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Biomedical subjects

H Siegmund

Publications and source records attributed to H Siegmund.

At least 19 recordsLinked to original sources
PubMed2001

Inhibitory action of nociceptin/orphanin FQ on functionally different thalamic neurons in urethane-anaesthetized rats.

1. In this study we administered nociceptin/orphanin FQ (NC) ionotophoretically onto neurons located in functionally distinct thalamic structures of urethane-anesthetized rats. Extracellular single unit recordings were made in the medial and lateral ventroposterior nucleus, posterior thalamic nucleus, zona incerta, lateral posterior nucleus, laterodorsal nucleus, ventrolateral nucleus and reticular nucleus. 2. NC decreased the firing rate in 60% of thalamic neurons. This decrease in firing rate was accompanied by a significant reduction in the number of high threshold bursts. 3. In about 20% of the neurons NC increased the firing rate. In most cells NC-induced increases in discharge rate could be blocked by the GABA(A) receptor antagonists bicuculline and SR 95531. 4. The NC receptor ligands [Phe(1)Psi(CH(2)-NH)Gly(2)] nociceptin(1-13)NH(2), Ac-RYYRIK-NH(2) and [Nphe(1)]NC(1-13)NH(2) were also evaluated. All these peptides inhibited NC-induced changes in firing rate. In addition, in some neurons where NC inhibited firing, [Nphe(1)]NC(1-13)NH(2) and Ac-RYYRIK-NH(2) elicited per se an increase in firing rate, suggesting the existence of tonic innervation of thalamic neurons by NC-containing fibres. 5. In NC-inhibited neurons nocistatin induced a significant increase in firing rate. 6. The present study demonstrated that NC regulates various thalamic nuclei related not only to somatosensory, but also to the visual and motor functions.

Action Potentials↗
PubMed2000

Optical imaging reveals characteristic seizure onsets, spread patterns, and propagation velocities in hippocampal-entorhinal cortex slices of juvenile rats.

We have combined recordings with extracellular microelectrodes or ion-sensitive electrodes and imaging of intrinsic optical signal changes to study the spatiotemporal pattern of seizure onset and spread during development. We have employed the entorhinal cortex-hippocampus brain slice preparation of juvenile rats at different stages of postnatal maturation. Three age groups were analyzed: 4-6 days (age group I), 10-14 days (age group II), and 20-23 days (age group III). Seizure-like events were induced by perfusion of slices with Mg(2+)-free artificial cerebrospinal fluid thereby removing the Mg(2+) block of the N-methyl-d-aspartate receptor. Seizure susceptibility was highest in age groups II and III. In age group I seizure-like events originated mainly in the hippocampus proper. Seizure-like events in age group II originated mainly in the entorhinal cortex and this tendency was even more pronounced in age group III. Invasion of the hippocampal formation via the perforant path-dentate gyrus and via the subiculum was seen in age groups I and II. In contrast, in age group III the hippocampus was invaded exclusively via the subiculum pathway. The velocity of spread at which seizure-like events propagated within different regions of the slice increased with postnatal age. The characteristics of onset, spread patterns, and propagation velocities as revealed by this study allow insight into the evolving properties of the developing brain.

Action Potentials↗
PubMed2000

Comparison of intrinsic optical signals associated with low Mg2+-and 4-aminopyridine-induced seizure-like events reveals characteristic features in adult rat limbic system.

PURPOSE: To analyze the intrinsic optical signal change associated with seizure-like events in two frequently used in vitro models-the low-Mg2+ and the 4-aminopyridine (4-AP) models-and to monitor regions of onset and spread patterns of these discharges by using imaging of intrinsic optical signals (IOS). METHODS: Combined hippocampal-entorhinal-cortex slices of adult rats were exposed to two different treatments: lowering extracellular Mg2+ concentrations or application of 100 microM 4-AP. The electrographic features of the discharges were monitored using extracellular microelectrodes. Optical imaging was achieved by infrared transillumination of the slice and analysis of changes in light transmission using a subtraction approach. The electrographic features were compared with the optical changes. Regions of onset and spread patterns were analyzed in relevant anatomic regions of the slice. RESULTS: Both lowering extracellular Mg2+ concentrations and application of 4-AP induced seizure-like events. The relative duration of the intrinsic optical signal change associated with seizure-like events in the low-Mg2+ model was significantly longer compared with that seen with those occurring in the 4-AP model, although duration of field potentials did not differ significantly in the two models. Seizure-like events of the low-Mg2+ model originated predominantly in the entorhinal cortex, with subsequent propagation toward the subiculum and neocortical structures. In contrast, no consistent region of onset or spread patterns were seen in the 4-AP model, indicating that the seizure initiation is not confined to a particular region in this model. CONCLUSIONS: We conclude that different forms of spontaneous epileptiform activity are associated with characteristic optical signal changes and that optical imaging represents an excellent method to assess regions of seizure onset and spread patterns.

