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Biomedical subjects

J Engel

Publications and source records attributed to J Engel.

At least 217 records · Page 12Linked to original sources
PubMed1996

Decreased neuronal burst discharge near site of seizure onset in epileptic human temporal lobes.

We examined auto-correlation and interval distribution characteristics of neuronal discharge from patients with complex partial seizures. The objective was to compare the interictal firing patterns of neurons in mesial temporal structures ipsilateral to the site of seizure onset with firing patterns of neurons in homologous contralateral structures. Spontaneous interictal recordings of 258 single neurons were acquired from 23 patients. A "burst area" measure was derived from the neuronal auto-correlation to assess the likelihood of grouped action potential discharge (burst discharge). Large burst area measures indicate a tendency for single neuronal burst discharge, but do not disclose information about interspike intervals within bursts. Although several measures based on single neuronal interspike interval distributions showed no overall difference between hemispheres, burst area was significantly reduced in mesial temporal structures ipsilateral to the site of seizure onset. Possible mechanisms of decreased burst discharge in epileptogenic regions include selective loss of burst-discharging neurons and increased recurrent inhibition.

Action Potentials↗
PubMed1996

Localized cerebellar hypometabolism in patients with complex partial seizures.

PURPOSE: We sought to determine the cause of cerebellar dysfunction in epilepsy and whether this dysfunction was directly related to seizures. METHODS: Cerebellar metabolism was evaluated in 48 patients with a well-defined region of seizure onset and with corresponding hypometabolism. Regions of interest (ROI) were drawn according to a standardized template. If the ROI/nonepileptogenic cortex count rate ratio was outside the 95% confidence interval (CI) of controls, the ROI was defined as abnormal. The ratios from cerebellar hemispheres (defined as ipsi- or contralateral to the seizure onset region), were compared among controls (n = 8); patients who had seizure onsets and corresponding hypometabolism mesially in a temporal lobe (patient group 1, n = 19); patients whose seizures had onset mesially in a temporal lobe but spread rapidly to the ipsilateral frontal lobe and who had hypometabolism both in the affected temporal lobe and frontal lobe (patient group 2, n = 23); and patients who had seizure onsets and corresponding hypometabolism in the frontal lobe (patient group 3, n = 6). RESULTS: Significant hypometabolism was noted in the contralateral cerebellum of patients in group 2 and 3 [p = 0.007 and p = 0.008, respectively; two-way analysis of variance (ANOVA)]. In contrast, patients in group 1 tended to have lower values in the ipsilateral cerebellum (p = 0.057). CONCLUSIONS: The observed cerebellar changes are consistent with animal data showing that cerebellar connections to frontal lobes are numerous and crossed, whereas the connections to mesial temporal lobes are less abundant, bilateral, with an ipsilateral predominance. The difference between the two groups of patients with mesial temporal seizures suggests that cerebellar dysfunction in partial epilepsy, at least to a certain extent, is related to mechanisms involved in seizure generation and spread.

Cerebellum↗
PubMed1996

Neuronal synchrony in relation to burst discharge in epileptic human temporal lobes.

