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Biomedical subjects

K Schwabe

Publications and source records attributed to K Schwabe.

At least 19 recordsLinked to original sources
PubMed2004

Role of the medial prefrontal cortex in N-methyl-D-aspartate receptor antagonist induced sensorimotor gating deficit in rats.

The medial prefrontal cortex (mPFC) regulates sensorimotor gating measured as prepulse inhibition (PPI) of startle. We here tested the effect of lesions of the mPFC on the PPI-disruptive effect of the non-competitive NMDA receptor antagonist dizocilpine in rats. Neurotoxic lesions of the mPFC were induced by ibotenic acid. Rats were tested for PPI after systemic injection of dizocilpine (0.15 mg/kg) and after injection of the dopamine receptor agonist apomorphine (2 mg/kg). Dizocilpine failed to disrupt PPI in rats with mPFC lesions while the PPI-disruptive effect of apomorphine was not affected. Startle response magnitude in the absence of prepulses was not affected by mPFC lesions or drugs. These data suggest that the mPFC is an important brain region within the neuronal circuit responsible for NMDA receptor antagonist induced PPI-deficits.

Animals↗
PubMed2004

The central piriform cortex: anatomical connections and anticonvulsant effect of GABA elevation in the kindling model.

The piriform cortex (PC) is thought to be critically involved in the generation and propagation of forebrain (limbic type) seizures in the rat. The PC extends over a large area at the ventrolateral side of the rat brain with an anterior part highly sensitive for bicuculline-induced and a central part most sensitive for electrically induced seizures. Therefore, distinct parts of the PC might be differentially involved in the generation and spread of seizure activity. Since previous studies indicated that a loss of GABAergic inhibition in the PC is involved in the generation of epileptic activity, we microinjected the GABA-transaminase blocker vigabatrin bilaterally in the anterior, central and posterior PC of previously amygdala-kindled rats and repeatedly tested its effect on kindled seizures. Vigabatrin was anticonvulsant in all groups for up to 13 days with a maximal effect 24 h after injection. However, the anticonvulsant effect on seizure generalization was strongest after microinjection in the central PC suggesting that GABAergic synapses in this part are critically involved in the development of generalized seizures. Since differences in anatomical connections of the PC regions may be responsible for differences in seizure susceptibility, we addressed this question by injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin in different PC subregions. Although there were similarities in the projections from different PC subregions, we also found differences between the PC subregions in their projections to structures known to be important in the limbic seizure network, such as the perirhinal cortex, nucleus accumbens, and striatum. These differences in anatomical connectivity between PC subregions may be involved in the differences in seizure susceptibility observed in the present and previous studies.

Animals↗
PubMed2004

Role of glutamate receptors in nucleus accumbens core and shell in spatial behaviour of rats.

The nucleus accumbens (NAC) is considered to be an important neural interface between corticolimbic and motor systems of the brain. Several studies have shown that the NAC is not only involved in motivation and reward-related processes but also in spatial behavior. We here investigated the involvement of different glutamate receptor subclasses within NAC core and shell subregions on behavior in a radial-maze. Rats were first trained in a four-arm-baited eight-arm radial maze task for baseline performance. Thereafter, the effects of microinjection of the nonselective glutamate receptor antagonist kynurenic acid (4.5 microg), the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (1 microg) and the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (0.75 microg) in NAC core and shell were tested on reference memory errors (RME) and working memory errors (WME). Moreover, the choice pattern of entries and duration of arm-entries were evaluated. Microinjection of all drugs increased RME. Additionally, non-NMDA receptor blockade in NAC shell but not core increased WME. After microinjection of all drugs into NAC core and shell rats preferentially choose the arms next to the previously visited arm. This work shows that glutamate receptors in both NAC subregions are important for spatial behavior. The deficits seen after glutamate receptor blockade may not be working- or reference memory-related but caused by a switch from a memory-dependent allocentric strategy to an egocentric response strategy.

2-Amino-5-phosphonovalerate↗
PubMed2004

Effects of neonatal excitotoxic lesions of the entorhinal cortex on cognitive functions in the adult rat.

