On bipolar cell responses in the teleost retina are generated by two distinct mechanisms.

1. ON Bipolar cells were recorded in slices obtained from hybrid bass retinas. Cells were identified as bipolar cells by position in the slice, by characteristic voltage- and ligand-gated currents, and by filling with the fluorescent dye Lucifer yellow. Cells were recorded with the use of either whole cell or perforated-patch techniques. Standard electrophysiological protocols were used. Drugs were applied by puffing and by local superfusion. 2. Application of exogenous glutamate to ON bipolar cells generated two characteristic responses. One effect of glutamate was to open a conductance with a reversal potential close to the chloride equilibrium potential. The other effect of glutamate was to close a conductance with a reversal potential near 0 mV. These two effects of glutamate on ON bipolar cells match the effects of light described previously with the use of intracellular recordings. Thus the effects of glutamate that we report here appear to underlie the rod and cone inputs to these cells. 3. Many of the ON bipolar cells recorded demonstrated both classes of responses to glutamate. To isolate the two responses, 500 microM glutamate was first applied, and then glutamate in the presence of 5 microM 2-amino-4-phosphonobutyric acid (APB). APB specifically blocks the effects of glutamate on the putative roddriven glutamate receptor (the glutamate-elicited conductance decrease), allowing us to study in isolation the effects of glutamate on the cone component, the glutamate-activated chloride current (IGlu). 4. By isolating IGlu as described above, and taking advantage of the fact that amphotericin-perforated-patch recordings limit the diffusion of chloride ions between the patch pipette and the cell body, we found the physiological reversal potential of IGlu to be -58.9 +/- 7.7 (SD) mV. 5. Both the putative rod- and cone-mediated glutamatergic inputs to these bipolar cells could be activated by driving the photoreceptors with puffs of potassium. The currents recorded with this technique were very similar to those seen with direct application of glutamate.

Outcome of AIDS patients requiring mechanical ventilation predicted by recursive partitioning.

Mechanical ventilatory support (VS) is often required for patients with AIDS. Patients, and/or their surrogates often ask the likely outcome of this intervention. To answer this question, we have developed a classification tree using clinical data from 71 patients with AIDS identified from the discharge abstracts of two hospitals between January 1990 and September 1994. These data were obtained at the time of hospital admission prior to any treatment and before VS was initiated. Survival was defined as discharge from the hospital that occurred in 13 of 72 admissions reviewed. A classification tree was developed by binary recursive partitioning. The output of the resulting tree was adjusted to produce a positive predictive value for death of 100% (95% confidence interval [95% CI], 94 to 100%) and a sensitivity and specificity of 98% (95% CI, 91 to 100%) and 100% (95% CI, 74 to 100%), respectively. The negative predictive value was 92% (95% CI, 64 to 100%). The tree predicted that patients with lactate dehydrogenase (LDH) levels less than 1,176 IU/L survived until hospital discharge, unless they had a positive blood culture, active tuberculosis prior to VS, a blood CD4 count less than 12 cells per cubic millimeter, or creatinine and hemoglobin values that were either above 2.4 mg/dL or less than 8.5 mg/dL, respectively. The remainder of the patients with an LDH level above 1,176 IU/L in this study died before hospital discharge. The classification tree requires prospective validation before it can be used as a predictive instrument. Nevertheless, this approach can be used to develop a concise summary of the local outcome experience of this circumstance in a manner that could be conveyed to patients and/or their surrogates.

A glutamate-elicited chloride current with transporter-like properties in rod photoreceptors of the tiger salamander.

Glutamate, when puffed near the synaptic terminals, elicits a current in rod photoreceptors. The current is strongly dependent upon both the intracellular and extracellular chloride concentration: its reversal potential follows the predicted Nernst potential for a chloride permeable channel. The glutamate-elicited current also requires the presence of extracellular sodium. This glutamate-elicited current is pharmacologically like a glutamate transporter: it is elicited, in order of efficacy, by L-glutamate, L-aspartate, L-cysteate, D-aspartate, and D-glutamate, all shown to activate glutamate transport in other systems. Furthermore, it is reduced by the glutamate transport antagonists dihydrokainate (DHKA) and D,L-threo-3-hydroxyaspartate (THA). THA, when applied alone, elicits a current similar to that elicited by glutamate. The current cannot be activated by the glutamate receptor agonists kainate, quisqualate, NMDA and APB, nor can it be blocked by the glutamate receptor antagonists CNQX and APV. Thus, the current does not appear to be mediated by a conventional glutamate receptor. Taken together, the ionic dependence and pharmacology of this current suggest that it is generated by glutamate transporter coupled to a chloride channel.

