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Biomedical subjects

U Jahnke

Publications and source records attributed to U Jahnke.

At least 19 recordsLinked to original sources
PubMed2001

Neutron energy spectra from the laser-induced Dd,n3He reaction.

Detailed neutron energy spectra were measured for the D(d,n)3He reaction induced in solid (CD2)(n) targets by irradiation with 50-fs 2 x 10(18) W/cm(2) light pulses from a 10-TW Ti:Sapphire laser. The neutrons were observed at two angles 5 degrees and 112 degrees relative to the incident laser beam. The neutron spectra at the two angles are characterized by peaks with large widths of about 700 keV full width at half maximum and a shift of 300 keV between them. Neutron energies of up to about 4 MeV were observed indicating that deuterons are accelerated up to an energy of 1 MeV in the laser produced plasma. Simulation calculations can describe qualitatively the neutron spectra by assuming isotropic deuteron acceleration and a reduction of the reaction probability by a factor of 1/3 for deuterons emitted from the front of the target. These calculations indicate in particular that it is necessary to assume deuterons moving both into and out of the front of the target in order to describe the neutron energy spectra at the two angles. The highest recorded mean neutron yield was about 10(4) neutrons per pulse. The neutron yield increases with the number of electrons emitted from the front of the target and with the intensity of the prompt gamma flash induced by the bremsstrahlung of energetic electrons.

Journal Article↗
PubMed1992

Corticospinal conduction studied with magnetic double stimulation in the intact human.

A group of 8 healthy normal subjects (24-36 years old, mean age 29 years) were investigated. Transcranial magnetic double stimulation of the motor cortex was carried out at different interstimulus intervals. With both stimuli suprathreshold, an attenuation of the test response was found at interstimulus intervals of less than 200 msec (target relaxed or contracted). The manifestation of this attenuation correlated with central signs in 31 patients with multiple sclerosis. This phenomenon is (at least at longer intervals) probably not a result of the refractory spinal motoneuron pool, but of a supraspinal inhibitory mechanism or lack of corticospinal drive caused otherwise. At interstimulus intervals between 10 and 30 msec, the test response increases significantly (magnetic double stimulation 10% suprathreshold, target relaxed). This result is also seen with voluntary muscle contraction and with vibration applied to a relaxed target muscle. The facilitatory effect is probably caused by slowly conducted corticospinal volleys enabling summation, with descending impulses generated by the test stimulus. With the conditioning stimulus subthreshold and target muscle relaxed an intracortical inhibition of the test response could be confirmed at short interstimulus intervals.

Adult↗
PubMed1991

The acyl-carrier protein in Neurospora crassa mitochondria is a subunit of NADH:ubiquinone reductase (complex I).

We determined the primary structure of a 9.6-kDa subunit of the respiratory chain NADH:ubiquinone reductase (complex I) from Neurospora crassa mitochondria and found a close relationship between this subunit and the bacterial or chloroplast acyl-carrier protein. The degree of sequence identity amounts to 80% in a region of 19 residues around the serine to which the phosphopantetheine is bound. The N-terminal presequence of the subunit has the characteristic features of a mitochondrial import sequence. We cultivated the auxotroph pan-2 mutant of N. crassa in the presence of [14C]pantothenate and recovered all radioactivity incorporated into mitochondrial protein in the 9.6-kDa subunit of complex I. We cultivated N. crassa in the presence of chloramphenicol to accumulate the nuclear-encoded peripheral arm of complex I. This pre-assembled arm also contains the 9.6-kDa subunit. These results demonstrate that an acyl-carrier protein with pantothenate as prosthetic group is a constituent part of complex I in N. crassa.

Acyl Carrier Protein↗
PubMed1990

The 49 K subunit of NADH: ubiquinone reductase (complex I) from Neurospora crassa mitochondria: primary structure of the gene and the protein.

