Glutamate in spinally projecting neurons of the rostral ventral medulla

Phosphate activated glutaminase (PAG), an enzyme of glutamate synthesis, was localized by immunohistochemistry in all PNMT-immunoreactive and all serotonin-immunoreactive neurons in the rostral ventral medulla of the rat. Between 71 and 83% of bulbospinal neurons localised in the rostral ventral medulla projecting to the intermediolateral cell column in the upper thoracic spinal cord contained PAG immunoreactivity. Of these bulbospinal PAG-immunoreactive neurons 17-27% contained PNMT immunoreactivity and 9-16% contained serotonin immunoreactivity. Other bulbospinal PAG-immunoreactive neurons (60-70%) contained neither PNMT- nor serotonin immunoreactivity. The results provide anatomical evidence suggestive of a glutamatergic input to the sympathetic preganglionic neurons of the spinal cord arising from different populations of neurons located in the rostral ventral medulla.