Normal motor neuron counts and NMJ integrity in P2 Smn-/-; SMN2 and P9 Smn2B/-mice. (A, B) Representative images of H & E staining of motor neurons in the ventral horn region of the L1 and L2 spinal cord region of P2 control and Smn-/-;SMN2 mice, and P9 control and Smn2B/- mice. Scale bar = 50 μm. (C, D) Quantification of motor neuron cell body number within the ventral horn of the lumbar (L1 and L2) region of the spinal cord for control and pre-symptomatic Smn-/-;SMN2 and Smn2B/- mice. (E, F) Representative images showing fully intact NMJs from TA muscles of control and pre-symptomatic Smn-/-;SMN2 (E) and Smn2B/-(F) mice. Post-synaptic acetylcholine receptors were labeled with α-bungarotoxin (red) while the pre-synaptic terminal was labeled with anti-NF (green) and anti-SV2 (green). Scale bar = 20 μm. (G, H) Quantification of the percentage of fully occupied endplates revealed no difference between control and pre-symptomatic Smn-/-;SMN2 and Smn2B/- mice. NF, neurofilament; NMJ, neuromuscular junction; SV2, synaptic vesicle protein 2; N = 3 for all experiments.