The course of depressive symptoms in Lewy body dementia and Alzheimer's disease.

BACKGROUND: Depressive symptoms frequently affect patients with neurocognitive disorders. In cross-sectional studies, patients with Lewy body dementia (DLB) showed higher levels of depressive symptoms than those with Alzheimer's disease (AD). We here describe the 5 year course of depressive symptoms in patients with DLB and AD. METHODS: Secondary analysis of a dementia study in Western Norway (DemVest) longitudinal cohort study. SETTING: This multicenter study was conducted in memory clinics in Western Norway. 187 patients newly diagnosed with AD (n = 111) and DLB (n = 76) were followed up annually for 5 years. Depressive symptoms were assessed using the Montgomery Åsberg Depression Rating Scale (MADRS). MADRS subclusters dysphoria, retardation, vegetative, anhedonia were analyzed. The impact of proximity of death and the role of risk factors for depression and dementia on the course of depressive symptoms were evaluated. RESULTS: We observed continuously increasing mean levels of depressive symptoms in DLB, while patients with AD showed a delayed increase at later follow-up visits. Increase in MADRS total score was mainly driven by increases in the anhedonia and retardation subclusters. Proximity to death was associated with an increase in depressive symptoms in DLB, while it tended to decrease in AD. Previous smoking and hearing loss were associated with higher MADRS scores during follow-up in the total sample. LIMITATIONS: Yearly assessment of depressive symptoms might be too infrequent. CONCLUSION: Depressive symptom load was consistently higher in DLB compared to AD during five years after diagnosis, but tended to become more similar at later stages.

Adult hippocampal neurogenesis and plasticity in the infrapyramidal bundle of the mossy fiber projection: I. Co-regulation by activity.

BESIDES THE MASSIVE PLASTICITY AT THE LEVEL OF SYNAPSES, WE FIND IN THE HIPPOCAMPUS OF ADULT MICE AND RATS TWO SYSTEMS WITH VERY STRONG MACROSCOPIC STRUCTURAL PLASTICITY: adult neurogenesis, that is the lifelong generation of new granule cells, and dynamic changes in the mossy fibers linking the dentate gyrus to area CA3. In particular the anatomy of the infrapyramidal mossy fiber tract (IMF) changes in response to a variety of extrinsic and intrinsic stimuli. Because mossy fibers are the axons of granule cells, the question arises whether these two types of plasticity are linked. Using immunohistochemistry for markers associated with axonal growth and pro-opiomelanocortin (POMC)-GFP mice to visualize the post-mitotic maturation phase of adult hippocampal neurogenesis, we found that newly generated mossy fibers preferentially but not exclusively contribute to the IMF. The neurogenic stimulus of an enriched environment increased the volume of the IMF. In addition, the IMF grew with a time course consistent with axonal outgrowth from the newborn neurons after the induction of neurogenic seizures using kainate. These results indicate that two aspects of plasticity in the adult hippocampus, mossy fiber size and neurogenesis, are related and may share underlying mechanisms. In a second part of this study, published separately (Krebs et al., 2011) we have addressed the question of whether there is a shared genetics underlying both traits.

Adult Hippocampal Neurogenesis and Plasticity in the Infrapyramidal Bundle of the Mossy Fiber Projection: II. Genetic Covariation and Identification of Nos1 as Linking Candidate Gene.

The hippocampus of adult rodents harbors two systems exhibiting structural plasticity beyond the level of synapses and dendrites. First, the persistent generation of granule cells (adult neurogenesis); second, dynamic changes in the mossy fibers (MF), in particular in the infrapyramidal mossy fiber (IMF) tract. Because MFs are the axons of granule cells, the question arises whether these two types of plasticity are linked. In the first part of this study (Römer et al., 2011) we have asked how both traits are regulated in relation to each other. In the present part, we asked whether, besides activity-dependent co-regulation, there would also be signs of genetic co-regulation and co-variance. For this purpose we used the BXD panel of recombinant inbred strains of mice, a unique genetic reference population that allows genetic association studies. In 31 BXD strains we did not find correlations between the traits describing the volume of the MF subfields and measures of adult neurogenesis. When we carried out quantitative trait locus mapping for these traits, we found that the map for IMF volume showed little overlap with the maps for the other parts of the projection or for adult neurogenesis, suggesting that to a large degree the IMF is regulated independently. The highest overlapping peak in the genome-wide association maps for IMF volume and the number of new neurons was on distal chromosome 5 (118.3-199.2 Mb) with an LRS score of 5.5 for IMF and 6.0 for new neurons. Within this interval we identified Nos1 (neuronal nitric oxide synthase) as a cis-acting (i.e., presumably autoregulatory) candidate gene. The expression of Nos1 is has been previously linked with both IMF and adult neurogenesis, supporting our findings. Despite explaining on its own very little of the variance in the highly multigenic traits studied, our results suggest Nos1 may play a part in the complex genetic control of adult neurogenesis and IMF morphology.

