α_2a and α_2c adrenoceptors on spinal neurons controlling penile erection

The thoracolumbar and lumbosacral spinal cord contain respectively sympathetic and parasympathetic preganglionic neurons that supply the organs of the pelvis including the penis. These neurons are influenced by supraspinal information and receive aminergic projections from the brainstem. The presence of the α₁- and α₂-adrenoceptor subtypes has been demonstrated in the rat spinal cord. In this species, we looked for the presence of α_2a- and α_2c-adrenoceptor subtypes in the sympathetic and parasympathetic preganglionic neurons controlling erection. In adult male rats, transsynaptic axonal transport of pseudorabies virus injected into the penis was combined with immunohistochemistry against α_2a- and α_2c-adrenoceptor subtypes. At 4 days survival time, neurons infected with the pseudorabies virus were solely found in the intermediolateral cell column and dorsal gray commissure of segment T12-L2 and in the intermediolateral cell column of segment L6-S1. Neurons and fibers immunoreactive for α_2a- and α_2c-adrenoceptor subtypes were mainly present in the intermediolateral cell column, the dorsal gray commissure and the ventral horn of the T12-L2 and L5-S1 spinal cord, the dorsal horn displayed only immunoreactive fibers. Pseudorabies virus-infected neurons in the autonomic nuclei were both immunoreactive for α_2a- and α_2c-adrenoceptor subtypes and closely apposed by α_2a- and α_2c-immunoreactive fibers. The results suggest an intraspinal modulation of the noradrenergic and adrenergic control of the autonomic outflow to the penis by pre- and postsynaptic α₂ adrenoceptors.