4-Aminopyridine↗
PubMed1999

Intrinsic optical signal measurements reveal characteristic features during different forms of spontaneous neuronal hyperactivity associated with ECS shrinkage in vitro.

We induced three different forms of spontaneous synchronous hyperactivity in adult rat hippocampal-entorhinal cortex slices in order to investigate effects on the intrinsic optical signal and associated changes in the extracellular space (ECS) volume. Low-Mg2+ artificial cerebrospinal fluid (ACSF) and the addition of 4-aminopyridine induced synchronous hyperactivity resulting mainly from increased synaptic transmission, while low-Ca2+ ACSF induced hyperactivity in the absence of evoked synaptic transmission. In the two models of enhanced synaptic transmission, spontaneous activity lead to an immediate increase of light transmission. In contrast, a decrease of light transmission took place during low-Ca2+-induced hyperactivity. All three forms of synchronous neuronal hyperactivity were associated with a shrinkage of the ECS volume, as revealed by the tetraethylammonium signal, measured with ion-sensitive microelectrodes. This indicates that the change in the intrinsic optical signal is not simply related to a shrinkage in ECS volume. We conclude that different forms of spontaneous synchronous neuronal hyperactivity are associated with characteristic optical signals and that the direction of the change in intrinsic optical signal does not reflect ECS shrinkage alone.

4-Aminopyridine↗
PubMed1995

"Human pancreas-specific protein" (procarboxypeptidase B): a valuable marker in pancreatitis?

Human pancreas-specific protein (PASP) has been characterized previously as a serum marker for pancreatitis. It was then identified as pancreatic procarboxypeptidase B (PCB). The aim of the present study was to verify the usefulness of PASP (PCB) as a serum marker in patients with acute (n = 20) and chronic (n = 12) pancreatitis and in those following endoscopic retrograde cholangiopancreaticography (ERCP) (n = 44). Serum PASP values were analyzed by radioimmunoassay, with a range of normal values between 15 and 111 ng/ml. Between April 1992 and September 1992, 20 subjects (19-86 years of age) with acute pancreatitis (alcoholic, 8; biliary, 8; other, 4) were studied. We found edematous pancreatitis in 17 cases and severe hemorrhagic pancreatitis in three cases. At admission, peak levels of PASP (average value, 1,976 +/- 329 ng/ml), pancreatic isoamylase (942 +/- 151 U/L) and lipase (2,946 +/- 534 U/L) were detected in 15 of 20, 16 of 20, and 12 of 20 cases, respectively. The etiology of the pancreatitis had no influence on the PASP values. Furthermore, 10 patients with alcoholic and two patients with nonalcoholic chronic pancreatitis (29-67 years of age) were studied. The average peak level of PASP was 1,229 +/- 434 ng/ml. In this group, PASP paralleled the time course of amylase and lipase. Maximal PASP, amylase, and lipase levels were found in 11 of 12, nine of 12, and five of 12 patients, respectively, on the day of admission. ERCP was performed in 44 patients (36-87 years of age), demonstrating common bile duct stones in 16 and bile or pancreatic ductal tumors in 15 cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1993

Gaze motor asymmetries in the perception of faces during a memory task.

