Use this URL to cite or link to this record in EThOS:
Title: Separate and interactive effects of catechol-o-methyltransferase and tetrahydrocannabinol on frontostriatal dopamine function
Author: Stumpenhorst, Katharina
ISNI:       0000 0004 7232 678X
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
The frontostriatal dopamine system modulates brain function and is affected by both genetic and environmental factors. Dysfunction of this system is associated with many pathological states, including schizophrenia. The enzyme catechol-O- methyltransferase (COMT) metabolises dopamine and its gene contains a polymorphism (Val158Met) that affects enzyme activity. Delta-9- tetrahydrocannabinol (THC), the main psychoactive component of cannabis, has been suggested to interact with this polymorphism to increase the risk for psychosis and cognitive impairments. Dopaminergic mechanisms are a plausible candidate for mediating this interaction. I used microdialysis coupled with high performance liquid chromatography (HPLC) to examine the effects of THC on extracellular dopamine and its metabolites in the nucleus accumbens, dorsal striatum and medial prefrontal cortex (mPFC) in freely moving mice. Following acute COMT inhibition with tolcapone, THC increased extracellular dopamine levels in the nucleus accumbens in tolcapone-, but not in vehicle-, treated mice. The introduction of the low activity Met allele into the COMT gene produced a highly specific, novel mouse model of the Val158Met polymorphism. In contrast to the effects of acute COMT inhibition, the Met allele protected against THC-induced changes in accumbal dopamine. No interactive neurochemical effects were observed in the dorsal striatum (pharmacological and genetic study) or in a preliminary study of the mPFC (genetic study only). On a progressive ratio task measuring motivational salience, the direction of the interactive effect between COMT genotype and THC differed between 2 independent cohorts and provided tentative leads that stress/arousal-dependent effects on COMT may have a confounding effect. My data provide evidence that COMT activity modulates the effect of THC on accumbal dopamine function, and suggest the mechanism through which this interaction is mediated differs between acute and lifelong reduction in COMT activity. Through the interactive effect on the dopaminergic system, the data provide a potential mechanism for the reported interaction between COMT and cannabis/THC in determining psychosis risk and cognitive impairments.
Supervisor: Bannerman, David ; Tunbridge, Elizabeth ; Harrison, Paul Sponsor: Wellcome Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Neurosciences ; cannabis ; schizophrenia ; THC ; dopamine ; gene-environment interaction ; psychosis ; COMT