Decreased Dorsomedial Striatum Direct Pathway Neuronal Activity Is Required for Learned Motor Coordination

Abstract

It has been suggested that the dorsomedial striatum (DMS) is engaged in the early stages of motor learning for goal-directed actions, whereas at later stages, control is transferred to the dorsolateral striatum (DLS), a process that enables learned motor actions to become a skill or habit. It is not known whether these striatal regions are simultaneously active while the expertise is acquired. To address this question, we developed a mouse "Treadmill Training Task" that tracks changes in mouse locomotor coordination during running practice and simultaneously provides a means to measure local neuronal activity using photometry. To measure change in motor coordination over treadmill practice sessions, we used DeepLabCut (DLC) and custom-built code to analyze body position and paw movements. By evaluating improvements in motor coordination during training with simultaneous neuronal calcium activity in the striatum, we found that DMS direct pathway neurons exhibited decreased activity as the mouse gained proficiency at running. In contrast, direct pathway activity in the DLS was similar throughout training. Pharmacological blockade of D1 dopamine receptors in these subregions during task performance demonstrated that dopamine neurotransmission in the direct pathway activity is necessary for efficient motor coordination learning. These results provide new tools to measure changes in fine motor skills with simultaneous recordings of brain activity and reveal fundamental features of the neuronal substrates of motor learning.

Keywords: direct pathway; dopamine; motor learning; skill acquisition; striatum; treadmill.

Graphical abstract

Figure 1.

A, Timeline of behavioral protocol in the Treadmill Training Task. On each training day, a mouse is connected to the photometry patch cord in its home cage and a 5-min calcium baseline signal recorded. After this habituation period, the mouse is placed on the treadmill and allowed to explore the environment for 30 s. The treadmill motor is then started at a velocity of 3 m/min, with the speed increased every 60 s up to 12 m/min, after which the treadmill is turned off for another 30 s. This protocol is repeated for 12 consecutive days. A photograph of the treadmill is shown in Extended Data Figure 1-1. B, Schematic of the behavioral analysis. Positions of mouse body parts are obtained by analysis with DeepLabCut. For head position, the ventral 2D field of view are divided into five zones and the probability of the head of the mouse to be in each zone calculated. Color code for the body part is indicated in the legend on the right. C, Samples of head positions on day 1 (top) and day 4 (bottom) for a control mouse. Each point represents the head position in one frame and all frames from one video/session are overlapped. On day 1, the head position was frequently toward the rear of the field, indicating the mouse was falling behind the belt speed and often hitting the back wall. By day 4, the animal was able to keep up with the moving belt, and so the position of the head was more consistently toward the front. Plots of the four paws are shown in Extended Data Figure 1-2. D, Process for obtaining the mouse motor coordination score. Motor coordination score is calculated from the expected value of the head position in the five zones, position along the y-axis (calculated from standard deviation, SD, of y-axis value), and step length (distance between steps for each paw), as detailed in Materials and Methods. E, Motor coordination score for a cohort of control animals. Control mice show significant improvement in the coordination score over the 12 d of testing (n = 9; one-way ANOVA p < 0.001, Bonferroni’s multiple comparisons test as detailed in main text). Mouse weight and data by sex is shown in Extended Data Figure 1-1.

Figure 2.

A, Raw sample fluorescence traces recorded during baseline with excitation at 405 nm (bottom trace), GCaMP6f isosbestic point, in comparison to calcium signal at 465 nm (top). B, Analyzed sample trace of D1-SPNs calcium signals recorded in the DMS of a mouse running on the Treadmill Training Task. Detected calcium events are indicated by red dots. Extended Data Figure 2-2 shows averaged calcium traces corresponding to changes in the treadmill acceleration (Extended Data Fig. 2-2A–D) and during important changes in head position (Extended Data Fig. 2-2E,F). C, Average event amplitude from treadmill recording. Running epochs at all treadmill speeds are averaged together and referred to as “on time.” The 30 s before running and after the treadmill is turned off are averaged together and referred to as “off time.” Day 1, day 3, day 7, and day 12 are shown. All other days are shown in Extended Data Figure 2-1. DMS D1-SPNs activity during on-time is comparable to off-time and home cage baseline on day 1 (n = 7; one-way ANOVA p = 0.66) and becomes significantly lower than off-time activity starting on day 3 (RM one-way ANOVA p < 0.05, Bonferroni’s multiple comparisons test *p < 0.05 DMS on-time vs DMS off-time), and then on day 7 (RM one-way ANOVA p < 0.01, Bonferroni’s multiple comparisons test *p < 0.05 DMS on-time vs DMS off-time and *p < 0.01 DMS on-time vs DMS home cage baseline) and day 12 (RM one-way ANOVA p < 0.05, Bonferroni’s multiple comparisons test *p < 0.05 DMS on-time vs DMS off-time and *p < 0.01 DMS on-time vs DMS home cage baseline), suggesting that activity in this region is lower once the skill is acquired. D, Average event amplitude from treadmill recording in the DLS. There are no changes between on and off time for D1-SPNs recorded from the DLS (n = 9; day 1: one-way ANOVA p = 0.73; day 3: one-way ANOVA p = 0.34; day 7: one-way ANOVA p = 0.53; day 12: one-way ANOVA p = 0.50). All days and event counts are shown in Extended Data Figure 2-1. Sample images showing site of GCaMP6f injection and optic fiber implants are shown in Extended Data Figure 2-3.

Figure 3.

Local D1 neuron inactivation in DMS or DLS during the Treadmill Training Task. Mice were locally injected with a solution of SCH39166, a D1-antagonist. A sample calcium trace after injection is shown in Extended Data Figure 3-1. All animals were injected for the first 6 d of the task (injection running for the first 3 min of the test each day). No drug was injected from day 7 to day 12. Mice were then left to rest for 7 d and tested again for five consecutive days (day 13 to day 17). Another injection of SCH39166 was administered on day 16. Injection days are indicated by green shading. A, D1 antagonism in the DMS caused delayed improvement in the performance, as shown by low coordination score from day 2 to day 5 when compared with saline injected animals (two-way ANOVA Time × Column factor p < 0.05, Bonferroni’s multiple comparisons test for day 2 **p < 0.01, day 4 p < 0.05, day 5 **p < 0.01; saline-injected animals received infusion in either the DMS or the DLS and the data were combined). Similar to DMS-injected animals, application of the same D1 antagonist to the DLS altered performance, with a delayed improvement of the coordination score particularly on day 5 (two-way ANOVA Time × Column factor p < 0.05, Bonferroni’s multiple comparisons test for day 5 #p < 0.05). B, After a week without treadmill, both DLS and DMS-injected animals performed similarly to the previous running day. Conversely to DMS-injected mice, DLS-injected animals showed a decrease in performance after a single injection on day 16 (one-way ANOVA p < 0.01, Bonferroni’s multiple comparisons test p = 0.47), but quickly recovered the following day with no injection. Injection of SCH39166 in the DMS on day 16 did not affect performance as compared with control animals (one-way ANOVA p = 0.85).