Glutamate-gated chloride channel with glutamate-transporter-like properties in cone photoreceptors of the tiger salamander.

1. Using the patch-clamp technique, we investigated whether the glutamate-elicited current in mechanically isolated cone photoreceptors from the salamander retina is generated by a Cl- channel or a glutamate transporter. 2. The current reversed near the equilibrium potential for Cl-, was decreased by three Cl- channel blockers, 5-nitro-2-(3-phenyl-propylamino) benzoic acid, 4,4'-diisothiocyanostilbene-2,2'-disulfonate, and diphenylamine 2,2'-dicarboxylic acid, and was eliminated when gluconate was substituted for both internal and external Cl-, features consistent with the current being mediated by a Cl- channel. 3. The single-channel conductance of the Cl- channel was estimated by noise analysis of the glutamate-elicited current fluctuations to be 0.7 pS with an open time of 2 ms. 4. The magnitude of the current was dependent on both internal and external Na+ and K+, features consistent with the current being related to the activation of a glutamate transporter. Yet changes in their concentrations did not affect the reversal potential of the current. 5. Taken together with earlier reports on this current showing that it has a glutamate-transporter-like pharmacology, our results suggest that the glutamate-elicited current is carried by a Cl- channel but gated by a glutamate receptor whose pharmacology and ionic requirement resemble those previously described for glutamate transporters.

A glutamate-activated chloride current in cone-driven ON bipolar cells of the white perch retina.

Cone-driven ON-type bipolar cells were patch clamped in white perch retinal slices. Application of glutamate activated a current (IGlu) that was mediated by a conductance increase. The reversal potential for IGlu followed ECl closely when the intracellular chloride concentration was varied. IGlu was not blocked by 100 microM picrotoxin or 1 microM strychnine, indicating that it was not caused by inhibitory input. IGlu is not mediated by a typical ionotropic glutamate receptor since it was not activated by kainate, AMPA, or NMDA, or blocked by kynurenic acid, CNQX, DNQX, or AP-V. Further, IGlu is not mediated by a known metabotropic glutamate receptor since it was not activated by quisqualic acid, AP-4, ACPD, or ibotenate. IGlu required the presence of extracellular sodium and could be partially inhibited by the glutamate uptake inhibitors THA and tPDC. This is suggestive of sodium-dependent glutamate transport. However, when intracellular sodium was greatly increased, neither the magnitude nor reversal potential of IGlu was substantively affected. Thus, IGlu appears to involve a chloride channel activated by a glutamate receptor with transporter-like pharmacology. IGlu is localized to the dendrites of the bipolar cell, where bipolar cells receive an endogenous glutamatergic input from photoreceptors. Further, the reversal potential of the light response in these cells is the same as that of IGlu. Thus, it seems likely that IGlu is the current responsible for the cone component of the ON bipolar cell light response in the teleost retina.

Low-cost data acquisition and analysis programs for electrophysiology.

In the laboratory, powerful personal computers are invaluable tools for data acquisition and analysis. The commercially available software for these purposes is often very expensive and does not always conform to the experimenter's needs. In our laboratory, we have developed two programs for acquisition and analysis of electrophysiological data from retinal neurons, although they can be used for many other types of data acquisition and analysis as well. These programs were written for IBM PC-compatible computer systems and are being distributed as shareware. Thus they are available for users to try out free of charge; if they are found to be of use, they can be purchased for a minimal cost. PATCHIT, the data-acquisition program can use one of several popular data-acquisition boards to simultaneously stimulate and record from an experimental preparation. TACK, the data analysis program was developed to analyze data recorded by PATCHIT and other data-acquisition programs. PATCHIT and TACK are powerful programs which are competitive with similar commercially available programs, but are sold at a much lower cost. Details on the development and operation of these programs are presented in this paper.

Identifying anterior segment crystals.

