Dopamine-dependent corticostriatal synaptic filtering regulates sensorimotor behavior

Abstract

Modulation of corticostriatal synaptic activity by dopamine is required for normal sensorimotor behaviors. After loss of nigrostriatal dopamine axons in Parkinson's disease, l-3,4-dihydroxyphenlalanine (l-DOPA) and dopamine D2-like receptor agonists are used as replacement therapy, although these drugs also trigger sensitized sensorimotor responses including dyskinesias and impulse control disorders. In mice, we lesioned dopamine projections to the left dorsal striatum and assayed unilateral sensorimotor deficits with the corridor test as well as presynaptic corticostriatal activity with the synaptic vesicle probe, FM1-43. Sham-lesioned mice acquired food equivalently on both sides, while D2 receptor activation filtered the less active corticostriatal terminals, a response that required coincident co-activation of mGlu-R5 metabotropic glutamate and CB1 endocannabinoid receptors. Lesioned mice did not acquire food from their right, but overused that side following treatment with l-DOPA. Synaptic filtering on the lesioned side was abolished by either l-DOPA or a D2 receptor agonist, but when combined with a CB1 receptor antagonist, l-DOPA or D2 agonists normalized both synaptic filtering and behavior. Thus, high-pass filtering of corticostriatal synapses by the coordinated activation of D2, mGlu-R5, and CB1 receptors is required for normal sensorimotor response to environmental cues.

Keywords: Parkinson’s; corticostriatal; dopamine; l-DOPA; synapses.

Figure 1. Behavioral response of sham and DA lesioned mice to l-DOPA and eCB receptor modulators

(A) Sham control mice exhibited no preference for use of the left limb. Subsequent treatment with vehicle or l-DOPA did not affect behavioral response. (B) 6-OHDA injected mice exhibited a strong preference for use of the left limb (n = 68). The following day, mice were injected with l-DOPA i.p. (5 mg/kg, 30 min prior to retesting; n = 41) or L-DOPA with either AM251 (1 mg/kg, n = 10) or URB597 (3 mg/kg; n = 8) 15 min prior to l-DOPA. The mice treated with l-DOPA alone showed an overcompensation of use of the affected limb. The mice treated with AM251 prior to l-DOPA displayed a normalization of right limb use without overcompensation. Treatment with URB597 prior to l-DOPA had no effect on limb asymmetry. *** p < 0.001, Mann-Whitney test.

Figure 2. Loading and unloading of corticostriatal terminals with FM 1-43

(A) Schematic of 30° angle coronal slice used to preserve cortical projections (A: anterior, P: posterior, S: superior, I: inferior). (B) Following deposition of Dil crystals in cortical layer V/VI neurons (center) in a 100 μm thick corticostriatal section, multiple intact cortical axons (arrows) display Dil label in dorsal striatum. Scale bar, 50 μm. (C) Excitatory postsynaptic potentials in motor striatal MSNs activated by a single pulse in layer V/VI prior to train stimuli used to load FM1-43 (black) and in the presence of the AMPA-R antagonist, NBQX (10 μM) and the NMDA antagonist, AP-5 (50 μM) (blue). (D) Representative western blot for DAT (70 kDA), TH (60 kDA), and β-actin (45 kDa) indicates that DA lesion by 6-OHDA produced a loss of 96 ± 4% of DAT expression and a loss of 82 ± 4% of TH expression (mean ± SEM, n = 39 paired slices). (E) Immunolabeling for DAT indicates that DA depletion is localized to dorsal striatum. (F) Electrical stimulation of motor cortex layer V in the presence of FM 1-43 labeled multiple puncta (arrows) in the dorsolateral striatum (left). Stimuli (10 Hz) beginning at t = 0 sec results in activity-dependent destaining. Scale bar, 5 μm. (G) Corticostriatal terminals were loaded with FM1-43 by 10 Hz stimuli in cortical layer V/VI. Following loading, a knife cut was made below the corpus callosum to destroy intact cortical axons that project to the dorsal striatum. Subsequent cortical layer V stimulation caused negligible FM1-43 destaining. Minor destaining was similar to that in unstimulated intact preparations, consistent with spontaneous release of FM1-43 from terminals or uncompensated bleaching (Wang 2012). Local striatal stimulation was required to unload FM1-43 from labeled corticostriatal terminals (right: striatal stimulation). (H) Averaged time-intensity analysis of fluorescent puncta shown in panel F. Stimulation of the motor cortex at 10 Hz (black) produced FM 1-43 destaining that followed first-order exponential kinetics. Minimal FM 1-43 destaining occurred when no stimuli (white) were applied.

