We describe a programmable multi-chip VLSI neuronal system that can be used for exploring spike-based information processing models. The system consists of a silicon retina, a PIC microcontroller, and a transceiver chip whose integrate-and-fire neurons are connected in a soft winner-take-all architecture. The circuit on this multi-neuron chip approximates a cortical microcircuit. The neurons can be configured for different computational properties by the virtual connections of a selected set of pixels on the silicon retina. The virtual wiring between the different chips is effected by an event-driven communication protocol that uses asynchronous digital pulses, similar to spikes in a neuronal system. We used the multi-chip spike-based system to synthesize orientation-tuned neurons using both a feedforward model and a feedback model. The performance of our analog hardware spiking model matched the experimental observations and digital simulations of continuous-valued neurons. The multi-chip VLSI system has advantages over computer neuronal models in that it is real-time, and the computational time does not scale with the size of the neuronal network.

Action Potentials↗

PubMedDate not supplied

Antifungal activity of Trillium grandiflorum constituents.

EtOH extracts of the rhizomes and aboveground portion of Trillium grandiflorum showed significant antifungal activity. Bioassay directed fractionation has led to the identification of the active components as the saponin glycosides 1 and 3.

Animals↗

PubMedDate not supplied

Coronary artery motion in electron beam tomography.

PURPOSE: The purpose of this work was to evaluate coronary artery motion characteristics and determine optimal electron beam tomography (EBT) scan time during the cardiac cycle to image the coronary arteries. METHOD: This study evaluated the movement of coronary arteries in 20 EBT cine studies, at rest and during stress, obtained for evaluating coronary artery disease. The proximal, middle, and distal segments of each coronary artery were measured at multiple times during the cardiac cycle. The motion distance (mm) and velocity (mm/s) of each segment of the coronary arteries were then measured to establish the motion that occurs in the x and y axes during different times in the cardiac cycle. RESULTS: Coronary artery velocity ranged from 22.4 to 108.6 mm/s. The least motion (and slowest speed) occurred between 30-50 and 40-60% of the R-R interval at rest and stress, respectively. The right coronary artery moved the greatest in the x and y planes (highest speed and spatial change), followed in decreasing order by the circumflex, left main, and left anterior descending arteries. The phase of the cardiac cycle with the greatest coronary artery motion was between 0 and 20% of the R-R interval. CONCLUSION: Coronary artery motion varies greatly throughout the cardiac cycle. To minimize cardiac motion during tomographic imaging of the coronary arteries, we recommend 40-50% R-R interval as an electrocardiographic trigger time and avoiding the use of image acquisition times of >100 ms.

Adult↗

PubMedDate not supplied

Microcanals of dentin associated with maxillary primary anterior teeth.

PURPOSE: This study was performed to estimate the prevalence of giant dentin tubules or microcanals in primary maxillary anterior teeth. METHODS: One hundred sixty eight extracted or exfoliated primary maxillary anterior teeth were sectioned and examined by optical microscopy and image analysis. Differences in the proportion of teeth with microcanals among tooth types were tested by using the Pearson chi-square test. RESULTS: Microcanals, having the appearance of enlarged dentin tubules, were found in approximately 20% of primary central and lateral incisors, but were significantly less prevalent (3%) in primary cuspids. Microcanals occurred in a mesial distal axial plane and ran between the DEJ and the pulp chamber. When present they numbered between 1 and 43, with mean numbers of 20 and 16 in central and lateral incisors, respectively. The microcanals ranged in size between 5 and 70 microns, compared to normal dentin tubule diameters of approximately 1 micron. CONCLUSIONS: Microcanals are relatively common in primary maxillary incisors, but uncommon in primary cuspids. Additional work is needed to establish their prevalence in various teeth of both primary and permanent dentition.

Chi-Square Distribution↗

PubMedDate not supplied

Sex determination in infants with ambiguous genitalia using the polymerase chain reaction of SRY gene.

It has long been known that testes arise only in the presence of a Y chromosome. The existence of a hypothetical gene, the testis-determining factor (TDF) on the Y chromosome, has therefore been postulated. SRY is the gene located in the sex-determining region of the human Y chromosome and has many of the properties expected for TDF. To evaluate the value of SRY PCR in sex determination, individuals with ambiguous genitalia were selected for study. By identification of the DNA sequence of SRY, a 609-bp fragment of PCR product, sex determination could be successfully made.

Base Sequence↗

PubMedDate not supplied

Molecular diagnosis of Gaucher disease type II.

Gaucher disease is a rare autosomal recessive lysosomal storage disorder in Chinese. A mutation at nucleotide 1448C (T-to-C) of the glucocerebrosidase gene is described in type 2 Gaucher disease. This mutation creates a Bcn I site in a polymerase chain reaction (PCR) amplified fragment. This technique was applied to a Chinese infant with type 2 Gaucher disease, and homozygosity for 1448C mutation was proved. This new finding can make prenatal diagnosis and carrier detection possible in Chinese population with type 2 Gaucher disease.

Base Sequence↗

PubMedDate not supplied

Sex determination in infants with ambiguous genitalia using the polymerase chain reaction of an X-Y homologous region.

A polymerase chain reaction (PCR) technique applicable for sex identification is described. The technique amplifies a part of the X-Y homologous amelogenin gene in which the Y counterpart has a 189 bp deletion within one of the introns. To evaluate the value of PCR of a X-Y homologous region in sex determination, individuals with ambiguous genitalia were selected for study. By identification of the X and Y sequences based on the difference in their sizes, sex determination could be successfully made.

Base Sequence↗