PubMed Health⌕ Search

Biomedical subjects

J Wenzel

Publications and source records attributed to J Wenzel.

At least 19 recordsLinked to original sources
PubMed1995

Brainstem auditory evoked potentials during a helium-oxygen saturation dive to 450 meters of seawater.

When divers are exposed to extreme atmospheric pressures they may exhibit symptoms of the high pressure nervous syndrome (HPNS). Although clinical HPNS symptoms are well described, little is known about the underlying pathophysiologic mechanisms. Special HPNS signs like vertigo and tremor suggested sensory-motor hyperexcitability resulting from brainstem dysfunction. We therefore studied brainstem auditory evoked potential (BAEP) repeatedly in four divers during an experimental deep helium-oxygen saturation dive to 450 meters of seawater (msw). Wave I (auditory nerve response) latency decreased whereas interpeak latencies (IPLs) I-III and I-V, which indicate respective cochleo-pontine and cochleo-mesencephalic transmission time, prolonged during the dive. IPLs III-V also prolonged the dive, but with greater variability among divers. Two divers showed a marked reversal of the normal attenuation effect of increased stimulus presentation rates on IV and V amplitudes during compression, an effect that subsided during the stay at bottom depth. This finding might indicate a relative enhancement of synaptic excitability and is presumed to be a feature of HPNS. Wave I latency reduction might at least partly be caused by accelerated sound conduction in dense helium. Additionally, an upward shift of middle ear resonance frequencies in helium can induce a basal shift of the main cochlear portion responding to the wide band clicks. This effect may reduce wave I latency due to greater relative input from the basal high frequency-short latency-cochlear neurons. Pressure-induced decrease of nerve conduction velocity, delay of synaptic transmission, and inhibitory modulation of midbrain auditory afferents possibly contributed to observed interpeak latency prolongations. Clinical HPNS signs, such as tiredness, dizziness, postural and intentional hand tremor, ataxia, and opsoclonus, were noted in three divers after reaching 300 msw and continued throughout the 37-h stay at bottom depth.

Adult↗
PubMed1994

Rapid development of somatic spines in stratum granulosum of the adult hippocampus in vitro.

Somatic spines on granule cells have been observed occasionally in the adult rat dentate gyrus in vivo. Here we evaluate the appearance and formation of somatic spines in s. granulosum from adult rat hippocampal slices immediately after slice preparation, 45 min, 3 h, and 5 h later. Initially somatic spines are extremely rare but, after 3 h in vitro, they are readily apparent. Some of these somatic spines form asymmetric synapses that have a spherical vesicle-containing presynaptic bouton and a postsynaptic density. Other somatic spines lack a postsynaptic density and may also lack an apposed presynaptic bouton (free somatic spines) as observed in single thin sections. Both the number of these free somatic spines and the number of somatic spine synapses increase in a time-dependent manner. No somatic spines were observed on CA1 pyramidal cells in the same hippocampal slices. Electrophysiological observations indicate that the formation of somatic spine synapses on granule cells in the hippocampal slice occurs without any apparent granule cell activation. The trigger event for this very rapid synaptogenesis in the adult dentate gyrus remains to be determined.

Animals↗
PubMed1993

Somatic ribosomal changes induced by long-term potentiation of the perforant path-hippocampal CA1 synapses.

The present study quantified ribosomes, as an ultrastructural marker of neuronal protein synthesis, following long-term potentiation (LTP) in the hippocampal CA1 region in vitro. Sixty min after LTP-inducing, high-frequency stimulation of the perforant path, the total number of ribosomes, the number of polysomes, and the number of membrane-bound ribosomes increased significantly. These increases are a postsynaptic morphological correlate consistent with enhanced protein synthesis following the induction of LTP in the perforant path-CA1 system.

Animals↗
PubMed1993

A case of breath holding and ascent-induced circulatory hypotension.