Figure 3. Chronic DA depletion sensitized responses to D2-R

For box and whisker plots, the line within the box indicates average of median t_1/2 values from the acute slices, the edges of the boxes represent 25^th and 75^th percentiles, and the whiskers indicate the 10^th and 90^th percentiles. (A) Diagram of corticostriatal projection on the intact side. (B) Distribution of median t_1/2 values indicating corticostriatal presynaptic activity in slices from sham-lesioned striata (Ctrl) in the presence of AMPA, NDMA and the selective mGlu-R1 antagonist, CPCCOEt. The D2-R agonist, quinpirole (0.5 μM: dose response shown below) decreased release (i.e., increased t_1/2 values), while the CB1-R antagonist, AM251 (AM) alone had no effect, but blocked the inhibition by quinpirole. The D2-R antagonist, sulpiride (Sul) had no effect. The CB1-R agonist, WIN55 212-2 (WIN) inhibited corticostriatal activity (n = 20 (Ctrl); 9 (Quin); 5 (Sul); 4 (WIN); 6 (AM); 7 (Quin+AM) * p < 0.05, ** p < 0.005, two-way ANOVA; *** p < 0.0001, Mann-Whitney test). (C) Diagram of corticostriatal projection on the lesioned side. (D) Distribution of median t_1/2 values in slices from 6-OHDA-treated lesioned striata, in response to ligands as in panel B, and with the mGlu-R₅ antagonist, MPEP (n = 4 (MPEP); 5 (Quin+MPEP); 4 (Quin+MPEP+AM), * p < 0.05, ** p < 0.005, two-way ANOVA; *** p < 0.0001, Mann-Whitney test). (E) Inhibition by quinpirole (0.5 μM) was enhanced in DA-depleted sections, indicating the induction of a hypersensitive D2-R response. l-DOPA administration in vivo (red) occluded the inhibitory effect of quinpirole at high concentrations of the agonist (n = 20 (Ctrl); 9 (Quin); 7 (L-dopa) * p < 0.05, ** p < 0.005, two-way ANOVA; *** p < 0.0001, Mann-Whitney test).

Figure 4. DA depletion modifies D2 and CB1 receptor-modulation of corticostriatal release

(A) The t_1/2 value for each punctum is displayed on the y-axis as a normal probability plot: a straight line indicates a normal distribution. Values are shown for controls (grey), and in the presence of quinpirole (blue), and quinpirole + AM251 (green). (B) No significant change occurred in fast-destaining terminals. (C-D) The inhibitory effect of quinpirole (blue) on intermediate- and slow-destaining terminals was blocked by quinpirole + AM251 (green) (n = 20 (Ctrl); 7 (Quin); 7 (Quin+AM) ** p < 0.001, *** p < 0.0001, Mann-Whitney test). (E) t_1/2 values in DA-depleted striatum (n = 14 (Ctrl); 9 (Quin); 7 (Quin+AM) ** p < 0.001, *** p < 0.0001, Mann-Whitney test). (F) Quinpirole inhibited destaining of fast, (G) intermediate, and (H) slow-destaining terminals. All terminal populations were blocked by AM251. (n = 6 to 8 slices; ** p < 0.001, *** p < 0.0001, Mann-Whitney test).

Figure 5. l-DOPA in vivo modifies corticostriatal activity

(A) Individual corticostriatal terminal kinetics. D2Rs were activated by quinpirole in vitro throughout the experiments. Destaining was slower in lesioned than sham-treated striatum. Pre-treatment with l-DOPA in vivo (red), enhanced corticostriatal destaining in lesioned striata, particularly by increasing synaptic vesicle fusion from the fast and slow-destaining terminals. (B-D), but in contrast to the intact side, quinpirole slowed the faster terminals in the lesioned side (B), so that normal high-pass filtering was absent. The activity in the lesioned hemisphere of mice administered AM251 prior to l-DOPA (orange) displayed a full recovery of quinpirole response identical to normal quinpirole response on the intact side. (B) t_1/2 values of FM1-43 release from kinetics from fast, (C) intermediate, and (D) slow-destaining terminals. ** p < 0.01, *** p < 0.001, Mann-Whitney test. # indicates that the population is also displayed in Figure 4 and is redisplayed here for purposes of comparison.

Figure 6. l-DOPA effects on corticostriatal terminal kinetics in the presence of D2-R activation and inhibition of endocannabinoid breakdown

(A) Individual corticostriatal terminal kinetics. (B) t_1/2 values for fast, (C) intermediate, and (D) slow-destaining terminals with treatments indicated (n = 20 (Ctrl-Nonlesion); 14 (Ctrl-Lesion) 7 (L-dopa) 6 (L-Dopa+URB); **p<0.005, ***p < 0.0001, Mann-Whitney test). # and ## indicates that the population is also displayed in Figure 4 or Figure 5 respectively and is redisplayed here for purposes of comparison.