Region-Dependent and Stage-Specific Effects of Stress, Environmental Enrichment and Antidepressant Treatment on Hippocampal Neurogenesis.

Region-dependent and stage-specific effects of stress, environmental enrichment and antidepressant treatment on hippocampal neurogenesis.

Hippocampus. 2013 Apr 17;
Tanti A, Westphal WP, Girault V, Brizard B, Devers S, Leguisquet AM, Surget A, Belzung C

Chronic stress and depression are associated with decreased levels of hippocampal neurogenesis. On the other hand, antidepressants as well as environmental enrichment may rely in part on their pro-neurogenic effects to improve cognition and mood. Because a functional heterogeneity has been consistently reported along the septo-temporal axis of the hippocampus, regional changes in neurogenesis could differentially contribute to these effects and affect distinct hippocampal functions. Mapping these regional changes could therefore provide a better understanding of the function of newborn neurons. While some studies report region-specific effects of stress and antidepressants on neurogenesis, it is unclear whether these changes affect distinct populations of newborn neurons according to their developmental stage in a region-specific manner. By using endogenous markers and BrdU labeling we quantified the regional changes in cell proliferation and survival as well as in the number of neuronal progenitors and immature neurons following unpredictable chronic mild stress (UCMS), environmental enrichment (EE) and chronic fluoxetine (20 mg/kg/day) treatment along the septo-temporal axis of the hippocampus. EE promoted cell proliferation and survival of 4-week-old newborn cells as well as increased the number and proportion of post-mitotic immature neurons specifically within the septal hippocampus. By contrast, UCMS uniformly decreased cell proliferation, survival and immature newborn neurons but differentially affected progenitor cells with a decrease restricted to the temporal regions of the hippocampus. Whereas fluoxetine treatment in control mice affected proliferation and survival specifically in the temporal hippocampus, it reversed most of the UCMS-induced alterations all along the septo-temporal axis. These results highlight that different factors known for exerting a mood improving effect differentially regulate neurogenesis along the septo-temporal axis of the hippocampus. Such region and stage specific effects may correlate to distinct functional properties of newborn neurons along the septo-temporal axis of the hippocampus which may contribute differently to the pathophysiology of affective disorders. © 2013 Wiley Periodicals, Inc. HubMed – depression


Depression in health practitioners: additional resources.

BMJ. 2013; 346: f2315
Clark AF

HubMed – depression


Oscillatory serotonin function in depression.

Synapse. 2013 Apr 17;
Salomon RM, Cowan RL

Oscillations in brain activities with periods of minutes to hours may be critical for normal mood behaviors. Ultradian (faster than circadian) rhythms of mood behaviors and associated central nervous system activities are altered in depression. Recent data suggest that ultradian rhythms in serotonin (5HT) function also change in depression. In two separate studies, 5HT metabolites in cerebrospinal fluid (CSF) were measured every 10 m for 24 h before and after chronic antidepressant treatment. Antidepressant treatments were associated with enhanced ultradian amplitudes of CSF metabolite levels. Another study used resting-state functional magnetic resonance imaging (fMRI) to measure amplitudes of dorsal raphé activation cycles following sham or active dietary depletions of the 5HT precursor (tryptophan). During depletion, amplitudes of dorsal raphé activation cycles increased with rapid 6 s periods (about 0.18 Hz) while functional connectivity weakened between dorsal raphé and thalamus at slower periods of 20 s (0.05 Hz). A third approach studied MDMA (ecstasy) users because of their chronically diminished 5HT function compared to non-MDMA polysubstance users (Karageorgiou et al., 2009). Compared to a non-MDMA using cohort, MDMA users showed diminished fMRI intra-regional coherence in motor regions along with altered functional connectivity, again suggesting effects of altered 5HT oscillatory function. These data support a hypothesis that qualities of ultradian oscillations in 5HT function may critically influence moods and behaviors. Dysfunctional 5HT rhythms in depression may be a common endpoint and biomarker for depression, linking dysfunction of slow brain network oscillators to 5HT mechanisms affected by commonly available treatments. 5HT oscillatory dysfunction may define illness subtypes and predict responses to serotonergic agents. Further studies of 5HT oscillations in depression are indicated. Synapse, 2013. © 2013 Wiley Periodicals, Inc. HubMed – depression