Effects of direct electric fields,noise, sex and age on maze learning in rats

Equal numbers of male and female rats of the King-Holtzman hybrid breed, divided into two age groups (group A₁: 21–30 days old and group A₂: 90–100 days old), were exposed to two levels of noise: N₀ = 30 db and N₁ = 90 db, (ref. 0.002µbar), and three levels of direct electric field intensities: E₀ = electric field strength of zero; E₁ = 1,600 v/m; and E₂ = 16,000 v/m. Time and error scores of 240 rats running a modified Lashley left-right maze with an escape-from-water motive served as criteria. A randomized complete blocks design with replications (2 × 3 × 2 × 2 × 10) was selected for treatment by analysis of variance. The results indicate that (a) adult rats pre-exposed to electric fields showed significantly lower error scores than young rats, regardless of sex or the noise condition; (b) after exposure to electric fields all rats swam faster than their controls; (c) after exposure to noise females showed significantly higher time scores than males under the same conditions, regardless of age; and (d) when subjected to the combined effect of electric fields and noise males showed significantly lower time scores than females under the same conditions, regardless of age.

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Zusammenfassung Zwei Altersgruppen (21–30 und 90–100 Tage) männlicher and weiblicher Ratten des King-Holtzman-Stammes wurden 2 Lärmintensitäten (30 db und 90 db) und 3 elektrischen Feldstärken (0, 1.600 v/m und 16.000 v/m) ausgesetzt und die Lernfähigkeit beim Schwimmen im modifizierten Lashley linksrechts Maze geprüft. Das Kriterium waren die Zeit und die Anzahl Fehler bei dem Versuch aus dem Wasser zu entkommen. Auswertung der Messungen durch Varianzanalyse unt er Nachbildung kompletter Blockentwürfe. Die Ergebnisse zeigen: (a) Erwachsene Ratten, die vorher elektrischen feldern ausgesetzt wurden, wiesen signifikant weniger fehler auf als junge Ratten, unabhängig vom Geschlecht und Lärmbedingungen; (b) nach der Exponierung in elektrischen Feldern schwammen alle Ratten schneller als die unbehandelten Kontrollen; (c) nach Lärmeexponierung zeigten weibliche Ratten signifikant höhere Trefferzeiten als Männchen unter den gleichen Bedingungen ohne Beziehung zum Alter und (d) bei gleichzeitiger Anwendung von elektrischen Feldern und Lärm wiesen die Männchen niedrigere Trefferzeiten auf als die Weibchen. Alter spielte dabei keine Rolle.

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Resume Des rats de la race King-Holzman, mâles et femelles, de deux groupes d'âge (21 à 30 et 90 à 100 jours) ont été exposes à deux intensités accoustiques (30 et 90 db) et à 3 champs électriques (0, 1.600 et 16. 000 v/m). On a alors examiné leur capacité d'apprendre à nager dans un labyrinthe droite-gauche de Lashley modifié. Les critères d'examen furent le temps et le nombre de fautes commises pour sortir de l'eau. Les observations furent ensuite traitées par l'analyse de variances en tenant compte de répétitions (2 × 3 × 2 × 2 × 10). Les résultats montrent: (a) Les rats adultes préalablement exposés à des champs électriques on fait moins fautes que de jeunes individus et cela de façon significative quels que soient le sexe ou les conditions de bruit; (b) après avoir été exposés à des champs électriques, tous les rats ont nagé plus vite que les bêtes de contrôle; (c) après exposition au bruit, les femelles ont présenté des temps de sortie significativement plus élevés que les mâles pris dans des conditions identiques et cela quel qu'en soit l'âge et (d) après exposition simultanée au bruit et aux champs électriques, les mâles se sont trouvés moins habiles que les femelles, sans incidence de l'âge.

     

Methacarn (methanol-Carnoy) fixation

Summary According to chemical data, methanol raises the shrinkage temperature of collagen significantly more than ethanol (86° C versus 70° C). Since increase of shrinkage temperature appears desirable in tissues to be embedded in paraffin, methanol was substituted for ethanol in Carnoy's fluid. This methanol-Carnoy mixture is referred to as methacarn solution. The fixation-embedding procedure was similar to that described in the study of Carnoy fixation. Methacarn-fixed sections showed little or no shrinkage and compared well with material fixed in Carnoy's or Zenker's fluid. Myofibrils, especially in endothelial and epithelial cells, were more prominent in methacarn- than in Carnoy-fixed tissues.A review of the chemical literature showed that methanol, ethanol and chloroform stabilize or even enhance helical conformations of proteins, presumably by strengthening of hydrogen bonds. Interference with hydrophobic bonds causes unfolding and/or structural rearrangements in globular proteins. The twin-helical structure of DNA collapses in alcoholic solutions. Hence, methacarn fixation can be expected to preserve the helical proteins in myofibrils and collagen, but the conformations of globular proteins and DNA will be significantly altered. Literature on conformational effects produced by fixatives used in electron microscopy was also reviewed. Glutaraldehyde and OsO₄ cause considerable loss of helix (22–29% and 39–66% respectively). KMnO₄ and glutaraldehyde followed by OsO₄ produce extensive transitions from helical to random-coil conformations similar to those seen in powerful denaturants such as 8 M urea. Evidently these fixatives are unsuitable for studies of helical proteins. In contrast ethylene glycol preserves helical conformations.     

