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Teaser, summary, work performed and final results

Periodic Reporting for period 3 - CoordinatedDopamine (Coordination of regional dopamine release in the striatum during habit formation and compulsive behaviour)


The basal ganglia consist of a set of brain structures that are responsible for the selection and execution of behavioral actions in a given context. Release of the neurotransmitter dopamine into the striatum, the main input nucleus of the basal ganglia, is a fundamental...


The basal ganglia consist of a set of brain structures that are responsible for the selection and execution of behavioral actions in a given context. Release of the neurotransmitter dopamine into the striatum, the main input nucleus of the basal ganglia, is a fundamental mechanism involved in learning and regulation of such actions. The striatum consists of multiple functional units, where the limbic striatum is thought to mediate motivational aspects of actions (e.g., goal-directedness) and the sensorimotor striatum their automation (e.g., habit formation).

A long-standing question in the field of neuroscience is how these limbic and sensorimotor domains communicate with each other, and specifically if they do so during the automation of action sequences (habit formation). An influential neuroscientific hypothesis suggests that such coordination is implemented by reciprocal neuronal connections between striatal projection neurons and the dopaminergic midbrain. Although very influential in theory the effectiveness of this limbic-sensorimotor “bridging” principle has yet to be verified. I hypothesize that during the automation of behavior regional dopamine signaling is governed by a striatal hierarchy that is based on the suggested reciprocal connections and that dysregulation of this coordination leads to compulsive execution of automatic actions characteristic of several psychiatric disorders.

To test this hypothesis, we will conduct electrochemical measurements with real-time resolution simultaneously in limbic and sensorimotor striatum to assess the regional coordination of dopamine release in behaving animals. We developed novel chronically implantable electrodes to enable longitudinal monitoring of dopamine release throughout the development of habitual behavior and its compulsive execution in transgenic rats - a species suitable for our complex behavioral assays. Novel rabies virus-mediated gene delivery for in vivo optogenetics in these rats will give us the unique opportunity to test whether specific loop pathways govern striatal dopamine transmission and are causally involved in habit formation and compulsive behavior.

Work performed

The first major achievements of this reporting period are the successful purchase, setup, and use of all of the experimental equipment proposed for the project. Electrochemical recordings in the brain have been “de-noised” sufficiently to enable meaningful measurements of neurotransmitter release in the brain, both in recording setups for anesthetized and freely moving rats. Furthermore, the breeding and genotyping of the TH-Cre rat line, critical for the proposal, and expression of several viral constructs in the brains of these rats, delivering proteins for experimental manipulation to dopamine neurons and connected cells, have been achieved. In summary, scientific equipment, biological reagents, and experimental animals were prepared successfully providing the foundation for experimental success of the project.

The next achievement is the successful application for authorization for the use of experimental animal research and the use of viruses for this research. Governmental licensing for animal experiments necessary for realization of the scientific proposal has been granted in a timely fashion. The umbrella license (CCD) for all experiments proposed is valid for the entire duration of the project. Individual experiment licenses (IVDs) for the current studies are in place.

The proposal relies on the implementation of complex and challenging behavioral tasks for rats. Programming software for the automated training of the animals and analysis of behavioral data have been achieved. Training of the animals in different novel behavioral tasks was optimized in pilot studies, and data collection is in progress now. For example, implementation of the cocaine self-administration paradigm in rats, an experimental test critical for the proposal, has been achieved. We overcame initial problems in the design and implantation of catheters for cocaine self-administration.
The greatest challenge thus far was achieving governmental licensing for the use of certain viral constructs. Regarding the use of AAV viruses, this obstacle was overcome. Regarding the use of rabies virus, partial success has been achieved. This partial success allowed to execute pilot studies that were proposed for the reporting period. These pilot studies revealed that our attempts to express rabies in the brain were insufficient. Subsequently, we successfully optimized viral expression. The remaining license for conducting brain recordings in rabies-infected animals under lower biosafety restrictions is still in progress.

The final major achievement is that we are able to reliably perform neurotransmitter recordings both in freely-moving and in anesthetized animals and detect release induced by optogenetic stimulation. In both cases, we proceeded from the pilot study phase to the data collection phase.

Final results

Basic science:
This project will potentially be of great impact because it addresses fundamental neuroscientific questions that have been asked since early anatomical discoveries in the 1970s, but are still left unanswered today. The identification of neuronal pathways mediating a progression from learning a new behavior to its automatic execution will have great impact on several neuroscience fields because such pathways, although assumed for decades, have yet to be verified. All fields related to the translation from motivation to action will be affected, including research restricted to motor systems and fields focused on motivation and emotion. Technological impact will be achieved by further advancing knowledge about the application of rabies virus-based gene delivery, until now used for anatomical tracing only, for in vivo optogenetics. This technology is of significant utility for many neuroscientists because it will enable more fine-tuned targeting and manipulation of specific neuronal circuits. Thus, my findings may provide proof-of-principle knowledge about a new, powerful tool in the manipulation of brain activity.

Translational science:
Although the research proposed in this application is fundamental in nature, the knowledge gained from these studies has potential for translational impact. This is due to the embedding of my research group in a larger clinical research team at the Psychiatry Department, where I am involved in frequent clinical and translational research meetings. These close ties provide optimal conditions for me to set up translational, multidisciplinary research, aiming to design experiments that test whether compulsive behavior in OCD is anxiety- or habit-driven. Pilot data from my project will be incorporated in translational grant proposals from this group.

Clinical potential:
My results have potential to supplement behavioral interventions aimed at the reversal of maladaptive habits in psychotherapy. For example, my studies may inform about the temporal relationship between the behavior and dopamine release in the brain. This knowledge could be utilized to introduce easy-to-employ behavioral interventions that are known to alter dopamine release in a time-sensitive manner. This way aberrant dopamine release associated with mental health disorders may be normalized. Such utilization will be discussed with clinicians in meetings with psychiatrists. However, the insights that my proposal will offer are not necessarily confined to the understanding of disorders alone. Implications could also be important for fine-tuning the balance between habits and goal-directed actions in healthy individuals in order to maintain a good quality of life.

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