Coherent contributions to isospin mixing in the mirror pair 67As and 67Se.

Isospin symmetry breaking has been investigated in mass A=67 mirror nuclei through the experimental determination of the E1 strengths of analog electromagnetic transitions. Lifetimes of excited states have been measured in (67)Se and (67)As with the centroid shift method. Through the comparison of the B(E1) strengths of the mirror 9/2(+)-->7/2(-) transitions, the isovector and the isoscalar components of the electromagnetic transition amplitude were extracted. The presence of a large isoscalar component provides evidence for coherent contributions to isospin mixing, probably involving the isovector giant monopole resonance.

Effective charges in the fp shell.

Following the heavy-ion fusion-evaporation reaction 32S+24Mg at 95 MeV beam energy the lifetimes of analogue states in the T(z)=+/-1/2 A=51 mirror nuclei 51Fe and 51Mn have been measured using the Cologne plunger device coupled to the GASP gamma-ray spectrometer. The deduced B(E2;27/2(-)-->23/2(-)) values afford a unique opportunity to probe isoscalar and isovector polarization charges and to derive effective proton and neutron charges, epsilon(p) and epsilon(n), in the fp shell. A comparison between the experimental results and several different large-scale shell-model calculations yields epsilon(p) approximately 1.15e and epsilon(n) approximately 0.80e.

Molecular determinants of the physicochemical properties of a critical prion protein region comprising residues 106-126.

Prion diseases are marked by the cerebral accumulation of conformationally modified forms of the cellular prion protein (PrP(C)), known as PrP(res). The region comprising the residues 106-126 of human PrP seems to have a key role in this conformational conversion, because a synthetic peptide homologous with this sequence (PrP106-126) adopts different secondary structures in different environments. To investigate the molecular determinants of the physicochemical characteristics of PrP106-126, we synthesized a series of analogues including PrP106-126 H(D), PrP106-126 A and PrP106-126 K, with l-His-->d-His, His-->Ala and His-->Lys substitutions respectively at position 111, PrP106-126 NH(2) with amidation of the C-terminus, PrP106-126 V with an Ala-->Val substition at position 117, and PrP106-126 VNH(2) with an Ala-->Val substitution at position 117 and amidation of the C-terminus. The analysis of the secondary structure and aggregation properties of PrP106-126 and its analogues showed the following. (1) His(111) is central to the conformational changes of PrP peptides. (2) Amidation of the C-terminal Gly(126) yields a predominantly random coil structure, abolishes the molecular polymorphism and decreases the propensity of PrP106-126 to generate amyloid fibrils. (3) PrP106-126 V, carrying an Ala-->Val substitution at position 117, does not demonstrate a fibrillogenic ability superior to that of PrP106-126. However, the presence of Val at position 117 increases the aggregation properties of the amidated peptide. (4) Amyloid fibrils are not required for neurotoxicity because the effects of PrP106-126 NH(2) on primary neuronal cultures were similar to those of the wild-type sequence. Conversely, astroglial proliferation is related to the presence of amyloid fibrils, suggesting that astrogliosis in prion encephalopathies without amyloid deposits is a mediated effect rather than a direct effect of disease-specific PrP isoforms.

Alternative splicing at the C-terminal but not at the N-terminal domain of the NMDA receptor NR1 is altered in the kindled hippocampus.

