Morphine is an extremely efficient analgesic drug however when used repetitively can have two major detrimental side effects: tolerance and addiction. Understanding the molecular mechanisms that lead to these side effects may ultimately help develop improved therapeutics without tolerance and addiction liability. The goal of this dissertation was to discover candidate genes involved in morphine tolerance and addiction. To accomplish this goal a specific behavior genetics approach in conjunction with microarray analysis was used to identify high-value candidate genes. The genes were further investigated by bioinformatics analysis, rtPCR, and in vivo shRNA knockdown.
To identify genes associated with tolerance two inbred genotypes which differ in morphine-related behaviors (C57BL/6J (B6), DBA2/J (D2)) and two reciprocal congenic genotypes (B6D2, D2B6) in which the proximal region of CH10 was introgressed into opposing backgrounds were used. The proximal region of CH10 has been implicated in morphine related behaviors. Tolerance following therapeutically-relevant doses of morphine developed most rapidly in the B6s followed by the B6D2s and did not develop in the D2s and only slightly in the D2B6s thus indicating a strong influence of the proximal region of CH10 in the development of tolerance. Gene expression profiling identified 81, 96, 106, and 82 genes involved in the development of tolerance in the periaquaductal gray (PAG), prefrontal cortex (PFC), temporal lobe (TL) and ventral striatum (VS) respectively. Bionformatics analysis highlighted genes associated with microRNA (miRNA) mechanisms in response to chronic administration.
In vivo knockdown of Dicer1, the miRNA processing gene, in the PFC of the B6 genotype verified Dicer1's role in the development of tolerance. Gene expression profiling identified 33 miRNAs involved in the development of tolerance.
B6 and D2 genotypes were also used to identify candidate genes in morphine addiction. Gene expression profiling identified total of 271 and 178 candidate genes in animals actively self-administering morphine, in the VS and ventral midbrain (VMB), respectively. Bionformatics analysis highlighted genes associated with miRNA mechanisms and synaptic plasticity.
These results indicate a significant role of miRNAs and neuroadaptation genes in tolerance and addiction. Ultimately, the candidate genes could be pharmacological targets to counteract tolerance and decrease addiction liability.
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|Advisor:||Elmer, Greg, Robinson, Phyllis|
|Commitee:||Brewster, Rachel, Lee, Norman, Shepard, Paul|
|School:||University of Maryland, Baltimore County|
|Department:||Neurosciences and Cognitive Science|
|School Location:||United States -- Maryland|
|Source:||DAI-B 70/09, Dissertation Abstracts International|
|Keywords:||Addiction, Analgesic tolerance, Morphine, RNA interference, Synaptic plasticity, microRNAs|
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