Striatal Neurons Expressing D and D Receptors are Morphologically Distinct and Differently Affected by Dopamine Denervation in Mice.

Assessment of the dopaminergic lesion induced by 6-OHDA injection in the medial forebrain bundle.(a) Transverse section taken through the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) that was immunostained for tyrosine hydroxylase (TH) to assess the dopaminergic lesion induced by stereotaxic injection of 6-OHDA in the right medial forebrain bundle. (b) Histogram showing the percentage of TH + cell loss in the SNc and the VTA, as expressed in percentage of intact side. (c) Transverse section taken through the striatum (STR) and immunostained for TH. (d) Histogram showing immunoreactivity of the STR and the nucleus accumbens (Acb) for the tyrosine hydroxylase (TH) and the dopamine transporter (DAT) in the 6-OHDA-lesioned side, as expressed in percentage of intact side. (e) Behavioural response induced by 6-OHDA lesion, as shown in number of contralateral and ipsilateral spontaneous rotations observed in 10 minutes. *P < 0.05, **P < 0.01, ***P < 0.001 for intact side vs. 6-OHDA-lesioned side, ****P < 0.0001 for ipsilateral vs. contralateral rotations, by Mann-Whitney test.

Neurochemical content of the D1/D2 MSNs.Transverse sections taken from the dorsolateral striatum of a D1/D2 transgenic mouse that were immunostained for enkephalin (ENK, a–d) or dynorphin (DYN, e–h). Thin arrows indicate D1 MSNs, thick arrows point to D2 MSNs and arrowheads to D1/D2 MSNs. The D1/D2 MSNs are immunoreactive for dynorphin but not for enkephalin in the D1/D2 transgenic mouse.

Densities of D1, D2 and D1/D2 MSNs in sham and 6-OHDA-lesioned mice.Histograms showing the density of D1 (a), D2 (b) and D1/D2 (c) MSNs in different regions of the striatum (STR) and the nucleus accumbens (Acb) of sham and 6-OHDA-lesioned mice. #P < 0.05, ##P < 0.01 vs. the shell compartment of the Acb and @P < 0.05, @@P < 0.01 vs. the core compartment of the Acb, by Kruskal-Wallis test.

Regional distribution of D1/D2 MSNs in the dorsal striatum and the nucleus accumbens.(a,b) Schematic representations of transverse sections taken at 0.26, −0.94 and 1.10 mm from bregma on which sectors that were sampled to provide unbiased stereological estimation of the number of D1, D2 and D1/D2 MSNs in the striatum (STR, a) and the nucleus accumbens (Acb, (b) are delineated. (c,d) Schematic representations of the distribution of D1/D2 MSNs at the pre and post-commissural level of the STR (c) as well as in the core (AcbC) and the shell (AcbSh) of the nucleus accumbens. The transverse section shown in (b) was immunostained for calbindin and used to delineate the AcbC from the AcbSh.

Dendritic domains of the D1, D2 and D1/D2 MSNs in sham-lesioned mice. (a–c) Histograms showing the total dendritic length (a), the number of dendritic branch points (b) and the overall spine density (c) of the D1 (red), the D2 (green) and the D1/D2 (yellow) striatal MSNs in sham-lesioned mice. (d) Sholl analysis of spine density of the 3 types of MSNs, as measured in sham-lesioned mice. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 for D1 vs. D2 vs. D1/D2 by One-way (a–c) or Two-way (d) ANOVA, followed by Bonferroni’s multiple comparison test.

Dendritic arborization of the D1, D2 and D1/D2 MSNs in 6-OHDA-lesioned mice.Histograms showing the total dendritic length and the number of dendritic branch points in sham (plain columns) and 6-OHDA (hatched columns) lesioned mice. The center and right columns provide schematic representations of D1 (red), D2 (green) and D1/D2 (yellow) MSNs dendritic arborization in sham (center column) and 6-OHDA (right column) lesioned mice. *P < 0.05, ****P < 0.0001 for sham vs. 6-OHDA-lesioned mice, by Student’s T-test.

Dendritic spine density of the D1, D2 and D1/D2 MSNs in sham and 6-OHDA-lesioned mice.Sholl analysis of spine density (left column) and histograms showing the overall spine density (center column) of the D1 ((a), red), D2 ((b), green) and D1/D2 ((c), yellow) striatal MSNs in sham (circles and plain columns) and 6-OHDA (square and hatched columns) lesioned mice. The right column provides representative examples of dendritic segments belonging to the D1, D2 or D1/D2 MSNs that were filled with Lucifer yellow in sham and 6-OHDA-lesioned mice. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 for sham vs. 6-OHDA by a Student’s T-test (histograms) or Two-way ANOVA followed by Bonferroni’s multiple comparison test (Sholl analysis).

D1/D2 double BAC transgenic mice.Confocal images from the Drd1a-tdTomato/Drd2-EGFP double BAC transgenic mice (D1/D2) in which the expression of a red fluorescent protein (tdTomato) is under control of the D1 promoter and the expression of a green fluorescent protein (EGFP) is under control of the D2 promoter. (a) Confocal image of a sagittal section from a D1/D2 transgenic mouse taken through the striatum (STR) and the substantia nigra (SN). (b) Example of a Lucifer yellow-injected MSN located in the dorsal STR. (c–e) High magnification of striatal MSNs that contain the D1 (red, thin arrows), the D2 (green, thick arrows) or both D1/D2 (yellow, arrowheads) dopamine receptors.