Effects of a Single Histoplasmin Skin Test on the Serological Diagnosis of Histoplasmosis

Numerous reports have indicated that a single histoplasmin skin test may stimulate humoral antibodies to Histoplasma capsulatum antigens in histoplasmin-hypersensitive individuals. Although these investigations concur that antibody elevations are evoked, they vary in the reported degree of incidence and response induced, and they cast doubt on the interpretation of serological tests in the diagnosis of histoplasmosis. Histoplasmin-hypersensitive subjects (114) were bled prior to administration of the skin test, 2 days later, at the time this test was read, and 15 and 30 days after testing. No significant antibody titers were observed at 2 days. At 15- and 30-day intervals, only 17 (15%) of the subjects demonstrated circulating antibodies. All 17 showed agar gel bands; 5 demonstrated no complement-fixation (CF) titers, 10 produced CF antibodies ranging from 1:8 to 1:16, and 2 demonstrated titers of 1:32. The data suggest that skin testing does not interfere significantly with antibody levels in sera drawn approximately 2 days after administration of antigen. However, since titers as high as 1:32 were obtained at later intervals, such reactions should be evaluated cautiously and only after consideration of clinical findings.     

The Kinetics of Distribution of the Fat-Soluble Inert Gas Cyclopropane in the Body

A kinetic analysis is made of the experimentally measured time course of respiratory uptake of the highly fat-soluble, inert gas cyclopropane by normal human subjects. The analysis is based on the well-known perfusion-limited model in which a number of body compartments are arranged in parallel with the lungs via the circulating blood. Three distinct body compartments are derived from the data. These are tentatively identified as: (a) adipose tissue (b) fat-poor tissue of low perfusion such as resting muscle, skin, and connective tissue (c) fat-poor tissue of high perfusion such as brain, heart, gut, liver, and kidney. Blood flow rates to the several compartments are also derived from the data. The rates to compartments (a) and (b) are each approximately 10 per cent of the estimated total cardiac output. The derived perfusion (blood flow rate/compartment weight) of the three compartments are in the range, respectively, (a) 2 to 4, (b) 1 to 2.5, (c) 25 to 75 ml/min/100 gm. Uncertainties arising from the experimental data and from simplifications of the model (neglect of lung fill-up phase of uptake and gross diffusion of cyclopropane from one tissue into another) are discussed. The present type of uptake experiment is significant for the problems of total body fat determination, of gross body composition in relation to weight change, of gross shunting of blood flow from one compartment to another, of anesthesia by fat-soluble substances, and of decompression sickness.     

Simplified Aldehyde-Fuchsin Staining of Neurosecretory Cells

Gomori's original aldehyde-fuchsin method has been modified by the combination of Halmi's counter stain with Gabe's preparation, consisting of basic fuchsin, 1 gm; boiling water, 200 ml; with HC1, 2 ml and paraldehyde, 2 ml added after cooling and filtering. The solution so made was allowed to ripen 3-4 days at room temperature, and the precipitate which formed was filtered off and dried at 55-60°C. The staining solution consisted of 0.5 gm of the dry precipitate dissolved in 100 ml of 70% alcohol. The staining follows original procedures except that it is very important to bring slides from water to 70% alcohol before placing them in the aldehyde-fuchsin solution and also to remove all excess staining solution by rinsing in 95% alcohol after staining. The staining solution is stable for at least 6 mo.     

Amino acid compostion of walls from single and filamentous cells of Clostridium acidiurici

Gaffar, Abdul (Brigham Young University, Provo, Utah), David R. Terry, and Richard D. Sagers. Amino acid composition of walls from single and filamentous cells of Clostridium acidiurici. J. Bacteriol. 91:1618-1624. 1966.-The walls from single and filamentous cells of Clostridium acidiurici were shown to contain 11 amino acids: aspartic acid, serine, glutamic acid, proline, d-alanine, glycine, valine, methionine, valine, leucine, phenylalanine, and lysine. In the walls from cells grown at 37 C, d-alanine was the amino acid present in largest quantity, but in the walls from cells grown at 44 C there was a 50% reduction in the d-alanine content while the levels of the other amino acids were unchanged. Filamentous cells grown at 44 C, then brought to 37 C and transferred to fresh medium, fragmented into short cells within 30 min. Alanine racemase activity was the same in extracts from cells grown at both 37 and 44 C, suggesting that this enzyme was not the major controlling factor in the low content of d-alanine in filaments grown at 44 C. Spent medium from cultures grown at 44 C contained a significant amount of d-alanine, whereas there was no evidence of this amino acid in the spent medium from cultures grown at 37 C.