Large-scale DNA-based typing of HLA-A and HLA-B at low resolution is highly accurate specific and reliable.

DNA-based typing of HLA class I alleles of the HLA-A and HLA-B loci using sequence-specific oligonucleotide primers and/or probes has been used for the large-scale typing of individuals for the National Marrow Donor Program unrelated donor registry. Typing was performed by 16 laboratories at a low level of resolution (e.g. A*01, B*07). The results of blinded quality control analysis for the first 12 months of the project show the typing to be highly accurate, specific and reliable. The total error rate based on 11,545 HLA-A and 11,428 HLA-B assignments was 1.1% for HLA-A and 1.9% for HLA-B. This level of accuracy is particularly remarkable because the quality control samples could not be distinguished from 64,180 donor samples tested at the same time by the laboratories.

A comparison of visual- and response-generated cues in a spatial DMTS task for rats.

In an attempt to clarify the nature of the memory cues used in a spatial, working memory task, rats were tested in a two-choice water maze. Each trial consisted of an information run, which forced the rat to the correct choice compartment, a retention period, and a test run. A response-associated cue condition, in which the relevant cue was the direction of the turn in the information run, was compared to a visual cue condition in which the animal had to remember whether the escape platform had been in the light or dark compartment. Of the subjects supplied with either visual or response-associated cues, the subjects allowed to employ response-associated cues did better, but the best performance occurred when both cues were available. When rats trained with both cues present were forced to choose between cues, they stopped using either and reverted to making a preferred right or left turn. The results support the idea that rats can form integrated, relational-cue memories which, in some circumstances, prove a hindrance to performance.

Scopolamine- and morphine-induced deficits in water maze alternation: failure to attenuate with glucose.

Glucose has previously been shown to improve performance on memory tasks and to ameliorate performance deficits induced by scopolamine or morphine. To test the generality of these observations, Sprague-Dawley rats were trained to alternate choices to reach an escape platform in a two-choice circular water maze. The rats attained a high level of alternation, alternating on a mean of 9 of 10 daily trials. Daily glucose injections (100 and 250 mg/ kg) failed to facilitate acquisition of the alternation. Single injections of scopolamine (0.5, 1.0, and 2.0 mg/kg), but not methylscopolamine (0.5 mg/kg), and daily injections of scopolamine (0.5 mg/kg) or morphine (5.0 mg/kg) impaired alternation performance. The scopolamine- and morphine-induced deficits in alternation behavior were not ameliorated by pretrial glucose injections at doses which have previously been found to be effective (100 and 250 mg/kg). The mechanism of glucose facilitation of memory is currently unknown. The present results show that glucose given at previously established effective doses does not activate the mechanism or produces too weak an effect to be observed in water maze alternation.

Individual aged rats are impaired on repeated reversal due to loss of different behavioral patterns.

Aged rodents compared to young rodents are impaired in making repeated reversals and more variable in performance on many tasks. In the present study, a comparison of ten aged (21 months) and 10 young (3 months) Sprague-Dawley rats on a repeated spatial discrimination reversal water escape task revealed that the deficient and variable performance of the aged rats was due to the aged animals developing deficits in different behavioral patterns that were necessary to perform the task. Individual aged rats had deficits in inhibiting an unlearned first choice tendency (perseveration), repeating a first choice that lead to escape on the preceding trial (win-stay deficit) or inhibiting a first choice that lead to confinement and delayed escape on the preceding trial (lose-shift deficit). Because the aged animals were deficient on one or more of the necessary behavioral processes, as a group they were deficient on the repeated reversal task. However, because the aged rats differed on the specific behavioral process(es) on which they were deficient, when evaluated on any one process they were more variable than were the younger rats.

The acetylene-ethylene assay for n(2) fixation: laboratory and field evaluation.

The methodology, characteristics and application of the sensitive C(2)H(2)-C(2)H(4) assay for N(2) fixation by nitrogenase preparations and bacterial cultures in the laboratory and by legumes and free-living bacteria in situ is presented in this comprehensive report. This assay is based on the N(2)ase-catalyzed reduction of C(2)H(2) to C(2)H(4), gas chromatographic isolation of C(2)H(2) and C(2)H(4), and quantitative measurement with a H(2)-flame analyzer. As little as 1 mumumole C(2)H(4) can be detected, providing a sensitivity 10(3)-fold greater than is possible with (15)N analysis.A simple, rapid and effective procedure utilizing syringe-type assay chambers is described for the analysis of C(2)H(2)-reducing activity in the field. Applications to field samples included an evaluation of N(2) fixation by commercially grown soybeans based on over 2000 analyses made during the course of the growing season. Assay values reflected the degree of nodulation of soybean plants and indicated a calculated seasonal N(2) fixation rate of 30 to 33 kg N(2) fixed per acre, in good agreement with literature estimates based on Kjeldahl analyses. The assay was successfully applied to measurements of N(2) fixation by other symbionts and by free living soil microorganisms, and was also used to assess the effects of light and temperature on the N(2) fixing activity of soybeans. The validity of measuring N(2) fixation in terms of C(2)H(2) reduction was established through extensive comparisons of these activities using defined systems, including purified N(2)ase preparations and pure cultures of N(2)-fixing bacteria.With this assay it now becomes possible and practicable to conduct comprehensive surveys of N(2) fixation, to make detailed comparisons among different N(2)-fixing symbionts, and to rapidly evaluate the effects of cultural practices and environmental factors on N(2) fixation. The knowledge obtained through extensive application of this assay should provide the basis for efforts leading to the maximum agricultural exploitation of the N(2) fixation reaction.