Microwave fixation and localization of calcium in synaptic terminals using x-ray microanalysis and electron energy loss spectroscopy imaging

Mouse brain fixation to preserve In vivo manganese enhancement for ex vivo manganese-enhanced MRI

PURPOSE

To develop a tissue fixation method that preserves in vivo manganese enhancement for ex vivo magnetic resonance imaging (MRI). The needs are clear, as conventional in vivo manganese-enhanced MRI (MEMRI) applied to live animals is time-limited, hence limited in spatial resolution and signal-to-noise ratio (SNR). Ex vivo applications can achieve superior spatial resolution and SNR through increased signal averaging and optimized radiofrequency coil designs. A tissue fixation method that preserves in vivo Mn(2+) enhancement postmortem is necessary for ex vivo MEMRI.

MATERIALS AND METHODS

T1 measurements and T1 -weighted MRI were performed on MnCl2 -administered mice. The mice were then euthanized and the brains were fixed using one of two brain tissue fixation methods: aldehyde solution or focused beam microwave irradiation (FBMI). MRI was then performed on the fixed brains.

RESULTS

T1 values and T1 -weighted signal contrasts were comparable between in vivo and ex vivo scans on aldehyde-fixed brains. FBMI resulted in the loss of Mn(2+) enhancement.

CONCLUSION

Aldehyde fixation, not FBMI, maintained in vivo manganese enhancement for ex vivo MEMRI.

Comprehensive screening for antigens overexpressed on carcinomas via isolation of human mAbs that may be therapeutic

Although several murine mAbs that have been humanized became useful therapeutic agents against a few malignancies, therapeutic Abs are not yet available for the majority of the human cancers because of our lack of knowledge of which antigens (Ags) can become useful targets. In the present study we established a procedure for comprehensive identification of such Ags through the extensive isolation of human mAbs that may become therapeutic. Using the phage-display Ab library we isolated a large number of human mAbs that bind to the surface of tumor cells. They were individually screened by immunostaining, and clones that preferentially and strongly stained the malignant cells were chosen. The Ags recognized by those clones were isolated by immunoprecipitation and identified by MS. We isolated 2,114 mAbs with unique sequences and identified 21 distinct Ags highly expressed on several carcinomas. Of those 2,114 mAbs 356 bound specifically to one of the 21 Ags. After preparing complete IgG(1) Abs the in vitro assay for Ab-dependent cell-mediated cytotoxicity (ADCC) and the in vivo assay in cancer-bearing athymic mice were performed to examine antitumor activity. The mAbs converted to IgG(1) revealed effective ADCC as well as antitumor activity in vivo. Because half of the 21 Ags showed distinct tumor-specific expression pattern and the mAbs isolated showed various characteristics with strong affinity to the Ag, it is likely that some of the Ags detected will become useful targets for the corresponding carcinoma therapy and that several mAbs will become therapeutic agents.

Synaptic vesicles: test for a role in presynaptic calcium regulation

Membrane-bound organelles such as mitochondria and the endoplasmic reticulum play an important role in neuronal Ca(2+) homeostasis. Synaptic vesicles (SVs), the organelles responsible for exocytosis of neurotransmitters, occupy more of the volume of presynaptic nerve terminals than any other organelle and, under some conditions, can accumulate Ca(2+). They are also closely associated with voltage-gated Ca(2+) channels (VGCCs) that trigger transmitter release by admitting Ca(2+) into the nerve terminal in response to action potentials (APs). We tested the hypothesis that SVs can modulate Ca(2+) signals in the presynaptic terminal. This has been a difficult question to address because neither pharmacological nor genetic approaches to block Ca(2+) permeation of the SV membrane have been available. To investigate the possible role of SVs in Ca(2+) regulation, we used imaging techniques to compare Ca(2+) dynamics in motor nerve terminals before and after depletion of SVs. We used the temperature-sensitive Drosophila dynamin mutant shibire, in which SVs can be eliminated by stimulation. There was no difference in the amplitude or time course of Ca(2+) responses during high-frequency trains of APs, or single APs, in individual presynaptic boutons before and after depletion of SVs. SVs have a limited role, if any, in the rapid sequestration of Ca(2+) within the neuronal cytosol or the synaptic microdomain. We also conclude that SVs are not important for regulation of synaptic VGCCs.