Several lines of evidence suggest that N-methyl-D-aspartate (NMDA) receptors significantly contribute to the development of kindling. In addition, a lasting enhancement of the NMDA receptor function has been suggested to play a significant role in the chronic hyperexcitability occurring in the hippocampus after kindling epileptogenesis. We have investigated whether hippocampal kindling induces changes in the NMDA receptor at the molecular level by assessing the expression of mRNAs of the different spliced variants at the N-terminal (exon 5) and C-terminal (exon 21) position of the NMDA receptor 1 (NR1) gene by means of the reverse transcription-polymerase chain reaction. Alternative splicing at exon 5 confers different sensitivity of the NMDA receptor to polyamines while exon 21 encodes a 37-amino acid insert containing the major phosphorylation sites for protein kinase C. One week after the acquisition of stage 5 of kindling in rats (generalized tonic-clonic seizures), the relative abundance of the two alternatively spliced forms at the C-terminal domain, respectively containing (+) or lacking (-) exon 21, was reversed compared to controls (implanted with electrodes but not stimulated) in the dorsal hippocampus ipsilateral and contralateral to the electrical stimulation. The exon 21+/exon 21- mRNA ratio for controls was 1.3 +/- 0.04 (mean +/- SE); for ipsilaterally kindled rats it was 0.64 +/- 0.05 (P < 0.05), and for contralaterally kindled rats it was 0.48 +/- 0.07 (P < 0.01). Similar bilateral effects were observed in the ventral hippocampus (temporal pole). No changes were found 4 weeks after stage 5 seizures and 1 week after the induction of a single afterdischarge. No significant alterations were induced by kindling in the relative abundance of the spliced variants containing or lacking exon 5. Our findings show selective changes in alternative splicing of the NR1 gene after repeated application of an epileptogenic stimulus. This may generate receptors with different functional properties, which may contribute to the increased sensitivity for the induction of generalized seizures during kindling.

Age-related changes in the relative abundance of NMDAR1 mRNA spliced variants in the rat brain.

We have investigated the age-dependent profile of two groups of NMDAR1 mRNA isoforms, the NR1(0)XX and the NR1(1)XX, which are characterized by the absence and the presence, respectively, of an N-terminal positioned 21 amino acid insert. mRNAs of the two spliced variants were investigated at different ages in discrete rat brain areas by means of the reverse transcription-polymerase chain reaction. The existence of regional variations was confirmed as well as a region-specific pattern of NR1(0)XX/1XX ratio and its age-dependent changes. At 6 months, the ratio was > 3 in prosencephalic structures and < 1 in metencephalic regions. The greatest age-related changes were found in the cerebellum that switched from a maximal ratio of 5.1 +/- 0.4 at day 6 through a progressive decay down to the value of 0.3 +/- 0.04 at 24 months. Age-dependent changes of the different NR1 spliced variant mRNAs are relevant to understand possible regulatory mechanisms of the pharmacological properties and functions of different NMDAR subtypes.

Dopamine-derived tetrahydroisoquinolines and Parkinson's disease.

The daily urinary excretion of salsolinol, 1,2-dehydrosalsolinol, and norsalsolinol, as free, glucuronide, and sulfate, has been measured in parkinsonian patients and age-matched controls in an attempt to examine whether the determination of dopamine-derived alkaloids in urine may be used as a marker of the decrease in brain dopamine levels associated with the disease. In contrast with a preliminary study where the daily urinary excretion of total salsolinol was significantly higher in young controls than in parkinsonians, in the present study no difference was found between parkinsonian patients and controls concerning salsolinol and norsalsolinol excretion. However, the urinary excretion of total 1,2-dehydrosalsolinol was significantly higher in the control group, owing to a statistically significant increase in its excretion as sulfate in this group. Further studies appear to be necessary to establish whether 1,2-dehydrosalsolinol, salsolinol, and/or any other dopamine-derived alkaloid may serve for the detection of subjects with dysfunctions of the dopaminergic system.

Age-related variations in relative abundance of alternative spliced D2 receptor mRNAs in brain areas of two rat strains.

Age-related reduction in the steady-state levels of messenger RNA for D2(415) and D2(444), the alternatively spliced form of dopamine D2 receptors, was observed in different rat brain areas using the sensitive reverse transcription (RT)-polymerase chain reaction (PCR) technique. In both Sprague-Dawley and Wistar aged rats, the decrease was more pronounced in the D2(444) isoform mRNA thus leading to a changed ratio in striatum as well as in the hippocampus.

