Biomedical subjects

Fritjof Helmchen

Publications and source records attributed to Fritjof Helmchen.

5 recordsLinked to original sources

PubMed2002

Ca2+ imaging in the mammalian brain in vivo.

Changes in intracellular free calcium ion concentration ([Ca(2+)](i)) have been visualized over more than two decades using fluorescent dyes and optical microscopy. So far, however, most imaging studies have been performed on isolated cells or brain tissue. Here, we review approaches to measure cellular [Ca(2+)](i) changes in vivo, i.e. within the intact brain of a living animal. In particular we describe the application of two-photon microscopy to the mammalian central nervous system, which has recently enabled studies of Ca(2+) dynamics in individual dendrites in anaesthetized rats. New developments in microscopy and labeling techniques are creating further opportunities to study Ca(2+) dynamics in vivo and are likely to make measurements of spatio-temporal [Ca(2+)](i) distributions feasible even in awake, behaving mammals.

Animals↗

PubMed2002

Enhanced two-photon excitation through optical fiber by single-mode propagation in a large core.

Multiphoton excitation through optical fibers is limited by pulse broadening caused by self-phase modulation. We show that for short fiber lengths (approximately 2 m) two-photon excitation efficiency at the fiber output can be substantially improved by single-mode propagation in a large-area multimode fiber (10-microm core diameter) instead of a standard 5.5-microm core fiber. Measurements and numerical simulations of postfiber spectra and pulse widths demonstrate that the increase in efficiency is due to a reduction of nonlinear pulse broadening. Single-mode propagation in a large-core fiber is thus suitable for multiphoton applications for which pulse recompression is not possible at the fiber end.

Journal Article↗

PubMed2002

Raising the speed limit--fast Ca(2+) handling in dendritic spines.

Ca2+ influx into dendritic spines is involved in the induction of both long-term potentiation (LTP) and long-term depression (LTD) by activating distinct biochemical cascades, depending on the stimulation protocol. Such conditional activation can be explained by the finding that removal of Ca2+ from spines is extremely rapid (approximately 15 ms) and promoted by a low endogenous buffering capacity. As a consequence, the time course of influx and binding kinetics are important determinants of how much Ca2+ binds to a particular enzyme. In addition structural factors, such as shape and dendritic location, could contribute to fine-tuning of spine Ca2+ handling and synaptic modification.

Action Potentials↗

PubMed2002

New developments in multiphoton microscopy.

Multiphoton laser-scanning microscopy is still developing rapidly, both technologically and by broadening its range of application. Technical progress has been made in the optimization of fluorophores, in increasing the imaging depth of multiphoton microscopy, and in microscope miniaturization. These advances further facilitate the study of neuronal structure and signaling in living and even in behaving animals, in particular in combination with the expression of fluorescent proteins. In addition, nonlinear optical contrast mechanisms other than multiphoton excitation of fluorescence are being explored.

Animals↗

PubMed2002

Miniaturization of fluorescence microscopes using fibre optics.

In both medical research and diagnostics characterization of biological tissue on the cellular level relies on high-resolution optical microscopy. In most cases, however, tissue is excised for microscopic investigation, in part because conventional microscopes are bulky instruments. Imaging of cells in the intact living organism has been difficult. Over the last decade several groups have developed miniature confocal microscopes that use fibre optics to deliver light to the specimen and to measure either reflected or excited fluorescence light. In addition, two-photon excitation recently has been employed in a small portable 'fibrescope'. A potential clinical application of these microscope probes is their endoscopic use for optical biopsy of inner organs or guidance of conventional biopsy. As a mobile research tool they may permit imaging of neuronal activity in the brain of awake, behaving animals. Here, we review technological approaches to build miniaturized fluorescence microscopes and discuss their potential applications.

Animals↗