Recent epidemiological studies indicate that obesity increases the incidence of depression. We examined the implication of leptin for obesity-associated depression. Leptin induced antidepressive behavior in normal mice in a forced swimming test (FST), and leptin-overexpressing transgenic mice with hyperleptinemia exhibited more antidepressive behavior in the FST than nontransgenic mice. In contrast, leptin-deficient ob/ob mice showed more severe depressive behavior in the FST than normal mice, and leptin administration substantially ameliorated this depressive behavior. Diet-induced obese (DIO) mice fed a high-fat diet showed more depressive behavior in the FST and in a sucrose preference test compared with mice fed a control diet (CD). In DIO mice, leptin induced neither antidepressive action nor increment of the number of c-Fos immunoreactive cells in the hippocampus. Diet substitution from high-fat diet to CD in DIO mice ameliorated the depressive behavior and restored leptin-induced antidepressive action. Brain-derived neurotrophic factor concentrations in the hippocampus were significantly lower in DIO mice than in CD mice. Leptin administration significantly increased hippocampal brain-derived neurotrophic factor concentrations in CD mice but not in DIO mice. The antidepressant activity of leptin in CD mice was significantly attenuated by treatment with K252a. These findings demonstrated that leptin induces an antidepressive state, and DIO mice, which exhibit severe depressive behavior, did not respond to leptin in both the FST and the biochemical changes in the hippocampus. Thus, depression associated with obesity is due, at least in part, to impaired leptin activity in the hippocampus.

An electrochemical method was tested in order to find a suitable experimental technique for the determinations of the activities of P2O5 in molten fluxes used for external dephosphorization of hot metal. This technique consists of equilibrating phosphorus‐containing copper with molten slag and measuring the equilibrium oxygen partial pressure by means of solid state galvanic cells. The activities of P2O5 in MgO—P2O5 were determined with this technique.

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The oxygen partial pressures of the equilibrium among solid magnesia, phosphorus-containing liquid copper and trimagnesium phosphate were measured by means of solid-oxide galvanic cells. These cells incorporated magnesia-stabilized zirconia as solid electrolyte and Mo +Mo0 2 as reference electrode at 1473,1 523 and 1 573 K.Then the activities of phosphorus in liquid copper, and the free energy of dissolution of diatomic phosphorus gas into liquid copper at infinite dilution refered to 1 wt. pet. were determined. Untersuchungen derPhosphoraktivitaten in fliissigem Kupfer mit galvanischen Zellen. Die Sauerstoff-Partialdrucke im Gleichgewicht zwischen festem Magnesium, phosphorhaltigem, ftussiqern Kupfer und Trimagnesium-Phosphat werden mit galvanischen Zellen gemessen. Diese Zellen beinhalten magnesiumstabilisierten Zirkon als festen Elektrolyten und Mo + Mo0 2 als Referenzelektrode bei 1473, 1523 und 1573 K. Anschlielsend werden die Phosphoraktivitaten in flussiqern Kupfer bestimmt. Die freie Enthalpie der Auflosunq von zweiatomigem Phosphorgas in flussiqem Kupfer bei unendlicher Verdunnunq bezieht sich auf 1Gew.-%.(1)