Purely Translational Realignment in Grid Cell Firing Patterns Following Nonmetric Context Change

Grid cells in entorhinal and parahippocampal cortices contribute to a network, centered on the hippocampal place cell system, that constructs a representation of spatial context for use in navigation and memory. In doing so, they use metric cues such as the distance and direction of nearby boundaries to position and orient their firing field arrays (grids). The present study investigated whether they also use purely nonmetric "context" information such as color and odor of the environment. We found that, indeed, purely nonmetric cues--sufficiently salient to cause changes in place cell firing patterns--can regulate grid positioning; they do so independently of orientation, and thus interact with linear but not directional spatial inputs. Grid cells responded homogeneously to context changes. We suggest that the grid and place cell networks receive context information directly and also from each other; the information is used by place cells to compute the final decision of the spatial system about which context the animal is in, and by grid cells to help inform the system about where the animal is within it.

Weighted cue integration in the rodent head direction system

How the brain combines information from different sensory modalities and of differing reliability is an important and still-unanswered question. Using the head direction (HD) system as a model, we explored the resolution of conflicts between landmarks and background cues. Sensory cue integration models predict averaging of the two cues, whereas attractor models predict capture of the signal by the dominant cue. We found that a visual landmark mostly captured the HD signal at low conflicts: however, there was an increasing propensity for the cells to integrate the cues thereafter. A large conflict presented to naive rats resulted in greater visual cue capture (less integration) than in experienced rats, revealing an effect of experience. We propose that weighted cue integration in HD cells arises from dynamic plasticity of the feed-forward inputs to the network, causing within-trial spatial redistribution of the visual inputs onto the ring. This suggests that an attractor network can implement decision processes about cue reliability using simple architecture and learning rules, thus providing a potential neural substrate for weighted cue integration.

Place field repetition and purely local remapping in a multicompartment environment

Hippocampal place cells support spatial memory using sensory information from the environment and self-motion information to localize their firing fields. Currently, there is disagreement about whether CA1 place cells can use pure self-motion information to disambiguate different compartments in environments containing multiple visually identical compartments. Some studies report that place cells can disambiguate different compartments, while others report that they do not. Furthermore, while numerous studies have examined remapping, there has been little examination of remapping in different subregions of a single environment. Is remapping purely local or do place fields in neighboring, unaffected, regions detect the change? We recorded place cells as rats foraged across a 4-compartment environment and report 3 new findings. First, we find that, unlike studies in which rats foraged in 2 compartments, place fields showed a high degree of spatial repetition with a slight degree of rate-based discrimination. Second, this repetition does not diminish with extended experience. Third, remapping was found to be purely local for both geometric change and contextual change. Our results reveal the limited capacity of the path integrator to drive pattern separation in hippocampal representations, and suggest that doorways may play a privileged role in segmenting the neural representation of space.

Pharmacokinetics of two new oral formulations of ibuprofen

Two new formulations of ibuprofen were studied in 600 mg coated tablets and granules, to allow an easier adjustment of its daily dosage now higher than in the past. Six healthy volunteers (3M and 3F, mean age 32.6 years took part in a 6 X 6 Latin Square single dose pharmacokinetic study comparing six oral formulations of ibuprofen: 600 mg coated tablets, 300, 400 and 600 mg resinated granules, 300 and 400 mg sugar-coated tablets available on the market as Brufen. The results show that there is a correlation between dose and the area under the blood concentration-time curve. The availability of ibuprofen was similar irrespective of whether it is given in the form of granules or in tablets. The short half-life and the widespread use of ibuprofen give an acceptable range of safety to these new formulations.

The determination of ethanol in whole blood by differential pH measurements

The application of a new technique based on the differential measurement of pH between two solutions to determine ethanol concentration in whole blood is reported. The ethanol is determined by measuring the change in pH following its enzymatic oxidation to acetaldehyde. The procedure correlates with the head space gas chromatographic method in the 0-108 mmol/l (0-5 g/l) ethanol whole blood concentration range according to the equation y = 1.344 + 1.013x (r = 0.997).

Precision and accuracy of a radioimmunoassay versus GLC procedure for quantitative determination of morphine compounds in biological materials

The authors, using GLC and RIA, have measured morphine in post-mortem biological material obtained from subjects died for heroin intoxication. Statistical analysis of the two sets of data indicated a high and satisfactory correlation. Recognizing the RIA was a more rapid and simple procedure the authors decide to study the recovery of morphine for various biological materials as determined by RIA. The results demonstrated that the initial concentration of morphine in the various organs did not affect the assay results, but the concentration in assay tubes was important. At concentrations between 10 and 40 ng/ml the recovery was excellent, with no important differences between the organs. It was concluded that the radioimmunological assay can be validly used in forensic medicine to measure morphine in biological materials.

Flash alkylation for the identification of barbiturates in biological material

The gas chromatographic identification of barbiturates isolated from biological material is not optimal, and due to their polar nature, it is difficult to obtain good resolution on most columns. To improve resolution, flash alkylation appeared to be a reasonable alternative. Methyl, ethyl, and butyl derivatives were prepared for various drugs found in the "acid-neutral" extract and the Kovats retention indices (Ir) were determined on SE-30, OV-17, and SP-2250. The Ir of the alkylated derivatives of the barbiturates are highly reproducible. One column and two alkylated derivatives can be used for the qualitative analysis of barbiturates in extracts of biological material, even when the Stas-Otto extract is used.

Use of the retention index in gas chromatographic studies of drugs

In earlier studies, it has been shown that the retention index (Ir) is a very reproducible measure of gas chromatographic mobility. Statistically comparing Ir values obtained here with those found in references has yielded very satisfying results. This will enable the use of Ir values in the screening phase of analysis for general unknowns using the great number of data offered by references; thus limiting the range of inquiry to no more than 6 or 7 drugs, provided that the unknown is between the scheduled ones. An index of analytical behavior that is an absolutely reproducible number will be necessary for computerizing toxicological analysis.

[Use of RIA (radioimmunoassay) technics in the identification of narcotics in biological fluids]

Radioimmunoassay has been compared with extraction thin-layer chromatography and gas-chromatography for the detection of morphine and barbiturate in urine. Radioimmunoassay has been found to be the most sensitive and rapid method and its use in large scale screening and forensic toxicology is considered.