Expression of L-type calcium channel α1-1.2 and α1-1.3 subunits on rat sacral motoneurons following chronic spinal cord injury

In the presence of the monoamines serotonin and norepinephrine, motoneurons readily generate large persistent inward currents (PICs). The resulting plateau potentials amplify and sustain motor output. Monoaminergic input to the cord originates in the brainstem and the sharp reduction in monoamine levels that occurs following acute spinal cord injury greatly decreases motoneuron excitability. However, recent studies in the adult sacral cord of the rat have shown that motoneurons reacquire the ability to generate PICs and plateau potentials within 1–2 months following spinal transection. Cav1.3 L-type calcium channels are involved in generating PICs in both healthy and injured animals. Additionally, expression of Cav1.2 and Cav1.3 L-type calcium channels is altered in several pathological conditions. Therefore, in this paper we analyzed the expression of L-type calcium channel α1 subunits within the motoneuron pool following a complete transection of the spinal cord at the level of the sacral vertebra (S)2 segment. The analysis was done both caudally (S4 segment) and rostrally [thoracic vertebra (T)6 segment] from the injury site. The S4 segment was significantly reduced in diameter when compared with control animals, and this reduction was more evident in the white matter. Cav1.2 α1 subunit expression significantly increased (26%) in the motoneuron pool located caudally but not rostrally from the injury site. In contrast, the expression of Cav1.3 α1 subunit remained unchanged in both S4 and T6 segments. The differential expression of the two α1 subunits in spinal injury suggests that Cav1.2 and Cav1.3 channels have different functions in neuronal adaptation following spinal cord injury.