The entorhinal cortex (EC) is involved in a variety of cognitive functions by virtue of its neuronal input from the neocortex and projection to the hippocampal formation and the limbic-striatal system. Neonatal lesions are increasingly considered useful models for disconnection syndromes such as schizophrenia. Therefore, we investigated the effects of neonatal EC lesions on adult rat behavior. Neonatal (postnatal day 7) lesions were inflicted by bilateral injections of ibotenate into the EC. Sham-lesioned (vehicle injection) and naive (unoperated) rats served as controls. Locomotor activity was measured in prepubertal and young adult rats. Adult rats were then tested for spatial learning in an eight-arm radial maze (reinforced delayed alternation) and for motivation (progressive ratio schedule of operant behavior). Finally, prepulse inhibition (PPI) of the acoustic startle reflex and locomotor activity were investigated with and without apomorphine (APO) challenge. Brain tissue damage was assessed using Nissl-staining. The total volume of the adult rat EC was reduced after neonatal ibotenate-injection. Neonatal EC-lesions increased perseveration only in a delayed task in the radial maze and induced a leftward-shift of breakpoints in operant responding. Lesions did not alter baseline locomotor activity, but enhanced the locomotor stimulating effect of APO. PPI was not affected by neonatal lesions of the EC with and without APO challenge. Neonatal lesions of the EC impaired the ability to hold information during delays and reduced motivation during operant behavior which reflects a state of anhedonia. Thus, they may serve as an animal model for certain aspects of schizophrenia.

Aging↗
PubMed2004

Bilateral microinjections of vigabatrin in the central piriform cortex retard amygdala kindling in rats.

The piriform cortex (PC) is the largest region of the mammalian olfactory cortex with strong connections to limbic structures, including the amygdala, hippocampus, and entorhinal cortex. Various previous studies in rodents suggest that the PC might be very important in the development and maintenance of limbic kindling, i.e. a widely used model of temporal lobe epilepsy. GABAergic inhibition in the transition zone between the anterior and posterior PC, termed here central PC, seems to be particularly involved in the processes leading to progression of kindled seizures. This prompted us to study whether elevation of GABA levels in this subregion of the PC by bilateral microinjection of vigabatrin is capable of suppressing amygdala kindling. Rats were stimulated once daily until fully kindled (stage 5) seizures had developed. Vigabatrin (10 microg) was injected 24 h before the first stimulation as well as 6 h before the 5th and 10th stimulation, which approximately doubled the number of stimulations required for kindling development compared with controls. This marked retardation of kindling acquisition was predominantly due to a significant inhibition of the progression from stage 1 to stage 2 and stage 3 to stage 4 seizures, demonstrating that microinjection of vigabatrin into the central PC markedly inhibits the progression and secondary generalization of focal seizures emanating from the amygdala.

Amygdala↗
PubMed2001

Persistent back pain after spinal anaesthesia in the non-obstetric setting: incidence and predisposing factors.

We determined the incidence of persistent back pain (PBP) after non-obstetrical spinal anaesthesia (SPA) and investigated factors predisposing to such pain in a prospective 1 yr follow-up study in 245 patients undergoing elective general or trauma surgery (218 patients undergoing single SPA, 27 undergoing two to six SPAs). All patients received a first questionnaire 3 months after the last SPA, and those reporting PBP after 3 months were sent a second questionnaire I year after the operation. Variables were PBP before and within 5 days, at 3 months and I year after SPA, patient satisfaction with SPA, patient characteristics and technical data. Statistical analysis was by contingency tables with Fisher's exact test and an unpaired t-test with logistic regression (P < 0.001 after Bonferroni correction was taken as significant). The response rate in patients who had a single SPA was 56% (122/218). Twenty-three of these 122 patients (18.9%) complained of back pain before SPA compared with 12/122 (10.7%, P = 0.0015) within 5 days after SPA. After 3 months, 15/122 patients (12.3%) reported PBP with 14 complaining of PBP before SPA (P < 0.0001), corresponding to an incidence of new PBP of 1/122 (0.8%). Multiple logistic regression revealed that pre-existing back pain was the only variable associated with PBP after 3 months (P < 0.0001). Patient characteristics and technical factors were not associated with PBP. Nine of the 15 patients with PBP after 3 months returned the second questionnaire: four still reported PBP (three of these had suffered from PBP before SPA). Despite PBP after 3 months, 13/15 patients said they would opt for SPA again. The response rate and results in patients who had had multiple SPAs were similiar to those who had had a single SPA.