We report a case of transient circulatory depression due to inadvertent apnea of a subject during decompression from a stimulated dive. The dive consisted of exposure to air at 5 bar and subsequent decompression stops. Arterial blood pressure and a lead II ECG were recorded continuously. During decompression from 1.6 to 1.3 bar, the subject inadvertently held his breath. Arterial pressure fell rapidly from 120/80 to 60/53 mmHg within 20 s. Recognizing that the subject held his breath, one of the supervisors ordered him to resume breathing, and arterial blood pressure was restored rapidly. This circulatory depression was probably due to reduced stroke volume such as described for the syncope of ascent: with the subject retaining his breath, the expanding lung volume increased intrathoracic pressure resulting in impaired venous return.

Atmosphere Exposure Chambers↗
PubMed1992

Parvalbumin-containing nonpyramidal neurons in intracortical transplants of rat hippocampal and neocortical tissue: a light and electron microscopic immunocytochemical study.

Previous immunocytochemical studies have shown that GABAergic nonpyramidal neurons of the rat hippocampus survive in intracerebral transplants. However, information is still lacking about the dendritic organization and the input synapses of these cells as well as their capacity to express the calcium-binding protein parvalbumin (PARV) under transplant conditions. In the present study, a monoclonal antibody against PARV was used to examine the dendritic morphology and the synaptic organization of parvalbumin-containing GABAergic neurons in hippocampal and dentate transplants. In addition, parvalbumin-containing nonpyramidal neurons were studied in neocortical transplants to compare the differentiation of grafted allocortical and neocortical nonpyramidal neurons. Tissue blocks of hippocampus and fascia dentata and of the parietal neocortex were taken from late embryonic rats (E 21 and E 16, respectively) and were transplanted into a cavity in the somatosensory cortex of young adult rats. After 3.5 or 7 months survival, the recipient brains were fixed by perfusion and immunostained for PARV. As in the hippocampal formation in situ, PARV-containing neurons in the hippocampal transplants were observed within and in the vicinity of the pyramidal and granule cell layer. In neocortical transplants, PARV-immunoreactive cells were distributed in all parts of the transplant with dendrites extending in various directions. In both hippocampal and neocortical transplants, immunoreactive dendrites were smooth and displayed the characteristic regular varicosities known from in situ studies of these cells. Numerous unlabeled terminals as well as a few immunoreactive boutons established synapses on the immunoreactive dendrites. PARV-positive terminals formed the typical pericellular baskets around the immunonegative cell bodies of pyramidal neurons and granule cells in the transplants. They established symmetric synapses with cell bodies and proximal dendrites. Synapses on axon initial segments were absent or rare. Our results demonstrate that allocortical as well as neocortical nonpyramidal neurons transplanted to the neocortex of adult recipients survive transplantation, express the calcium-binding protein parvalbumin, and develop a cell-specific morphology.

Animals↗
PubMed1992

Human brainstem auditory-evoked potentials in deep experimental diving to pressures up to 62.5 bar.

The neural mechanisms underlying the high pressure neurologic syndrome (HPNS), which limit man's safe advance to extreme diving depths, are still unclear. This work was aimed at a better understanding of HPNS through study of brainstem auditory-evoked potentials (BAEP). BAEP were repeatedly recorded within 2 experimental chamber dives, Titan VIII (2 divers, maximum depth of 560 msw, compression time to bottom 109 h) and Titan XI (3 divers, maximum depth of 615 msw, compression time to bottom 240 h). Prolongation of the IV/V-complex occurred in 2 divers upon reaching 525 msw during Titan VIII compression and was accompanied by vestibular disturbances and amplitude increases of finger tremor. Both categories of changes--clinical signs and IV/V delay--gradually diminished during a 4-day stay at 545 msw, suggesting that they depended on excessive compression rates and insufficient acclimation time. Longer holding times at intermittent depths during Titan XI clearly reduced both HPNS symptoms and magnitude of prolongation of IV/V latencies. Wave I and wave III latency did not significantly change, pointing to a suppression of pontomesencephalic transmission. We infer that pressure suppresses synaptic transmission or triggers an increase of cortical or subcortical efferent inhibitory modulation of upper pontine and midbrain auditory afferents. Postdive controls revealed no persistent changes of BAEP measures in either the Titan VIII or XI divers.

