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Biomedical subjects

U Kuhnt

Publications and source records attributed to U Kuhnt.

At least 55 records · Page 3Linked to original sources
PubMed1987

Quantal analysis of paired-pulse facilitation in guinea pig hippocampal slices.

Intracellular excitatory postsynaptic potentials (EPSPs) were recorded in area CA1 of hippocampal slices from guinea pigs. With paired-pulse stimulation of stratum radiatum, the second stimulus (interval of 40-50 ms) produced an EPSP with enlarged amplitude. Two methods of quantal analysis showed an increase in quantal content of the facilitated EPSP and a smaller increase in quantal size. The correlation between amplitudes of the first and second EPSP was usually insignificant. The results favour a presynaptic location of the mechanisms of the paired-pulse facilitation and suggest increases in the average of transmitter quanta released by presynaptic volley as well as increases in the amount of transmitter in each quantum.

Animals↗
PubMed1987

Semiquantitative evaluation of histochemically detectable calcium binding in mammalian brain slices.

A method is described for the electron histochemical demonstration of Ca in the central nervous system, based on fixation on Ca-containing paraformaldehyde solution and the subsequent complexing of Ca by ammonium oxalate. The method resulted in highly electron-dense deposits, with good ultrastructural preservation. The Ca content of the deposits was proved by physico-chemical analysis. The high electron density permitted the counting of deposits and thereby an estimation of their numerical density, via planimetry of electron micrographs. Since pre- and postsynaptic localizations could be distinguished on the basis of ultrastructure, this procedure is regarded as a unique semiquantitative method for estimation of the tissue Ca binding of mammalian brain slices.

Animals↗
PubMed1986

Increased Ca-uptake of presynaptic terminals during long-term potentiation in hippocampal slices.

A combined electrophysiological and neurochemical study was performed on the CA1 area of hippocampal slices in an attempt to identify changes in presynaptic nerve terminal function in long-term potentiation (LTP). After controlled induction of LTP in CA1, the activated region was subjected to subcellular fractionation followed by 45Ca2+ uptake determinations. Synaptosomes prepared from slices in which LTP has been induced showed a faster risetime and a higher level of saturation for K+-induced Ca-uptake than those derived from unstimulated and stimulated control slices. These findings point to a participation of presynaptic terminals in long-term potentiation.

Animals↗
PubMed1985

Increased binding of calcium in the hippocampal slice during long-term potentiation.

Long-term potentiation (LTP) of CA1 pyramidal neurons was induced by tetanic stimulation in the stratum radiatum of hippocampal slices from guinea pigs. Unstimulated and stimulated slices were treated using a histochemical procedure enabling the electron microscopic (EM) visualization of Ca binding sites. Electron-dense, Ca-containing deposits were found in low numbers in unstimulated slices on pre- and postsynaptic sites. In the stratum radiatum of tetanized slices the overall number of deposits as well as the number of deposits in dendrites was clearly increased. The results support the hypothesis that Ca-dependent postsynaptic mechanisms are important for the generation of LTP.

Animals↗
PubMed1983

Stimulation-dependent calcium binding sites in the guinea pig hippocampal slice: an electrophysiological and electron microscopic study.

Transverse slices of the hippocampus of guinea pigs were prepared in order to investigate Ca2+ binding sites in CA1. Electrical stimulation (Schaffer collaterals and stratum oriens) combined with different aminopyridine compounds (AP) were used for neuronal activation. With histochemical methods Ca2+ binding sites were identified and localized at the electron microscopic level as electron dense deposits of granular or elongated shape. After electrical stimulation, electron dense deposits of 30-50 nm diameter were spread at low density over all layers of CA1. Electrical stimulation combined with application of aminopyridine compounds led to electron dense deposits of 60-400 nm diameter, mainly restricted to the activated input layers. Deposits were predominantly found at presynaptic sides, with few at dendrites and glial cells. Application of aminopyridine alone led to very few deposits, spread over the total CA1 area. The results indicate that aminopyridines, if combined with electrical stimulation, display a strong presynaptic action, which results in a remarkable Ca2+-translocation at the preterminal and terminal level. On the dendritic side aminopyridines in the concentrations used for the study weakly activate Ca2+ movements.

Aminopyridines↗
PubMed1981

Representation of the visual field in the optic tract and optic chiasma of the cat.

The fibre arrangement in the optic chiasma (OC) and tract (OT) was investigated with anatomical and physiological methods. In silver impregnated material, principal fibre streams can be demonstrated. In the OC, fibre bundles from each eye cross in a regular basket weave pattern, but deviations of single fibres from the predominant stream are often seen. In the OT, fibres run essentially parallel, and crossings of individual fibres are mainly restricted to the periphery of the tract, or around capillaries. Fibres in the upper segment of the OT are of thin, in the lower segments of thick diameter. Individual fibres labelled by HRP injected in the lateral geniculate body (LGB) run essentially parallel over long distances. Ventromedially to the LGB, bifurcations are found with one branch entering the LGB, the other continuing. 57% of OT-fibres had a receptive field (RF) in the contralateral, 43% in the homolateral eye; 60% in the lower, 40% in the upper visual field; and 6% had a RF in the homolateral visual field, mostly near the vertical meridian. Fibres from the central area were underrepresented in our sample. Fibres from the two eyes were mixed. The RFs of consecutively recorded fibres showed a systematic progression only exceptionally. After plotting RFs of a single penetration on a transformed isodensity ganglion cell map of the visual field, the RF's were distributed along elongated paths on this map. In the OT, such paths ran parallel or slightly inclined relative to the horizontal meridian. They were restricted to either the upper or the lower quadrant or to a path along the horizontal meridian. In the OC, the RF-paths mostly crossed the horizontal meridian at an obtuse angle (average 70 degrees). Thus, the visual field representation rotates by nearly 90 degrees from the OC to the OT. In the OC, the central area is located anteriorly, in the OT dorsally, with the upper visual quadrant laterally and the lower medially. Fibres from the two eyes were mixed and, within the range of the scatter, RFs from the homo- and contralateral eye were in register. It is concluded, that the distribution of fibres in the OC and the OT show a basic retinotopic organization superimposed by scatter.

