The role of the cannabinoid system in the neurochemistry underlying reward processes

PhD ceremony: Mr. J. Kleijn, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: The role of the cannabinoid system in the neurochemistry underlying reward processes

Promotor(s): prof. B.H.C. Westerink

Faculty: Mathematics and Natural Sciences

The cannabinoid system is involved in a large number of processes throughout the central nervous system. One of the most extinguished is the proposed modulatory role the cannabinoid system could have in reward processes. The thesis of Jelle Kleijn shows that in nicotine-induced reward processes the Nucleus Accumbens (NAc) shell region might be more important than just a signal receiving center, as local stimulation of nicotinic receptors initiated a dopamine response typical for reward. It is hypothesized that the cannabinoid system is involved in these processes. To study this involvement a microdialysis method was developed to sample and analyze endogenous cannabinoids (ECs). Nicotine-induced an increase in all the four sampled ECs, however none of them seemed to be the specific modulator of nicotine induced reward processes.

The research of Kleijn also shows an interaction between the amphetamine induced dopamine increase and the CB-1 receptors. Among the four regions monitored this interaction was particular evident in the NAc shell, as a CB-1 receptor antagonist inhibited the amphetamine –incuded increase in dopamine release in this area.

Furthermore, Kleijn's thesis includes a study showing the modulatory effect of the CB-1 receptor in the effectiveness of a SSRI, citalopram. Although the results have to be repeated in additional chronical and clinical models, they might explain the fact that depressed patients using cannabis display a particular high failure rate when treated with SSRI’s.

Taken together the research of Kleijn may serve as a starting point for various studies in which endocannabinoid signaling – detected by an in vivo method - is the focus.