Pentobarbital Antagonizes the A1 Adenosine Receptor-Mediated Inhibition of Hippocampal Neurotransmitter Release

Barbiturates have been shown to be competitive antagonists at A1 adenosine receptors in radioligand binding studies. The present study investigates the effects of pentobarbital on the A1 receptor-mediated inhibition of neurotransmitter release from rabbit hippocampal slices. The inhibition of the electrically evoked release of [3H]noradrenaline by the A1 receptor agonist (R)-N6-phenylisopropyladenosine (R-PIA) was antagonized by pentobarbital with an apparent pA2 value of 3.5. Low concentrations of pentobarbital alone altered neither basal nor evoked release of [3H]noradrenaline, whereas 1,000 microM pentobarbital enhanced the basal and reduced the evoked release. In the presence of 8-phenyltheophylline, pentobarbital (200 microM and 1,000 microM) reduced the evoked noradrenaline release. Pentobarbital also antagonized the inhibition of [3H]acetylcholine release by R-PIA. In contrast to the noradrenaline release model, the evoked release of acetylcholine was enhanced by the presence of pentobarbital (50-500 microM), an effect that was lost in the presence of 8-phenyltheophylline. These results indicate that pentobarbital, in addition to a direct inhibitory action at higher concentrations, has a facilitatory effect on neurotransmitter release by blocking presynaptic A1 adenosine receptors. The possible relevance of these findings for the excitatory effects of barbiturates is discussed.     

Rat Brain Glyceraldehyde-3-Phosphate Dehydrogenase Interacts with the Recombinant Cytoplasmic Domain of Alzheimer's β-Amyloid Precursor Protein

Abstract: Abundant senile plaques are a histological hallmark in the brain of Alzheimer's disease patients. Such plaques consist of, among many other constituents, aggregated βA4 amyloid peptide. This peptide is derived from an amyloid precursor protein (APP) by irregular proteolytic processing and is considered to be involved in the development of Alzheimer's disease. To study possible interactions of brain proteins with 0A4 amyloid or other fragments of APP, βA4 amyloid and βA4 amyloid extended to the C-terminus of APP were recombinantly produced as fusion proteins termed "Amy" and "AmyC," respectively. Using Amy and AmyC affinity chromatography, a 35-kDa protein from rat brain was isolated that bound tightly to AmyC but not to Amy, thus indicating an interaction of the protein with the C-terminus of APP. This 35-kDa protein was identified as the glycolytic enzyme gIyceraldehyde-3-phosphate dehydrogenase (GAPDH). Binding of GAPDH to AmyC but not to Amy was confirmed by gel filtration. Although AmyC slightly reduced the V_max of GAPDH, the same reduction was observed in the presence of Amy. These findings suggest that the interaction of the cytoplasmic domain of APP with GAPDH is unlikely to influence directly the rate of glycolysis but may serve another function.     

Teratocarcinoma transplantation rejection loci: Genetic localization of the Gt-1 locus on chromosome 17 and the expression of alternate alleles

A series of congenic mice on the BALB/c genetic background have been employed to localize a teratocarcinoma transplantation rejection locus, Gt-1, to the K side of the H-2 locus on chromosome 17. Previous studies have placed the Gt-1 ^sv allele about 8 centimorgans away from the H-2 ^b or H-2 ^bv1 locus. Teratocarcinomas derived from 129/sv mice, Gt-1 ^sv (H-2K ^bv1/H-2D ^bv1), are rejected by BALB/c (H-2K ^d/H-2D^d) and BALB-G mice (H-2K ^d/H2D-^b, but form tumors in BALB-B (H-2K ^b/H2D ^b) and BALB/5R5 mice (H-2K ^b/H2D ^d). In the reciprocal tumor-rejection test, a BALB/c teratocarcinoma was rejected by immunized BALB·B mice, but formed tumors in the immunized isogenic BALB/c mouse. These studies demonstrate the reciprocal expression of two Gt-1 alleles, one Gt-1 ^c, in BALB/c mice, and the other, Gt-1 ^sv, in the congenic BALB·B mice. Shedlovsky and co-workers have placed the Gt-1 locus in a similar location on the K side of the H-2 locus on chromosome 17.     

Abundance and diversity of peracarid taxa (Crustacea, Malacostraca) along a transect through the Beagle Channel, Patagonia

During the joint Chilean-German-Italian Magellan “Victor Hensen” Campaign in November 1994, samples were taken on a cruise of the RV Victor Hensen in order to obtain faunistic information from the Beagle Channel. Peracarida are an important fraction of the macrobenthos and were sampled in high numbers. Using an epibenthic sledge, 104,618 individuals were collected in total, comprising 62,860 Amphipoda, 14,685 Cumacea, 17,992 Isopoda, 7,168 Mysidacea and 1,893 Tanaidacea. To allow comparisons between stations, these numbers were standardized to a 1,000 m trawling distance, yielding about 368,000 individuals from all stations. Peracarida were most abundant at station 1213, southeast of Isla Picton, in the oceanic area close to the eastern entrance of the Beagle Channel (166,361 ind./1,000 m). Generally, stations off the eastern entrance were characterized by a high number of Peracarida. In the Beagle Channel itself, however, the abundance decreased from east to west with a single peak in peracarid number in the channel east of Punta Yámana. Numbers were much lower at the western entrance (792 ind./1,000 m) and even fewer Peracarida were collected in the Magdalena Channel off Punta Sánchez. Lowest numbers were recorded close to the glacier Romanche and west of Isla Picton at two locations. The composition of peracarid crustaceans was analysed in relation to the background of hydrographical and sedimentological differences, nutrient availability, and knowledge of the other associated fauna in the Beagle Channel. The available data lead us to conclude that abundance and composition of peracarid taxa in and south of the Beagle Channel (off the eastern entrance) seem to be influenced mainly by sediment composition and hydrographical characteristics as indicated above. Received: 18 October 1996 / Accepted: 19 December 1996     

Covalently bound FAD in D-6-hydroxynicotine oxidase from Arthrobacter oxidans

In Arthrobacter oxidans, an enzymatically inactive protein which is in a close biosynthetic relationship to the active D-6-hydroxynicotine oxidase and may serve as a precursor for its formation was purified and shown to be homogeneous by gel electrophoresis. It consists of one polypeptide chain of about the same molecular weight (50 000 daltons) as the active enzyme. The purified protein lacks the absorption in the visible range characteristic of flavoproteins. Amino acid analysis and peptide mapping yielded similar results for both proteins. They also share the same C-terminal amino acids,-lysinetyrosine; the N-terminal residue is serine in the case of D-6-hydroxynicotine oxidase while that of the coinduced protein was found to be blocked.