Animals↗
PubMed1980

Hyperpolarization of hypothalamic parvocellular neurons by 17 beta-estradiol and their identification through intracellular staining with procion yellow.

Intracellular recordings and injections of procion yellow (PY) were made in parvocellular neurons in hypothalamic slices of female guinea pigs. Eighty-five neurons, with an average resting membrane potential of -35 mV, were recorded in the arcuate (ARC) ventromedial (VM), and in the cell-poor zones between the ARC and VM. Eleven of the ARC neurons and four neurons from the cell-poor zone could be driven antidromically by median eminence (ME) stimulation, nine other neurons from the three areas could be driven orthodromically by stria terminalis (ST) stimulation. Twenty-eight parvocellular neurons were tested with 17 beta-estradiol (E2), which was applied in the bathing medium as the free steroid. Eleven neurons (nine ARC and two cell-poor-zone neurons) were hyperpolarized 2 to 24 mV by 10(-10) M E2 concentrations. 10(-8) M estrone concentration was without effect on three of these cells. Through the intracellular injection of PY, the estrogen-sensitive neurons (N = 11) were identified as small fusiform cells with few dendrites. Spine-like appendages were found on only one of these cells. None of the larger pyramidal-like neurons of these areas responded to the application of E2.

Animals↗
PubMed1979

Transynaptic transport of procion yellow in the central nervous system.

Intracellular recordings were performed in slices of the lateral geniculate body, the visual cortex, and the hippocampus of guinea pigs. After recording, Procion Yellow was iontophoretically injected. During the injection period the neurones were activated antidromically and/or transynaptically. Up to 6 h after dye injection slices were fixed in a buffered formaldehyde/sucrose solution and later histologically processed. In the lateral geniculate body, after orthodromic stimulation across the optic tract, optic tract fibers were stained secondarily. Orthodromic activation across intrageniculate connections led to secondarily stained geniculate neurones. In the visual cortex orthodromic activation of the injected neurones across white matter led to secondarily stained fibres travelling in the direction to the white matter or to secondarily stained neurones in the vicinity of the injected neurone. In the hippocampus anti- and orthodromic activation across the alveus or the mossy fibre pathway led to a secondary staining of neighbouring pyramidal neurones and to a secondary staining of fibres which where afferent to the injected neurone. All slices where Procion Yellow was detected in the extracellular space were rejected. These findings led to the conclusion that Procion Yellow must have been transported across chemical synapses from the post- to the presynaptic side. The transport occurred only if the concerned synapses were activated.

Animals↗
PubMed1979

Morphological features of physiologically identified hypothalamic neurons as revealed by intracellular marking.

In the in vitro slice preparation intracellular recordings and injections of procion yellow (PY) were made in neurons of the hypothalamus. Of these neurons, one medial preoptic-anterior hypothalamus (MPO-AH) and four arcuate-ventromedial hypothalamus (ARC-VM) neurons were driven by electrical stimulation of the median eminence area (ME). Two other MPO-AH and five other ARC-VM neurons were driven by stimulation of the stria terminalis (ST). On the basis of the PY injections two morphologically distinct cell types were delineated: a larger multipolar cell type with a polygonal perikaryon was found with equal frequency in the MPO-AH and the ARC-VM. A smaller fusiform cell type was encountered mainly in the ARC-VM. On the secondary dendrites of both cell types spine-like appendages were seldom seen, but dendritic swellings were common. Some of the dendrites projected to capillaries in both areas and presumably contacted them. The axons were usually tortuous and could only be traced a short distance.

Animals↗
PubMed1976

Visual pattern evoked responses and blink reflexes in assessment of MS diagnosis. A clinical study of 135 multiple sclerosis/pathol.

VEPs were measured after pattern reversal in 135 MS patients and 30 control subjects. Neurological findings were documented in a standard manner. An extensive ophthalmological examination of all subjects was part of the study. The latency of P2 was abnormally delayed in 82% of the "definite", in 60% of the "probable" and in 65% of the "possible" MS groups respectively. The VEP was more often delayed in relation to ophthalmological disturbances. Changes in the MS classification had to be made in more than 10% of the patients, due to delay of VEP latency. These were patients with a "spinal" form of MS, which is known to create diagnostic problems. Optically and electrically evoked blink reflexes were recorded in 107 MS patients. All patients with mesencephalic lesions had delayed responses of the optically evoked reflex. 74% of the patients with caudal brainstem lesions had delayed latencies of the components of the electrically evoked blink reflex. The blink reflex was delayed in 18 additional patients without brainstem signs. The possibility of delineating clinically silent brainstem lesions by investigating blink reflexes is discussed.

Adolescent↗