Epithelial polarity and cell separation in the neoplastic l(1)dlg-1 mutant of Drosophila.

Lethal (1) discs-large-1 [l(1)dlg-1] is a non-epithelial overgrowth or neoplastic mutant of Drosophila, which results in tumor-like imaginal discs and enlarged larvae that never pupariate. In an ultrastructural analysis we found that the wing discs develop convoluted monolayers of epithelial cells characterized by well-defined apical-basal polarity and that these layered cells secrete large amounts of basement membrane material. Immuno-EM indicates that Drosophila laminin and collagen are components of this matrix.

Reduction of conductance-based neuron models.

We present a scheme for systematically reducing the number of differential equations required for biophysically realistic neuron models. The techniques are general, are designed to be applicable to a large set of such models and retain in the reduced system as high a degree of fidelity to the original system as possible. As examples, we provide reductions of the Hodgkin-Huxley system and the A-current model of Connor et al.

Development of the paramedian lobule of the cerebellum in wild-type and tottering mice.

The mutant mouse tottering, (tg/tg), and the compound heterozygote mouse (tg/tg1a) exhibit three neurological disorders: ataxia, petit mal-like absence seizures and myoclonic intermittent movement disorders which are independent of the absence seizures. The tottering mouse carries an autosomal recessive single gene mutation on chromosome 8, and behavioral symptoms are first observed in the 3rd to 4th week of age. Using an additional genetic marker, Oligosyndactyly (Os), it is possible to distinguish tg/tg and tg/tg1a mice from wild-type mice at birth; nonaffected heterozygous littermates carry the Os mutation while tottering and compound heterozygous mice do not carry the Os gene.

Increased methionine-enkephalin levels in genetically epileptic (tg/tg) mice.

Recent experimental data indicate that endogenous brain ligands for the opioid receptors such as enkephalins, beta-endorphin (beta-End) and dynorphin (Dyn) may be involved in both generalized and partial seizures. The "tottering" (tg/tg) mouse provides an electrophysiological representation of generalized spontaneous human epilepsy. These mice exhibit behavioral absence seizures with accompanying spike-wave discharges.

Quality assessment/assurance activities in U.S. dental schools.

Quality of health care services has become a major social issue. Accordingly, activities directed toward the assessment and assurance of quality are receiving increased attention in dentistry and dental education. The purpose of this study was to determine the status of quality assessment/assurance (QA) programs in U.

Light harmony of crowns and roots: understanding and managing the black line phenomenon.

Today's patients and clinicians have high expectations for aesthetic excellence. In order to deliver excellence, dental health care providers must be more aware of the complexity of nature, particularly when the anterior segments of natural dentition are involved. This article addresses the relationship of soft tissues, crowns, and roots and their relationship to light transmission and perception.

Oscillating Networks: Control of Burst Duration by Electrically Coupled Neurons.

The pyloric network of the stomatogastric ganglion in crustacea is a central pattern generator that can produce the same basic rhythm over a wide frequency range. Three electrically coupled neurons, the anterior burster (AB) neuron and two pyloric dilator (PD) neurons, act as a pacemaker unit for the pyloric network. The functional characteristics of the pacemaker network are the result of electrical coupling between neurons with quite different intrinsic properties, each contributing a basic feature to the complete circuit.

The path integral for dendritic trees.

We construct the path integral for determining the potential on any dendritic tree described by a linear cable equation. This is done by generalizing Brownian motion from a line to a tree. We also construct the path integral for dendritic structures with spatially-varying and/or time-dependent membrane conductivities due, for example, to synaptic inputs.

Changes in mesenchymal cell-shape, matrix collagen and tenascin accompany bud formation in the early chick lung.

In the chick, lung branches arise as buds from the center of the pre-existing mesobronchial tube. Budding is known to be controlled by the mesenchyme. We have investigated mesenchymal properties in budding vs non-budding regions of the early chick lung, including sources of mesenchyme, cell shapes and densities, morphology and composition of the basement membrane, and distribution of the ECM components collagen, fibronectin and tenascin.

Modulation of function and gated learning in a network memory.

Memory and learning are studied in a model neural network made from component cells with a variety of realistic intrinsic dynamic behaviors. Modulation of intrinsic cellular characteristics causes a network to switch between two entirely different modes of operation. In one mode the network acts as a selective, long-term associative memory, whereas in the other it is a nonselective, short-term latching memory.

Glutathione levels in specific brain regions of genetically epileptic (tg/tg) mice.

The tottering (tg/tg) mouse is a genetic model of human generalized epilepsy; these mice exhibit spontaneous absence seizures accompanied by bilaterally synchronous spike-wave discharges (6). The mechanism(s) for seizure activity are unknown in these mice. Several recent studies have suggested that membrane lipid peroxidation may be causally involved in some forms of experimentally induced epilepsies (18).

