Short-term treatment with the antidepressant fluoxetine triggers pyramidal dendritic spine synapse formation in rat hippocampus.
ABSTRACT The pathomechanism of major depressive disorder and the neurobiological basis of antidepressant therapy are still largely unknown. It has been proposed that disturbed hippocampal activity could underlie some of the cognitive and vegetative symptoms of depression, at least in part because of loss of pyramidal cell synaptic contacts, a process that is likely to be reversed by antidepressant treatment. Here we provide evidence that daily administration of the antidepressant fluoxetine to ovariectomized female rats for 5 days induces a robust increase in pyramidal cell dendritic spine synapse density in the hippocampal CA1 field, with similar changes appearing in CA3 after 2 weeks of treatment. This rapid synaptic remodelling might represent an early step in the fluoxetine-induced cascade of responses that spread across the entire hippocampal circuitry, leading to the restoration of normal function in the hippocampus. Hippocampal synaptic remodelling might provide a potential mechanism to explain certain aspects of antidepressant therapy and mood disorders, especially those associated with changes in reproductive state in women, that cannot be reconciled adequately with current theories for depression.
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ABSTRACT: Increasing evidences have been accumulated during recent years suggesting a role for antidepressant drugs (ADs) as hippocampal neurogenesis enhancers, but the information about the transductional mechanisms involved in this response is very limited. We have studied in the adult rat hippocampus the effects of chronic treatment with the dual reuptake inhibitor (SNRI) venlafaxine on both cellular proliferation rate and expression of key effectors of several signaling pathways. Increased cell proliferation (BrdU incorporation) in subgranular zone (SGZ) was achieved after chronic treatment with a high dose (40 mg/kg/day) of venlafaxine. However, significant increases in the immunoreactivity of hippocampal beta-catenin in SGZ were already detected after administration of a lower dose of the drug (10 mg/kg/day). Western blot and immunoelectron microscopy studies demonstrated an increased presence of beta-catenin at the nuclear level. An increase in cytosolic AKT levels was also observed in venlafaxine-treated animals. These results suggest that the hippocampal proliferative effect of chronic venlafaxine, only evident when both serotonin (5-HT) and noradrenaline/norepinephrine (NE) reuptake systems are inhibited, requires a strong activation of intracellular signaling through Wnt (beta-catenin translocation) and AKT/PKB pathways. This activation would probably result in an increase of the expression of cell cycle regulator genes. Furthermore pERK2/ERK2 rate was also increased in the hippocampus of AD-treated animals, while no differences in the levels of CREB and p-CREB were observed. These results illustrate the complexity of the intracellular events underlying the neurogenetic responses of ADs. They also support the relevance of such effects for the therapeutic effects of these drugs.Neuropharmacology 08/2008; 55(1):18-26. DOI:10.1016/j.neuropharm.2008.04.012 · 4.82 Impact Factor
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ABSTRACT: Accumulating evidence indicate that structural synaptic plasticity in limbic areas plays a vital role not only in normal brain functions, such as cognition and mood, but also in the development of neurological and mental disorders. We have learned from studies investigating neuronal remodeling that estrogens have an exceptional synaptogenic potential that seems to be specific to limbic areas of the adult female brain. On the other hand, structural synaptic plasticity in the adult male brain and the synaptogenic effect of androgens received relatively little attention. During the last five years, the Leranth laboratory provided conclusive evidence that the hippocampus and prefrontal cortex of adult male rodents and non-human primates retain considerable structural synaptic plasticity similar to the female, and that androgens are capable of inducing spine synapse growth in both the hippocampus and prefrontal cortex similar to estrogens. Our recent work also demonstrates that androgen-induced remodeling of spine synapses in the prefrontal cortex of adult male rats is dependent, at least to some extent, on functional androgen receptors, while being entirely independent of the androgen receptor in the hippocampus. Based on these findings and on their many beneficial effects, we believe that androgens hold a great and undeservingly neglected therapeutic potential that could be employed to reverse synaptic pathology in various neurocognitive and neuropsychiatric disorders.Hormones and Behavior 06/2008; 53(5):638-46. DOI:10.1016/j.yhbeh.2007.12.007 · 4.51 Impact Factor
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ABSTRACT: We assessed whether daily separation of Mongolian gerbils (Meriones unguiculatus) from mothers and siblings during postnatal days 4-20 would produce behavioral and neurochemical changes in adulthood that parallel some features of depression in humans. Neonatal separation altered the behavior of adult females in the open field test but not in the tail suspension test, and did not affect behavior of males. Separated males, but not females, showed a significant decrease in hippocampal brain derived neurotrophic factor (BDNF) relative to controls. Western blot and optical densitometry measurements in the hippocampus did not reveal significant group differences in synaptophysin levels in either sex, but there was a tendency toward decreased levels of synaptophysin in the entire hippocampus as well as the CA1 hippocampal subregion of separated males. Repeated separation of neonates from mothers and siblings led to subtle behavioral and neurochemical changes during adulthood that were expressed differently in male and female gerbils.Pharmacology Biochemistry and Behavior 03/2008; 88(4):533-41. DOI:10.1016/j.pbb.2007.10.012 · 2.82 Impact Factor