Chronic cold stress alters the basal and evoked electrophysiological activity of rat locus coeruleus neurons

In vivo extracellular single-unit recording techniques revealed that chronic cold stress significantly alters both the basal and the evoked electrophysiological activity of noradrenergic neurons in the locus coeruleus of the anaesthetized rat. Following 17-21 days of chronic cold exposure (5 degrees C), the single-unit activity of histologically-identified locus coeruleus neurons in chloral hydrate-anaesthetized rats was recorded and analysed in terms of their basal firing rate and pattern of spike activity, as well as their response to footshock stimulation. There was no significant difference in the incidence of spontaneously active cells/electrode track between cold-stressed rats and control rats. However, the basal spike activity of locus coeruleus cells recorded from cold-stressed rats differed significantly from that of control rats along two dimensions: i) they displayed significantly higher basal firing rates (mean = 1.88 Hz vs 1.20 Hz, respectively); and ii) they frequently exhibited spontaneous burst-firing activity that was not observed in control rats (observed in 15/17 cold-stressed rats vs 1/26 control rats). The evoked spike activity of locus coeruleus cells in cold-stressed rats also differed significantly from that of control rats along two dimensions: i) they were more likely to respond to footshock stimulation (mean = 90.3% vs 74.4%, respectively); and ii) these responses were more likely to consist of multispike bursts of action potentials (mean = 8 bursts/50 stimulations vs 1 burst/50 stimulations, respectively). These results indicate that alterations in the electrophysiological activity of noradrenergic locus coeruleus neurons may contribute to the phenomenon of stress-induced sensitization of norepinephrine release that is thought to underlie some of the neuropathological changes that accompany long-term stress.     

Effect of multivitamins on plasma homocysteine and folate levels in patients on hemodialysis

Three new triterpene lactones, lancilactones A (1), B (2), and C (3), together with the known kadsulactone A (4), were isolated from the stems and roots of Kadsura lancilimba. Their structures and stereochemistries were determined primarily from mass and NMR spectral data. Compound 3 inhibited HIV replication with an EC50 value of 1.4 microg/mL and a therapeutic index of greater than 71.4.     

Vasopeptidase inhibitors: incorporation of geminal and spirocyclic substituted azepinones in mercaptoacyl dipeptides

A series of 7-(di)alkyl and spirocyclic substituted azepinones were generated and incorporated as conformationally restricted dipeptide surrogates in mercaptoacyl dipeptides. Clear structure-activity relationships with respect to both angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) activity in vitro were observed. The best in this series, compound 1g, a geminally dimethylated C-7-substituted azepinone, demonstrated excellent blood pressure lowering in animal models. Compound 1g (BMS-189921) is characterized by a good duration of activity and excellent oral efficacy in models relevant to ACE or NEP inhibition, and its activity is comparable to that of the clinically efficacious agent omapatrilat. Consequently this inhibitor has been advanced clinically for the treatment of hypertension and congestive heart failure.     

Nonimmune hydrops fetalis: fetal and neonatal outcome during 1983-1992

Prognostic factors for survival of 62 fetuses and neonates with nonimmune hydrops fetalis (NIHF) were studied retrospectively. Twenty-eight infants survived >/=28 days which is 45% for all fetuses and newborns diagnosed with NIHF and 61% for liveborns with unresolved NIHF. Univariate analysis identified that mortality was associated with the presence of >/=2 serous cavity effusions and a need for chest compressions at birth. Multivariate logistic regression analysis confirmed that the presence of >/=2 serous cavity effusions was significantly associated with mortality from NIHF <28 days after birth [OR = 48.2 (CI 3.6, 662.9) (p < 0.004)]. We conclude that, compared to published cases from the 1970s and early 1980s, survival of liveborns with NIHF seems improved. The decrease in stillbirths is more notable. The severity of hydrops at birth is the key determinant for survival.     

Directed mutagenesis studies of the metal binding site at the subunit interface of Escherichia coli inorganic pyrophosphatase

Recent crystallographic studies on Escherichia coli inorganic pyrophosphatase (E-PPase) have identified three Mg2+ ions/enzyme hexamer in water-filled cavities formed by Asn24, Ala25, and Asp26 at the trimer-trimer interface (Kankare, J., Salminen, T., Lahti, R., Cooperman, B., Baykov, A. A., and Goldman, A. (1996) Biochemistry 35, 4670-4677). Here we show that D26S and D26N substitutions decrease the stoichiometry of tight Mg2+ binding to E-PPase by approximately 0.5 mol/mol monomer and increase hexamer stability in acidic medium. Mg2+ markedly decelerates the dissociation of enzyme hexamer into trimers at pH 5.0 and accelerates hexamer formation from trimers at pH 7.2 with wild type E-PPase and the N24D variant, in contrast to the D26S and D26N variants, when little or no effect is seen. The catalytic parameters describing the dependences of enzyme activity on substrate and Mg2+ concentrations are of the same magnitude for wild type E-PPase and the three variants. The affinity of the intertrimer site for Mg2+ at pH 7.2 is intermediate between those of two Mg2+ binding sites found in the E-PPase active site. It is concluded that the metal ion binding site found at the trimer-trimer interface of E-PPase is a high affinity site whose occupancy by Mg2+ greatly stabilizes the enzyme hexamer but has little effect on catalysis.