Adult↗
PubMed2000

Development of kindling and spontaneous seizures after massed stimulation of different loci in the rat piriform cortex.

Massed electrical stimulation of the anterior piriform cortex (PC) in rats using short (5 min) interstimulus intervals has previously been reported to induce severe chronic epilepsy with spontaneous seizures and has thus proposed to represent a novel model of temporal lobe epilepsy. In the present study, we used this stimulation protocol to evaluate the frequency and severity of recurrent spontaneous seizures produced in this way. In addition to the locus in the anterior PC previously used for massed stimulation (MS), we also stimulated rats via a locus in the transition zone between anterior and posterior PC ("central PC"), which previously was found to be more sensitive to electrical stimulation than various other loci in the anterior or posterior PC. During MS (71 stimulations for 1 s each at twice afterdischarge threshold), focal and infrequent secondary generalized seizures occurred in both groups, but there was no consistent progressive increase in seizure severity with increasing number of seizures, possibly as a result of postictal inhibitory processes. Following MS, rats were restimulated after 1, 2, 4, and 7 weeks, using five stimuli at 5-min interstimulus periods at each retest period. In both PC-implanted groups, seizure severity and seizure duration progressively increased over the period of the retests, indicating a delayed development of kindling. Spontaneous seizures were only observed rarely, so that MS of the PC is certainly no effective means of producing recurrent spontaneous seizures.

Animals↗
PubMed2000

Bilateral lesions of the central but not anterior or posterior parts of the piriform cortex retard amygdala kindling in rats.

The piriform cortex is thought to be involved in temporal lobe seizure propagation, such as that occurring during kindling of the amygdala or hippocampus. A number of observations suggested that the circuits of the piriform cortex might act as a critical pathway for limbic seizure discharges to assess motor systems, but direct evidence for this suggestion is scarce. Furthermore, the piriform cortex is not a homogeneous structure, which complicates studies on its role in limbic epileptogenesis. We have previously reported data indicating that the central part of the piriform cortex might be particularly involved during amygdala kindling. In order to further evaluate the role of different parts of the piriform cortex during kindling development, we bilaterally destroyed either the central, anterior or posterior piriform cortex by microinjections of ibotenate two weeks before onset of amygdala kindling. Lesions of the anterior piriform cortex hardly affected kindling acquisition, except that fewer animals exhibited stage 3 (unilateral forelimb) seizures compared to sham controls. Lesions of the central piriform cortex significantly retarded kindling, which was due to a decreased progression from stage 3 to stage 4/5 seizures, i.e. the lesioned rats needed significantly longer for the acquisition of generalized clonic seizures in the late stages of kindling development. Lesions of the posterior piriform cortex did not significantly affect kindling development. The data demonstrate that different parts of the piriform cortex mediate qualitatively different effects on amygdala kindling. The central piriform cortex seems to be a neural substrate involved in the continuous development of kindling from stage 3 to stages 4/5, indicating that this part of the piriform cortex may have preferred access, either directly or indirectly, to structures capable of supporting generalized kindled seizure expression.

Amygdala↗
PubMed2000

Effects of lesions of the perirhinal cortex on amygdala kindling in rats.

The perirhinal cortex (PRC), the region of temporal cortex adjacent to the rhinal sulcus, has been suggested as a critical substrate for the development and expression of generalized motor seizures in the late stages of kindling development. For further investigation of the role of the PRC in limbic kindling, excitotoxic lesions centered on PRC by microinjection of ibotenate were performed in rats 2 weeks before onset of amygdala kindling. Rats with large bilateral or unilateral PRC lesions showed the same rate and pattern of kindling development as sham-lesioned controls. The only significant difference to controls was a higher afterdischarge threshold in the fully kindled state of lesioned rats. These data do not indicate a critical role for the bilateral involvement of the PRC in kindling from other limbic brain regions.

