SUMMARY The energy‐filtering electron microscopical modes of electron energy‐loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) have been applied to the cytochemical detection of Ca 2+ ‐ATPase activity in synaptic terminals in the brain of a cichlid fish. Using a recently developed modification of an enzyme‐histochemical method, cerium phosphate was precipitated as a marker of high‐affinity Ca 2+ ‐ATPase activity. This is considered to be a marker for the plasmalemma‐bound calcium pump, an enzyme which plays a crucial role in the regulation of the cytoplasmic calcium concentrations and therefore of the reactivity of nerve cells. High‐affinity Ca 2+ ‐ATPase activity is located preferentially at the inner side of synaptic plasma membranes and enables a discrimination of different types of synapse. It is only by using EELS and ESI that the very small amounts of high‐affinity Ca 2+ ‐ATPase reaction product can be analysed reliably and located precisely. These new electron microscopical techniques offer powerful tools for cytochemical studies.
(2001). Aquatic invertebrate communities of a south German bog stream, a multivariate approach. SIL Proceedings, 1922-2010: Vol. 27, No. 7, pp. 3886-3890.
The brain of Antarctic fish of the perciform suborder Notothenioidea was analysed with lightand electronmicroscopical methods. The overall organization and ultrastructure of the optic tectum is very similar to that of fish from temperate climates. However, unusual structures were observed in neurons and glial cells, sometimes in high frequencies. The structures are ovoid or elongated, about 200‐600 nm in diameter and surrounded by two layers of membranes in a uniform distance of about 30 nm. The enclosed inter‐membrane space is similar to extracellular space, both in size and in cytochemical calcium precipitation, while the interior of the structures resembles cytoplasm. These structures are sometimes connected to neuronal processes, so that they seem to originate by a sort of budding process, but most of them are isolated as can be concluded from thick sections of up to 800 nm thickness, analysed with energy‐filtering transmission electron microscopy (EFTEM). These unusual objects are present in high abundance in members of the white‐blooded Antarctic fish family Channichthyidae. These so‐called icefish lack haemoglobin and exhibit the highest degree of cold adaptation. The red‐blooded notothenoid fish had smaller amounts of these structures and they were observed even in fish from temperate climates (trout, carp, cichlid fish). In fish from temperate climates the unusual substructures were more abundant during adaptation to cold water temperatures (winter) than to warm conditions (summer). Therefore, the findings may indicate a general phenomenon of cold adaptation with unusual interactions of neurons and glial cells, but the precise function is not yet understood.
Neuroblastomas and cell lines derived from these tumors bear the oncodevelopmental antigen polysialic acid (PSA) bound to the neural cell adhesion molecule. Polysialyation of neural cell adhesion molecule can be achieved by two different polysialyltransferases, ST8SiaII and ST8SiaIV. This study was undertaken to investigate the pattern of polysialyltransferases expressed in the human neuroblastoma cell line SH-SY5Y. Reverse transcription-PCR showed simultaneous expression of the two enzymes, and in situ hybridization demonstrated that the polysialyltransferase mRNA expression parallels immunoreactivity with the PSA-specific monoclonal antibody 735. After retinoic acid-induced differentiation, only the PSA-positive, neuron-like cell type gave clear signals for ST8SiaII and ST8SiaIV in in situ hybridization, whereas both signals were drastically reduced in the weakly PSA-positive substrate adherent phenotype. Like the SH-SY5Y cells, a primary, PSA-positive neuroblastoma specimen revealed expression of the two polysialyltransferases. To investigate the role of PSA for cell growth and differentiation, SH-SY5Y cells were treated with the PSA-specific endo-N-acetylneuraminidase E. Although loss of PSA was accompanied with a marked reduction of cell growth, it did not interfere with retinoic acid-induced differentiation. Together, our results suggest that PSA surface expression is regulated on the level of polysialyltransferase transcription. Moreover, the similarity to the primary neuroblastoma tissue makes SH-SY5Y cells a suitable model system to examine further the role of polysialylation in tumor cell growth and the orchestration of PSA synthesis in neuroblastoma.
