Commissural neurons in the cat upper cervical spinal cord.

We have begun a study of the intrinsic circuitry of the cat's upper cervical cord, in part to elucidate the role of spinal interneurons in vestibulocollic reflexes. Using retrograde labelling with Fluoro-Gold and intraspinal microstimulation, we have identified commissural neurons projecting to the contralateral ventral horn. Neurons tended to be in the medial half of lamina VIII. Approximately half of the neurons were propriospinal neurons that could be activated antidromically from the rostral border of the cervical enlargement. Most of the tested, spontaneously active neurons were driven by stimulation of the ipsi- and/or contralateral vestibular nerve, in some cases disynaptically.