling and experiments with a cyborg, we propose a neuronal mechanism that promotes a behavioural switch between surge and casting. We show how multiphasic On/Off pheromone-sensitive neurons may guide action selection based on signalling presence or loss of the pheromone. A Hodgkin-Huxley-type neuron model with a small-conductance calcium-activated potassium (SK) channel reproduces physiological On/Off responses. Using this model as a command neuron and the antennae of tethered moths as pheromone sensors, we demonstrate the efficiency of multiphasic patterning in driving a robotic searcher toward the source. Taken together, our results suggest that multiphasic On/Off responses may mediate olfactory navigation and that SK channels may account for these responses.     

Dinucleoside tetraphosphate variations in cultured tumor cells during their cell cycle and growth

Asynchronous and synchronized cultures of A549 and HTC cells were used to detect possible, cell cycle or cell density specific variations in the intracellular pools of dinucleoside tetraphosphates (Ap4X). No important variations of the nucleotide pools were observed during cell growth. When HTC cells were released from mitotic arrest, a decrease by a factor of N3 Ap4X and ATP levels was observed when the cells entered the G1 phase. This decrease is essentially due to cell doubling. When A549 cells were released from an arrest at the G1/S boundary, the nucleotide pool size increased slightly during the G2 phase just before mitosis. This result is in agreement with both earlier data from our laboratory and the observed decrease in Ap4X pool after release from mitotic-arrested HTC cells. These results suggest that the Ap4X and ATP pools are only subjected to very small variations during the cell cycle, essentially in the G2 phase and after mitosis.     

Regulation of Vacuolar pH of Plant Cells: I. Isolation and Properties of Vacuoles Suitable for P NMR Studies

For the first time, the ³¹P nuclear magnetic resonance technique has been used to study the properties of isolated vacuoles of plant cells, namely the vacuolar pH and the inorganic phosphate content. Catharanthus roseus cells incubated for 15 hours on a culture medium enriched with 10 millimolar inorganic phosphate accumulated large amounts of inorganic phosphate in their vacuoles. Vacuolar phosphate ions were largely retained in the vacuoles when protoplasts were prepared from the cells and vacuoles isolated from the protoplasts. Vacuolar inorganic phosphate concentrations up to 150 millimolar were routinely obtained. Suspensions prepared with 2 to 3 × 10⁶ vacuoles per milliliter from the enriched C. roseus cells have an internal pH value of 5.50 ± 0.06 and a mean trans-tonoplast ΔpH of 1.56 ± 0.07. Reliable determinations of vacuolar and external pH could be made by using accumulation times as low as 2 minutes. These conditions are suitable to follow the kinetics of H⁺ exchanges at the tonoplast. The ³¹P nuclear magnetic resonance technique also offered the possibility of monitoring simultaneously the stability of the trans-tonoplast pH and phosphate gradients. Both appeared to be reasonably stable over several hours. The buffering capacity of the vacuolar sap around pH 5.5 has been estimated by several procedures to be 36 ± 2 microequivalents per milliliter per pH unit. The increase of the buffering capacity due to the accumulation of phosphate in the vacuoles is, in large part, compensated by a decrease of the intravacuolar malate content.     

Neuromedin U-immunoreactivity in the nervous system of the small intestine of the pig and its coexistence with substance P and CGRP

Summary In the small intestine of the pig, neuromedin U (NMU)-immunoreactivity was mainly confined to the nerve plexus of the inner submucosal and mucosal regions. After colchicine treatment, a high number of immunoreactive nerve cell bodies was observed in the plexus submucosus internus (Meissner), whereas only a low number was found in the plexus submucosus externus (Schabadasch). The plexus myentericus as well as the aganglionic nerve meshworks in the circular and longitudinal smooth muscle layers almost completely lacked NMU-immunoreactivity. Double-labeling experiments demonstrated the occurrence of distinct NMU-containing neuron populations in the plexus submucosus internus: (1) relatively large type-II neurons revealing immunoreactivity for NMU and calcitonin gene-related peptide (CGRP) and/or substance P (SP); (2) a group of small NMU- and SP-immunoreactive neurons; (3) a relatively low number of small neurons displaying immunoreactivity for NMU but not for SP. Based on its distributional pattern, it is concluded that NMU plays an important role in the regulation and control of mucosal functions.