Clustering with neural networks

Partitioning a set ofN patterns in ad-dimensional metric space intoK clusters — in a way that those in a given cluster are more similar to each other than the rest — is a problem of interest in many fields, such as, image analysis, taxonomy, astrophysics, etc. As there are approximatelyK ^N/K! possible ways of partitioning the patterns amongK clusters, finding the best solution is beyond exhaustive search whenN is large. We show that this problem, in spite of its exponential complexity, can be formulated as an optimization problem for which very good, but not necessarily optimal, solutions can be found by using a Hopfield model of neural networks. To obtain a very good solution, the network must start from many randomly selected initial states. The network is simulated on the MPP, a 128 × 128 SIMD array machine, where we use the massive parallelism not only in solving the differential equations that govern the evolution of the network, but also in starting the network from many initial states at once thus obtaining many solutions in one run. We achieve speedups of two to three orders of magnitude over serial implementations and the promise through Analog VLSI implementations of further speedups of three to six orders of magnitude.Supported by a National Research Council-NASA Research Associatship     

Effects of oxytocin and methacholine on cyclic nucleotide levels of rabbit myometrium

The effects of oxytocin and methacholine on cyclic nucleotide levels in estrogen-primed rabbit myometrium were studied in the presence and absence of 1-methyl-3-isobutyl xanthine (MIX), a phosphodiesterase inhibitor. In the absence of MIX, methacholine increased guanosine 3',5'-cyclic monophosphate (cGMP) levels at a time when contraction was decreasing, but had no influence on adenosine 3',5'-cyclic monophosphate (cAMP) levels. In contrast, oxytocin did not elevate cGMP, but rapidly decreased cAMP levels. MIX (1 mM) increased both cAMP and cGMP levels. Oxytocin or methacholine further increased cGMP, indicating activation of guanylate cyclase. Oxytocin- but not methacholine-induced stimulation of guanylate cyclase was abolished in Ca2+-free solution. Oxytocin increased cAMP over the levels produced by MIX alone, whereas methacholine decreased cAMP below the MIX control values; these effects were insensitive to indomethacin. Tissue levels of cGMP and cAMP did not directly correlate with isometric tension. The results also indicate that both oxytocin and methacholine stimulate guanylate cyclase but have opposing effects on adenylate cyclase of rabbit myometrium.     

Cytochemical Ca2+ Distribution in Activated Discoglossus pictus Eggs: A Gradient in the Predetermined Site of Fertilization

The K-pyroantimonate/OsO₄ (PA) cytochemical method coupled with EGTA and X-ray microanalytical controls has been used to localize Ca²⁺ at egg activation in Discoglossus pictus eggs. The results show that: 1) the PA method is able to selectively localize Ca²⁺ pools mobilized by activating stimuli; 2) the smooth endoplasmic reticulum (SER) elements located in the animal dimple region, i.e. in the predetermined site of fertilization, are the first egg components labeled by precipitates; 3) a decreasing gradient of precipitates is present from the center beyond the boundaries of the dimple region; 4) precipitates are lacking in the remainder of the egg even at late times after activation.
The possibilities are discussed that a) SER is the major Ca²⁺-releasing store at activation in Discoglossus , and b) the observed gradient of pyroantimonate-detected Ca²⁺ reflects an ionic Ca²⁺ gradient.     

Cytogenetic findings in 4952 prenatal diagnoses. An Italian collaborative study

Summary The development of prenatal diagnosis in Italy was made difficult by the restrictions of the old abortion law and only in recent years has a consistent number of cases been investigated. We report the experience on prenatal chromosome diagnosis of ten Italian centers participating in a collaborative study on 4952 diagnoses performed from 1972 to 1980. The main indication groups were: advanced maternal age (2882 cases), previous child with chromosome anomaly from parents with normal karyotype (847 cases), and chromosome anomaly in one parent (97 cases). The other indications for amniocentesis, including cases without a cytogenetic risk, have been assembled into a miscellaneous group (1126 cases). We found 125 abnormal fetal karyotypes (2.5%) of which 89 were unbalanced (1.8%). The frequencies and types of chromosome anomalies are reported in detail for each indication group and are compared with the corresponding ones from the European Munich Conference. The great majority of these Italian data were not included in the Munich report.     

Synthesis and enantioselectivity of the enantiomers of PG9 and SM21, new potent analgesic and cognition-enhancing drugs

The enantiomers of two α-tropanyl esters, SM₂₁ (1) and PG₉ (2), derived from (+)-R-hyoscyamine, that act by increasing the central cholinergic tone, were obtained by esterification after resolution of the corresponding racemic acids [(−)-S-1, (−)-R-2 and (+)-S-2] and by stereospecific synthesis [(+)-R-1]. Their analgesic and cognition-enhancing activities were tested in mice and their ACh-releasing properties determined on rat parietal cortex. These compounds show enantioselectivity in analgesic and cognition-enhancing tests on mice, the eutomers being the isomers which possess the same spatial arrangement of the groups on the chiral atom as (+)-R hyoscyamine [(+)-R-SM₂₁, (+)-S-PG₉]. The ACh-releasing effect of the enantiomers of SM₂₁ in rats is in agreement with the results in mice, while PG₉ enantiomers do not show any appreciable enantioselectivity in this test. On the basis of the different effects of the 5-HT₄ antagonist SDZ 205557 on analgesia induced by the enantiomers of 1 and 2 and by (+)-R-hyoscyamine and the α-tropanyl ester of 2-phenylpropionic acid 3, a mechanism of action is proposed for this class of compounds. © 1996 Wiley-Liss, Inc.     

Fatty acid content in wild type and WZSL mutant of Euglena gracilis

The effects of growth conditions on fatty acid profilewere examined in the photosynthetic wild type and inthe spontaneous non-photosynthetic WZSL mutant of theunicellular flagellate Euglena gracilis. Inthe light, the amount of polyunsaturated fatty acids(PUFAs) is higher in the wild type than in the mutant,independent of the carbon source. Among importantPUFAs, linolenic acid (18:3 3) is present inhigh amount only in wild type cells grown in the lightwith any of the tested carbon sources. The content ofother PUFAs, such as arachidonic acid (20:46), EPA (20:5 3) and DHA (22:63), is not correlated with the presence oflight or chloroplasts.The main effect of the dark in both strains is tolower the content of PUFAs and mono-unsaturated fattyacids and to increase the content of saturated fattyacids with all the carbon sources.