Neuronal inhibition by the peptide FMRFamide involves opening of S K+ channels

Neurotransmitters modulate the activity of ion channels through a variety of second messengers, including cyclic AMP, cyclic GMP and the products of phosphatidylinositol breakdown. Little is known about how different transmitters acting through different second-messenger systems interact within a cell to regulate single ion channels. We here describe the reciprocal actions of serotonin and the molluscan neuropeptide, FMRFamide, on individual K+ channels in Aplysia sensory neurons. In these cells, serotonin causes prolonged all-or-none closure of a class of background conductance K+ channels (the S channels) through cAMP-dependent protein phosphorylation. Using single-channel recording, we have found that FMRFamide produces two actions on the S channels; it increases the probability of opening of the S channels via a cAMP-independent second-messenger system and it reverses the closures of S channels produced by serotonin or cAMP.     

系统发育史的重建

不同的物种是怎样进化形成不同的形态 ,这仍是现代进化生物学中研究的主要课题。近年来 ,对这一问题的研究已集中在由于进化时间的不同而导致进化机制变化的模型上 ,并在解开机体发育期间控制形态表现的分子机理方面取得了惊人的进展。值得注意的是 :形态的表型和一些调节基因的突变大致反映了物种间所表现的差异。通过分析生物的系统发育 ,重新构建系统发育史 ,可以阐明控制发育过程和进化发育的相关时间的遗传网络的分子进化机制。与系统发育进化有关的信息影印在组成它们的基因片段上。存在于这些发育位点的信息可以使人们追踪到发育调节…     

A new puffing pattern induced by temperature shock and DNP in drosophila

Riassunto Si è notato che shocks di temperatura possono indurre una variazione di «puffing pattern» in ghiandole salivari di Drosophila. Tali «puffing» sono perfettamente reversibili e rappresentano zone di intensa sintesi di RNA. Si è notato che DNP e Na salicilato portano a simili variazioni di «puffing pattern».     

Clark's Nutcrackers harvest sugar pine seeds from cones

This is the first report of Clark’s Nutcrackers ( Nucifraga columbiana ) harvesting seeds from the cones of sugar pine ( Pinus lambertiana ), based on observations over several years in Crater Lake National Park, Oregon. The harvesting period in late September corresponded to peak cone-opening dates. Nutcrackers placed harvested seeds in their throat pouches, a behavior associated with seed caching.     

Clonal selection drives genetic divergence of metastatic medulloblastoma

Medulloblastoma, the most common malignant paediatric brain tumour, arises in the cerebellum and disseminates through the cerebrospinal fluid in the leptomeningeal space to coat the brain and spinal cord. Dissemination, a marker of poor prognosis, is found in up to 40% of children at diagnosis and in most children at the time of recurrence. Affected children therefore are treated with radiation to the entire developing brain and spinal cord, followed by high-dose chemotherapy, with the ensuing deleterious effects on the developing nervous system. The mechanisms of dissemination through the cerebrospinal fluid are poorly studied, and medulloblastoma metastases have been assumed to be biologically similar to the primary tumour. Here we show that in both mouse and human medulloblastoma, the metastases from an individual are extremely similar to each other but are divergent from the matched primary tumour. Clonal genetic events in the metastases can be demonstrated in a restricted subclone of the primary tumour, suggesting that only rare cells within the primary tumour have the ability to metastasize. Failure to account for the bicompartmental nature of metastatic medulloblastoma could be a major barrier to the development of effective targeted therapies.     

High-affinity NGF binding requires coexpression of the trk proto-oncogene and the low-affinity NGF receptor.

Nerve growth factor (NGF) interacts with two different low-affinity receptors that can be distinguished by affinity crosslinking. Reconstitution experiments by membrane fusion and transient transfection into heterologous cells indicate that high-affinity NGF binding requires coexpression and binding to both the low-affinity NGF receptor and the tyrosine kinase trk gene product. These studies reveal a new growth factor receptor-mediated mechanism of cellular differentiation involving trk and the low-affinity NGF receptor.     

Rauwolfia alkaloids XXVI. Stereochemistry at C-17

Zusammenfassung Bei der Behandlung von 3-epi--Yohimbin mitp-Toluol-sulfochlorid in Pyridin bei 5° wird mit grosser Leichtigkeit und ausgezeichneter Ausbeute ein quaternäres Tosylat erhalten. Dieser Befund, zusammen mit der bekannten sterischen Beziehung zwischen 3-epi--Yohimbin und Deserpidin, stützt die Annahme dertrans-Konfiguration der Substituenten in 16- und 17-Stellung auch im Deserpidin. Ein Vergleich der optischen Drehungen von Reserpinderivaten spricht für analogen räumlichen Bau des Kohlenstoffatoms 17 im Reserpin.     

Initializing K-means Batch Clustering: A Critical Evaluation of Several Techniques

K-means clustering is arguably the most popular technique for partitioning data. Unfortunately, K-means suffers from the well-known problem of locally optimal solutions. Furthermore, the final partition is dependent upon the initial configuration, making the choice of starting partitions all the more important. This paper evaluates 12 procedures proposed in the literature and provides recommendations for best practices.