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Biomedical subjects

H Breer

Publications and source records attributed to H Breer.

156 records · Page 9Linked to original sources
PubMed1981

Myelin deposition in the optic tectum of trout as monitored by enzymatic and morphometric analyses.

The activity of arylsulfatase A and 2'3'-cyclic nucleotide 3'-phosphohydrolase was studied in the brain of trout in parallel to the structural differentiation of tissue from early larval stages into adulthood. Whereas in the optic tectum, phosphodiesterase activity could not be detected before the second month after hatching in brainstem, the enzyme had already reached 80% of adult level. In tectum it was from the fourth to the seventh month that this enzyme dramatically increased, thereby reaching about the adult level. The developmental profile of arylsulfatase A was profoundly different, since 1) considerable activity was found in tectum at early larval stages and 2) the activity showed a peak between two and six months and then dropped markedly. Morphometric analysis of the two myelinated layers of trout tectum support and extend the biochemical results leading to the conclusion that the phosphodiesterase activity reflects the prevailing degree of myelination, whereas the developmental profile of the sulfolipid-metabolizing enzyme indicates the rate of myelin accumulation.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1981

Calcium binding sites of synaptosomes from insect nervous system as probed by trivalent terbium ions.

Terbium binding to synaptosomes from the central nervous system of the locust was studied by fluorescence spectroscopy and electron microscopy. The protein-sensitized fluorescence of terbium was used to characterize the calcium binding sites of synaptosomes. As judged by electron microscopy and x-ray analysis, terbium ions produced electron-dense patches in regular arrays on the outer surface of synaptosomal membranes and induced marked aggregation of synaptic vesicles in isolated terminals.

Animals↗
PubMed1978

A structural model of cholinergic synaptic vesicles from the electric organ of Torpedo marmorata deduced from density measurements at different osmotic pressures.

Density measurements made on cholinergic synaptic vesicles from the electric organs of Torpedo marmorata at different osmotic pressures are consistent with the following structural model of the vesicle. The particle behaves like a sphere 80-100 nm in diameter bounded by a semi-permeable membrane. The bulk of its soluble constituents are in true solution at physiological osmolalities. The limiting membrane is approximately 4-5 nm thick, suggesting that it contains large areas of phospholipid bilayer exposed to its bathing medium. The limiting membrane takes up about 26% (v/v) of the particle, a further 34% (v/v) of which is osmotically active water and 31% (v/v) hydrated core material at 800 mosmol/1. The buoyant density of the membrane is 1.132 g . cm-3. The density of the hydrated core material is approximately 1.05 g . cm-3. The membrane is selectively permeable to small molecules when subjected to hypo-osmotic stress. It is proposed that this occurs by the formation of small transient pores in the lipid bilayer of the membrane, which are induced by stretching caused by the osmotic pressure change.

Acetylcholine↗
PubMed1977

Adenosine triphosphatase activity associated with purified cholinergic synaptic vesicles of Torpedo marmorata.

A rapid method for purifying Torpedo electric organ vesicles is described, which employs an isoosmotic continuous sucrose-glycine gradient followed by chromagography on CPG-10-3000 porous glass beads. The synaptic vesicles have a buoyant density of 1.057 g/ml. The purified vesicles are free of cholinesterase, lactate dehydrogenase and Na+, K+-stimulated ATPase activity. They contain a ouabaininsensitive, Na+, K+-inhibited, Mg2+, Ca2+-stimulated ATPase activity. This is further stimulated by acetylcholine but not by choline.

Acetylcholine↗
PubMedDate not supplied

Elements of the olfactory signaling pathways in insect antennae.

Owing to their enormous ability to recognize airborne molecules, insects have long been used as model systems for studying various aspects of olfaction. Modern biological techniques have opened new avenues for exploring the molecular mechanisms underlying the complex signaling processes in chemosensory neurons. Biochemical and molecular analyses have allowed the identification of molecular elements of the olfactory reaction pathways and have shed light on mechanisms that account for the sensitivity and specificity of the chemosensory system.

Amino Acid Sequence↗
PubMedDate not supplied

Cloning of biogenic amine receptors from moths (Bombyx mori and Heliothis virescens).

Based on the similarity of genes which code for guanine-nucleotide binding protein- (G-protein-) coupled receptors, cDNA clones encoding new members of the receptor family have been isolated from Bombyx mori and Heliothis virescens. The deduced protein structures exhibit highest similarity to tyramine/octopamine and serotonin receptors of Drosophila. One of the receptor clones (K50Hel) was permanently expressed in the mammalian cell line LLC-PK1. In stimulation experiments its responded to octopamine leading to an inhibition of adenylate cyclase activity in a dose-dependent manner. Pharmacological studies revealed a higher affinity for mianserin than for yohimbine suggesting, that the K50Hel clone encoded a neuronal type 3 octopamine receptor. As revealed by in situ hybridization, this receptor type is expressed in the central nervous system and antennae of moth.

Amino Acid Sequence↗
PubMedDate not supplied

Channel properties of an insect neuronal acetylcholine receptor protein reconstituted in planar lipid bilayers.

A pentameric membrane protein composed of four types of polypeptide has been identified as the minimal structural unit responsible for the electrogenic action of acetylcholine on electrocytes and muscle cells. Because many populations of central and peripheral neurons also have nicotinic acetylcholine receptors (AChRs), considerable effort has recently gone into identifying the neuronal receptor. The central nervous tissue of insects contains very high concentrations of nicotinic AChRs, and we have recently purified an alpha-toxin binding protein, a putative AChR, from neuronal membranes of locusts. It is a component of high relative molecular mass, clearly composed of identical subunits, a structure predicted for an ancestral AChR protein. To verify that the purified polypeptides not only represent ligand binding sites but that they are indeed functional receptors, we have now reconstituted the isolated protein in a planar lipid bilayer. We show that in this system cholinergic agonists activate functional ion channels, that have properties comparable to those exhibited by the peripheral AChRs in vertebrates; thus, for the first time a functional acetylcholine receptor channel has been identified in nerve cells.

Acetylcholine↗