From the Schnauzenorgan to the back: Morphological comparison of mormyromast electroreceptor organs at different skin regions of Gnathonemus petersii

The nocturnally active weakly electric fish Gnathonemus petersii is known to employ active electrolocation for the detection of objects and for orientation in its environment. The fish emits pulse‐type electric signals with an electric organ and perceives these signals with more than 3,000 epidermal electroreceptor organs, the mormyromasts, which are distributed over the animal's skin surface. In this study, we measured the metric dimensions of the mormyromasts from different body regions to find structural and functional specialization of the various body parts. We focused on the two foveal regions of G. petersii, which are located at the elongated and movable chin (the Schnauzenorgan; SO) and at the nasal region (NR), the skin region between the mouth and the nares. These two foveal regions were compared to the dorsal part (back) of the fish, which contains typical nonfoveal mormyromasts. While the gross anatomy of the mormyromasts from all skin regions is similar, the metric dimensions of the main substructures differed. The mormyromasts at the SO are the smallest and contain the smallest receptor cells. In addition, the number of receptor cells per organ is lowest at the SO. In contrast, at the back the biggest receptor organs with the highest amount of receptor cells per organ occur. The mormyromasts at the NR are in several respects intermediate between those from the back and the SO. However, mormyromasts at the NR are longer than those at all other skin regions, the canal leading from the receptor pore to the inner chambers were the longest and the overlaying epidermal layers are the thickest. These results show that mormyromasts and the epidermis they are embedded in at both foveal regions differ specifically from those found on the rest of the body. The morphological specializations lead to functional specialization of the two foveae. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin

doi:10.1111/j.1741‐2358.2009.00333.x
Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin Objective: The purpose of this study was to verify the effect of microwave treatment on the shear bond strength of commercial types of teeth to acrylic resin, when the glossy ridge laps were unmodified (groups 1 and 5), bur abraded (groups 2 and 6), bur grooved (groups 3 and 7) or etched by monomer (groups 4 and 8). Background: Controversial findings have shown that mechanical or chemical changes in ridge‐lap surface of the tooth increase or decrease the bond strength between tooth and acrylic resin, and the microwave disinfection may cause different changes on this bond strength. Materials and methods: Eighty specimens (n = 10) were made with the acrylic resin bonded to tooth glossy ridge lap, polymerised in water at 74°C for 9 h, and deflasked after flask cooling. Specimens of the groups 5, 6, 7 and 8 were individually immersed in 150 ml of water and submitted to microwave treatment in an oven at 650 W for 3 min. Control specimens (groups 1, 2, 3 and 4) were not microwave treated. Shear bond strength test was performed in an Instron machine with a cross‐speed of 1 mm/min. Collected data were submitted to anova and Tukey’s test (α = 0.05). Results: Microwave treatment decreased the shear bond strength values of the tooth/resin bond. In the microwaved and non‐microwaved procedures, mechanical retention improved the shear bond strength when compared with the control and monomer treatments. Conclusion: Shear bond strength of the tooth/resin bond was influenced by the microwave treatment and different commercial teeth association, and was lower for the Biotone tooth.     

Can zoosporic true fungi grow or survive in extreme or stressful environments?

Zoosporic true fungi are thought to be ubiquitous in many ecosystems, especially in cool, moist soils and freshwater habitats which are rich in organic matter. However, some of the habitats where these fungi are found may periodically experience extreme conditions, such as soils in extremely dry, hot and cold climates, acidic and alkaline soils, polluted rivers, anaerobic soil and water, saline soil and water, periglacial soils, oligotrophic soils, tree canopies and hydrothermal vents. It is clear that many ecotypes of zoosporic true fungi have indeed adapted to extreme or stressful environmental conditions. This conclusion is supported by studies in both the field and in the laboratory. Therefore, in our opinion, at least some true zoosporic fungi can be considered to be extremophiles.     

Über den bau der eischale von bulimus (Helicidae)

Zusammenfassung Der kohlensaure Kalk der untersuchten Helicideneischalen — Bulimus maximus (Durchmesser der Schale 23,6 x 25,1 mm, Dicke 0,25 mm), nicht näher bestimmte Schneckeneischale aus Sta. Catharina Brazil (Durchmesser 22,5 x 16,3 mm, Dicke 0,15 mm) — ist Calcit gemäß Optik (negativ einachsiges Konoskopbild) and Meigenscher Reaktion (in Übereinstimmung mit Kellys Beobachtungen bei Bulimus oblongus). Der Phosphatgehalt der Schale ist äuBerst gering trotz reichlichen Vorkommens der KELLyschen Phosphatkörnehen; diese sind in Wirklichkeit Gaseinschüisse. Erhitzen von Schalenstiicken braunt den Kalk bei Verkohlung der organischen Substanz durch and durch ; these durchsetzt also die Calcitkristalle, in Übereinstimmung mit Kellys Erfahrungen beim Entkalken. Erhitzen his zum Verbrennen der organischen Substanz (Wiederweißwerden der Schalenstücke) hebt die Doppelbrechung auf (Umwandlung des Calciumcarbonats in -oxyd); zugleich erscheint bräunliche Trübung im durchfallenden Licht wohl infolge des Austretens der Kohlensäure.Die Mammillenschicht auf der Innenseite der Schale besteht aus einzelnen Calcitindividuen oder Gruppen von solchen; diese Kristallkörnchen wachsen (zum Teil) zu den annähernd senkrecht stehenden Prismen aus, deren optische Achse rneist gegen die Schalenfläche geneigt ist. Vor allem bei Bulimus maximus lassen die Prismen eine innere grobgeschichtete and eine äußere feinstreifige Lage unterscheiden; die erste enthält die Gaseinschliisse, die sich bei der Schneckeneischale aus Sta. Catharina Brazil bis in die Mammillen hinein finden, and von rundlicher Form sind, während she bei Bulimus maximus zum Teil spaltenartig erscheinen. An manchen Stellen der Eischale aus Sta. Catharina Brazil tragen die Mamillen an ihrem freien Ende Scheiben aus radial gestellten Kalknadeln oder Rosetten aus größeren Kristallen, die bis zur Berührung benachbarter auswachsen können.     

Influence of orotic acid upon post-excitatory facilitation released by stimulation of the tooth pulp]

The influence of orotic acid on post-excitatory facilitation of evoked potentials released by electric stimulation of the tooth pulp in the sensomotor cortex was studied. 15-360 min following application of 100 mg/kg orotic acid, increase in amplitude of potentials released by stimulation of the tooth pulp, reinforcement of the post-excitatory facilitation observable 5 msec after stimulation occurred.