Time: 12: 30-13:30, Sept.29, 2019

Venue: 医学科学楼B323 (B323, Medical Science Building, Tsinghua University)

Host:  苑克鑫(Dr.Kexin Yuan)

Speaker：刘苗苗

Topic: The posterior tail of striatum plays an important role in tonal associative learning

摘要

The striatum is traditionally divided into three subdivisions based on connection and function, including dorsomedial striatum, dorsolateral striatum, and ventral striatum. These subdivisions are critically involved in various brain functions, including associative learning. Very recently, the posterior tail of the striatum (TS) started to be considered as the fourth subdivision because of its independent dopamine source, and the understanding of its function is still very limited. Although a few studies have shown the essential role of TS neurons in learned discrimination task, whether and how these neurons might play a specific role during associative learning remains unknown. To address this question, we adopted a Go-Nogo behavioral task, in which mice learn to associate one tone with reward (sucrose water) and the other tone with punishment (air puff). We firstly expressed GCaMP6 in the TS of Vgat-ires-Cre mice, then we made fiberphotometry recordings from TS neurons expressing GCaMP6 during the training. We found that the medial and lateral part of the TS showed differential responses to tonal cues. The medial part demonstrated significantly stronger adaptation to tones in the first day of training than the lateral part did.. To find out whether difference in connection might account for the difference in neural responses, we used retrograde mono-transynaptic rabies virus to identify the inputs of medial and lateral TS. We found that the lateral part received more inputs from the auditory cortices, while the medial part received substantially more inputs from somatosensory cortices. Our immunohistological results showed that medial TS is rich of D1R neurons and almost absent of D2R neurons, while lateral TS has more D2R neurons than D1R neurons, suggesting that D2R neurons, which are located laterally, might be more important for associative learning using tonal cues. To test this hypothesis, we optogenetically activated either D1R or D2R neurons during training. We found that both the activation of D1R and D2R neurons significantly accelerated learning process by improving the performance of correct rejection. However, the improved performance was preserved after days of light stimulation only in mice received D2R activation. The performance of mice received D1R activation dropped to control level in the first day of light-off. These data suggest that TS neurons are indeed involved in tonal associative learning, and that D2R neurons might play a more important role.