Components of positional information in the developing wing margin of the Lyra mutant of Drosophila.

A number of parameters characteristic of the wing margin precursor in imaginal discs of Drosophila are known: the zone of non-proliferating cells or ZNC (O'Brochta and Bryant 1985), aldehyde oxidase (AO) and other enzyme staining patterns (Sprey et al. 1982), E1C antigen localization in a narrow band along the margin (Piovant and Lena 1988). To test our hypothesis that such parameters, and others, act in concert to determine margin identity and the positional information that specifies the bristles and hairs appropriate to the anterior, posterior and distal margins, we have examined these parameters in the dominant mutant Lyra, in which much of the anterior and posterior margins is missing.

The effect of electrical coupling on the frequency of model neuronal oscillators.

Neurons with oscillatory properties are a common feature of the nervous system, but little is known about how neural oscillators shape the behavior of neuronal networks or how network interactions influence the properties of neural oscillators. Mathematical models are used to examine the effect of electrically coupling an oscillatory neuron to a second neuron that is either silent or tonically firing. Models of oscillatory neurons with varying degrees of complexity show that this coupling can either increase or decrease the frequency of an oscillator, depending on its membrane potential wave form, the state of the neuron to which it is coupled, and the strength of the coupling.

Quantitative re-evaluation of descending serotonergic and non-serotonergic projections from the medulla of the rodent: evidence for extensive co-existence of serotonin and peptides in the same spinally projecting neurons, but not from the nucleus raphe magnus.

A quantitative analysis of serotonin (5-HT) and spinally-projecting neurons was re-evaluated in the rodent. The findings indicate that most (nearly 90%) of the medullary 5-HT neurons projected to the lumbar spinal cord, and most (up to 85%) of the spinally projecting neurons within the distribution of the serotonergic neurons contained 5-HT immunoreactivity. However, in nucleus raphe magnus (NRM) only about two-thirds of the projection cells were 5-HT immunoreactive.

Somatodendritic release of endogenous dopamine: in vivo dialysis in the A10 dopamine region.

Using in vivo dialysis in the A10 region of the anesthetized rat, somatodendritic release of endogenous dopamine was demonstrated. Although endogenous dopamine release from the A10 region was enhanced by amphetamine pretreatment in a dose-related manner, the amount of dopamine released was markedly less than the axonal release of dopamine measured simultaneously in the nucleus accumbens.

Evaluating the anti-plaque capabilities of a copper-containing prophylaxis paste.

The purpose of this study was to evaluate a dental prophylaxis paste containing mono-copper citrate (MCC) for short term anti-plaque capabilities. In addition to other baseline data, plaque scores were recorded on 36 paid volunteer subjects from the dental school student, staff, and faculty populations. After scaling, two quadrants of each subject's dentition were polished with the MCC containing paste and two quadrants with the placebo paste, using a diagonal split mouth double blind design.

The fetal hydantoin syndrome: answers from a mouse model.

In spite of a large body of literature suggesting that prenatal exposure to hydantoin anticonvulsant drugs can be teratogenic in humans, resulting in offspring with congenital malformations, the wide phenotypic variability of this syndrome has led many clinicians to question its very existence. Because solutions to major teratologic questions may be impossible to find within the constraints of human clinical or epidemiologic investigations, we have developed an animal model for the fetal hydantoin syndrome. With this model, we have been able to demonstrate the dose-related teratogenic effects of phenytoin on mouse development and the positive correlation between increasing maternal plasma phenytoin concentrations and the risk for congenital anomalies among offspring.

The origins and trajectories of somatostatin reticulospinal neurons: a potential neurotransmitter candidate of the dorsal reticulospinal pathway.

Somatostatin (SOMA)-immunoreactive neurons present in the nucleus gigantocellularis and nucleus raphe magnus formed the origins of a descending pathway from the rostral medulla to the spinal cord. This descending pathway was traced through the central medullary tegmentum and dorsolateral funiculus to innervate the dorsal horn. The location, trajectories and presumed inhibitory nature of SOMA in the spinal cord suggest that SOMA maybe a potential neurotransmitter candidate for the classic dorsal reticulospinal pathway.

A model of autocatalytic replication.

The catalytic effects that existing polymer chains have on the formation of new chains are modeled using ideas from spin glasses and neural networks. Computer simulation shows that isolated groups of chains in this model are capable of accurately replicating a wide variety of complex structures without templating. Replication in the model arises spontaneously and rapidly, leading to an extremely simple realization of a system exhibiting Darwinian evolution.