Ultrastructure of nervous tissue developing in the anterior chamber of the eye. 1. Perikaryons and dendrites

Embryonic tissues of septum and hippocampus were transplanted into the anterior eye chamber (AEC) of adult rats. The morphology of initial embryonic tissues and of transplants within 3 to 4 months of cultivation in AEC was studied. The transplanted tissue consists of neuroblasts and immature neurones: no synaptic contacts are observed. Within 3 to 4 months, highly differentiated neurones establishing synaptic contacts can be seen in the transplants. At the same time the fine structure of perikaryons and dendrites undergoes some changes: increased vacuolization, transformation of ergastoplasm into lamellar bodies. These can be due to an elevated functional activity of some neurones. Another group of morphological abnormalities (increased number of dendrite processes and microphyllopodia, somatic spines, dendrite cones of growth, tight junctions between perikaryons) suggests incomplete tissue maturation. These might be due to the absence of normal afferent and trophic influences in AEC.     

Mineralization of soil nitrogen in three forest communities from the New England region of New South Wales

Nitrogen (N) mineralization rates and the temperature response patterns of mineral N production in surface (0–7.6 cm) soils were compared in laboratory incubation studies based on disturbed, composite samples. Seasonal variation in the field levels of mineral N, and mineralization potential of intact (7.6 × 5.6 cm diameter) soil cores, were also investigated. Ammonification proceeded rapidly in each soil. Nitrification did not occur in grassy forest (GF) soil but was active in both layered forest (LF) and mossy forest (MF) soils, especially the former. Total mineral N production was greatest in MF and least in LF. Ammonification in disturbed samples was maximal at 50°C in all three soils with a secondary peak at 10°C in LF soil. Nitrification in LF and MF soils was most rapid at 25°C. Several species of ammonifying bacteria with different temperature optima were isolated, indicating that the process of ammonification is a composite of the activities of a variety of decomposer microbes. Mean field levels of mineral N and NH₄–N throughout the year were greatest in MF and least in LF. Seasonal fluctuations in NH₄–N were evident, concentrations being universally low in mid-winter (about 1.5 μgg^-1), increasing to a maximum in late summer (about 5 μg g^-1 in LF: 16–18 μg g^-1 in GF and MF). Field levels of NO₃–N were more constant and never more than 5 μg g^-1 in any community. Both total mineralization and ammonification in intact cores were greatest in MF and least in LF while nitrification was greatest in LF and almost negligible in GF, thus confirming the results obtained with disturbed samples. The potential for mineralization was large in mid-winter when the amount of mineral N was very low, and small in late summer when field levels were higher: this is interpreted as indicating that seasonal climatic factors regulate the availability of substrates for decomposers. Spatial variability in field levels of mineral N and mineral N production in the laboratory was evidenced by significant ‘sampling site’ effects in each community: however, at the sampling intensity used, the presence of bark mounds around Eucalyptus saligna trees could not be shown to affect these attributes. The inability of GF soil to nitrify when incubated in the laboratory could not be ascribed to a high C/N ratio, low pH, lack of substrate ammonium, or a low population of autotrophic nitrifying bacteria. No attempt was made to investigate the presence of allelopathic nitrification inhibitors. No evidence was obtained to support the view that nitrification is atypical of climax communities in situ. The most productive forest (LF) had the greatest capacity to nitrify and the least productive community (GF) the smallest capacity to do so.     

An Immunohistochemical Study of Localization of the Calcium-Binding Protein Recoverin in Retina of the Newt Pleurodeles waltl

The presence and localization of the calcium-binding protein recoverin, initially found in photoreceptors of the bovine eye, were immunochemically studied in retina of the new Pleurodeles waltl. Polyclonal monospecific antibodies against recoverin were raised and the methods of immunoblotting and indirect immunofluorescence were used. A protein with an apparent molecular mass of 26 kDa was found in the retina extract, which was specifically stained by the antibodies against recoverin. Localization of recoverin was studied on the retina sections: an intense reaction was found in the inner segments and a weak reaction was found in the basal part of the outer segments of photoreceptors and in Landolt's clubs of displaced bipolars. The results we obtained suggest for the first time the presence of recoverin in the retina of a representative of the Urodeles and indicate to interspecific conservativeness of this protein and differences of its localization in the retina photoreceptors in different species. The data obtained open a possibility of using recoverin as a marker protein of photoreceptors and displaced bipolars in studies of retina regeneration in newts.     

Cryofractographic study of intercellular junctions in the populations of agar-cultivated Bordetella pertussis

The characteristic feature of replicas obtained from the freeze-fractures of B. pertussis unfixed cultures developing on casein charcoal agar for 1-7 days is the associative growth of highly polymorphic cells, ensured by the ramified system of intercellular connections (IC) formed by the derivatives of the outer layers of the cell wall. This proves that the associative location of bacterial cells, linked by numerous IC, in the preparation is not the artefact appearing in the process of their chemical fixation. In replicas obtained from the freeze-fractures of B. pertussis cultures, previously fixed with glutaraldehyde, osmic acid and uranyl acetate, oval cells with the cytoplasm having a relatively homogeneous structure and with the smoothed-out three-layer cell wall prevail. As a rule, IC are limited to the sites of direct contacts between individual cells.