Methods for analysis of Ca(2+)/H(+) antiport activity in synaptic vesicles isolated from sheep brain cortex

The involvement of Ca(2+)-storage organelles in the modulation of synaptic transmission is well-established [M.K. Bennett, Ca(2+) and the regulation of neurotransmitter secretion, Curr. Opin. Neurobiol. 7 (1997) 316-322 [1]; M.J. Berridge, Neuronal calcium signaling, Neuron 21 (1998) 13-26 [2]; Ph. Fossier, L. Tauc, G. Baux, Calcium transients and neurotransmitter release at an identified synapse, Trends Neurosci. 22 (1999) 161-166 [7] ]. Various Ca(2+) sequestering reservoirs (mitochondria, endoplasmic reticulum and synaptic vesicles) have been reported at the level of brain nerve terminals [P. Kostyuk, A. Verkhratsky, Calcium stores in neurons and glia, Neuroscience 63 (1994) 381-404 [18]; V. Mizuhira, H. Hasegawa, Microwave fixation and localization of calcium in synaptic terminals using X-ray microanalysis and electron energy loss spectroscopy imaging, Brain Res. Bull. 43 (1997) 53-58 [21]; A. Parducz, Y. Dunant, Transient increase of calcium in synaptic vesicles after stimulation, Neuroscience 52 (1993) 27-33 [23]; O.H. Petersen, Can Ca(2+) be released from secretory granules or synaptic vesicles?, Trends Neurosci. 19 (1996) 411-413 [24] ]. However, the knowledge of the specific contribution of each compartment for spatial and temporal control of the cytoplasmic Ca(2+) concentration requires detailed characterization of the Ca(2+) uptake and Ca(2+) release mechanisms by the distinct intracellular stores. In this work, we described rapid and simple experimental procedures for analysis of a Ca(2+)/H(+) antiport system that transport Ca(2+) into synaptic vesicles at expenses of the energy of a DeltapH generated either by activity of the proton pump or by a pH jumping of the vesicles passively loaded with protons. This secondary active Ca(2+) transport system requires high Ca(2+)100 microM) for activation, it is dependent on the chemical component (DeltapH) of the proton electrochemical gradient across the synaptic vesicle membrane and its selectivity is essentially determined by the size of the transported cation [P.P. Gonçalves, S.M. Meireles, C. Gravato, M.G. P. Vale, Ca(2+)-H(+)-Antiport activity in synaptic vesicles isolated from sheep brain cortex, Neurosci. Lett. 247 (1998) 87-90 [10]; P.P. Gonçalves, S.M. Meireles, P. Neves, M.G.P. Vale, Ionic selectivity of the Ca(2+)/H(+) antiport in synaptic vesicles of sheep brain cortex, Mol. Brain Res. 67 (1999) 283-291 [11]; P.P. Gonçalves, S.M. Meireles, P. Neves, M.G.P. Vale, Synaptic vesicle Ca(2+)/H(+) antiport: dependence on the proton electrochemical gradient, Mol. Brain Res. 71 (1999) 178-184 [12] ]. The protocols described here allow to ascertain the characteristics of the Ca(2+)/H(+) antiport in synaptic vesicles and, therefore, may be useful for clarification of the physiological role of synaptic vesicles in fast buffering of Ca(2+) at various sites of the neurotransmission machinery.

Calcium transients and neurotransmitter release at an identified synapse

It is widely accepted that the modulation of the presynaptic Ca2+ influx is one of the main mechanisms by which neurotransmitter release can be controlled. The well-identified cholinergic synapse in the buccal ganglion of Aplysia has been used to study the modulations that affect presynaptic Ca2+ transients and to relate this to quantal evoked neurotransmitter release. Three types of Ca2+ channel (L, N and P) are present in the presynaptic neurone at this synapse. Influxes of Ca2+ through N- and P-type channels trigger the release of ACh with only N-type Ca2+ channels being regulated by presynaptic neuromodulator receptors. In addition, presynaptic Ca2+ stores, via complex mechanisms of Ca2+ uptake and Ca2+ release, control the Ca2+ concentration that triggers this evoked ACh release.