In 33 male and female adult volunteers, eye position recordings were performed by means of an infrared reflection technique. Slides of randomly shuffled black-and-white photographs (7.5 x 10 degrees) of faces and vases were projected for 6 or 20 sec respectively in a visual memory task. In each series, 10 slides of art nouveau vases and of the "inner part" of masked Caucasian faces were used. During recording the head was fixed by a bite-board. (a) For faces the preferred targets of the centre of gaze were the eyes, the mouth and nose region, for vases the contours and some prominent ornaments. (b) Left-right asymmetries in the gaze-movement sampling strategy appeared with faces, but not with vases. In faces, the overall time that the centre of gaze remained in the left half of the field of gaze was significantly longer than in the right half. (c) When, however, the amplitude of the gaze excursions into the left and right halves of the inspected items was taken as a measure and normalized, a preference for the right gaze field was observed. (d) The relative left-right bias during face inspection was stronger with the 6 sec than with the 20 sec inspection period and significantly stronger in female than in male subjects for the 6 sec tasks. (e) Left/right inversion of the face stimuli did not abolish the side bias. Thus the asymmetric sampling strategy when faces were inspected as compared to vases was due to "internal" factors on the part of the subjects. It is hypothesized that a left-right asymmetry in hemispheric visual data processing for face stimuli was the cause of a left-right asymmetry in gaze motor strategies when faces were inspected.

Adult↗
PubMed1991

Causes and signs of temporomandibular joint pain and dysfunction: an electromyographical investigation.

The spontaneous muscular activity of the masseter and two non-masticatory muscles, and their activity under conditions of noise and flickering light, were recorded in 30 patients with mandibular dysfunction, and in 25 control subjects. The mood of the subjects during the investigation, and the possible presence of emotional disturbances was evaluated by means of questionnaires. The enhanced muscular activity of the masseter muscle differentiated patients from the control group, although it does not constitute a pathognomic sign. Unilaterality of complaints, and dysfunctions of differing intensity were not reflected in differential EMG findings. One-fifth of the patients exhibited neck muscle activity occurring simultaneously with the masseter activity. The effect of the applied stimuli on the muscular activity was not homogeneous, leading to activation in some cases and inhibition in others. Symptoms of anxiety could be observed in seven TMJ patients. Anxious patients showed higher levels of muscular activity and emotional irritability during the experiment than non-anxious patients.

Action Potentials↗
PubMed1987

Eye and head movements to visual and auditory targets.

Coordinated eye-head movements evoked by the presentation of visual, auditory and combined audio-visual targets were studied in 24 human subjects. At 60 deg located targets latencies of eye and head movements were shorter for auditory than for visual stimuli. Latencies were shorter for bisensory than for monosensory targets. The eye and head latencies were differently influenced by the modality of the stimulus when the eccentricity of the target was changed, but not by the variation of the stimulus duration. The different responses of the eye and the head depending on target modality and target eccentricity can be partially attributed to perceptual and central processing mechanisms, and are important to answer the question about the initial event in coordinated eye-head orientation.

Acoustic Stimulation↗
PubMed1982

Effector pattern of the audio-visual targeting reflex in cats.

The development of the effector pattern of the unconditioned and instrumental conditioned audio-visual targeting reflex was studied. EOG and EMG electrodes were implanted to analyze the movements of the pinna, eye and head, when the animals localized a sound source placed in different positions in space. When the acoustic stimulus was repeated, the unconditioned targeting reflex was characterized by a rapid intra- and intersessional habituation of the three motor components. In the second part of the experiment the unconditioned targeting reflex was reinforced by food to build up an instrumental conditioned targeting reflex. It was shown, that under both experimental conditions the targeting reflex began with the auricular component, followed by the oculo-cephalic response. After conditioning the latencies were decreased in comparison with the unconditioned reactions. The shortest latencies and most stable responses were found in the pinna muscles ipsilateral to the sound source. After conditioning the resistance to extinction was increased for all three motor components, but the pinna movement ipsilateral to the sound source was again the component most resistant to extinction.

Animals↗
PubMed1981

Effects of motor denervation of the external ear muscles on the audio-visual targeting reflex in cats.

The effect of uni- and bilateral denervation of muscles of the pinna on the audio-visual targeting reflex reinforced by food was studied. In comparison with the normal group the unilaterally denervated animals showed a decreased capacity to localize sound sources placed behind the animal ipsi- and contralaterally to the operated side. The denervation of the second ear in these animals induced a further decrease of the localization scores, especially of the sources placed behind them. The localization behavior strategies were different depending on the integrity of the innervation of muscles of the pinna. The stimulation of the operated side with tones of a 30 dB higher intensity than in the normal side did not improve the animals’performance in localizing the sound sources. The shortening of duration from 500 to 50 ms reduced, the capacity to localize the loudspeakers placed ipsilaterally to the denervated side, especially those behind the animal. The role for the targeting reflex of the feedback information from the muscles controlling the pinna movements, and the significance of the postural changes induced by the tone are discussed.

Animals↗