Biomedical subjects

H Neumeister

Publications and source records attributed to H Neumeister.

11 recordsLinked to original sources

PubMed2004

Dynamical analysis reveals individuality of locomotion in goldfish.

Goldfish swimming was analysed quantitatively to determine if it exhibits distinctive individual spatio-temporal patterns. Due to the inherent variability in fish locomotion, this hypothesis was tested using five nonlinear measures, complemented by mean velocity. A library was constructed of 75 trajectories, each of 5 min duration, acquired from five fish swimming in a constant and relatively homogeneous environment. Three nonlinear measures, the 'characteristic fractal dimension' and 'Richardson dimension', both quantifying the degree to which a trajectory departs from a straight line, and 'relative dispersion', characterizing the variance as a function of the duration, have coefficients of variation less than 7%, in contrast to mean velocity (30%). A discriminant analysis, or classification system, based on all six measures revealed that trajectories are indeed highly individualistic, with the probability that any two trajectories generated from different fish are equivalent being less than 1%. That is, the combination of these measures allows a given trajectory to be assigned to its source with a high degree of confidence. The Richardson dimension and the 'Hurst exponent', which quantifies persistence, were the most effective measures.

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PubMed2001

Temperature-dependent expression of a squid Kv1 channel in Sf9 cells and functional comparison with the native delayed rectifier.

SqKv1A is a cDNA that encodes a Kv1 (Shaker-type) alpha-subunit expressed only in the giant axon and the parental giant fiber lobe (GFL) neurons of the squid stellate ganglion. We incorporated SqKv1A into a recombinant baculovirus for expression in the insect Sf9 cell line. Whole-cell patch-clamp recordings reveal that very few cells display functional potassium current (IK) if cultured at the standard postinfection temperature of 27 degrees C. At 18 degrees C, less SqKv1A protein is produced than at 27 degrees C, but cells with IK currents are much more numerous and can survive for at least 20 days postinfection (vs. approximately 5 days at 27 degrees C). Activation and deactivation kinetics of SqKv1A in Sf9 cells are slower (approximately 3- and 10-fold, respectively) than those of native channels in GFL neurons, but have similar voltage dependencies. The two cell types show only subtle differences in steady-state voltage-dependence of conductance and inactivation. Rates of IK inactivation in 20 mM external K are identical in the two cell types, but the sensitivity of inactivation to external tetraethylammonium (TEA) and K ions differ: inactivation of SqKv1A in Sf9 cells is slowed by external TEA and K ions, whereas inactivation of GFL IK is largely insensitive. Functional differences are discussed in terms of factors that may be specific to cell-type, including the presence of presently unidentified Kv1 subunits in GFL neurons that might form heteromultimers with SqKv1A.

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PubMed2001

MR microscopy of cobalt-labeled nerve cells and pathways in an invertebrate brain (Sepia officinalis, Cephalopoda).

This article describes a novel application of contrast-enhanced MR microscopy to trace nerve cells and pathways through small invertebrate brains. Using the cuttlefish Sepia officinalis (Cephalopoda) as a model, the cells and pathways of one of the brain nerves were labeled with paramagnetic cobalt(II) ions by conventional centripetal cobalt iontophoresis. In MR microscopy, the cobalt-labeled cell bodies and pathways became hypointense in 9.4 T spin echo images. Their course and distribution were identical with those seen with conventional histological techniques after cobalt sulphide precipitation (with or without subsequent silver intensification). Magn Reson Med 45:575-579, 2001.

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PubMed2000

Effects of temperature on escape jetting in the squid Loligo opalescens.

In Loligo opalescens, a sudden visual stimulus (flash) elicits a stereotyped, short-latency escape response that is controlled primarily by the giant axon system at 15 C. We used this startle response as an assay to examine the effects of acute temperature changes down to 6 C on behavioral and physiological aspects of escape jetting. In free-swimming squid, latency, distance traveled and peak velocity for single escape jets all increased as temperature decreased. In restrained squid, intra-mantle pressure transients during escape jets increased in latency, duration and amplitude at low temperature. Recordings of stellar nerve activity revealed repetitive firing of the giant motor axon accompanied by increased activity in the non-giant motor axons that run in parallel. Selective stimulation of giant and non-giant motor axons in isolated nerve-muscle preparations failed to show the effects seen in vivo, i.e. increased peak force and increased neural activity at low temperature. Taken together, these results suggest that L. opalescens is able to compensate escape jetting performance for the effects of acute temperature reduction. A major portion of this compensation appears to occur in the central nervous system and involves alterations in the recruitment pattern of both the giant and non-giant axon systems.

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PubMed1997

Structure and function of the Nautilus statocyst.

The two equilibrium receptor organs (statocysts) of Nautilus are avoid sacks, half-filled with numerous small, free-moving statoconia and half with endolymph. The inner surface of each statocyst is lined with 130,000-150,000 primary sensory hair cells. The hair cells are of two morphological types. Type A hair cells carry 10-15 kinocilia arranged in a single ciliary row; they are present in the ventral half of the statocyst. Type B hair cells carry 8-10 irregularly arranged kinocilia; they are present in the dorsal half of the statocyst. Both type of hair cells are morphologically polarized. To test whether these features allow the Nautilus statocyst to sense angular accelerations, behavioural experiments were performed to measure statocyst-dependent funnel movements during sinusoidal oscillations of restrained Nautilus around a vertical body axis. Such dynamic rotatory stimulation caused horizontal phase-locked movements of the funnel. The funnel movements were either in the same direction (compensatory funnel response), or in the opposite direction (funnel follow response) to that of the applied rotation. Compensatory funnel movements were also seen during optokinetic stimulation (with a black and white stripe pattern) and during stimulations in which optokinetic and statocyst stimulations were combined. These morphological and behavioural findings show that the statocysts of Nautilus, in addition to their function as gravity receptor organs, are able to detect rotatory movements (angular accelerations) without the specialized receptor systems (crista/cupula systems) that are found in the statocysts of coleoid cephalopods. The findings further indicate that both statocyst and visual inputs control compensatory funnel movements.

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PubMed1983