Adult↗
PubMed1992

[Morphometric-stereological study of hippocampal long term potentiation with special consideration of the analysis of variance with two-way hierarchical classification].

Regarding the hippocampal formation and especially the external two thirds of it's dentate molecular layer a lot of possible morphological changes after long-term potentiation (LTP) have been described in literature. The present morphometric-stereological study of vesicles in axo-spino-dendritic synapses of the inner third of the molecular layer was done under the aspect of heterosynaptic influences following LTP. Because of the hierarchical link of the three analytic levels (test-group, animal, synapse), for statistical interpretation we used the analysis of variance with two-way hierarchical classification. Between the 3 groups (passive control, active control, LTP-group) we found no significant differences. Because of the great differences between the vesicles even within a single synapse we subsequently investigated the middle third of the molecular layer, i.e. the terminal area of the stimulated perforant path. No differences between the three groups we found here either. There was no confirmation for the expected greater homogenization of the synapses based on the uniform input. As a result of this study pure morphological studies without selective staining of specific population of synapses are considered inadvisable. Only with the help of selective staining in the area of the synapses possible differences between the groups may be found.

Analysis of Variance↗
PubMed1991

The influence of long-term potentiation on the spatial relationship between astrocyte processes and potentiated synapses in the dentate gyrus neuropil of rat brain.

The influence of long-term potentiation (induced by repeated high-frequency stimulation of the perforant pathway) on the distribution pattern of astrocyte processes in the neuropil of the hippocampal dentate area containing the potentiated synapses was investigated by quantitative electronmicroscopy. It has been found that significant changes occurred in the ramification of astrocyte processes as well as in their topographic relation to synaptic complexes. When comparing the results obtained in LTP animals with active control or sham-operated animals, we found significant higher numerical density, but smaller volume, higher surface density and closer apposition of astrocyte processes to the synaptic clefts, boutons terminaux or spines in the potentiated synapses containing neuropil. The glial reaction to synaptic activation has been seen most pronounced 8 h after the LTP induction. The results are pointing to a participation of the glia cells in the maintenance of the LTP effect as well as to a metabolic coupling between synaptic transmission and glia function for equilibrating the homeostasis by clearing the extracellular space next to the transmission zones.

Animals↗
PubMed1991

Heterosynaptic changes in number and shape of the transmission zones of axo-spino-dendritic synapses in the central nervous system following long-term potentiation.

Regarding the hippocampal formation and especially the external two thirds of it's dentate molecular layer a lot of possible morphological changes after long-term potentiation (LTP) have been described in literature. The present morphometric-stereological study of axo-spino-dendritic synapses from the inner third of the molecular layer was done under the aspect of heterosynaptic influences following LTP. We were looking for differences in the number of transmission zones, in the total length of the transmission zone and in the qualitative shape of the single transmission membrane. Because of the hierarchical link of the three analytic levels (test-group, animal, synapse), for statistical interpretation we used the analysis of variance with two-way hierarchical classification. We detected large differences between the single synapses but not significant differences between the 3 groups (passive control, active control, LTP-group). Our quantitative studies showed the same results also in the middle third of the molecular layer (Grabs et al. 1991). Pure morphological studies should be done under selective staining of specified population of synapses to differ in stimulated and non-stimulated synapses. Only with the help of selective staining in the area of the synapses possible differences between the groups may be found.

Animals↗
PubMed1990

Spinules in axospinous synapses of the rat dentate gyrus: changes in density following long-term potentiation.

Following high frequency stimulation of the perforant path the density of axospinous synapses from the middle third of the molecular layer of the rat dentate gyrus did not change significantly. By contrast, within this synaptic population the density of axospinous synapses containing synaptic spinules increased markedly. We interpret these results in terms of a structural modification related to enhanced synaptic efficacy.

Animals↗
PubMed1990

Interactions between imipramine and morphine on motility in rats: possible relation to antidepressant effects?