Kinetics and brain uptake of S 9795, a new xanthine derivate, in rats.

The relationships between plasma and brain concentrations of S 9795 and its main metabolites after single intravenous doses of S 9795 were examined in rats by high-performance liquid chromatography with UV detection. S 9795 disappeared from plasma and brain almost in parallel, with comparable elimination t1/2 of about 0.8 h, regardless of the dose administered. The volume of distribution was high (about 3 1/kg) but total clearance was also high (about 40 ml/min/kg) and this explains the relatively short plasma and brain t1/2 of the drug in the rat. Among the possible metabolites examined, the N-dearylated metabolite S 10238 rapidly appeared in both plasma and brain. Thereafter, S 10238 was likewise eliminated in parallel from both compartments, although at a slower rate (t1/2 of about 1.4 h) than its parent compound. Norcyclizine, a metabolite resulting from cleavage of the parent drug side-chain, was detected only in the brain and only at the highest dose tested. The brain AUC to plasma AUC ratio was slightly less than 1 for S 9795, about 0.1 for S 10238 and possibly more than 2 for norcyclizine, this latter being present in rat plasma at concentrations below the limits of sensitivity of the method (0.08 nmol/ml). The results indicate that S 9795 and some of its metabolites enter the central nervous system, although to different extents, and support the hypothesis that the lack of central effects of S 9795 is probably the consequence of the poor adenosine brain receptor antagonism by this compound.

The alpha 2-adrenoceptor antagonist activity of ipsapirone and gepirone is mediated by their common metabolite 1-(2-pyrimidinyl)-piperazine (PmP).

Ipsapirone and gepirone, analogs of buspirone, a newly developed antianxiety agent, form 1-(2-pyrimidinyl)-piperazine (PmP) during their biotransformation in rats. After oral administration (10 mg/kg) of a parent drug, e.g. ipsapirone or gepirone, the metabolite appears in significant amounts in plasma, with maximal concentrations of 0.9 and 1.4 nmol/ml respectively. The metabolite half-life ranged from about 140 to 200 min. Ipsapirone is eliminated more slowly than gepirone, with a half-life of about 100 and 30 min, respectively. The metabolite to parent drug ratios for the areas under the plasma concentration-time curve (AUC) were 1 for ipsapirone and 14 for gepirone. PmP (0.5-2 mg/kg p.o), ipsapirone, gepirone and buspirone (5-20 mg/kg p.o.) dose dependently antagonized the slowing of gastrointestinal transit induced by clonidine 0.1 mg/kg s.c. The doses inhibiting the antitransit effect of clonidine by 50% were 0.8 mg/kg for PmP, 14 mg/kg for ipsapirone and 9 mg/kg for both gepirone and buspirone. Analysis of small intestinal longitudinal muscle of rats given the ED50 of PmP, ipsapirone, gepirone, buspirone showed that PmP concentrations in the longitudinal muscle (with attached myenteric plexus) fell within a relatively narrow range and were consistent with the appropriate transit scores. The plasma was also tested for anticlonidine activity. These data indicate that PmP formation is a pharmacologically significant metabolic process for the buspirone-related drugs, ipsapirone and gepirone, and that this metabolite is responsible for the alpha 2-adrenoceptor blocking activity exerted by these drugs in vivo in the rat.

1-(o-Methoxyphenyl)piperazine is a metabolite of drugs bearing a methoxyphenylpiperazine side-chain.

Drugs bearing an o-methoxyphenylpiperazine (oOCH3PP) moiety in the side-chain of their molecule may form oOCH3PP during biotransformation in-vivo in the rat. This has been verified by combined gas chromatography-mass spectrometry of urine from rats given orally a series of relatively new o-methoxyphenylpiperazine-substituted derivatives. The metabolite is reported to be biochemically and pharmacologically active and therefore its formation may have pharmacological significance, at least for derivatives undergoing extensive cleavage of the arylpiperazine side-chain.