1. Synchronous interactions between neurons in mesial temporal structures of patients with complex partial seizures were studied using cross-correlation analyses. We recorded spontaneous activity from 293 neurons in 24 patients during the interictal state. Patients had depth microelectrodes chronically implanted in amygdala, hippocampal formation, and parahippocampal gyrus to record epileptic activity. One hundred twenty-five cells were recorded from the temporal lobe commonly initiating seizures (ipsilateral temporal lobe), and 168 cells from the contralateral temporal lobe. Eight hundred forty-three cross-correlograms were constructed between all pairs of simultaneously recorded neurons. Cross-correlogram peaks or troughs that exceeded confidence limits within 200 ms of the origin were considered evidence of synchronous neuronal interaction. 2. Synchronous neuronal interactions were observed in 223 of 843 cross-correlograms. Eighty-six percent of these 223 cross-correlograms showed significant central peaks (peak interactions), suggesting excitatory interactions, whereas the remainder displayed significant central troughs (trough interactions), suggesting inhibitory interactions. 3. Cross-correlograms constructed using cells from the ipsilateral temporal lobe (ipsilateral cross-correlograms) were more likely to display significant central troughs (14/262) than cross-correlograms constructed using cells from the contralateral temporal lobe (6/376; contralateral cross-correlograms). Similarly, cross-correlograms constructed using one cell from each hemisphere (11/205; bilateral cross-correlograms) were also more likely to display significant central troughs (trough interactions) than contralateral cross-correlograms. Both ipsilateral (77/262) and contralateral cross-correlograms (102/376) were more likely to display significant central peaks (peak interactions) than bilateral cross-correlograms (13/205). 4. Cells from different structures in the ipsilateral temporal lobe were more likely to display significant trough interactions (10/ 114) than neurons in different contralateral structures. We also compared the proportion of significant peak interactions between cells within the ipsilateral and contralateral sides of each structure. Neurons in the contralateral entorhinal cortex were more likely to show peak interactions (21/55) than cells from the ipsilateral entorhinal cortex (3/31). Also, cells in the ipsilateral presubiculum showed a higher proportion of peak interactions (9/16) than their contralateral homologues (5/30). 5. Neuronal burst discharges were defined as three or more action potentials (or spikes) separated by interspike intervals of < or = 30 ms, or two spikes separated by an interval of < or = 15 ms. The contribution of burst discharge to synchronous peak interaction was compared between temporal lobes. Cells used to construct ipsilateral cross-correlograms displaying significant central peaks (n = 154) were found to have significantly reduced burst discharge contributions to the observed synchronous peaks in comparison with their contralateral homologues (n = 204). When cross-correlograms were separated by regions, burst discharge contributions to synchronous peak interactions between cells in the ipsilateral hippocampus (n = 72) were significantly smaller than the contributions from cells in the contralateral hippocampus (n = 44). 6. The results suggest that in the interictal state, synchronous neuronal burst discharge is not a distinguishing feature of epileptogenic regions of patients with complex partial seizures, but inhibitory neuronal interactions are increased in regions of seizure initiation. Increases in the strength and spread of local inhibition in seizure initiating regions in these patients may result in a greater proportion of inhibitory interactions and could also cause increased synchrony between isolated action potentials.(ABSTRACT TRUNCATED)

Action Potentials↗
PubMed1995

Outcomes in 248 patients who had diagnostic evaluations for epilepsy surgery.

Surgery for intractable epilepsy is a widely used treatment that is not readily assessed by randomised trials. We evaluated the impact of epilepsy surgery on seizures, medication use, employment, and the quality of life in 248 adults and adolescents consecutively referred to one medical centre between 1974 and 1990. Outcomes were determined through self-administered questionnaire and medical record review for 202 surgery and 46 non-surgery patients whose treatment was usually determined by the presence or absence of an epileptogenic focus. Surgery and non-surgery patients differed at baseline only in median monthly seizure frequency (surgery lower than non-surgery). After adjustment for baseline covariates, surgery patients at follow-up had greater decline in average monthly seizure frequency (-11.9 vs - 1.5; difference -10.4, 95% CI -20.5, -0.3) and took fewer antiepileptic medications (average number 1.4 vs 2.0; difference -0.67, 95% CI -0.94, -0.40). Although quality-of-life scores were higher (p < 0.05) with surgery on 5 of 11 scales that were administered only at follow-up, there were no significant differences in employment status or prospectively assessed quality of life. Relative to a non-surgery group, patients treated surgically had better seizure control with less antiepileptic medication. The impact of epilepsy surgery on quality of life and employment needs to be assessed in larger prospective studies.

Adolescent↗
PubMed1995

The C-terminal portion of BM-40 (SPARC/osteonectin) is an autonomously folding and crystallisable domain that binds calcium and collagen IV.

The extracellular glycoprotein BM-40 consists of three domains, an acidic domain I, a follistatin (FS)-like domain II and a calcium-binding EC domain with an EF-hand related motif. BM-40 and several other related proteins (QR1, SC1/hevin, testican and tsc-36/FRP) are members of a novel modular protein family that share the FS domain followed by an EC domain. We have expressed this pair of FS and EC domains (mutant delta I) and the calcium-binding EC domain alone (mutant delta I, II) of human BM-40 as recombinant proteins in human 293 cells. Circular dichroism demonstrated that both mutants were obtained as folded proteins with a distinct three-dimensional conformation. In addition, mutant delta I, II could be readily crystallized and diffraction patterns with a resolution limit of 2.4 A resolution were obtained. Calcium binding to this fragment was ten times weaker (Kd = 0.8 microM) than for the wild-type protein. Identical reversible increases in alpha-helicity upon calcium binding were observed for the 150-residue long mutant delta I, II and for BM-40 (286 residues). A 26-residue synthetic peptide corresponding to the EF-hand related motif exhibited much weaker calcium binding. The apparent dissociation constant decreased with increasing peptide concentration (from Kd 2.4 mM at 1 microM, to Kd 0.3 mM at 100 microM peptide concentration) and calcium binding was accompanied by dimerization of the peptide. This suggests that for strong calcium binding the EF-hand related motif has to be embedded into a larger protein domain that can form an autonomously folding protein module. The EC domain was also shown by surface plasmon resonance assay to be responsible for calcium-dependent binding to collagen IV with an affinity (Kd = 19 microM) only sixfold lower than that of intact human BM-40.

