Clustering of charged colloidal particles in the microgravity environment of space.

We conducted a charge-charge clustering experiment of positively and negatively charged colloidal particles in aqueous media under a microgravity environment at the International Space Station. A special setup was used to mix the colloid particles in microgravity and then these structures were immobilized in gel cured using ultraviolet (UV) light. The samples returned to the ground were observed by optical microscopy. The space sample of polystyrene particles with a specific gravity ρ (=1.05) close to the medium had an average association number of ~50% larger than the ground control and better structural symmetry. The effect of electrostatic interactions on the clustering was also confirmed for titania particles (ρ ~ 3), whose association structures were only possible in the microgravity environment without any sedimentation they generally suffer on the ground. This study suggests that even slight sedimentation and convection on the ground significantly affect the structure formation of colloids. Knowledge from this study will help us to develop a model which will be used to design photonic materials and better drugs.

Chronic treatment with imipramine and lithium increases cell proliferation in the hippocampus in adrenocorticotropic hormone-treated rats.

Adult hippocampal neurogenesis is reported to change in animal models of depression and antidepressants. We have used the mitotic marker 5-bromo-2'-deoxyyridine to address the effects of imipramine and lithium on cell proliferation and survival following chronic treatment with adrenocorticotropic hormone (ACTH) in the subgranular zone of the hippocampal dentate gyrus. ACTH treatment for 14 d decreased adult hippocampal cell proliferation and survival. Coadministration of imipramine and lithium for 14 d blocked the loss of cell proliferation but not cell survival resulting from the chronic treatment with ACTH. The coadministration of imipramine and lithium may have treatment-resistant antidepressive properties, which may be attributed, in part, to a normalization of hippocampal cell proliferation.

Effects of imipramine and lithium on the suppression of cell proliferation in the dentate gyrus of the hippocampus in adrenocorticotropic hormone-treated rats.

We examined the influence of chronic adrenocorticotropic hormone (ACTH) treatment on the number of Ki-67-positive cells in the dentate gyrus of the hippocampus in rats. ACTH treatment for 14 days decreased the number of such cells. The administration of imipramine or lithium alone for 14 days had no effect in saline-treated rats. The effect of ACTH was blocked by the administration of imipramine. Furthermore, the coadministration of imipramine and lithium for 14 days significantly increased the number of Ki-67-positive cells in both the saline and ACTH-treated rats. The coadministration of imipramine and lithium normalized the cell proliferation in the dentate gyrus of the hippocampus in rats treated with ACTH.

[Investigation on the mechanisms for the suppression of cell proliferation in the dentate gyrus of the hippocampus in ACTH treated rats].

We previously reported that adrenocorticotropic hormone (ACTH)-treated rats serve as a valuable animal model for tricyclic antidepressant-resistant depressive conditions. The present study was undertaken to investigate the changes in neurogenesis in the hippocampus of ACTH-treated rats. Chronic treatment of ACTH decreased the number of bromodeoxyuridine-labeled cells in the dentate gyrus, and the coadministration of imipramine and lithium, and electroconvulsive stimuli recovered these reductions. Furthermore, chronic ACTH treatment also decreased the expression of brain-derived neurotrophic factor, and the coadministration of imipramine and lithium, and electroconvulsive stimuli recovered these reductions. These results suggest that antidepressant-resistant depression is caused by the suppression of neurogenesis, and the coadministration of imipramine and lithium, and electroconvulsive stimuli exert an antidepressant-like effect by recovering proliferative signals and neurogenesis.