Bright Light Therapy for Winter Depression—Is Phase Advancing Beneficial?

Bright light is the recommended treatment for winter seasonal affective disorder (SAD). Previously we showed that the antidepressant effect of morning (but not evening) light was greater than placebo after 3 weeks of treatment. Here, we determined if the magnitude and direction of circadian rhythm phase shifts produced by the bright light in the previous study were related to the antidepressant effects. Twenty-six SAD patients from the original sample of 96 had their rectal temperature continuously monitored while they participated in a placebo-controlled parallel design conducted over six winters. After a baseline week, there were three treatments for 4 weeks—morning light, evening light, or morning placebo. Bright light was produced by light boxes (~6000 lux). Placebos were sham negative ion generators. All treatments were 1.5 h in duration. Depression ratings were made weekly by blind raters. Circadian phase shifts were determined from changes in the timing of the core body temperature minimum (Tmin). Morning light advanced and evening light delayed the Tmin by about 1 h. The placebo treatment did not alter circadian phase. As the sleep schedule was held constant, morning light increased and evening light decreased the Tmin to wake interval, or phase angle between circadian rhythms and sleep. Phase advance shifts and increases in the phase angle were only weakly associated with antidepressant response. However, there was an inverted U-shaped function showing that regardless of treatment assignment the greatest antidepressant effects occurred when the phase angle was about 3 h, and that patients who moved closer to this phase angle benefited more than those who moved farther from it. However 46% of our sample had a phase angle within 30 min of this 3 h interval at baseline. So it does not appear that an abnormal phase angle can entirely account for the etiology of SAD. A majority (75%) of the responders by strict joint criteria had a phase angle within this range after treatment, so it appears that obtaining the ideal phase relationship may account for some, but not all of the antidepressant response. In any case, regardless of the mechanism for the antidepressant effect of morning light, it can be enhanced when patients sleep at the ideal circadian phase and reduced when they sleep at a more abnormal circadian phase.     

Tetramerization and interdomain flexibility of the replication initiation controller YabA enables simultaneous binding to multiple partners

YabA negatively regulates initiation of DNA replication in low-GC Gram-positive bacteria. The protein exerts its control through interactions with the initiator protein DnaA and the sliding clamp DnaN. Here, we combined X-ray crystallography, X-ray scattering (SAXS), modeling and biophysical approaches, with in vivo experimental data to gain insight into YabA function. The crystal structure of the N-terminal domain (NTD) of YabA solved at 2.7 Å resolution reveals an extended α-helix that contributes to an intermolecular four-helix bundle. Homology modeling and biochemical analysis indicates that the C-terminal domain (CTD) of YabA is a small Zn-binding domain. Multi-angle light scattering and SAXS demonstrate that YabA is a tetramer in which the CTDs are independent and connected to the N-terminal four-helix bundle via flexible linkers. While YabA can simultaneously interact with both DnaA and DnaN, we found that an isolated CTD can bind to either DnaA or DnaN, individually. Site-directed mutagenesis and yeast-two hybrid assays identified DnaA and DnaN binding sites on the YabA CTD that partially overlap and point to a mutually exclusive mode of interaction. Our study defines YabA as a novel structural hub and explains how the protein tetramer uses independent CTDs to bind multiple partners to orchestrate replication initiation in the bacterial cell.     

Maintenance or stimulation of steroidogenic enzymes and testosterone production in rat Leydig cells by continuous and pulsatile infusions of luteinizing hormone during passive immunization against gonadotrophin-releasing hormone.

The importance of the pulsatility of luteinizing hormone (LH) secretion in maintaining key enzymes in the testosterone biosynthetic pathway in Leydig cells was studied using rats in which LH secretion was suppressed by passive immunization against gonadotropin-releasing hormone (GnRH) and replaced by continuous or pulsatile i.v. infusions of exogenous LH, all delivering the same daily dose of the hormone (300 ng per 100 g NIDDK-ovine LH-24). Continuous infusions (12.5 ng per 100 g h-1) were compared with infusions of 1 min pulses every 2 h (25 ng per 100 g) and every 4 h (50 ng per 100 g). After 5 days of treatment in vivo with sheep anti-GnRH serum (or normal sheep serum) and LH (or vehicle), Leydig cells were purified and assayed in vitro for maximum production of testosterone stimulated by human chorionic gonadotrophin (hCG) and supported by 25-hydroxycholesterol and for the activities of cholesterol side-chain cleavage, delta 5-3 beta-hydroxysteroid dehydrogenase-delta 5-4-isomerase (3 beta-HSD-isomerase) and 17 alpha-hydroxylase. Relative contents of cholesterol side-chain cleavage and 17 alpha-hydroxylase were also quantified by western and immunoblotting analysis. Activity of 3 beta-HSD-isomerase was reduced by about 40% by anti-GnRH treatment and was increased by all LH regimens in anti-GnRH-treated animals, with no consistent pattern in the effects of the different LH regimens. Results for testosterone-producing capacity and the other two enzymes differed in several respects. Treatment with anti-GnRH serum markedly reduced basal, hCG-stimulated and 25-hydroxycholesterol-supported testosterone production (by 80-90%) and the activities of cholesterol side-chain cleavage (about 80%) and 17 alpha-hydroxylase (about 65%). Infusion of exogenous LH in any of the regimens tested prevented these changes or increased the activities to values greater than those in normal serum-treated controls. Differences in immunodetectable contents of the two enzymes generally paralleled those in enzyme activities. There was a consistent trend in the effects of LH replacement regimens on these parameters of steroidogenic activity: continuous infusions were more effective than pulses at 2 h intervals and these in turn were more effective than pulses at 4 h intervals, suggesting that the frequency of LH exposure is more important than the amplitude of individual exposures in maintaining Leydig cell steroidogenic function.(ABSTRACT TRUNCATED AT 400 WORDS)