Amino Acid Sequence↗
PubMed1995

The function of the NC1 domains in type IV collagen.

At its C terminus, the collagen IV molecule bears a globular NC1 domain, to which two functions have been assigned. In the macromolecular network of collagen IV, two molecules are connected via their NC1 domains, which form a hexameric complex, stabilized by intermolecular disulfide bonds. In addition, the NC1 domains are thought to be responsible for chain selection and assembly. In order to understand the role of the NC1 domains during these steps, hexameric complexes were isolated and further investigated. SDS-polyacrylamide gel electrophoresis and Western blot revealed disulfide-linked alpha 1 (IV)NC1 and alpha 2(IV)NC1 homodimers but no heterodimers. The hexamers were dissociated at low pH, separated into monomers and dimers, and submitted to reconstitution experiments. Only alpha 1(IV)NC1 dimers were able to reconstitute a hexameric complex. alpha(IV)-NC1 and alpha 2(IV)NC1 monomers as well as the alpha 2(IV)NC1 dimers showed only a low tendency to form complexes. It is assumed that during formation of the collagen IV network, lateral aggregation of the molecules via the triple helical domains brings the C termini of two molecules into close vicinity and that subsequently the weak interactions observed between the NC1 subdomains provide the correct alignment for a disulfide exchange. It is, however, questionable whether the low affinity between the NC1 subdomains alone is sufficient for chain assembly and alignment of the alpha(IV) chains before molecule formation.

Collagen↗
PubMed1995

Electron microscopic evidence for a mucin-like region in chick muscle alpha-dystroglycan.

alpha-Dystroglycan has been isolated from chicken cardiac muscle and its molecular weight was estimated to be approximately 135 kDa. The avian protein interacts with murine Engelbreth-Holm-Swarm (EHS) tumor laminin via interaction with the C-terminal LG4 and LG5 domains (fragment E3) of the laminin alpha-chain. This laminin binding is calcium-dependent and can be competed by heparin. Electron microscopy investigation on the shape of alpha-dystroglycan suggests that the core protein consists of two roughly globular domains connected by a segment which most likely corresponds to a mucin-like central region also predicted by sequence analysis on mammalian isoforms. This segment may act as a spacer in the dystrophin-associated glycoproteins complex exposing the N-terminal domain of alpha-dystroglycan to laminin in the extracellular space.

Animals↗
PubMed1995

Selective chain recognition in the C-terminal alpha-helical coiled-coil region of laminin.

Recombinant fragments alpha, beta, and gamma were prepared comprising about 100 C-terminal residues of the corresponding polypeptide chains in the three-stranded alpha-helical coiled-coil domain of laminin. Circular dichroism spectra, thermal transition profiles, non-denaturing gels, analytical ultracentrifugation, and calorimetry indicated alpha-helicity and high thermal stabilities for the beta gamma heterodimer and homoassociates of beta. Very little or no coiled-coil formation was found for alpha and gamma. The thermal melting profiles and their concentration dependencies were quantitatively described by a two-state mechanism in which two unfolded chains combine to a fully alpha-helical dimer. For the beta gamma dimer the melting temperature was Tm = 42 degrees C at a chain concentration of 25 microM in 5 mM sodium phosphate buffer (pH 7.4). Addition of 100 mM NaCl decreased the Tm slightly but the relative stability of beta gamma and beta beta coiled-coils was not significantly changed, indicating that electrostatic interactions alone are not responsible for chain selection. Upon addition of 1 M urea the Tm value dropped by about 10 degrees C. The enthalpy changes for the formation of the coiled-coil were delta H degrees = -304(+/- 30) kJ/mol for the beta gamma heterodimer and -198(+/- 20) kJ/mol for the beta-homoassociates. Gibbs free energies and entropies amounted to delta G degrees = -42.8 kJ and delta S degrees = -876 J/mol K for the heteroassembly and -37.8 kJ/mol and -537 J/mol K for the homoassembly of beta. This low preference for heteroassociation of the fragment is smaller than the chain selectivity observed for larger fragments and intact laminin. Deletion of ten residues from the C-terminal region of the gamma-fragment which were recently reported as an essential assembly-site was not sufficient to abolish heteroassociation. Interaction of alpha-fragment with double-stranded beta gamma coiled-coils reflected the formation of a three-stranded coiled-coil in laminin but for the small recombinant fragments association between alpha and beta-homoassociates was also observed. The C-terminal 100 residues in the coiled-coil domain are therefore not alone responsible for the high specificity of chain selection in laminin.