Amygdala↗
PubMed1997

Pharmacodynamic modelling of the analgesic effects of piritramide in postoperative patients.

BACKGROUND: The concentration-effect relationship of piritramide, a synthetic opioid analgesic predominantly used for postoperative analgesia and analgosedation, has not been reported so far. METHODS: Twenty-four patients of both genders aged 58.1 (11.7) yr (mean (SD)) received inhalational anaesthesia for abdominal surgery. Postoperative pain was assessed with a visual analogue scale (VAS). Analgesia was provided with piritramide, infused at a rate of 7 micrograms.kg-1.min-1 until analgesia was considered sufficient (VAS < 25) or up to a maximum dose of 0.2 mg/kg. The plasma concentrations of piritramide were determined by gas chromatography. An inhibitory fractional sigmoid Emax-model was used to describe the relation between effect site concentration and perceived pain. RESULTS: The equilibration half-life between plasma and effect site concentrations (T1/2 (keo)) was 16.8 min (median; range: 4.4-41.6 min). The steady-state plasma concentration required to produce 50% of maximum analgesia (EC50) was 12.1 ng/ml (range: 2.9-29.8 ng/ml) and correlated with initial pain intensity. The slope factor gamma was 1.9 (range: 0.5-6.1) and increased with age. Clinically relevant respiratory depression did not occur. Due to the relatively large equilibration half-life of the effect compartment, the context-sensitive half-time of the effect site concentrations after short-time administration (< 2 h) clearly exceeded those of alfentanil, sufentanil, and fentanyl. CONCLUSIONS: The analgesic effect of piritramide was adequately described by an inhibitory fractional Emax-model. In order to overcome the pronounced hysteresis, piritramide should initially be administered as an intravenous bolus of at least 5 mg.

Adult↗
PubMed1995

[Effect of lowered cholesterol on the course of coronary heart disease. An analysis of the results of controlled, angiographically documented intervention studies].

AIM: To find out from published reports whether the tendency of coronary heart disease (CHD) to progress can be retarded by lowering total and LDL cholesterol concentrations. METHODS: After a data-base search a meta-analysis was undertaken of all those randomized, controlled and angiographically documented studies which contained informations about the effect of cholesterol reduction on the course of CHD over a period of at least 2 years. A total of 12 studies covering 3781 patients met the stated criteria. RESULTS: The different lipid-lowering measures (usually drugs) achieved a statistically significant reduction of the number of patients with progression of the coronary angiographic findings and a significant increase in the number of those with actual regression. The number of coronary incidents, such as myocardial infarction, unstable angina, sudden cardiac death, necessary aortocoronary bypass operations or percutaneous transluminal coronary angioplasty was lower by 34% in the groups with measures to influence cholesterol metabolism than in the untreated groups. In the studies in which coronary arteriograms were evaluated quantitatively there was an annual increase in the mean degree of stenosis of 1.01% in the untreated and 0.37% in the treated groups. CONCLUSIONS: The difference in the increase of the mean degree of stenosis is probably not only important because of the resulting haemodynamic changes in myocardial perfusion. The quantitatively only slightly increased trend towards progression in the untreated groups can be interpreted as a marker for an active process of atherogenesis with a tendency of plaques to break off and of plaque thromboses.

Anticholesteremic Agents↗
PubMed1995

Reversal of multidrug resistance by novel cyclosporin A analogues and the cyclopeptolide SDZ 214-103 biosynthesized in vitro.

It was shown that cyclopeptolide SDZ 214-103 (10 microM) is more active in rhodamine-123 accumulation in actinomycin-D-resistant human lymphoma cells CCRF/ACTD400 than cyclosporin A (10 microM), but equipotent in the doxorubicin-resistant Friend erythroleukemia cell line F4-6/ADR. In F4-6/ADR cells, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay showed comparable cytotoxic effects of doxorubicin at various concentrations in the presence of SDZ 214-103 and cyclosporin A. For the other novel cyclosporin A analogues minor multidrug-resistance-modulating potency was demonstrated. At equipotent modulating doses of verapamil (10 microM) and cyclosporin A (10 microM) in the MTT assay regarding doxorubicin cytotoxicity, cyclosporin A was efficient in the rhodamine-123-uptake assay while verapamil was not active when identical incubation times were used.