The aim of the present study was to evaluate whether morphine and the more modern antidepressant drug imipramine have common effects on behavior after both acute and chronic administration, and, in particular, to establish whether they act synergistically. In rats, morphine (15 mg/kg i.p.) produced a pronounced hypokinesia, followed by locomotor activation and stereotyped behavior. After repeated administration (eight times), tolerance to the hypokinesia developed, whereas locomotor activation and stereotypies occurred earlier and were more pronounced. Subacute pretreatment with imipramine (twice daily 10 mg/kg i.p. for eight days) enhanced and prolonged hypokinesia and delayed the manifestation of stereotypies and locomotor activation. In contrast, chronic treatment with imipramine (for 29 days) no longer inhibited morphine-induced stereotypies and locomotor activation, but seemed to enhance them when they were tested in rats repeatedly treated with morphine. When the same rats were tested with morphine (15 mg/kg) seven days after withdrawal of morphine and imipramine, morphine produced increased stereotypies and a slight enhancement of locomotion. The experimental conditions used excluded the possibility that conditioning phenomena might explain the enhancement of (probably dopamine-mediated) behavior. Furthermore, the results demonstrated that 1) acute administration of morphine and subacute administration of imipramine may act in a synergistic way, and 2) repeated administration of morphine and chronic treatment with imipramine also act synergistically, although contrary to the acute actions of both drugs. These interactions might be of therapeutic or toxicological relevance.

Animals↗
PubMed1990

Nitrogen partial pressures in man after decompression from simulated scuba dives.

In five subjects arterial and central venous nitrogen partial pressures (PN2) were measured after decompression from a chamber dive following a decompression schedule for scuba diving. The simulated dives consisted of exposure at rest to air at 6 bar for 30 min. corresponding to a depth of 50 m. Afterwards the subjects were decompressed with decompression stops at 2.5, 2.2, 1.9, 1.6 and 1.3 bar with a total decompression time of 73 min. Immediately after decompression and every 40 min. until the 240th min. arterial and central venous blood samples were analyzed for PN2 using a manometric Van Slyke apparatus. Venous PN2 remained elevated until 160 min. after decompression indicating still incomplete nitrogen wash-out at least two hours after decompression had been accomplished. Bubble formation is discussed as a cause for prolonged nitrogen elimination. Our data confirm that nitrogen elimination is prolonged after decompression from simulated dives at rest.

Arteries↗
PubMed1990

Effects of morphine on gamma-aminobutyric acid turnover in the basal ganglia. Possible correlation with its biphasic action on motility.

Morphine (15 mg/kg i.p.) produces a biphasic action on motility: hypokinesia and muscular rigidity ("catatonia"), followed by a hyperkinesia in association with some stereotyped behaviour. In the present studies, alterations in GABA (gamma-aminobutyric acid) turnover were studied in possible correlation with changes in motility. As a criterion of GABA turnover its accumulation after inhibition of GABA transaminase by gamma-acetylene GABA (GAG) was measured. During the first, depressory phase only, GABA turnover was increased in the substantia nigra. In contrast, GABA turnover was continuously enhanced during both phases of morphine's action in the nucleus accumbens. No significant alterations were observed in striatum or globus pallidus. These findings seem to be consistent with the assumption of at least a short- and a long-lasting action of morphine on the basal ganglia.

Alkynes↗
PubMed1990

[The individual variability of pyramidal neurons in the neocortex of the rat].

In Golgi-Kopsch impregnated pyramid neurons of the neocortex (regio precentralis agranularis and area striata) of adult rats the individual variability was investigated. As parameters served the dendritic lengths, spine numbers and spine densities along the dendritic orders (basal and apical), within single dendritic fields, the apical and basal parts of the dendritic tree and of the whole neuron. The statistical tests gave the following results: Pyramid neurons in the regio precentralis agranularis are more variable than pyramid neurons in the area striata. Within the area striata the lamina III-pyramid neurons are more invariable than the lamina V-pyramid neurons. The basal dendrites are statistically more invariable than the apical dendrites. The dendritic lengths are less variable than the spine values. In general, the variability is different in particular subdivisions of the neurons analyzed as well as for the parameter chosen. The variability of neuronal structures depends from genetical factors and from a functional training. The knowledges about this variability are still insufficient. They are of considerable importance for the planning of experiments followed by statistical analyses.

