Enkephalin knockout male mice are resistant to chronic mild stress

Enhanced stress reactivity or sensitivity to chronic stress increases the susceptibility to mood pathologies such as major depression. The opioid peptide enkephalin is an important modulator of the stress response. Previous studies using preproenkephalin knockout (PENK KO) mice showed that these animals exhibit abnormal stress reactivity and show increased anxiety behavior in acute stress situations. However, the consequence of enkephalin deficiency in the reactivity to chronic stress conditions is not known. In this study, we therefore submitted wild-type (WT) and PENK KO male mice to chronic stress conditions, using the chronic mild stress (CMS) protocol. Subsequently, we studied the CMS effects on the behavioral and hormonal level and also performed gene expression analyses. In WT animals, CMS increased the expression of the enkephalin gene in the paraventricular nucleus (PVN) of the hypothalamus and elevated the corticosterone levels. In addition, WT mice exhibited enhanced anxiety in the zero-maze test and depression-related behaviors in the sucrose preference and forced swim tests. Surprisingly, in PENK KO mice, we did not detect anxiety and depression-related behavioral changes after the CMS procedure, and even measured a decreased hormonal stress response. These results indicate that PENK KO mice are resistant to the CMS effects, suggesting that enkephalin enhances the reactivity to chronic stress.

The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling

The mechanisms underlying the initiation/onset of, and the recovery from, depression are still largely unknown; views that neurogenesis in the hippocampus may be important for the pathogenesis and amelioration of depressive symptoms have gained currency over the years although the original evidence has been challenged. In this study, an unpredictable chronic mild stress protocol was used to induce a depressive-like phenotype in rats. In the last 2 weeks of stress exposure, animals were treated with the antidepressants fluoxetine, imipramine, CP 156,526 or SSR 1494515, alone or combined with methylazoxymethanol, a cytostatic agent used to arrest neurogenesis. We found that antidepressants retain their therapeutic efficacy in reducing both measured indices of depression-like behavior (learned helplessness and anhedonia), even when neurogenesis is blocked. Instead, our experiments suggest re-establishment of neuronal plasticity (dendritic remodeling and synaptic contacts) in the hippocampus and prefrontal cortex, rather than neurogenesis, as the basis for the restoration of behavioral homeostasis by antidepressants.

[The epidemiology of proximal femur fracture at the Hospital da Horta (Azores)]

The aim of this study was to know the incidence of osteoporotic hip fracture in a defined area of the Azores. The catchment area included the islands of Faial, Pico, Flores and Corvo, with 11,617 subjects aged 50 or more: 5,373 males and 6,244 females. The time period of the survey was 1991 to 1993. Data was obtained from the records of the Orthopedic Department of Hospital Horta. Thirty seven fractures were diagnosed during the time survey: 12 in 1991, 13 in 1992 and 12 in 1993. The age-adjusted mean incidence rates of hip fracture for the population over 49 years old was 10.3/10,000: 5.6/10,000 in men and 14.4/10,000 in women. Most fractures occurred in women over the age of 65 years. The ratio of male to female cases was 1:3. The mean age of all patients was 77 +/- 8 years of age: 72 +/- 8 in males and 79 +/- 6 in females (p = 0.05). About 70 percent of these patients were treated surgically. The acute mortality rate was 8 percent and the mean age of the deceased patients, 82 +/- 6, was significantly higher than the mean age of the survivors, 73 +/- 6 (p = 0.01).