Figure 3.

Morphology of embryonic and early postnatal MSNs. (A) Cluster of seven neurobiotin-filled (left) and Nkx2.1-negative (middle) MSNs (merge) revealed by double immunocytochemistry performed after whole cell recording of a single MSN in a P2 striatal slice. (B) Neurolucida reconstruction of neurobiotin-filled Nkx-negative neurons (MSNs) at the indicated ages. Dendrites and axons were MSNs had 2.8 ± 0.3 primary dendrites at E16–E18 (n = 23), 3.9 ± 0.4 at P0 (n = 19), 5.1 ± 1.1 at P2 (n = 9), and 5.8 ± 0.3 at P7 (n = 11). They gave rise to 6–25 dendritic ends (6 at E16–18, 13 at P0, 17 at P2, 18 at P5, and 25 at P7). The total dendritic length was multiplied by 5 between E16–18 and P7 (339 ± 64 μm at E16–18, 646 ± 148 μm at P0, 574 ± 123 μm at P2, 818 ± 161 μm at P5, and 1751 ± 219 μm at P7). Dendritic spines were virtually absent at all ages. Average cell capacitance progressively increased from E16 to P7 (14.3 ± 0.9 pF at P2, n = 47, compared to 51.7 ± 5.3 pF, n = 74 at P30; p < 0.001). Axons coursing down to the globus pallidus were identified in few E18 MSNs but were consistently observed for P5–P7 MSNs. Same scale bar (50 μm) from E14 to P5.