Animals↗
PubMed1990

Development of enolase isoenzymes in various regions of the human brain.

Various brain regions from 4 fetuses (21st to 28th gestational week) and from a 3-month-old infant were investigated for the total enolase activity and their isoenzyme distribution. In the brain tissue from a 3-month-old infant, the activity of the so-called neuron-specific enolase amounted to about 50% of the total enolase activity. In various brain regions different developmental patterns emerged for nonneuronal (NNE) and neuron-specific enolase (NSE). By the 21st gestational week the medulla, pons and thalamus had already reached a relatively high NSE activity (about 60-90% of that of the 3-month values), whereas the cortex regions had 10-30% only. It is concluded that in phylogenetically old regions, the switch from NNE to NSE-subunits appears before the 21st gestational week, in the phylogenetically young regions between the 21st and 28th gestational week.

Brain↗
PubMed1990

Nitrogen partial pressures in man after decompression from simulated scuba dives at rest and during exercise.

In 5 subjects arterial and central venous nitrogen partial pressures (PN2) were measured after decompression from a chamber dive following a decompression schedule for scuba diving. The simulated dives consisted of exposure to air at 6 bar for 30 min corresponding to a depth of 50 m. Afterward the subjects were decompressed with decompression stops at 2.5, 2.2, 1.9, 1.6, and 1.3 bar with a total decompression time of 67 min. In 3 of the subjects the measurements were repeated after they had exercised (workload 75 W) during bottom time. Immediately after decompression and every 40 min until Minute 240 arterial and central venous blood samples were analyzed for PN2 using a manometric Van Slyke apparatus. Venous PN2 remained elevated until 160 min after decompression, indicating still incomplete nitrogen washout for at least 2 h after decompression had been accomplished. We did not find any difference in PN2 values after decompression from dives at rest and after exercise. Applying a computer program based on a wide range of theoretical tissue half-times nitrogen elimination proved to be consistent with Haldanian theories when using our decompression profile. Our data confirm that nitrogen elimination is prolonged after decompression from simulated dives at rest and after exercise.

Adult↗
PubMed1989

Morphine-induced alterations of local cerebral glucose utilization in the basal ganglia of rats.

The actions of various doses of morphine on the local cerebral glucose utilization (LCGU) were studied by means of the autoradiographic [14C]2-deoxyglucose technique. Morphine (1-15 mg/kg i.p.) decreased LCGU in most areas of the basal ganglia (caudate nucleus, globus pallidus, nucleus accumbens), but not in the substantia nigra pars compacta. LCGU was also decreased in limbic nuclei, such as septum, hippocampus and amygdala, and in most thalamic areas. In most cortical regions, a decrease was found as well. Findings in some efferent nuclei seemed of particular interest, namely in the substantia nigra pars reticulata, anteroventral and lateral nucleus of the thalamus and the subthalamic nucleus, where decreases in LCGU were found after administration of 7.5 mg/kg or sometimes lower doses, but not after 15 mg/kg of morphine. The decreases seem to reflect a general depressory effect of morphine on neuronal activity which is known from electrophysiological studies. Part of these effects might be, in addition, due to an activation of dopaminergic neurons, since dopamine mainly acts as an inhibitory neurotransmitter. This dopaminergic activation leads to characteristic behavioral effects after lower doses of morphine. The largest dose used (15 mg/kg) produces muscular rigidity, probably by a direct action on the striatum. This effect antagonizes and masks the dopaminomimetic effects. The results suggest that it also antagonizes the functional alterations in some efferent nuclei of the basal ganglia manifest after lower doses of morphine. Local injections of morphine (15 micrograms) led to decreases of LCGU in the various parts of the striatum, but to increases in lateral and anteroventral thalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