Cyclosporins↗
PubMed1995

[Spontaneous remission of a vascularized left atrial space-occupying lesion].

We report on a 73-year-old woman with mitral stenosis and an echocardiographically and angiocardiographically proven vascularized mass at the superior part of the left atrium. The patient was put on anticoagulation with phenprocoumon. An echocardiographical follow up 10 months later revealed the disappearance of this mass; only a stalklike structure was present at the site of the former mass. Clinical presentation, echocardiographic and angiocardiographic findings are consistent with a vascularized atrial thrombus. Nevertheless, currently available imaging procedures cannot definitely discriminate vascularized thrombus, myxoma and hemangioma.

Aged↗
PubMed1995

[Determinants of arterial embolism with special reference to atheromatous changes of the thoracic aorta].

Potential sources of arterial embolism were evaluated with special emphasis on aortic atheromatosis in patients who underwent transesophageal echocardiography for various clinical reasons. Among 375 patients, 166 had suffered from cerebrovascular disease or peripheral embolism and 209 were free from symptoms of embolism. Univariate analysis revealed that atheromatosis of the aortic arch and descending aorta as well as cardiac thrombi, aneurysms of the interatrial septum and arterial hypertension were significantly more common in patients who had a history of embolism or ischemic stroke. In a stepwise multiple regression analysis, aortic arch atheromatosis (odds ratio 1.7, 95% CI 1.1-2.6), cardiac thrombi (odds ratio 4.1, 95% CI 1.7-9.8), atrial septal aneurysm (odds ratio 3.0, 95% CI 1.2-7.8) and arterial hypertension (odds ratio 1.8, 95% CI 1.1-3.0) were determined as independent predictors of embolic symptoms. We conclude that atheromatous lesions of the aortic arch are an independent risk factor for arterial embolism and ischemic stroke among other well known sources of embolism.

Aged↗
PubMed1991

Ribonucleotide reductase in melanoma tissue. EPR detection in human amelanotic melanoma and quenching of the tyrosine radical by 4-hydroxyanisole.

The characteristic EPR doublet of tyrosine radicals of the growth-regulating enzyme ribonucleotide reductase was detected in human melanoma tissue grown in nude mice. This was possible through the use of an amelanotic melanoma that does not exhibit disturbing EPR signals from melanin. The content of tyrosine radicals is higher in young tumor tissues than in older ones. The clinically applied antimelanotic drug, 4-hydroxyanisole, inhibits ribonucleotide reductase in Ehrlich ascites tumor cells as demonstrated by a pronounced quenching of tyrosine radicals (IC50 = 5 microM). In amelanotic melanoma tissue tyrosine radicals of the enzyme are also quenched by 4-hydroxyanisole in concentrations down to 50 microM. Thus, the inactivation of ribonucleotide reductase, which provides deoxyribonucleotides for DNA synthesis, may be a hitherto unexpected mechanism for the antitumor action of 4-hydroxyanisole.

Animals↗
PubMed1990

[Synthesis of chlormadinol acetate-3-beta-O-alpha-1-arabinofuranosides with positive inotropic action].

The synthesis of chlormadinol acetate-3 beta-O-alpha-L-arabinofuranoside (3; 17 alpha-Acetoxy-6-chloro-pregna-4,6-diene-20-one-3 beta-O-alpha-L- arabinofuranoside) is described. Glycosidation of chlormadinol acetate (1) was accomplished with excess 2,3,5-tri-O-benzyl-alpha-L-arabinofuranosyl chloride, Fétizon reagent, mercury cyanide and bromide in toluene at room temperature. Debenzoylation into compound 3 was carried out with methanol/methylen chloride saturated with ammonia at low temperature. Surprisingly, substance 3 shows positive inotropic effects on cats in vivo, whereas the aglycone 1 produces negative inotropy.

Animals↗