A series of 22 patients with crystals in the anterior segment of the eye was examined by specular microscopy. Of 10 patients with hypermature cataract and hyperrefringent bodies in the anterior chamber cholesterol crystals were identified in four patients and in six of the 10 in whom aspirate was obtained cholesterol crystals were demonstrated in three, two of these having shown crystals on specular microscopy. In 10 patients with intracorneal crystalline deposits, cholesterol crystals were found on specular microscopy, including one case of Schnyder's crystalline corneal dystrophy. Of two patients with multiple myeloma, corneal crystals were demonstrated in one. Crystals of the anterior segment of the eye are most likely to be cholesterol, and identification is important for future treatment.

The identification of corneal guttae.

The deposits of cornea guttata, which often precede Fuchs' endothelial dystrophy, represent a risk factor in patients undergoing intraocular surgery, rendering a cornea unsuitable for use as donor material. These corneal guttae clinically resemble subendothelial blebs that accompany various corneal and anterior segment inflammatory conditions so that confusion between the two groups is possible. In differentiating the two groups it is noted that (a) guttae are more elevated and usually appear in the relief mode; (b) the endothelial mosaic, if present, is usually relatively normal around the guttae; (c) both guttae and blebs may be contiguous and even confluent; (d) guttae are more regular and endothelial cells are often arranged regularly around them; (e) although small guttae may occur, if guttae are at all numerous, large ones are also usually present; and (f) inflammatory cells are rarely present in the relief mode with guttae but are always present with blebs associated with uveitis.

Bullous keratopathy due to nonguttate corneal endothelial dystrophy.

Corneal oedema and bullous keratopathy may occur following intraocular surgery or arise spontaneously in nonguttate eyes. In some patients the fellow eye shows a relatively normal endothelial cell count with abnormal pleomorphism and polymegathism of the endothelial cells, while in others it shows a markedly lowered endothelial cell count with no evidence of corneal guttae. A survey of 17 such patients suggested the following classification. 1. Nonguttate corneal endothelial dystrophy with irregular endothelial cell morphology but a relatively normal endothelial cell count occurring following surgery (eight patients) or spontaneously (four patients). 2. Nonguttate corneal endothelial dystrophy with grossly reduced endothelial cell count occurring spontaneously (two patients). Three additional post-surgical patients showed a relatively normal endothelial cell count and only mild changes in the morphology of the corneal endothelium. These findings support the presence of a nonguttate corneal endothelial dystrophy in both the spontaneous and some of the post-surgical cases.

Can rational prescribing be assessed?

The prescribing of a group of young general practitioners was assessed, before and after educational intervention, using five parameters of rational prescribing. The proportion of drugs prescribed by their generic name, and the proportion falling within a basic formulary for general practice increased significantly even though the participating doctors had neither been involved in the compilation of the formulary nor been given a copy of it. Items prescribed bygeneric name rose from 45 to 74% and the proportions of new and repeat items within the formulary rose by 73 to 83% and 68 to 77% respectively. It appears that discussions about rational prescribing lead to similar changes in prescribing as involvement in the compilation of a formulary.The notion of an ;essential drugs list' for general practice is described, and three easily applied measures of rational prescribing are suggested: (1) the proportion of patients not given a prescription, (2) the proportion of drugs written in their generic form and (3) the proportion of drugs falling within a general practice ;essential drugs list'.

Repeat prescribing: a study prior to the imposition of the limited list.

A diverse group of general practitioners from separate practices kept a record of their repeat prescriptions for a week in March 1985, just prior to the imposition of the Government's limited list of drugs which could be prescribed on the National Health Service. Up to one-fifth of repeat prescriptions needed to be altered to comply with the eventual list. An unexpected finding was the wide differences among the doctors in the proportion of repeat prescriptions that were written as the approved generic names. While the anxieties about generic prescribing have yet to be resolved, the problems of converting repeat prescriptions into generic names requires not only a change in doctors' behaviour, but also clear explanation to reception staff and patients. Such a change could produce considerable financial savings, and might be more effective in this than further imposed restrictions.

Development of a limited formulary for general practice.

Over a period of 1 year, a diverse group of general practitioners from separate practices constructed a limited formulary for general practice. The formulary contains 137 drugs and is intended to provide adequate and appropriate treatment for 90% of general practice patients. The study provides a model for development of agreed local formularies which do not infringe clinical freedom and offer an alternative to imposed limited lists as a means of reducing the cost of prescriptions. Development of such a list can be an enjoyable and dynamic educational exercise and can lead to more rational and safer prescribing.