Enriched environment and physical activity reduce microglia and influence the fate of NG2 cells in the amygdala of adult mice.

Proliferative cells expressing proteoglycan neuron-glia 2 (NG2) are considered to represent parenchymal precursor cells in the adult brain and are thought to differentiate primarily into oligodendrocytes. We have studied cell genesis in the adult amygdala and found that, up to 1 year after the labeling of proliferating cells with bromodeoxyuridine, most proliferating NG2 cells remain NG2 cells, and only a few slowly differentiate into mature oligodendrocytes, as assessed by the expression of 2',3'-cyclic nucleotide 3'-phosphodiesterase. We have detected no signs of neurogenesis but have confirmed the expression of "neuronal" markers such as Doublecortin in NG2 cells. Nestin-expressing NG2 cells in the amygdala show electrophysiological properties known for oligodendrocyte precursor cells in the corpus callosum. Application of the glutamate agonist kainate elicits a "complex" response consisting of a rapid and long-lasting blockade of the resting K(+) conductance, a transient cationic current, and a transient increase of an outwardly directed K(+) conductance, suggesting the responsiveness of NG2 cells to excitation. Proliferation of NG2 cells increases in response to behavioral stimuli of activity, voluntary wheel running, and environmental enrichment. In addition to reducing the number of newborn microglia, behavioral activity results in a decrease in S100ß-expressing newborn NG2 cells in the amygdala. Because S100ß expression in NG2 cells ceases with oligodendrocyte maturation, this finding suggests that NG2 cells in the amygdala undergo activity-dependent functional alterations, without resulting in a measurable increase in new mature oligodendrocytes over the time period covered by the present study. The adult amygdala thus shows signs of mixed activity-dependent plasticity: reduced numbers of microglia and, presumably, an altered fate of NG2 cells.

Finasteride-induced depression: new insights into possible pathomechanisms.

5-alpha-reductase is involved as a rate-imitating enzyme in the metabolism of steroids. Several 5-alpha-reduced steroids such as dihydrotestosterone, allopregnanolone or tetrahydrocorticosterone have neurotrophic, neuroprotective, and anxiolytic properties. Reduced 5-alpha-reductase activity has been observed during depressive illness in humans. Finasteride inhibits 5-alpha-reductase and can robustly induce anxious and depressive behaviors in rodents. In humans finasteride treatment has been linked to an increase of depressive symptoms. A recent study reported that finasteride treatment inhibits hippocampal neurogenesis in mice. As hippocampal neurogenesis has been linked to emotional behavior, this could be of possible relevance for the pathophysiology of affective disorders. Further studies are needed to evaluate potential neuropsychiatric side effects of finasteride treatment in humans.

Cortisol metabolism in depressed patients and healthy controls.

