L-Quisqualic acid transport into hippocampal neurons by a cystine-sensitive carrier is required for the induction of quisqualate sensitization

A brief exposure of hippocampal slices to L-quisqualic acid sensitizes CA1 pyramidal neurons 30-250-fold to depolarization by two classes of excitatory amino acid analogues: (1) those whose depolarizing effects are rapidly terminated following washout, e.g. L-2-amino-4-phosphonobutanoic acid (L-AP4) and L-2-amino-6-phosphonohexanoic acid (L-AP6) and (2) those whose depolarizing effects persist following washout, e.g. L-aspartate-beta-hydroxamate (L-AbetaH). This process has been termed quisqualate sensitization. In this study we directly examine the role of amino acid transport systems in the induction of quisqualate sensitization. We report that L-quisqualate is a low-affinity substrate (K(M)=0.54 mM) for a high capacity (V(max)=0.9 nmol (mg protein)(-1) min(-1)) Na(+)-dependent transport system(s) and a high-affinity substrate (K(M)=0.033 mM) for a low-capacity (V(max)=0.051 nmol (mg protein)(-1) min(-1)) transporter with properties similar to the cystine/glutamate exchange carrier, System x(c-). We present evidence that suggests that System x(c-) participates in quisqualate sensitization. First, simultaneous application of L-quisqualate and inhibitors of System x(c-), but not inhibitors of Na(+)-dependent glutamate transporters, prevents the subsequent sensitization of hippocampal neurons to phosphonates or L-AbetaH. Second, L-quisqualic acid only sensitizes hippocampal neurons to other substrates of System x(c-), including cystine. Third, immunocytochemical analysis of L-quisqualate uptake demonstrates that only inhibitors of System x(c-) inhibit the highly concentrative uptake of L-quisqualate into a widely dispersed group of GABAergic hippocampal interneurons. We conclude that quisqualate sensitization is a direct consequence of the unique interaction of various excitatory amino acids, namely L-quisqualate, cystine, and phosphonates, with the exchange carrier, System x(c-). Therefore, the results of this study have important implications for the mechanism by which L-quisqualate, and other substrates of this transporter which are also excitatory amino acid agonists (such as glutamate and beta-N-oxalyl-L-alpha,beta-diaminopropionic acid, beta-L-ODAP) may trigger neurotoxicity.

The Objective Structured Clinical Examination (OSCE) in the clinical clerkship: an overview

The Objective Structured Clinical Examination (OSCE) for student assessment is well established, with an extensive body of research documenting that this is a valid means to assess clinical skills that are fundamental to the practice of medicine. The OSCE consists of a circuit of stations which tests a range of skills and learning to assess undergraduate medical students. A well-constructed OSCE provides important information about candidate performance and the quality of training. It is used at the University of South Dakota School of Medicine (USDSM) in assessment of third year medical students during their Obstetrics Clerkship, and as a teaching tool in the Pediatric Clerkship. On August 10, 1996, the USDSM administered an OSCE for the first time to third year medical students. The purpose of this article is to present state of the art information about setting up OSCE based on our recent experience and to provide practical examples of OSCE questions which can be addressed in the clinical setting. The narrative, references and examples give guidelines for the preparation of OSCE testing. The OSCE provided a standardized way of assessing clinical competence. Both students and faculty were very satisfied with the examination, and felt that the material tested was relevant and appropriate. The OSCE process does serve to identify areas of weakness in the curriculum and/or teaching methods, and thus can serve as a mechanism to improve educational effectiveness.

Intra-amniotic prostaglandin F2alpha and urea for midtrimester abortion

Intra-amniotic prostaglandin F2alpha, in doses of 2.5 to 20 mg, combined with 80 gm of urea, was an effective, safe, simple, and economical midtrimester abortifacient in 115 patients. The mean abortal time, 15.8 hours, was significantly less than that in prior series in which intra-amniotic hypertonic saline or urea was administered together with constant, intravenous oxytocin infusion. The use of intracervical laminaria tents did not shorten the abortal time. Only eight patients had not aborted within 30 hours; only two had not aborted within 36 hours; and only six received a second intra-amniotic injection. Operative removal of the placenta, when necessary, was accomplished under intravenous sedation in a treatment room. The incidence of infection, nausea, vomiting, and other complications was low.