Potassium accumulation as dynamic modulator of neurohypophysial excitability.

Activity-dependent modulation of excitable responses from neurohypophysial axons and their secretory swellings has long been recognized as an important regulator of arginine vasopressin and oxytocin release during patterned stimulation. Various activity-dependent mechanisms, including action potential broadening, potassium accumulation, and autocrine or paracrine feedback, have been proposed as underlying mechanisms. However, the relevance of any specific mechanism on net excitability in the intact preparation, during different levels of overall activation, and during realistic stimulation with trains of action potentials has remained largely undetermined. Using high-speed optical recordings and potentiometric dyes, we have quantified the dynamics of global excitability under physiologically more realistic conditions, that is in the intact neurohypophysis during trains of stimuli at varying frequencies and levels of overall activity. Net excitability facilitated during stimulation at low frequencies or at low activity. During persistent high-intensity or high-frequency stimulation, net excitability became severely depressed. Depression of excitable responses was strongly affected by manipulations of extracellular potassium levels, including changes to resting [K(+)](out), increases of interstitial spaces with hypertonic solutions and inhibition of Na(+)/K(+) ATPase activity. Application of the GABA(A) receptor blocker bicuculline or manipulations of Ca(2+) influx showed little effect. Numerical simulation of K(+) accumulation on action potentials of individual axons reproduced optically recorded population responses, including the overall depression of action potential (AP) amplitudes, modest AP broadening and the prominent loss of hyperpolarizing undershoots. Hence, extracellular potassium accumulation dominates activity-dependent depression of neurohypophysial excitability under elevated stimulation conditions. The intricate dependence on the short-term stimulation history and its resulting feedback on neurohypophysial excitability renders [K(+)](out) accumulation a surprisingly complex mechanism for regulating axonal excitability and subsequent neuroendocrine release.

An ultra-stable non-coherent light source for optical measurements in neuroscience and cell physiology.

We demonstrate that high power light-emitting diodes (LED's) exhibit low-frequency noise characteristics that are clearly superior to those of quartz tungsten halogen lamps, the non-coherent light source most commonly employed when freedom from intensity variation is critical. Their extreme stability over tens of seconds (combined with readily selectable wavelength) makes high power LED's ideal light sources for DC recording of optical changes, from living cells and tissues, that last more than a few hundred milliseconds. These optical signals (DeltaI/I(0)) may be intrinsic (light scattering, absorbance or fluorescence) or extrinsic (absorbance or fluorescence from probe molecules) and we show that changes as small as approximately 8 x 10(-5) can be recorded without signal averaging when LED's are used as monochromatic light sources. Here, rapid and slow changes in the intrinsic optical properties of mammalian peptidergic nerve terminals are used to illustrate the advantages of high power LED's compared to filament bulbs.

Changes in FAD and NADH fluorescence in neurosecretory terminals are triggered by calcium entry and by ADP production.

We measured changes in the intrinsic fluorescence (IF) of the neurosecretory terminals of the mouse neurohypophysis during brief (1-2 s) trains of stimuli. With fluorescence excitation at either 350 +/- 20 or 450 +/- 50 nm, and with emission measured, respectively, at 450 +/- 50 or > or = 520 nm, DeltaF/F(o) was approximately 5-8 % for a 2 s train of 30 action potentials. The IF changes lagged the onset of stimulation by approximately 100 ms and were eliminated by 1 microM tetrodotoxin (TTX). The signals were partially inhibited by 500 microM Cd(2+), by substitution of Mg(2+) for Ca(2+), by Ca(2+)-free Ringer's with 0.5 mM EGTA, and by 50 microM ouabain. The IF signals were also sensitive to the mitochondrial metabolic inhibitors CCCP (0.3 microM), FCCP (0.3 microM), and NaN(3) (0.3 mM), and their amplitude reflected the partial pressure of oxygen (pO(2)) in the bath. Resting fluorescence at both 350 nm and 450 nm exhibited significant bleaching. Flavin adenine dinucleotide (FAD) is fluorescent, while its reduced form FADH(2) is relatively non-fluorescent; conversely, NADH is fluorescent, while its oxidized form NAD is non-fluorescent. Thus, our experiments suggest that the stimulus-coupled rise in [Ca(2+)](i) triggers an increase in FAD and NAD as FADH(2) and NADH are oxidized, but that elevation of [Ca(2+)](i), alone cannot account for the totality of changes in intrinsic fluorescence.