Amino Acid Sequence↗
PubMed1995

Stabilization of the alpha-helical coiled-coil domain in laminin by C-terminal disulfide bonds.

The long arm of laminin in which three polypeptide chains alpha, beta, and gamma are assembled in an alpha-helical coiled-coil structure is stabilized by non-covalent interactions and disulfide bridges. The stabilizing role of the disulfide linkage between the beta and gamma-chains at the C-terminal region of the assembly domain was investigated with about 100-residue long recombinant fragments. Circular dichroism spectra and electron micrographs were identical for linked and non-linked species and indicated two-stranded coiled-coil structures with about 100% alpha-helicity at 20 degrees C. Thermal transition profiles revealed an increase of the melting temperature from 42 degrees C to 60.4 degrees C upon disulfide formation at a chain concentration of 25 microM. The enthalpy of interaction was identical for the two species but the negative entropy involved in joining the two chains was reduced by the disulfide bonds. At chain concentrations of 10 microM the Gibbs free energy delta G was by 17.5 kJ/mol more negative for the disulfide-linked than for the unlinked chains. Because of the concentration dependence of the entropy of the non-linked chains, this difference decreased with increasing concentration and, by extrapolation at chain concentrations of 10 mM, the stability of both structures would be the same. As a competing reaction, beta-chains associated to four-stranded bundles which probably consist of pairs of two-stranded coiled-coils. After disulfide formation a biphasic transition curve was observed which indicated two different ways of connecting the chains in the bundle.

Circular Dichroism↗
PubMed1995

Evidence of a defined spatial arrangement of hyaluronate in the central filament of cartilage proteoglycan aggregates.

Aggregates of proteoglycans from the Swarm rat chondrosarcoma reassembled in vitro have been studied by rotary-shadowing electron microscopy, and shown to be similar to native structures that have never been dissociated [Mörgelin, Engel, Heinegård and Paulsson (1992) J. Biol. Chem. 267, 14275-14284]. A hyaluronate with defined chain length (HAshort) has now been prepared by autoclaving high-Mr hyaluronate and fractionation to a narrow size distribution by gel filtration. Proteoglycan monomers, core protein, hyaluronate-binding region and link protein were combined with HAshort. Free chains of HAshort and reconstituted complexes with proteoglycan, link protein and aggrecan fragments were examined by electron microscopy after rotary shadowing. Length measurements showed that the hyaluronate was condensed to about half of its original length on binding intact aggrecan monomers, any aggrecan fragment or link protein alone. This strongly implies that hyaluronate adopts a defined spatial arrangement within the central filament of the aggregate, probably different from its secondary structure in solution. No differences in length were observed between link-free and link-stabilized aggregates.

Animals↗
PubMed1995

Structural comparison of cuticle and interstitial collagens from annelids living in shallow sea-water and at deep-sea hydrothermal vents.

Two types of annelid collagens of different sizes were purified, one from acetic acid extracts of the cuticle (length 2.5 microns) and the other, after pepsin digestion, from interstitial spaces of the body wall (0.3 micron). They were obtained from Alvinella pompejana, Alvinella caudata and Paralvinella grasslei collected at 2600 m depth around anoxic hydrothermal vents and from Arenicola marina and Nereis diversicolor living in shallow sea-water habitats. The length of the corresponding collagens from different species and their amino acid compositions including the hydroxylation of proline were remarkably similar. The melting point of the triple helix, however, differed between the Alvinella species (approximately 45 degrees C), Paralvinella (approximately 35 degrees C) and the shallow sea-water annelids (approximately 28 degrees C), indicating adaption to habitats with different temperatures. The cuticle collagens of the annelids possess a globular domain, which is apparently involved in oligomer formation, and show similar fragment pattern. Almost identical cross-striation patterns of segment-long-spacing segments of the interstitial collagens indicated sequence similarity, which was confirmed by partial Edman degradation of alpha-chains. These data showed almost complete identity between the two Alvinella species and a lower sequence identity with Paralvinella (approximately 95%), Arenicola (67 to 72%) and the vent vestimentiferan Riftia pachyptila (64 to 71%). The data suggest a close evolutionary relationship between these worms, despite a clear separation of habitat preference and thermal stability of the collagens.

Amino Acid Sequence↗