Autosomal dominant pseudoxanthoma elasticum

Two families are described, each with a unique clinical variant of pseudoxanthoma elasticum (PXE) inherited in autosomal dominant fashion. Dominant type I PXE is characterized by a classical flexurally distributed rash, severe and frequent angina of effort, intermittent claudication and hypertension, and a very severe choroidoretinitis, often complicated by blindness. Dominant type II PXE, on the other hand, is a much milder form of the disease, with a macular rash (though identical histological changes), no vascular changes, and a very mild retinal degeneration, which does not progress to either blindness or choroidoretinitis. Younger members of these families often have prominent choroidal vessels. Formal analysis of the two pedigrees and all the pooled genetic data supported the autosomal dominant transmission of both these traits.     

Affective spectrum disorder: does antidepressant response identify a family of disorders with a common pathophysiology?

Response to pharmacologic treatments may identify groups of disorders with a common pathophysiology. The authors applied a treatment-response model, based on four classes of antidepressants (tricyclic types, monoamine oxidase inhibitors, serotonin uptake inhibitors, and atypical agents), to the medical literature. The model identified eight disorders that may share a pathophysiologic abnormality: major depression, bulimia, panic disorder, obsessive-compulsive disorder, attention deficit disorder with hyperactivity, cataplexy, migraine, and irritable bowel syndrome. Phenomenologic and family studies support this grouping. If the model is validated, this family of disorders, which the authors term "affective spectrum disorder," would represent one of the most prevalent diseases in the population.     

Age-related differences in sensitivity to organophosphorus pesticides

Organophosphorus (OP) pesticides are used extensively throughout the world to control undesirable pest species. The primary mechanism of action for OP insecticides is inhibition of acetylcholinesterase (AChE), an enzyme dynamically involved in cholinergic neurotransmission. Extensive inhibition of AChE leads to accumulation of acetylcholine in the synapse, disruption of normal impulse flow and subsequent signs of toxicity, including autonomic dysfunction, involuntary movements, muscle fasciculations and a host of others. It is generally believed that young individuals are more sensitive to the neurotoxic effects of these agents relative to adults. Essentially all studies addressing age-related differences in sensitivity to these toxicants have examined responses to acute exposures, however, using acute toxicity (lethality) as the endpoint. As the biochemical mechanism of toxicity for this class of toxicants (inhibition of AChE) is well known and considering that low level, repeated exposures are of great concern to the general public, we propose that evidence of neurochemical alterations, especially when exposures occur during development and maturation, is a more relevant endpoint of toxicity than lethality for estimating susceptibility. This report briefly summarizes previous and ongoing work in our laboratory which examines the relative sensitivity to these toxicants between young and adult rats.     

Orientation and luminance polarity tuning of the transient-vergence system.

Previously, Edwards, Pope & Schoor, Vision Research, 38, 705-717, demonstrated that transient disparity vergence appears to be mediated by a system that employs a single low-pass sensitive spatial channel whose performance is not reduced by dichoptic mixed contrasts (no contrast paradox) or dichoptic mixed spatial frequencies. This broadband tuning to both contrast and spatial frequency may be indicative of a second-order or non-linear envelope extraction system. The current study tests for lack of tuning to orientation and luminance polarity which are typically taken as evidence of a second-order system. We found that when the transient vergence system was simultaneously presented with both convergent and divergent disparities, there was a small but distinct bias in favor of responding in the direction defined by matched orientations or luminance polarities over unmatched pairs. Although less frequent, responses to orthogonal carriers or opposite luminance polarities were possible. The vergence system could match a horizontal with a vertical carrier, or a light gaussian with a dark gaussian. The degree of orientation or luminance polarity tuning varied inversely with the disparity magnitude over the range of 2.5-5 degrees, and the orientation tuning peaked at a spatial frequency about 2 cpd. At all disparities tested, however, the tuning was very broad, and other candidate features for mediating transient-vergence need to be investigated.