Dependence of transient and residual calcium dynamics on action-potential patterning during neuropeptide secretion.

Secretion of the neuropeptide arginine vasopressin (AVP) from the neurohypophysis is optimized by short phasic bursts of action potentials with a mean intraburst frequency around 10 Hz. Several hypotheses, most prominently action-potential broadening and buildup of residual calcium, have been proposed to explain this frequency dependence of AVP release. However, how either of these mechanisms would optimize release at any given frequency remains an open question. We have addressed this issue by correlating the frequency-dependence of intraterminal calcium dynamics and AVP release during action-potential stimulation. By monitoring the intraterminal calcium changes with low-affinity indicator dyes and millisecond time resolution, the signal could be dissected into three separate components: rapid Ca(2+) rises (Delta[Ca(2+)](tr)) related to action-potential depolarization, Ca(2+) extrusion and/or uptake, and a gradual increase in residual calcium (Delta[Ca(2+)](res)) throughout the stimulus train. Action-potential stimulation modulated all three components in a manner dependent on both the stimulation frequency and number of stimuli. Overall, the cumulative Delta[Ca(2+)](tr) amplitude initially increased with f(Stim) and then rapidly deteriorated, with a maximum around f(Stim)

[2 benign bone lesions in a tubular bone: misinterpretation of clinical and radiological findings]. / Zwei gutartige Knochenläsionen an einem Röhrenknochen: Missinterpretation von klinischen und radiologischen Befunden.

INTRODUCTION: Bone lesions are common at puberty. Most of them are detected by chance at examination for other reasons. The nonossifying fibroma does not produce any clinical symptoms and normally is diagnosed by chance. A spontaneous healing is discussed. The osteoid osteoma is characterized by its nocturnal pain and relief of pain at therapy with salicylates. Operative procedures are indicated for healing. CASE: A 12-year-old girl presented with radiological signs of a nonossifying fibroma. Because of local radionuclid uptake and clinical symptoms an operative procedure was carried out. Postoperative remaining pain resulted in radiological detection of a nearby osteoid osteoma and local operative therapy. CONCLUSION: Two benign bone lesions at one tubular bone are an extremely rare situation. The clinical symptoms and the radionuclid uptake are misinterpretated and falsely assigned to the nonossifying fibroma. All clinical symptoms and radiological signs have to be correlate correctly with the diagnosis and consecutive therapy in order to avoid a misinterpretation of obvious clear radiological results.

Caffeine interaction with fluorescent calcium indicator dyes.

We report that caffeine, in millimolar concentrations, interacts strongly with four common calcium indicator dyes: mag-fura-2, magnesium green, fura-2, and fluo-3. Fluorescence intensities are either noticeably enhanced (mag-fura-2, fura-2) or diminished (magnesium green, fluo-3). The caffeine-induced changes in the fluorescence spectra are clearly distinct from those of metal ion binding at the indicator chelation sites. Binding affinities for calcium of either mag-fura-2 or magnesium green increased only slightly in the presence of caffeine. Caffeine also alters the fluorescence intensities of two other fluorescent dyes lacking a chelation site, fluorescein and sulforhodamine 101, implicating the fluorophore itself as the interaction site for caffeine. In the absence of caffeine, variation of solution hydrophobicity by means of water/dioxane mixtures yielded results similar to those for caffeine. These observations suggest that hydrophobic substances, in general, can alter dye fluorescence in a dye-specific manner. For the particular case of caffeine, and perhaps other commonly used pharmacological agents, the dye interactions can seriously distort fluorescence measurements of intracellular ion concentrations with metal indicator dyes.