|Ph.D Student||Drigues Noam|
|Subject||Rat Hippocampal Gene Expression after Chronic Administration|
of Antidepressant Drugs Employing cDNA Microarray
|Department||Department of Medicine||Supervisor||Professor Emeritus Moussa Youdim|
|Full Thesis text|
The novel neurotrophic hypothesis suggests that the effect of antidepressant drugs results from long-term regulation of neuronal gene expression and promotion of neuronal survival. However, sporadic observations, using regular molecular assays, can only suggest on gene expression changes elicited by antidepressant drugs. We hypothesize that there is a subset of genes that is required for the therapeutic effect of different classes of antidepressant drugs.
Sprague Dawley rats were chronically treated with Moclobemide, Clorgyline or Amitriptyline and exhibited reduced immobility in the forced swimming test and changes in hippocampal amine levels. 58 genes were upregulated and 31 were downregulated by at least two of the three antidepressant drugs. The percentage of genes changed by each antidepressant drug was greater when it was calculated from set of genes changed by a different drug, a fact that strengthen the belief that changes in gene expression are a genuine outcome of antidepressant drugs treatment. The designed new drug Ladostigil, combining cholinesterase and monoamine oxidase inhibition, administered chronically, inhibited rat brain monoamine oxidase-A and -B and increased serotonin in the hippocampus. Ladostigil also exhibited antidepressant-like behavior in rats in the forced swimming test and showed high homology in gene expression with the three antidepressants used. The most prominent set of genes differentially expressed after treatment with antidepressant drugs relates to neurogenesis and synapse formation, including synaptophysin and neogenin, known to mediate attraction of growing axons. Using real-time reverse transcription-polymerase chain reaction, high correlation between the expressions of these two genes was found that implies a significant role for neogenin in the effect of antidepressant drugs. We clarified that cultured mature hippocampal slices maintain proper cellular and synaptic distribution that allows neurotransmission in-vitro and found that synaptophysin protein expression is enhanced by exposure of hippocampal slices to serotonin.
By using the cDNA microarray technique as a “fishing net” we were able to find common genes important to the action of antidepressant drugs further suggesting that these drugs regulate establishment of new connections between neurons. We can conclude that the set of common genes changed by different antidepressant drugs is relevant to their molecular basis of action. Our results illustrate the feasibility of the hippocampal slice culture system as a model for the analysis of synaptogenesis mechanisms in central neurons.