BACKGROUND: Chronic stress as well as major depressive disorders are associated with hypercortisolemia and impaired hypothalamic-pituitary-adrenocortical axis functioning. The aim of this study was to determine whether in major depression changes in the activity patterns of local modulators of glucocorticoid action might contribute to an increase in cortisol bioavailability and if they change during antidepressant treatment and clinical response. METHODS: Concentrations of urinary total cortisol (UFF), urinary total cortisone (UFE), tetrahydrocortisone (THE), tetrahydrocortisol (THF) and allo-THF (5alpha-THF) were measured in 10-hour nocturnal urine samples of 19 depressed patients and 15 healthy controls. The activity of 11beta-hydroxysteroid dehydrogenases (11beta-HSD) as well as 5alpha- and 5beta-reductases was assessed by calculating the ratios of glucocorticoid metabolites. Patients were treated for 28 days with either mirtazapine or venlafaxine. Enzyme activity was observed during the course of treatment and compared to healthy controls. Responders to treatment were selected for this analysis. RESULTS: Depressed patients showed reduced 5alpha-reductase activity manifested as a significantly lower amount of 5alpha-THF (102.8 +/- 167.2 vs. 194.6 +/- 165.8 microg, p = 0.019). The increase in the UFF/UFE ratio (0.73 +/- 0.32 vs. 0.29 +/- 0.13, p < 0.0001) indicates reduced activity of renal 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2). During pharmacological treatment, 5alpha-reductase activity in patients returned to the level of the control group, while the decrease in 11beta-HSD2 activity persisted until day 28. CONCLUSIONS: Our results show changes in activity of intracellular modulators of steroid action in major depressive disorders, particularly a reduced activity of the intracellular cortisol-deactivating enzymes 5alpha-reductase and 11beta-HSD2. These changes suggest an increase in cortisol bioavailability within tissues.

Imaging new neurons in vivo: a pioneering tool to study the cellular biology of depression?

Hippocampal neurogenesis has been implicated in the pathogenesis of and recovery from depression. However, most of the underlying studies were endpoint investigations in experimental animals yielding conflicting results, and it has been under debate to which extent these results could be transferred to human patients. Now, researchers have developed a powerful new tool to address these questions by a non-invasive method in humans and animals in vivo, using magnetic resonance spectroscopy to detect a biomarker for proliferating progenitor cells that give rise to new neurons. This makes it possible to study the role of neural progenitor cells in a wide variety of human brain disorders.

Variability of doublecortin-associated dendrite maturation in adult hippocampal neurogenesis is independent of the regulation of precursor cell proliferation.

BACKGROUND: In the course of adult hippocampal neurogenesis most regulation takes place during the phase of doublecortin (DCX) expression, either as pro-proliferative effect on precursor cells or as survival-promoting effect on postmitotic cells. We here obtained quantitative data about the proliferative population and the dynamics of postmitotic dendrite development during the period of DCX expression. The question was, whether any indication could be obtained that the initiation of dendrite development is timely bound to the exit from the cell cycle. Alternatively, the temporal course of morphological maturation might be subject to additional regulatory events. RESULTS: We found that (1) 20% of the DCX population were precursor cells in cell cycle, whereas more than 70% were postmitotic, (2) the time span until newborn cells had reached the most mature stage associated with DCX expression varied between 3 days and several weeks, (3) positive or negative regulation of precursor cell proliferation did not alter the pattern and dynamics of dendrite development. Dendrite maturation was largely independent of close contacts to astrocytes. CONCLUSION: These data imply that dendrite maturation of immature neurons is initiated at varying times after cell cycle exit, is variable in duration, and is controlled independently of the regulation of precursor cell proliferation. We conclude that in addition to the major regulatory events in cell proliferation and selective survival, additional micro-regulatory events influence the course of adult hippocampal neurogenesis.

Seizures induce proliferation and dispersion of doublecortin-positive hippocampal progenitor cells.

One neuropathological hallmark of temporal lobe epilepsy is granule cell dispersion, a widening of the hippocampal granule cell layer (GCL) with abnormally positioned excitatory neurons. The finding that seizure activity also induces adult hippocampal neurogenesis was taken largely as indicative of a regenerative attempt, not as part of the pathology. The aim of our study was to characterize a potential relationship between granule cell dispersion and seizure-induced neurogenesis. Kainic acid (KA)-induced seizures in mice led to increased cell proliferation and new neurons persisted for months after the seizures. We show that the proliferative stimulus did not affect nestin-expressing early precursor cells that primarily respond to physiologic mitogenic stimuli, but stimulated the division of late type-3 progenitor cells, which express doublecortin (DCX), a protein associated with cell migration. This delayed proliferation presumably interfered with migration, leading to a significant dispersion of DCX-positive progenitors and early postmitotic neurons within the dentate gyrus granule cell layer. We propose that initial seizures induce ectopic precursor cell proliferation resulting in the dispersion of immature neurons within the adult granule cell layer. Thus, seizure-generated neurons might contribute to the disease process of epilepsy.