2021 Fiscal Year Research-status Report
Differential dopamine dynamics of DMS and DLS projecting SNc neurons during reversal learning
| Project/Area Number |
21K15184
|
|---|
| Research Institution | Tokyo Medical and Dental University |
|---|
Principal Investigator |
|
|---|
| Project Period (FY) |
2021-04-01 – 2024-03-31
|
| Keywords | dLight / Dopamine / Basal ganglia / Striatum / Goal directed behavior |
|---|
| Outline of Annual Research Achievements |
Elucidation of the changes of the phasic activity of the DMS and DLS projecting SNc neurons in rats performing a probabilistic reward-based task. We used TH-Cre transgenic rats for dopaminergic neurons identification. We injected AAV2-EF1α-Flex-ChRWR/Venus into the SNc. DMS or DLS projecting SNc neurons were identified using light evoked collision test. We evaluated the activity of these identified neurons in relation with their dependence to past reward experience. We observed that the past reward representation conveyed to the DS differs between two distinct nigrostriatal pathways. During action selection, information of the reward experience was most strongly represented in DLS projecting neurons. On the other hand, only DMS projecting neurons activity during outcome period was influenced by past rewards.
Study of the dynamics of local dopamine release in the DMS and DLS during operant task conditions using the optical sensor dLight. In order to investigate how dopamine release in DS is dependent of the reward experience, we injected AAV into DMS or DLS to express dLight and monitored the fluorescence using fiber photometry. dLight signal showed robust task-related increasing. After the movement onset, DMS and DLS dopamine signal was higher when the reward history was higher. However, during the outcome period, the signal was stronger when reward experience was lower, being consistent with positive RPE. Dopamine release may convey different information that dopamine cell firing, dopamine local release dynamics may be controlled in different ways.
|
| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We could successfully identify DMS and DLS projecting SNc neurons using TH-cre transgenic rats, and optogenetic and electrophysiological technics. We could evaluate the activity of identified neurons during task performance and investigate the relationship of these neurons to reward experience.
Additionally, we successfully evaluated the local dopamine release in DMS or DLS using the dopamine sensor dLight. So far, we have tried different viral vectors for the successful expression and adequate acquisition of dLight signal during task performance. We evaluated the signal obtained from five different vectors: AAV2.1-32wH-hSynI-dLight1.1, AAV2.1-32wH-CamKIIa-dLight1.1, AAV2.1-32wH-hSynI-dLight1.2, AAV2.1-32wH-CamKIIa-dLight1.2, and AAV9-Syn-dLight1.3b. The signal we obtained from the latter (dLight1.3b) showed the best signal-to-noise ratio and higher amplitude. We used dLight1.3b for further analysis.
|
| Strategy for Future Research Activity |
1.Evaluation of different neuron population of striatum and SNc (e.g. cholinergic and GABAergic interneurons).
2.Performing optogenetical manipulation experiments (stimulation using channelrhodopsin; inhibition using Achearhodopsin) to evaluate the contribution of SNc dopaminergic neurons on task performance (i.e. reward history dependence, decision update, reaction time, movement velocity, choice bias).
3.Evaluation of SNc neuronal activity and dLight signal relation to action-outcome contingency change.
4.Simultaneous evaluation of local dopamine release in striatum (dLight) and striatal neurons activity (RCaMP) using fiber photometry.
|
| Causes of Carryover |
For optical manipulation and identification experiments, using optical fiber, we evaluated different kinds of optical fibers (different diameters, shape, etc), different types of light sources, different type of custom made manipulators, etc. Because of the fact of being custom made, there may be some delay in the fabrication process and in the trial and error of different approaches.
|