The primary structure of the 49 K subunit of the respiratory chain NADH:ubiquinone reductase (complex I) from Neurospora crassa was determined by sequencing cDNA, genomic DNA and the N-terminus of the mature protein. The sequence lengths correlate to a molecular mass of 54,002 daltons for the preprotein and 49,239 daltons for the mature protein. The presequence consists of 42 amino acids of typical composition for sequences which target nuclear-encoded proteins into mitochondria. The mature protein consists of 436 amino acids and shows 64% similarity to a 49 K subunit of bovine heart NADH:ubiquinone reductase and 33% to a predicted translation product of an open reading frame in the chloroplast DNAs of Marchantia polymorpha and Nicotiana tabacum. Evidence for an iron-sulfur cluster in the subunit is discussed.

Amino Acid Sequence↗
PubMed1987

The multiple causes of multiple sclerosis: the importance of age of infections in childhood.

The geographic distribution of multiple sclerosis (MS) may relate to the age of initial exposure and degree of sensitization to common viruses or bacteria which have proteins with epitopes (antigenic determinants) which are homologous with potentially encephalitogenic peptides in central myelin proteins, such as basic protein and proteolipid protein. Comparable homologies may exist for the as-yet-undefined nonencephalitogenic myelin antigen(s) which evoke demyelinating factors (probably complement-fixing antibodies). Many of these homologous epitopes occur in microorganisms that also possess adjuvant activity for evoking not only the sensitized T-cells but also the antibodies that cross-react with the target antigens in central myelin. If sufficient sensitization to myelin basic protein or proteolipid protein occurs, especially in infections of young adults, the individual develops acute disseminated encephalomyelitis, exactly comparable to ordinary acute experimental allergic encephalomyelitis (EAE). If very young children are infected, however, practically complete resistance develops, and neither acute disseminated encephalomyelitis nor MS follows. In between these two extremes, especially in slightly older children in whom insufficient sensitization occurs to induce acute disseminated encephalomyelitis, the individual may become resistant to acute disseminated encephalomyelitis, but susceptible to chronic relapsing or progressive disseminated encephalomyelitis, otherwise generally recognized as MS. This is exactly comparable to a recently described variant of chronic EAE in which demyelinating antibodies and large subpial plaques of demyelination occur. The similarity of this form of chronic EAE or chronic disseminated encephalomyelitis to one form of MS is emphasized.

Antigens, Bacterial↗
PubMed1987

The causes of the syndromes of Landry (1859) and of Guillain, Barré and Strohl (1916).

Post-infectious and post-vaccinal peripheral neuritis or encephalomyelitis have frequently been considered the human equivalents of experimental allergic neuritis (EAN) or encephalomyelitis (EAE). The major basis for these comparisons between diseases in humans and experimental animals rests on the classical observations of "paralytic accidents" of Pasteur-type vaccination against rabies. These old observations in humans injected with brain tissue indicate a remarkable heterogeneity of periphéral as well as central nervous system syndromes, quite in contrast with the remarkable specificity for either peripheral or central involvement in most experimental animals. The syndromes of Landry (1859) and of Guillain, Barré and Strohl (1916) differ clinically and pathologically, the latter a purely peripheral neuritis and the former a mixture of transverse myelitis and facial neuritis. Each can be caused by many different factors, including 1) direct infection by wild or attenuated rabies virus, 2) direct auto-sensitization by myelin antigens in the vaccine and 3) indirect or cross-reactive sensitization by viral or bacterial antigenic determinants (epitopes) with sufficient chemical homology with aminoacid sequences in central or peripheral myelin antigens to be recognized as immunological homologies.

Animals↗
PubMed1985

Sequence homology between certain viral proteins and proteins related to encephalomyelitis and neuritis.

Post-infectious or post-vaccinal demyelinating encephalomyelitis and neuritis may be due to immunological cross-reactions evoked by specific viral antigenic determinants (epitopes) that are homologous to regions in the target myelins of the central and peripheral nervous systems. Such homologies have been found by computer searches in which decapeptides in two human myelin proteins were compared with proteins of viruses known to infect humans. These viruses include measles, Epstein-Barr, influenza A and B, and others that cause upper respiratory infections. Several regions identified in myelin basic protein and P2 protein can be related to experimental allergic encephalomyelitis or neuritis in laboratory animals.

Animals↗
PubMed1984

[Not Available].

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Education, Medical↗